摘要:

/- one-stop immediate access to all atomic spectrometry literature published since 7 985 including conference papers. jAASbase is a unique database that provides a fully comprehensive up-to-date source of over 23,. 000 analytical atomic spectrometry references. It is designed to meet every atomic spectroscopists information needs - a convenient desktop tool. As a subscriber you will enjoy the following benefits of JAASbase @ Simplicity of use even for the non-specialist @ Economy of effort and expense @ A vast store of references @ Flexibility that fosters thorough searches @ Adaptability - you can add your own data @ Helpdesk and user literature gives added assurance that you can quickly master JAASbase Idealist Software f 21 0.00 $368.00 1994 Subscription Details JAAS Backfile (1 986-93) jAASbase Updates EC €99.00 EC €280.00 EC USA $174.00 USA $490.00 USA (VAT chargeable in the UK) To order JAASbase and for further information please contact Sales and Promotion Department Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF United Kingdom. TeI +44 (0)223 420066.Fax +44 (0)223 423623. ROYAL SOCIETY OF Information Services/- one-stop immediate access to all atomic spectrometry literature published since 7 985 including conference papers. jAASbase is a unique database that provides a fully comprehensive up-to-date source of over 23,. 000 analytical atomic spectrometry references. It is designed to meet every atomic spectroscopists information needs - a convenient desktop tool. As a subscriber you will enjoy the following benefits of JAASbase @ Simplicity of use even for the non-specialist @ Economy of effort and expense @ A vast store of references @ Flexibility that fosters thorough searches @ Adaptability - you can add your own data @ Helpdesk and user literature gives added assurance that you can quickly master JAASbase Idealist Software f 21 0.00 $368.00 1994 Subscription Details JAAS Backfile (1 986-93) jAASbase Updates EC €99.00 EC €280.00 EC USA $174.00 USA $490.00 USA (VAT chargeable in the UK) To order JAASbase and for further information please contact Sales and Promotion Department Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF United Kingdom. TeI +44 (0)223 420066. Fax +44 (0)223 423623. ROYAL SOCIETY OF Information Services

ISSN:0267-9477    

DOI:10.1039/JA99409BP005

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 29N 25th Anniversary of the Atomic Spectroscopy Group Atomic Spectroscopy Group Meeting Ambleside UK March 23-24,1994 To celebrate the 25th Anniversary of the Atomic Spectroscopy Group the Group invited some past officers of the Committee to attend the annual Atomic Spectrometry Updates meeting. The meeting was held this year in the pictur- esque location of Ambleside in the English Lake District. Included along- side this short account are two reports gwen by the chairmen of the morning and afternoon sessions Dr. J. B. Dawson and Dr. W. J. Price. Unfortunately Dr. Dawson was unable to present his remarks in person so this task was undertaken by the Chairman of the Group Dr. B. L. Sharp. An historical perspective of the Group which was originally written in 1974 has been updated and is included here for clarity.The history of the Group falls into three distinct periods and during each period there has been a change in the title and to some extent the scope of the Group. Atomic absorption spectroscopy was inaugurated as an analytical technique by Dr. A. Walsh in 1955 and represented an important milestone in the history of analytical chemistry at least as significant as many of the previous discoveries such as polarography or chromatography. In the field of metals analysis this essen- tially simple and elegant concept was to have a revolutionary effect and its appli- cations have grown steadily since the introduction of commercial instruments in 1960. At its inception an Atomic Absorption Spectroscopy Discussion Panel was formed in 1962 under the auspices of the Physical Methods Group.Dr. (then Mr.) W. T. Elwell was Chairman and Mr. D. Moore Honorary Secretary. At the first meeting at 6.30pm on Wednesday 12 December 1962 in Burlington House London D. J. David (Division of Plant Industries Canberra ACT Australia) gave a paper on ‘Aspects on Atomic Absorption Analysis’. In 1964 the Discussion Panel was reconstituted with full Group status under the title ‘Atomic Absorption Spectroscopy Group’ a change which marked the growing recognition of the technique as being of fundamental importance to the science of analytical chemistry. In 1969 the Group Committee reviewed developments in the field of atomic spectroscopy and felt it should make itself responsible for covering all aspects of the interaction of light and free atoms involving the three processes of atomic emission absorption and flu- orescence. The third and final change in the Group title to Atomic Spectroscopy Atomic Spectroscopy Group members who celebrated the 25th Anniversary of the Group Group acknowledged this decision and consequently it was concerned with emis- sion flame photometry atomic absorp- tion and atomic fluorescence.This was subsequently extended to include all aspects of analytical spectroscopy includ- ing relevant techniques of surface analysis. In 1969 the 2nd International Conference on Atomic Absorption Spectroscopy was organized by the Group under the Chairmanship of Dr. J. B. Dawson and held in the University of Sheffield.Over 400 delegates from twenty countries took part and the first plenary lecture was given by Dr. A. Walsh from Australia. The Committee noted in 1970 the rapidly increasing number of original papers on analytical atomic spectroscopy and decided to form a separate com- mittee to consider the best way of keeping informed of all these advances. The Committee recommended that this could best be done by an annual report which would be a critical appraisal of work published over the previous year. Correspondents in 20 countries agreed to cooperate in this venture and report on developments within their spheres of interest. The first volume of Annual Reports on Analytical Spectroscopy appeared in June 1972 and reviewed over 1000 references on the subject published during 1971. Subsequent edi- tions appeared until it was decided to re-format the volumes and include it as a separate section of the newly launched Journal of Analytical Atomic Spectrometry (JAAS).Atomic Spect- rometry Updates as it is now called continues to be published bimonthly in JAAS and has recently been comple- mented by the introduction of a com- puter database of atomic spectromety reference information JAASbase. As the range of applications of atomic spectroscopy continues to expand and the sophistication and accuracy of instru- ments increases the Committee has to provide for a steadily growing number of analysts who are interested in the techniques. Meetings have been held in every geographical region and joint meetings with particular interested groups and organizations are an import- ant aspect of the Group’s activities.Of particular note is the series of meetings30N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 entitled Biennial National Atomic Spectroscopy Symposium the seventh of which will be held at the University of Hull on the 20-22 July 1994. The meeting now incorporates a presenta- tion from the winner of the Hilger Spectroscopy Prize an award for the best young worker in atomic spectroscopy. Next year will see the most ambitious meeting as yet organized by the Committee the European Winter Conference on Plasma Spectrochemistry 8-13 January 1995. This meeting which is being held for the first time in the UK will be based in Cambridge. The scientific programme consists of plenary invited and contributed lectures as well as poster sessions.The plenary lecturers are Professor M. Blades (Universjty of British Columbia Canada) Professor K. Niemax (ISAS Dortmund Germany) Professor Skip Kingston (University of Pittsburgh USA) Professor L. Ebdon (University of Plymouth UK) and Professor J. Caruso (University of Cincinnati USA). The development of the scientific base of the Group is reflected in the broad base of Committee membership which includes representatives from Industry Academia Manufacturing and Govern- ment Laboratories. Interested individuals who seek Committee membership are encouraged to contact the Honorary Secretary Dr. John R. Dean (Depart- ment of Chemical and Life Sciences University of Northumbria at Newcastle Ellison Building Newcastle upon Tyne UK NE1 8ST. Tel.091-227-3517; fax. 09 1-227-35 19) for informal discussions at their convenience. John R. Dean Honorary Secretary Atomic Spectroscopy Group 25 Years of Atomic Spectroscopy in Environmental Analysis It is 25 years since the Atomic Spectroscopy Group (ASG) was inaugur- ated. The present committee have invited Dr. John Price and myself as early members of the Group to chair this meeting and to set the scene with some comments on the contribution of atomic spectroscopy to environmental analysis. Dr. Price at the opening of this after- noon’s session will reflect on his personal experiences over 40 years of develop- ments in analytical atomic spectroscopy and I shall review the evolution of the ASG and attempt an overview of pro- gress in environmental analysis over the last 25 years.The Group evolved naturally from the Atomic Absorption Discussion Panel which was set up under the aegis of the Physical Methods of Analysis Group of the * Society for Analytical Chemistry with its first meeting in December 1962 with Sir Alan Walsh as speaker. The Society was an enlightened body as it encouraged membership of its specialist sections for a modest fee without any obligation to become full members of the Society though naturally it was hoped this would follow in due course as it did in my own case. However being a physicist by training and a Yorkshireman by birth my reluctance to rush into full membership of a chemical society costing more money is perhaps understandable! However I have never had cause to regret joining the Society and have found great professional and personal satisfaction through my long association with it and its members.In 1964 the Discussion Panel became a Group in its own right. At this point I would like to pay a tribute to the late Dr. W. T. Elwell (‘Bill’ Elwell) and Mr. Derek Moore who as first Chairman and Secretary respectively made vital contributions to the initial and sub- sequent success of the Group. Bill Elwell was a pioneer of AAS and in collabor- ation with J. A. F. Gidley published the first book devoted to AAS in 1961. This partnership between chemist and physi- cist was a feature of the early days of AAS another notable one being that of Alan Walsh a physicist and John Willis a chemist at CSIRO in Melbourne.In ‘addition to arranging scientific meetings the AAS Group committee of the mid-1960s launched three major initiatives. Firstly it persuaded the manufacturers of analytical reagents to create a new range of higher purity materials for AAS analysis to overcome the limitations of existing products that had been revealed by the greater analyt- ical specificity and sensitivity of AAS. Secondly it endeavoured to standardize terms in AAS and their definitions and finally to set about organizing an inter- national conference on AAS to be held in Sheffield in 1969. In all these ventures the Group enjoyed the support and encouragement of the Society for Analytical Chemistry (SAC). The reagent and international conference enterprises were highly successful; terminology is still being argued over even today! IUPAC took over that responsibility many years ago.At the 1969 AGM of the AASG and after a good deal of debate in committee the then Chairman of the Group Dr. W. J. Price proposed ‘that the name of the Group should be changed to the Atomic Spectroscopy Group with terms of reference to include the analytical applications of atomic absorption atomic fluorescence flame emission and emission spectroscopy’. This proposal was unanimously accepted by all the members present (Proc. Soc. Anal. Chem. 1970 7,25). Over the years the terms of reference of the Group have evolved to accommodate the change in analytical atomic spectroscopy practice and now it is hard to imagine a branch of atomic spectroscopy practice that has not been catered for by the Group.Arising from the success of the 1969 Sheffield Conference the Group resolved to enter the realms of publishing by producing Xnnual Reports on Analytical Atomic Spectroscopy (ARAAS) whose first edition appeared in 1972 and reviewed the publications of 197 1. Though the ‘Reports’ operated indepen- dently of the ASG there were close links between the two bodies such that when the finances of the ‘Reports’ produced an operating surplus it was resolved to spend the money for the benefit of analytical atomic spectroscopy in the UK by paying the expenses of overseas ARAAS Board Members to attend the annual board meeting and to hold a joint ARAAS/ASG meeting at which the overseas visitors would be the guest lecturers. The first such joint meeting was held in January 1974 when the speakers were T.C. Rains NBS Washington DC USA and N. Omenetto Euratom Ispra Italy. Though ARAAS metamorphosed into the Atomic Spectrometry Updates (ASU) section of the Journal of Analytical Atomic Spectrometry (JAAS) in 1986 this prac- tice of holding a meeting early each year continues to this day when our overseas visitor is Professor A. Sanz-Medel Oveido Spain. In the early 1980s the ASG committee jointly with the Spectroscopy Group of the Institute of Physics launched a new series of conferences. These were the Biennial National Atomic Spectroscopic Symposia (BNASS) the first of which was held in Sheffield in 1982; this year’s meeting will be held in Hull with a notable programme of UK and over- seas speakers. Over the past 30 years the ASG and its forerunner the AA Discussion Panel has been a major force in the develop- ment of analytical atomic spectroscopy both in this country and overseas.During this time great changes have taken place in the application of atomic spectroscopy to environmental problems and by way of introducing our scientific programme I would like to spend a few moments examining those changes.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 31N As sources of information I have drawn on Analytical Abstracts for 1968 and 1993 and have considered environ- mental analysis to be represented by the section headings of Air and Particulates Waters Soils Plants and Related Materials. By collecting data from Analytical Abstracts it is likely that the survey results will be at least slightly biased in favour of analytical method development rather than analytical prac- tice nevertheless the pattern of change is likely to be representative of develop- ments over the past 25 years.First I should like to comment upon the general development of activity in environmental analysis. In 1968 some 7 800 papers were recorded in Analytical Abstracts of which 7.5% related to environmental analysis by 1993 the figures were 18200 papers with 8.2% being on environmental analysis a 2.3- fold increase in total number of papers with 2.6-fold increase in those relating to the environment. In 1968 27 countries contributed papers while in 1993 the number had risen to 42 with 50% of the countries contributing 90% of the papers.These figures however must carry the ‘health warning’ that not only do they reflect growth in environmental analysis but also improved abstracting efficiency. Nevertheless several interesting obser- vations can be made. ( i ) The USA was the number 1 source of papers in both 1968 and 1993. (ii) The UK was ranked 2nd in 1968 but has fallen to 5th in 1993 even though its output in recorded papers had risen (iii) The USSR was 3rd in 1968 but is now 8th with only 10% growth in output. (iv) Japan was 5th in 1968 and now is 2nd an %fold increase. (u) Germany has moved from 4th in 1968 to 3rd in 1993. (vi) China has blossomed from no papers recorded in Analytical Abstracts in 1968 to 130 papers in 1993 and to 4th place. (uii) Finally I should mention Spain which has risen from 15th in 1968 to 7th place in 1993 with an impressive 16-fold increase in publications.I should now like to turn to consider- by 50%. ing the elements that have been deter- mined in environmental materials. Of the papers on environmental analysis in 1968 some 33% related to elemental analysis. The latter figure has risen to 43% of the environmental papers in 1993 and represents a growth of over 3-fold in the number of papes on elements since 1968. As I shall report in more detail in a few moments this reflects the increasing contribution of atomic spectroscopy to environmental analysis. In 1968 some 60 elements were deter- mined and this figure rose slightly to 70 in 1993 however under half of the elements determined account for over 90% of the total number of citations.The 10 most frequently determined elements i.e. only 15y0 of the total number of elements account for over 50% of the total element citations in both 1969 and 1993 but only 4 elements Cu Fe Pb and Zn are in the ‘top ten’ for both years. Nickel has fallen from 4th to 20th Hg from 6th to 17th while Cd has risen from 33rd to 3rd A1 from 20th to 8th and Sn from 17th to 7th. The reasons for these changes can only be a matter for conjecture but may well include perceived environmental impact analytical facility curiosity or even ‘fashion’! From the range of elements and matrices that have been examined to date there has accumulated an extens- ive literature base from which future studies can be launched. To me one of the most interesting observations to emerge from my examin- ation of Analytical Abstracts was the fact that most determinations of elements are made by non-atomic spectroscopic methods.In 1968 only 18% of papers on the determination of elements in environmental samples employed atomic spectroscopy however by 1993 the pro- portion had doubled to 36%. The non- atomic methods reported in both years included colorimetry spectrophotome- try fluorimetry titrimetry electrochem- istry radiochemistry chromatography and catalysis. The earlier years’ papers also included gravimetric and turbidi- metric methods while in 1993 chemi- and photo-luminescence determinations were reported. Though atomic emission was probably the first of the atomic spectroscopic techniques used in environmental analysis even by 1968 it accounted for only 38% of atomic papers while atomic absorption methods stood at 56% and the remaining 6% were by XRF.By 1993 the proportion of AA papers had fallen to 42% and AE to 31% while XRF had risen to 12% and AF and MS had appeared at 3% and 12% respectively. Atomic fluorescence is one of those tantalizing techniques that offers the promise of great sensitivity but does not quite manage to blossom as a universal technique in practical analysis. In all spectroscopies most papers were devoted to the determi- nation of a single element. In the case of non-atomic methods the proportion of single element papers was 80% while for analysis based on atomic spectroscopy it was lower at 50%. The greater proportion of multi- elemental analysis carried out by the atomic methods may well reflect the greater ease and speed of those methods.The proportions of single-element deter- mination remained constant between 1968 to 1993. The simultaneous determi- nations of five or more elements is usually effected by methods such as neutron activation analysis ICP-AES ICP-MS and XRF. It is tempting to predict that with powerful analytical techniques linked to computers the simultaneous measurement of many elements in environmental material will greatly increase. However my experience over many years in the field of elemental analysis of clinical material suggests that this is not likely to be the direction of developments in the near future owing to the lack of knowledge of the environ- mental effects of the individual element in its different forms and its interaction with other components of the environ- ment which may affect its bioavailability.In these opening remarks I have attempted to highlight developments effected by the ASG and in environ- mental analysis over the past 25 years now it is time to return to the present and to open the scientific meeting of today. John B. Dawson Otley West Yorkshire UK LS212BQ A Quarter of a Century ... and More This year 1994 (plus or minus a year or so) is a year of anniversaries. The Atomic Spectroscopy Group is 25 years old (30 if you count in the Atomic Absorption Spectroscopy Group and 32 if you go back to its origins in the Atomic Absorption Discussion Panel). It is also 25 years since John Dawson uttered those fateful words ‘We must go into the publishing business .. .’. We did and ARAAS was born growing up and maturing eventually into ASU. It is a tribute to John’s foresight that the concept and organization of ASU are almost identical with his first ideas for ARAAS and that they are still working so well. I have a personal anniversary round about this time; it is almost 50 years since I began to work in atomic spec- troscopy. I will not bore you with a detailed account of that time though many of the problems we met still exist. However today we have different solutions. In the mid-forties we were working on spectrographic analysis of cast iron. Steel3 2N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 was easy or relatively so and there was actually a limited form of foundry con- trol in some places based on streamlining the procedures of developing and reading the photographic plate.But cast iron was often a thoroughly unholy and heterogeneous mixture and the first major lesson we learned was that the test piece must be homogeneous and in the same form chemically and physically as the standards. That is still a require- ment at the point of measurement in most branches of spectroscopy and has led to so many ‘sample transformation’ techniques e.g. prior dissolution spark- or laser-ablation or glow discharge prior to ICP-AES or MS which form a large proportion of the methods which we review today. Sheffield was naturally an important centre for spectrographic analysis par- ticularly for those working with ferrous metals. We received a lot of help from our contacts with experts at the Bragg Laboratory then part of the Inspectorate of Naval Ordnance and also from our membership of the Sheffield Spectrographic Discussion Group.Second lesson benefit as much as poss- ible from other people’s experience-but check it out carefully first. I subsequently had to devise a method for rapid analysis of slags and refractor- ies. The American practice was to blast the virtually untreated sample with very high powered arcs. It did not work for us so our eventual method was to fuse the sample in borax adding cobalt oxide as internal standard pulverize mix with graphite compress into pellets and excite with a controlled arc. The standards were simple mixtures of pure oxides. It worked well and we even uncovered an error in the published analysis of a BCS refractory.Another useful principle emerged the reduction of major elements in disparate samples to minor levels in a common matrix in order to obtain consistent and proportional response. Today this would probably be explained in terms of controlling the relationship between the excitation potential of the analyte atoms and the temperature of the atom cell. There was a change of scene in 1952 when I became Spectroscopist in Manchester to Magnesium Elektron Limited a company developing manu- facturing and licensing alloys for the aircraft industry. Usually solution methods were an important part of calibration as few standard materials were available then. That company also began producing hafnium-free zirconium for nuclear purposes by counter-current extraction.These two elements are chemically so similar that spectrographic analysis was the only means available for controlling the aqueous solutions from the plant. The brand-new technique of XRF simply did not have the sensi- tivity. But we did have a problem at very low levels of hafnium the most sensitive line falls on the side of a minor zirconium line and with the Feldman porous cup method (if anyone remem- bers that!) the background level could be extremely variable. We devised a display comparator which both pro- jected the spectrum and displayed its profile over a suitable wavelength range on a CRT. The hafnium concentration was calculated from measurements made on the spectrum profile. Probably the most similar technique today is the wavelength modulation used in some ICP methods.In 1956 we installed an ARL Quantometer and very profitably trans- ferred all our alloy and foundry control analysis. But the hafnium-zirconium problem could not be transferred. The answer had to be worked out from the profile. I believe that many people today operating AES direct readers or AAS instruments who have not actually worked with photographed spectra may find it difficult to visualize the nature of problems caused by background band or line interference. Experience with photographed spectra should be part of the training of all atomic spectroscopists. My emission career ended when I became chief analyst but I still took the opportunity to do some preliminary experiments on a new-fangled idea in atomic spectroscopy-atomic absorp- tion.In spite of having to modify a very old PE flame photometer some interes- ting results were forthcoming. Early in 1961 I moved to Cambridge to build up an applications laboratory for Unicam Instruments as it then was for UV IR and flame AES. The idea of the ICP as an emission source was then just beginning to gain ground and we hooked up our flame photometer the SP900 to a Radyne generator. This was promising for some simple matrices but my emission experience convinced me that much better resolution would be needed with such a source. Soon there came an invitation to attend the first meeting in December 1962 of the SAC Atomic Absorption Spectroscopy Discussion Panel. This was to be chaired by Dr. W. T. Elwell whom I knew well from MEL days.The speaker was D. J. David from Canberra and his subject ‘Aspects of Atomic Absorption’. His exposition of the technique of AA and its current problems was so clear that I actually began to understand Walsh’s original paper! Back in Cambridge an AA accessory was made for the flame photometer and the design of an AA spectrometer soon put in hand. This came out about 1966 though of couse Perkin-Elmer and Techtron were well ahead by that time. Nevertheless there began a fascinating period of method and instrument devel- opment. Our early work like most others’ concerned mainly the measure- ment of trace elements in many different media including the environment. Much of it was solving problems or developing methods for potential users.At one time we were concerned to find more than 100ppm of tin in canned orange and pineapple juices. We published the method and results in 1969 thinking it might cause a small stir but there seemed to be no reaction whatsoever from the expected quarters. Meanwhile the AASG had begun to organize for 1969 in Sheffield what we planned to be the first international conference on AA. In fact it turned out to be the second the Czechs under Ivan Rubeska managed to arrange one earlier! These conferences were continued in other countries as the International Conference on Atomic Spectroscopy (ICAS) series now incorporated into CSI. At the 1969 AGM when I happened to be Chairman the AASG with much encouragement from Professor Tom West and the SAC Council became the ASG.At about this time general interest began to be shown in ‘flameless’ AA though L‘vov had been working on it since the mid-fifties. In the Applications Tables of A R M S volume 1 (1972) about 240 methods using flame AAS were cited and 43 flameless including rods tubes and ribbons but not cold vapour Hg. This proportion of about 1:6 represented almost entirely papers on method devel- opment so there would have been considerably fewer in actual use. Flame chemistry was understood quite well but there was still a long way to go with ETA. By 1980 about one in three of all AA instruments sold had ETA the market having gone in favour of the Massmann and mini-Massmann designs. No doubt the proportion today is very much higher as flame AA is replaced in larger laboratories by ICP spectrometry.The value of informal discussions between experts was supremely well highlighted at the ETA symposium which followed the CSI-ICAS meeting in Prague in 1977. I am sure that that event paved the way for the considerable amount of progress made in the under- standing of graphite furnace atomization processes from then to the present time. 1979 was a busy year when the ASG together with the Spectroscopy Group of the Institute of Physics organized the XXI CSI-8 ICAS meeting in Cambridge. It was also the year when the ASG elected to recognize X-ray as well as optical spectroscopy (and incidentally my second term as Chairman). Of special interest to me during this period before ICPs were as versatile and popular as they are now and FAAS was by far the best way of handling solutionJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL.9 33N samples was the use of AA for the accurate determination of major elements. With stable electronics sources and flames and of course good analyt- ical practice standard deviations of better than 0.2% are easily possible. Good coefficients of variation also lead to better detection limits so that good stability is important at both ends of the concentration scale. At the 10th anniversary of ARAAS in 1980 the Executive Committee asked me to write a review of 'Benchmark Achievements in AA' and this appeared in ARAAS volume 10. It was clear that AA was being adopted more and more as the basis of official standard and reference methods. This was the best possible recognition of accuracy and reliability. A listing of such methods together with available standard mate- rials appeared subsequently in ARAAS volume 12. It would be interesting to know how the position has advanced today some 12 years later. Atomic emission (solid sampling and ICP) and XRF would naturally now be included. It is probable however that many ana- lysts will take the view that spectroscopic methods are so universally accepted that their role in standard methodology is no longer a matter either of note or even of concern. That too is progress. It is pleasing to see that the papers in the second session of this meeting will touch on quality and accreditation in environmental analysis and on precision in XRF and ICP-AES. Also 40 years after my encounter with an early XRF machine the size of a small bus I welcome a recent development hand- held XRF. My thanks are due to Doug Miles Chairman of ASU and Dr. Barry Sharp Chairman of ASG and their Committees for their kind invitation to me to chair this session. I wish them continuing success in so effectively supporting and assisting those working in atomic spec- troscopy not only in this country but the world over. W. John Price Budleigh Salterton Devon UK EX9 7DQ Atomic Spectrometry Updates (AS U) members enjoying the annual dinner

ISSN:0267-9477    

DOI:10.1039/JA994090029N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 33N Conference Report Atomic Spectrometry Probing the Environment March 24 1994 Ambleside UK This year the annual board meeting of Atomic Spectrometry Updates (ASU) coincided with the 25th anniversary of the formation of the Atomic Spectroscopy Group (ASG). To mark the occasion several of the founding members of the ASG were on hand to reflect on the development of atomic spectrometry over the intervening years. The venue chosen was the scenic village of Ambleside in the Lake District at least we were told it was scenic when it was possible to see through the down- pour. Despite the aquatic nature of the area and ‘Captain Nemo’s Undersea Adventure’ on the way to the ASU dinner the previous evening the del- egates paddled their way to the meeting in good time and air/sea rescue was not required. Unfortunately Dr.John Dawson could not be present at the beginning of the meeting so his introductory address was presented by Dr. Barry Sharp; however Dr. Dawson arrived half way through and found himself in the unusual position of listening to his own address. He presented some interesting statistics on the growth in publications in atomic spectrometry over the 25 year period probably the most significant of which was that the UK has fallen from 2nd to 5th place in the ranking despite a 50% increase in output. Unsurprisingly we have been overtaken by countries such as Japan Germany and China though this could just as easily reflect the stimulus and high profile afforded to atomic spectrometry by pioneers such as the founder members of the ASG rather than any failing on the part of UK science.Let us hope that we ensure the continuation of high quality and innov- ative research that has put the UK at the forefront in atomic spectrometry over the years. The first lecture was given by Professor Alfred0 Sanz-Medel (Oviedo Spain) who was attending as an overseas member of the ASU board. He described research into the use of organized media to enhance the generation of volatile hydrides for determinations by AAS. Interestingly he presented evidence for the formation of elemental Cd vapour from CdHz (which can be generated using organized media) thereby facilitating its determination by cold vapour AAS. Professor Malcolm Cresser (Aberdeen) followed this with an illuminating (no pun intended) talk on tracking microor- ganisms in soil by means of genetic tagging with a gene for bioluminescence and fluorescence microscopy for detec- tion.Other techniques such as radioiso- tope labelling were also touched upon and their relative merits discussed. Dr. Mike Foulkes (Plymouth) gave an interesting presentation on the speciation of arsenic in seaweed-derived ‘health food’ and chicken by anion-exchange and reversed-phase chromatography coupled to ICP-MS. He highlighted the need for appropriate extraction sample preparation and clean-up procedures in Atomic Spectrometry Updates (AS U) members enjoying the annual dinner34N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 Professor Alfred0 Sanz-Medel (L) the overseas ASU Board member who pre- sented a lecture at the meeting with the ASU Chairman Doug Miles order to maintain the integrity of the analytes.Such samples contain surpris- ingly high levels of arsenic species (ppm levels) though fortunately these tend to be in relatively non-toxic forms. The afternoon session got underway with an historical perspective by Dr. John Price covering SO years of atomic spectrometry. It seems that many of the problems which dogged the analyst during the 1940s are the same ones which are seen today which is just as well otherwise all the researchers would be out of a job. Dr. Ernie Newman (Elgar Associates) gave a timely overview of quality assur- ance with respect to laboratory oper- ation and management. Dr. Newman emphasized the role of quality pro- cedures in identifying problems before they get bad thereby minimizing the need for fire-fighting after the event.Mr. Peter Watkins (Imperial College) demonstrated how straightforward stat- istical techniques can be used to obtain meaningful estimates of precision and uncertainty from duplicate determi- nations of elements in rocks by ICP- AES and XRF. The session was rounded off by Dr. Phil Potts (Open University) with an evaluation of a portable XRF instrument (hand-held no less!). He presented some impressive results for the analysis of reference materials and discussed the problems associated with real samples where the surfaces of the rocks are weathered and irregular. Detection limits at the low ppm level were obtained for several elements which makes the instru- ment suitable for screening in the field. One word of caution however the X-ray source was 241Am (in the interests of portability) so the necessary lead under- pants may negate any weight advantage. Another successful meeting was enjoyed by all the attendees and some good science was once again presented. Next year’s meeting will be held in Bristol see you there. E. Hywel Evans Department of Environmental Sciences University of Plymouth Plymouth UK PL48AA

