摘要:

JASPE2 8(8j 61 N-66N 1053-1 122 337R-405R 9 9 ) Typeset by Burgess Thames View Abingdon Oxfordshire December 1993 Printed in Great Britain by Journal of Analytical Atomic Spectrometry Including Atomic Spectrometry Updates CONTENTS NEWS AND VIEWS 61 N Obituary-David A Hickman 61 N Reconstruction of Boris L'vov's Electrothermal Atomizer-Judith Egan-Shuttler 61 N Gordon Kirkbright Bursary 62N Book Review-Adam McMahon 63N Diary of Conferences and Courses 65N Future Issues PAPERS 1053 1059 1067 1075 1085 1091 1097 1103 1109 1113 1117 1121 Determination of Ultratrace Levels of Heavy Metals in Arctic Snow by Electro- thermal Vaporization Inductively Coupled Plasma Mass Spectrometry-Ralph E Sturgeon Scott N Willie James Zheng Akira Kudo D Conrad Gregoire Determination of Palladium and Platinum in Fresh Waters by Inductively Coupled Plasma Mass Spectrometry and Activated Charcoal Preconcentration-Gwendy E M Hall J C.Pelchat Determination of Selenium in Marine Certified Reference Materials by Hydride Generation Inductively Coupled Plasma Mass Spectrometry-Hiroaki Tao Joseph W H Lam James W McLaren Arsenic Speciation in Seafood Samples With Emphasis on Minor Constituents an tnvestigation Using High-performance Liquid Chromatography With Detection by Inductively Coupled Plasma Mass Spectrometry-Erik H Larsen Gunnar Pritzl Steen Honore Hansen Speciation of Arsenic by Ion Chromatography and Off -line Hydride Generation Electrothermal Atomic Absorption Spectrometry-Han Heng-bin Liu Yan-bing Mou Shi-fen Ni Zhe-mmg Electrothermal Vaporization for Sample Introduction in Microwave-induced Plasma Atomic Absorption Spectrometry-Ytxiang Duan Xingyou Li Qinhan Jin Improvement in Mercury Cold Vapour Atomic Techniques by Resorting to Organized Assemblies and On-line Membrane Drying of Vapour-B Aizpun Fernandez M R Fernandez de la Campa Alfred0 Sanz-Medel Improvement in Detection Limits in Graphite Furnace Diode Laser Atomic Absorption Spectrometry by Wavelength Modulation Technique.Plenary Lecture-Christoph Schnurer-Patschan Aleksandr Zybin Henning Groll Kay Niemax Preliminary Study on the Use of Palladium as a Chemical Modifier for the Determination of Silicon by Electrothermal Atomic Absorption Spectrometry-Zhixra Zhuang Pengyuan Yang Xiaoru Wang Zhiwei Deng Benli Huang Effect of Aqueous Organic Solvents on the Determination of Trace Elements by Flame Atomic Absorption Spectrometry and Inductively Coupled Plasma Atomic Emission Spectrometry-M Todorovic S Vidovic.Z IIIC Indirect Flame Atomic Absorption Spectrometric Determination of Papaverine Strychnine and Cocaine by Continuous Precipitation With Dragendorff's Reagent-Marceltna Eisman Mercedes Gallego Miguel Valcarcel CUMULATIVE AUTVOR INDEX ATOMIC SPECTROMETRY 337R Industrial Analysis Metals Chemicals and Advanced Materials-John Marshall UPDATE John Carroll James S. Crighton Charles L. R. Barnard 377R References continued on inside back cover 0267-9477C199318:l-YJASPE2 8(8j 61 N-66N 1053-1 122 337R-405R 9 9 ) Typeset by Burgess Thames View Abingdon Oxfordshire December 1993 Printed in Great Britain by Journal of Analytical Atomic Spectrometry Including Atomic Spectrometry Updates CONTENTS NEWS AND VIEWS 61 N Obituary-David A Hickman 61 N Reconstruction of Boris L'vov's Electrothermal Atomizer-Judith Egan-Shuttler 61 N Gordon Kirkbright Bursary 62N Book Review-Adam McMahon 63N Diary of Conferences and Courses 65N Future Issues PAPERS 1053 1059 1067 1075 1085 1091 1097 1103 1109 1113 1117 1121 Determination of Ultratrace Levels of Heavy Metals in Arctic Snow by Electro- thermal Vaporization Inductively Coupled Plasma Mass Spectrometry-Ralph E Sturgeon Scott N Willie James Zheng Akira Kudo D Conrad Gregoire Determination of Palladium and Platinum in Fresh Waters by Inductively Coupled Plasma Mass Spectrometry and Activated Charcoal Preconcentration-Gwendy E M Hall J C.Pelchat Determination of Selenium in Marine Certified Reference Materials by Hydride Generation Inductively Coupled Plasma Mass Spectrometry-Hiroaki Tao Joseph W H Lam James W McLaren Arsenic Speciation in Seafood Samples With Emphasis on Minor Constituents an tnvestigation Using High-performance Liquid Chromatography With Detection by Inductively Coupled Plasma Mass Spectrometry-Erik H Larsen Gunnar Pritzl Steen Honore Hansen Speciation of Arsenic by Ion Chromatography and Off -line Hydride Generation Electrothermal Atomic Absorption Spectrometry-Han Heng-bin Liu Yan-bing Mou Shi-fen Ni Zhe-mmg Electrothermal Vaporization for Sample Introduction in Microwave-induced Plasma Atomic Absorption Spectrometry-Ytxiang Duan Xingyou Li Qinhan Jin Improvement in Mercury Cold Vapour Atomic Techniques by Resorting to Organized Assemblies and On-line Membrane Drying of Vapour-B Aizpun Fernandez M R Fernandez de la Campa Alfred0 Sanz-Medel Improvement in Detection Limits in Graphite Furnace Diode Laser Atomic Absorption Spectrometry by Wavelength Modulation Technique.Plenary Lecture-Christoph Schnurer-Patschan Aleksandr Zybin Henning Groll Kay Niemax Preliminary Study on the Use of Palladium as a Chemical Modifier for the Determination of Silicon by Electrothermal Atomic Absorption Spectrometry-Zhixra Zhuang Pengyuan Yang Xiaoru Wang Zhiwei Deng Benli Huang Effect of Aqueous Organic Solvents on the Determination of Trace Elements by Flame Atomic Absorption Spectrometry and Inductively Coupled Plasma Atomic Emission Spectrometry-M Todorovic S Vidovic. Z IIIC Indirect Flame Atomic Absorption Spectrometric Determination of Papaverine Strychnine and Cocaine by Continuous Precipitation With Dragendorff's Reagent-Marceltna Eisman Mercedes Gallego Miguel Valcarcel CUMULATIVE AUTVOR INDEX ATOMIC SPECTROMETRY 337R Industrial Analysis Metals Chemicals and Advanced Materials-John Marshall UPDATE John Carroll James S. Crighton Charles L. R. Barnard 377R References continued on inside back cover 0267-9477C199318:l-Y

ISSN:0267-9477    

DOI:10.1039/JA99308FX001

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

2N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Atomic Spectrometry Viewpoint R. Sam Houk Ames Laboratory US Department of Energy and Department of Chemistry Iowa State University Ames /A 5001 1 USA During Professor Houk’s (R. S. H.) attendance at the Third Durham Plasma Conference in September 1992 Dr. Barry L. Sharp (B. L. S.) Chairman of the Editorial Board and Douglas L. Miles (D. L. M.) Chairman of the ASU Board interviewed him about his work on inductively coupled plasma mass spectrometry. B. L. S. Sam your name is synony- mous with inductively coupled plasma mass spectrometry (ICP-MS) to most analytical chemists. Perhaps you would like to tell us a little bit about your background from being a graduate stu- dent onwards. R. S. H. I started graduate school in 1974; you saw a picture at this confer- ence of what I looked like then.I quickly became enchanted with the ICP. This was one of the three great religious experiences in my life the other two being spectacular sporting plays by the Pittsburgh Steelers* and Pittsburgh Pirates.t I decided I wanted to work on ICPs and so naturally I joined Professor Verner Fassel at Iowa State. They had a very large group and I was one more pea in a pod essentially. During my first year some papers were published by Alan Gray on elemental * ‘The Immaculate Reception’ Franco Harris’ 60 yd. touchdown reception with 22 s remaining to beat the Oakland Raiders 13-7 on 23 December 1972. Q Who was the intended receiver? t Bill Mazeraski’s solo home run off Ralph Terry to beat the New York Yankees 10-9 in the seventh game of the 1960 World Series.Q Who was the winning pitcher? analysis of solutions by mass spectro- metry using a d.c. capillary arc plasma. These papers showed excellent detec- tion limits fairly clean spectra and lots of potential for the general idea of taking atmospheric pressure plasmas injecting sample solutions and ex- tracting ions into a mass spectrometer. The first paper we saw was in Analyti- cal Chemistry in March of 1975. The various copies of Analytical Chemistry were delivered to everyone in Fassel’s group at more or less the same time. Fassel was in his office I was in mine and we opened the packets of the journals more or less simultaneously and leafed through the paper for a few minutes. Then we each immediately left our offices and started walking toward each other and met exactly half way between his office and mine.So it was decided that this was an interesting idea and we would have a try at doing MS with an ICP. I also had worked in a mass spectrometry group in AMES which was run by Harry Svec who was a very well known mass spectrometrist. As it turned out I did a joint Ph.D. project with both Fassel and Svec. B. L. S. This meeting in the corridor were you both meeting with the same notion that the ICP was the thing to go with? You didn’t have any original notions on following down the capillary transfer road? R. S. H. Our opinion of the paper was exactly the same that these were very intriguing results but that the ICP should be more tolerant towards in- jected samples and should have lower matrix effects.Such a plasma ought to prove better as a source than the capillary arc system that Alan Gray used; in fact we could not understand why Alan Gray and Applied Research Laboratories (ARL) didn’t immedi- ately move on to ICP work. It turned out that ARL essentially dropped that project. Fassel was a consultant for the American version of ARL at that time on ICP emission spectroscopy. My understanding is that he urged them very strongly to follow that project up but they didn’t. I think this is an important illustration of the fact of an important relationship between instru- ment companies and academic or government laboratories. None of the instrument companies have enough resources to start fundamentally oriented projects on their own.The university or the government labora- tories must continue this work to the point where it is clear that a goodJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 3N commercial product will emerge. It is a mistake to say that instrument manu- facturers can develop their own instru- ments. None of them could afford to take a loss on even one such instru- ment if it weren’t for the demon- stration by some other group usually funded by the government that a research idea can be developed into a viable product. B. L. S. I have the impression with this particular technique that the in- strument companies actually became involved at an earlier stage than for most other analytical techniques. If you look at the optical side there had been quite a lot of academic work done and systems demonstrated in Fassel’s group for example before manufac- turers really took a serious interest.Whereas it is my impression that with the MS technique the manufacturers came in at a fairly early stage perhaps because it was not necessarily equip- ment that could be home-built anyway. I think Alan’s equipment was from components suppled to him by VG for example. R. S. H. I think so. I agree with the assessment that commercial ICP-MS instruments followed more quickly on the initial development in our lab and in Alan’s lab in Surrey than was the case in ICP emission. One reason was that all but one of the difficult prob- lems with the ICP had already been worked out by the initial experiments. Methods for good impedance match- ing networks proper torch design serviceable nebulizers methods for minimizing the radiofrequency inter- ference and radiation had been sorted out already by the emission people and to be able to take a commercial ICP with a good stable matching net- work helped us a lot.We altered things slightly for mass spectroscopy but basi- cally went with existing ICP techno- logy that was already well developed. D. L. M. Was there any direct com- mercial interest or link in your Ph.D. work? R. S. H. No but ARL was certainly aware of our experiments. Towards the latter years of the 197Os perhaps late 1978 or early 1979 we learned that Don Douglas and Barry French at SCIEX were experimenting with a microwave plasma on the two stage sampling interface sampler and skim- mer which have become the ne plus ultra of ICP-MS now.In fact Don Douglas’ paper on microwave plasma MS was published just one month after ours on ICP-MS. B. L. S. At what point did the critical change from boundary layer sampling to continuum sampling of the plasma come; that was the critical issue wasn’t it really? R. S. H. That was what turned it from a research curiosity into a practi- cal analytical tool. The key was in developing ways to minimize the ex- tent of electrical discharge between the plasma and sample orifice. Ways to do this were found more or less empiri- cally but with some fundamental backing in c.a. 1982 at SCIEX and in the lab at Surrey. We roughly chimed in during 1983 with similar notions. I remember clearly in the Summer of 1983 when as soon as softball season ended I headed for the labora- tory and did some things to get our mass spectrometer up to speed for continuum sampling.Certain tricks like drilling out the sampling orifice as large as possible was one major factor in diminishing the extent of the dis- charge. By the way the fundamental reasons why factors like orifice size and aerosol gas flow rate should affect the severity of the secondary discharge are still not understood. B. L. S. For a short time Alan Gray came over and worked with you. Was that a particularly fruitful cooperation? R. S. H. Yes it certainly was. He first visited for one day in March of 1978 and he was over in August of 1978 for a whole month the hottest month of the hottest year Iowa has ever had! We got a lot done in that month.We had some spectra in July but we improved things by leaps and bounds in the month while he visited. He has re- turned for visits several times since; in 1981 he even left his appendix be- hind! He actually made many close friends in AMES mainly by visiting churches. He has friends there still that are not related to ICP-MS. D. L. M. Looking back at that early work do you think there are any parti- cular mistakes? Everyone looks back with twenty/twenty vision. If you could go back again do you think you would have avoided any false moves? R. S. H. There were probably more false moves than true ones. I think the biggest technical error was that the first ion lens I tried to make was too long and too big. I should have just tried to put the quadrupole up as close to the sampler as possible; that would have simplified matters greatly.I think we should have arrived at a serviceable boundary layer sampler much sooner than we did. We tried to make quite sophisticated ones with sharply pointed cones and laser-drilled holes and so forth. We should have just struck to simpler things and got some ions through. We started building an instrument in 1976 based on prelimi- nary experiments in which we ex- tracted ions into a simple vacuum system with a Faraday cup detector. We had an MS more or less functional in about mid-1977 but we really first saw spectra from the ICP in June 1978. We should have cut that year of interregnum down substantially. It’s easy to know what works now but it was not so easy at the time.D. L. M. In the UK because of the history of the funding of the develop- ment of ICP-MS which fairly early on involved the British Geological Survey and the Natural Environment Research Council and Alan Date working with Alan Gray there was obviously one direction in which its application was seen from the very early stages i.e. geological analysis. Was there a simi- lar sort of target market seen in your work? R. S. H. Yes our work in AMES was funded by the EPA (Environmental Protection Agency) and it was a really sweet deal. We were funded at a very serviceable level for both equipment and personnel for five years from EPA. We didn’t each have to write much in the way of a proposal. There was a fellow from EPA named Chuck Taylor who was visiting AMES to evaluate ICP emission spectroscopy as a certifiable EPA method and also had some background in spark source mass spectrometry.He heard about our ex- periments and we sat around one afternoon and discussed the possibili- ties for ICP-MS. Chuck went back to his immediate boss in Athens GA a man named Charlie Anderson who incidentally was Fassel’s first Ph.D. by the way. They rustled some money up for us and we were funded just like that. This has seldom if ever hap- pened since of course. B. L. S. It seems an irony then that EPA still has not certijed some of their methods by ICP-MS. R. S. H. My understanding is that EPA has had a viable method for drinking water in place for some time. I do not know why their method has not been formally issued yet. Since 1981 my project has been supported by the Office of Basic Energy Sciences by the US Department of Energy (DOE).The work has always been done in a DOE laboratory at AMES but the early phases were supported by EPA. It is very gratifying to see the impact of ICP-MS on scientific prob-4N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 lems pertinent to energy technology environmental monitoring analysis of nuclear fuel monitoring of radio- nuclides isotope ratios and elemental analysis for the semiconductor petro- leum and materials industries. B. L. S. Were you at all surprised at the relatively slow rate of entry of academic groups into the ICP-MS field compared with their enthusiasm for ICP-A ES? R. S. H. I guess I was not greatly surprised by this because of the higher initial cost of mass spectrometers.It is a little harder to total up the resources necessary to move into ICP-MS. I’m not sure that the movement of acade- mics into ICP-MS has been all that much slower than it was into ICP emission spectroscopy. I think most of the academic groups in North America the United States and Canada that were in ICP emission spectroscopy are now also in ICP-MS. They really converted within only a couple of years or so after the commer- cial introduction of the technique. B. L. S. There’s been a lot of interest recently in plasmas in furnaces FANES for example and we’ve seen mass spectrometers used as diagnostic devices in looking at furnace mecha- nisms. Do you see that area as a possible analytical route or do you think MS with furnaces will remain just a diagnostic area? R.S. H. I think there are very interesting things to do with mass spectrometric sampling of either ions or neutrals from furnaces. The neutral atoms would then be ionized subse- quently in a vacuum system. We are interested for example in trying to do isotope selective ionization by photo- ionization from elements vaporized in furnaces to differentiate two isotopes of different elements of the same nom- inal mass. So there is a lot of interest- ing work to be done on furnaces as either atomization or ionization sources for MS. Perhaps with some of the new advances in nebulization methods for ICPs it will be possible to do nearly as well in terms of analysing very small volumes of solution just with a straight ICP as with the furnace.B. L. S. The ICP-MS using a quadru- pole is now beginning to mature as a technique. We are seeing a slight em- phasis away from people reporting the performance of the system to reporting the limitations of the system particu- larly of quadrupoles. I believe you are working on a two quadrupole system at the moment. Do you want to tell us something about that? R. S. H. Our twin quadrupole system measures one isotope ratio simultane- ously without mass scanning. Hope- fully source noise will therefore be averaged out. We hope to obtain high precision even with noisy or transient samples from electrothermal vaporiza- tion laser ablation or chromato- graphy. Also the two detectors can be operated at different gain so that a very large or very small ratio can be measured.This instrument is near completion and we hope to report some results soon. There is a lot of recent work with other types of mass analysers coupled to the ICP. Double focusing instru- ments are now commercially avail- able. Projects with time-of-flight and ion trap mass spectrometers are in the early stages. Each type of mass ana- lyser has advantages and disadvan- tages. The quadrupole is by far the most common mass analyser in or- ganic MS; 1 suspect it will remain so in ICP-MS as well at least in the near future. B. L. S. Your group’s been very much involved in new developments in sam- ple introduction and I think I in right in saying you believe this to be one of the most important areas for development. Would you like to expand on that? R.S. H. For many years I went to meetings on atomic spectroscopy and listened to people (professors mainly) complaining about the deficiencies of nebulizers without doing much about them. In fact we held the fort for ultrasonic nebulization for many years. We have used it extensively for solution nebulization and ICP-MS for many years now. I always felt that the ugly reputation of ultrasonic nebuliza- tion was due solely to deficiencies and hasty production of the first commer- cial version of the device. With proper engineering and attention to detail these devices can indeed be made robust and reliable for routine analyti- cal work. Recently largely owing to the efforts of Dan Wiederin and Sam Shum we have looked at a new version of the direct injection nebulizer.This is a highly efficient nebulizer which puts nearly all the sample into the ICP and is well suited for analysis of small samples and determination of memory-prone elements such as B Hg I and 0 s . Its low dead volume also makes it ideal for interfacing chroma- tographic separations to ICP-MS for speciation measurements. We are very keen on the direct injection nebulizer for either these special analyses or as a general purpose nebulizer. B. L. S. Closely linked to the question of sample introduction is the coupling of techniques such as ICP-MS specia- tion. I think everyone realizes that a lot of the future of elemental analysis lies not in determining the total elemental content but the active species. Where do you see this Jield developing say in the next Jive or six years? R.S. H. I can see two main ap- proaches to speciation. The first is the continued effort to couple chromato- graphy with spectroscopic detection. Of these the mass spectrometer has a substantial advantage in sensitivity which is particularly valuable because the sample is usually diluted by the chromatographic separation. The multi-element capability of ICP-MS has not been used much yet for specia- tion. There will probably be limits to multi-element speciation unless we can find global chromatographic con- ditions that separate all the species from all the elements in the same run. The second general approach to spe- ciation that is really interesting now is the possibility of using electrospray to generate intact ions that are more or less representative of the species pre- sent in the original sample solution.Electrospray work by Paul Kebarle Gary Horlick and Don Douglas at SCIEX has shown that it is possible to get metal ion spectra that can be related to the chemical form of the element. This is a very exciting devel- opment. It is certainly true that within the next ten years or so we ought to be moving towards a society where the allowable levels of trace elements dic- tated by our benevolent governments are based upon real measurements of their actual chemical effects on the environment rather than simply rely- ing on the total amount of the element present. One of the duties of the atomic spectroscopist is to provide the analytical technology necessary to support more enlightened regulatory efforts.B. L. S. Can I just ask for your general point of view about research students? Do you find they come to you knowing about wanting to work on ICP-MS or do you put it to them as just one question? What kind of background do you look for in potential research students somebody with an ICP background a physicist or maybe an environmental chemist? R. S. H. Well most students do come with a specific interest in ICP spectro- scopy or at least analytical atomic spectroscopy although there are some with interest in mass spectrometry. I have had a couple of students with prior experience with the ICP particu- larly Jeff Crain who is now at ArgonneJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 5N National Laboratory who had done some ICP emission work and Dan Wiederin who spent a summer with me as an undergraduate research trainee doing ICP-MS work.The main thing that I like to see in a student is the ability and the psychological make- up to get into the laboratory and work with hidher hands on a mass spectro- meter. I look for confidence in physical ability independence and creativity as well but my students need to be able to do things with their hands. It is sharp work. I personally had experi- ence in carpentry with my father which was very helpful. D. L. M. ICP-MS worldwide ifyou like has applications to all sorts of areas in the UK particularly on the geological and environmental side for reasons we spoke of earlier. That is true I think also in Canada for example.Is it true in the US? R. S. H. Clearly environmental monitoring is the main application of ICP-MS in the US. There are relatively few ICP-MS papers from geologists at US conferences in analytical chemis- try so my impression is that ICP-MS is used less for geological purposes in the US than in Canada or the UK. Britain especially has a strong heri- tage in ICP-MS from Alan Date whose early work on geochemical applications was so important D. L. M. What about industrial or metallurgical analysis? Is ICP used widely there? R. S. H. It is used widely by those organizations for environmental mon- itoring of waste water effluent and so forth. There is of course a substantial use in the semiconductor industry. In fact the first high resolution ICP-MS machine in the States was installed by IBM in New Jersey for analysis of the high purity chemicals needed there.My own reading is that ICP-MS is not used as much in steel production and metallurgical and materials sciences as it could be. Matrix effects are often the limiting factor for such analyses so providing instruments with lower ma- trix effects should be one main objec- tive for future ICP-MS development. For that matter many of the analytical needs in the metals industry were met perfectly well by spark emission spectroscopy years ago. B. L. S. At a time when the Western market is being dominated by too many manufacturers in competition a turning point it seems in the ICP-MS market is that more manufacturers are now about to launch products and they do that because they expect the market to grow substantially.Do you think their faith is justified? R. S. H. Yes it isinterestingwhether they are at a turning point or a Turner point for ICP-MS. I think the market for ICP mass spectrometry will con- tinue to creep up although there may be a quantum leap when EPA eventu- ally does certify or issue their method. I do not see ICP-MS replacing ICP emission spectroscopy in the near future for the reason that the machines are too expensive for many labs. The community is very interested in the commercial and scientific viability of moderate cost ICP-MS machines such as that provided by VG. If the advan- tages of ICP-MS are really available for $100000 to $150000 many more labs would jump right in. Otherwise I see steady growth but not a tre- mendous explosion in the market for ICP-MS.D. L. M. The so-called hybrid machine half optical halfICP-MS has haunted the literature for years. Do you think it is a viable analytical system? R. S. H. This is a hard question to answer; Ke Hu my latest Ph.D. stu- dent is now working at Thermo Jarrel Ash because of his expertise in con- structing mass spectrometers. I saw this instrument at the Pittsburgh Con- ference in New Orleans last year; I was standing right next to a disguised VG salesman by the way. We had done quite a few optical measurements of the properties of the gas just outside the sampler orifice. Analytically I see technical problems with trying to ob- serve both emission and mass spectro- metry at the same time. It is going to be hard to find operating conditions that are good for both instruments at the same time.Under the best ICP-MS conditions the sampling cone blocks most of the emission. In ICP emission it is generally necessary to observe radiation from a relatively high slit in order to average out matrix effects. Such spatial averaging will be difficult if the sampler cone is in the way. My personal opinion about using the emis- sion instrument mainly to identify the elements is that you can do just as well with the MS alone. D. L. M. Look into your crystal ball if you will. In ten years what do you think thejeld will look like? What kind of plasma mass spectrometric related techniques will exist? R. S. H. In ten years I can think of two main objectives for the field. One area is much better precision and stability than the present instruments provide; in fact this is another impor- tant reason why the materials and the metals industry have been a little slow in embracing ICP-MS.To measure the composition of an alloy precision is of critical importance more so than de- tection limits. An instrument in which the absolute beam stability is 5% is not even in their ball park. Improving the basic precision without having to re- sort to internal standardization or other similar tricks is an important goal. We must first understand where the sources of imprecision lie which is somewhat difficult; isolating each par- ticular source of noise is not an easy thing. The second main area of improve- ment that I can see is substantial reduction in the matrix or non-spec- troscopic interference effects.We need to be able to analyse almost any kind of solid at 0.1% dilution factor with no more than a 10% enhancement or suppression of the analyte signal. Judi- cious (or fortuitous) modification of the ion lenses is one possible approach to the attenuation of matrix effects. D. L. M. What about plasmas in gases other than argon? R. S. H. I saw work here just yester- day on a very nice helium microwave plasma. It has a hole through the centre takes nebulized water appar- ently with good stability and also shows little matrix effect and quite efficient ionization of bromine arsenic and selenium. That looks pretty good. Alternatively perhaps the optimum ICP for MS will be mainly argon with modest amounts of hydrogen nitro- gen helium or xenon.So far these mixed gas plasmas have shown both advantages and disadvantages. For example xenon in the axial channel greatly simplifies the background spec- trum but at the cost of analyte signal. There is more to be done yet in this area. Fred Smith is still recovering from the rigours of breathing dilute argon-xenon mixtures! B. L. S. One of the disadvantages of the MS technique compared with the optical technique is that the sample actually finishes up to some extent inside the mass spectrometer. The transfer eficiency of the current sys- tems is rather poor and it would be helpfur if it could be made better. Can you see any way in which that might be tackled? R. S. H. If we could make an ICP-MS device with better overall ion transmission efficiency we could then dilute the sample and that alone might help to alternate the matrix interfer- ence effects.With the VG double6N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 L to R Barry Sharp Sam Houk and Doug Miles focusing instrument they are already MS instruments the absolute detec- achieving quite high ion transmission tion is somewhere between 1 x lo6 efficiency. They estimate that they can and 1 x lo8 atoms in the plasma. get one analyte ion to the detector for Another thing that Ke Hu did was to roughly 500 analyte ions in the see if an ICP-MS device could be plasma. With quadrupole-based ICP- used as a source of metal ions for ion deposition or implantation. We did some things to the interface and ion lens to increase the beam intensity to over 1 x lo1* ions s-l; it’s not clear that these modifications are valuable for an analytical instrument however. D. L. M. Can we congratulate you Sam on your upcoming receipt of the Maurice F. Hasler Award? R. S. H. I learned in September that I am to be given the Maurice F. Hasler Award by the Spectroscopy Society of Pittsburgh. This award is named for the founder of Applied Research Lab- oratories and is sponsored by ARL. It is given to those who have contributed to the practice of spectroscopy and I am flattered to feel that someone at least thinks that I have achieved this even though I have finished up learn- ing about isotopes instead of wave- lengths. In particular it is uplifting when you consider the previous recipi- ents of the Award people such as Sir Alan Walsh Velmer Fassel George Pimentel and quite a few other emi- nent analytical spectroscopists. I want to be sure to thank Velmer Fassel for nominating me. I must also thank all my students and co-workers; they each contributed to this award in some measure.