ISSN:0267-9477    

DOI:10.1039/JA994090033N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

34N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 Book Review Modern Methods of Trace Element Determination C. Vandecastelle and C. B. Block. Pp. vvi+330. John Wiley & Sons. 1993. Price 245.00. ISBN 0 471 94039 9. I found this book informative and enjoy- able to read. The work is very well written and the style is clear and concise throughout. Following a brief introductory chap- ter Chapter two discusses a wide range of procedures for sample decomposition separation and preconcentration. The emphasis is on practical aspects and potential errors in decomposition methods (as well as how to minimize them) are highlighted. Chapter three is an introduction to ‘the analytical method’ covering topics such as cali- bration simple statistics and interference. The concept of detection limit is described and an introduction to quality control including the use of CRMs given.Chapter four introduces spectro- chemical methods giving a general description of the operation of light sources (line continuum and lasers) gratings and detectors. The following chapters each deal with a particular analytical technique (or comparison between techniques) and cover all key aspects including description of the fundamental physical basis of the tech- nique detailed description of the instrumentation available example applications and recent/novel develop- ments (e.g. HR-ICP-MS and FANES). The topics included are atomic absorp- tion emission and fluorescence spec- trometries mass spectrometry (with emphasis on ICP-MS) X-ray based methods and activation analysis.The final chapter deals very briefly with the topic of speciation. Although hardly doing justice to this important topic (only a couple of examples are given each of the use of a hyphenated instru- mental technique) it is encouraging that the subject is at least mentioned. Each chapter concludes with a useful though far from exhaustive list of references and indications of suitable texts for further reading. The level of the book is probably most appropriate for advanced undergraduate and instructional postgraduate students in analytical chemistry although at &45 for the hardback edition it may be a little too expensive to become a compul- sory purchase. It would also naturally be of use to lecturers involved in prepar- ing/teaching such courses. A strength of this book is its accessi- bility to non-specialists.Because of the clarity of presentation and the fact that no prior knowledge of analytical science is presumed it would provide a useful introduction to the capabilities (and limitations) of modern methods for scien- tist from a variety of disciplines. In the example applications particular empha- sis is placed on the environmental and biological fields which means the book might be particularly appropriate to the needs of biological and environmental scientists. Perhaps the next time a colleague from a neighbouring department asks why when you have a room full of shiny equipment you can’t give him/her a complete elemental analysis on two hun- dred samples of the new chemical/ material/organism he/she has devel- oped-before lunch-this is just the book you need to loan them! Christine Davidson Department of Pure and Applied Chemistry University of Strathclyde Glasgow UK GI 1XL

ISSN:0267-9477    

DOI:10.1039/JA994090034N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 35N Diary of Conferences and Courses 1994 Seventh Biennial National Atomic Spec- troscopy Symposium July 20-22 University of Hull Hull UK Details can be found in J. Anal. At. Spectrom. 1992 7 49N. For further information contact Dr Steve Hill Department of Environ- mental Sciences University of Plymouth Drake Circus Plymouth Devon UK PL4 8AA. 13th International Mass Spectrometry Conference August 29-September 2 Budapest Hungary For further information contact Hung- arian Chemical Society; FO u. 68 H-1027 Budapest Hungary. Telephone 361 201 6883; fax 316 15 61215. EURACHEM Workshop on Evaluation of Measurement Uncertainty in Chemi- cal Analysis September 5- 6 Graz University of Technology Austria In this workshop a draft document of EURACHEM on matters of uncertainty will be introduced and discussed.The Symposium will address matters such as What is meant by ‘Measurement Uncertainty’? How is uncertainty evaluated? What information is it intended to give? How will it affect the requirements for accredit ation? After a general introduction of important concepts of traceability and uncertainty as they apply to chemistry special contributions are expected on Uncertainty in Sampling Uncertainty in Sample Preparation Uncertainty in Calibration and Refer- ence Materials In several working groups on environ- mental analysis food analysis materials analysis and clinical analysis typical worked examples from each field will be presented. The members of each working group are then urged to contribute their views and experience in similar situations.These contributions will be considered and worked into the final EURACHEM Guide on Uncertainty in Chemical Analysis to be issued later in 1994. For further information contact Pro- fessor w. Wegscheider Technische Univ- ersitat Graz Technikerstrasse 4 A-8010 Graz Austria. 4th International Conference on Plasma Source Mass Spectrometry September 11-16 A conference sponsored by Finnigan MAT For further information contact Dr Grenville Holland The Conference Sec- retary Department of Geological Sci- ences Science Laboratories South Road Durham City UK DU1 3LE or Dr Mark Nicholls Finnigan MAT Ltd. Paradise Heme1 Hempstead Hertford- shire UK HP2 4TG. Telephone 0442 233555; fax 0442 233666. EUCMOS XXII XXII European Con- gress on Molecular Spectroscopy September 11-16 Essen Germany Details can be found in J.Anal. At. Spectrom. 1993 8 49N. For further details contact Gesellsch- aft Deutscher Chemiker Abt. Tagungen P.O. Box 90 04 40 W-6000 Frankfurt 90 Germany. Telephone +49 697917-366; fax +49 69 7917-475; telex 4 170 497 gdch d. Geoanalysis 9 4 An International Sym- posium on the Analysis of Geological and Environmental Materials September 18-22 Charlotte Mason Conference Centre Ambleside UK Details can be found in J. Anal. At. Spectrom. 1993 8 49N. For further information contact Mr. D. L. Miles Analytical Geochemistry Group British Geological Survey Kingsley Dunham Centre Keyworth UK NG12 5GG. Telephone 0602 363100; fax 0602 363200. 7th International Symposium on Environ- mental Radiochemical Analysis September 21-23 Bournemouth UK Dates to Note Synopses of papers January 28 1994.Final date for registration July 15 1994. For further details contact Dr. P. Warwick Department of Chemistry Loughborough University of Tech- nology Loughborough Leicestershire UK LEll 3TU. Telephone 0509 222585 or 0509 222545; fax 0509 233163. 6th International Colloquium on Solid Sampling With Atomic Spectroscopy October 11-13 Amsterdam The Netherlands Details can be found in J. Anal. At. Spectrom. 1993 8 59N. For further information contact Dr. R. F. M. Herber Coronel Labora- tory University of Amsterdam Meiberg- dreef 15 NL-1105 AZ Amsterdam The Netherlands. Third Rio Symposium on Atomic Spectrometry November 6-12 Venezuela Details can be found in J.Anal. At. Spectrom. 1993 8 64N. For further information contact Pro- fessor Jose Alvarado Universidad Simon Bolivar Departamento de Quimica Laboratorio de Absorcidn Atbmica Apartado postal No. 89000 Caracas 1080-A Venezuela. Fax (0058-2-) 93832215719 13415763355 19621695. Analytica ’94-Second National Sym- posium on Analytical Science December 1994 Western Cape South Africa Detals can be found in J. Anal. At. Spectrom. 1993 8 60N. For further information contact Dr. I. M. Moodie c/o PO Box 1970 Tygerberg 7505 South Africa. Fax 021 -932-457 5.36N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 Vth COMTOX Symposium cology and Clinical Chemistry July 10-13 on Toxi- of Metals University of British Columbia Van- couver British Columbia Canada The Vth COMTOX Symposium organized by the Association of Clinical Scientists will be held at the University of British Columbia on 10-13 July 1995 in the week between the VIIth Inter- national Congress of Toxicology in Seattle WAY and the American Associ- ation for Clinical Chemistry meeting in Anaheim CA.The Symposium is a Satellite Meeting of the International Congress of Toxicology. In goals scope and format the COMTOX Symposium will resemble previous COMTOX Symposia on Metals (Monte Carlo 1977; Montreal 1983; Kitakyushu 1986; Helsinki 1990) which were attended by 300-500 scien- tists and physicians with expertise in toxicology clinical chemistry analytical chemistry pathology metabolic dis- orders nutrition and occupational medi- cine. The programme will include plenary and keynote lectures platform sessions analytical workshops posters with discussion and commercial exhibits.Submissions of Abstracts The four major themes of the scientific program are analysis of metals in bio- logical materials; molecular biology and toxicology of metals; metals in health and disease and occupational and environmental exposures. The Program Committee invites scien- tists and physicians throughout the world to submit abstracts of papers for presentation at the Vth COMTOX Sym- posium on Toxicology and Clinical Chemistry of Metals. As many partici- pants as possible will be offered an opportunity to present papers on work relevant to the main themes of the Symposium as listed below. Abstracts must be received by 15 January 1995 accompanied by a Registration Form and payment. Authors may indicate their preference for oral or poster presen- tation but the Program Committee reserves the right to assign papers to the platform or poster sessions.To encour- age attendance by young scientists regis- tration fees will be reduced for fifty graduate students post-doctoral fellows or physicians-in-training who present oral papers or posters. Symposium Venue The University of 'British Columbia (UBC) was selected for the COMTOX Symposium because it has an outstand- ing programme in metal toxicology extensive instrumentation for activation analysis of metals at its TRIUMF facility and active research projects on trace metals in relation to nutrition molecular biology pathology pharmacology gen- etic diseases occupational medicine and environmental health.Facilities and Accommodations Academic facilities at UBC include a modern well equipped auditorium com- plex with conference rooms exhibit spaces and laboratories ideally suited for the COMTOX Symposium. The University offers convenient comfort- able and economical lodging athletic facilities (golf tennis swimming) a gra- cious faculty club and the UBC Museum of Anthropology. Accommodations will also be available at the first class Landis Hotel for participants who prefer to stay downtown and travel to the campus by taxi or bus. For further details contact F. William Sunderman Jr. MD Department of Lab- oratory Medicine University of Con- necticut Medical School Room C-2050 263 Farmington CT 06030-2225 USA. Telephone 203-679-2328. 1995 Colloquium Spectroscopicum Inter- national (CSI) XXIX August 27-September 1 Leipzig Germany Details can be found in J . Anal. At. Spectrom. 1993 8 50N.

ISSN:0267-9477    

DOI:10.1039/JA994090035N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

36N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 Future Issues Will lnclude- Signal Enhancement and Reduction of Interferences in Inductively Coupled Plasma Mass Spectrometry With an Argon-Trifluoromethane Mixed Aerosol Carrier Gas-I. Platzner A. L . Polettini J. V. Sala F. Mousty and P. R. Trincherini Pulse Optimization Criteria for the Micro-cavity Hollow Cathode Discharge Emission Source-J. C. Williams P. D. Mixon S. T. Griffin and J. C. Williams Jr. Easily Ionized Element Interference Effects in Furnace Atomization Plasma Emission Spectrometry-S. Imai and R. E. Sturgeon Flame Atomic Absorption Spectrometric Determination of Cadmium in Biological Samples Using a Preconcentration Flow System with an Activated Carbon Column and Dithizone as a Chelating Agent-Y. Petit De Pena M.Gallego and M. Valcarcel Determination of Transition Metals in the Primary Water of Pressurized Water Reactors by Inductively Coupled Plasma Mass Spectrometry-R. J. Rosenberg P. K. G. Manninen and R. Zilliacus Multi-element Analysis of Archeological Bronze Objects Using ICP-AES Aspects of Sample Preparation and Spectral Line Selection-I. B. Brenner I. Segal and A. Kloner Reduction of Polyatomic Interferences in Inductively Coupled Plasma Mass Spectrometry by Selection of Instrumental Parameters and Using an Argon-Nitrogen Plasma Effect on Multi-element Analyses-F. Laborda M. Baxter H. M. Crews and J. Dennis Determination of Boron in Cell Suspensions Using Electrothermal Atomic Absorption Spectrometry- M. Papaspyrou C. Mohl M. J. Schwuger and L. E. Feinendegen Furnace Atomization Plasma Emission Spectrometry at Controlled Pressures- R. E. Sturgeon S. N. Willie and S. Imai Analysis of Zirconium Alloys by Inductively Coupled Plasma Atomic Emission Spectrometry-I. Steffan and G. Vujicic Direct Analysis of Materials Using Direct Sample Insertion Devices and Mixed Gas Inductively Coupled Plasma Atomic Emission Spectrometry- G. Horlick and X. R. Liu

ISSN:0267-9477    

DOI:10.1039/JA994090036N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

1995 European Winter Conference on Plasma Spectrochemistry 8-13 January 1995 CAMBRIDGE UK Short Courses A series of short courses of one half day duration will take place on Sunday 8th January. Notes and tuition material will be distributed with each course. Courses 1 and 2 Short Courses on ICP-MS Professor R.S. Houk Ames Laboratory Iowa State University USA Course 1 (AM) Instrumentation and Theory The course will cover fundamental aspects of ICP-MS including:- a) Molecular beam sampling b) Quadrupole and high resolution c) Vacuum technology d) Ion sources e) Detection systems and data hand1 ing f) Sample introduction technologies analys ers Course 2 (PM) Advanced Topics The course will cover more advanced topics on ICP-MS particularly relevant to problem solving. Each topic will be illustrated with relevant applications examples.a) Interferences (spectroscopic and non-spectroscopic and methods of alleviation b) Isotopic analysis c) Chromatographic methods d) Overview of commercial instrumentation Course 3 (PM) Sample Preparation for ICPs Dr S.J. Haswell Hull University UK The course will focus on important aspects of sampling and sample preparation with particular emphasis on ICP measurements. a) Batch methods f o r wet oxidation b) Recent trends in microwave preparation for ICP-MS atomic spectrometry general analytical techniques c) On-line sample preparation d) Extraction methods e) On-line chemical processing f) Miniaturization Course 4 (PM) Speciation Professor O.X. Donard University of Bordeaux France The course will focus on practical aspects of speciation analysis with particular emphasis on ICP and other plasma sampling systems.Sample collection and handling preservation and preparation prior to injection into hyphenated systems using atomic spectrometry and ICP-AES or ICP-MS as detectors will be illustrated with applications from current topical fields . a) Sampling and sample pretreatment b) Separative techniques Differential chemistry Gas liquid ion and SCF c ) Interfacing chromatography techniques to ICPs and other plasma sources and detectors chromatographies Course 5 (AM) Quality Systems in the Laboratory Professor L. Ebdon Dr E.H. Evans University of Plymouth UK The course will discuss how high quality analytical data can be produced in the laboratory that are accurate reliable and adequate f o r the intended purpose.a) Quality assurance principles b) Sampling and sample preparation c) Personnel aspects d) Statistics for quality control e Use of reference materials and f) Equipment and records maintenance g) Audits and accreditation. traceability Course 6 (AM) Sample Presentation for ICPS Dr C McLeod Sheffield Hallam University UK The course is intended as a problem solving workshop and will attempt to rationalise the choice of sampling system for ICP spectrometries by use of practical examples. a) Nebulisation techniques Traditional and high efficiency The role of desolvation Hydride Other vapour techniques e . g . b) Vapour generation Hg oso c) Microsampling systems d) Flow injection e) Laser ablation1995 European Winter Conference on Plasma Spectrochemistry 8-13 January 1995 CAMBRIDGE UK Short Courses A series of short courses of one half day duration will take place on Sunday 8th January. Notes and tuition material will be distributed with each course.Courses 1 and 2 Short Courses on ICP-MS Professor R.S. Houk Ames Laboratory Iowa State University USA Course 1 (AM) Instrumentation and Theory The course will cover fundamental aspects of ICP-MS including:- a) Molecular beam sampling b) Quadrupole and high resolution c) Vacuum technology d) Ion sources e) Detection systems and data hand1 ing f) Sample introduction technologies analys ers Course 2 (PM) Advanced Topics The course will cover more advanced topics on ICP-MS particularly relevant to problem solving. Each topic will be illustrated with relevant applications examples.a) Interferences (spectroscopic and non-spectroscopic and methods of alleviation b) Isotopic analysis c) Chromatographic methods d) Overview of commercial instrumentation Course 3 (PM) Sample Preparation for ICPs Dr S.J. Haswell Hull University UK The course will focus on important aspects of sampling and sample preparation with particular emphasis on ICP measurements. a) Batch methods f o r wet oxidation b) Recent trends in microwave preparation for ICP-MS atomic spectrometry general analytical techniques c) On-line sample preparation d) Extraction methods e) On-line chemical processing f) Miniaturization Course 4 (PM) Speciation Professor O.X. Donard University of Bordeaux France The course will focus on practical aspects of speciation analysis with particular emphasis on ICP and other plasma sampling systems.Sample collection and handling preservation and preparation prior to injection into hyphenated systems using atomic spectrometry and ICP-AES or ICP-MS as detectors will be illustrated with applications from current topical fields . a) Sampling and sample pretreatment b) Separative techniques Differential chemistry Gas liquid ion and SCF c ) Interfacing chromatography techniques to ICPs and other plasma sources and detectors chromatographies Course 5 (AM) Quality Systems in the Laboratory Professor L. Ebdon Dr E.H. Evans University of Plymouth UK The course will discuss how high quality analytical data can be produced in the laboratory that are accurate reliable and adequate f o r the intended purpose. a) Quality assurance principles b) Sampling and sample preparation c) Personnel aspects d) Statistics for quality control e Use of reference materials and f) Equipment and records maintenance g) Audits and accreditation. traceability Course 6 (AM) Sample Presentation for ICPS Dr C McLeod Sheffield Hallam University UK The course is intended as a problem solving workshop and will attempt to rationalise the choice of sampling system for ICP spectrometries by use of practical examples. a) Nebulisation techniques Traditional and high efficiency The role of desolvation Hydride Other vapour techniques e . g . b) Vapour generation Hg oso c) Microsampling systems d) Flow injection e) Laser ablation

ISSN:0267-9477    

DOI:10.1039/JA99409FX037

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

1995 European Winter Conference on Plasma Spectrochemistry 8-13 January 1995 CAMBRIDGE UK Short Courses A series of short courses of one half day duration will take place on Sunday 8th January. Notes and tuition material will be distributed with each course. Courses 1 and 2 Short Courses on ICP-MS Professor R.S. Houk Ames Laboratory Iowa State University USA Course 1 (AM) Instrumentation and Theory The course will cover fundamental aspects of ICP-MS including:- a) Molecular beam sampling b) Quadrupole and high resolution c) Vacuum technology d) Ion sources e) Detection systems and data hand1 ing f) Sample introduction technologies analys ers Course 2 (PM) Advanced Topics The course will cover more advanced topics on ICP-MS particularly relevant to problem solving. Each topic will be illustrated with relevant applications examples.a) Interferences (spectroscopic and non-spectroscopic and methods of alleviation b) Isotopic analysis c) Chromatographic methods d) Overview of commercial instrumentation Course 3 (PM) Sample Preparation for ICPs Dr S.J. Haswell Hull University UK The course will focus on important aspects of sampling and sample preparation with particular emphasis on ICP measurements. a) Batch methods f o r wet oxidation b) Recent trends in microwave preparation for ICP-MS atomic spectrometry general analytical techniques c) On-line sample preparation d) Extraction methods e) On-line chemical processing f) Miniaturization Course 4 (PM) Speciation Professor O.X. Donard University of Bordeaux France The course will focus on practical aspects of speciation analysis with particular emphasis on ICP and other plasma sampling systems.Sample collection and handling preservation and preparation prior to injection into hyphenated systems using atomic spectrometry and ICP-AES or ICP-MS as detectors will be illustrated with applications from current topical fields . a) Sampling and sample pretreatment b) Separative techniques Differential chemistry Gas liquid ion and SCF c ) Interfacing chromatography techniques to ICPs and other plasma sources and detectors chromatographies Course 5 (AM) Quality Systems in the Laboratory Professor L. Ebdon Dr E.H. Evans University of Plymouth UK The course will discuss how high quality analytical data can be produced in the laboratory that are accurate reliable and adequate f o r the intended purpose.a) Quality assurance principles b) Sampling and sample preparation c) Personnel aspects d) Statistics for quality control e Use of reference materials and f) Equipment and records maintenance g) Audits and accreditation. traceability Course 6 (AM) Sample Presentation for ICPS Dr C McLeod Sheffield Hallam University UK The course is intended as a problem solving workshop and will attempt to rationalise the choice of sampling system for ICP spectrometries by use of practical examples. a) Nebulisation techniques Traditional and high efficiency The role of desolvation Hydride Other vapour techniques e . g . b) Vapour generation Hg oso c) Microsampling systems d) Flow injection e) Laser ablation1995 European Winter Conference on Plasma Spectrochemistry 8-13 January 1995 CAMBRIDGE UK Short Courses A series of short courses of one half day duration will take place on Sunday 8th January. Notes and tuition material will be distributed with each course.Courses 1 and 2 Short Courses on ICP-MS Professor R.S. Houk Ames Laboratory Iowa State University USA Course 1 (AM) Instrumentation and Theory The course will cover fundamental aspects of ICP-MS including:- a) Molecular beam sampling b) Quadrupole and high resolution c) Vacuum technology d) Ion sources e) Detection systems and data hand1 ing f) Sample introduction technologies analys ers Course 2 (PM) Advanced Topics The course will cover more advanced topics on ICP-MS particularly relevant to problem solving. Each topic will be illustrated with relevant applications examples.a) Interferences (spectroscopic and non-spectroscopic and methods of alleviation b) Isotopic analysis c) Chromatographic methods d) Overview of commercial instrumentation Course 3 (PM) Sample Preparation for ICPs Dr S.J. Haswell Hull University UK The course will focus on important aspects of sampling and sample preparation with particular emphasis on ICP measurements. a) Batch methods f o r wet oxidation b) Recent trends in microwave preparation for ICP-MS atomic spectrometry general analytical techniques c) On-line sample preparation d) Extraction methods e) On-line chemical processing f) Miniaturization Course 4 (PM) Speciation Professor O.X. Donard University of Bordeaux France The course will focus on practical aspects of speciation analysis with particular emphasis on ICP and other plasma sampling systems.Sample collection and handling preservation and preparation prior to injection into hyphenated systems using atomic spectrometry and ICP-AES or ICP-MS as detectors will be illustrated with applications from current topical fields . a) Sampling and sample pretreatment b) Separative techniques Differential chemistry Gas liquid ion and SCF c ) Interfacing chromatography techniques to ICPs and other plasma sources and detectors chromatographies Course 5 (AM) Quality Systems in the Laboratory Professor L. Ebdon Dr E.H. Evans University of Plymouth UK The course will discuss how high quality analytical data can be produced in the laboratory that are accurate reliable and adequate f o r the intended purpose. a) Quality assurance principles b) Sampling and sample preparation c) Personnel aspects d) Statistics for quality control e Use of reference materials and f) Equipment and records maintenance g) Audits and accreditation. traceability Course 6 (AM) Sample Presentation for ICPS Dr C McLeod Sheffield Hallam University UK The course is intended as a problem solving workshop and will attempt to rationalise the choice of sampling system for ICP spectrometries by use of practical examples. a) Nebulisation techniques Traditional and high efficiency The role of desolvation Hydride Other vapour techniques e . g . b) Vapour generation Hg oso c) Microsampling systems d) Flow injection e) Laser ablation

ISSN:0267-9477    

DOI:10.1039/JA99409BX039

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

9411 265. 94/1266. 94,4267. 9411268. 9411269. 9411 270. 94/1271. 9411272. 9411273. 94/1274. 94/1275. 9411276. 9411277. 149R JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 ATOMIC SPECTROMETRY UPDATED REFERENCES The address given in a reference is that of the first named author and is not necessarily the same for any co-author. Shum S. C. K. Johnson S. K. Pang H.-m. Houk R. S. Spatially resolved measurements of size and velocity distributions of aerosol droplets from a direct injection nebulizer Appl. Spectrosc. 1993 47 575. (Ames Laboratory US Dept. Energy Dept. Chem. Iowa State Univ. Ames IA 50011 USA). Boudreau D. Hubert J. Atmospheric-pressure argon surface-wave plasma (SWP) as an ion source in elemental mass spectrometry Appl. Spectrosc. 1993 47 609. (Dept. Chem.Univ. Montreal P.O. Box 6128 Station A Montrkal Qukbec Canada H3C 357). Niemczyk T. M. Chu C.-p. Influence of water on spatial excitation behaviour in the DCP Appl. Spectrosc. 1993 47 807. (Dept. Chem. Univ. New Mexico Albuquerque NM 87131 USA). Cheung N.-h. Yeung E. S. Single-shot elemental analysis of liquids based on laser vaporization at fluences below breakdown Appl. Spectrosc. 1993 47 882. (Ames Lab. USDOE Dept. Chem. Iowa State Univ. Ames IA 50011 USA). McCleary K. A Ducatte G. R. Renfro D. H. Long G. L. Evaluation of a demountable tangential flow torch for microwave-induced plasma atomic emission spectrometry Appl. Spectrosc. 1993 47 994. (Dept. Chem. Virginia Polytech. Inst. State Univ. Blacksburg Brownrigg J. T. Wavelength calibration methods for low-resolution photodiode array spectrometers Appl.Spectrosc. 1993 47 1007. (American Holographic 521 Great Rd. Littleton MA 01460 USA). Jaganathan J. Aggarwal I. Graphite furnace atomic absorption spectrometric determination of iron cobalt nickel and copper at parts-per-billion level in high- purity lanthanum fluoride Appl. Spectrosc. 1993 47 1169. (Opt. Sci. Div. Code 5605 Naval Res. Lab. Washington D.C. 20375-5338 USA). Zheng Y.-s. Su X.-g. Quan Z. Factors influencing characteristic mass in the graphite furnace A@. Spectrosc. 1993 47 1222. (Dept. Chem. Jilin Univ. Changchun 130023 China). Skelly Frame E. M. King J. A. Jr. Anderson D. A. Balz W. E. Direct determination of palladium and cobalt in phenol by atomic spectroscopy Appl. Spectrosc. 1993 47 1276. (GE Corp.Res. Dev. Schenectady NY 12301 USA). Beebe K. R. Blaser W. W. Bredeweg R. A. Chauvel J. P. Jr. Harner R. S. LaPack M. Leugers A. Martin D. P. Wright L. G. Yalvac E. D. Process analytical chemistry Anal. Chem. 1993 65 199. (Anal. Sci. Lab. Dow Chem. USA Midland MI 48640 USA). McGuire G. E. Ray M. A. Simko S. J. Perkins F. K. Brandow S. L. Dobisz E. A. Nemanich R. J. Chourasia A. R. Chopra D. R. Surface characteriz- ation Anal. Chem. 1993 65 311r. (Cent. Microelectron. Syst. Technol. MCNC Research Triangle Park NC 27709 USA). Vela N. P. Olson L. K. Caruso J. A. Elemental speciation with plasma mass spectrometry Anal. Chem. 1993 65 585A. (Dept. Chem. Univ. Cincinnati Cincinnati OH 45221-0172 USA). Turnlund J. R. Keyes W. R. Peiffer G. L. Isotope ratios of molybdenum determined by thermal ionization mass spectrometry for stable isotope studies of molyb- denum metabolism in humans Anal.Chem. 1993 65 VA 24061-0212 USA). 94/1278. 9411279. 9411280. 941128 1. 9411282. 941 1283. 9411284. 94/1285. 9411286. 9411287. 9411288. 9411289. 1717. (West Hum. Nut. Res. Cent. ARS Presidio San Francisco CA 94129 USA). Benninghoven A. Hagenhoff B. Niehuis E. Surface MS probing real-world samples Anal. Chem. 1993 65 630A. (Phys. Inst. Univ. Munster D-W-4400 Milnster Germany). Ottolini L. Bottazzi P. Vannucci R. Quantification of lithium beryllium and boron in silicates by second- ary-ion mass spectrometry using conventional energy filtering Anal. Chem. 1993 65 1960. (Cent. Stud. Cristallochim. Cristallogr. CNR 1-27 100 Pavia Italy). Dixon P.R. Perrin R. E. Rokop D. J. Maeck R. Janecky D. R. Banar J. P. Measurement of iron isotopes (54Fe 56Fe 57Fe and 58Fe) in sub-microgram quantities of iron Anal. Chew. 1993 65 2125. (Los Alamos Natl. Lab. Los Alamos NM 87545 USA). Alves L. C. Allen L. A. Houk R. S. Measurement of vanadium nickel and arsenic in sea-water and urine reference materials by inductively coupled plasma mass spectrometry with cryogenic desolvation Anal. Chem. 1993 65 2468. (Ames Lab. Iowa State Univ. Ames IA 50011 USA). Duckworth D. C. Donohue D L. Smith D. H. Lewis T. A. Marcus R. K. Design and characterization of a radiofrequency powered glow discharge source for double-focusing mass spectrometers Anal. Chem. 1993 65 2478. (Anal. Chem. Div. Oak Ridge Natl. Lab. Oak Ridge TN 37831-6375 USA).Smith R. G. Determination of mercury in environmen- tal samples by isotope dilution-ICP-MS Anal. Chem. 1993 65 2485. (Skidaway Inst. Oceanogr. Savannah GA 31416 USA). Ohorodnik S. K. Harrison W. W. Cryogenic coil for glow discharge sources Anal. Chem. 1993 65 2542. (Dept. Chem. Univ. 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Use of modified crystal decanters with no lead migration for cognac storage J. Food Prot. 1992,55 806. (Bur. Natl. Interprofess. 16100 Cognac France). Igwegbe A. O. Belhaj H. M. Hassan T. M. Gibali A.S. Effect of a highway’s traffic on the level of lead and cadmium in fruits and vegetables grown along the roadsides J. Food SaJ 1992 13 7. (Fac. Agric. Al-Fateh Univ. Tripoli Libya). 9411816. 94/18 17. 9411818. 9411 8 19. 941 1820. 94/ 1 82 1. 9411 822. 9411 823. 94,4824. 9411 825. 9411826. 9411827. 94,4828. 9411829. 9411 830. Nriagu J. O. Lawson G. Wong H. K. T. Azcue J. M. Protocol for minimizing contamination in the analysis of trace metals in Great Lakes waters J. Great Lakes Res. 1993 19 175. (Natl. Water Res. Inst. Burlington Ontario Canada L7R 4A6). Meyn J. P. Danger T. Petermann K. Huber G. Spectroscopic characterization of vanadium( 4 +)-doped alumina and yttrium aluminate J. Lumin. 1993 55 55. (Inst. Laser-Phys. Univ. Hamburg 2000 Hamburg 36 Germany).Kinoshita H. Ikegawa H. Optical emission measure- ment of high-uniformity and high-density oxygen supermagnetron plasma J. Nucl. Muter. 1993,200,296. (Res. Inst. Electron. Shizuoka Univ. Hamamatsu Japan 432). Healy K. E. Ducheyne P. Passive dissolution kinetics of titanium in vitro J. Mater. Sci. Mater. Med. 1993 4,117. (Dept. Bioeng. Univ. Pennsylvania Philadelphia Barocchi F. Sampoli M. Hensel F. Rathenow J. Winter R. Experimental determination of the de-polarized interaction-induced light scattering spec- trum of mercury vapour at T= 793 K J. Non-Cryst. Solids 1993 156 663. (Dept. Phys. Univ. Florence Florence Italy). Eisman M. Gallego M. Valcarcel M. Automatic determination of amylocaine and bromhexine by atomic absorption spectrometry J. Pharm. Biomed.Anal. 1993 11 301. (Fac. Sci. Univ. Cordoba Cordoba Spain 14004). Nerin C. Cacho J. Garnica A. Indirect determination of diphenhydramine hydrochloride by atomic absorp- tion spectrometry J. Pharm. Biomed. Anal. 1993 11 41 1. (ETSII Univ. Zaragoza Zaragoza Spain). Gumgum B. Hamamci C. Effect of different mineral acids on emission intensity in ICP spectrochemistry J. Quant. Spectrosc. Radiat. Transfer 1993 50 55. (Fac. Sci. Univ. Dicle Diyarbakir Turkey). Suzuki K. Shikama T. Ochiai A. Purification of uranium metal JJAP Ser. 1993 8 15. (Inst. Mater. Res. Tohoku Univ. Sendai Japan 980). Zheng Y.-s. Peng Y. Effect of surface property of graphite tube on dissipation of atomic vapour Jilin Daxue Ziran Kexue Xuebao 1992 3 85. (Dept. Chem. Jilin Univ. Changchun China).Du X.-g. Duan Y.4 Liu J. Jin Q.-h. Evaluation of microwave plasma torch in the determination of mercury by AES Jilin Dame Ziran Kexue Xuebao 1992 3 113. (Dept. Chem. Jilin Univ. Changchun China). Saito Y. Inagaki M. Optical emission studies on chemical species in an arc flame of fullerene-metalloful- lerene generator Jpn. J. Appl. Phys. Part 2 1993 32 L954. (Fac. Eng. Mie Univ. Tsu Japan 514). Kohri M. Ide K. Okochi H. Inoue Y. Solid phase extraction of organotin Kankyo Kagaku 1993 3 400. (Natl. Res. Inst. Met. Tokyo Japan 153). Kawabata K. Kawaguchi Y. Inoue Y. Determination of arsenic and selenium in sea-water by ICP atomic absorption spectrometry Kankyo Kagaku 1993,3,406. (Yokogawa Anal. Syst. Musashino Japan 180). Namiki K. Natsui K. Matsubara M. Automatic optimization of analytical conditions ETAA and its applications for environmental samples Kankyo Kagaku 1993 3 466.(Seiko Instrum. Tokyo Japan 135). PA 19104-6392 USA).JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 169R 94/1804. 9411 805. 94/1806. 94/1807. 9411808. 94/1809. 94/18 10. 9411811. 9411 8 12. 9411 8 13. 9411 8 14. 941 1 8 1 5. titanium-K XANES study of titania-yttria stabilized tetragonal zirconia polycrystals J. Am. Ceram. SOC. 1993 76 197. (Inst. Werkstoffwiss. Max Planck Inst. Metallforsch. W-7000 Stuttgart 80 Germany). Kuhnert B. R. Kuhnert P. M. Lazebnik N. Erhard P. Relationship between placental cadmium zinc and copper J. Am. Coll. Nutr. 1993 12 31. (Dept. Obstet. Gynecol. MetroHealth Med. Cent. Cleveland OH USA). Golloch A. Haveresch-Kock M.Fischer W. G. Electrothermal vaporization and pyrolysis of materials for environmental analysis J. Anal. Appl. Pyrolysis 1993 25 37. (FB 6-Instrum. Anal. Univ. GH Duisburg W-4100 Duisburg Germany). Daniels R. S. Wigfield D. C. Cold-vapour mercury atomic absorption spectrometry hydrogen chloride as the cause of the double peak phenomenon J. Anal. Toxicol. 1993 17 196. (Ottawa Carleton Chem. Inst. Carleton Univ. Ottawa Ontario Canada K1S 5B6). Rodriguez-Otero J. L. Paseiro P. Simal J. Terradillos L. Cepeda A. Determination of sodium potassium calcium magnesium copper iron manga- nese and total cationic milliequivalents in Spanish commercial honeys J. Apic. Res. 1992 31 65. (Dept. QA Nutr. Bromatol. Fac. Vet. Lugo Spain 27002). Mehlman G. Chrisey D. B. Burkhalter P.G. Horwitz J. S. Newman D. A. Vacuum ultraviolet spectroscopy study of excimer laser generated plasmas J . Appl. Phys. 1993 74 53. (SFA Inc. Landover MD 20785 USA). Stoffels W. W. Stoffels E. Koresen G. M. W. De Hoog F G. Detection of particulates in an r.f. plasma by laser evaporation and subsequent discharge for- mation J. Appl. Phys. 1993 74 2959. (Dept. Phys. Eindhoven Univ. Technol. 5600 MB Eindhoven The Netherlands). Tam S. Fajardo M. E. Matrix isolation spectroscopy of metal atoms generated by laser ablation. 111. The sodium-argon sodium-krypton and sodium-xenon systems J. Chem. Phys. 1993 99 854. (Propul. Dir.-RKFE Phillips Lab. Edwards Air Force Base CA 93524-7680 USA). Haider N. Husain D. Kabir M. Investigation of the collisional behaviour of electronically excited ger- manium atoms Ge [(4p)’( lD,)] by time-resolved atomic resonance absorption spectroscopy in the ultra- violet J.Chem. SOC. Faraday Trans. 1993 89(11) 1653. (Dept. Chem. Univ. Cambridge Cambridge UK CB2 1EW). Dowling T. M. Uden P. C. Alkyltin speciation in sea- water with on-line hydride conversion and gas chroma- tography-atomic emission detection J. Chromatogr. 1993,644 153. (Dept. Chem. Lederle Grad. Res. Tower A Univ. Massachusetts Amherst MA 01003 USA). Berglund A. An in vitro and in viuo study of the release of mercury vapour from different types of amalgam alloys J. Dent. Res. 1993 72 939. (Fac. Odontol. Univ. Umea S-901 87 Umea Sweden). Vidal J. P. Chetaneau B. Cantagrel R. Use of modified crystal decanters with no lead migration for cognac storage J.Food Prot. 1992,55 806. (Bur. Natl. Interprofess. 16100 Cognac France). Igwegbe A. O. Belhaj H. M. Hassan T. M. Gibali A. S. Effect of a highway’s traffic on the level of lead and cadmium in fruits and vegetables grown along the roadsides J. Food SaJ 1992 13 7. (Fac. Agric. Al-Fateh Univ. Tripoli Libya). 9411816. 94/18 17. 9411818. 9411 8 19. 941 1820. 94/ 1 82 1. 9411 822. 9411 823. 94,4824. 9411 825. 9411826. 9411827. 94,4828. 9411829. 9411 830. Nriagu J. O. Lawson G. Wong H. K. T. Azcue J. M. Protocol for minimizing contamination in the analysis of trace metals in Great Lakes waters J. Great Lakes Res. 1993 19 175. (Natl. Water Res. Inst. Burlington Ontario Canada L7R 4A6). Meyn J. P. Danger T. Petermann K. Huber G. Spectroscopic characterization of vanadium( 4 +)-doped alumina and yttrium aluminate J.Lumin. 1993 55 55. (Inst. Laser-Phys. Univ. Hamburg 2000 Hamburg 36 Germany). Kinoshita H. Ikegawa H. Optical emission measure- ment of high-uniformity and high-density oxygen supermagnetron plasma J. Nucl. Muter. 1993,200,296. (Res. Inst. Electron. Shizuoka Univ. Hamamatsu Japan 432). Healy K. E. Ducheyne P. Passive dissolution kinetics of titanium in vitro J. Mater. Sci. Mater. Med. 1993 4,117. (Dept. Bioeng. Univ. Pennsylvania Philadelphia Barocchi F. Sampoli M. Hensel F. Rathenow J. Winter R. Experimental determination of the de-polarized interaction-induced light scattering spec- trum of mercury vapour at T= 793 K J. Non-Cryst. Solids 1993 156 663. (Dept. Phys. Univ. Florence Florence Italy). Eisman M. Gallego M. Valcarcel M. Automatic determination of amylocaine and bromhexine by atomic absorption spectrometry J.Pharm. Biomed. Anal. 1993 11 301. (Fac. Sci. Univ. Cordoba Cordoba Spain 14004). Nerin C. Cacho J. Garnica A. Indirect determination of diphenhydramine hydrochloride by atomic absorp- tion spectrometry J. Pharm. Biomed. Anal. 1993 11 41 1. (ETSII Univ. Zaragoza Zaragoza Spain). Gumgum B. Hamamci C. Effect of different mineral acids on emission intensity in ICP spectrochemistry J. Quant. Spectrosc. Radiat. Transfer 1993 50 55. (Fac. Sci. Univ. Dicle Diyarbakir Turkey). Suzuki K. Shikama T. Ochiai A. Purification of uranium metal JJAP Ser. 1993 8 15. (Inst. Mater. Res. Tohoku Univ. Sendai Japan 980). Zheng Y.-s. Peng Y. Effect of surface property of graphite tube on dissipation of atomic vapour Jilin Daxue Ziran Kexue Xuebao 1992 3 85.(Dept. Chem. Jilin Univ. Changchun China). Du X.-g. Duan Y.4 Liu J. Jin Q.-h. Evaluation of microwave plasma torch in the determination of mercury by AES Jilin Dame Ziran Kexue Xuebao 1992 3 113. (Dept. Chem. Jilin Univ. Changchun China). Saito Y. Inagaki M. Optical emission studies on chemical species in an arc flame of fullerene-metalloful- lerene generator Jpn. J. Appl. Phys. Part 2 1993 32 L954. (Fac. Eng. Mie Univ. Tsu Japan 514). Kohri M. Ide K. Okochi H. Inoue Y. Solid phase extraction of organotin Kankyo Kagaku 1993 3 400. (Natl. Res. Inst. Met. Tokyo Japan 153). Kawabata K. Kawaguchi Y. Inoue Y. Determination of arsenic and selenium in sea-water by ICP atomic absorption spectrometry Kankyo Kagaku 1993,3,406. (Yokogawa Anal. Syst. Musashino Japan 180).Namiki K. Natsui K. Matsubara M. Automatic optimization of analytical conditions ETAA and its applications for environmental samples Kankyo Kagaku 1993 3 466. (Seiko Instrum. Tokyo Japan 135). PA 19104-6392 USA).