ISSN:0267-9477    

DOI:10.1039/JA993080002N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

JASPE2 8(1) 1N-l4N 1-144 1R-78R (1993) H February 1993 Ill I I Journal of Analytical Atomic Spectrometn/ Including Atomic Spectrometry Updates CONTENTS ~ NEWS AND VIEWS 1 N Editorial-Judith Egan-Shuttler 2N Atomic Spectrometry Viewpoint-R Sam Houk 6N Conference Report-Rx Cox 8N 1 1 N 14N Papers in Future Issues Book Reviews-Michael H. Ramsey W Perkins H. T Delves and Phil Potts Diary of Conferences and Courses PAPERS 1 19 25 35 41 45 51 59 65 71 79 85 89 93 103 109 Interferences in Inductively Coupled Plasma Mass Spectrometry. A Review -E Hywel Evans Jeffrey J Giglio I sotope Ratio Measu I ement of Lead Neodymium and Neodym ium-Sama rium Mixtures Hafnium and Hafnium-Lutetium Mixtures With a Double Focusing Multiple Collector Inductively Coupled Plasma Mass Spectrometer-Andrew J Walder I Platzner Philip A Freedman Preliminary Assessment af Laser Ablation Inductively Coupled Plasma Mass Spectrometry for Quantitative Multi-element Determination in Silicates-John G Williams and Kym E Janiis Optimization and Use of Flow Injection Vapour Generation Inductively Coupled Plasma Mass Spectrometry for the Determination of Arsenic Antimony and Mercury in Water and Sea-water at Ultratrace Levels-Andreas Stroh Uwe Vollkopf Figures of Merit for Two-step Furnace Atomization Plasma Emission Spectrometry-K E Finders Ohlsson Ralph E Sturgeon Scott N Willie Van T Luong Differentiation Between Organic and Inorganic Chlorine by Electrothermal Vaporization Inductively Coupled Plasma Mass Spectrometry Application to the Determination of Polychlorinated Biphenyls in Waste Oils-Peter Richner Samuel Wunderli Applications of Ultrasonic Nebulization in the Analysis of Petroleum and Petrochemicals by Inductively Coupled Plasma Atomic Emission Spectrometry-Robert I Botto Evaluation of a Modified Electrothermal Vaporization Sample Introduction System for the Analysis of Liquids by Inductively Coupled Plasma Atomic Emission Spectrometry-J M Ren.Eric D Salid Evaluation of a Linear-flow Torch for Inductively Coupled Plasma Atomic Emission Spectrometry-Norman N Sesi Paul J Galley Gary M Hieftje Development of an Atomic Fluorescence Spectrometer for the Hydride-forming Elements-Warren T Corns Peter B Stockwell Les Ebdon Steve J Hill Simple Nitric Acid Dissolution Method for Electrothermal Atomic Absorption Spectrometric Analysis of Atmospheric Aerosol Samples Collected by a Berner- type Low-pressure Impactor-Tuomo A Pakkanen Risto E Hiilamo Willy Maenhaut Behaviour of Cadmium Cobalt and Lead in Chlorine-containing Organic Solvents in Electrothermal Atomic Absorption Spectrometry-Emil Tserovsky Sonja Arpadjan lrina Karadjova Determination of Impurities in Germanium Tetrachloride Germanium Dioxide and High-purity Germanium by Zeeman-effect Electrothermal Atomic Absorption Spectrometry-E Sei7timenti G Mazzetto E Milella Determination of Scandium Yttrium and Eight Rare Earth Elements in Silicate Rocks and Six New Geological Reference Materials by Simultaneous Multi- element Electrothermal Atomic Absorption Spectrometry With Zeeman-effect Background Correction-Joy G Sen Gupta Rapid Furnace Programmes for the Slurry-Electrothermal Atomic Absorption Spectrometric Determination of Chromium Lead and Copper in Diatomaceous Earth-Ignacio Lopez Garcia Jesirs Arroyo Cortez Manuel Hernandez Cordoba Effect of Surfactants in Flame Atomic Absorption Spectrometry With Pneumatic Nebulization Influence of Hydrophobic Chain Length-Ana I Ruiz Antonio Canals Vincente Hernandis continued on rnsrde back cover 0267-9477C199311 1 - 8 Typeset by Burgess Thames View Abingdon Oxfordshire Printed in Great Britain by PAGE3ROS’ Page Bros.Norwich115 119 127 131 133 137 Sensitive 'One Drop' Flame Atomic Absorptiometric Determination of Cadmium in Botanical Samples Using Direct Nebulization of Chloroform Extract-lsao Kojima Shiny Kondo Determination of Butyltin Compounds in River Sediment Samples by Gas Chromatography-Atomic Absorption Spectrometry Following In Situ Derivatization With Sodium Tetraethylborate-Yong Cai Spyridon Rapsomanikts Meinrat 0 Andreae Accurate Determination of Selenium in the Presence of Iron by Deuterium Arc Electrothermal Atomic Absorption Spectrometry-Sunil Jai Kumar S. Gangadharan CUMULATIVE AUTHOR INDEX INSTRUCTIONS TO AUTHORS IUPAC PUBLICATIONS ON NOMENCLATURE AND SYMBOLISM ATOMIC SPEC~f"VlETRY 1 UPDATE Environmental Analysis-Malcolm S. Cresser Janet Armstrong Jennifer Cook John R. Dean Peter Watkins Mark Cave 45R References Hollow Cathode Lamps WHY PAY A FORTUNE GBC Scientific Equipment U.K Ltd. 13 Frederick Sanger Road The Surrey Research Park Guildford Surrey GU2 5YD Tei 0483 304988 Fax 0483 303071

ISSN:0267-9477    

DOI:10.1039/JA99308BX003

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

6N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Conference Report September 13-1 8 1992 The 3rd International Conference on Plasma Source Mass Spectrometry University of Durham UK In the magnificent city of Durham 160 delegates from around the globe assembled for a packed week of plasma source mass spectrometry and socializing. Sam Houk got the confer- ence off to a lively start with a presen- tation ambitiously entitled ‘ 1492- 1992 ICP-MS and the Age of Dis- covery’ in which he compared the early development of ICP-MS to Columbus’ Atlantic voyage to much amusement all round. Having thus warmed up his audience Sam went on to describe recent work in Ames Lab- oratory on the reduction of matrix interferences in ICP-MS using desol- vation and a novel lens configuration.Improvement of isotope ratio preci- sion was the main theme for the remainder of the Instrumentation Theory session. In this context Andrew Walder of VG Elemental described the newest ICP-MS proto- type-a magnetic sector instrument with nine detectors capable of simulta- neous measurement. High precision isotope ratio measurement is the main application intended with RSDs in the range 0.006-0.02°/o. It certainly sounded impressive the price was not mentioned and was probably unmen- tionable! Flow injection and desolvation are currently the fashionable variants for introducing solution samples to ICP-MS appearing throughout the conference as well as in the Sample Introduction Session. Cameron McLeod was unfortunately unable to give his presentation on mercury spe- ciation but Sam Houk stepped in with a presentation on the Direct Injection Nebulizer (who doesn’t carry a spare lecture with them?!).The Industrial Applications Session illustrated two cases where special sample handling procedures are re- quired. Albrecht Brenner (IBM) Ber- told Gercker (Ciba-Geigy) and Bruno Delahaye (IBM) described the analysis of high purity materials for the semi- conductor industry using clean room facilities to protect the samples. Pre- sentations were given by Maria Betti and Jose Garcia Alonso (CEC Karls- ruhe) on the analysis of radioactive materials where the ICP and the sam- ple introduction systems were con- tained in a glove box to protect the analysts. Determinations of trace im- purities in rare earth elements and oxides were treated with two different approaches by workers from Japan,JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 7N Dr. The0 Lutz (Trace Analytic Morges Switzerland) and Dr. Helen Crews (MAFF Norwich UK) King and Queen for the evening at the banquet in Durham Castle Naoko Shibata (National Chemical Laboratory from Industry) used ETV- ICP-MS and described an investigation of oxide ion levels whilst in a poster presentation Takaban et al. (Marubun Corporation) used a high resolution ICP-MS to measure the doubly charged ions of REE impurities. Ten minutes before the start of the session the chairperson for Geological Applications might have been wonder- ing whether the invited speaker was going to turn up. In fact they were one and the same person and Kym Jarvis did indeed arrive to deliver her lecture on the use of laser ablation and slurry sample introduction for determina- tion of PGMs and gold in geological materials.Laser ablation loomed large throughout the session with both the bulk solid sampling and the spatial resolution properties of this method being exploited. Jenny Cook (British Geological Survey) described the use of a frequency quadrupled Nd:YAG laser to give a very small crater 5 pm in diameter) for high spatial resolution. Interesting data on the distribution of REE and Th in monazite nodules were compared with results of electron mi- croprobe analyses. This session in- cluded a review by Bill Perkins of the geochemical and environmental ICP- MS work carried out at UCW Aber- ystwyth which led to him and Nick Pearce sharing the 1992 Alan Date Memorial Award.The Solid Sampling Session on Wednesday morning turned away from the ICP-MS domination of the conference and put the spotlight on GDMS. After an overview of the fundamentals of the glow discharge source by Professor Gijbels (Univer- sity of Antwerp) the presentations ranged widely through the analysis of conducting and non-conducting solids and depth profile measurements re- turning to more fundamental studies reported by Rod Mason to conclude the session. For a non-specialist in GDMS the session provided an en- lightening snap-shot of the capabilities and advantages of the technique. The Gods were kind and Wednes- day afternoon brought glorious sun- shine for the optional excursions to Hadrian’s Wall or the Beamish Open Air Museum.An invigorating change from the lecture theatre both trips were much appreciated by participat- ing delegates. In an unusual arrangement the con- ference dinner was held on the penulti- mate night of the conference in the impressive setting of the Durham Castle Banqueting Hall. A superb meal was followed by presentation of the Alan Date Memorial Award by Jan Date hilarious speeches live music partying and many bleary eyes at breakfast. Jan Date presenting the Alan Date Mem- orial Award to Drs. Bill Perkins and Nick Pearce (University College of Wales Aberystwyth) Helen Crews (MAFF) commenced the Life Sciences session with an over- view of the ICP-MS applications in the MAFF Food Sciences Laboratory. Compared with the other techniques measurement of many trace element concentrations and isotope ratios in biological materials is relatively simple using ICP-MS.Stable isotopes are being used ever more widely in studies of trace element effects in human health. In this session zinc copper and lead isotope uptake studies were discussed by Helen Crews Tom Lyon (Glasgow Royal Infirmary) and Les Dale (CSIRO) respectively the last describing the determination of isotope ratios in sweat for a study of lead uptake through the skin. Thursday afternoon brought the En- vironmental Applications Session with Dr. The0 Lutz (Trace Analytic Morges Switzerland) presedzting the award for best poster to Dr. Paolo Bianco (Camera Commercia Torino Italy)8N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 an interesting divergence of emphasis. Carlo Vandecasteele started the ses- sion by reminding us that environmen- tal analysis does not always demand the best possible limits of detection and supported this statement with data attained using a VG PQe ‘eco- nomy model’ ICP mass spectrometer. Nick Pearce (UCW Aberystwyth) fol- lowed with a presentation on the water chemistry of acid mine drainage and limits of detection were no restriction here with horrendously high levels of toxic metals involved. Detection limits took on more importance in the pre- sentation by Shin-ichi Yamasaki (National Institute of Agro-Environ- mental Sciences Japan) who used a high resolution ICP mass spectro- meter with an ultrasonic nebulizer to measure first row transition metals and actinides in river water. Limits of detection were blank limited to 1 ppt for copper and nickel but below 0.5 ppt for other first row transition metals and down to 0.01 ppq (pg dm-3) in low resolution mode for neptunium and plutonium.This running out of units was a feature of all the high resolution ICP-MS presentations of the con- fernce although the sampling and con- tamination problems must increase by orders of magnitude as the detection limit drops. The final session of the conference on Friday morning was a look to the future. Scott Tanner (SCIEX) gave a lecture on the most promising aspects of ICP-MS applications and instru- mentation development from his point of view admitting to being much more comfortable once he had got onto hardware and mentioned some space charge! He also described a new sam- ple introduction device developed at SCIEX the monodisperse Dried Mi- croparticulate Injector (MDM) which produces a stream of identically sized droplets and uses much reduced sam- ple uptake rates.Takafumi Hirata (Geological Survey of Japan) talked about a quadrupole mass spectrometer he has built with thermal ionization source. The message ‘The future of plasma source mass spectrometry is TIMS’ did not convince the audience. Alan Gray summed up the con- ference with a confession to some dis- appointment as a physicist at the substantial excess of applications over instrumentation papers but the fact that people were actually using ICP- MS made him feel ‘it had all been worthwhile’. He looked forward to the advance of ICP-MS with high resolution mass spectrometers and the continued improvement in sample in- troduction methods. Thus the dele- gates dispersed with a call from Barry Sharp to attend CSI and its satellites ringing in their ears thankful for the intervening months to prepare their presentations and their livers for the next onslaught! Ros Cox AEA Environment and Energy Harwell Laboratory Didcot Oxfordshire UK