ISSN:0267-9477    

DOI:10.1039/JA994090149R

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 565 Inductively Coupled Plasmas in Atomic Fluorescence Spectrometry A Review S. Greenfield Department of Chemistry University of Technology Loughborough Leicestershire UK L E l 7 3TU Summary of Contents 1 Introduction and Basic Theory 1.1 Total Absorption Factor 1.2 Ideal Fluorescence Intensity 1.3 Types of Fluorescence 1.4 Quenching of Fluorescence 1.5 Basic Instrumental Configuration 2 Evolutionary Steps 3 The ICP as a Source in AFS 3.1 Type of Source 3.2 Plasma Torches and Operating Parameters 3.3 With Flames as Atomizer 3.4 With Electrothermal Atomization 4 The ICP as an Atomizer in AFS 4.1 With Electrodeless Discharge Lamp as Source 4.2 With Hollow Cathode Lamp as Source 4.3 With Laser as Source 4.4 With Mercury Vapour Lamp and Continuum Sources 5.1 Low Power Systems 5.2 High Power (ASIA) Systems 5 The ICP as Atomizer with ICP as Source 6 Applications 7 The Present and Future of the ICP in AFS 7.1 Freedom from Spectral Interference 7.2 Linear Dynamic Range 7.3 Freedom from Chemical and Ionization Interference Effects 7.4 Limits of Detection 7.5 Precision 7.6 Other Factors 7.7 Epilogue 8 References Keywords Inductively coupled plasma; atomic fluorescence spectrometry; review 1 Introduction and Basic Theory Before discussing the role that the inductively coupled plasma (ICP) has played in atomic fluorescence spectrometry (AFS) it is perhaps pertinent to highlight the differences and the similarities between the techniques of atomic absorption spec- trometry (AAS) atomic emission spectrometry (AES) and AFS and to give some of the background theory of AFS as an aide memoire to those readers with only a peripheral interest in and/or knowledge of the subject.(A list of abbreviations used in the text is provided in Table 7.) In both AAS and AFS the analyte atoms are excited by means of an external light source. However in AAS the fraction of radiation absorbed as a result of this radiational excitation is measured whereas in AFS the measured parameter is the portion (entering the spectrometer) of atomic fluorescence (AF) radiation resulting from the radiational de-activation of a fraction of the excited atoms. By way of contrast in AES the analyte atoms are excited by thermally induced collisions although as in AFS the measured parameter is that portion of the radiation emitted when a fraction of the excited atoms undergoes radiational deactivation.It must be pointed out immediately (since it has a bearing on spectral selectivity) that there are very many more spectral transitions in AES than in either of the other two techniques mainly due to the high temperature of the sources used in AES coupled with the fact that the spectra of both AAS and AFS are relatively simple being confined principally to resonance lines or other low lying levels. 1.1 Total Absorption Factor The expression relating AF to atom concentration is quite complex as it is necessary to account for a number of factors which it would be inappropriate to discuss at length in this review. Fortunately it is possible to avoid developing a com- plete expression by relating an ideal fluorescence intensity to a quantity known as the total absorption factor AT This concept is developed fully by Kirkbright and Sargent.' The AT factor gives an indication of how much radiation is actually absorbed by the atom cloud and is based on a knowledge of the light entering and leaving the cell containing the atoms.Absorbed radiation intensity A1 Incident radiation intensity I. (1) - AT = -566 JOURNAL OF ANA.LYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 It can be shown theoretically that with continuum sources when the concentration of absorbing atoms is low AT increases linearly. When the concentration of absorbing atoms is high AT is proportional to the square root of the concentration. On the other hand with sharp line sources AT varies linearly at low concentrations but is independent of concentration at high concentrations.1.2 Ideal Fluorescence Intensity Assuming that a single frequency is used in the absorption of energy necessary to excite the particular transition under consideration the fluorescence cell is within the solid angle viewed by the detector and there is no loss of energy by re-absorption the intensity of the fluorescence I in a direction perpendicular to the exciting light beam can be related to AT and other factors in the following manner where lo is the radiant flux in W cm-'; o is the width of the exciting beam; R is the solid angle in steradians over which the excited fluorescence is detected and measured (47r is simply the total number of radians over which fluorescence is emitted from the cell); A is the total absorption factor for the spectral line at which the fluorescence is excited; 4 is the fluorescence yield and is the fraction of absorbed photons per unit time which is re-emitted as fluorescence radiation per unit time.The value of $J is dependent not only on the number of different pathways by which an atom may return to the ground state for a particular fluorescence transition but also on the quench- ing of fluorescence (of which more will be written later). The expression serves only as an illustration of the basis of more rigorous expressions which can be found in the literature of the Although the relationship between the fluorescence signal and the concentration of ground state atoms is linear at low atom concentrations as suggested in eqn.(2) this is not so at high concentrations where in real life self-absorption occurs. In this case the curve of growth (COG) becomes parallel to the concentration axis with continuum sources and assumes a negative slope with line sources. 1.3 Types of Fluorescence There are a number of possible discrete processes by which an atom can absorb radiation and re-emit fluorescence radiation and these are illustrated in Fig. 1. For instance the two processes may take place between the same upper and lower energy levels. The lower level may be the ground state or a low lying excited state. In these cases the light energy absorbed and emitted is of the same wavelength and the process is called resonance fluorescence or excited resonance fluorescence respectively.If only the upper level is common to the radiational exci- tation and de-excitation processes we have direct line fluor- escence and the wavelength of the exciting radiation will be different from that of the emitted radiation. Again the lower level may be the ground state or a low lying-excited state. When the excitation energy is higher than the fluorescence energy the process is known as Stokes direct line fluorescence. If the excitation energy is lower than the fluorescence energy we have anti-Stokes direct line fluorescence. Different upper levels can be involved in the radiational excitation and de-excitation involving collisional gains and losses of energy. These processes are known as step-wise line fluorescence.If as a result of absorption of radiation the excited atom loses a fraction of its energy by a de-exciting collision before re-emitting its fluorescence radiation the pro- cess is known as Stokes step-wise line fluorescence. Where the excitation process involves a collisional excitation following A+ hv+A A* + M+A+ M* 1 M*-+M+hv' 1 Fig. 1 Types of fluorescence (a) Resonance; (b) excited resonance; (c) Stokes direct line; ( d ) excited Stokes direct line; (e) anti-Stokes direct line; cf) Stokes stepwise; (g) thermally assisted stepwise; (h) thermally assisted anti-Stokes stepwise; and 0) sensitized (A donor; M acceptor) the radiational excitation to a higher energy level and this is followed by a radiational re-excitation to a level other than the ground level the process is known as thermally assisted step-wise line fluorescence.In the latter case if the de-excitation is to the ground level the process is called thermally assisted anti-Stokes stepwise line fluorescence. Finally sensitized fluorescence occurs when an atom or molecule (donor) excited by an external light source transfers its excitation energy to the analyte atoms (acceptor) by collision and the acceptor then undergoes radiative de-activation resulting in atomic fluorescence. 1.4 Quenching of Fluorescence The population of the excited state in atomic fluorescence is comparatively large in terms of thermal equilibrium. The lifetime of the excited atoms is very brief and fluorescence results from the de-activation of these atoms. If however collisions occur between excited atoms and other atoms molecules and electrons present in the atomizer de-activation will occur without any fluorescence radiation being emitted.This process is known as quenching. 1.5 Basic Instrumental Configuration The basic instrumental layout for the production and measure- ment of atomic fluorescence is shown in Fig. 2. There are of course many variations on this basic scheme. The radiation for activation is directed optically from a line or continuum source through an atom cloud produced from an analyte introduced into a relatively low temperature atomizer. This atomizer can be a flame heated graphite rod or plasma among others. The fluorescence radiation which results from de-activation of atoms which have been excited by the incident radiation falling on the atom cloud is normally measured at right angles to this beam although this is not necessarily so as the fluorescence is isotropic.Obviously however the fluorescence is viewed the incident beam should not be allowed to enter the collection optics. The fluorescence radiation is resolved in a low resolution monochromator of low f number (often a filter will suffice) and the intensity is measured by means of a detector which is generally a photomultiplier tube (PMT). The output of theJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 567 Fig. 2 Typical instrumental arrangements for AFS A Source; B atomizer; C monochromator; D lock-in amplifier; E data read-out; Y modulated radiation (modulated current to the source or optical chopper); and X fluorescence radiation detector is fed to a lock-in amplifier and hence to the data output.The source radiation is generally modulated either by modulating the current supplied to the source or by interrupt- ing the beam by means of a 'chopper'. The lock-in amplifier is tuned to the modulation frequency and this provides for discrimination between the fluorescence signal and the emission radiation from the atomizer. However the PMT does collect the emission from the atomizer as a d.c. signal and this will therefore increase the noise on the output from the PMT and could in extreme cases lead to saturation of the tube. 2 Evolutionary Steps A better understanding of the reasons for employing the ICP in AFS can be obtained by considering the innovative steps which have led to this use before examining in detail the present state of the art.The use of an ICP in AFS as an atomizer and/or narrow line source was preceded by its use for such purposes in AAS. Thus in 1966 Wendt and Fassell used an ICP as an atomizer in AAS.4 The necessary path- length was obtained by the use of multi-pass optics. They reported good limits of detection (LODs) and sensitivities for a number of elements. They also commented on the relative freedom from chemical interference which they found. This use of an ICP as an atomizer was confirmed by Greenfield et ~ l . ~ who obtained an absorption path length of some 33 cm by the use of a T-shaped plasma torch with a hollow cathode lamp (HCL) as source. These workers also used an ICP as a source in AAS with an air-C,Hz flame as an atomizer.They obtained similar results to those they obtained using the former configuration of HCL as a source and ICP as an atomizer. No significant line broadening was found and half-line widths comparable with those of HCL were reported. These workers also postulated the use of two ICPs in AAS one as source the other as atomizer a configur- ation that was later to be used in AFS.6,7 The first use of an ICP in AFS was that of Hussein and Nickless' who used it as a source in flame AFS. Relatively poor LODs were obtained for reasons it is idle to speculate upon since there are many factors affecting the use of a plasma as a source which were not known at the time. It was some seven years later before the TCP was again mentioned in the scientific literature in connection with AFS.Montaser and Fassel using a plasma torch with an extended outer tube as an atomizer and electrodeless discharge lamps (EDLs) as sources reported superior LODs to those obtained by ICP-AES for the elements Cu Zn and Hg. Around 1978 Pollard et u1.l' used a continuous wave (CW) dye laser as a source with an ICP as an atomizer in AFS. They concluded that the system they described was not analyti- cally useful because of the limited wavelength range of the CW laser employed its high cost and the fact that they did not obtain improved LODs compared with ICP-AES. Also around this time Omenetto et u1.l' showed by consideration of emis- sion excitation and fluorescence COGS that the ICP viewed at normal observation heights is a line source.In an interesting use of the properties of an ICP as a line source Tallant12 replaced an arc lamp with an ICP as a source in molecular fluorescence and obtained comparable sensitivities. Epstein et aZ.13 used an ICP as a source and a flame as a resonance monochromator in AFS. They also developed a scatter correc- tion procedure based upon self absorption in the ICP. This period saw the first use of pulsed dye laser excitation in the ICP; both a flashlamp-pumped dye-laser and an N laser- pumped dye-laser were used. This group of workers14 con- cluded that whilst the initial evaluation had not indicated the technique to be superior to ICP-AES there was reason for thinking that further improvement could be made. In 1981 an important paper appeared by Demers and Allemand,15 in which they described a single channel AF instrument utilizing an ICP generated in a torch with an extended outer tube as an atomizer and pulsed HCLs as sources.In this paper they demonstrated experimentally the many advantages of the AFS technique per se and in particular when an ICP is used as an atomizer. The importance of this work lies in the fact that it was the precursor to the introduction of the first commercially available AF spectrometer incorporat- ing an ICP as an atomizer.lG1' A paper by Omenettol' was published in 1982 in which an ICP-AF system was described where a graphite rod was used as an atomizer. The LODs obtained for a number of elements were said to be even better than those reported in the literature for electrothermal atomic absorption spectrometry (ETAAS).A year later Kosinski et ~ 1 . ~ reported on the use of two low power ICPs one as source and the other as atomizer in an AF system. Around this time Greenfield7 described a similar system on which work had started quite independently in 198 1 incorpor- ating a high power ICP as source and a low power ICP as atomizer in a single instrument to which was given the acronym ASIA (atomizer source inductively coupled plasmas in atomic fluorescence spectrometry) which served to dis- tinguish it from the low power system of Kosinski et al. No results were reported. Long et ~ 1 . ~ ' described the use of high frequency (h.f.) power line filtering units to reduce electronic noise in ICP-AFS and so improve LODs.This was to be used in later work. During studies of spatial distributions of absorbing species Walters et aL21 used an extended sleeve torch with a high-flow nebulizer and with added C,H8 to form a pencil plasma. They demon- strated the possible reaction of carbon radicals C with oxides and monohydroxides of the analyte to form CO. A preliminary communication22 appeared in 1984 in which Omenetto et al. described the use of an excimer (XeCl) pumped dye laser as source and a conventional ICP torch as atomizer in an AFS system. The laser was continuously tunable from 217nm to the near IR and the LODs reported were greatly superior to those reported by BoumansZ3 for ICP-AES and Demers and Allemand'' for HCL-ICP-AFS and included refractory elements.This communication was quickly followed by two more paper^'^,'^ from the same group describing the important parameters for analytical use of laser excited AFS and the analytical characteristics of a number of elements in atomic and ionic AFS. They concluded that a Nd:YAG pumped dye laser might be an even better system. Long and Winefordner26 using a similar ICP-ICP-AFS568 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 system to that used by Kosinski et aL6 but with greatly improved optics which increased the light collection efficiency from 1 to 13% obtained LODs one to two orders of magnitude better than the previous work. These workers demonstrated the advantages of the pencil plasma and the use of C3H8 to determine refractory elements. D e m e r ~ ~ ~ also reported on the use of C3H8 in the determination of refractory elements by ICP-AFS and on the use of 0 to reduce the intense radiation resulting from the incomplete combustion of organic solvents when nebulized into the plasma.In the same paper there were details of a flushed chamber for use when determining S and P by AFS in the vacuum UV and an account of the use of a graphite central tube. At about this time Greenfield and Thomsen2* published their early results from the ASIA system. The COGs for emission excitation and fluorescence were given. The fluor- escence COG showed the characteristic shape for a line source. The LODs reported were mainly equal to or better than those previously reported for plasma systems other than those involving lasers as sources.This was particularly true for the refractory elements. Omenetto et aL2' were the first to report on laser induced double-resonance ionic fluorescence in the ICP in which two pulsed dye lasers were simultaneously directed into an ICP. One laser excited to one level and the second continued the excitation to a higher level. The technique was reported as being highly selective and very sensitive. A group which included Long and Winefordner reported on an extension of previous work using TCP-ICP-AFS3' in which they reported improved LODs. They also used an ICP as a resonance monochromator (RM) to extend the linear dynamic range of the technique and commented on the freedom from line broadening interference continuum interference molecular interference interference from spectral overlaps and some matrix interferences.Some ion effects were reported. These workers3' suggested the possibility of running two plasmas from one generator a possibility which was later to be estab- lished as fact.31 Krupa and Winef~rdner~~ investigated the effect of power on ICP absorption emission and fluorescence signals using an extended sleeve torch. In 1986 T a ~ b i ~ ~ presented his thesis on auto-fluorescence. This work was based on an idea that originated with the late Gordon Kirkbright in which a single ICP acts as both source and atomizer to produce fluorescence in the tail-flame. Taobi suggested that at low analyte concentration in the plasma the core continuum emission was probably solely responsible for exciting the fluorescence whereas at high analyte concentration the atomic or ionic emission from the analyte nebulized into the plasma may act as the sole excitation source.The LODs obtained were in the low pg ml-' range. The same year saw the use of stimulated raman scattering (SRS) as a source for exciting fluorescence in plasmas generated in conventional plasma t o r ~ h e s . ~ ~ ~ ~ The LODs obtained were only comparable with those obtainable by ICP-AES. These workers found that LODs obtained at conventional obser- vation heights in conventional torches were not significantly inferior to those measured at an observation height of 55-75 mm in plasmas formed in elongated torches. They also found that using ultrasonic nebulization LODs were improved by a factor of 400 over pneumatic nebulization. In 1987 Greenfield et ~ 1 .~ ~ published what was said to be the first study of non-resonance transitions in AFS using a dual plasma system. It was shown that this system ASIA demonstrated remarkable freedom from spectral interference in resonance fluorescence and an even greater freedom in non- resonance mode. This period saw a comparison of two methods of optimization when applied to AFS.37 It was shown that the a1 ternating variable search (AVS) method was much faster than the simplex method which sometimes failed to terminate. D e r n e r ~ ~ ~ claimed improved sensitivity by the use of boosted discharge hollow cathode lamps (BDHCL) in HCL-ICP-AFS. This sensitivity was further improved by the use of a concentric nebulizer with a recessed sample tube and the addition of an attached impact bead.A progress report on ASIA3' was given in 1988 which outlined the attributes of the technique. Examples were given of the freedom of the technique from background shifts and spectral overlaps resonance and non-resonance spectra linear dynamic range LODs freedom from matrix effects and the production of two plasmas from one generator. In further work4' the effect of PO4 Al Na and K on the atomic and ionic fluorescence of Ca was studied. Interference effects were found which could be interpreted in terms of stable compound formation ionization suppression and fluorescence quenching. It was shown that these effects could be removed by optimizing the operating parameters for minimum interference. In 1988 work was carried out using a pulsed flash tube as a source in ICP-AFS.41 The source gave high selectivity and poor LODs but was judged to be a useful source for multi- element analysis.In a later paper42 this group used a pulsed flash tube to produce double resonance fluorescence. Greenfield et ~ ~ 1 . 4 ~ compared a high power ICP with BDHCL as sources in AFS. The LOD obtained with the plasma were at least an order of magnitude lower than those obtained with the BDHCL. This group also reported in 1990 on a version of ASIA with improved 3 The ICP as a Source in AFS 3.1 Type of Source The ICP acts as a line source in AFS if its overall spectral emission profile is narrower than its absorption profile in the atomizer. Conversely it acts as a continuum source if at high concentrations self-absorption has broadened the emission profile sufficiently for it to be larger than the absorption profile.The early work referred to in the previous section suggested that the ICP was a line source." used a pressure scanning Fabry-Perot interferometer to measure the ICP emission profiles of a number of elements. They found that the profile depended on the observation height and although self-absorption and self- reversal was observed at certain heights not normally used for observation at other heights there was an absence of such phenomena. In the absence of self-reversal the emission COG of an ICP will show a slope of unity at low atom concentrations in the source and a slope of 0.5 at high concentrations when self- absorption becomes evident.The excitation COG produced by measuring the fluorescence radiation from a fixed low concentration of atoms in the atomizer when an increasing concentration is nebulized into the ICP source will show a slope of unity at low atom concentration in the source and zero slope at high concentration in the source. When self- reversal occurs both COGs will show a negative slope. The fluorescence COG obtained when a constant concentration of atoms is fed into the ICP source and an increasing concen- tration of atoms is fed into the atomizer will show a slope of unity at low concentrations with both line and continuum sources but at high concentration of atoms in the atomizer the slope will be unity for a continuum source and -0.5 for a line source. Omenetto et a2.l' showed how this behaviour might be expected from theory and then demonstrated practi- cally using the chopped radiation from an ICP as a source and a shielded air-C,H flame as an atomizer that for the elements Zn Mg and Ca log-log plots of the emission excitation and fluorescence COG had limiting slopes consistent with a line source and that self-absorption was not pronounced at high concentrations (i.e.20000 pg ml-1 of Mg). Self-reversal Human and * Strictly it is a region of the plasma tail-flame which can be called the line source. The fire-ball itself is a continuum source.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 569 only occurred at observation heights not normally used. These workers concluded that the ICP was an optically thin source and that it was essentially a line source.These conclusions have been substantiated by a number of other ~ ~ r k e r ~ ~ y ~ ~ p ~ ~ * ~ ~ using similar methods. The ICP meets the general requirements for an excitation source for AFS insofar as it has a high radiation over the centre of the absorption line of the analyte atom it has good short-term and long-term stability it is available for a large number of elements is easy to operate and has a long lifetime. The intensity of the radiation produced by an ICP is pro- portional to the concentration of the excited species in the tail-flame (up to the on-set of self-absorption where pro- portionality decreases) which in turn is related to the power supplied to the plasma and the concentration of the appropriate element in the solution nebulized into the plasma.3.2 Plasma Torches and Operating Parameters When the small Fassel torch is used as a source in AFS the impression gained from reading the literature is that the generator is run at maximum power which is variously quoted as being between 1.0-2.0kW at 27MHz what this power refers to is rarely if ever stated It is probably the power at the work coil; the actual power in the plasma is possibly considerably lower. The concentration of the element in the solution nebulized into the plasma is quoted as being between 1.0-2.0% m/v. However Omenetto et uZ." give emission and excitation COGS for Zn Mg and Ca indicating that the signal is still rising after these concentrations have been reached. The limiting factor at higher concentrations is probably the block- ing of the injector tube by deposits.So far as can be gathered from the confusion of terms used to describe them the argon gas flows range from 10.0-15.0 1 min-' for the outer gas flow and where used from 0.4-1.8 1 min-' for the intermediate gas flow. The inner gas flow carrying the aerosol ranges from 0.5-1.0 1 min-l and the uptake rate of solution to the concen- tric or cross-flow nebulizers varies from 0.5-1.00 ml min- '. The observation height used varies from 10.0-30.0 mm above the work coil. Although it is sometimes stated in the literature that these values are optimized it is doubtful whether a true global optimization using a recognised method is meant more probably the statement refers to a limited univariate search.When the large Greenfield torch is used as a source in AFS much greater powers and concentrations are used and the operating gas flows are also higher.28 The power used at 7 MHz varies according to the element from 3.5-7.3 kW in the plasma measured calorimetrically. The efficiency of coup- ling is approximately 50%. The concentrations of the solutions nebulized (through a Babington type nebulizer) vary from 5% m/v B to 50% m/v Zn (as HBF4 and ZnCl respectively). It has been reported that these levels can be handled quite easily with only the occasional blockage of the injector tube. Using the original nomenclature the coolant gas flow of air is 30.01min-l. The plasma gas flow of argon varies from 20.0-30.0 1 min-l and the injector flow from 2.0-4.0 1 min-'.The uptake rate is 3.0 ml min-' and the height of observation varies from 13 to 25 mm above the coil. All the values quoted for the Greenfield torch have been optimized by the AVS method.37 3.3 With Flames as Atomizers There are far fewer spectral interferences in AFS than in AES or even in AAS. This is undoubtedly due to certain stringent conditions which fortunately are not often met in AFS. Firstly the emission profile of the source must overlap with the absorption profile of the interfering element in the atomizer. In this instance the atomizer is the flame. Secondly the population of the interfering element in the correct energy level must be significantly high. Thirdly the amount of energy absorbed by the interfering element to that emitted as fluor- escence radiation must be significant.This freedom from spectral interference has been observed in a number of instances when an ICP has been used as a source with flames as atomizers. Thus although the major Zn resonance line at 213.856nm is subject to direct spectral interference by the Cu non-resonance transition at 213.853 nm it has been reported46 that trace amounts of Zn can be determined in high-purity Cu by ICP flame AFS. That this is possible is due to several factors the ICP is a narrow line source; there is no significant fluorescence excited at the 213.853 Cu line owing to a relatively low thermal population in the flame of the 11203 cm-' energy level; and the quantum efficiency of the fluorescence process is low. It was pointed out that this particular determination is not possible by ICP-AES with the spectrometers typically used and can only be per- formed by AAS if a separation of the Cu is made or high resolution AAS is used with wavelength modulation and line- nulling.An investigation was carried out by Omenetto et ~ 1 . ~ ~ on the interference between the Cd 228.802nm line and the As 228.812 nm line where there is only 0.01 nm separation between the two lines. These workers were able to show that the determination of trace amounts of Cd in an As matrix by ICP flame AFS was completely free from interference since no signal was observed when 10000 pg ml-' of pure Cd solution was aspirated into the ICP and 1000 pg ml-I of As solution into the flame. In a later paper48 these workers demonstrated how Pd could be determined in nuclear waste by utilizing the spectral selectivity of AFS.According to these workers all analytically useful lines of Pd are subject to severe spectral interference when analysing for Pd using ICP-AES with a typical spectrometer. Their solution to this problem was to atomize the sample in an argon shielded air-C2H2 flame and excite it with the emissions from a pure 5000 pg ml- ' solution of Pd fed into the ICP torch. The ICP incorporated in a polychromator was used as the source without any modification other than the addition of a mechanical chopper lens shielded flame and low resolution monochromator. With this adjunct it was found possible to determine Pd at a wavelength of 363.47 nm without interference despite an almost coincident argon line at 363.44 nm.There are a number of other examples of the selectivity of the technique which appear later in this review under various headings. That the ICP is an intense source is confirmed by the LODs obtained by a succession of workers11~46~47*49 using separated flames as atomizers. These are shown in Table 1. Montaser4' compared LODs obtained with an ICP as source with LODs obtained on the same elements with an EDL as source using similar atomizers. He obtained equal values with the EDL for Pb Zn Ca Mn Ni Be and Sc two to four times lower values for Cu Co Sn Fe Se Cr Te and Hg five to ten times lower values for Ag Cd Mg and T1 and sixteen times lower values for Sb. However unless the optical geometry in each case gave equal collection efficiency and both sources were operating under optimum conditions it would be wise not to take too simplistic a view of these results.Epstein et ~ 1 . ~ ~ pointed out that they were only collecting 2% of their source radiation and that the use of an off-axis ellipsoidal reflector would increase the transfer of energy by at least an order of magnitude and result in an improvement in LODs. These workers also pointed out that the LODs they obtained46 (Table 1) could be improved by increasing the integration time and/or increasing the concentration of the element under consideration in the solution fed to the source ICP. In the same paper it was reported that the analytical COG for ICP excited flame AFS was linear over slightly less than four orders of magnitude and that the precision was of the order of 1-2% relative standard deviation (RSD).They further commented that the long term stability of the system was excellent. Scatter was said to be the most significant interference in resonance AFS (obviously in other transitions where the570 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 Table 1 flame or electrothermal atomizer LODs (ng ml-')* obtained by AFS with ICP as source and Ref. 11 Element Ag A1 As Be Ca 23 Cd c o Cr c u Fe Hg Mg 4 Mn Mo - Ni Pb Pd Sb sc Se Sn Te TI v Zn 13 - - - - - - - - - - - - - - - - - - - - - 49 12 - - 15 30 9 30 45 12 120 90 6 12 75 60 1200 30 600 1500 150 135 9 - - - 46 - 1000 5000 4 0.8 11 2 2 6 0.09 2 400 800 - - - - - - - - - - 400 0.5 Flame atomization ETA * Normalised to 3 x sb. ?Although not explicitly stated it is deduced that the sample size was 5 p1.wavelength of the exciting radiation is different from that of the fluorescence produced there will not be a scatter problem). This scatter interference can take two forms scatter off lenses burner heads etc. and scatter from unvolatilized particles in the atomizer flame. These scatter interferences can be mistaken for AF and must be corrected for. Specular reflection is corrected for by a blank reading but particle scatter requires more sophisticated methods. Larkins and Willisso proposed what is known as the two-line technique as a method for correction of scatter. This is based on the narrow linewidth of the AF and the assumption that the scatter signal does not change significantly in the wavelength region of the AF line.Another line from the source which does not excite significant analyte or matrix fluorescence is found near to the analyte line and the scatter signal is measured at that line corrected for the relative intensities of the two lines and subtracted from the signal excited by the analyte source line. Epstein et u Z . ~ ~ reported that the ICP was the ideal source for scatter correction using the two-line method because of the large number of ion lines excited by the plasma (whereas the ionic population of flames is low) and these ion lines along with other non- resonance transitions are available for scatter correction. An interesting extension of the foregoing method of cor- recting for scatter is that of Omenetto et a!." They aspirated into the source plasma a solution containing both the analyte and the element used to monitor the scattering signal and achieved the correction simultaneously by subtracting the signals obtained from two high luminosity monochromators facing the flame and each other.One monochromator was centred on the AF line and the other on the scattering wavelength. The subtraction was accomplished with a two channel differential lock-in amplifier. The system was cali- brated as in the sequential method by aspirating a pure scattering solution into the flame. The effectiveness of the method was demonstrated for Cd atomized in a separated air-C2H2 flame in the presence of a 106-fold excess of Al. Epstein et ~ 1 . ~ ~ also described a scatter correction technique based on the shape of the excitation COG.In the concentration range on the plateau region of the COG the fluorescence will not increase appreciably while the emission intensity and thus the scatter will increase. If two different high concentrations of the element being determined are aspirated into the plasma and if the effect of the two different concentrations on the AF and AE signals are known the scatter signal can be calculated. In a later paper13 Epstein et a!. applied this latter scatter correction procedure to the determination of Cd and Fe in Fly Ash. In the same paper they demonstrated the versatility of the ICP as a source in AFS by aspirating a constant low amount of the element of interest into the flame and the sample analyte into the ICP. Under these conditions the flame atomizer acts as an RM* with a narrow bandpass which is of the order of 0.002-0.004 nm the half-width of the absorption line in the flame.The net result of this RM mode was to extend the analytical COG to high concentrations. Thus in the example of the Fe 248.3 nm line the total overlapped linear range was from 0.006 to 1OOOmgml-'. However this mode was said to be only suitable for high concentrations as the reported LOD for the RM mode was only 2 mg ml-I compared with 6 ng ml-' for the normal AFS mode. They gave a list of 12 elements whose LODs varied from 0.4-60 pg ml-' using air-C2H and air-H flames as resonance monochromators with an ICP as a source. They suggested that from the values obtained with a reasonable dilution factor of 100 they would give LODs in a solid sample of the order of 0.004% for Mg to 0.15% for Pd using a shielded air-H flame.As has been mentioned these workers found no spectral interference between the Cd 228.802 nm line and that of As at 228.812nm in the AFS mode. However in the RM mode lOOOmgml-' of As aspirated into the ICP was roughly equivalent to 0.6mgml-' of Cd with Cd in the resonance monochromator. Excellent results were obtained for both conventional AFS and RM modes for the separation of Pd at 363.5 nm from concomitants in nuclear waste. Examples of freedom from chemical interference were given in which signals for Cr and Mn were shown to be essentially identical whether obtained by aspirating into the plasma 1000mgml-' of the solution of each individual element or of a simulated stainless- steel matrix with a 5+ 1 ratio between Fe and the element considered.Similar results were obtained for Ni with the same matrix. The RM mode was also investigated by Omenetto et 3.4 With Electrothermal Atomization It was felt by Omenettolg that the replacement of the flame as an RM with a more efficient atomizer such as the electrically heated carbon rod would have the effect of decreasing the LOD. This was demonstrated to be true with reductions of more than an order of magnitude being obtained. Because of the increased sensitivity a fluorescence signal was also observed with just plasma background (with water) focused onto the region above the rod thus setting a limit to the technique. The relative increase compared with water of the background and the fluorescence signal when aspirating 1000 mg ml-' of several elements into the ICP was investigated. Direct spectral inter- ference was shown to be present with 5 ml of a 100 mg ml-' solution of Zn on the carbon rod from Cu Ni and V and some increase in reflected background light which it was reported could be removed by using a smaller monochromator bandwidth.In further experiments this worker used the carbon rod atomizer in conventional AFS with spectacular results as the LODs in Table 1 show. They can be seen to be much lower ~~ * To distinguish one from the other AFS will refer to the conven- tional arrangement in which the sample solution is introduced into the atomizer and a solution of the element(s) of interest into the ICP source; RM will mean the converse arrangement.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL.9 57 1 than the LOD obtained when flames are used as atomizers and were said to be better than the LODs reported in the literature for graphite furnace AA. It was later reported52 that the precision for Mg and Cd in the ETA-RM mode was 2.7 and 4.3% RSD respectively and from the recorder tracings shown it would appear that for Cd in the AFS mode it was of the order of 13% RSD. This figure was from five results in which 5 pl of a 1 ng ml-’ solution was placed in the atomizer and a solution of 10000 pg ml-l of Cd was aspirated into the plasma. 4 The ICP as an Atomizer in AFS 4.1 With Electrodeless Discharge Lamp as Source In a preamble to a paper by Montaser and Fassel’ it was suggested that a number of elements with resonance lines below 300 nm should show lower LODs in AFS than in AES if a sufficiently intense source could be found.It was also stated that when H2-air or H2-02 flames had been used as atomizers incomplete volatilization had been found leading to scattering and thus these flames had been restricted to relatively volatile elements. When flames with higher tempera- ture such as N20-C2H2 had been employed high background and quenching had occurred. These authors suggested that an ICP should be a useful atomizer. It has a high temperature and long residence time which might be expected to give a high degree of volatilization and atomization and an increase in freedom from physical and chemical interference. The high degree of volatilization should reduce scattering and the argon atmosphere should reduce quenching.(It should also be noted that another advantage of an ICP as an atomizer is the remoteness of the observation zone from the plasma core itself thus leading to lower backgrounds). Montaser and Fassel’ pointed out that with the usual design of ICP torch the tail-flame disperses and expands at distances of around 20 mm above the load coil to cause dilution of the atomic vapour and lead to air entrainment. Using microwave excited EDL as source they designed ICP torches with extended outer tubes having a constriction down to 1Omm i.d. which they used as atomizer. Below this diameter the acoustic noise level was said to rise and melting of the tube occurred. It was also said of these torches that the AF signal increased when the nebulizer gas flow rate was increased from 1.4 to 2.6 1 min-l.Montaser et al.’ had found when experimenting with conventional torches that with a forward power of 700 W the background emission increased by about 5 orders of magnitude when the observation height was changed from 20-120 mm above the load coil. When the power was increased to lo00 W the background increased by 3 orders when the observation height was 120 mm. However the background was less sensitive to power when the observation height was moved close to the work coil. It was concluded that as far as background was concerned AF measurements should be con- ducted at low power levels and at a distance well above the load coil. The above experiments were repeated measuring the AF signal.In contrast to the background emission signals the AF signal from Cd reached a maximum 45-65 mm above the work coil at a power of 800 W. The maximum variation of the AF signal with observation height was approximately a factor of 5. A 20% increase in forward power caused a similar decrease in AF signal. Forward power below 650 W caused plasma instability. The signal to noise ratio (S/N) also reached a maximum at an observation height some 45-65 mm above the coil. Higher forward power generally reduced the S/N. At 800 W it was found that with a carrier gas flow rate of 2.41min-’ higher plasma gas flow rates reduced the back- ground although when the observation height was moved closer to the coil the plasma background became less sensitive to plasma gas flow.Similar results were reported for variations in carrier gas flow rates. In the case of the AF signal for Cd a change in plasma gas flow from 9-19 1 min-’ resulted in only a small variation in signal caused it was suggested by dilution of the atomic vapour. The S/N decreased due to increased turbulence. Higher powers reduced the signal. For AF measurements the optimum plasma gas flow rate was found to be 10-121min-l. The aerosol gas flow rate had a profound effect. The signal changed by a factor of 5 when the rate was changed from 1 to 2.41min-l. It was concluded that at higher flow rates more sample was introduced into the plasma and that the plasma background was reduced due to the cooling effect of the higher flow rate and the introduction of more water into the axial channel of the plasma.As has already been stated these experiments with conven- tional torches led to the design of torches with extended sleeves. The conclusions reached with regard to the operation of the conventional torches were found to be broadly valid for the extended torches. The LODs were given for Cd Zn and Hg and are shown in Table2. Linear dynamic ranges were 5 x lo5 for the Cd 1 x lo5 for Zn and 5 x lo3 for Hg. No scattering effect was observed for up to 10000 pg ml-’ of A1 but the baseline noise was slightly increased. The AF signal was not significantly different when Cd and Zn were determined in the presence of 10000 pg ml-’ of 17 species. The author is not aware of the publication of other papers reporting the use of an ICP as atomizer in AFS with EDL as sources.4.2 With Hollow Cathode Lamp as Source Demers and Allemand” evaluated the use of pulsed HCLs as excitation sources and an ICP as an atomization cell in AFS. They employed a conventional 2.5 kW generator at 27.12 MHz and a Fassel type torch with a 48 mm extension to the outer tube to produce the atomizer plasma. The operating conditions were normal for ICP-AES except that the h.f. power was much lower the observation height was much higher and the spectral bandpass was much greater. The modulated signals were measured by a lock-in amplifier. These workers demonstrated the inherent simplicity of the AF spectrum by comparing the spectra in the 220-440nm region of V in a No. 2 heating oil obtained by ICP-AES and by HCL-ICP-AFS‘ In the former they showed a plethora of intense lines and in the latter a much simpler spectrum corresponding to strong atomic resonance transitions. Of thirty elements studied the spectra consisted of only the principal atomic resonance transitions and in some cases direct line transitions.Ionic fluorescence transitions were not observed for any family of elements studied except the alkaline earths. For these the ionic lines detected were Ba I1 455.4 nm Ca I1 393.4 and 396.8 nm Mg I1 279.5 and 280.3 nm and Sr I1 407.8 and 421.5 nm. Except for Ba these lines were about 50 times less intense than the principal atomic transitions. They com- mented that in ICP-AES these lines are usually at least an order of magnitude more intense than the principal atomic transitions of these elements.The HCL-ICP-AFS spectrum of the oil showed no baseline shift quite unlike ICP-AES spectra in general. The baseline showed noise which only became significant above about 350nm in regions where intense emission bands from the organic solvent occurred. Aqueous samples were said to show considerable baseline noise in the region of the hydroxyl emission bands at 281 and 307 nm. Demers and Allemand’’ in further experiments showed quite conclusively that HCL-ICP-AFS is not susceptible to spectral line overlap interference. In the first experiment they installed an Fe HCL and aspirated a 1000 pg ml-l Ni solution into the ICP and observed the spectrum obtained between 200 and 550nm. This experiment was repeated with an Ni HCL in position while aspirating a 1000 pg ml-l Fe solution.Despite572 Table 2 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 LODs (ng ml-')* obtained by AFS with ICP as an atomizer and EDL HCL and BDHCL as source EDLt HCLt HCLt,$ HCLg BDHCLI BDHCLI EDLt HCLt HCLt,$ HCLg BDHCLI BDHCLT Ref. Element Ag A1 As Au B Ba Be Bi Ca Cd c o Cr c s c u Eu Fe Ga Ge Hf Hg In K Li Mg Mn Mo Na Nb 9 15 38 <0.1 5 0.3 - 60 - 0.2 2 <0.1 0.4 0.4 0.2 0.3 - - - - 50 5 2 0.6 - - - - 8 0.2 - 62 <0.1 5 25 0.3 60 25 0.5 4 <0.1 < 0.1 0.5 0.6 3 0.1 20 0.5 4 25 400 6 3 0.6 < 0.1 <0.1 0.2 8 <0.1 600 Element Ni P Pb Pd Pt Rb Re Rh Ru S Sb sc Se Si Sn Sr Ta Te Ti T1 U V W Y Yb Zn Zr 15 27 15 15 - 20000 37.5 300 - - - 2000 60 - - - 225 - 300" 700 90 200 1.1 - - - 225" 80 10.5 - 135" 100 4500" - 58 38 62 0.2 2000 6 3 15 1 400 0.3 10 2000 7 5 10 40 25 0.3 1500 3 25 25 5000 20 300 300 1 <0.1 400 * Normalized to 3 x sb.1 In dioxane. § USN with desolvation. f Modified concentric pneumatic nebulizer with desolvation. 1) In No. 2 home heating oil. With cross-flow pneumatic nebulizer. the numerous intense lines emitted by the Fe HCL throughout this region and the complex atomic fluorescence spectrum exhibited by Ni in this region no baseline shift was detected during either scan. The bandpass used was 3.2 nm. This of course meant that over the spectral region measured no spectral line overlap interference occurred between Ni and Fe. These experiments were carried out at concentrations five orders of magnitude above their respective LODs.In the second set of experiments conducted by Demers and Allemand," nine of about fifteen spectral line overlap inter- ferences actually observed to date in AASS3 were investigated for their severity in HCL-ICP-AFS. The inverse interference was also investigated. In all cases the separation between the pairs of lines did not exceed 0.05 nm and in most cases were much smaller even amounting to total overlap in the case of V and Si. With the pairs of lines Cd(As) In (Co) Zn (Fe) and Pb (Sb) more than 1000Opgml-l of the interferent (the element in parenthesis) was required before its presence was detected. The pairs Co (In) Sb (Ni) and Si (V) required 1500-2500 pg ml-' of the interferent; Ni (Sb) Sb (Pb) and A1 (V) required 105-300 pg ml-' and As (Cd) Co (Hg) Hg (Co) Fe (Zn) V (Si) Zn (Cu) and Cu (Zn) required 14-75 pg ml-l before interference was noticed.With the pair V (Al) interference occurred in the presence of only 0.75 pg ml-' of V. It is obvious that the stringent conditions that have to be met before spectral interference can take place referred to in sub- section 3.3 have been met in the case of the A1 and V pair at 308.215 nm. However in those cases where a comparison with AA was possible the degree of spectral overlap was significantly less for HCL-ICP-AFS than for AAS except for Ni interference on Sb where the two techniques were comparable. Demers and Allemand concluded that the widths of the absorption lines in the wings in the ICP under AFS measuring conditions range from comparable to somewhat narrower than in flames and furnaces and in turn that the frequency and severity of spectral line overlap interferences in HCL-ICP-AFS should be at worst comparable with AAS.In further experiments these workers found that h.f. power and observation height in the ICP were the two most important factors in determining LODs for the HCL-ICP-AFS system although plasma gas flow and torch configuration did have an effect. In non-optimized studies and using conventional torches they found that LODs improved with decreasing power or increasing observation height up to about 50 mm. This trend was typical of elements that were easy to dissociate but difficult to ionize. With this category of elements the signal intensities changed only slightly with observation height and were almost constant over a broad range of powers; however the baseline noise decreased as the observation height increased or the h.f.power decreased. With Na an easily dissociated easily ionized element the signal intensity decreased asympytotically with increasing power. As a result of this the degradation in LODs with increasing power was steeper. On the other hand it was reported that the LOD of the alkaline earths and many of the refractory elements varied by a small amount over h.f. power ranges of as much as 400 W because the increase in baseline noise with increasing power was offset by increases in analyte signal intensities. All subsequent work was performed with the plasma torch with an extended outer tube. It was found that the observation heights were around 65-75 mm and 55-60 mm above the injector nozzle for the non-refractory and refractory elements respectively.Also similar LODs were obtained ifJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 573 increases in the power were offset by increases in obserLatioti height. The LODs obtained for their system of HCL-ICP-AFS are shown in Table 2.15 With the caveat that LODs should differ by a f x t o r of more than 3 to be considered to be significantly different Demers and Allemand's claimed that these LODs. when compared with LODs obtained by AAS were equal foi the majority of elements. better in some cases (Ca Hg TI and Mn) and never worse for any element when data obtained from the same solvent were compared. Compared with ICP- AES the LODs obtained for the refractory elements were much worse.With respect to the LODs of the other elements most were equal to those of ICP-AES and TI and Na gave better LODs by HCL-ICP-AFS. It was further claimed by these workers that around the modulation frequency of 500 Hz which they used. the noise was 'white' and therefore the LODs could be improved by increasing the integration time. since the magnitude of the noise decreased as the square root of the integration time. (It is interesting to note that when an ICP is used as a source with an ICP as an atomizer the noise remains more or less constant with integration time as it does in ICP- AES). It was also claimed that the linear dynamic range of the HCL-ICP-AFS system was superior to that of AAS and comparable with ICP-AES (i.e.four to five orders of magnitude). I n the same paper" Demers and Allemand investigated some interelenient interferences. in particular the classic com- pound formation interferences of PO and A1 on the emissions of Ca 1 and the ionization interference of Na on Ca and Zn. At low to medium powers the effect of PO was to produce the classic 'knee' in the interference curve. At higher powers (>go0 W) the interference was absent as it is in ICP-AES. The Ca-A1 system showed a niarked depression at low powers and an elevation at higher powers. Ionization effects were not noticed in the Zn-Na system whereas Ca exhibited either a small enhancement or a depression depending on the concen- tration or the power. The usefulness of these experiments is somewhat diminished since.so far as can be gathered from the paper a formal global optimization of all the parameters for minimum interference was not carried out. Later work by other workers show that such an optimization can have a profound effect on the degree of interference. Of course as in ICP-AES such an optimization will in some instances degrade the LOD. Background interference due to radiative recombination continua and other d.c. or low frequency background shifts were said to be avoided because ax. coupled detection elec- tronics were used to discriminate against d.c. signals while the 50 Hz low-frequency filter of the a.c. amplifier of the lock-in amplifier rejected low frequency background changes. High frequency variations of background appeared as increased noise.Background interference from line broadening was investi- gated by studying the results from a number of experiments. An A1 HCL was installed in the instrument the monochroma- tor was set to 396 nm and a 100OOpg~' Ca solution was aspirated. Despite a separation of only 0.6 nm between the Ca IT 396.8 nm line in the plasma and the A1 radiation from the HCL of 396.2 nni no baseline shift w7as observed. In a similar experiment aspirating 10 000 pg ml-' Mg solutions with the monochromator set at 280nm and an Mn HCL in place the baseline did not shift. In this case the Mg TI lines at 279.6 and 280.3 nm could have interfered if they overlapped the nearby intense 279.5 279.8 and 280.1 nm lines from the Mn HCL. Line broadening interference was also absent from the intense Mg I 285.2 nm line using an Sn HCL with intense lines at 284.0 and 286.3 nm. Background interferences from reflected light were said to range from undetectable to three times greater than the LOD of Zn which was the worst case.Interference from molecular absorption was thought to be highly unlikely. Attempts were made to detect interferences from molecular fluorescence by putting V and Fe HCLs in place and scanning across the 250-500 nm region while aspirating organic solvent. No base- line shifts were observed indicating no molecular fluorescence from CN CH and other bands from the solvent. Molecular absorptions of SrOH and CaOH have been observed at 670 and 545 nm;s4 with Li and Ba HCLs in place. no mole- cular fluorescence was detected at these wavelengths when 10000 pg ml-' solutions of Sr and Ca respectively.were aspirated. Strong d.c. molecular emission from these salts was said to increase the baseline noise. Molecular fluorescence was eventually observed from the 306.4nm hydroxyl bandhead with a Bi HCL in place. (This Bi HCL has a principal emission line at 306.7 nm). The molecular fluorescence signal observed was only about four times larger than the background signal. Since the signal came from the solvent it was suggested that it would be subtracted out during normal analytical procedures. It was also reported that at 100 mm observation height the molecular fluorescence signal was absent while the SIN for Bi was unchanged. Demers and Allemand15 presumed that the virtual absence of molecular fluorescence in HCL-ICP-AFS was due to the inert atmosphere in the plasma and to the fact that the excitation of any molecular species was extremely inefficient.as it occurs only over the width of the emission line of the HCL. Light scatter by non-volatilized particles was investigated by these workers by aspirating solutions containing high concentrations of a wide range of salts into the ICP with a Zn HCL in place (except for Zn metal when a Cd HCL was used). Some 43 compounds with concentrations varying from 1 to 40% m/v were aspirated. The element concentration was I '/o m,'v except for Na which was 16% m/v. Despite the low power used 550 W nominal no detectable scatter signals were found. Demers Allemand commented that Doolan and S m ~ t h e ~ ~ using an N20-C2H2 flame as an atomization cell on much the same compounds had also not detected any light scattering.They concluded that it was therefore hardly surprising that no light scattering had been found with HCL-ICP-AFS since the sample temperature reached in the ICP was probably greater than that reached in the flame. When 10000 pg m l - - ' of Fe particles < 8 and < 14 mm in diameter were aspirated noisy signals equivalent to 10 and 6 ng ml-' of Zn respectively were finally observed. I t was concluded that for samples which are true single-phase solutions scattered light should not be a problem for virtually all types of samples that can be aspirated comfortably with the available nebulizers. In order to minimize clogging and drift by the nebulizer in the above investigation.a sample aspirating tube of 0.55 mm i.d. was used. The tube caused low-frequency pulsing inside the spray chamber. However the LODs were unaffected as the pulsing frequency was well below the frequency (500 Hz) at which the fluorescence signals were detected. It was sug- gested that modulation of the signals above the flicker noise frequencies permitted the use of cruder nebulizers and less precise control of the plasma gas flows without affecting the LOD. This comprehensive investigation by Demers and Allemand" demonstrated the many attributes of an AFS system based on an ICP as an atomization cell. I n particular. they claimed that HCL-ICP-AFS was virtually free from spectral interferences and numerous background interferences which plagued ICP-AES and had a large dynamic range with excellent LODs for many elements.They also claimed that the use of an ICP as an atomizer removed many of the drawbacks of previous AFS systems such as particulate scatter molecular fluorescence and matrix effects. The paperI5 was the precursor to the launch in 1981 of the Baird AFS instrument which was described in two presented at the 1981 Pittsburg Conference. This instrument comprised a centrally placed atomizer plasma around which were put a number of units each of574 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 which consisted of a pulsed HCL lenses filter and PMT. The radiation from the HCL was directed by means of a lens at a particular portion of the tail-flame of the ICP and the fluorescence produced was passed by an up and over con- figuration through another lens and interference filter onto the PMT.The HCLs each for a different element were pulsed in random sequence and the signals from the PMTs were collected by synchronously gated electronics. The instrument had twelve channels and could be said to be simultaneous multi-element in operation. In the two paper^'^$'^ presented at the conference Demers and Allemand showed that the Baird instrumental set-up was capable of reproducing the excellent results which they had achieved with the prototype arrangement. They also gave details of further experiments which they had performed with the new instrument for instance it was found that elements whose principal AF lines lie below 350 nm gave LODs which were not degraded by the presence of a high concentration of concomitants such as NaCl and Ni.In fact in several instances some slight improvement occurred which they attributed to the matrix removing the hydroxyl and other bands on top of the ICP background noise and thus reducing the ICP back- ground noise. Above about 400 nm where the atomic emission (AE) signals are intense some degradation of the LODs did occur especially in the presence of Ni but this degradation was no more than an order of magnitude worse. The effects of compound forming elements such as P and A1 in Ca fluor- escence were further investigated at high and low powers and various observation heights with much the same freedom from interference being observed. Likewise the effect of easily ionized elements such as Na was much the same as with the prototype instrument.These workers suggested that their work had demonstrated that HCL-ICP-AFS was susceptible to rare instances of spec- tral overlap fewer than in AAS and dramatically fewer than in ICP-AES and rare light scattering background interferences. They cited the freedom from the following interferences to which ICP-AES is prone unresolved spectral lines line broad- ening recombination continua stray light molecular emission nebulizer drift h.f. power drift and spectrometer drift. They further cited the interferences which can be experienced in AAS but not in HCL-ICP-AFS spectral overlap (rare but more frequent than in HCL-ICP-AFS) molecular absorption light scattering and excitation source drift.on the use of the Baird instrument to determine refractory elements and also the determination of elements in organic solvents. In the same paper he cites the use of flushed chambers to determine S and P and also the use of a graphite central tube to reduce Si contamination (mentioned in Section 2). Demer~,~ added a low flow of C3H (10 ml min-') to the nebulizer spray chamber via a second inlet. He observed a narrow region of green coloured emission characteristic of C Swan band emission extending 10-20mm beyond the outer tube of the extended torch. At higher flow rates (40 ml min-') the green emission extended into a triangular shaped flame extending 40-50mm beyond the end of the outer tube. He found that elements which form moderately strong oxides such as Al Ba Cay Cr Sn Sr and Yb gave enhanced signals and lower LODs with enough C3H8 to form a narrow green emission and measuring about 10 mm above the green region. Elements with strong oxide-forming tendencies such as B Si Ti V W etc.required the higher flow of C3Hg and measure- ments were made in the green zone about 20mm above the outer tube. It was suggested that the presence of C radicals from any C-containing gas reduces the formation of metal oxides by the refractory elements at high observation heights. In a later paper Greenfield and Thomsen28 showed that for a fixed concentration of W the same fluorescence signal was observed on the addition of either CH or C4H10 to the carrier gas. The proportions of CH C,Hs and C4H10 corresponded In 1985 Demers to a constant number of carbon atoms delivered into the plasma.This provided support for the theory that the role of the hydrocarbon is to provide C atoms to react with the available oxygen. (It has been reported56 that although the introduction of C3H8 into the plasma promotes the reduction of oxides into free metal atoms it does at the same time lower the energy of the plasma. Therefore the addition of C3H8 lowers the emission signal of refractory oxides because the less energetic plasma is not able to sustain the same population of the excited state even if the ground state population is enhanced through metal oxide reduction. The signal from AFS or AAS determination of refractory oxides where the popu- lation of the excited state is accomplished through radiative excitation is enhanced if C3H is added.) When an organic solvent is introduced into an ICP operated at low power in addition to a green coloured reducing emission along the outer edge of the axial channel there is a yellowish emission at the centre of the axial channel.This latter emission is due to incomplete combustion of the organic solvent resulting in luminous carbon particles which in turn cause noisy base- lines. DemersZ7 found that by introducing 300 ml min-' of O2 into the spray chamber by the same inlet as was previously used for C3H8 introduction complete combustion was obtained. However refractory elements could not be deter- mined at all. If the flow of 0 was reduced to 75-100 ml min-' the green reducing emission region re-appeared though greatly reduced in size and intensity; the yellow emission was also reduced in size and intensity.Under these conditions the refractory elements could be determined. The LODs of many elements were found to be higher than those observed with aqueous samples. Unfortunately with commonly used solvents such as isobutyl methyl ketone (IBMK) (CH3)&H etc. as 0 is introduced the green reducing emission region is always eliminated before the useless yellow emission region. Demer~,~ found that this dilemma was avoided by the use of dioxane as the organic solvent. Dioxane contains 36% of O2 and when nebulized into the ICP along with about 100 ml min-l of 0 introduced as previously described eliminates the yellow emis- sion without lessening the desired green Swann bands. In the same paper,27 Demers gave details of the determi- nation of S and P by the use of a chamber extending from the front face of the HCL to about 5 mm from the outer tube of the torch and back to the detector.This chamber was flushed with Ar at a rate of 1.5 lmin-' for 4min. It was found necessary to incorporate this chamber into the system because the principal AF lines of S and P are in the vacuum UV near 180 nm and in this region the Schumann-Runge bands of O2 absorb the radiation from the excitation source and the fluorescence produced. The LODs in water for S and P were 1 and 20 pg m1-' respectively and linear calibration curves up to 10000 pg ml-' were obtained. The S signal intensities of a number of S containing compounds all at the same concentration with respect to S were found to be identical suggesting complete dissociation in the ICP.It was further discovered by Demers that since the central tube of the Baird torch is very close to the plasma erosion of Si occurred causing random fluctuations in the Si signal and background emission. To overcome this problem a commercial graphite electrode with a hole bored through it was fitted to the top half of the injector tube. As was expected erosion of Si was no longer detectable. An added benefit was a reduction in the h.f. power levels necessary to determine refractory elements. The acoustical noise power spectra of the Fassel type' ICP- AES torch and a variant having an extended outer tube with and without a neck at the t0p,'7'~ showed that whereas the torch with an extended outer tube was free of peaks the torch with a neck at the top exhibited a large pneumatic noise peak at around 500Hz the same as the electronic detection fre- quency over the power range 550-900 W.This resulted in a degradation in LOD over this power range.