ISSN:0267-9477    

DOI:10.1039/JA993080006N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

8N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Book Reviews ~~ Statistics in Spectroscopy Howard Mark and Gerry Workman. Pp. xiii + 3 13. Academic Press. 199 1. Price E54.40. ISBN 0 12 472530 9. This slim volume is really a collection of the short articles that were origi- nally published in ‘Spectroscopy’. Their compilation in one volume has the advantage of convenience for ref- erence but several drawbacks. The 38 chapters in 3 13 pages corresponding to the original articles do not make a logical division of the subject matter. For example the division of Chapter 30 ‘Pitfalls of statistics,’ from Chapter 3 1 ‘Pitfalls of statistics continued’ is unhelpful and generally leads to un- necessary repetition. The writing style is very colloquial which can work well in a single article but does tend to pall when chapters are read consecutively as a book.The description of the statistical methods is generally good assuming little prior knowledge of statistics. In the latter chapters however this does tend to grate when that knowledge has already been covered in a previous chapter. Referencing between chapters is generally poor. For example h e a r regression is described in one chapter but the critically important tests for whether the regression parameters are statistically significant are not dis- cussed in that chapter. The reader is told only that they will be discussed ‘in a later chapter’ unspecified. There is a wide coverage of the traditional statis- tical techniques for univariate and bivariate measurements.Multivariate techniques such as the increasingly popular principal component analysis are not covered; nor are the non- parametric techniques. Overall the book will be useful to suggest as a second alternative to the standard texts such as Miller and Miller (1988 Ellis Horwood). The informal style may help to clarify the techniques to some readers. It is how- ever unlikely to become a classic reference work in the field of statistics for the analytical chemist. Michael H. Ramsey Department of Geology Imperial College London SW7 ZBP UK Handbook of Inductively Coupled Plasma Mass Spectrometry Edited by K. E. Jarvis A. L. Gray and R. S. Houk. Pp. xi + 380. Blackie. 1991. Price €72. ISBN 0 216 92912 1; USA 0 412 02501 9. This book is presented as a handbook of inductively coupled plasma mass spectrometry (ICP-MS) and in all re- spects fulfills that function. The book is divided into 11 chapters each deal- ing with a specific aspect of the instru- mentation or applications.Chapter 1 covers the origin and development of the technique and two of the principal authors (A.L.G. and R.S.H.) were based at the two laboratories where the first experi- mental ICP mass spectrometers were built. Both have therefore been in- volved with ICP-MS since its incep- tion and are the best qualified persons to review the origins and development of ICP-MS. The chapter gives a brief description of the development which will provide the newcomer with an insight into the early period of ICP- MS and because of the comprehensive references provided allow the inter- ested reader to find more detailed descriptions if necessary.Chapter 2 covers the instrumenta- tion available for ICP-MS. Each com- ponent is described in detail providing information about its function and optimization. The variations available from the principal commercial manu- facturers are described and the merits of each evaluated. There is no bias in the description of these options. This chapter is excellent and will help to overcome the ‘black box’ approach toJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 9N such sophisticated analytical instru- mentation. Chapter 3 contributed by J. G. Williams covers the field of instru- ment options. This chapter forms a complement to Chapter 2 and de- scribes the component parts which in solution introduction mode can either be modified or a number of options are available.The components covered are nebulizers; spray chambers; torches and the interface. The descrip- tion of nebulizers deals with concen- tric cross-flow Babington frit and ultrasonic types. In the sub-section on the function of the spray chamber wash-out times and thermal stability are described. Torch types and the interface are explained although the new micro-skimmer system used in VG instruments is not described. Chapter 4 contributed by J. G. Williams covers sample introduction for liquids and gases. This is a long and comprehensive chapter which deals with liquid other than by nebuliza- tion and gaseous sample introduction. The chapter again covers the main options available from instrument manufacturers as well as several ‘home-made’ modifications.In Chap- ter 4 the emphasis changes to illus- tration by reference to analytical applications showing how analytical requirements have driven the develop- ment of these additional sampling techniques. Electrothermal vaporiza- tion (ETV) is explained and illustrated by reference to geological bio-medical and environmental examples. Vapour generation for hydrides together with volatile mercury OsO and reactive gases is presented and illustrated with examples. The section on liquid chro- matography (LC) contains a useful table summarizing the range of appli- cations of LC-ICP-MS. Flow injection is described and its advantages enume- rated followed by a short section on applications.Finally the direct sample insertion method is briefly covered. The references given throughout are comprehensive allowing the reader to find the key works in each of the topics covered. Chapter 5 is concerned with inter- ferences. In any handbook such a section is of vital importance. This chapter covers the subject matter in a systematic and comprehensive fashion. The interferences are divided into two types ‘spectroscopic’ and ‘non-spectroscopic’ and each type is described. The chapter makes exten- sive use of published studies many by the authors themselves to provide the reader with an understanding of the measures that must be taken to mini- mize the problems. This excellent chapter explains the theoretical con- siderations of interferences (such as oxides polyatomic species and refrac- tory formation) and offers some help in minimizing some of the problems.For both the new user and the experi- enced operator reading this chapter could eliminate many costly hours of collecting useless data. Chapter 6 covers calibration and data handling. The chapter begins with a description of the different modes of data acquistion and then describes methods of calibration. The basis of the so-called ‘semi-quantitative Cali- bration’ is explained followed by a section on fully quantitative analysis. Calibration techniques and the func- tion of internal standards are de- scribed. In this section the potential problems posed by the incorrect choice of internal standards are displayed. The chapter ends with a description of the isotope dilution method including its advantages and disadvantages. Chapter 7 contributed by I.Jarvis deals with sample preparation for ICP- MS. This is a long chapter which comprehensively covers a wide range of topics. The reagents commonly used in sample preparation are reviewed and the laboratory apparatus de- scribed. Recommendations are made on the choice of both reagent and apparatus. Sample digestion is sen- sibly divided into open acid diges- tion closed acid digestion (including microwave digestion) and alkali fu- sion. Detailed methods are described for a range of sample types (plant animal geological environmental and metal) which will prove valuable to those faced with new or difficult sample types. The merits of closed digestion procedures are discussed and specific methods described.The chap- ter concludes with a section on separa- tion and preconcentration methods giving details of methods for rare earth elements precious metals and Hf Nb Ta and Zr in geological samples. Chapter 8 is concerned with elemen- tal analysis of solutions and applica- tions. This chapter complements the material presented in Chapter 7. The start of the chapter contains a table of preferred isotopes for elemental analy- sis which also gives information about interferences and sample preparation methods. A suggestion is made for a typical quantitative multi-element procedure. The chapter is sub-divided into sections dealing with different areas of application geological envi- ronmental nuclear industrial and bio- logical. Within these sections groups of elements are considered instrumental parameters listed and results obtained for reference materials given.In this section there is extensive information on potential interference problems which is useful for those planning ICP- MS applications for specific sample types. Chapter 9 contributed by J. W. McLaren deals with the analysis of natural waters by ICP-MS. Following a useful introduction section which covers some of the regulatory con- siderations for detection limits in fresh waters the author describes sampling procedures. The chapter is then divi- ded into sections on the direct an- alysis chemical separation and/or preconcentration for water analysis. Methods for the analysis of sea-water are described as well as the preconcen- tration of fresh water.In the last section calibration strategies are re- viewed. Chapter 10 covers the analysis of solid samples. This chapter deals with a wide range of methods of solid sample introduction but concentrates on two slurry nebulization and laser ablation. A brief discussion of the problems of calibration with such techniques is presented. The section on slurry nebulization deals with the important aspects of grinding tech- niques dispersing agents particle size distribution applications detection limits precision and accuracy. Two specific applications the determina- tion of chlorine and the determination of the rare earth elements are de- scribed. Results for some reference materials are presented. The section on laser ablation briefly explains the construction and operation of a laser and then covers system configuration laser operation sample preparation calibration interferences detection limits practical considerations and applications.In the laser ablation sec- tion many of the possible advantages such as the reduction of polyatomic interferences in a dry plasma and the ability to perform spatial analysis are given. The results from a number of unpublished studies are presented illustrating the potential of the laser for bulk sample analysis. Three short sections conclude the chapter covering direct sample insertion powdered solids and arc nebulization. Chapter 11 considers isotope ratio measurement. The authors review traditional methods for these deter- minations and then deal with the instrument performance of the ICP mass spectrometer.The main part of the chapter is concerned with applica- tions and methods and is divided according to the element concerned. The elements for which applications exist are arranged in ascending mass. The applications described are geo- logical bio-medical and environmen- tal. The elements described are Li B Fe Zn Rh and Os Pb and U. The chapter ends with a short section on other elements.1 ON JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 The handbook has three appendices. The first listing the sources of refer- ence materials cited in the text and the second tabulating the naturally occur- ring isotopes relative abundances atomic mass and first and second ionization energies. The third appen- dix is a useful glossary. The comprehensive reference sec- tion reflects the fact that the book is very well referenced throughout.This book is both comprehensive in its subject matter and logically laid out and illustrated throughout and is hard- bound. No ICP-MS laboratory should be without a copy and anyone consi- dering using an ICP-MS should con- sult this book. The book is expensive at E72.00 and as such I feel that laboratories and libraries will be able to purchase it but the price may be beyond the individual purchaser. Per- haps the publishers can be persuaded to produce a soft cover version that is more reasonably priced. W. Perkins Institute of Earth Sciences University College of Wales Aberystwyth UK Applications of Plasma Source Mass Spectrometry Edited by Grenville Holland and Andrew N.Eaton. Pp viii + 222. Royal Society of Chemistry. 1991. f37.50. ISBN 085186 566 6. This book contains 21 of the papers presented at the 2nd International Conference on Plasma Source Mass Spectrometry held at Durham in Sep- tember 1990. The contributions range widely from fundamental aspects of ion formation and transmission into the mass spectrometer to analyses of a variety of different types of sample. Three chapters deal with applica- tions of new high resolution (HR) double-focusing instruments. Tsumara and Yamaski used ultrasonic nebuliza- tion and measured directly incredibly low levels 0.5-23 pg 1-I of rare earth elements plus U and Th in terrestrial waters. Except for La and Dy they achieved excellent agreement with results obtaining using normal resolu- tion ICP-MS following copre- cipitation on Fe(OH),.Yamasaki et al. used HR-ICP-MS also with ultrasonic nebulization to measure trace ele- ments in plant Standard Reference Materials (SRMs) following mi- crowave-heated acid digestion. The result for eight elements in 10 SRMs was in agreement with the certified values but interference from Arc and from CaO and NaCl caused overesti- mates of Cr and Ni respectively. Walsh et al. used pneumatic nebuliza- tion of semiconductor grade acids and reagents for the direct analysis of trace elements at the pg g-I level. The high resolution overcame many polyatomic ion interferences e.g. from ArNH nominal mass 55 on 55Mn. The effects of plasma gas flow rates and r.f. power on the axial distribu- tions of ions and ion oxides in ICP-MS were studied by Jakubowski et al.who used a computer-controlled stepper motor to vary sampling depth in the plasma. Turner gives an excellent dis- cussion of the causes of mass-bias effects in ICP-MS and describes the use of a three aperture ion extraction system to eliminate them. Glow discharge MS is comprehen- sively reviewed by Stuewer who details ways to overcome interferences and to ensure analytical accuracy. Two papers deal with the use of laser ablation for analysis by ICP-MS. Abell used time resolved analysis to optim- ize laser energy and repetition rate and also investigated pre-ablation times and depth of focus. With optimized laser parameters excellent RSDs (1.0-2.7%) were obtained for the analysis of minor elements in steels.Denoyer found that although loose powders could be analysed directly using laser ablation the results were more accurate and precise when the samples were pelletized using either plaster cellulose or paraffin. Electrothermal vaporization (ETV) and hydride generation (HG) proce- dures for sample introduction into an r.f. plasma were evaluated by Vollkopf et al. Using ETV-ICP-MS the detec- tion limits were excellent with either single ion (1-70 fg) or multi-element (3-40 fg) modes for analysis. The RSDs for multi-element analysis at only 1 pg 1 - I were in the range 10-25%. Using HG-ICP-MS with a flow injection system detection limits of 3-15 ng 1-I were obtained for As Sb Bi Te and Hg; the detection limit for Se was 60 ng I-'. Ek et al. also used a continuous flow HG system for measuring Se in biological samples following HN03-HC104 digestion and HC1 conversion of selenate into selen- ite.A separately nebulized solution of In was used as internal standard. This method gave excellent agreement with certified values for Se in five different biological reference materials i. e. bone liver muscle oyster tissue and wheatflour. Two chapters demonstrateclearly the suitability of ICP-MS for multi-element analysis of waters. Johansson and Lilje- fors report data that is in agreement within +- 1 O% with certified values for 13 elements in a reference water using only a semiquantitative procedure. Veldeman et al. analysed thermal waters for 12 elements by ICP-MS following filtration and acidification and obtained results that agreed well with those from INAA and four spectroscopic methods.Samples requiring more involved pre-treatment are discussed by Kawa- saki et al. and by Ishanullah and East. The former compared seven different methods of preparation of organic fertilizers for multi-element analysis whereas the latter gave extensive de- tails of preparation of several environ- mental samples for measurement of 99Tc. Three chapters are concerned with the analysis of biological samples Lutz et al. critically evaluated the constitu- ents of a diluent which enabled whole blood to be analysed for many trace elements following a simple dilution. The retention and distribution of platinum in animals following the ad- ministration of cisplatin was studied by Tothill et a[.who were able to measure levels below 1 ng g-l in blood and in tissues. Templeton and Vaughan describe the use of principal component analysis (PCA) to correct for isobaric interferences in the mea- surement of Fe and Ni in body fluids. Using the spectra from pure standards of Ca Na plus K and acid digestion blanks they were able to correct inter- ferences and detect 1 pg 1-' of Ni in urine and to measure enriched 57Fe and 58Fe concentrations in whole blood affording the possibility of dual isotope dilution studies. An unusual application of ICP-MS to aid gold prospecting is reported by Perry and van Loon who used the weakly bound gold content of humus samples (ppb levels) as an indication of bedrock gold mineralization. Camp- bell et al. used isotope dilution with ICP-MS to give accurate and precise determination of lead in plant and river sediment reference materials.A good analytical protocol is described by Vanhaecke et al. for measuring B in Ti. The detection limit was lowered by 0.4 pg 1-l by using a PTFE spray chamber. The only criticisms of this book are the variety of type-faces used which presumably relate to the editors policy of minimum intervention and the order of presentation of the chapters. Notwithstanding these the editors have produced a book with a wealth of data on ICP-MS which will be of value to all who use this technique and at a price which is less than that of a litre of vacuum-pump oil. H. T. Delves Trace Element Unit Southampton General Hospital Southampton SO9 4XY UKJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 1 IN XRF Analysis of Ceramics Minerals and Allied Materials Harry Bennett and Graham Oliver. Pp. xv + 298. Wiley. 1992. Price f 45. ISBN 0 471 93457 7. There are several notable and refresh- ing aspects to this book. The first is the outer cover. At first glance what ap- pears to be a spectacular abstract painting in reds and oranges is re- vealed on closer inspection to be a photograph of a molten glass being poured out of a platinum crucible into a casting dish. Second the contents which are drawn directly from the per- sonal experience of the two authors Harry Bennett now retired from the British Ceramic Research Association and Graham Oliver who is employed by its successor Ceram Research Ltd. at Stoke-on-Trent UK.This is a book about the fusion of samples using a suitable flux and casting dish for analy- sis by XRF. As such it is essential reading for anyone employing this form of sample presentation. The book has 19 chapters and 5 appendices. Chapter 1 (1 1 pp.) is an introduction which covers both the impact that the introduction of XRF had on analysis in the ceramics industry and the aims and scope of the present book. Chapter 2 (25 pp.) covers apparatus and equip- ment and gives a valuable over-view of crushing grinding splitting and drying procedures and equipment for fusing samples (and includes details of the author’s prototype platinum crucible for the combined fusion and casting of glass discs). Instrumentation for XRF is summarized briefly. The determina- tion of elements that cannot be deter- mined by XRF are considered in Chapter 3 (8 pp.) in particular borate sulfur carbon lithia halogens sele- nium and volatile or alloying elements.Considerable attention is paid to loss- on-ignition measurements in Chapter 4 (1 9 pp.). Given the current turmoil within the CEC I could not help smiling at the selection of 1025 “C as the commonly accepted temperature for LO1 measurements as a com- promise between 1000 “C (accepted widely in the UK) and 1050 “C (as used on the European continent). Having covered the preliminaries the decomposition of samples by fu- sion is covered comprehensively in Chapter 5 (27 pp.) which includes a wealth of practical experience. Aspects of XRF analysis conditions are con- sidered in Chapters 6 (‘Selection of instrumental parameters’ 10 pp.) and Chapter 7 (‘Element line selection’ 40 pp.).The latter includes sections on individual elements with a commen- tary on the mode of occurrence of the element in ceramic samples selection of spectrometer conditions (with a justification) and an outline of analyti- cal problems which may be encoun- tered. ‘The Standard Procedure’ is described in Chapter 8 (9 pp.) ‘Cali- bration’ in Chapter 9 (2 1 pp.) ‘Presen- tation of the sample bead and comple- tion of the analysis’ in Chapter 10 (8 pp.) and ‘Routine techniques for ma- terial types’ in Chapter l l (7 pp.). The last seven chapters are devoted to procedures for particular categories of samples as follows calcium-rich ma- terials (Chapter 1 3); magnesium-rich materials (Chapter 14); zirconium- bearing materials (Chapter 1 5); vari- ous oxides and titanates (Chapter 16); glasses glazes and frits (Chapter 17); reduced materials (Chapter 18) and samples of unknown composition (Chapter 19). The Appendices sum- marize further practical information covering loss-on-ignition procedures and specific fusion techniques for a wide range of sample types what to do about problem elements or oxides values in relevant certified reference materials and finally details of labora- tory accreditation requirements with particular emphasis on the UK’s NA- MAS scheme. This volume is fairly specific in scope. The general instrumental char- acteristics of XRF specific details of instrumentation and correction proce- dures and alternative forms of sample preparation are not considered in de- tail. However given the wealth of practical expertise within the stated scope this is no disadvantage. For anyone interested in or involved with XRF using samples prepared as glass discs this book is essential reading and should be available for consulta- tion within the laboratory. Phil Potts Department of Earth Sciences Open University Milton Keynes

ISSN:0267-9477    

DOI:10.1039/JA993080008N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 11N Diary of Conferences and Courses 1993 Deauville Conference Scientific Appa- ratus Symposium (SAS) May 4-6 1993 Deauville Normandy France New products and innovations which are to be presented at SAS concern as much the scientific applications and the technical procedures as they do the apparatus themselves. In order to pro- vide visitors with all the necessary and timely information they seek SAS 93 will present in conjunction with the Scientific Apparatus Exhibition poster sessions; scientific and technical communication conferences; and workshops where the specific applica- tions of the apparatus will be demon- strated. A committee of knowledgeable scientists from the analytical sector will be responsible for the technical programme.With this close collabora- tion SAS 93 will benefit from a strict scientific framework and thus the necessary rigorous management which will guarantee excellent quality and a worthwhile event. For further information contact Nicko and Cri Associates 7 rue d’Argent 75002 Paris France. Tele- phone (33)l 42 33 47 66; fax (33)l 40 41 92 41. XXVIII Colloquium Spectroscopicum Internationale June 28-July 7 University of York UK The XXVIII Colloquium Spectroscop- icum Internationale is organized by the Association of British Spectroscop- ists (ABS). On behalf of the Organizing Committee you are cordially invited to attend this meeting which will be held on the campus of the University of York. The CSI has always aimed to cover all branches of analytical spectroscopy although traditionally the emphasis has been on atomic spectroscopy.In selecting the plenary and invited speakers the Scientific Committee has endeavoured to present a wide-ranging overview of all branches of analytical spectroscopy. The balance of the sessions for contributed papers both lectures and posters will of course depend on the papers offered but contributions on a comprehensive range of topics are encouraged. The exhibition will be similarly wide-rang- ing. Plenary and invited speakers will include M. L. Gross (Nebraska); R. E.12N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Hester (York); D. King (Cambridge); C. L. Wilkins (California); and J. D. Winefordner (Florida). Invited lectures in Atomic Spectro- scopy (with ICP-MS) will be given by J.A. Caruso; A. Kh Gilmutdinov J. A. Holcombe R. S. Houk K. Niemax B. L. Sharp M. Thompson and J. Williams. Invited lectures in molecular spec- troscopy will be given by F. Bright; P. Hendra; R. Narayanaswamy; D. Phillips; M. Poliakoff; J. M. Ramsey; J. Reffner; and M. Sigrist. Contributed papers will be pre- sented on the following topics. Basic theory techniques and instrumen- tation of atomic spectroscopy (emission absorption fluorescence); computer applications and chemome- trics; electron spectroscopy; gamma spectroscopy; laser spectroscopy; mass spectrometry (inorganic and organic); methods of surface analysis and depth profiling; molecular spectroscopy (UV VIS and IR fluorescence); Mossbauer spectroscopy; nuclear magnetic reso- nance spectroscopy; photoacoustic spectroscopy; Raman spectroscopy; and X-ray spectroscopy. Applications of spectroscopy in the analysis of biological samples; environmental samples; food and agricultural pro- ducts; geological materials; industrial products and metals and alloys.Instrument Exhibition An extensive exhibition will be held close to the lecture halls. Most major manufacturers of equipment for atomic emission and absorption spec- troscopy molecular spectroscopy and mass spectrometry will be exhibiting. In addition suppliers of data systems and auxiliary equipment will be well represented as will major publishers. Fees 1. 2. 3. 4. 5. 6. 7. Full inclusive fee (regis- trat ion accommodation meals social events) Non-residential registra- tion fee (including meals and social events) Inclusive student fee (confirmation of status from supervisor re- quired) Special discounted fee Single day delegate (lunch included) Accompanying person inclusive fee Accompanying person non-residential fee (with meals and social events) Late registration sur- charge to be paid with fee received after March 3 1.f 425 f 325 f 200 f 200 f 90 f 250 f 125 E30 For further information contact XXVIII Colloquium Spectroscopicum Internationale Department of Chemistry (CSI Secretariat) Lough- borough University of Technology Loughborough Leicestershire UK LEll 3TU. h e - and Post-CSI Symposia Following the tradition that has been established at recent CSI there are a number of pre- and post-CSI symposia on various specialist topics.These are summarized below. 3rd Kingston Conference Analytical Spectroscopy in the Earth Sciences June 28-29 Kingston University Surrey UK The 3rd Kingston Conference will be devoted to innovative developments and applications of analytical spectro- scopy in the full range of Earth Sciences from petrology to stratigra- phy oceanology to hydrology mineral exploration to environmental geoche- mistry. Invited speakers include C. Gregoire (Geological Survey of Canada) M. Ingham (British Geologi- cal Survey) F. Lichte (US Geological Survey) G. Turner FRS (Manchester University). Inclusive residential fee f 198. Introductory Chemometrics-Short Course June 29 University of York York UK A one-day tutorial for those who think that Chemometrics may be of use to them but are not quite sure what it is! There will be introductory talks on spectroscopic data reduction multi- variate analysis maximum entropy techniques application of Fourier transformations to data smoothing applications of chemometrics in atomic spectroscopy and in pyrolysis mass spectrometry with ample time for questions and discussion.Inclusive non-residential fee f 35. Vapour Generation Techniques Theory and Practice-Short Course June 29 University of York York UK The course will focus on the design and development of vapour generation techniques and their coupling to vari- ous atomic spectroscopic systems. De- sign criteria will be described and practical examples discussed including speciation of arsenic and mercury. The course numbers will be limited so that each participant can undertake practi- cal work with atomic fluorescence techniques including sensitivity en- hancement and matrix effects.Inclusive non-residential fee f 95. 5th Surrey Conference on Plasma Source Mass Spectrometry Lumley Castle Hotel Co. Durham UK This conference will cover the analysis of inorganic materials with sessions on instrumentation and theory; sam- ple introduction techniques; analysis of solid samples; and applications of ICP-MS to biological geological and industrial samples. Inclusive residential fee f 320. July 4-6 Spectroscopic Data Handling-Short Course July 4-6 University of York York UK The symposium will consist of talks discussion periods and practical ses- sions; PC systems will be installed to allow participants to work in pairs.Topics will include Data Transfer (networks in the analytical laboratory PC-based VAX-VMS UNIX-TCP- IP etc.); archiving transfer standards (JCAMP-DX netCDF); data manipu- lation; and good spectroscopic labora- tory practice (IS0 9000 NAMAS etc.). Inclusive residential fee f 300. Applications of Glow Discharges in Optical and Mass Spectrometry University of York York UK The symposium will cover all glow discharges used for analytical applica- tions (except sealed hollow cathode lamps for AAS). Topics will include sources for OES and MS; applications in bulk and surface analysis; non- conducting samples; and fundamental processes. The meeting will incorpor- ate the 2nd European Workshop on Glow Discharge Surface Analysis. Inclusive residential fee f 220.July 4-7 Graphite Atomizer Techniques in Ana- lytical Spectroscopy University of Durham Co. Durham UK The format will be similar to that of the successful XXVII CSI Pre-Sympo- July 4-7JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 13N sium in Loftus in 1991. Topics will include reaction and interference mechanisms; temperature and atom distribution measurements; absolute analysis; coupling with hydride gener- ation; chromatography and flow injec- tion; laser applications and solid and slurry sampling; metal and other non- graphite surfaces; and all applications in these areas. Inclusive residential fee f200. Trace Elements in Clinical Chemistry July 7 University of Durham Co. Durham UK A one day meeting on the application of analytical data to clinical practice e.g.factors influencing the gastro- intestinal absorption of aluminium; biological monitoring for occupational exposure (e.g. Al Co Cr Ni); and release of metals from prosthetic im- plants. Non-residential fee f 20. For further information on the Pre- and Post-Symposia contact XXVIII Colloquium Spectroscopicum Interna- tionale Department of Chemistry (CSI Secretariat) Loughborough University of Technology Lough- borough Leicestershire UK LE1 1 3TU. 39th Canadian Spectroscopy Confer- ence August 16-18 Quebec Canada For further information contact 39th Canadian Spectroscopy Conference Department de Chimie Pavillon Vachon UniversitC Laval Quebec Canada GlK 7P4. Telephone (418) 656 3282; fax (418) 656 7916. 6th Hungaro-Italian Symposium on Spectrochemistry Advances in Envi- ronmental Sciences August 23-27 Mislzok- Lilla fured Hungary For further information contact Gy.Zaray L. Eotvos University Institute of Inorganic and Organic Chemistry P. 0. Box 32 H-1518 Budapest 112 Hungary. Telephone 361 181 9778; fax 361 181 1974. 9th International Conference on Four- ier Transform Spectroscopy Calgary Canada For further information contact Mrs. Lois Kokoski The University of Cal- gary Conference Office 2500 Univer- sity Dr. NW Calgary Alberta Canada T2N 1N4. Telephone (403) 220 5051; fax (403) 289 7287. August 23-27 Euroanalysis VIII The Eighth Euro- pean Conference on Analytical Chemis- try September 5- 1 1 University of Edinburgh UK Details can be found in J. Anal. At. Spectrom. 1992 7 49N. For further information contact Miss P.E. Hutchinson Conference Orga- nizer Analytical Division The Royal Society of Chemistry Burlington House Piccadilly London UK WlV OBN. Telephone 071 437 8656; fax 071 734 1227. 5th Beijing Conference and Exhibition on Instrumental Analysis October 11-16 Beijing China Details can be found in J. Anal. At. Spectrom. 1992 7 39N. For further information contact The Secretariat of BCEIA Room 5412 Building 4 Xi Yuan Hotel 10046 Beijing P. R. China. Telephone 86 1 83 13388/5412; telex 20056 BCEIA CN; fax 86 1 8320908. 20th Annual Meeting of the Federation of Analytical Chemistry and Spectro- scopy Societies (FACSS) October 17-22 Detroit MI USA For further information contact FACSS P. 0. Box 278 Manhattan KS 66502-0003. Telephone 301 846 4797. 3rd International Conference LASER M2P December 8-10 1993 Lyon France The Third International Conference LASER M2P will cover the fields of material engineering; medicine and biology; and physics and chemistry.The scope of the programme is to sum up the research activities involv- ing lasers to consider future prospects for laser sources and applications and to stimulate interdisciplinary ex- changes. The conference will combine invited presentations in plenary sessions on topics of general interest and specia- lized sessions devoted to each of the fields mentioned above with invited and contributed oral presentations and posters. The conference will also pro- vide the opportunity for round table discussions on special cross discipli- nary issues. For further information contact Centre Jacques Cartier Conference Laser M2P 86 rue Pasteur 69365 Lyon Cedex 07 France. Telephone (33) 78 69 72 21; fax (33) 78 61 07 71.1994 1994 Winter Conference Spectrochemistry January 10-15 1994 San Diego CA USA Details can be found in Spectrom. 1992 7 49N. on Plasma 1. Anal. At. For further information contact Dr. R. M. Barnes 1994 Winter Confer- ence on Plasma Spectrochemistry c/o ICP In formation Newsletter Depart- ment of Chemistry GRC Towers University of Massachusetts Amherst MA 0 1003-0035 USA. Telephone 4 13 545 2294; fax 413 545 4490. Seventh Biennial National Atomic Spectroscopy Symposium University of Hull Hull UK Details can be found in J. Anal. At. Spectrom. 1992 7 49N. July 20-22,1994 For further information contact Dr. Steve Hill Department of Environ- mental Sciences University of Ply- mouth Drake Circus Plymouth Devon UK PL4 8AA. 13th International Mass Spectrometry Conference August 29-September 2 Budapest Hungary For further information contact Hun- garian Chemical Society FO u. 68 H- 1027 Budapest Hungary. Telephone 361 201 6883; fax 316 15 61215.

ISSN:0267-9477    

DOI:10.1039/JA993080011N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

14N JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 ~- Future Issues will Include Shadow Spectral Filming Method of Investigating Electrothermal Atomiza- tion. Part 3. Dynamics of Longitudinal Propagation of an Analyte Within Graphite Furnaces-A. K. Gilmutdi- nov Y. A. Zakharov and A. V. Voloshin Improvement of Accuracy for the Determination of Transient Signals Using the Kalman Filter. Part 2. Computer Controlled Batch Hydride Generator With Data Acquisition and Kalman Filtering For Noise Reduc- tion-Ian D. Brindle and Shaoguang Zheng Graphite Furnace Atomic Absorption Spectrometry Using a Linear Photo- diode Array and a Continuum Source -James M. Harnly Inductively Coupled Plasma-Micro- wave Induced Plasma Tandem Source for Atomic Emission Spectrometry- Gary M.Hieftje and Matthew W. Borer Design Considerations for a Pressure- differential Tandem Source for Use in Atomic Spectrometry-Gary M. Hieftje and Matthew W. Borer Automated Two-speed Peristaltic Pump Controller for Reduced Sample Wash-out Time and Analysis of Small Sample Volumes-Henry P. Longerich Determination of Cadmium in Bio- logical Materials by Tungsten Coil Atomic Absorption Spectrometry- Maria F. Gine Joaquim A. Nobrega Francisco J. Kmg Vhia A. Sass Boaventura F. Reis and H. Berndt Detection of Vanadium by Laser- excited Atomic Fluorescence Spectro- metry in a Side-heated Graphite Furnace-Sten SjiistriSm Ove Axner and M. Norberg On-line Preconcentration of Alumi- nium Gallium and Indium with Quinolin-8-01 for Determination by Atomic Spectrometry-Bashir Mohammad Allan M.Ure and David Littlejohn Flow Injection ETAAS for As Specia- tion Using the Fleitmann Reaction. -M. Burguera and J. L. Burguera Determination of Arsenic(v) and Arsenic(n1) Species in Environmental Samples by Coprecipitation With Zirconium Hydroxide and Pre-atom- ization Atomic Absorption Spectro- metry-Yalei Chen Wenqi Qi Jieshan Cao and Mou-sen Chang Measurement of Trace Elements in Ceramic and Quartz Materials by Laser Ablation-Microwave Induced Plasma Atomic Emission Spectroscopy- Adeline Ciocan Lars Hiddemann Jurgen Uebbing and Kay Niemax Investigation of High-temperature Re- actions on Graphite With Rutherford Backscattering Spectrometry Inter- action of Cadmium Lead and Silver With a Phosphate Modifier-Corinne Eloi J. David Robertson and Vahid Majidi On-line Method for the Analysis of Sea-water by Inductively Coupled Plasma Mass Spectrometry-J.W. McLaren Kunihiko Akatsuka Maria A. Azeredo Joseph W. Lam and Shier S. Berman Role of Oxygen in the Determination of Oxide-forming Elements by Graph- ite Furnace Atomic Absorption Spec- trometry. Part 1. Effect of Oxygen on the Reactions of Thallium-Lothar Hahn German Miiller-Vogt and Wolf- gang Wend1 Determination of Cadmium Cobalt Iron Nickel and Lead in Venezuelan Cigarettes by Graphite Furnace Atomic Absorption Spectrometry- Jose Alvarado and Ana Rita Cristiano Determination of Lead in Biological Materials by Microwave-assisted Mineralization and Flow Injection Graphite Furnace Atomic Absorption Spectrometry-J. L. Burguera and M. Burguera Simultaneous Determination of Ar- senic Bismuth and Tin in Steels and Nickel Alloys by Inductively Coupled Plasma Atomic Emission Spectrome- try-Elisa Akemi Ozaki and Elizabeth de Oliveira Atomic Spectrometry in Environmen- tal Analysis Jam Today or Jam To- morrow-Malcolm S.Cresser Study of the Matrix Effect of Easily and Non-easily Ionizable Elements in an Inductively Coupled Argon Plasma. Part 1. Spectroscopic Diagnostics -Mirjana R. Tripkovic and I. D. Hol- claj tner-Antunovic Determination of Rare Earth Elements in Single Mineral Grains by Laser Ablation Microprobe-Inductively Coupled Plasma Mass Spectrometry -Preliminary Study-Simon Chenery and Jennifer M. Cook Determination of Rubidium and Strontium in Silicate Rocks by Energy Dispersive and Wavelength Dispersive X-Ray Fluorescence Analysis Com- parative Evaluation of Precision- P.C. Webb Philip J. Potts and J. S. Watson Study of the Matrix Effect of Easily and Non-easily Ionizable Elements in an Inductively Coupled Argon Plasma. Part 2. Equilibrium Plasma Composi- tion-I. D. Holclajtner-Antunovic and Mirjana R. Tripkovic Radiation Versus Conduction in Heated Spray Chamber Desolvation for Inductively Coupled Plasma- Alan R. Eastgate Robert C. Fry and Grant H. Gower Elucidation of Mechanisms that Con- trol the Electrothermal Atomization of Tin Chloride-Garrett N. Brown and David L. Styris Speciation of Mercury in Fish Samples by Solvent Extraction Methylmercury Reduction Directly in the Organic Medium and Cold Vapour Atomic Absorption Spectrometry-Maria do Carmo Rezende Reinaldo C. Campos and A. J Curtius Application of High Resolution Four- ier Transform Spectrometry to the Study of Glow Discharge Sources. Part 1. Excitation of Iron and Chromium Spectra in a Microwave Boosted Glow Discharge Source- Edward B. M. Steers and Anne P. Thorne Laser Ablation Ion Trap Mass Spectro- metry of Metal Ceramic and Polymer Samples-C. G. Gill and Michael W. Blades.