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY. MAY 1994 VOL. 9 575 To conclude this informative paper," Demers reported on a comparison between power. length of outer tube of the torch and the classical depressive effect of P on the emission of Ca. By observing the Ca signal with increasing amounts of P at the same height with respect to the end of the outer tube of the torch he found that severe Ca signal depression occurred at powers below 900 W when using a conventional torch. I n contrast the torch with an extended tube was free from this interference at powers as low as 500 W.Demers concluded that with the long torch quenching by air entrainment was delayed a s was the rate of decrease of the plasma axial temperature. Since the magnitude of the depression with the short torch was strongly dependent on power and at a given power the magnitude of the depression only changed by 10% when the observation height was varied from 40 to 80 mm from the central tube Demers stated that the absence of matrix interference when using the long torch was due primarily to the greater temperature rather than the greater residence time. Jansen and Demerss8 investigated the performance of the Baird instrument under compromise conditions in order to be able to carry out simultaneous multi-element analysis.Using Cu as being representative of those elements such as Ag Cd Pb Ni and Se that are easily dissociated and weakly ionized in the ICP they found the signal intensity of these elements to be virtually independent of the h.f. power when using nominal operating conditions. The small decrease in signal with increased observation height which occurred probably resulted from the diffusion of atoms out of the irradiated volume and or fluorescence quenching. At a given h.f. power the LODs were virtually unchanged over a 30mm variation i n observation height. This. it was concluded was due to the fact that the increase in noise at lower heights as a result of the greater intensity of the plasma background was compen- sated for by a corresponding increase in signal intensity.The alkali metals are also easily dissociated in the ICP but they are also significantly ionized. Using K as an example these workers found that with increasing h.f. power ionization increased and the signal decreased. Since the baseline noise also increases with power the LOD also increased. The observation height was of little importance over the 110-140mm range. In general it was found that both the alkali and Cu-like elements gave the best LODs at low h.f. powers and high observation heights. As has been stated i t is necessary to inject C,H into the ICP in order to determine refractory elements. The range of observation heights for these elements is lower than for other elements about 80-100 mni above the central tube tip.At higher observation heights the reducing atmosphere diminishes. At lower heights the baseline noise increases faster than the signals and photodetector saturation becomes a problem. The best LOD for Mo occurs at low h.f. power. compatible with that for all easily dissociated elements. Boron on the other hand gives virtually no signal at low powers and requires about 200 W more power than Mo to obtain its best LOD. Obviously some compromise in operating conditions is necessary for it to be possible to carry out simultaneous analysis of a range of elements. Jansen and Demers" calculated that the degradation in LODs resulting from the selection of the optimum power for B would be about 4-fold for Cu and Mo-like elements. but about 30-fold for K-like elements.They concluded that it was fortunate that the LOD of the alkali metals was in the sub-ng ml-' range under optimum conditions so despite the large degradation in LOD at higher h.f. power the sensitivity was still likely to be satisfactory for most applications. On the question of matrix interferences these workers found that solute vaporization interferences are generally eliminated or at least greatly reduced by increasing the plasma temperature. Higher plasma temperatures are obtainable by decreasing the flow rate of the carrier gas increasing the h.f. power or less effectively by rcducing the sample uptake rate. In short as in ICP-AES one should optimize operating parameters for minimum inter- ference preferably in a formal manner. The final part of this paper58 was concerned with the development of an ultrasonic nebulizer (USN) with a desolv- ator for use with the Baird instrument.In this work the signal intensities obtained using the USN with and without desolv- ation were compared with those obtained by the cross-flow nebulizer normally fitted to the Baird instrument. For this comparison only easily dissociated weakly ionized elements were selected so that the relative signal intensities would represent measures of the relative numbers of ground state atoms reaching the plasma undistorted by temperature effects and the environment in the plasma. The average signal enhancement with USN was about &fold when desolvation was used and about 5-fold without desolvation. The baseline noise levels were virtually identical with and without desolv- ation and when compared with pneumatic nebulization.Consequently the net LOD improvement obtained using USN is due to improved transport efficiencies. I t was further noticed that whereas some 750 W of h.f. power is normally required to eliminate the interference of an increasing concentration of P on Ca fluorescence using pneumatic nebulization only 500 W was required when using USN with desolvation. When desolvation was not used. the depression was severe pointing to an increase in plasma temperature when water is removed. The HCL-ICP-AFS LODs obtained with USN and aerosol desolvation are shown in Table 2. The limitation on HCL operating current is in most cases that current where light is re-absorbed by ground state atoms in the cathode.This problem can be overcome by using a secondary boost discharge passed through a cylindrical cath- ode to the anode. The boost discharge is optimized for a particular sputtering current thereby exciting and removing any ground state atoms in front of the cathode that would otherwise absorb much of the emitted light. The BDHCLs were first proposed by Sullivan and Wal~h,'~ later modified by Lowe.60 In an attempt to obtain lower LODs Lancione and Drew"' fitted a Baird AFS with a BDHCL and a USN with a desolvator. They showed that a USN with a desolvator and a standard HCL in the instrument gave an order of magnitude improvement in LOD for Ag and Au over the same instrument fitted with a pneumatic nebulizer and a standard HCL. When the instrument was fitted with a USN plus a desolvator and a BDHCL there was a further factor of 3-5 improvement.Overall the LOD fell from 15 to 0.5 ng ml- for Au and from 2 to 0.04 ng ml - ' for Ag. Demers3' reported on the improvement likely to result by the use of BDHCL with the Baird instrument. He found that elements with high spluttering rates andlor high vapour press- ure together with high excitation energies exhibited a large gain in signal with BDHCL. Elements such as Ca the alkalis and the rare earths which exhibit good spluttering rates and have low excitation energies showed little or no gain with BDHCL. The BDHCLs are also of no benefit with those elements that splutter poorly such as most of the refractory elements. With such elements excitation with conventional HCL is already efficient because the number of fill gas ions available with sufficient energy to produce excitation is large relative to the number of ground state atoms spluttered.In these circumstances conventional HCL of such elements can be operated safely at much higher currents t o produce greater AF signals. In this same paper38 Demers described a modified concentric nebulizer in which the tip of the sample tube is recessed relative to the tip of the carrier gas tube and the annular spacing modified to permit operating a t gas flow rates of 2 1 min - I optimal for HCL-ICP-AFS. In addition an impact bead was placed very close to the nebulizer nozzle. The aerosol produced was also desolvated as for the USN nebulizer. He found that at uptake rates of < 1 ml min-' the signals with the modified concentric nebulizer with desolvation were about 6 times576 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL.9 greater than with the previously used cross-flow nebulizer somewhat less than the order of magnitude improvement obtained with the USN plus desolvator. An 8-fold improvement in signal over that obtained with the cross-flow nebulizer was obtained when the uptake rate of the modified concentric nebulizer was increased to 5mlmin-l. The LOD obtained with the Baird instrument using the modified concentric pneu- matic nebulizer with desolvation HCL with greater operating currents or BDHCL as appropriate are shown in Table 2. Since mid-1991 the Baird instrument has not been available commercially. However in 1992 Demers and Montaser pub- lished a comprehensive account62 of the theory and practice of HCL-ICP-AFS.This account as well as showing state-of- the-art LOD (Table 2) contained information on scatter effects with HCL-ICP-AFS not previously presented in detail. Aluminium Ca La Si Y and Zr at concentrations of 0.5% m/v were said to produce scatter signals 210xabove the LOD; Be Dy Er Gd Mg Nb Sc Sr Ta and Th produced scatter signals <10xabove the LOD; some 47 elements including B Mo Ti W V and U produced no scatter signals and at concentrations of 0.1%0 only Al La Si and Y still showed a scatter signal < 10 x above the LOD. None of the elements tested exhibited scatter signals in organic solvents. It is interesting to compare these results with the results from Demers earlier work'' where some 43 compounds with a concentration range from 1 to 40% m/v failed to give scatter signals which were detectable. Forty-two of these same com- pounds were examined in the above study.62 Thirty-three were not detected at element levels of 0.5% m/v.Three gave a signal c10xabove the LOD and six gave a signal 210xabove the LOD. Nickel and Co were two of the elements giving no inter- ference at element concentrations of 0.5% m/v. However Sanzolone and Meier63 were unable to determine these elements in acid mine and reference water samples due to scatter problems as is reported in Section 6. 4.3 With Laser as Source A team" from the chemistry department of the University of Florida investigated the possibility of using a CW argon ion pumped dye laser as an excitation source with a conventional ICP torch as an atomizer.They regarded their work as a continuation of that by Smith et ~ 1 . ~ using a similar source but with an N20-C2H2 flame as atomizer. (Smith had con- sidered the possibility of overcoming the limited wavelength range of the source by utilizing lower excited states and non- resonance transitions to increase the number of measurable elements). It was thought that the higher excitation tempera- tures of the ICP would increase the populations of lower excited states and give greater flexibility with the CW-laser- ICP system than was available with the previous CW-laser- flame studies. The source which was used was a Rhodamine 6G CW-dye laser pumped by all the lines of a 5 W- argon ion laser.The laser beam was chopped at 260 Hz and focused into the ICP. The ICP was mounted on an adjustable ( X Y Z ) table so that any part of the plasma could be illuminated by the laser without itself being disturbed with respect to the monochroma- tor. The AF signals were measured with a synchronous detec- tion system. At a position 0.5-2.5 cm above the coil the fluorescence signal could not be separated from the background and/or analyte emission noise at powers of 1.2-1.5 kW (presumably at the work coil). At similar powers the AE LOD for Na measured 3 cm above the coil was 0.2 pg m1-l. This poor LOD was attributed to instability of the tail-flame. By decreas- ing the power of the plasma in order to reduce the background and by measuring the AF in the so-called analyte pencil region 1.5 cm above the coil the S/N was greatly improved and the AF signal was 20 times greater than the AE signal.The linear dynamic range was found to be at least 5 orders of magnitude for Na and Ba. A number of elements amongst which were included Mo Rh Sc Sr Cd and U gave no measurable fluorescence at levels of 1000 pg m1-l. Contrary to the expec- tations of these workers elements having AF lines involving lower excited states resulted in poorer LODs with the ICP than with a flame. In fact many elements having potentially useful atomic transitions did not produce AF signals even though AE signals were observed at the levels involved. These workers concluded that AF in the ICP was possible using a CW laser source. However the system was not analytically useful because of the limited wavelength range of the CW laser the high cost of the equipment and the mediocre LODs produced compared with ICP-AES.used both a flashlamp-pumped dye laser and a nitrogen laser-pumped dye laser to excite atomic and ionic fluorescence in the ICP. For the two elements investigated with the flashlamp pumped laser Fe and Sn they reported LODs two orders of magnitude worse than the best ICP-AES results reported in the literature with pneumatic nebulization and almost identical to LODs obtained with their own instrumentation. A comparison of LODs produced by laser excited ICP-AFS (L-ICP-AFS) and flame AFS excited by the same source showed the latter to be three orders better. This difference could not be explained away by differences in the optical systems used in each case.It was concluded that the major reason for the difference was the greater background emission (and noise) of the ICP. (Although not stated it is presumed that a conventional torch was used). The effect of h.f. power on the S/N of the AF signal for 10 pg ml-' of Fe was that the background increased by a factor of about 18 as the power was increased from 0.65 to 1.25 kW but the S/N decreased by a factor of 4 characteristic of a shot-noise limited system. It was considered that while detector/electronic noise was a major source of noise at low ICP power levels the dominant noise was ICP background emission shot noise. At higher power levels (1.25 kW) the ICP background emission flicker was the only major source of noise.The noise sources in an ICP analysis will therefore vary from detector/electronic noise at very low background emission intensities through a region of moderate background emission intensity where background emission shot-noise is dominant to a region of high back- ground emission intensities where background emission flicker is the major noise source. It was suggested that the best region for AFS analysis was the emission shot-noise limited region. In the detector/electronic region the S/N could be improved by increasing the optical throughput. In the flicker noise region the background noise could be reduced at a rate faster than the signal by decreasing the spectral bandpass. Similar results to the foregoing were obtained when these workers14 used the nitrogen laser-pumped dye laser as exci- tation source.The expected improvements in the L-ICP-AFS LOD arising from an improvement in quantum efficiency and the restricted volume of the analyte in the plasma did not materialize. Any improvement was more than offset by the increase in the background intensity of the plasma compared with separated flames (again it is necessary to stress that a conventional torch was used not a long-sleeved torch). It was concluded that whilst this initial evaluation of L-ICP-AFS had not indicated that the technique was superior to ICP- AES or laser flame AFS the application of multipass optical cells as well as the use of more powerful laser sources should improve LODs enough for the advantages inherent in the technique to be realized. Furthermore L-ICP-AFS was still a powerful diagnostic tool in studies of the ICP.This was borne out by Omenetto et who used an N laser pumped tuneable dye laser to obtain ionic and atomic fluorescence profiles of Ba in an argon plasma. They obtained spatially resolved profiles along and across the observation axis without the need of an Abel inversion procedure. Profiles were obtained Epstein etJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 577 at different observation heights and with different powers. They found that at low heights the ion profile resembled a hollow pencil with a typical double-peaked asymmetrical distri- bution; the atom profile seemed to be complementary to the ion profile. Uchida et used excitation by a pulsed dye laser to measure vertical distributions of analyte atoms and ions along the central axis of a plasma.They also reported that ionic and excited state fluorescence are strongly observed in the ICP and that the spontaneous transition probability value of the fluorescence line is a dominant factor affecting sensitivity. It was said that laser excited analyte species are not in a Boltzmann distribution and that thermally assisted collisions are observed only when within 1.2 eV of the radiat- ively excited level. Fluorescence LODs in the analytical region of the plasma were said to be two orders poorer than those for AE and are shown in Table 3. Uchida et ~ 2 1 . ~ ~ 7 ~ ~ showed that it was possible to measure the lifetime of excited atoms and ions in the ICP by the use of a short pulse dye laser and measurement of fluorescent decay.They showed that in most cases the overall quantum efficiency given by the ratio between the measured lifetime and the calculated radiative lifetime ranged between 0.7 and 1.0 for the lines investigated. evaluated the use of the long-sleeved torch in L-ICP-AFS using a tuneable dye laser with a pulsed N laser as primary source. They found that the horizontal distribution of resonance ionic fluorescence intensity for Ca ions at 393.4nm was symmetrical with the maximum on the central axis of the plasma. The fluorescence intensity decreased and the profile broadened with an increase in observation height. Comparison of the profiles with those obtained with conventional short torches showed that the extended-sleeve torch was fairly effective in preventing diffusion of analyte atoms into the surrounding air.When measured at 45mm above the top of the coil the intensity of the atomic line for Ga decreased with increasing power. The atomic line for Mo gave a maximum fluorescence peak at 1.0 kW (equivalent to 3500K) and for Ca the ionic fluorescence was maximal at about 0.9 kW (3300 K). Similar results were obtained for Kosinski et resonance ionic fluorescence for Ba at 455.4 nm and for Sr at 407.8 and 421.6nm. In contrast the Y ionic fluorescence at 508.7/371.0 nm anti-Stokes fluorescence needed high power. The background intensity level and its reproducibility were about the same at each h.f. power. Vertical distribution of excitation temperature at powers of 0.7 and l.OkW along the central axis of the ICP showed a decrease in temperature with increasing observation height.At 0.7 kW at high positions the temperature was roughly that of an N,O-C,H2 flame. The vertical distribution of resonance- fluorescence intensities along the central axis of the plasma for Ga I 403.3 nm (at 0.7 kW) Mo I 386.4 nm (1.0 kW) and Ca I1 393.4 (1.0 kW) were shown to be affected by lateral diffusion to the same extent but in the case of Ca the decreasing temperature would it was said result in a depopulation of the first ionic state. The Mo intensity decreased even more because of it was said the formation of monoxides. In an attempt to improve sensitivity the use of an expanded dye-laser beam of about 10 mm diameter at the ICP position and a monochromator slit-height of 10 mm was investigated.The fluorescence intensities were 3-5 times as large as those obtained with the 3 mm beam and slit-height previously used. The background intensity caused by scattering also increased but the increase in noise was small. As a result the S/N was improved appreciably depending on the type of fluorescence observed. The S/N was much better for non-resonance lines. The LOD obtained for a number of elements are shown in Table 3 -and in general the LOD obtained with the short torch66 under conditions of 1.0 kW h.f. power 154 kPa carrier gas pressure (cross-flow nebulizer) and 20 mm observation height produced superior LOD values for ionic excited-state fluorescence and for the refractory elements. For other lines the long torch gave LODs 1-3 orders of magnitude better than those obtained with the short torch.The linear dynamic range was shown to extend over four orders of magnitude. Inter-element effects were observed. Phosphorus slightly lowered the ionic fluorescence of Ca but it was suggested that this was partly due to an increase in sample viscosity. Also Table 3 LODs (ng mi-')* obtained by AFS with ICP as an atomizer and dye laser as source Ref. 22t 57$ 661- Element Ag - - - A1 0.4 7.5 - AS - - - AU - - - B 4 - - Ba 0.7 1.5 12 Ca - 1.5 60 Ce - - - c u - - - Dy - - - Er - - - Ga 1 6 - EU - - - Gd - - - Hf - - - Hg - - - Ir - - - La - - - Lu - - - Mg - - - Mo 5 150 4500 Nb - - - Nd - - - Element P Pb Pd Pr Pt Ru Sb s c Se Si Sn Sr Ta Tb Te Ti TI Tm v Y Yb Zn Zr * Normalized to 3 x sb. 7 With conventional short torch.$ Extended sleeve torch. 9 Double resonance ionic fluorescence. 1 Stimulated Raman scattering. 11 Ultrasonic nebulization.578 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 the Ca ionic fluorescence was decreased in the presence of A1 but this decrease was lessened at higher temperatures as might be expected. The effect of Na on the Ca ion line at 0.7 kW was to reduce its intensity rapidly. At 1.0 and 1.2 kW h.f. power the intensity increases to a maximum at about 100 pg ml-I of Na and then falls again. This enhancement is not due to an ionization interference. The emission spectra and fluorescence spectra between 370 and 372nm were compared for a 100 pgml-' Y solution containing 5000 pg ml-' of Fe as matrix.Even with a 50-fold bandpass the spectral profile for fluorescence showed no overlap between the Y I1 371.03 nm line and the Fe 370.925 nm line in contrast to the emission spectra. The Y emission at 371.030 nm slightly overlapped the Fe line at 370.925 nm. In ICP-AES such overlap becomes a significant interference when the analyte concentration is low. It has been stated previously that Kosinski et ~ 1 . ~ ~ found that the horizontal distribution of resonance ionic fluorescence intensity and hence the population densities for Ca ions at 393.4nm were symmetrical with a maximum on the centre axis of a plasma produced in a long-sleeve torch. In further investigations Walters et aL2' used a saturated absorption spectroscopic method to directly determine spatial distri- butions of absorbing species in two types of plasma torch.The measurement was made by constantly monitoring the intensity of a probe beam which was stated to be a function of the absorbing species in the atom cell. The probe beam came from an excimer laser pumped dye laser via a beam splitter and neutral density filters. The absorption signal changed when a high-intensity pulsed laser beam intersected the probe beam and saturation of the absorbing species occurred in the volume. The high-intensity beam was obtained via the aforementioned beam splitter. The perturbation of the absorption signal was considered to be directly related to the number of absorbing species in the intersecting volume the size of which determined the spatial resolution. Therefore by moving the intersecting point through the atom cell an accurate spatial distribution of the absorbing species along the path of travel could be made.This method was said to apply to atoms ions and molecules as long as saturation can be obtained for the specific transition used in the absorption measurement. The method2' was used to obtain a spatial distribution of ground state atoms with the resonance transition of Sr 460.7 nm. A short torch was used initially with a high flow rate nebulizer operating at 3 1 min-' and a plasma gas flow rate of 15 1 min-'. The power was stated to be 1.25 kW. The lateral spatial distribution of the Sr atoms was measured at heights between 25 and 85mm above the load coil. These investigators reported a lack of radial symmetry in the plasma plume.At 25 mm height the Sr atoms were localized more in the centre of the plasma while at 40mm the atom concen- tration was lower in the centre. From 55 to 70mm the dip in the centre disappeared and the distribution of atoms tended to spread out from 55 to 85 mm above the load coil. The spatial distribution of Ba I1 ions was also studied by the absorption method using the small torch and a low flow rate nebulizer. The distributions were fairly symmetric and narrower than the Sr atom distributions. At a height of 7 mm above the work coil the Ba I1 distribution was highly concave. At 15 mm the dip was small and at 25 mm it had disappeared. When using a torch with an extended sleeve at h.f. powers of 500 W with torch gas flows of 10 1 min-' of argon and carrier gas flows of 3 lmin-' of the same gas the spatial distributions found were significantly different from those found with the short torch.As is normal when using a Baird torch (which this was) the aerosol tube was positioned between the first and second coils of the work coil. The lateral spatial distribution of Sr atoms for the long tail-flame produced by the torch were not radially symmetrical at lower heights although they improved towards 90 mm observation height. The base widths of the distribution were much broader than those found in the short torch. The hollow core or channel extended up to 90mm above the coil while the Sr atom concentration in the centre also increased with increasing height of observation. When C,H was added to the nebuliz- ation gas at approximately 50 ml min-' the distributions had a similar shape with the dip in the centre being somewhat smaller. The interesting feature was that the distribution bulged to the sides especially at low heights where the influence of the C3H was still significant.This was attributed to the result of carbon radicals reacting with the oxides and monohydrox- ides to form CO. The same extended-sleeve torch was placed in a position such that the aerosol tube was 5 mm below the work coil and the power was increased to 650 W and only argon was used at 10 and 3 1 min-' for cooling and nebulizer respectively. The lateral spatial distributions of Sr atoms under these conditions and at heights from 45 to 90mm showed good radial symmetrical distribution with no dip in the centre unlike the distributions obtained with the pencil plasma (sic.Kosinski et at h.f. powers of 1.0 kW). Radial distribution profiles of ground state atoms and/or ions for Ca Mn and Cu in an ICP (short torch) were measured by Huang et aL6' using an excimer (XeC1) pumped dye laser as excitation source. Three dimensional maps of relative inten- sity radius and observation height were constructed giving radial emission and fluorescence profiles for atomic and ionic lines from which the following observations were made. (i) All emission profiles at 5 and 10 mm observation heights had dips with the dip at 5 mm being much greater than that at 10 min; emission profiles at 15 and 20 mm heights were generally bell- shaped but did have small dips. (ii) All fluorescence profiles for all heights were bell-shaped except for a slight dip in the Ca I1 profiles at 5 and 10min observation heights.(iii) The emission distributions had greater half-widths than the fluor- escence distribution for the same atom or ion and for identical experimental conditions. (iv) The variation of fluorescence intensity with height was not consistent with the variation of emission intensity with height; the Ca I1 fluorescence signal was larger at 0.7 kW than at 0.55 or 1.0 kW whereas the Cu I fluorescence signal was the largest at 0.55 kW and the smallest at 1.0 kW. (v) It was possible to estimate the variation of fluorescence and emission distributions for atom and ion lines with height. For Ca I and Ca I1 AF and AE the maximum signals were near to 10 mm; for Mn I and Mn I1 AF and AE the signals appeared to change little with observation heights from 10-20 mm; for Cu I AF the signal dropped slightly with height and for Cu I AE the signal seemed to be reaching a plateau around 20 mm.(vi) The non-symmetrical nature of the plasma used evident from the AF profiles cast some doubt on the validity of the emission profiles since these were obtained by an Abel inversion. In 1986 a note by Gillson and Horlick7' appeared in the literature describing a study of the effect of easily ionizable element (EIE) interferences in the ICP in which a pulsed N pumped dye laser was used to produce AF in an MAK torch. They found that the general effect of EIE was to depress Ca I1 fluorescence and that the effect lessened as the power and/or the observation height was increased.At powers of 0.75 kW and heights of 25 mm above the work coil the Ca I AF profile increased dramatically as the concentration of EIE was increased from a 100-fold to a 1000-fold molar excess. These workers concluded that the effect of EIEs in an ICP was complex and highly spatially dependent and that it was difficult to spatially 'deconvolute' exact mechanisms for the effect even with the ground state data they presented. Two p a p e r ~ ~ l ~ ~ followed this note again by Gilson and Horlick in the first of these the same pulsed dye laser was used to spatially map the distribution of ground state neutral atom and ion species in an ICP produced in a Fassel type torch. A power study of ground state Ca I1 fluorescence at 1 1 min-' carrier gas flow rate showed that as the power was increased a peaking inJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL.9 579 either profile area or maximum profile height was seen regard- less of the observation height. A peak appeared low in the plasma at 0.75 kW which shifted to 1.0 kW higher in the plasma. In the case of Ca I fluorescence power studies a general disappearance of ground state atoms was seen as the power was raised. This is consistent with a rise in temperature the atoms becoming excited and also ionized. The Ca I profiles at 0.5 kW and a carrier gas flow rate of 1 1 min-’ were uniform in shape as were their ion counterparts. However at higher powers the profiles differed noticeably. Above an observation height of 25 mm from the load coil and powers above 0.5 kW a dip was observed in the centre of the profile.This is consistent with re-combination occurring in the cool regions at the perimeter of the tail-flame high above load coil. At an observation height of 19 mm and power of 1.0 kW and when the carrier gas flow was reduced from 1 to 0.65 1 min-l a dramatic loss of ground state ions occurred and a central depression in the profile developed at the lower flow rate which became very evident when the power was reduced to 0.5 kW. These workers found that at powers above 0.5 kW and a flow rate of 0.85 1 min-l ground state atoms had more or less disappeared. They concluded that as the flow rate decreased the major effect appeared to be increased dilution of the analyte resulting in an overall drop in fluor- escence intensity.(Absorbance measurements offered con- firmatory evidence that the decrease of fluorescence intensity was real.) A further conclusion was that up to 20% of the reduction in signal intensity might also be due to reduced sample uptake at lower flow rates. In the second paper7’ Gilson and Horlick repeated the study carried out in the previous paper but used a commercially available MAK torch and also carried out extensive emission measurements. It was found that plasmas sustained with the two torches (MAK and Fassel) differed most at a flow rate of 11 min-’. At this flow rate the MAK torch profiles were narrower probably due to greater confinement of analyte within the central channel. The lower part of the channel was also cooler in the case of the MAK torch at 1 lmin-I.These differences most likely occur because of the straigh t-bore injector tube on the MAK torch. The differences decreased as the flow rate was decreased. Huang et al.73 investigated the effect of h.f. power on laser induced fluorescence and emission spectroscopy using a Baird torch with an extended sleeve and an XeCl excimer pumped dye laser as source. They found that emission and fluorescence signals varied with h.f. power obeying one of two trends; either the signal dropped as the power was increased because of a decrease in the ground state population and increases in excited state and ionic population as with Ca Na and Zn or the signal increased with power as with B P and Zr where dissociation of stable oxide molecules increases with power.These workers also studied the effect of an EIE K on the fluorescence of Ca as a function of h.f. power. In the case of the Ca I line with and without 1000 yg ml-’ of K there was a 4-fold increase in signal with K and with the Ca I1 line there was a >lOO-fold decrease with the addition of I(. It must be stressed that these results only relate to a fixed observation height of 10mm above the work coil. At other observation heights and operating parameters the results would in all probability be quite different.40 As has been reported in Section 2 of this review a milestone in the progress of L-ICP-AFS was reached by Omenetto et al.” These workers used as a source a dye laser (which was continuously tunable between 217 nm to the near infrared) pumped by an excimer laser operated at the XeCl wavelength (308 nm).Their atomizer was a plasma produced in a conven- tional (short) torch at powers of 0.75-1.0 kW. They used non- resonance transitions for all the elements they investigated thus avoiding any scatter problems and increasing the spectral selectivity. The elements which they investigated included refractory elements such as Zr V Si A1 and B. At the LOD the limiting noise was found to be background emission noise from the plasma. The LODs obtained (Table 3) were largely superior to other fluorescence results and in most cases were also better than emission values. This communication2’ was followed by a paper by Omenetto and Humanz4 in which they discussed the important param- eters for the analytical use of laser AFS.The parameters they discussed were the primary excitation step choice of excitation line excitation and detection optics the atomizer and the detection system. Some of the conclusions reached by these workers in this important paper were as follows. The maximum attainable spectral irradiance should be sought and therefore laser power has to be maximized rather than pulse energy and the duration of the laser pulse plays a very important role. If in order to achieve saturation the beam diameter has to be decreased so as to increase the spectral irradiance the total number of atoms in the sample volume will decrease thereby reducing the signal level. If the laser power is high the best solution will be to expand the beam in the atomizer until the solid angle requirements are fulfilled while still maintaining saturated conditions within the entire sample volume.The excimer-pumped dye laser is a versatile analytical laser set-up; however the Nd:YAG pumped dye laser may be even better. The flame as atomizer is rather limited in the number of elements that can be determined; if the laser meets the same requirements put forward for flame work the inductively coupled argon plasma is the appropriate alternative to the flame. The most widely used data processing system is a PMT wired for fast response and a box-car integrator where a variable gate can be operated by a suitable reference signal so as to collect information only during the laser firing thereby avoiding the processing of the background signal (which is not related to the laser) for most of the time.For a given duration of the fluorescence pulse the gate width should be adjusted so as to obtain the maximum signal. When working in the exponential averaging mode in no case should the gate width be larger than the fluorescence pulse since a loss in the signal level will result on the other hand the use of a gate width smaller than the fluorescence pulse results in a marginal signal loss and provides the advantage of increasing the number of pulses averaged for the same time constant. More detail of this work with an excimer-pumped dye laser and ICP was given in a closely following paper25 in which an account was given of the analytical characteristics of Al B Ba Ga Mo Pb Si Sn Ti V Y Zr and U in atomic and ionic AFS.The advantages of the ICP as atom/ion reservoir were found to be as in AES its relative freedom from chemical and ionization interferences. It has a wide choice of analytical line combinations thus the best sensitivity for some elements is obtained with ionic lines whereas atom lines are best for others. Many transitions are suitable for excitation not only resonance lines of the elements. Collisionally assisted fluor- escence gives very strong signals in many cases. Non-resonance fluorescence yields extremely good LODs in most cases due to the wide choice of analytical line pairs. This means that the classical scattering problem of AFS is eliminated. The quantum efficiency in the ICP is high in several cases due to the Ar atmosphere.The advantages of the high power pulsed laser as an excitation source were said to be the following. Owing to the short duration of the laser pulse high temperature atomizers can be used since the background emission signal from the atomizer during the pulse is relatively small thus the fluor- escence to background emission ratio is high. Because of such high fluorescence to emission ratios a monochromator with good resolving power and moderate light throughput can be used. The analytical signal is weakly dependent on the laser fluctuations due to the saturation of the transitions when pumped by a high power laser beam. An important advantage of the pulsed dye laser is its tunability over a wide wave- length range.580 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL.9 The advantages of the combined system L-ICP-AFS were given as the following. Good sensitivity and low LOD. Extremely high selectivity with non-resonance measurements there is virtually no chance of spectral interference because of this. Wavelengths giving the best LOD can always be used in contrast to AES where spectral interferences necessitate the use of less sensitive lines. The L-AFS system offers the possibil- ity of collecting the signal from a small volume of the plasma enabling the analytical scientist to select the zone of homogen- ous-temperature that is most free from interference effects. The disadvantages of the system were said to be as follows L-ICP-AFS is a single element technique since transition of the analyte atom is excited (in fact from this comes the freedom from spectral interference arising from the simplicity of the spectrum) the major disadvantage is the complexity and high cost of the equipment.