ISSN:0267-9477    

DOI:10.1039/JA993080014N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 19 Isotope Ratio Measurement of Lead Neodymium and Neodymium-Samarium Mixtures Hafnium and Hafnium-Lutetium Mixtures With a Double Focusing Multiple Collector Inductively Coupled Plasma Mass Spectrometer* Andrew J. Walder and 1. Platzneri Fisons Instruments VG Elemental Ion Path Road Three Winsford Cheshire UK CW7 3BX Philip A. Freedman Fisons Instruments VG Isotech Aston Way Middlewich Cheshire UK CWlO OHT An inductively coupled plasma (ICP) source coupled to a double focusing magnetic sector mass analyser equipped with seven Faraday detectors has been used to measure the isotopic ratios of lead reference materials using a thallium correction technique. The addition of thallium to the lead standards and the subsequent simultaneous measurement of the thallium and lead isotopes allowed a correction for mass discrimination.Measurement of six samples of National Institute of Standards and Technology (NIST) (formerly National Bureau of Standards) Standard Reference Material Pb-982 revealed 208Pb:204Pb = 36.702 f 0.022 207Pb:204Pb= 17.1 41 f 0.009 and 206Pb:204Pb=36.71 1 2 0.021 compared with the NIST certified values of 36.744 k 0.050 17.1 59 f 0.025 and 36.738 f 0.037 respectively. All errors are given as 20. The measurement of each sample used approximately 200 ng of lead and took 100 s. Measurement of six neodymium samples (obtained from Scripps Institute of Oceanography La Jolla CA USA) where internal normalization to 146Nd:'45Nd is possible revealed a 143Nd:144Nd ratio of 0.51 1825 f 0.000039 compared with the accepted value of 0.51 1859.Measurement of six La Jolla neodymium samples contaminated with a similar concentration of samarium revealed a 143Nd:'44Nd ratio of 0.51 1854 rf 0.000059. The measurement of each mixed sample used approximately 100 ng of neodymium. Similarly measurement of six samples of Johnson Matthey Company (JMC) 475 Hafnium normalized to 179Hf:'77Hf revealed a 176Hf:177Hf ratio of 0.2821 94 f 0.000020 compared with the accepted value of 0.2821 95 rf 0.00001 5. Measurement of six samples of JMC 475 Hafnium contaminated with a similar concentration of lutetium revealed a 176Hf:'77Hf ratio of 0.28221 3 k 0.000023. The measurement of each mixed sample used approximately 400 ng of hafnium. Keywords Inductively coupled plasma mass spectrometry; magnetic sector mass spectrometry; lead isotopic ratio measurement; thallium based mass discrimination correction; neodymium and hafnium isotope ratio measurement The measurement of isotopic ratios using an inductively coupled plasma (ICP) source coupled to a double focusing magnetic sector mass analyser equipped with seven Faraday detectors has previously been described.' The use of several Faraday detectors allows each isotope to be measured simultaneously thus removing signal noise as a limitation on analytical precision.A magnetic sector mass analyser produces flat topped peaks which allows the accurate measurement of each isotope. Isotopic ratio measurements of uranium and lead standard reference materials (SRMs) demonstrated levels of precision comparable to that ob- tained by thermal ionization mass spectrometry (TIMS).For example a relative standard deviation (RSD) of 0.022% was obtained from the 206Pb:204Pb measurement of six samples of National Bureau of Standards (NBS) [now National Institute of Standards and Technology (NIST)] Standard Reference Material (SRM) Pb-98 1. In common with all mass spectrometry plasma ion sources this new instrument transmits the heavier isotope in preference to the lighter; this mass discrimination effect is time independent and can be experimentally established. A solution of known isotopic composition was therefore analysed prior to the analysis of a sample to determine the magnitude ofmass bias. Lead has four naturally occurring isotopes three of which *08Pb 207Pb and loaPb are radioactive decay pro- ducts the fourth 204Pb is not of radiogenic origin and is *Presented in part at the 40th American Society for Mass Spectrometry Conference on Mass Spectrometry and Allied Topics Washington DC USA May 31-June 5 1992.?Visiting scientist at VG Elemental Winsford Cheshire UK; permanent address NRCN PO Box 9001 Beer-Sheva Israel. considered a stable reference isotope. The measurements of lead isotopic ratios are therefore used in geological and environmental studies. The measurement of lead isotopic ratios by quadrupole based ICP mass spectrometry (ICP- MS) is generally inferior to TIMS. Methods and applica- tions have been described in recent publications by Date and Gray2 and Jarvis et al.3 External precisions of approxi- mately 0.5% are possible by ICP-MS compared with 0.05% by TIMS.Existing plasma technology is therefore inade- quate for most geological dating purposes. Levels of precision are acceptable in some areas of environmental studies for example in determining the environmental effects of lead additives within petrol. Ketterer et al.4 have described how the measurement of the isotopic ratio of thallium (205Tl:203Tl) can be used as a correction for the measurement of lead isotopic ratios using a quadrupole based ICP mass spectrometer. This technique originally suggested by Longerich et al.5 improved the precision of lead isotopic ratio analysis and removed the need for the analysis of calibration standards for mass bias corrections. They achieved RSDs of 0.2% a level suitable for the routine analysis of environmental samples.An objective of this study was to apply the thallium correction technique to the analysis of lead SRMs using the plasma based multi-collector mass spectrometry system. The previous study' also included isotope ratio measure- ment of NIST SRM Sr-987. Measurement of the non- radiogenic 86Sr:88Sratio allows an internal calibration for mass discrimination which was used to correct the mea- sured 87Sr:86Sr ratio. This correction procedure was applied as the measurement proceeded thus small variations in mass bias which limit the attainable precision of uranium and lead measurements were removed. Superior levels of20 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 precision were therefore achieved.An RSD of 0.008% was obtained from the 87Sr:86Sr measurement of ten samples of SRM Sr-987. A second objective of this study was to extend this correction procedure to the isotope ratio measurement of other elements. Neodymium and hafnium reference ma- terials were selected because of their importance to the geological community as chronometers6 and because their isotope ratios are well established by TIMS. However natural samples of neodymium and hafnium will contain samarium and lutetium respectively thus the measure- ment of their isotope ratios must be corrected for the presence of these interfering species. Correction procedures are well established by TIMS and it was a further objective of this study to apply these correction procedures to these dual element systems using the plasma source MS system.Experimental Instrumentation The mass spectrometer system is equipped with an ICP source similar to that used on the VG PlasmaTrace mass spectrometer. The sampling and skimmer cones are both held at 5700 V which provides the acceleration potential for the ions as they enter the mass spectrometer. The circular ion beam is matched to a vertical slit profile required by the mass spectrometer using two d.c. quadrupole lens doublets. The adjustable slit at this point is the entrance definingslit on the PlasmaTrace instrument. To achieve the high abundance sensitivity necessary for the analysis of minor isotopes a further stage of differential pumping is incorporated. A second (0.3 mm wide x 5 mm high) defining slit is provided the first slit being imaged onto the second using a compound electrostatic lens.This aperture forms the entrance to the double focusing mass spectrometer. The mass spectrometer achieves a 540 mm dispersion and incorporates seven adjustable Faraday collectors on an image plane normal to the optic axis. Using 1 mm defining slits at the entrance of each collector the resolution of the instrument is fixed at 400 (5% valley definition). As the image of the source defining slit is significantly narrower than the collector slits the instrument peak shape exhibits a 'top hat' shape the central section showing a high degree of flat peak. This ensures that the recorded signal amplitude is insensitive to external events and allows a high degree of accuracy to be obtained in the measurement.This is in contrast to the Gaussian peak-shape characteristic of quadrupole based mass spectrometers. By simultaneously measuring each isotope of interest the effects of plasma noise are eliminated and hence very precise isotope ratio measurements are possible. The collector system is equipped with seven Faraday detectors which are refer- enced as low 2 low 1 axial high 1 high 2 high 3 and high 4. Analytical Procedure Samples were introduced into the plasma with a peristaltic pumping system via a Meinhard nebulizer. The preampli- fiers associated with each detector were calibrated with respect to the axial preamplifier at the beginning of each days analysis. No correction for variations in detector efficiency were made.The NIST SRMs Pb-981 Pb-982 and Pb-983 were selected for analysis. Each standard was diluted to a concentration of 1 pg ml-' using de-ionized water. Each standard was doped with thallium [Johnson Matthey Specpure ICPIdirect current plasma (DCP) standard] to a 1 pg ml-L concentration. Each Faraday collector was dedi- cated to a particular isotope i.e. 203Tl-lo~ 2 204Pb-lo~ 1 20sT1-axial *06Pb-high 1 *07Pb-high 2 208Pb-high 3. Six samples of each standard were analysed. Each sample was analysed for 100 s the analysis period comprising ten measurements each of 10 s duration. Sample-usage rate was approximately 0.1 ml min-' thus the analysis of each sample used approximately 200 ng of lead. Each sample analysis was preceded by a 3 min wash-out period. The total ion current recorded at the Faraday detectors was approxi- mately 6 x 1 0-l1 A for each lead standard; a similar current was recorded for the thallium solution. A neodymium reference material (obtained from Scripps Institute of Oceanography La Jolla CA USA) was also selected for analysis and diluted to a concentration of 1 pg ml-' using de-ionized water.The neodymium was also contaminated with samarium (Johnson Matthey Specpure ICP/DCP standard) to give a 0.5 pg ml-l samarium-0.5 pg ml-' neodymium mixture. Each Faraday detector was dedictated to a particular isotope i.e. 143Nd-lo~ 1 144Nd + L44Sm-axial 145Nd-high 1 146Nd-high 2 and 147Sm- high 3. Six samples of neodymium and six samples of neodymium-samarium mixture were analysed. Each sample was analysed for 200 s the analysis period consisting of 20 measurements each of 10 s duration.The sample solution was recirculated resulting in a neodymium-usage rate of approxi- mately 0.01 ml min-'. The analysis of each neodymium sample used approximately 200 ng while the analysis of each neodymium-samarium sample used approximately 1 00 ng of neodymium. Each sample analysis waspreceded by a 3 min wash-out period. The total ion current recorded at the Faraday detector for the pure neodymium solution wasabout 2 x lo-'' A. Johnson Matthey reference material 475 Hafnium was also chosen for analysis and diluted toaconcentration of 1 pgml-' using de-ionized water. The hafnium was also contaminated with lutetium (Johnson Matthey Specpure ICP/DCP stan- dard) to give a 0.5 pg ml-I lutetium-1.0 pg ml-' hafnium mixture.Again each Faraday detector was dedicated to a particular isotope i.e. L75Lu-low 2 176Lu+ 176Hf-lo~ 1 177Hf- axial and L79Hf-high 2. Six samples ofhafnium and six samples of the hafnium-lutetium mixture were analysed. Each pure hafnium sample was analysed for 500 s i.e. 100 measure- ments each of 5 s duration. Each hafnium-lutetium mixture sample was analysed for 1000 s i.e. 100 measurements each of 10 s duration. The sample solution was recirculated resulting in a hafnium usage of 0.0 1 ml min-l. Theanalysisof each pure hafnium sample used approximately 300 ng while the analysis of each hafnium-lutetium sample used approxi- mately 400 ng of hafnium. Each sample analysis was preceded with a 3 min wash-out period. The ion current recorded at the Faraday detectors for the pure hafnium solution was about 2 x lo-" A.Results and Discussion Space charge effects within the plasma region and supersonic gaseous expansion between the cones are responsible for the preferential transmission of the heavier isotopes into the mass spectrometer. The effect is time independent and its magnitude is approximately 1.2% per atomic mass unit 144p. Eqn. 1 has been shown to predict this mass discrimination' R = R,,,( 1 + c p where R, = true value R,,,,= measured value C= mass bias factor and dm=mass difference. Comparison of the measured ratio with the true ratio can thus be used to determine the magnitude of the correction factor (1 + C). Lead Isotope Ratio Measurement Isotopic ratio measurements of six representative samples of SRMs Pb-981 Pb-982 and Pb-983 corrected for massJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 21 Table 1 Analysis of NIST SRM Pb-98 1; values in parentheses are the %SE Sample 208pb:204pb 207pb:204pb 206pb:204pb 1 36.695 (0.017) 15.484 (0.019) 16.939 (0.013) 2 36.695 (0.008) 15.484 (0.007) 16.940 (0.009) 3 36.692 (0.026) 15.487 (0.027) 16.939 (0.024) 4 36.696 (0.013) 15.486 (0.016) 16.939 (0.012) 5 36.676 (0.009) 15.477 (0.010) 16.930 (0.007) 6 36.690 (0.0 12) 15.480 (0.0 17) 16.937 (0.0 12) Mean 36.69 1 15.483 16.937 2 0 0.0 15 0.008 0.008 %RSD* 0.02 1 0.025 0.022 NIST value 36.721 15.49 1 16.937 2 0 0.036 0.01 5 0.01 1 *%RSD calculated from la. 208Pb:206Pb 2.1663 (0.005) 2.166 1 (0.003) 2.166 1 (0.004) 2.1663 (0.004) 2.1662 (0.004) 2.1663 (0.002) 2.1662 0.0002 0.005 2.1681 0.0008 207pb:206pb 0.9 14 1 1 (0.008) 0.9 1407 (0.003) 0.9 1424 (0.003) 0.91419 (0.005) 0.91413 (0.004) 0.9 1394 (0.0 1 1) 0.9141 1 0.0002 1 0.01 1 0.9 1464 0.00033 Table 2 Analysis of NIST SRM Pb-982; values in parentheses are the %SE Sample 208pb:204pb 207pb:204Pb 206pb:204pb 1 36.705 (0.015) 17.140 (0.012) 36.714 (0.014) 2 36.705 (0.021) 17.143 (0.022) 36.715 (0.020) 3 36.685 (0.013) 17.134 (0.012) 36.694 (0.010) 4 36.694 (0.01 5) 17.138 (0.01 6) 36.705 (0.01 5) 5 36.717 (0.025) 17.147 (0.022) 36.725 (0.022) 6 36.707 (0.01 1) 17.143 (0.010) 36.714 (0.010) Mean 36.702 17.141 36.71 1 2a 0.022 0.009 0.02 1 %RSD* 0.030 0.027 0.029 NIST value 36.744 17.159 36.738 20 0.050 0.025 0.037 *%RSD calculated from la.208Pb:206Pb 0.99974 (0.004) 0.99972 (0.006) 0.99972 (0.004) 0.99969 (0.003) 0.99976 (0.004) 0.99978 (0.005) 0.99974 0.00006 0.003 1 .OOO 16 0.00036 207Pb:2MPb 0.46685 (0.005) 0.46692 (0.005) 0.46696 (0.006) 0.46693 (0.003) 0.46690 (0.003) 0.46694 (0.005) 0.4 6 6 9 2 0.00008 0.008 0.46707 0.00020 Table 3 Analysis of NIST SRM Pb-983; values in parentheses are the %SE Sample 208pb:204pb 207pb:204pb 206Pb1204pb 1 36.90 (0.10) 192.8 (0.10) 2708.5 (0.10) 2 37.07 (0.09) 193.6 (0.10) 2719.7 (0.10) 3 37.23 (0.16) 194.7 (0.16) 2735.4 (0.16) 4 37.15 (0.10) 194.3 (0.09) 2729.9 (0.10) 5 36.90 (0.12) 193.0 (0.12) 27 12.0 (0.12) 6 37.22 (0.15) 194.5 (0.16) 2732.2 (0.16) Mean 37.08 193.8 2723.0 20 0.30 1.6 22.4 O/oRSD* 0.40 0.4 1 0.41 NIST value 36.71 191.9 2695 20 2.04 10.5 145 *%RSD calculated from la.208Pb:206Pb 0.013623 (0.010) 0.01 3620 (0.008) 0.01 3609 (0.007) 0.01 3608 (0.004) 0.01 3604 (0.009) 0.01 3623 (0.005) 0.01 36 15 0.0000 1 7 0.062 0.01 36 19 0.000024 207pb1206pb 0.07 1 177 (0.004) 0.07 1 165 (0.005) 0.07 1 17 1 (0.004) 0.07 1 179 (0.002) 0.07 1 178 (0.002) 0.07 1 176 (0.004) 0.07 1 174 0.00001 1 0.008 0.07 120 1 0.000040 discrimination are shown in Tables 1,2 and 3 respectively. The measurement of the 205Tl:203Tl ratio was used to correct the measured values of 208Pb:204Pb 207Pb:204Pb 206Pb:204Pb 208Pb:206Pb and 207Pb:206Pb ratios. The value of the 2osTl:203Tl ratio of 2.387 f 0.0010 (30) is given by Dunstan et a1.7 The confidence in each sample measurement (inter- nal precision) is expressed as per cent. standard error (YoSE).The confidence in the mean of the six samples is expressed both as a per cent. relative standard deviation (YoRSD) and as a 95% confidence level (20). The NIST certified value of each isotopic ratio together with its 95% confidence level is also given. The mass discrimination correction applied in this work assumes that the factor (1+C) for lead and thallium depends only upon mass and is therefore of the same magnitude. To check this assumption the mass bias values are calculated for thallium and Pb-982 using eqn. (I) i.e. 1 + CTI=[2.387 1/(20ST1:203T1)measJ0~5 (2) I +Cpb982=[1.OOO16 l(208Pb:206Pb)meas]0.5 (3) where 2.3871 and 1.00016 are certified 205Tl:203Tl and 208Pb-982:206Pb-982 ratios respectively. The correction factors calculated for each sample of the Tl:Pb-982 solution are shown in Table 4 together with their mean values.The difference between the means is within experimental error and therefore justifies the use of the correction. The measurement of isotopic ratios of SRMs Pb-98 1 Pb- 982 and Pb-983 reveal levels of internal and external precision and accuracy comparable to that obtained by TIMS. Analysis times are approximately 100 s per sample compared with at least 25 min per sample by TIMS. The levels of external precision obtained using the thallium correction technique are superior to those quoted by NIST. By reducing both sample uptake rate and analysis time sample usage has been reduced from approximately 1.6 pg in the previous study' to approximately 200 ng in this study. Analysis time has been reduced from 300 to 100 s.The levels of internal and external precision are similar in both studies proving the effectiveness of using thallium as an internal correction for the measurement of lead isotopic22 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Table 4 Calculated bias correction factors for 205T1:203T1 and 208Pb-9 8 2 206Pb-9 82 Sample Bias factor 20sT1:203T1 Bias factor 208Pb-982:206Pb-982 1 1.01044 2 1.01 132 3 1 .O 1066 4 1.01 121 5 1.01 112 6 1.01 157 Mean 1.01 105 2a 0.00084 %RSD* 0.042 * %RSD calculated from la. 1.01022 1.01 198 1 .O 1 045 1.01098 1.01094 1.01 138 1.01099 0.00 1 27 0.063 ratios. Further reduction in sample usage could be achieved with the recirculation of the large volume of nebulized solution which does not reach the plasma.Isotopic ratio measurements of SRMs Pb-982 and Pb-983 agree with the certified values quoted by NIST within 20. The measurement of SRM Pb-981 agrees with NIST for all ratios except 20sPb:206Pb. The NIST certified value is 2.168 1 k 0.0008 while a value of 2.1662 k 0.0002 is mea- sured here a difference of twice the sum of the two 95% confidence errors. This discrepancy has also been noted by Platzner,s where thermal ionization analysis of SRM Pb- 98 1 revealed a 208Pb:206Pb ratio of 2.16605 k 0.00063. Values of 2.1650 k 0.001 8 and 2.1630 k 0.0020 also deter- mined by thermal ionization were reported by Hamlin et uL9 and Gulson et u1.,l0 respectively errors are given as 20 in each case. Neodymium Isotope Ratio Measurement The left hand columns of Table 5 give details of the analysis of six samples of pure La Jolla neodymium. Each sample was analysed for 20 measurements each of 10 s duration.Comparison of the measured 146Nd:145Nd ratio with a value of 2.07179 was used to determine the value of mass bias which was then used to correct the 143Nd:144Nd measured value. This correction procedure was applied after each 10 s measurement and is similar to that applied to the lead and thallium mixtures. The 143Nd:144Nd ratio is shown for each sample together with the confidence in its measurement internal precision expressed as a %SE. The mean of the six samples is given at the bottom of the column together with the %RSD and as a 95% confidence level (20). Comparison of the measured value of 0.5 1 1825 f 0.000039 with the La Jolla value of 0.5 1 1859 show the accuracy of the technique.The right hand columns of Table 5 give details of the Sm I 143 144 145 146 147 Relative atomic mass Fig. 1 Schematic diagram illustrating the isotopic components of the neodymium-samarium mixture; black shading represents the isotopes of the interfering species and grey shading the isotopic ratio of analytical interest results of analysis of six samples of a La Jolla neodymium- samarium mixture. A graphical representation of each isotopic component is given in Fig. 1. The 144Sm interferes with 144Nd and must therefore be corrected. Comparison of the measured 146Nd:14sNd ratio with a value of 2.07 179 was used to determine the value of mass bias. The 144Sm interference with 14*Nd was corrected with the measure- ment of 147Sm assuming that the 147Sm:144Sm ratio equals 4.8389.lI The measured 143Nd:144Nd ratio corrected for interference was then corrected for mass bias.Each of these corrections was performed after each 10 s measurement. The mean 143Nd:144Nd ratio determined for each sample is shown with its %SE. The mean of the six samples is given at the bottom of the column together with its %RSD and 20. Comparison of the mean value of 0.5 1 1854 +_ 0.000058 with the established value of 0.5 1 1859 shows the accuracy of the technique and the effectiveness of the proposed correction methods for mass bias effects and interfering species. Hafnium Isotope Ratio Measurement The left hand columns of Table 6 give details of the analysis of six samples of pure JMC 475 Hafnium. Each sample was analysed for 100 measurements each of 5 s duration.Cornparison of the measured 179Hf:177Hf ratio with the accepted value of 0.732512 was used to determine the value of mass bias this value was then used to correct the 176Hf:177Hf measured values. This correction was applied as the measurement proceeded. The corrected 176Hf:177Hf ratio is shown for each sample together with the confidence in its measurement %SE. The mean of six samples is given at the bottom of the column together with its %RSD and 20 Table 5 Analysis of La Jolla neodymium and a La Jolla neodymium-samarium mixture; 143Nd:144Nd ratio normalized to 146Nd:145Nd= 2.07 179 147Sm:144Sm assumed to be 4.8389 1.0 ppm La Jolla neodymium 0.5 ppm La Jolla neodymium-samarium Sample l43Nd1144Nd O/o S E 143Nd1144Nd %SE I 2 3 4 5 6 Mean 2a %RSD* Accepted 0.5 1 1830 0.5 1 1794 0.51 1855 0.5 1 1824 0.51 1820 0.51 1827 0.5 1 1825 0.000039 0.0038 0.5 1 1859 0.0023 0.5 1 1840 0.0027 0.5 1 1838 0.0020 0.5 1 1888 0.001 7 0.5 1 1845 0.00 16 0.51 1891 0.0022 0.51 1819 0.51 1854 0.000059 0.0057 0.5 1 1859 0.003 1 0.0035 0.004 1 0.003 1 0.0053 0.0036 *RSD calculated from la.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 23 Table 6 Analysis of JMC 475 Hafnium and a JMC 475 Hafnium-lutetium mixture; 17aHf:177Hf ratio normalized to 179Hf:177Hf=0.7325 17aLu:17sLu assumed at 0.026525 Sample 1 2 3 4 5 6 Mean 20 %RSD* Accepted 1.0 ppm JMC 475 Hafnium 176Hf:177Hf YoSE 0.282 187 0.0020 0.282 188 0.00 18 0.282 189 0.00 18 0.282203 0.0035 0.282 187 0.0029 0.2822 10 0.0029 0.282 194 0.000020 0.0035 0.282 195 *RSD calculated from la.1.0 ppm JMC 475 Hafnium and 0.5 ppm lutetium 176Hf I77Hf 0.282208 0.282205 0.282202 0.2822 18 0.2822 1 1 0.282233 0.2822 13 0.000023 0.0040 0.282195 %SE 0.0026 0.0028 0.003 1 0.0029 0.0028 0.0029 value.The mean value of 0.282 194 f 0.000022 agrees with the value of 0.282 195 f 0.00001 5 determined by Patchett.Iz The right hand column of Table 6 gives details of the results of six samples of a JMC 475 Hafnium-lutetium mixture. A graphical representation of each isotopic com- ponent is given in Fig. 2. The 176Lu interferes with 176Hf. Comparison of the measured 179Hf:177Hf ratio with the accepted value of 0.7325 was used to determine the value of mass bias.The I’l6Lu interference with 176Hf was corrected with the measurement of 175Lu assuming that the 176Lu:175Lu ratio equals 0.026526.13 The measured 176Hf:177Hf ratio corrected for interference was then cor- rected for mass bias. Each of these corrections was performed as the analysis proceeded. The mean corrected 176Hf:177Hf ratio determined for each sample is shown with its YoSE. The mean of the six samples is given at the foot of the column together with its %RSD and 20. Comparison of the mean value of 0.2822 13 -t 0.000023 with the established value of 0.282195 again shows the accuracy of the tech- niques and the effectiveness of the proposed correction methods for mass bias effects and interfering species. Conclusion The effectiveness of this novel MS system for the high accuracy and high precision measurement of isotope ratios has been shown.Isotope ratios have been measured to a Lu I 175 176 177 178 179 Relative atomic mass Fig. 2 Schematic diagram illustrating the isotopic components of the hafnium-lutetium mixture; black shading represents the isotopes of the interfering species and grey shading the isotopic ratio of analytical interest precision comparable to that obtained by TIMS. Two methods of mass bias correction have been demonstrated and discussed. The first method involved contamination of a lead sample solution with thallium to allow an internal correction for mass bias a technique which would be very difficult if not impossible by TIMS. This technique also removed the need for a separate calibration analysis.The second method utilized the stable isotopic components of both neodymium and hafnium to correct internally for mass bias this method was also extended to include the correction for interfering species. This has demonstrated the effectiveness of the proposed methods for high accuracy and high precision isotope ratio measurements. The use of more efficient sample nebulization systems such as ultra- sonic or desolvation techniques will further reduce sample consumption by up to an order of magnitude. References 1 Walder A. J. and Freedman P. A. J. Anal. At. Spectrom. 1992 7 571. 2 Date A. R. and Gray A. L. Applications of Inductively Coupled Plasma Mass Spectrometry Blackie Glasgow 1988. 3 Jarvis K. E. Gray A. L. and Houk R. S. Handbook of Inductively Coupled Plasma Mass Spectrometry Blackie Glas- gow and London 1992. 4 Ketterer M. E. Peters M. J. and Tisdale P. J. J. Anal. At. Spectrom. 1991 6 439. 5 Longerich H. P. Fryer B. J. and Strong D. F. Spectrochim. Acta Part B 1987 42 39. 6 Faure G. Principles of Isotope Geology Wiley New York 1986. 7 Dunstan L. P. Gramlich J. W. Barnes I. L. and Purdy W. C. J. Rex Natl. Bur. Stand. 1980 85 1. 8 Platzner I. Int. J. Mass Spectrom. Ion Processes 1987 77 155. 9 Hamilin B. Manhes G. Albarede F. and Allegre C. J. Geochim. Cosmochim. Acta 1985 49 173. 10 Gulson B. L. Korsch M. J. Cameron M. Vaasjoki M. Mizon K. J. Porritt P. M. Carr G. R. Kamper C. Dean J. A. and Calvez J. Y. Int. J. Mass. Spectrom. Ion Processes 1984 59 125. 1 1 DeBievre P. Gallet M. Holden N. E. and Barnes I. L. J. Phys. Chem. Ref Data 1984 13 865. 12 Patchett P. J. Geochim. Cosmochim. Acta 1983 47 81. 13 DeBikvre P. Gallet M. Holden N. E. and Barnes I. L. J. Phys. Chem. Ref Data 1984 13 872. Paper 2/0228 7E Received May 5 1992 Accepted October 15 1992

ISSN:0267-9477    

DOI:10.1039/JA9930800019

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 25 Preliminary Assessment of Laser Ablation Inductively Coupled Plasma Mass Spectrometry for Quantitative Multi-element Determination in Silicates John G. Williams and Kym E. Jarvis ICP-MS Facility Department of Geology Royal Holloway University of London Egham Surrey UK TW20 OEX A Nd:YAG (yttrium aluminium garnet) laser was used to ablate pressed powder pellets of seven silicate rock reference materials for sample introduction into an inductively coupled plasma mass spectrometer. Laser operating parameters such as mode (fixed-Q or Q-switch) energy and number of shots per site were optimized to meet the criterion of maximum analyte signal without excessive loading of the plasma with ablated material. To compensate for differential laser sampling (ie.variable amounts of material being removed during each analysis) 55Mn was used as an internal standard for multi-element determinations and l3'Ba for the rare earth elements (REE) Hf Ta and W. Relative responses for the major elements indicate that the chemistry and mineralogy of individual rock samples influence the ablation behaviour and that samples with very similar chemical and mineralogical compositions exhibit similar elemental sensitivities. Alkali alkaline earth and hydride-forming elements also show similar behaviour to the major components. Multi-element detection limits were typically less than a few hundred ng g-l. The accuracy of major element determinations for the materials studied was generally better than +5% relative with a precision of 10% relative standard deviation (RSD).Trace elements in Groups I II Ill REE volatile elements or those which exhibit refractory characteristic displayed good accuracy with precision of generally <lo% RSD. The quantitative determination of major and trace elements in silicate rocks is therefore possible providing that standards and samples are closely matched both in terms of bulk chemistry and physical (mineralogical) composition. Keywords Laser ablation; inductively coupled plasma mass spectrometry; quantitative analysis; silicate rocks; reference materials The initial development of inductively coupled plasma mass spectrometry (ICP-MS) was carried out almost entirely using liquid samples.' Although there were several considerations the main reason was that the existing simple technology for liquid sample introduction into a flame or plasma for atomic absorption or emission spectrometry could be transferred to ICP-MS with little modification.Introducing solutions into an ICP is very convenient with simple switching between samples and straightforward calibration with synthetic solutions. In addition pro- duction of a solution from initially solid materials can eliminate sample inhomogeneity problems and usually reduces matrix effects. However during the development of the technique it was soon realized that the rapid data collection capability of ICP-MS could be used to good effect in the direct analysis of solids using laser ablation (LA) for sample introduction.' In addition the advantages that ICP- MS possesses over other atomic analytical techniques such as simple spectra high sensitivity low background and sub- ng ml-' limits of detection could in principle make LA- ICP-MS a very potent technique.Lasers in Atomic Spectrometry The potential use of lasers as excitation devices for spectrometric analysis was recognized soon after the first report of laser action in ruby in 1960.2 The subsequent development of different forms of laser microanalysis have been reviewed by Moenke-Blankenburg3 and the advan- tages of laser vaporization for micro-sampling in a variety of materials using analytical atomic spectroscopy have been discussed by Dittrich and Wennri~h.~ The role of lasers in MS falls into two distinctive categories. In the first the laser is used both to ablate and ionize the sample while.in the second laser energy is used only to introduce material into an ionizing device. Plasmas generated by laser radiation contain a high concentration of ions offering the possibility of spatially resolved mass spectrometric investigations. The first instru- ments combining a high-energy laser and a mass spectro- meter were commercialized in 1977. In laser microprobe mass spectrometry sample vaporization and ionization is a single-step process brought about by a pulse of laser radiation focused onto the surface of a sample. The ions produced are subsequently separated using a time of flight (TOF) mass spectrometer. This technique with a spatial resolution of several micrometers has been used in surface and bulk analysis of organic and inorganic material^.^ Two-step analytical processes where the sampling and ionization are separate lead to an increase in the ion yield.One example of a two-step analytical process is resonant ionization mass spectrometry. In geological applications sample vaporization is generally achieved using a conven- tional thermal ionization mass spectrometry source but (photo-)ionization is subsequently carried out using a laser which is tuned to a frequency relevant to the selected analyte elements. Mass analysis can be carried out using a quadrupole TOF or sector mass spectrometer. In the work described below a highly practical two-step analytical process is used where a pulsed laser source is used to ablate locally the sample material.The ablated sample is transported to an atmospheric pressure ICP where ions of all elements present are generated with subsequent detection by MS. This approach has the advantage that each step in the process can be optimized separately and therefore more readily controlled. There is considerable interest in utilizing LA with plasma spectrometry for the direct analysis of solid samples. Attractive features of the technique include the capability for in situ micro-analysis and the ability to analyse both conducting and non-conducting materials. Considerable scope exists for application of the technique and to date most studies have been directed to metallurgical industrial or geological samples using either ICP atomic emission spectrometry (AES),697*8 direct current plasma AES9 or ICP- GrayIS reported the first investigations on LA-ICP-MS with a system that was analogous to that of earlier work reported on LA-ICP-AES.' In the former work was carried out using a 1 J ruby laser (JK Type 2000) operating at a MS.10-1426 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 wavelength of 694 nm with a maximum repetition rate of 1 shot per second (1 Hz) and in either fixed-Q or Q-switched mode (see under Laser Operation Mode). The applicability of the technique to the direct analysis of solid geological materials was demonstrated both for trace element deter- minations and isotope ratio measurements. Later work by Arrowsmith16 showed that a pulsed Nd:YAG laser operat- ing at a wavelength of 1064 nm with high repetition rates (10-20 Hz) and a maximum energy of 160 mJ offered improved precision and duty cycle.This type of laser is currently proving to be the most popular for LA-ICP-MS although other designs such as continuous wave Nd:YAG13 lasers are being studied. Recent developments in the application of high resolution LA systems has also been reported by Pearce et a1.l' The majority of published work on LA-ICP-MS has concentrated on the diagnostics of the system e.g. the generation of calibration elucidation of relative response factors19 and parameter optimization.20 Despite the potential of LA for solid sample analysis of geological materials to date virtually no fully quantitative data have been reported with the notable exception of the work by Imailo and a recent study by Perkins et aL2' which showed that for the analysis of carbonate samples Ba Mg Mn and Sr could be determined with an accuracy of better than & 1 O% when the samples were prepared as fused glass discs. Laser Operation Mode For most commercially available systems the laser may be operated in either the fixed-Q (or normal) and Q-switched mode.In fixed-Q mode laser radiation emerges when the threshold conditions for laser operation are reached follow- ing a pulse from the flashtube. Pulse widths are typically 100 to 1000 ps. In Q-switched mode the excited atoms are held in the optical medium using a light seal. Upon release of this seal either one single pulse or a few giant pulses of maximum power are obtained. In this mode pulses of 10-1000 ns are obtained.The nature of the interaction between the laser beam and the sample surface is highly dependent on the mode of laser operation used. In general crater depth is greater in fixed-Q mode. In Q-switched mode the crater is shallow but the width is greater than that obtained in fixed-Q mode. Further discussion of these phenomena are given in ref. 3. Experimental Sample Preparation The preparation of geological samples for LA-ICP-MS may be carried out in a number of different ways. Simple cut slabs have been used1° and particularly small samples such as single crystals may be mounted in resin blocks with the surface ground down to provide a flat substrate for analysis. In general the surface does not need to be level for more than about a 200 pm distance across the area to be analysed providing that the range of the laser focusing is sufficient.I6 In this work reference materials (RMs) were prepared as pressed powder pellets.Preparation of pressed pellets Certified RMs were prepared as provided by the supplier. The maximum grain size in these materials is expected to be between 60 and 70 pm with an average of about 40 pm. Powders were oven dried at 105 "C for 24 h prior to preparation. Sub-samples of 2-3 g depending on the density of the material were weighed into disposable plastic weighing boats. To each was added 250-300 p1 of 1 Oh m/v of a poly(viny1 alcohol) binder (Mowiol 8-88 Hoechst) the exact volume being dependent on the nature of the sample. Some samples are particularly absorbent while others form strong coherent pellets with only 200 pl of liquid binder.In this study a liquid binder is preferred since it is relatively easy to mix of high purity with respect to elemental contamination and does not result in a dilution of the sample. Solid poly(viny1 chloride) binders have been used for geological sample preparation15 but typically about 20% by volume of binder is added resulting in a significant dilution factor and problems of inhomogeneity may arise. The powder and binder were thoroughly mixed (2-3 min) using a spatula transferred into a 1 cm die and pressed to 10 tonnes. The resulting pellets were oven dried at 105 "C for 12 h and subsequently stored in a drying oven to prevent water absorption. Care was taken to prevent contamination of either side of the pellet such that both surfaces could be used for analysis.Reference Materials The major element composition and colour of the seven RMs used in this work are shown in Table 1. Of these well characterized materials three are basic rocks of similar major element composition [US Geological Survey (USGS) BIR-1 W-2 DNC-I] and of similar initial grain size. Also included are two evolved rocks (USGS AGV-1 G-2) of similar chemical compositions but with very different 'initial' grain sizes (i.e. the original geological crystallinity of the sample before it was ground) and two sediments [USGS SCo-1 and National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 2704 Buffalo River Sediment]. The influence of particle size mineralogy and pellet colour on the ablation process are not well understood.For example dark coloured materials usually couple well to the laser radiation resulting in an efficient ablation. By contrast white surfaces may reflect a majority of the laser radiation resulting in little Table 1 Major element composition (O/o m/m) of the seven RMs used in this study; reference values from Govindaraju2* AGV- 1 G-2 BIR-1 DNC-1 w-2 sco- 1 NIST SRM 2704 Compound Andesite Granite Basalt Diabase Diabase Sediment Sediment 58.79 17.14 6.76 1.53 4.94 1.05 4.26 2.9 1 0.092 0.49 69.08 15.38 2.66 0.75 1.96 0.48 4.08 4.48 0.032 0.14 47.77 15.35 11.26 9.68 13.24 0.96 1.75 0.027 0.171 0.046 47.04 18.30 9.93 10.05 11.27 0.48 1.87 0.229 0.149 0.085 52.44 15.35 10.74 6.37 10.87 1.06 2.14 0.627 0.163 0.131 62.78 13.67 5.14 2.72 2.62 0.63 0.90 2.77 0.053 0.206 62.2 1 11.54 5.88 1.99 3.64 0.76 0.74 2.4 1 0.072 0.229 Colour Light grey Light grey Grey Grey Grey Taupe Dark brownJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 1500 27 ( a ) - Table 2 ICP-MS operating conditions for LA-ICP-MS Instrument VG Elemental Forward power/kW 1.5 Plasma gas Argon Outer gas flow rate/] min-' Intermediate gas flow rate/l min-' PlasmaQuad PQ2 + Reflected power/W <5 Carrier gas flow rate/] min-' 14 1 .o 0.5 Scan conditions Dwell time/ps Channels Sweeps Scan width multi-element Skipped regions multi-element Scan width REE Hf Ta W Skipped regions REE Hf Ta W 80 4096 115 mlz 6-240 m/z 11-22 32-41 and 79.5-80.5 m/z 88-1 84 m/z 90- 130 material being ablated. Thus materials chosen reflect this range of properties.System Optimization ICP-MS For accurate analysis by ICP-MS correct system optimiza- tion is essential such that the conditions used give maximum analyte sensitivity whilst minimizing potential interferences from polyatomic and refractory oxide ions.23 During analysis by LA no water vapour is introduced into the ICP and the optimum conditions are therefore some- what different to those used for conventional solution analysis. The conditions shown in Table 2 were determined experimentally and give maximum sensitivity whilst min- imizing interference effects. Tuning of the ion lenses was initially carried out with the mass spectrometer set to rest at 12C with the carrier gas entering the plasma via the ablation chamber. No ablations were carried out at this stage. The measured signal from I2C (resulting from air entrained in the plasma) was relatively high (equivalent to x 1 pg g-l of a mono-isotopic fully ionized element such as Co) and of a steady state.In practice these operating conditions are very close to those which are appropriate for any analyte element. Fine tuning of the lenses was subsequently carried out at 59C0 and 140Ce during continuous ablation of a sample containing several hundred pg g-l of these elements. Laser Optimization of the LA system itself is more complex and a number of parameters must be established before quantita- tive measurements can be made. These include the mode of laser operation amount of energy delivered to the laser and hence output the rate at which shots are fired number of shots per site pattern of ablation sites and the number of replicate analyses.These variables have been rigorously assessed for the pressed powder pellets. The LA system used in this work has no device for the direct detection of energy in each shot. Therefore the laser output energy can only be inferred from the voltage input to the laser flashlamps. The effect of laser mode (fixed-Q or Q-switched) is critical to the sensitivity and precision of analyses and should be evaluated in each matrix under consideration. In addition the amount of laser energy required to ablate is highly dependent on the physical nature of the sample. The effect of increasing laser energy in each of the two modes of operation is shown in Fig. 1 for RM W-2.The relative behaviour of Mn and Pb is rather different. In the Q- 7 1000 i500 5 700 750 800 850 900 950 1000 0 0 0 700 750 800 850 900 950 1000 Laser flashlamp voltageN Fig. 1 Relative behaviour of (a) Mn and (b) Pb in RM W-2 using A fixed-Q (free running) and B Q-switched mode of laser operat ion switched mode Mn shows a clear increase in sensitivity up to 850 V while beyond this point an increase in energy results in a gradual loss of sensitivity. By contrast Pb shows a steady increase in sensitivity from low to high power. Using fixed-Q mode however the behaviour of these elements is very similar. This feature coupled with the generation of neat steep-sided ablation craters (a feature that would be advantageous for discrete profiling of a sample) has led to the preferred choice of fixed-Q mode in this work. In practice the choice of laser energy is limited by the range of elemental concentrations required.Throughout this work 800 V were used which gave good trace element sensitivity whilst ensuring that major element peaks remained within the linear measurement range. Repeated shots were fired at a rate of one every 0.05 s (20 Hz). To determine the optimum number of shots required at each site depth profiles were constructed for Mn and Pb in W-2 RMs. A single shot was fired at the sample surface and the maximum sensitivity recorded. This process was re- peated ten times on the same spot. By the fifth shot sensitivity was reduced in all cases by about 50% and therefore little advantage is gained by firing more than this number of shots at a single site.The reason for this rapid decrease in signal is not entirely clear and may be a result of the laser becoming de-focused with depth or simply that ablated particulate material is unable to escape from the pit as increasing depths are reached. The total number of sites that are required for a single analysis is dependent on several factors. Firstly if a bulk analysis is required then sufficient surface and substrate area should be sampled to ensure that a representative proportion of material is analysed. Using the fixed-Q mode under the conditions listed in Table 3 a pit is produced which is approximately equal in diameter and depth typically 50- I00 pm. The sensitivity obtained is also partly Table 3 Laser operating conditions for quantitative elemental determination in silicate pressed powder pellets Laser type Wavelengthhm 1064 Laser mode Laser input energy/V 800 Shot repetition rate/Hz 20 Shots per site 5 Sampling scheme Nd:YAG (Spectron Laser Systems) fixed Q (free running) maximum output 600 mJ 6 x 4 raster i.e. 24 sites per analysis28 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 determined by the amount of sample carried into the ICP during the time period of the analysis. However exceeding the load that the plasma is able to vaporize and ionize leads to blocking of the sampling cone and plasma torch injector in a matter of minutes resulting in a rapid loss of analyte signal. There is therefore no advantage in ablating excessive amounts of material. Secondly if only a few sites are taken ( < 5 ) precision is generally poorer than when larger num- bers are sampled.The physical arrangement of the sampling sites may be constrained by the size and shape of the pellet. For normal mode analysis it is important that each site is completely separated from its neighbour in order to ensure good repeatability. The data given here were obtained using a sampling scheme of 5 shots per site with a raster pattern of 6 x 4 sites. The total mass of material ablated during a 30 s analysis is approximately 35 pg assuming 100% transport efficiency. During an equivalent analysis using conven- tional solution nebulization the amount of sample intro- duced into the ICP was about 20 pg. The sampling of relatively small masses of material during LA may be an important limiting factor for the accurate determination of certain trace elements.Sample heterogeneity is overcome in solution analysis by sub-sampling of >O. 1 g of material. In the present application however the relatively small mass ( ~ 2 0 pg) analysed during a 30 s data acquisition may not always be representative of the bulk sample. These factors should therefore be borne in mind when assessing analytical accuracy. Internal Correction Internal standards are widely used in many analytical techniques where signal variability occurs on both a short or long timescale. A single element is usually chosen whose behaviour matches that of the analytes of interest. The reasons for the signal fluctuation may be many fold but are often due to instability of electrical components or in the case of ICP spectrometry plasma noise.For conventional solution nebulization ICP-MS analysis internal standardi- zation may result in improved precision compared with uncorrected data although other forms of data manipula- tion such as drift monitoring may further improve data quality if the fluctuation in signal response is progressive with time.24 For sample introduction by LA repeated analysis of the same sample may show significant differ- ences in sensitivity from one analysis to another. Indeed the sensitivity from one sample to another will also vary and this is thought to result from the removal of different masses of material during ablation. To compensate for this differential sampling it is necessary to employ an internal standard.For multi-element determinations SSMn was chosen. The concentration of this element from sample to sample varies over a relatively narrow range it displays good sensitivity but is not sufficiently high in concentration to cause peak saturation. Manganese is in addition well characterized in the RMs studied. Narrow range scan determinations of rare earth elements (REE) were made using 137Ba as internal standard. Barium is well character- ized in the RMs studied is relatively abundant and lies close in mass to the REE. Results and Discussion Multi-element Data Major elements When laser light is absorbed by solids a variety of heating phenomena occur. These include surface heating vaporiza- tion dissociation and excitation of the surface materials and a phase change inside the sample.The interaction of laser radiation with the sample is a complex process and may be affected by a number of criteria. A part of the laser light is not only absorbed at the sample surface but also to a depth of some micrometers. The temperature is raised above the boiling-point of an individual element com- pound or mineral in the case of geological samples and evaporation begins. This process is followed by a change in state of the material at the ablation site which results in a high speed eruption and the formation of a crater in the surface of the sample. The volume heated depends on the thermal conductivity of the material.4 During the ablation of a rock sample in this case of silicate composition it is the major mineral components that will most strongly influence the ablation behaviour.Although in the RMs considered here Si02 is the major component its content varies from 47.04 (DNC-1) to 69.08% (G-2). There is a corresponding difference in the composition of the other major elements (Table 1). These RMs may be sub-divided depending on their physicochemical nature. Basic igneous rocks W-2 BIR-1 and DNC-1 are characterized by relatively low silica content and fine initial grain size SCo- 1 and NIST SRM 2704 are sediments with a similar major element compositon to that of AGV-1 but with a different geological origin and AGV- 1 and G-2 are intermediate/acid igneous rocks with silica contents up to about 70% m/m. The relative responses for some major elements in six RMs are shown in Table 4.Although there are a range of sensitivities within the basic rocks between one element and another (e.g. A1 displays about 25% of the sensitivity of Na) all three rocks exhibit similar responses for any individual element. The two sediments display a similar pattern and for some elements (e.g. Al) relative sensitivity is uniform throughout both the sediment and basic rock groups. The sediments can however be clearly separated into a distinctive group based on their over-all relative Table 4 Relative responses* for some major elements in six standard silicate RMs by LA-ICP-MS Basic rocks Sediments Acid rock Element W-2 BIR-1 DNC-1 G-2 NIST 2704 SCO-1 Si A1 Fe Mg Ca Na K Ti P ndt nd 10 11 35 36 30 29 20 20 40 44 nd nd 35 29 1.7 1 .o nd 9 37 30 15 39 nd 36 1.6 nd 4 30 25 6 10 nd 26 0.5 nd 10 33 20 18 12 nd 21 1.8 nd 10 42 19 13 18 nd 27 1.6 *Results given in counts g pg-I corrected to s5Mn as an internal standard and for isotopic abundance. tnd = Not determined.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 29 1600 rn + .- 5 1200 2 2 & 800 w .