(The above selected passages from these excellent and informative papers22*24,25 are intended only to give the gist of the contents as it would be outside the scope of this review to give more detail it is recommended that the original papers should be consulted for their derivation.) Huang et ~ 1 . ~ ~ using an excimer (XeCl) pumped pulsed dye laser with frequency-doubled output as excitation source and an ICP as an atomizer studied the AF of Ag Au Hf Ir Mo Nb Pd Pt Ru Ta and Zr. Since the experimental conditions were said to be similar to those in ref. 57 it is presumed that a torch with an extended sleeve was used.However the operating conditions were as follows 650-700 W forward power; 10-30 mm observation height; coolant flow rate 15 1 min-l of Ar without any intermediate gas; nebulizer flow rates 1-1.5 1 min-'; pump laser energy per pulse 50 mJ; dye laser energy per pulse fundamental 0.5-2.0 mJ frequency doubled 5-40 pJ; monochromator slit-width 1167 pm; box- car averager gate width 5 ns; and input time constant 10 ps. It is presumed that a univariate optimization was carried out to obtain the optimum conditions although this does not appear to be explicitly stated. The LODs obtained by these workers for the elements quoted are shown in Table 3. The calibration graphs obtained had a linear dynamic range of over four orders of magnitude except for Au where it was three orders.In the first use of double-resonance fluorescence (DRF) Omenetto et aL2' used an excimer laser operated with XeCl at 308 nm and 10 Hz whose output was split so as to simul- taneously pump two dye lasers whose output was diverted with mirrors into an ICP powered by a standard commercial ICP unit. The excitation of a selected level is achieved with one laser beam tuned to the appropriate frequency. Higher excitation levels are effectively populated when the second laser beam coincident in time and space with the first one is tuned to a transition starting from the level reached by the first laser or from collisionally populated nearby levels. Omenetto et ~ 1 . ~ ~ pointed out that the single resonance fluor- escence technique is already spectrally very selective and the addition of a second excitation step combined with an increased choice of fluorescence wavelengths can only make it more so. The DRF was said to be subject to scattering problems if either laser is within the bandpass of the monochromator.However scattering is overcome in either technique if fluor- escence is measured at a wavelength different from 2 2 or 2 1 i.e. non-resonance fluorescence. (The subscripts indicate energy levels in a three level system). It was suggested that DRF offered a unique way of correcting for scatter when measuring resonance fluorescence (2 2) since the signal measured at 2 2 would be essentially zero when the first laser tuned at A12 IS not present because of the negligible thermal population of level 2.Any residual signal observed under these circumstances will be due only to scattering. It was further claimed that with DRF the signal can in principle be located in a spectral region where the atomizer emission noise is reduced. The LODs and transition wavelengths were given for Ca Sr Ba and Mg and these are shown in Table 3. The technique of DRF was said to offer the possibility of monitoring high lying states for diagnostic purposes which are not accessible in conventional emission spectroscopy and offer high spatial resolution due to the fact that the signal is generated only at the intersection of the two laser beams. However the technique is complex since two lasers are needed and care is required in order to achieve temporal as well as spatial coincidence of the two beams in the atomizer.Leong et ~ 1 . ~ ~ (see also Leong,') evaluated SRS in H at liquid N temperatures as a tunable sharp line ultraviolet laser source for the excitation of the AF of elements such as As Se Te and Zn whose resonance lines are usually more than 40000 cm-' above the ground state. To populate these states requires primary radiation of shorter wavelength than can be provided by laser-frequency doubling techniques. However these wavelengths are within the range that can be reached through SRS of dye laser primary radiation. The SRS was produced in a cell with sapphire windows containing H,. The cell was surrounded by a jacket filled with liquid N which was itself surrounded by a vacuum cell. The primary radiation which was scattered in the cell came from a YAG pumped dye laser.The scattered radiation from the cell was directed into an ICP. The LOD obtained for a number of elements and shown in Table 3 were only comparable with those achievable by ICP-AES. Linear calibration graphs covering the concentration range from the LOD to three orders above were obtained. These workers also demonstrated the superior- ity of ultrasonic over pneumatic nebulization. They addition- ally claimed that the LODs obtained with a conventional torch at observation heights of 15-20 mm were not significantly different from those obtained in long-sleeved torches at heights of 55-75 mm.9 ( K ~ s i n s k i ~ ~ measured excitation temperatures in both conventional short torches and torches with extended sleeves following an optimization of carrier flow rate h.f.power observation height and dye laser beam diameter. The temperature was found to be lower in the long torch. He concluded that this torch should be used for most elements. However excited-state fluorescence might be better performed with a conventional torch due to its higher excitation temperature.) Tremblay et ~ 1 . ~ ~ published LODs for a number of rare earth elements (Table 3) obtained by non-resonance fluor- escence spectrometry using an excimer laser to pump a dye laser as source and an ICP as an atomizer. In a later paper77 DRF was used in the determination of rare earth elements. Those workers also quoted LODs; these are given in Table 3. In a further use of L-ICP-AFS as a diagnostic tool Bates and Olesik7' determined the effect of sample aerosol transport rate on ICP-AES and AFS.They found that large decreases in ion emission responsivity (defined as the ratio of relative emission of fluorescence intensity to the amount of analyte introduced into the plasma) result as the amount of aerosol entering the plasma is increased. The change in ion responsivity was believed not to be due to a change in the number of ions per amount of sample entering the plasma but to the decreas- ing fractions of ions that are excited and emit light with increasing transport rate. In contrast fluorescence responsivi- ties in the normal analytical zone showed smaller changes with variations in sample transport rate. Therefore fluorescence intensities increase with increases in transport rate.Finally to complete this section the reader's attention is drawn to a comprehensive review of laser-excited AFS in flames plasmas and electrothermal atomizers by Butcher et 4.4 With Mercury Vapour Lamp and Continuum Sources Lancione and Drew" determined Hg with the Baird instrument by replacing the conventional HCL with a low pressure Hg vapour lamp. Using a pneumatic cross-flow nebulizer an LOD of 30 ng ml-' was obtained. A continuous cold vapour gener- ator was also developed which could be used with the cross-JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 58 1 flow nebulizer. This allowed Hg to be determined with an LOD of 0.2 ng ml-' along with 11 other elements. When operated with the ICP turned off an LOD of 0.04ngml-' was obtained for Hg but no other elements could be determined.In principle a continuum source is attractive in AFS as it allows simultaneous excitation of many elements. Mignardi et ~ 2 1 . ~ ' used a pulsed continuum Xe flash-tube for this purpose along with an ICP generated in both long and short torches as an atomization cell. With the long torch they found the AF signal to be practically constant at observation heights 45-65mm above the load coil whereas with the short torch the signal rapidly decreased with increasing observation height. The variation in signal with increasing h.f. power was similar for both torches but the signal was significantly larger with the short torch. A similar difference was observed for the effect of monochromator slit-width on the S/N and again the short torch gave much the better performance.(Despite this the LODs for Cd were essentially the same with both torches). A multi-element scan of a synthetic mixture of elements giving Cd I V 11 Ca I Ba I1 and Na I transitions with a short torch gave good separation of lines. The most intense fluorescence line of V was not used as it came in the midst of OH banding and instead the next most intense line was used at 292.4 nm. The LODs were given for the five elements; these were at least an order of magnitude or more poorer than previously published fluorescence figures. In later work4' AF double resonance of Cd atoms was investigated with a similar source and atomizer. Although double resonance was observed it was concluded that there was no advantage as this could present a greater potential for spectral interference with a multi-element matrix.Further since a continuum source is non-selective only an appropriate choice of filters (practical in a limited number of cases) would enable the selectivity obtained with a line source to be achieved. Table 4 LODs (ng ml-')* obtained by AFS with ICP as source and an ICP as atomizer Ref. Element A1 B Ba Ca c o Cr c u Fe Hf Ho K Li Mg Mn Mo Na Nd Ni P Pb Pt Si Sm Sr Tb Th v w Y Yb Zn Zr ICP-ICP- AES ASIA 6 (< l%)t 12000 - - 3 60 1350 45 150 - - - - - 13.5 2250 150 ND§ 150 - - - - 45000 ND§ 1500 - - - - 45 9 - 30 (13%) 15 15 1.35 0.6 15 0.6 45 15 150 - - - 0.3 - - 1.5 - - 120 45 10.5 30 0.3 - - 150 60 30 15 3 15 - 28 (1-2%) 55.5 55.5 7.5 0.45 7.5 3 - - - - - 7.5 - - - 0.15 - - - - - 120 - - - - - 1350 - - 611 - 81 44 (1-2%) (1-2%) 20.5 45' 561 28 8 3.5 0.5 0.2 21 9.5 8 3 0.4 19 5 - - - 7 3.2 - 63 0.2 0.1 - - 21 6 27 - - - - - 120$ 54.5 5 The ICP as Atomizer with ICP as Source 5.1 Low Power Systems The first results to be published on the use of an ICP as source and as atomizer in AFS were those of Kosinski et aL6 They used as source a conventional short torch and powers of around 2.0 kW with 15 1 min-' Ar support gas to produce the plasma.The atomizer plasma was produced in a Baird torch with extended outer sleeve and powers of 0.7 kW for atomic lines and 1.0 kW for ionic lines of refractory elements. Again the support gas was Ar at 15 1 min-' and the nebulizing gas pressure was 140 kPa. A 20 mg ml-' analyte excitation solution was used in the source plasma for all elements with the exception of A1 and Na which clogged the nebulizer at these concentrations.A 10 mg ml-' solution was used for these elements at a pressure to the nebulizer (Model PN 5601 Plasma Therm) of 280 kPa. The atomizer nebulizer (Model T230-Ae Meinhard) was operated at a pressure of 245 kPa. The observation height for the source was 10-30mm above the coil and for the atomizer 80mm for non-refractory elements and 60mm for all other elements. The rest of the equipment was as usual. The chopping frequency was 550 Hz. The usual COGS for emission excitation and fluorescence were obtained with limiting slopes consistent with a line source. Excitation temperatures were obtained for the atomizer using a three line slope calculation by measuring Fe atomic emission lines at 382.0 382.4 and 382.6nm.The temperatures were found to be 3290K (0.7 kW 80mm observation height); 3540 K (1.0 kW 60 mm); 3810 K (1.2 kW 60 mm). The LODs found by these workers are shown in Table4 and are mostly an order of magnitude worse than previously reported figures for ICP-flame-AFS and L-ICP-AFS. Chemical interferences were reported. Thus increasing amounts of Al * Normalized to 3 x sb. t Source radiation collection efficiency given in parentheses. $ C,H added to injector flow. 9 ND =not detectable. 7 C,H,OH solution. 11 Monochromator grating blazed at 500 hence poor sensitivity. had an enhancement effect on Ca ionic fluorescence intensity as did Na. The PO had a slight depressant effect which may have been due to an increase in the viscosity of the nebulized solution.No attempt appeared to have been made to optimize operating conditions for minimum interference which as was to be shown in a later paper often reduces if not removes such interference. Freedom from spectral interference was demonstrated by measuring Zn (213.856 nm) at a concentration of 10 pg ml-' in the presence of Cu (non-resonance line 213.853nm) at a concentration of 5000 pg ml-'; no significant excitation of the Cu line occurred when a 20mgml-' solution of Zn was aspirated into the source plasma. Nickel and Co are also subject to similar spectral interference but when investigated no significant Ni fluorescence occurred when Co excitation was used and conversely no significant Co fluorescence was seen with Ni excitation. Noise and scatter studies were carried out for Zn 213.9 nm and Na at 589 nm.The analytical precision (4 s time constant 10 s integration time 16 consecutive readings) for the measure- ment of solutions of high concentration was 2% for Zn and 10% for Na. There was no significant difference in the precision when the measurements were carried out in a matrix containing 10 mg ml-' of Ca. However there was an increase in scattered radiation. The precision for low concentrations was 3-4 times worse than for solutions of high concentration. The scatter signal due to the Cu matrix at the Zn and Na lines gave a 2-3582 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 times increase in signal over the blank level respectively.Scatter due to the Ca matrix did not act as a significant noise source. The precision for the low concentration analysis was similar to that with and without the Ca matrix. It was concluded that if scatter was present it could be subtracted out by using the two-line technique. A final conclusion was that the efficiency of transfer of radiation from source to atomizer was only about 1% and that this could be improved by use of an ellipsoidal reflector placed behind the plasma. In an attempt to improve the light collection efficiency of the ICP-ICP-AFS system of Kosinski Long and Winefordner26 added a 5 cm diameter concave spherical mirror with a focal length of 5cm which they placed behind the source ICP. They also added a condensing lens with similar diameter and focal length to collect the radiation from the ICP.After chopping the parallel beam of light from this lens the beam was collected by another lens of 5 cm diameter with a focal length of 10 cm. These workers claimed a light collection efficiency of 13% compared with the 1 % attained previously.6 A further improvement was to install h.f. filters in the power lines and in the detection electronics in order to reduce noise and improve the LOD.20 The atomization cell was produced in a Baird torch with extended sleeve. Two configurations were used for the Baird atomizer torch. In the 'normal' mode an h.f. power of 500-700 W was used for all elements except for V when 1.0 kW was used together with 14.0 1 min-' of Ar introduced into the outer tube and 1.41min-1 of Ar to produce the aerosol.The observation height was 60mm above the coil and the aerosol tube was 5 mm below the bottom turn of the coil. In a so-called 'pencil' configuration:' the aerosol tube was positioned between the first and second turn of the load coil and the flow rates were 9.1 1 min-' for the outer tube and 3.9 1 min-' for the nebulizer. Propane was added to the nebulizing gas via the spray chamber as required. The LOD values which were obtained with this improved layout are shown in Table 4. When conditions were set for laminar flow in the torch and with a high nebulizer injection rate the plasma could be made to have a tail-flame 20-30 cm long. The high flow rate of the nebulizer gas was said to permit the introduction of C3H8 into the plasma without affecting its stability.(The effect of the addition of C3H8 has already been discussed in Section 4.2). The relative merits of the conventional and long tailed plasma were evaluated on the basis of LODs the analytical sensitivity and the standard deviation of the blank. The elements Ca Cu and Mo were chosen for the evaluation. With the use of a conventional plasma an LOD of 4 ng ml-I was obtained for Cu whereas the pencil plasma gave 5 ng ml-' at the same height of 60 mm above the load coil. However in the latter case the sensitivity had dropped by 60% and the standard deviation by 50%. At a height of 100 mm above the coil the LOD dropped to 1 ng ml-' with the sensitivity increasing from 640 to 885. This value is still 50% below that obtained with the conventional plasma.It was suggested that the decreased sensitivity might have come from a reduced transport efficiency due to the high flow rate of nebulizer gas. With Ca the conventional mode of operation yielded an LOD of 0.4 ngml-' while the pencil mode with no C3H8 gave a value of 6ngml-'. Here the standard deviation of the background increased 600% and the sensitivity decreased 60%. When C3H was added at a rate of 12 ml min-' the LOD dropped to 1 ngml-' with the standard deviation of the background falling and the sensitivity rising from 523 to 937. With a flow rate of 20 ml min-' of C3H8 the sensitivity did not increase but the noise increased probably due to soot formation. The effect of C3H8 was seen clearly in the case of Mo. The conventional mode gave an LOD of 100ngml-'.With the pencil plasma no signal could be observed even at 100 pg ml-' of Mo. When C3H8 was introduced the signal returned and an LOD of 300 ng ml-' was obtained for a flow rate of 28 ml min-' of C3H8. From this data these workers deduced that the conventional plasma is better for refractory elements. The use of C3H increases the analytical sensitivity of the pencil plasma but it is still inferior to the conventional mode. Further work using similar equipment was undertaken by Krupa et They used an extended-sleeve torch and an observation height of 55mm above the load coil. Because of the different power dependencies of elements with low molecu- lar dissociation energies and the elements that form stable metal oxides with rather high dissociation energies the LODs of the former were determined at 700 W whilst the LODs of the latter were determined at 1200 W.Limits of detection were given for 22 elements and these are shown in Table 4. It was suggested by these workers3' that the LOD obtained by ICP- AES HCL-ICP-AFS and ICP-ICP-AFS were approximately equal in the case of the non-refractory elements. With Na the high degree of ionization of this element low in the plasma gave poorer LODs in ICP-AES than it did in AFS as moving the observation height higher in the atomizer tail-flame in the case of ICP-ICP-AFS reduced the temperature and degree of ionization. The LOD of K in emission was similarly affected and any advantage of the higher observation height in ICP-ICP-AFS was off-set by the high degree of ionization of K in the source plasma resulting in poor atomic irradiation.The LODs of the refractory elements for ICP-ICP-AFS and ICP-AES were said to be similar with the exception of V where the most intense line of this element appears in the midst of the OH bandhead. The increased plasma emission in this region increased the background shot-noise and hence gave higher LODs. The HCL output is primarily atomic resonance radiation and since the refractory elements are not efficiently atomized at low powers the LODs of these elements is relatively poor in HCL- ICP-AFS. This situation is not improved by increasing the power in the plasma as this only increases the degree of ionization. On the other hand the source plasma in ICP-ICP- AFS can excite ionic transitions and it was suggested that working with higher powers in the atomizer plasma would be an advantage for this reason.Krupa et aL3' also demonstrated that the linear dynamic range of ICP-ICP-AFS can be extended by using the technique in the RM mode. In one example of this the COG of Cu I at 324.7nm was shown to extend over 5 orders of magnitude (< 1 ng ml-' to > 100 pg ml-'). This range was extended to 1% (10 pg ml-' to 10000 pg ml-') by using the RM mode. These workers commented on the absence of spectral inter- ference with ICP-ICP-AFS i.e. no collisional broadening interference of Ca on Al absence of ion recombination continua and freedom from molecular fluorescence interference. They gave examples of contrived direct spectral overlaps and the interferent LODs thereof Ba 455.4042 nm (Zr 455.3967 nm) 8 pg ml-'; Ca 393.3666 nm (Hf 393.3664 nm) 3 pg ml-'; Ca 393.3666 nm (Co 393.3654 nm) 9 pg ml-'; Ca 393.3666 nm (Fe 393.3605 nm) 20 pg ml-'; Zn 213.8560 nm; (Cu 213.8507 nm) 100 pg ml-'; Si 251.6123 nm (V 251.6118 nm) 600 pg ml-'; A1 396.1527 nm (Mo 396.1503 nm)>2000 pgml-l; Zn 213.8560 nm (Ni 213.8580 nm) 3000pg ml-'; Ba 455.4042 nm (Mo 455.4028 nm)> 10000 pg ml-'; Cu 324.7540 nm (Mn 324.7542 nm)>10000 pg ml-'; Mg 279.0787 nm (Fe 279.1008 nm) > 10000 pg ml-'; the interferent is given in parenthesis.They pointed out that there are substantially fewer spectral interferences in AFS than in AES. Krupa et aL3' commented on the freedom from inter-element effects when using the ICP in AES and found similar freedom when using the ICP in AFS. They found that 50000 pg ml-' of or produced no depression or enhancement of the fluorescence signal of 1 pgml-' of Ca solution.They found that the fluorescence signal of a 1 pgml-' solution of Ca gave an enhancement at the Ca I wavelength and a depression at the Ca I1 wavelength on the addition ofJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 583 1-10000 pg ml-' of Na. However no mention was made of optimizing operating conditions for minimum interference. Finally these workers analysed a National Institute for Standards and Technology (NIST) Standard Reference Material (SRM) 364 (high C steel) by ICP-ICP-AFS in the AFS mode for Cu Cr Zn and for Fe in the RM mode. The mass percentage solid concentrations varied between 96.7% Fe to 0.0005% Zn and only one solution (1.2206 g 1 - I ) was necessary for the analysis.No matrix matching of standards or matrix blank was used. The average relative error and relative standard deviation (RSD) were both 1%. In a later paper32 Krupa and Winefordner re-confirmed the fact that the fluorescence intensity of the non-refractory elements is inversely proportional to h.f. power in the atomizer whereas the sensitivity for refractory elements increases with increasing power in the atomizer. With the alkaline earth elements however they found more than one maximum in the fluorescence uersus power curves. 5.2 High Power (ASIA) Systems Following the first reporting7 of the ASIA system (see Section 2) incorporating a high power plasma generated in a Greenfield type torch as source and a low powered plasma generated in a Baird long-sleeved torch as atomizer first results from this combination were given in a paper by Greenfield and Thomsen.28 These workers gave power in the source plasma versus fluorescence intensity curves for the elements W and Cu which showed no maximum and the optimum power was taken to be that at which a further increase in power of 1 kW produced less than 5% increase in fluorescence signal a purely arbitrary decision.For the non-refractory elements the power in the atomizer plasma was very low typically 400 W or less. Below 350 W a plasma could not be sustained. The refractory elements all required higher powers in the atomizer and all but Ba of those studied required the use of C3H8 in the nebulizer gas (0-5Omlmin-').A flow rate of around 2.01min-' of Ar was used to produce the aerosol for the atomizer plasma in the Baird torch. This together with the positioning of the torch in the work coil gave a long tail- flame. Observation heights in this plasma varied considerably from one element to another from 70 to 140mm above the coil. Optimum operating conditions were given for the determi- nation of W and Cu. At the start of each experiment 15 parameters were optimized by the AVS method.37 The COGS were reported for emission excitation and fluor- escence. In emission at concentrations of 10% m/v Cu (as CuSO,) or more aspirated into the source plasma there was appreciable self-absorption. This was duplicated for W at concentrations of 20% m/v W (as tungstosilicic acid) or greater.The excitation COG showed that there was little to be gained by aspirating a Cu solution containing more than 20% m/v Cu; this was the case for the majority of elements studied with the exception of W where self-absorption did not occur when 40% m/v W (as tungstosilicic acid) was used in the source plasma. This trend was echoed in the fluorescence COG where the point at which self-reversal was observed for W occurred at a much greater concentration than for Cu 7500 pg ml-' W compared with 1000 pg ml- ' for Cu. The theoretically pre- dicted slopes for the fluorescence COG of a positive slope of unity and a negative slope of -0.5 were obtained. The LODs were given for a number of elements (Table4) in both fluorescence and emission on the same instrumental set-up.It was noted that the monochromator used suffered a decrease in sensitivity below 300 nm. Continuing their work on the ASIA system Greenfield and Thomsen" investigated further the effect of organic additives for the detection of refractory elements (see Section 4.2). They found that W along with B and Si could not be made to give a fluorescence signal without the presence of a carbon- containing compound such as alkane gas introduced into the injector flow or an alcohol in solution. It was shown that the optimum flow rate for each gas was proportional to the number of C atoms delivered to the plasma and corresponded to a full green tail-flame. The effect of C,H,OH on the fluorescence signal from W was also demonstrated. No gaseous hydrocarbon was used during this experiment.The maximum signal was obtained with 70% m/v C,H,OH which also corresponded with a full green tail-flame. The same effect was also achieved using C,H,OH (propan-2-01). Greater signal intensity ( x 2) for W was achieqed using C2H50H solution than was achieved with C3H8. New LODs were given for the refractory elements (see Table 4). It was shown that when determining B in fluorescence on the ASIA instrument with the addition of carbonaceous mate- rial a background signal was generated at 2=249.8 nm that is a fluorescence or scattering signal other than B. It was therefore suggested that great care must be taken when sel- ecting a reducing environment for refractory element analysis. If the hydrocarbon can generate a signal then it is possible that atoms molecules or particles added to the plasma may have quenching properties.It is probably quenching which occurs when an excess of hydrocarbon is added and the CO and C 0 2 produced in the combustion process efficiently quench fluorescence. When determining A1 it was found that better LODs were obtained using alkane gas than with C2H50H or no reductant. Methane because of the high flow rates needed gave less noise on the signal. No background signal was generated when 80% m/v C,H50H solutions were aspirated but the A1 signal was depressed. Inexplicably two observation heights existed with equal signal intensity determined at each one deep in the green tail-flame and one just above the green zone. These workers showed82 how wide monochromator slit settings could be used in AFS to obtain complete observation of the fluor- escence cell and that with many elements there are several fluorescence frequencies falling within the monochromator bandpass which are unresolved and further enhance the fluor- escence sensitivity.If spectral resolution is required narrower bandpasses could be used without much loss in sensitivity or increase in LOD since background noise levels improve accordingly. The fitting of power line filters and earth chokes2' to both generators reduced the LOD for Pb from 80 to 11 ng ml-'. In a demonstration of the spectral selectivity of AF the spectrum of a solution containing 10 pg ml-I of Pb was shown with spectra of 1000 pg ml-' of Fe and 200 pg ml-' of Cr.A solution of 20% m/v Pb was aspirated in the source plasma in each case. It was pointed out that in ICP-AES the Pb 283.31 nm line is interfered with by Fe at 283.24 283.31 and 283.34 nm and Cr at 283.35 283.34 and 283.43 nm.83 In AFS Fe and Cr are not excited whereas all the Pb lines at 280.199 282.32 283.306 and 287.332 nm were clearly visible. This freedom from spectral interference was clearly demon- strated in another paper84 describing the freedom from back- ground shifts due to radiative recombination continua and freedom from collisional broadening interference. They cited the work of Larson and Fasse18' who showed that 2500 pg ml-' of A1 will produce a background shift of one order of magnitude in the 190-220 nm region in ICP-AES. Because ASIA employs a.c.coupled electronics this type of interference (which is essentially a d.c. shift) is eliminated even when 10000 pg ml-' of A1 is added. Larson et ~ 1 . ~ ~ also showed the interference of 1000 pg ml-' of Ca on the A1 lines at 394.4 and 396.2 nm occasioned by collisional broadening of the Ca I1 393.4 and 396.8 nm lines. In ASIA it was showng4 that 10000 pg ml-' of Ca did not show the same marked effect. This paper84 also discussed the use of direct line fluorescence in determining Ba. The two most intense lines of Ba occur at 455.403 and 614.72 nm. These were investigated using a filter between the source and atomizer plasmas which isolated the 455.403 nm line. When the filter was absent the observed fluorescence was caused by a combination of resonance and non-resonance584 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL.9 fluorescence transitions resulting from the multiple line exci- tation of the source. With the filter in place there was a marked reduction in the signal as was expected from the known transmittance of the filter but it was clear that the observed fluorescence at the two wavelengths studied was due to the 455.403 nm line excitation i.e. resonance fluorescence at 455.403 nm and non-resonance at 614.172 nm. It was pointed out that apart from the possibility of avoiding spectral inter- ference non-resonance fluorescence would avoid any problem of scattered light and enable multi-pass optics to be used. In the same papers4 the classic interference of Cu on Zn which is observed in both AES and AA and was shown to be absent in ICP-flame-AFS by Epstein et ~ l .~ ~ was also shown to be absent in ASIA. In an attempt to reduce the physical size of the ASIA assembly (and to reduce the cost) Greenfield and Thomsen3' showed how two ICP could be run from one free-running h.f. generator. Two work coils were wound in series with a reverse turn in the second coil in order that the current would be flowing in the same direction when the coils were near to each other. The generator was retuned by changing the capacitance in the tank circuit. Argon was ionized in an atomizer torch placed in one coil by means of a Tesla coil and h.f. current applied. When a plasma formed the current was increased and ionized gas passed through a torch in the second coil. The power was increased until the second plasma formed.This arrangement was successful and two plasmas 6.5 cm apart were produced one in each of the separate torches. Only the total power of the generator could be varied which was rated at 4kW maximum but this power was ratioed between the two torches according to the number of turns on each coil. It was found that the two plasmas could only be initiated if the ratio was no larger than 3.5 to 2.0 turns. This ratio gave approximately 2.5 kW in one torch and 1.5 kW in the other (not confirmed calorimetrically). Although this value of 1.5 kW (in what would be the atomizer plasma) is large compared with the usual 350-800 W it was suggested that a concen- tration of ground state atoms in the atomizer could be achieved by cooling the plasma with a sheath gas.(Another possibility would be an atomizer torch with a greatly extended outer sleeve and increased observation heights). In further studies designed to emphasise the selectivity of AFS in general and ASIA in particular Greenfield et gave a number of examples with spectra of spectral interferences which occur in AES but not in AFS. The main part of these studies was concerned with the non-resonance transitions of Pb and was believed by the authors to be the first study of these types of transition with a dual-plasma AF system. All the fluorescence mechanisms resonance Stokes direct line anti-Stokes direct line stepwise-line and thermally assisted fluorescence were observed and verified. The most intense transitions were found to be resonance at 283.31 nm and direct-line fluorescence at 405.78 and 363.96 nm with reason- ably intense stepwise-fluorescence at 368.35 nm.It was sug- gested that observation of stepwise-line fluorescence indicated that there was good mixing of the 7s energy levels which is indicative of a system with good collisional mixing but with low quenching properties.' The fluorescence intensity of Pb was recorded at 283.31 and 405.78 nm when 217 nm excitation was used. This was attributed to the Pb atoms in the 6d state which had lost energy by some means possibly by collision with other atoms or molecules in the fluorescence cell and decayed to the 7s state before returning to the ground state with emission of radiation at 283.31 nm and to the metastable 3Pz state with emission of fluorescence at 405.78 nm.Quenching in the tail-flame was estimated at 4% and it was suggested that this was possibly due to the collision of the excited state Pb atoms with other Pb atoms water molecules OH radicals Ar atoms or ions and electrons. Of these water OH and electrons were considered to be the most likely candidates as other species have very low quenching cross-sections. It was also recorded that the resonance line at 283.31 nm is interfered with by the water bandhead at 281.13 nm at power levels of 350-750 W normally used in the atomizer plasma. However this bandhead is absent in the emission spectrum of the excitation source when operated at high powers (5-6 kW)*' and therefore with this high power being used to excite fluorescence in the atomizer there cannot be any OH excited fluorescence in the spectrum.A study of chemical and ionization interferences when using the ASIA system was made by Greenfield et a/.,' They also demonstrated a linear dynamic range of approximately 6 orders of magnitude for the fluorescence signal at the Ca 422.7 nm line. These workers found that when the operating parameters had been optimized for the best LOD by the AVS method,37 PO had no effect upon the fluorescence signal of Ca I up to a PO concentration of 10000 pg rn1-I. The Ca concentration was 1 pgml-'. On the other hand A1 showed a marked depression in the Ca I fluorescence signal. Sodium and K gave first an enhancement and then a depression of signal. The effect of A1 on Ca fluorescence was judged to be that of stable compound formation.The effect of the alkali metals was thought to be an ionization effect followed by quenching. On re-optimization for the figure of merit minimum inter- ference the results obtained were quite different. Again PO had no effect A1 could be tolerated up to a concentration of 900 pg ml-' and Na and K up to a concentration of approxi- mately 1000 and 100 pg ml-' respectively before any effect (a depression) was seen in the fluorescence signal from a 1 pg ml-' solution of Ca. These experiments confirmed the efficacy of the AVS optimization and also the spatial dependence of the reactions in the plasma. However it should be noted that optimizing for minimum interference will of necessity degrade the LOD obtained. When the experiments were repeated with the 1 pgml-' of Ca but with measurements at C393.4 and 396.8 nm lines (Ca 11) it was found that when the system was optimized for the best LOD PO4 had no effect but Al Na and K had the expected depressive effect.Re-optimization for minimum interference showed no interference from PO4 and Na and K could be tolerated up to about 300 pg ml-'. The interference of A1 on the Ca I1 fluorescence could not be reduced. In all it was concluded that the effects described were of the same general order as those experienced in ICP-AES and much less than in AAS. A progress report on the whole of the work on ASIA was presented at the 1988 Winter Conference on Plasma Spectrochemistry and subsequently published.39 This was fol- lowed by a further report in which results from an improved system were given.The improvements consisted of replacing the original monochromator which had anf No. around 15 and whose grating was blazed at 500 nm with an instrument with anfNo. of 4.5. In addition the two lenses used to collect the fluorescence radiation were replaced with a single lens giving a 1.67 times magnification onto the 2 cm high entrance slit of the new monochromator. This magnification had been calculated to give the best collection efficiency. It should be pointed out that despite these improvements the collection efficiency between the two plasmas was only of the order of 1-2%. Nevertheless the improvements gave much better LODs (see Table 4) and it was stated that of 16 elements listed all the non-refractory elements had similar or better LODs than could be obtained by ICP-AES.In the case of the refractory elements all had LODs less than an order of magnitude worse than those obtainable by ICP-AES with the exception of W which was 14 times worse. It was concluded that by improvements in the transfer of energy from the source to the atomizer plasma and by the reduction of the noise and background in the system these LOD could be reduced. Experiments were also carried out to improve nebulizer trans- port efficiency by desolvating the aerosol. It was found thatJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 585 55% of the emission signal that was obtained when a 20% m/v solution of Cu (as CuSO,) was nebulized into the source plasma could be obtained using a 0.15% m/v solution of Cu if a heated spray chamber and desolvator were introduced into the nebulizer system.Unfortunately it was reported that at this concentration black CuO started to deposit on the walls of the spray-chamber. Pulsing of the aerosol was also reported due it was thought to large aerosol droplets hitting the walls of the heated spray chamber producing 'bursts' of steam. 