- a - a3 C 0 2 400 a 0 1 2 3 4 5 6 co nce n t ra t i o n/l o4 pg g-' Fig. 2 Offset in relative sensitivity for Mg in A the basic rocks compared with B the sedimentary rocks and G-2 elemental responses. The highest silica sample G-2. usually displays very low sensitivity particularly when compared with the basic rocks. The distinction in relative sensitivity is illustrated in Fig. 2 for Mg where it can be seen that the basic rocks lie on a significantly different slope to that of the sediment RMs.Differences in relative sensitivity may be expected from samples of differing chemical composition (e.g. (3-2 and W-2). However significant differences are also observed between samples of similar chemical composition but with different geological origins and histories (broadly expressed by degree of crystallinity initial grain size and mineralogy). Sub-division of geological rock types is made taking into account not only similiarities in chemistry but more importantly in mineralogy. The observed differences in relative elemental behaviour is likely to be closely con- trolled by the physical properties of the individual minerals in which the elements occur rather than by the bulk rock chemistry.Hence although broadly similar in chemical composition G-2 and SCo- 1 are different in mineralogical composition. Simple chemical matching of standards and samples is clearly not sufficient if quantitative data are required. Trace elements In the RMs analysed some trace (< 1000 pg g-') elements are contained within silicate mineral phases often substi- tuted for the major elements. However many trace ele- ments are located in minor non-silicate phases where they may in fact be present at the mass per cent. level. Evaluating the relative behaviour of these elements has proved complex and only general statements may be made concern- ing the prediction of elemental behaviour in these matrices. The relative responses for a number of trace (and major) elements are shown in Table 5 with various sub-divisions highlighting different chemical properties and groupings in the Periodic Table.In a number of cases concentration data are not available for all of the RMs and in individual cases elements are below the detection limit. The alkali metals display a wide range of sensitivity both within a single sample and between sample type groups with G-2 displaying particularly poor sensitivity. The alkaline earths by contrast display rather similar sensitivi- ties for each element in all sample types with the notable exception of G-2. It should therefore be possible to make quantitative measurements certainly within a rock group and in some instances between groups. It is relevant to note that extensive Sr and Ba substitution for Ca occurs in certain silicate minerals e.g.feldspar and this fact com- bined with the similar chemical behaviour of these elements may be the reason why similar sensitivities are recorded. In general the alkaline earths behave in a more predictable and coherent fashion than the alkali metals and this observation also holds true for some other geological matrices under study in this laboratory e.g. CaPO (unpublished data). Those elements that are relatively volatile and can form hydride species are also shown in Table 5. Although the data are a little sparse in general sensitivity is higher than the alkaline earth elements with the exception of As where sensitivity is poor in all of the rock groups studied. This latter point may reflect the low degree of elemental ionization for As in the ICP.In order to characterize behaviour patterns further elements have been sub-divided into arbitrary categories based on elemental boiling-point since enhanced sensitivity has already been observed for some elements with low boiling-points (Table 6). However there are no clear relationships displayed either within a single rock group or with boiling-point. Sensitivity is therefore not simply related to the physical properties of an element but seems to be more closely controlled by the physical location of that element in a particular mineral in the silicate rock matrix. Some of the elements for which data are presented in Table 6 occur in silicate rocks as the major component in minor phases such as phosphates (e.g. P in apatite) oxides (e.g. Table 5 Relative responses* for some trace elements in six silicate RMs Element W-2 BIR-1 DNC-1 G-2 SRM 2704 Alkali metals- Li 112 87 1 1 1 78 - Na 40 44 39 10 12 Rb 49 - 48 21 - Ca 66 - - 33 - Alkaline earths- Mg 30 29 30 25 20 Ca 20 20 15 6 18 Sr 17 21 17 4 Ba 19 26 19 7 16 - Volatile elements- 10 As 9 - - - Sn - 457 - 124 - Sb 131 57 131 - 102 Te Pb 137 121 235 41 170 - - - - - sco- 1 93 18 39 48 19 13 19 19 14 140 101 178 - *Results given in counts g pg-' corrected to 55Mn as internal standard and for isotopic abundance30 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 Table 6 Relative responses* for some trace elements in six silicate RMs categorized by boiling-point Element W-2 BIR- 1 DNC- 1 G-2 SRM 2704 Boiling-point < 10 000 K- 49 - 48 21 - 10 Rb c s 66 As 9 P 1.7 1 .o 1.6 0.5 1.8 - 33 - - - - - Boiling-point 1000- 1 500 K- Na 40 44 39 10 12 Mg 30 29 30 25 20 Zn 40 28 47 23 56 95 Cd - - - - Boiling-point 1 500-2000 K- - Li 112 87 11 78 Ca 20 20 15 6 18 Sr 17 21 17 4 Ba 19 26 19 7 16 T1 - - - 67 128 - Boiling-point 2000-2500 K- IS IS IS IS 121 235 41 170 Mn 1st Pb 137 Sb 131 57 131 - 102 Boiling point >2500 K (in order of increasing temperature)- Sn - (457)$ - 124 Ga 55 54 55 33 A1 10 11 9 4 c u 43 23 54 12 Cr 39 27 29 91 Ni 25 23 32 Fe 35 36 37 30 sc 18 14 13 18 c o 29 31 35 18 13 Nd 36 Ti 35 29 36 26 Y 20 20 19 13 V 38 38 44 30 Ce 35 32 31 18 La 17 - 21 8 12 Pr 20 18 B 23 - 278 U 107 - Zr 35 21 37 16 Nb 41 8 27 26 10 Th 36 33 Hf 37 Ta - 380 W - - - - - - - - - - - - - - - - - - 10 34 46 21 33 26 21 29 - - - - 43 *Results given as counts g pg-’ corrected to 5sMn as internal standard and for isotopic abundance.?IS= internal standard. $Value in parentheses represents an unreliable reference value. sco- 1 39 48 14 1.6 18 19 41 93 13 19 19 124 IS 178 101 140 95 10 33 33 22 42 16 30 25 27 14 31 23 13 24 15 56 8 35 17 55 136 - Cr in spinel) sulfides (e.g. Cu in chalcopyrite) and also Ti in sphene and Zr in zircon. The degree of release of specific elements from the solid as vapour during the ablation is difficult to predict (using fixed-Q mode part of the sample is removed as vapour and part as particulate). However it is clear that extremely close matrix matching is required in terms of both chemical and physical form and that mineralogy plays an important role in determining elemen- tal sensitivity.Further studies are currently underway to try to elucidate these problems. Multi-element Results It is clear from the above data that to make fully quantitative measurements appropriate standards are re- quired matched both in chemical and mineralogical com- position. To test the accuracy of LA-ICP-MS for a wide range of elements W-2 was used as a standard in a single- point calibration (forced through the origin) and BIR-1 and DNC- 1 analysed against that calibration. The remaining RMs G-2 SCo-1 and NIST SRM 2704 were not considered further. Detection limits were calculated for all elements for which concentration data are available in either of the three basic RMs. Measurement of an appropriate ‘blank’ for such calculations has received some attention in the literature.A number of alternative methods have been suggested including collecting spectra whilst no laser action is taking place15 or by analysing of a solid poly(tetrafluor0- ethylene) block which might represent the solid bindersJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 31 Table 7 Multi-element limits of detection (LOD) calculated as the concentration equivalent to three times the standard deviation of the background counts at mlz 193 (n= 10) Element Mass (mlz) LOD/pg g-l Element Mass (mlz) LOD/pg g-' Li B Na Mg A1 P Ca sc Ti V Cr Mn Fe c o Ni cu Zn Ga AS Rb 7 1 1 23 24 27 31 44 45 46 51 52 55 57 59 60 63 66 69 75 85 0.05 0.31 0.14 0.24 0.58 3.20 0.30 1.96 0.15 0.17 0.12 7.37 0.19 0.87 0.19 0.50 0.17 0.62 0.16 13.3 Sr Y Zr Nb Cd Sn Sb c s Ba La Ce Pr Nd Hf Ta W TI Pb Th U 88 89 90 93 1 1 1 120 121 133 138 139 140 141 146 178 181 182 205 208 232 238 0.40 0.28 0.3 1 0.14 0.19 0.1 I 0.07 0.08 0.4 1 0.34 0.18 0.28 0.90 0.32 0.08 0.03 0.1 1 0.08 0.15 0.05 used during sample preparati~n.~~ However neither of these approaches is entirely satisfactory and no generally agreed method has been proposed.An alternative technique is measurement of background counts at a single mass position where an element is not present in the sample. This procedure is appropriate for most elements since many polyatomic peaks which would normally result in enhanced backgrounds (4-g. 40Ar1601H at mlz 57) are absent in the dry plasma. Although the method is not entirely satisfac- tory it provides a useful measure of a lower limit for quantitative measurement.Detection limits (Table 7) are calculated here as the concentration equal to three times the standard deviation of the background counts at mlz 193 for ten scans recorded during the acquisition of elemental data. Correction has been made for isotopic abundance. The scan range was from mlz 6 to 240. Concentrations are reported as pg g-l and although they range from 0.03 (W) to 13.3 (Ca) pg g-l typical values are a few hundred ng g-' or less. Major elements All of the major elements lie in the lower part of the mass range below mlz 60 and concentrations range from < 120 to 97 000 pg g-l over two orders of magnitude (Table 8). The precision on the raw integrals (n= 5) is typically better than 10% relative standard deviation (RSD) with the exception of Ti which is poorer.The accuracy of the results when compared with what are considered highly reliable refer- ence values (& t 2 % relative) is generally better than f 5% relative. Those elements that display poorer accuracy particularly P and Ti tend to occur at the lowest concentra- tion while in addition P is poorly ionized in the ICP (only about 37%) resulting in low sensitivity (Table 6). It is also worth noting that the errors reported on the reference values for P are between 25 and 50% relative. The accuracy of the data presented here is not un-typical of that obtained during conventional solution analysis by ICP-MS where sample dilution factors are typically between 10 000 and 50 000 although still not of the standard expected for the determina- tion of major elements by competitive techniques.Trace elements The results for the trace elements are more wide ranging in terms of accuracy and precision and therefore for ease of discussion have been sub-divided into five categories. Uncertainties in the trace element reference values should be taken into account when assessing the accuracy of the measured data. Several factors may affect the quality of the results including the uncertainty on the values used for W-2 as the calibration standard and the precision of individual measurements. However taking into account these factors some general statements may be made. The term 'good accuracy' is used below to identify the measured data which are statistically indistinguishable from the recommended values taking into account the errors reported on these values.To evaluate fully the accuracy of the technique a broad range of sample types and greater number of RMs would be required. Alkaline earths and alkali metals Of the two RMs analysed results for DNC-1 display a higher degree of accuracy within this elemental group with excellent results for Ba Li and Sr (Table 9). The precision of the raw integrals is generally better than 10% RSD. ~ ~~ Table 8 LA-ICP-MS data for two basic rocks using a single-point calibration for major elements; n= 5 Relative Measured Reference* error RSD Oxide (% m/m) (% m/m) (%) (Oh) A 1 2 0 3 18.13 15.35 + 18 4 Fe2°3 11.63 11.26 + 3 9 9.28 9.68 -4 8 CaO 13.24 +0.4 4 Na20 1.95 1.75 + I 1 5 Mgo 13.19 Ti02 0.77 0.96 - 19 17 PZOS 0.027 0.046 - 40 1 1 BIR- I - DNC- 1 - A1203 17.66 18.30 -3 4 Fe203 10.35 9.93 +4 7 MgO 9.94 10.05 - 1 5 CaO 8.57 11.27 - 24 4 Na,O 1.83 1.87 -2 3 Ti02 0.49 0.48 + 2 23 PZOS 0.078 0.085 + 8 8 *Reference values from Govindaraju.2232 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 Table 9 LA-ICP-MS data for two basic rocks using a single-point calibration for alkali and alkaline earth elements Table 11 calibration for refractory elements LA-ICP-MS data for two basic rocks using a single-point Relative Measured/ Reference*/ error RSD Element Pg g-' Pg g-' (Ole) (O/O) Li 2.64 3.4 -1- 0.4 - 22 8 Na2Ot 1.95 1.75 + 1 1 5 Sr 134 108+ 14 + 24 4 Ba 10.7 7.7 t- 2.2 + 39 5 CaOt 13.19 13.24 + 0.4 4 Li 5.03 5.1 + 0.5 - 1 16 Na2Ot 1.83 1.87 - 2 3 Sr 146 14526 +0.7 6 Ba 113 114k 16 -0.6 7 CaOt 8.57 11.27 - 24 4 BIR- I- DNC- I- *Reference values from Govindaraju22 with errors from Gladney toh m/m.et al. 25 Measured Reference*/ Error RSD Element Pg g-' Pug g-' ( OiO ) (O/O) Y 16.0 16-1-2 0 1 1 Zr 13.5 2 2 k 7 - 39 10 Nb 0.37 2-1-0.5 - 82 41 Ce 2.26 2.55 1.1 - 9 12 BIR- I - DNC-I- Y 16.7 18-1-3 - 7 9 Zr 43.4 41 -t7 +6 25 Nb I .98 3t-0.7 - 34 34 Ce 9.19 10.6-1- 2.4 - 13 18 *Reference values from GovindarajuZ2 with errors from Gladney et al. 25 Table 12 LA-ICP-MS data for two basic rocks using a single-point calibration for Group I11 metals and volatile and hydride forming elements Table 10 LA-ICP-MS measured for two basic rocks using a single- point calibration for first row transition elements Element BIR- 1- s c V Cr c o Ni c u Zn s c V Cr c o Ni c u Zn DNC- I - Measuredl Pg g-' 34 316 265 55 158 68 50 22 170 217 66 325 123 77 Reference*/ PI2 g-' 44*4 313+23 382 -1- 38 5 1.4 -1- 3.4 166-1- 16 126-1-5 71 -1-9 31 -t 1.4 148+9 285 -1- 32 54.7 + 3.7 247+ 18 96+9 66-1-5 Relative error (Yo) - 24 + 1 -31 +7 - 5 - 46 - 30 - 30 + 15 - 24 +21 +31 + 28 + 16 RSD (O/o) 2 19 24 7 7 8 13 6 25 13 10 1 1 24 5 Relative Measuredl Reference*/ error RSD Element Pg g-' Pg g-' (O/O) (Yo) A1203t 18.13 15.35 + 18 4 BIR- 1 - Ga 15.7 16-1-2 - 2 6 DNC- I- A1203t 17.66 18.30 -3 4 Ga 15.1 15+2 +0.8 8 BIR- I - Sb 0.34 0.58k0.16 -41 18 Pb 2.82 3.2 -1- 0.8 - 12 23 DNC- I- Sb 0.96 0.96 -1- 0.15 0 33 Pb 10.8 + 72 28 6.3+ 1 *Reference values from Govindaraju22 with errors from Gladney to/o m/m.et al. 25 *Reference values from Govindaraju22 with errors from Gladney et al.25 First row transition metals The precision of measurements within this group are very variable from 2 to 25% RSD and are not directly related to concentration (Table 10). Of the 20 results reported only five have an accuracy of better than 20% relative. Refactories The elements within this group include those which may be difficult to determine accurately in solution owing to a number of dissolution/stability problems26 and therefore their accurate determination by LA-ICP-MS could offer a viable alternative method of analysis. The precision ranges from 9 to 40% RSD reflecting the rather low counts and low concentrations (Table 1 1).Counts for Nb in BIR-1 are only just above the detection limit for this element and therefore poor accuracy and precision is not unexpected. However measured values for Ce Y and Zr (and Nb in DNC-1) all fall within the reference values reported for both samples and therefore display a high degree of accuracy within the limitations noted above. Tantalum Hf and W also fall within this category but there are insufficient data available here to comment further. Group 111 metals Only two elements are available from this group either because reference data are unavailable (e.g. B) or elemental concentrations fall below the detection limit (e.g. In). Gallium substitution for A1 can occur in silicate minerals and hence they are reported together. Both elements display good precision (< 10% RSD) and the measured data for Ga are very accurate when compared with the recommended values (Table 12).Volatile and hydride forming elements The relative sensitivity for both Sb and Pb is high with detection limits of about 80 ng g-' (Table 12). The accuracy for Sb even at the sub-ppm level is good measurements on both RMs being within the range of the reference values. Certain elemental groups therefore display good accu- racy e.g. refractories Group I11 metals hydrides and to some extent the alkali metals and alkaline earths when determined by LA-ICP-MS in basic rock matrices. The transition metals present a more complex picture and atJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 33 Table 13 Limits of detection (LOD) for REE Hf Ta and W calculated as the concentration equivalent to three times the standard deviation of the background count at m/z 185; n= 10 Mass LOD/ Element (m/z) Pg g-’ La Ce Pr Nd Sm Eu Gd Tb DY Ho Er Tm Yb Lu Hf Ta W 139 140 141 146 147 151 157 159 163 165 167 169 172 175 178 181 182 0.01 3 0.0 12 0.01 1 0.072 0.084 0.032 0.083 0.0 14 0.056 0.015 0.057 0.0 18 0.063 0.0 15 0.059 0.016 0.0 19 this stage little more can be concluded from these data without further experimental work.To evaluate the possi- bility that error had been introduced by the use of a single- point standard calibration a new calibration was generated using both W-2 and BIR- 1. The remaining basic RM DNC- 1 was then analysed as the ‘unknown’ against this calibra- tion. Accuracy of these new data showed no improvement (and was poorer in a few cases) over the original single- point calibration.Determination of REE Hf Ta and W In addition to the multi-element determinations discussed above analyses were carried out by scanning only the higher part of the mass range from rnlz 137 to 184. Under these conditions improved sensitivity can be obtained for the REE Hf Ta and W elements which typically occur in silicate rocks at concentrations from 0.1 to 100 pg g-l. Detection limits (see under Multi-element Results) have been calculated for these elements using rnlz 185 as a background point. Values reported (Table 13) are typically 1000 1 . . iTj 200 = m . = m m La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Element Fig. 3 Relative responses (counts gpg-I corrected to I3’Ba) for the REE in AGV-1 a few tens of ng g-l and are almost an order of magnitude lower than those available using a wide range scan.There are clear advantages therefore to the selection of elemental groups which lie in discrete parts of the mass range if particularly good sensitivity is required. The relative responses for the REE in AGV-1 are shown in Fig. 3 corrected for isotopic abundance and concentra- tion. Although the relative responses are fairly uniform there is a general decrease in sensitivity from light to heavy REE. Replicate analyses of G-2 have been used to calibrate and measure concentrations in AGV-1. Two runs each consisting of five replicate analyses of G-2 were averaged and a calibration graph constructed from the mean inte- grals.Five replicates of AGV-1 were averaged giving a precision of 5% RSD for the higher abundance light and middle REE (La-Gd) and better than 10% RSD for the lower concentration heavier elements. The accuracy for all elements determined was very good and all measured concentrations with the exception of Eu and Hf lie within the error of the reference values (Table 14). The Hf figure is high by nearly loo% and this may reflect its rather inhomogeneous distribution a feature common to many silicate samples. Con c 1 us i o n System optimization experiments have been carried out to establish those conditions which are best suited for quanti- Table 14 Quantitative REE determination in USGS AGV-1 by LA-ICP-MS Element La Ce Pr Nd Sm Eu Gd Tb DY Ho Er Tm Yb Lu Hf Ta W Isotope w.4 139 140 141 143/ 145/ 146$ 147 151 157 159 163 165 167 169 172 175 178 181 182/ 184$ Measured/ Pg g-‘ 35.9 63.5 33.1 8.82 5.98 1.32 5.10 0.698 4.27 0.7 10 1.80 0.31 1 1.86 0.217 8.35 0.843 0.376 RSD (%I 3 4 3 3 4 5 5 6 6 8 8 5 7 13 4 5 9 Working value*/ ,Ug g-’ 38 67 7.6 33 5.9 1.64 5.0 0.7 3.6 0.67 1.7 0.34 1.72 0.27 5.1 0.90 0.55 Consensus value*/ Pg g-‘ 38k3 66k6 6.5k0.9 34k5 5.9 k 0.5 1.66k0.1 1 5.2 k 0.6 3.8 k 0.4 0.73 +0.08 1.61 k0.22 0.32 k 0.05 1.67 +.0.17 0.28 k 0.03 5.1 k 0.4 0.92 k 0.12 0.53 k0.09 0.71 kO.1 *Working values from Govindaraju.22 ?Consensus values from Gladney et al.25 $Mean concentration used.34 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 tative elemental determination at major minor and trace levels in silicate rock matrices.The ICP-MS instrument was operated at a higher forward power (1.5 kW) and carrier gas flow rate (1.0 min-I) than that used for conventional solution nebulization. A number of laser operating para- meters were also optimized resulting in the use of fixed-Q mode 800 V laser energy a shot repetition rate of 20 Hz with five shots per site and a total of 24 sites per analysis. Under these conditions sensitivity was good with detection limits better than 50 ng g-I for many elements whilst major element concentrations (e.g. 97 000 pg g-’ for Al) were still within the linear range of the ion detector. Internal standardization was necessary to compensate for differential ablation within a single sample and between samples 55Mn being used for wide scans and 13’Ba for the narrow mass range scans for the REE and heavier trace elements.As a result of this study further work will be carried out to evaluate the role of multiple internal standardization using elements from each of the chemical groups identified. Relative elemental responses varied from one element to another by over an order of magnitude and in some cases were found to be sample dependent. Quantitative measurements could be made under these optimum conditions providing that samples and standards were closely matched both in terms of bulk chemistry and more importantly mineralogy. Accuracy and precision were therefore assessed for the basic rocks. Major elements showed good accuracy and precision. Trace element data were more mixed but certain elemental groups i.e.refrac- tories Group I11 metals hydride forming elements and to some extent the alkaline earths showed good accuracy when compared with working values. Transition metal behaviour was more difficult to predict with many ele- ments showing poor accuracy and precision. A narrow mass range scan across the upper part of the mass range gave an improvement in detection limit for the REE Hf Ta and W by nearly an order of magnitude. Accurate REE determinations were made down to a few hundred ng g-’. The ICP-MS Facility Royal Holloway University of Lon- don is supported by the Natural Environment Research Council and the Ministry of Defence and this continued support is gratefully acknowledged. Thanks are also due to Dr W. Perkins (Aberystwyth) for providing us with laser time during the early part of this work.1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 References Gray A. L. and Date A. R. Analyst 1983 108 1033. Mainman T. H. Nature (London) 1960 187 493. Moenke-Blankenburg L. Laser Micro Analysis Wiley-Inter- science New York 1989. Dittrich K. and Wennich R. Prog. Anal. ,4t. Spectrosc. 1984 7 139. Verbueken A. H. Bruynseels F. J. Van Grieken R. and Adams F. Laser Microprobe Mass Spectrometry eds. Adams F. Gijbels R. and Van Grieken R. Wiley New York vol. 95 in Chemical Analysis 1988 pp. 173-256. Carr J. W. and Horlick G. Spectrochim. Acta Part B 1982 37 1. Thompson M. Goulter J. E. and Sieper F. Analyst 1981 106 32. Thompson M. Chenery S. and Brett L. J. Anal. At. Spectrom. 1989 4 1 1 . Mitchell P. G. Ruggles J. A. Sneddon J. and Radziemski L. J. Anal. Lett. 1985 18 1723. Imai N. Anal. Chim. Acta 1990 235 381. Marshall J. Franks J. Abell I. and Tye C. J. Anal. At. Spectrom. I99 1 6 145. Mochizuki T. Sakashita A. Iwata H. Kagaya T. Shima- mura T. and Blair P. Anal. Sci. 1988 4 403. Mochizuki T. Sakashita A. Tsuji T. Iwata H. Ishibashi Y. and Gunji N. Anal. Sci. 1991 7 479. Mochizuki T. Sakashita A. Iwata H. Ishibashi Y. and Gunji N. Anal. Sci. 1991 7 151. Gray A. L. Analyst 1985 110 551. Arrowsmith P. Anal. Chem. 1987 59 1437. Pearce J. G. Perkins W. T. Abell I. Duller G. A. T. and Fuge R. J. Anal. At. Spectrom. 1992 7 53. Darke S. A. Long S. E. Pickford C. J. and Tyson J. F. Fresenius’ J. Anal. Chem. 1990 337 284. Hager J. W. Anal. Chem. 1989 61 1243. Arrowsmith P. and Hughes S. K. Appl. Spectrosc. 1988,42 1231. Perkins W. T. Fuge R. and Pearce N. J. G. J. Anal. At. Spectrom. 1991 6 445. Govindaraju K. Geostand. Newsl. 1989 13 1 . Gray A. L. and Williams J. G. J. Anal. At. Spectrom. 1987 2 599. Jarvis K. E. Gray A. L. and Houk R. S. Handbook of Inductively Coupled Plasma Mass Spectrometry Blackie Glas- gow 1992. Gladney E. S. Burns C. E. and Roelandts I. Geostand. Newsl. 1983 7 3. Jarvis K. E. Chem. Geol. 1990 83 89. Paper 2 /02828J Received May 29 1992 Acceuted Seutember 9. 1992