6 Applications In Table 5 are gathered the results of numerous examples of analyses which have been performed on a variety of materials by AFS in which an ICP has been used as a source and/or as an atomizer. Demers and Montaser62 have also published a list of applications that supplements Table 5. In many instances AFS has been chosen because of the selectivity of the technique. Thus Epstein et determined a trace quantity of Zn in an unalloyed Cu and reported no significant fluorescence excited at the 213.853 nm line.These workers also determined Zn in a sample of fly ash and Zn and Cd in simulated fresh water. No interferences were found and excellent agreement with the certified values were obtained. The determination of Zn and Cu in Florida orange juice was completed without any spectral interferences although in ICP- AES a number of bands occur in the vicinity of the 213.9 nm Zn line and emission from phosphate in the juice produces a strong emission at 213.62nm. Argon lines and OH bands observed in ICP-AES around the Cu 324.7 nm line caused no interference in the determination of Cu by ICP-F-AFS. Cavalli et a).:' using the emission from an ICP unit (ARL Model 3400 emission quantometer) as a source and an Ar separated air-C2H2 flame as an atomizer determined Cd in lake sediments.These workers used the ionic line of Co at 228.62nm to correct for scattering at the Cd I line at 228.8. This method proved to be effective and reliable. Excellent results were obtained for various samples of lake sediment. A sample of fly ash was also analysed by this ICP-F-AFS procedure and gave a value of 4.53 & 0.08 pg g-' Cd as against 4.56 0.35 pg g-' obtained by an analytical round robin. The ability of the Baird HCL-ICP-AFS instrument to per- form simultaneous multi-element analysis was demonstrated by Demers et ~ 1 . ' ~ They analysed the SRM 362 water sample for a number of trace elements. The calibrating standard was a multi-element aqueous solution in 2% HN03. No effort was made to matrix match and the results obtained were excellent.An analysis of low and high alloy SRM steels was also made. Spectral line interferences were absent and a simultaneous analysis was obtained using a 200-fold dilution of the samples to get all the elements in the linear range. In another experiment the precisions obtainable during the simultaneous determi- nation of Au Pd Pt and Rh were found to be at the 10 pg ml-I level and 10 s integration time 0.94 0.84 0.80 and 0.48% respectively. With 100 s integration time the RSDs were 0.32 0.26 0.24 and O.l6% respectively. At the 100 pg ml-I level the comparable figures were 0.29 0.55 0.74 and 0.38% with 10 s integration time and 0.12 0.13 0.26 and 0.11% with 100 s integration time.The determination of Pd in sample solutions of nuclear waste by ICP-AES with other than a high resolution mono- chromator is made difficult because of severe spectral inter- ference that occurs at all the analytically useful wavelengths of Pd. Cavalli et showed that interferences from Ar Y Zr Sm and Nd lines might be expected at the Pd lines at 363.47 324.27 340.45 and 360.95 nm. However they found that they could determine Pd in the wastes by conventional AFS and by the RM mode. They used the torch contained within the same commercial ICP-AES unit previously used87 and an Ar shielded-air-C,H flame as atomizer. In the AFS mode 5000 pg ml-' solution of Pd was introduced into the ICP while the sample solution (diluted 1 +9) was nebulized into the flame.A quartz lens was used to focus the plasma plume onto the flame. No collecting lenses were used to monitor the fluorescence at 363.47 nm with the 0.1 m focal length mono- chromator whose entrance slit was located 5cm away from the flame at right angles to the main optical axis. The RM mode gave almost coincidental analytical results and in neither case was scatter a problem. Lancione and Drewg8 used a Baird instrument to determine a number of elements in iron ore slag low alloy steel and stainless steel. Excellent results were obtained without matrix matching and calibration graphs were produced with linear dynamic ranges of around 4 orders of magnitude. In a later papersg these workers discussed the analysis of precious metals with the Baird AFS instrument and gave examples of analyses they had conducted. In another paper,61 following the introduc- tion of BDHCL and an ultrasonic nebulizer to the Baird AFS Lancione and Drew obtained LODs for Au and Ag of 0.5 and 0.04 ng ml-' (2 x sb) respectively.They went on to show how these low LODs and high sensitivity could be obtained in the analysis of unalloyed Cu for the Au and of water for Ag (without matrix matching in the case of the unalloyed Cu). The ICP-AES analysis of Ni plating solution is difficult because of the close packed lines in its spectrum. In addition the solution contains brighteners stabilizers and other addi- tives which contribute to the complex spectral background. In AFS the spectrum of Ni is relatively simple. Lancionego used a Baird AFS to determine a number of secondary elements in Ni sulfamate plating bath solution by the method of standard additions and obtained around 100% recoveries from spiked solutions.In work carried out at the US Geological Survey Laboratories at Denver Co USA Sanzolone and Meier63 determined Ca Mg Na Cd Cu Fe Li and Zn in acid mine and reference water samples using the Baird instrument. A systematic study was carried out of the operating parameters to get the best LOD for each element. Calcium Mg and Na were determined as a group using a 1+100 dilution of the sample. Cadmium Cu Fe K Li and Zn were determined on the undiluted sample. Mean and standard deviation of the LODs were determined on two separate days and the results were pooled. An LOD was also determined with a 40 cycle integration and gave the expected reduction in LOD.Propane was used where appropriate. The linear dynamic range was determined to be about 4 orders of magnitude. Detailed statistics on replicate analyses and the agreement between values obtained and those recommended for the reference water samples (too detailed to be included in Table 5) were given. The HCL-ICP-AFS analyses were found to be free from cross-talk interference between modules. It was concluded that the method had good precision and accuracy and that it compared favourably with ICP-AES in sensitivity and pre- cision. The analysis of 100 samples per day per analyst was said to be easily accomplished. In a later paper,g1 Sanzolone described the determination of Cd Cu Fe Pb Mn and Zn in a variety of geological materials.Again a wealth of statistical information was given and it was claimed that the results for the elements determined were well within the accuracy require- ments of geochemical exploration. Precision was determined in replicates of 16 geological reference samples and the RSD was given as being <5% except for a few instances where the LOD was approached. An attempt was also made to determine Co and Ni on the samples but this attempt failed because of scatter problems. Attempts to correct for scatter using the two line method failed since when the scatter signal approaches or surpasses the fluorescence signal small errors in the scatter signal correction system give rise to large errors in the scatter corrected results.Cobalt and Ni are moderately sensitive elements in fluorescence and it was found that the values obtained using scatter correction were either over or under compensated. Other correction procedures were not tried.586 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 Table 5 Application of AFS with an ICP as source and/or atomizer to various sample materials Ref. 46* 8 3 18L§ 487 88 I1 89 11 61 90* 938 Sample type Unalloyed Cu (SRM 394) Unalloyed Cu (SRM 396) Fresh Water (SRM 1643) Fresh Water (SRM 1643) Fly Ash (SRM 1633) Lake Sediments Lake Sediments Lake Sediments Lake Sediments Water (SRM 1643a) Water (SRM 1643a) Water (SRM 1643a) Water (SRM 1643a) Water (SRM 1643a) Water (SRM 1643a) Water (SRM 1643a) Water (SRM 1643a) Water (SRM 1643a) Water (SRM 1643a) Water (SRM 1643a) Stainless Steel (SRM 106b) Stainless Steel (SRM 106b) Stainless Steel (SRM 106b) Stainless Steel (SRM 106b) Stainless Steel (SRM 106b) Stainless Steel (SRM 106b) Stainless Steel (SRM 106b) Low Alloy Steel (SRM 362) Low Alloy Steel (SRM 362) Low Alloy Steel (SRM 362) Low Alloy Steel (SRM 362) Low Alloy Steel (SRM 362) Low Alloy Steel (SRM 362) Low Alloy Steel (SRM 362) Low Alloy Steel (SRM 362) Synthetic nuclear waste Synthetic nuclear waste Iron ore Iron ore Slag Slag Gold alloy Gold alloy Gold alloy Gold alloy Brazing alloy Brazing alloy Brazing alloy Brazing alloy Brazing alloy Brazing alloy Unalloyed Cu (NBS 454) Water (NBS 1643a) Water (NBS 1643b) Ni sulphamate Plating Solution Ni sulphamate Plating Solution Ni sulphamate Plating Solution Ni sulphamate Plating Solution Ni sulphamate Plating Solution Ni sulphamate Plating Solution Ni sulphamate Plating Solution Wear Metal in Oil (SRM 1084) Wear Metal in Oil (SRM 1084) Wear Metal in Oil (SRM 1084) Wear Metal in Oil (SRM 1084) Element Zn Zn Zn Cd Zn Cd Cd Cd Cd Ag Be Cd c o Cr c u Fe Mn Ni Sr Zn c o Cr c u Mn Ni Mo Si A1 c o Cr c u Mn Ni Mo Si Pd Pd A1 Si A1 Mn Au Pd Ag Pt Ag c u Ni Cd Pb Zn Au Ag Ag Cr c o c u Fe Pb Mn Zn A1 Cr c u Fe Acceptable or certified value 375 & 38 4.7k0.3 0.065 k 0.003 0.008 * 0.00 1 210k20 22 40 29 58 2.8 f 0.3 19f2 10f 1 19f2 17f2 18f2 88 +4 31 + 2 55f3 239 5 72f4 0.101% 18.45 Yo 0.1 72 yo 1.64% 12.26% 2.38% 0.509 Yo 0.095% 0.3% 0.3 ?'a 0.5% 1.04% 0.59% 0.068 Yo 0.39% 260 260 0.51 3.8 5.14 0.4 95.7 2.84 1.02 0.3 1 70f 1 28+ 1 0.75 & 0.25 < 0.002 < 0.002 < 0.002 7.5 f0.5 pg g-' 2.8f0.3 ngml-' 9.8 f0.8 ng ml-' 1 (spike) 2 (spike) 2 (spike) 2 (spike) 2 (spike) 2 (spike) 2 (spike) 98f2 100 f 3 98f4 100+4 AFS result 376 k 3 4.8f0.1 0.0656 f 0.0008 0.0079 219$.4 20 43 31 57 3.4 f 0.5 18.6 f 1 10.4 f 0.5 18.5* 1.8 20f2.5 19.5 & 1.3 88 f 2.5 31.3 f 0.8 56 f 1.5 240 2.5 70.2 f 0.6 0.111 k0.002 18.63 f 0.2 0.174 f 0.002 1.5 f 0.01 12.19 f 0.1 2.38 f0.4 0.51 f0.02 0.095 0.002 0.288 k 0.003 0.33 1 f 0.005 0.483 f 0.003 0.994 f 0.0 1 0.59 f 0.006 0.068 + 0.004 0.39 f 0.02 250 (AFS) 250 (RM) 0.64 3.5 5.35 0.45 95.8 2.88 1.01 0.33 70.7 + 0.2 28.7k0.1 0.62 f 0.02 < 0.0001 <0.001 0.005 f 0.0001 7.63 f0.09 pg g-' 2.74f0.16 ng ml-' 9.95k0.14 ng ml-' 0.94 1.96 2.13 2.16 1.88 2.05 2.15 96f8 99f4 101 f 4 103 f 7 continued-JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL.9 587 Table 5 - continued Wear Metal in Oil (SRM 1084) Wear Metal in Oil (SRM 1084) Wear Metal in Oil (SRM 1085) Wear Metal in Oil (SRM 1085) Wear Metal in Oil (SRM 1085) Wear Metal in Oil (SRM 1085) Wear Metal in Oil (SRM 1085) Wear Metal in Oil (SRM 1085) 95 Rice-flour (SRM) Rice-flour (SRM) Rice-flour (SRM) Rice-flour (SRM) Wheat-flour (SRM) Wheat-flour (SRM) Wheat-flour (SRM) Wheat-flour (SRM) Tomato leaves (SRM) Tomato leaves (SRM) Tomato leaves (SRM) Tomato leaves (SRM) Tomato leaves (SRM) Tomato leaves (SRM) Citrus (SRM) Citrus (SRM) Citrus (SRM) Citrus (SRM) Citrus (SRM) Pine Needles Pine Needles Pine Needles Pine Needles 967 Geological Ref Mat.(SARM-7) Geological Ref Mat. (SARM-7) Geological Ref Mat. (SARM-7) Mg Ni A1 Cr Cu Fe Mg Ni Fe Zn Ca K Fe Zn Ca K Cr Fe Zn Ca K Mg Cr Fe Zn Ca K Cr Fe Ca K A U Pd Pt 98+4 101 +4 296 & 4 298 f 5 295 f 10 300 f 4 297 k 3 303 7 8.7 k 0.6 pg ml-' 19.4+ 1.0 pg ml-1 0.014 + 0.002 %m/m 0.1 12 + 0.002% m/m 18.3 -+_ 1 pg ml-' 10.6 _+ 1 pg ml-' 0.019f0.001% m/m 0.136 f 0.004% m/m 4.5 L0.5 pg ml-' 690k25 pgml-' 62f6 pg ml-' 4.46 k 0.03% m/m 0.8 f 0.2 pg ml-' 90k 10 pg ml-' 29+2 pg ml-' 3.15f0.1% m/m 1.82 -t 0.06% m/m 2.6f0.2 pg ml-' 200f 10 pg ml-' 0.4 1 -+_ 0.02% m/m 0.37 f0.02% m/m 3 0.03% m/m 0.7 0.31-tO.015 1.53 f0.032 3.74 f 0.045 98+9 103 + 5 295 & 7 302 f 8 298 f 5 296 + 6 299 k 3 302 & 2 8.6& 1.3 pg ml-' 19.1 + 1.5 pg ml-' 0.016 rt_ 0.001 O h m/m 0.102 f 0.007% m/m 18.7 f 1.1 pg ml-' 9.6f0.8 pg ml-' 0.021 f 0.001 YO m/m 0.126 & 0.007% m/m 4.3k0.3 pg ml-' 414223 pgml-' 63f3 pgml-l 1.94+0.11% m/m 3.32k 0.29% m/m 0.63 f 0.08 % m/m 0.9k0.1 pgml-' 60f6 pgml-' 34k1 pgml-' 2.14+0.31% m/m 1.60+_0.07% m/m 2.9f0.4 pg ml-' 141 +9 pg ml-' 0.4 f 0.04% m/m 0.36 + 0.05% m/m 0.29 f 0.04 1.58 & 0.06 3.78 0.2 * Values in pg g-'.7 Values in ng g-'. 1 Water values in ng ml-'. 9 Steel values in YO m/m. 1 Values in pg rn1-I. I/ Values in YO m/m. Berthoud et ~ 1 . ~ ~ in what they claimed was the first demon- stration of laser induced fluorescence of Pu in an ICP used a Nd:Yag laser to pump a dye laser acting as a source in an AFS system incorporating an ICP as an atomizer. These workers observed direct line fluorescence of Pu but did not observe any collisionally assisted fluorescence. They demon- strated the selectivity of the AFS technique by measuring Pu fluorescence in the presence of U.The LOD obtained was given as 50 ng ml-' (the factor x sb was not stated) but further analytical results were not given. It was suggested that the technique was very suitable for numerous applications in the nuclear industry and could be extended to other elements such as Tc and Np. Yeah et a1.93 evaluated the HCL-ICP-AFS (Baird) system for the measurement of Na Cu Ni Ag Fe Al Cr and Mg in a variety of organic solvents and applied their findings to the measurement of these elements in lubricating oil. The fluor- escence signals and S/N were found to be greatest in kerosene out of the ten or so solvents studied.The LODs for A1 and Cr were given as 0.1 pg ml-' (3 x sb) whereas the LOD for the other metals Na Cu Fe Ni Ag and Mg were below 0.1 pg rnl-I. The linear range of the calibration curves extended over 4 orders of magnitude. For all the analytes the spectral selectivity (defined as the ratio of concentration ngml-I of interferent giving the same fluorescence signal as 1 ng ml-I of analyte) exceeds lo2 and in most cases lo4 despite the use of interference filters as the spectral isolation device for each module. The fluorescence signals for all elements varied by less than 3% over a 4 h period. Yeah et al. concluded that the system was well adapted to the measurement of trace levels of organometallics in organic solvents and should find consider- able use for wear metals in jet engine lubricating oils.Sansoni et ~ 1 . ~ ~ compared multi-element analysis by ICP-MS for practically matrix-free natural waters coming from a granitic area and therefore rich in trace elements with ICP- AES HCL-ICP-AFS (Baird) and AAS. They found the within- run repeatibility of the AFS method to be reasonable with regard to the measuring time of 20 s in multi-element operation. The between-run reproducibility determined with two slightly different sets of operating conditions but for all 12 elements the same experimental parameters was unsatisfactory. They concluded that several element concentrations were too near to the LOD. Details of the operating parameters were given but not how they were obtained or whether they had been optimized in any formal sense.Zhu et dg5 in a paper largely concerned with the verification of the effects of altering the operating parameters of the Baird instrument determined Cr Fe Zn K and Mg in rice and wheat flours tomato and citrus leaves and pine needles. The technique of ICP-AFS was evaluated as a method for determining Au Pt and Pd in geological materials by C a ~ g h l i n ~ ~ using a Baird AFS 2000 equipped with BDHCL. Sensitivity for Pt was further increased by simultaneously pulsing two Pt HCLs as the excitation source. Samples were prepared by fire assay using Pb cupellation and collection with Ag. The resultant bead was dissolved in nitric acid-aqua regia. It was considered possible using a fused sample of 20 g and a final solution volume of 5 ml to achieve LODs in the solid of588 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL.9 0.3 ng g-' for Au 3 ng g-' for Pt and 0.2 ng g-' for Pd. Linear dynamic ranges of 5 orders of magnitude for Au and Pd were obtained. Platinum had lower sensitivity and is linear over 4 orders. For all elements linearity extended up to a concen- tration of 10000 ng m1-l. This worker experienced some prob- lems of sample introduction because of the high acidity of the samples. The Au signal in 25% v/v aqua regia was half the value in distilled water. This suppression was reduced by adding a surfactant. The only spectral interference observed was that of Fe 217.903 nm on the Pt 217.904 nm but this was corrected for by use of a correction factor. (The use of a monochromator on the Pt detector would have eliminated this interference).Long term precision was monitored by the analy- sis of in-house reference materials. Data was acquired over a 4 month period with over 200 samples. The averages and standard deviations were as follows sample numbered PT70 Au 31 f 3 Pt 70+7 Pd 147f 7 (ng ml-l) and sample num- bered PT25 Au 105 f 15 Pt 25 & 5 Pd 39 +2 ng ml-'. In conclusion to this section it is interesting to note that isotopic resolution has been achieved in laser excited AF using an ICP as an atomizer by resolving the 235U/238U splitting of the U I1 285.6 nm t r a n ~ i t i o n . ~ ~ This fact may have potentialities for the future. 7 The Present and Future of the ICP in AFS The future of the ICP in AFS is inextricably bound up with that of AFS itself. For this reason it is pertinent to discuss the state-of-the-art of this technique and to do so with particular reference to the use of the ICP.One way of carrying out this exercise is to compare AFS with other spectroscopies on the basis of what has become known as figures of merit (FOM). These figures are selectivity dynamic range freedom from chemical and ionization interferences LOD and precision. To these important FOM may be added other factors such as cost ease of operation and the capability of simultaneous multi-element analytical determination. The pertinent spectro- scopies for comparison must be AAS ETAAS ICP-AES and ICP-MS. From the present review there is a mass of evidence on the various FOM to suggest that unequivocal statements can be made in some instances and qualified statements with varying degrees of uncertainty in others. Hence it seems that the proposed basis of comparison is at least tenable. 7.1 Freedom From Spectral Interference There can be no doubt that AFS has greater freedom from spectral overlap interference than has AAS and most certainly ICP-AES and ICP-MS.In fact with non-resonance measure- ment spectral overlap interference is virtually irnpos~ible.~~ The reasons why this should be so have been discussed in the body of this review. In addition because in AFS the exciting radiation is modulated and the fluorescence is detected by ax. coupled electronics background interference due to radiative recombination continua and other d.c. or low frequency back- ground shifts is avoided.Thus all else being equal if spectral selectivity is of paramount importance AFS must be the preferred technique especially so with the advantages accrued when used in combination with an ICP. 7.2 Linear Dynamic Range With an ICP as an atom/ion cell AFS has a linear dynamic range variously quoted as being between 4 and 6 orders of magnitude as has ICP-AES. This long range is due not only to the sensitivity of these techniques with their low LODs but also to the optical thinness of the ICP and hence an extended conccntration range before the onset of self-absorption; ICP-MS also has similar linear dynamic range. In contrast AAS has very limited range. Therefore if it is desired to analyse wide concentration ranges from one solution ICP-AFS ICP- AES and ICP-MS are the preferred techniques. Also the concentration range of AFS can be extended to higher concen- trations by working in the RM mode.7.3 Freedom from Chemical and Ionization Interference Effects The ICP-AFS and ICP-AES techniques have greater relative freedom from these types of interference than have other spectroscopies. However this statement is based on experimen- tal evidence from studies of what are regarded as classic examples of this type of interference e.g. the effect of PO4 Al K and Na on Ca I emission and so are by no means exhaustive. Furthermore this type of interference is spatially dependent and therefore operating parameters must be selected preferably by a global optimization to give minimum interference. Non- observation of this fact has given rise to conflicting evidence in the literature.Certainly ICP-AFS and AES because of the high temperature of the ICP used show greater freedom from these interferences than does AAS. Hieftje and Vickers9' have stated that numerous matrix interferences have been docu- mented in ICP-MS. Some of these effects are similar to those which occur in ICP-AES others are peculiar to ICP-MS. O l e ~ i k ~ ~ has similarly reported that matrix-induced errors in ICP-MS are more severe than in ICP-AES. He further states that almost any element present at high concentration (> 100 yg m1-l) can cause errors in ICP-MS. 7.4 Limits of Detection The fluorescence signal is proportional to the incident radiation falling on the atom/ion cell. Since the efficiency of transfer of energy from the source to the cell is largely dependent upon the optical system chosen which varies from one experimental set-up to another a direct comparison of the LOD obtained is not straightforward. Thus from Table 6 it might appear that the LODs obtained by ICP-ICP-AFS (ref.30) are with a few exceptions either way equal to those obtained by ASIA (ref. 44). However reference to Table 4 shows that the efficiency of the optical system is quoted as 13% in the one case (ref. 30) and 1-2% in the other (ref. 44). Therefore it is reasonable to assume that if both systems had similar optics the LOD would be quite different. The efficiency of transfer is not always quoted. For a comparison to be made between two different systems both should be operating under optimum conditions.Rarely or so it seems is a proper optimization of all the operating parameters carried out essential in a system which is spatially dependent. At best a univariate search of a few parameters seems to satisfy many workers in the field. There is ample evidence that a properly conducted ~ptimization~~ can dra- matically alter the LOD. Care should therefore be exercised in comparing LODs from different systems or claming that one source or atomizer is better than another. Greenfield et ~ 1 . ~ ~ used a high power ICP as an excitation source and obtained LODs for Pb Ni and Cu that were 5-7 times superior to those from corresponding BDHCL. However the difference could be due to the inability of the circular source to illuminate the same volume in the atomizer plasma as could the ICP source.In this work the lamp was not run in the continuous wave mode but was operated with a 50% duty cycle. Demers and MontaseF2 stated that AF signals from BDHCL operated in the pulsed mode would be comparable to or slightly greater than those from an ICP. The use of shorter duty cycles means that for a given average current the peak current will be higher than for a 50% duty cycle. Watson'00 gives as an example a Varian Spectra 400 Z operating with a 10% duty cycle and goes on to state that this means that the peak current is 5 times that found with conventional operation. However this does not lead to a corresponding increase in lamp intensity which is element dependent and is usually only increased between 2 and 3.5-fold for a given mean current.For theJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 Table 6 Comparison of spectroscopies on the basis of LODs (ng ml-')* 589 Element Ag A1 AS B Ba Ca Cd c o Cr c u Fe Hf Hg Mg Mn Mo Na Ni P Pb Pt Sb Si Sn Sr v w Y Yb Zn Zr Element Ag A1 As B Ba Ca Cd c o Cr c u Fe Hf Hg Mg Mn Mo Na Ni P Pb Pt Sb Si Sn Sr V W Y Yb Zn Zr ICP-F 3 1000 5000 - - 4 0.7 11 2 2 6 90 0.09 2 400 60 60 1200 1500 400 - _. - - - - - - - 0.5 - ASIA 20.5 28 - - 3.5 0.2 9.5 3 0.4 5 - - - - - 63 0.1 0.1 - 27 - - 54.5 - - - 428 - - 2 - Ref. 47 46 46 - - 46 47 46 46 46 46 49 46 46 46 47 49 49 49 46 - - - - - - - - - 46 - Ref. 44 44 44 44 44 44 44 44 - - - - - - - 44 44 44 44 - - - 44 - - - 44 _. - 44 - AAS 45 150 1000 15 1.5 1.5 0.8 9 3 1.5 5 300 300 0.15 1.5 45 0.3 6 75000 15 60 45 90 150 3 60 1500 75 8 1.5 450 GFAAg 0.05 0.3 0.5 0.9 0.03 0.02 0.4 0.08 0.25 0.3 1.5 0.01 0.09 0.20 0.05 0.80 320 0.15 5 0.4 2.5 0.5 0.06 0.3 45 - - - - 0.3 - HCL-ICP Ref.? < 0.1 5 25 60 25 <0.1 <O.l 0.4 0.4 0.1 0.3 400 5 < 0.1 0.2 8 <0.1 0.2 2000 5 15 7 40 25 20 200 300 0.7 <0.1 400 0.3 Ref.$ 108 - - - - - - - - - - - __ - - - - - - - - - - - - - - - - - - 62 62 62 62 62 62 62 38 38 62 38 62 38 62 62 62 62 62 62 38 62 62 62 62 62 62 58 62 38 62 62 ICP-AES 1.5 6 30 3 0.15 0.15 1.5 3 3 1.5 1.5 - 30 0.15 0.6 7.5 6 6 45 30 30 90 5 60 0.075 3 30 0.3 1.5 1.5 - ~~ Ref.? 74 22 34 22 22 29 - - - 34 74 34 29 22 - - - - 34 22 74 34 22 22 57 57 57 75 34 74 - ICP-ICP 15 15 - - 1.35 0.6 30 6 0.6 7.5 - 45 - 0.3 13.5 1.5 150 150 120 45 10.6 0.3 - - - 60 30 15 3 15 - TCP-MS Ref.$ 0.003 108 0.006 - 0.006 - 0.09 - 0.002 - 2 0.003 - 0.0009 - 0.02 - 0.003 - 0.4 0.0006 - 0.004 - 0.007 __ 0.002 " - 0.003 - 0.05 - 0.005 - 0.3 0.001 - 0.002 __ 0.001 0.7 0.002 0.0008 0.002 0.001 - 0.0009 - 0.001 - 0.003 - 0.004 __ - - - - - - - - Ref.30 30 30 30 26 26 30 26 30 30 26 26 30 6 30 - - - - - - - 30 30 30 30 30 30 30 - - * Normalized to 3 x sb. 7 Refs. 57 and 74 extended-sleeve torch as atomizer; ref. 29 double resonance ionic fluorescence; refs. 22 29 and 75 conventional short torch $ Ref. 108 for all elements. 5 20 pl samples. L'vov platform. as atomizer; ref. 34 stimulated Raman scattering; and ref. 34 and 58 with ultrasonic nebulization.590 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL.9 Table 7 List of abbreviations AAS AES AFS ASIA A T AVS BDHCL COG cw DRF EDL ETE ETA FOM HCL h.f. ICP L LOD MS PMT RM RSD sb s/N SRM SRS USN Atomic absorption spectrometry Atomic emission spectrometry Atomic fluorescence spectrometry Atomizer source inductively coupled plasmas in atomic fluorescence spectrometry Total absorption factor Alternating variable search Boosted-discharge hollow cathode lamp Curves of growth Continuous wave Double-resonance fluorescence Electrodeless discharge lamp Easily ionizable element Electrothermal atomization Figure of merit Hollow cathode lamp High-frequency Inductively coupled plasma Laser Limit of detection Mass spectrometry Photomultiplier tube Resonance monochromator Relative standard deviation Standard deviation of the blank Signal-to-noise ratio Standard Reference Material Stimulated Raman scattering Ultrasonic nebulizer BDHCL operating in this mode only produces small increases in output typically about twice that of normal operation.This is noticeable on the Spectra 4002 where the BDHCL is usually about five times as bright as a normal HCL whereas under conventional operating conditions it is about ten times as bright. Watson'" also states that a disadvantage of operating with these short duty cycles is that in order to obtain reasonable lamp life the average current needs to be reduced. The problem is that if the same mean current is used although the heat will be the same sputtering is increased due to the greater momentum of the Ne ions caused by the higher accelerating voltage present in the short duty cycle high current discharge.An even more serious problem is that because of the higher velocity of the Ne ions ion-pumping is much more serious and this can easily lead to premature failure of the lamp due to gas clean-up. As a result of the need to use lower currents the use of short duty cycle operation only leads to an increase in output for a conventional HCL of about 2 times without an unacceptable reduction in lamp life while for the BDHCL very little increase can be obtained unless lamp life is sacrificed. The purpose of the foregoing polemic is to highlight certain difficulties in comparing LODs. However some broad con- clusions can be drawn from Table 6. The technique with the greatest sensitivity and lowest LOD is ICP-MS and the next most sensitive is ETAAS.One possible exception but neverthe- less with a consistent trend is ICP-ETA-AFS where the LOD based on a limited sample is possibly lower than in ETAAS but not as low as ICP-MS. It is also probably safe to assert that the best of the AFS results are lower than in AAS and that the LODs for the non-refractory elements are equal to or in many cases better than in ICP-AES. The refractory elements all give worse LODs in AFS than in ICP-AES. Any further comparisons are increasingly difficult to make. 7.5 Precision This is another 'grey' area about which one can only draw general conclusions. Thompson and Walsh"' suggested that for ICP-AES at concentrations about 1000 times the LOD 10 sequential 5 s integrations should give an RSD of 0.2-0.5%.However they further stated that for practical analysis an RSD of about 1 YO was more appropriate. For HCL-ICP-AFS Demers and Montaser62 indicate that the RSD is element dependent. Silver Cd Hg Pb and Zn may be expected to give an RSD of 0.2-0.6Y0. On the other hand the refractory elements give an RSD of 1-2%. Alkalis give the worst RSD of around 2-3%. Taylor and Garbarinolo2 give an RSD of 2-7% for a number of elements in ICP-MS. Moore103 gives an RSD of 0.5-1.0% for ICP-AES 0.5-1% for FAAS and 2 to 5% for ETAAS. Pintaio4 gives 5 to 10% for ETAAS. If one stated that the YO RSD for the spectroscopies were about equal for ICP-AES HCL-ICP-AFS and FAAS rather worse for ICP-MS and much worse for ETAAS that would broadly represent the present position.7.6 Other Factors Although the cost of instrumentation for ICP-MS is coming down it is still expensive. This also applies to the sophisticated end of the ICP-AES instrumentation but not to the same extent. Both types of instrument require knowledge and experi- ence for their true potential to be exploited. Both are capable of genuine simultaneous multi-element operation. In the same upper end of the market is AFS instrumentation involving the use of dye lasers as source and an ICP as atomizer. This latter combination not only requires skill and expertise for its operation but is not a simultaneous multi-element system unlike similar instrumentation involving two ICP which can be as expensive but is capable of such operation. The possibility exists for such dual plasma AFS instrumentation to become cheaper if both plasmas are powered from one g e n e r a t ~ r .~ ~ Moving down the scale of cost one has the sequential ICP- AES instruments which can and do have a high level of sophistication but are not capable of simultaneous multi- element operation. In the same category of price and sophisti- cation are the upper end of the AAS instruments which are sequential in operation (although theoretically capable of multi-element operation). Until it was taken off the market one could have placed at the top end of this grouping the HCL-TCP-AFS instrument of the Baird Corporation. Also in this grouping must be placed the 'DIY' instrumentation for AFS using an ICP as an atomizer ignoring (for the moment) its use as a source.Such basic instrumentation has beenJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MAY 1994 VOL. 9 59 1 described in Section 1.5; it requires knowledge and skill to assemble but once this has been done it is simple to operate. In its basic form it is sequential but with imagination and sophistication it need not be. At the bottom end of this price range are the simple AAS machines which are not only inexpensive but are easy to operate and produce good results. 7.7 Epilogue Having examined the facts presented in the body of this review and the comparisons which have been made of ICP-AFS with other spectroscopies there would seem to be sufficient grounds for believing that the technique has much to commend it to the practising analytical scientist.However the fact remains that it does not enjoy great popularity. Lack of knowledge apart a possible reason for this state of affairs is that in the past attempts to introduce commercial AFS instruments such as the relatively expensive instrument based on the work of Mitchell and Johannsonlo5 have not been successful. Now following the withdrawal of the Baird instrument from the market place (so far as is known for commercial and not technical reasons) there is no commercial instrumentation available. In support of this hypothesis the early history of ICP-AES can be cited. Following the publication of the first paperLo6 describing the use of the annular ICP as a source in AES it was some 10 years before this particular technique (ICP-AES) became popular and this was with the advent of commercial instrumentation.The economic climate of the time was more conducive to ‘DIY’ than it is today but even so few workers assembled their own equipment so it is not altogether surpris- ing to find even fewer willing to do so today. Manufacturers of scientific equipment are primarily con- cerned with sales and not with pushing back the frontiers of science. Therefore they are not willing to develop instruments (an expensive business) for which they have little evidence of a large demand. On the other hand analytical scientists will not advance the technique of ICP-AFS without off-the-shelf instruments to work with and therefore advancement is slow and there is little demand for such equipment a classic ‘chicken and egg’ situation. There is one way out of this impasse.Throughout this review there have been examples of the use of the ICP in existing ICP-AES instruments as a light source in AFS with or graphite furnaceig as atomizers the latter with great effect. The plasma has been shown to be an excellent line source and it only requires simple optics to transfer the emission from a source analyte to an external atomizer. [It has been suggested62 that there is a danger in nebulizing per cent concentrations of toxic elements into the plasma (atmos- phere). This is something of a non sequitur. Obviously there is danger in inhaling toxic materials. Equally obviously whatever the use of the ICP steps should be taken to ensure that the extraction system is efficient and safe and due regard given to what happens to the discharge. This may involve totally enclosing the torch-box and putting it under negative pressure.It may also involve scrubbing of the exhaust gases. How far these precautions are necessary will depend on the application. That this is easily accomplished is demonstrated by the many examples of the determination by ICP-AES of trace elements in toxic matrices which include radioactive by-products.] There are some 65 elements which emit radiation in the ICP and each element will have a large number of usable wavelengths so that the scope for selection for all types of fluorescence is large. The external atomizer could be a separated flame or an existing commercial ETA apparatus. Possibly some of the optics and electronics of the dedicated instrument could be utilized but if not the additional equipment required to carry out AFS is relatively simple and inexpensive. (This approach has already been applied to ICP-MS to enable AES to be carried out concurrently with MS using fibre optics to transfer the radiation from the ion source plasma to an atomic emission spectrometer.lo7) Conversely the ICP in a dedicated instrument could be used as an atomizer (possibly with a change of torch) with an external BDHCL unit as source.Again simple optics are all that is required to transfer the light energy from the source to the atomizer and there is no doubt that in the case of AES instruments the existing monochromator would be more than sufficient for the task. 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ISSN:0267-9477    

DOI:10.1039/JA9940900565

出版商:RSC    

年代:1994

数据来源: RSC