ISSN:0267-9477    

DOI:10.1039/JA9930800025

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 35 Optimization and Use of Flow Injection Vapour Generation Inductively Coupled Plasma Mass Spectrometry for the Determination of Arsenic Antimony and Mercury in Water and Sea-water at Ultratrace Levels Andreas Stroh and Uwe Vollkopf Bodenseewerk Perkin-Elmer GmbH Postfach I0 I I 64 W-7770 Oberlingen Germany Vapour generation flow injection inductively coupled plasma mass spectrometry (FI-ICP-MS) was used for the determination of As Sb and Hg in four international water reference materials (National Research Council of Canada). A commercially available FI device was easily connected to the ICP-MS system. Flow injection parameters such as sample volume purge gas flow rate and concentration of reductant were investigated and optimized (univariate) as were different sample pre-reduction techniques.The precision and accuracy of the results obtained show the applicability of this method to the determination of vapour-forming elements at ultratrace levels in environmental samples. Detection limits are in the range 0.5-7 ng I-' for Bi Sb %e Te Hg and As (with pre-reduction). Keywords Flow injection inductively coupled plasma mass spectrometry; on-line vapour generation; optimization of flow injection parameters; matrix effects; certified reference materials for water Inductively coupled plasma mass spectrometry (ICP-MS) has proved to be a very powerful technique for trace multi- element and isotopic determinations in many types of samples. 1-4 In this technique predominantly singly-charged positive ions are generated in an argon plasma source and then transferred into and analysed with a quadrupole mass analyser.For the majority of the elements listed in the Periodic Table the degree of ionization in an Ar plasma is >9Ooh. However for As Se and Hg the number of ions produced in the plasma source drops dramatically to 48.87 30.53 and 32.31% respecti~ely.~ The reason for this is the high ionization potential of these elements As 9.8 1 eV; Se 9.752 eV; and Hg 10.437 eV,6 which are much closer to the Ar ionization potential (Ar 15.759 eV) than most other elements. This leads to a decrease of detection power for these elements however in most cases ICP-MS detection limits are still sufficient for their determination. In samples that contain very low concentrations of As/Se and Hg elements (e.g.unpolluted surface water biological or clinical materials) or samples that have to be diluted because they have a harsh sample matrix detection capabil- ities are restricted making analysis difficult or even impossible. As ICP-MS is also considered to be a very flexible detection technique alternate sample introduction systems can be easily used in conjunction with ICP-MS such as laser sampling electrothermal vaporization (ETV) ultra- sonic nebulization high-performance liquid chromato- graphy and flow injection (FI).'-13 Flow injection was first described by Ruzicka and HansenI4 in 1975 and since then has emerged as a versatile sampling tool capable of enhancing considerably the analytical capabilities of atomic absorption spectrometry (AAS) ICP atomic emission spec- trometry and ICP-MS.15-z1 Hydride generation is frequently used in analytical chemistry to improve the sensitivity of measurements of volatile vapour-forming elements such as As Sb Bi Se Te Ge Sn and Pb which are thought to be harmful at much lower levels than previously believed. Vapour generation is commonly performed using organiczz or inorganicz3 phase vapour generation. Heitkemper and CarusoZ4 have used sample introduction by continuous flow hydride generation for the determination of As Cd Pb and Cu in National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1566a Oyster Tissue with ICP-MS. Sample introduction by FI with a sample loop of 500 pl was used.One of the advantages of the FI technique over continuous flow vapour generation is the significantly lower reagent and sample consumption. Together with the hydride-forming elements As and Sb on- line detection of Hg cold vapour was performed. The aim of the study was the development of an FI vapour generation ICP-MS method for the determination of As Sb and Hg in waters at ultratrace levels. Experimental Instrumentation The ICP mass spectrometer used for this work was an Elan 5000 (Perkin-Elmer SCIEX Norwalk CT USA). The system was equipped with a four-channel mass flow controller to ensure gas flqw stability. A FIAS-200 (Boden- seewerk Perkin-Elmer Uberlingen Germany) equipped with a random access AS-90 autosampler (Perkin-Elmer) for on-line FI vapour generation was used.Operating conditions used for the ICP mass spectrometer and the FIAS-200 are summarized in Tables 1 and 2 respectively. All operating parameters of the FI accessory are controlled from the transient signal software application which is incorporated in the Elan user software. Data acquisition was performed using multichannel analysis with only one channel per mass unit. No time is wasted using multiple points per mass unit so the speed of analysis is increased and time resolution for observing the transients is guaran- teed. This means that it is possible to determine more than 75 elements using a single transient signal. The timing and Table 1 Operating conditions of the Elan 5000 ICP mass spectrometer Forward power/W 1100 15 0.8 Purge gas flow rate/l min-I 1 .oo Outer gas flow rate/l min-I Intermediate gas flow rate/l min-l Sampler cone Platinum Skimmer cone Platinum Operating pressure InterfaceIPa Quadrupole/Pa Data acquisition Dwell time/ms No.of readings 266.6-400 800 x Multichannel analysis one point per mass (peak hopping) 20 6036 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 Table 2 Instrument parameters of the FIAS-200 FI device Pump 11 Pump 21 Step Time/s rev min-I rev min-I 1 10 100 0 2 8 I00 0 3 2 100 0 4 10 0 120 5 1 75 0 6 60 50 0 Valve position Fill Fill Fill Inject Fill Fill Remarks Rinse tubing Fill sample loop Start measurement Start hydride generation Back to fill position Rinse tubing and loop (only between samples) duration of the quadrupole scan cycles are also computer controlled when working with the FI device. Integrated transient signal software allows calculation of analytical results based on both transient signal peak height and peak area.The optimization of the ICP-MS operating parameters such as purge (carrier) gas flow rate and ion optic settings was simply performed by continuously aspirating a test solution typically a mixed standard solution containing 10 ng m1-I of Mg Rh and Pb. The FI manifold is shown in Fig. 1. The gas-liquid phase separator has been described e l s e ~ h e r e ~ ~ - ~ ~ and was used to extract the volatile vapour-forming elements from the liquid sample. For vapour generation FI-ICP-MS the normal spray chamber including the nebulizer was re- moved from the torch adapter. A 1000 mm length of poly(tetrafluoroethy1ene) (PTFE) tubing (1.75 mm i.d.) connected the gas-liquid separator with the torch adapter of the Ar plasma. Argon purge gas supply was taken from the nebulizer gas mass flow controller which was directly connected with the gas inlet of the FI device.Thus the change from conventional solution aspiration to vapour generation FI can be performed in less than 3 min. Because the generator-interface design of the mass spectrometer used in this study ensures fixed ion energies,27 the optimum operating conditions are identical for a wet plasma (contin- uous solution nebulization) and dry plasma (vapour genera- tion laser sampling ETV). Because of this behaviour no special optimization of the ICP mass spectrometer was necessary for the FI vapour generation study.Reagents and Sample Pre-treatment As sample reductant NaBH (96% m/v Merck No. 6371 Darmstadt Germany) was used. The NaBH solutions were stabilized with 0.05% m/v NaOH (Merck No. 6495 solid). As acid carrier for the samples 3% v/v nitric acid purified by sub-boiling distillation (BSP 929 Berghof Eningen mI min-' Fig. 1 FI manifold for vapour generation FI-ICP-MS P 1 and P2 pumps; C chemifold; W waste; L sample loop; G gas-liquid separator; V injection valve; and AS autosampler Germany) was used. All reagents were diluted/dissolved with ultra pure de-ionized water (Barnstead Nanopure Boston MA USA) and prepared fresh daily. For the initial basic studies multi-element solutions were prepared with 2 pg 1-i of Bi and Sb and 5 pg 1-i of As Se Te and Hg without any further sample pre-treatment.For quantitative mea- surements it is important to pre-reduce the samples to ensure the same valence state of the elements. This is necessary because the sensitivity of the hydride forming process is different depending on the valence of the element e.g. AsItt and AsV. The pre-reduction procedure is different for the vapour-forming elements. Arsenic and Sb have to be mixed with a solution containing 5% m/v ascorbic acid (Merck No. 500074) and 5% m/v KI (Merck No. 5044). Unfortunately this reductant mixture is strong enough to reduce Se and Te to the elemental state (SeO TeO) hence reducing the advantage of ICP-MS as a fast multi- elemental technique. As an alternative pre-reductant 5% m/v KBr (Merck No. 4904) which has been tested in the past,28 was examined.The sample was heated at 50 "C for 50 min after the addition of 1 ml Of 5% m/v KBr solution or with an excess of 6 mol 1-i HC1 at 90 "C for 15 min. It was found that neither of these two methods reduces As and Sb to the + 3 oxidation state thus it was not possible to use identical sample preparation procedures for all the analyte elements of interest. If all vapour-forming elements (As Sb Se Te Bi Hg Sn Ge and Hg) must be determined in the same sample(s) it is necessary to split the sample into two aliquots and to prepare these as required. It may be possible to overcome this problem by adding KI after mixing the sample with the NaBH r e d ~ c t a n t ~ ~ or by mixing the pre- reductant with the NaBH4,23 although these approaches were not examined in this study Bi and Hg were found to need no special sample pre-treatment steps.Aliquots ( 10 ml) of thoroughly mixed water samples were taken and acidified with 3 ml of concentrated HCl. A mixture of 1 ml of 5% m/v u-5% m/v ascorbic acid was added to ensure reduction of As and Sb. After 15 min reaction time 500 pl of a 100 pg 1-i Bi solution were added and the sample solution diluted to a final volume of 25 ml. This solution contained 2 pg 1-l of Bi added as internal standard. Results and Discussion Acid Carrier Hydrochloric acid is typically used as the acid carrier in hydride generation AAS. In this study the use of HCl as acid carrier for vapour generation ICP-MS was avoided because chlorine vapour generated in the phase separator was expected to enter the plasma ion source with the a n a l y t e ~ .~ ~ This could then result in an ArCl interference at m/z 75 which is the only stable isotope of As. The influence of increasing C1 content in the sample solution on the signals of m/z 75 and 77 is shown in Fig. 2. The C1 matrix was simulated by various HCl concentrations from 0.3 to 3.0% v/v. Both masses that can be interfered with by ArCl species (35Cl and 37Cl) were analysed in order to examine whetherJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 37 Concentration HCI (% vhr) Fig. 2 Influence of C1 content in the measurement solution on signal intensities of A relative atomic mass 75 and B relative atomic mass 77 1000000 'VJ VJ B = I - II Y d 1 .o 2.0 0.2 0.02 0.002 0.0002 0.00002 Concentration NaBH (% m/v) Fig.3 Dependence of A As hydride and B Hg cold vapour generation signal intensity on NaBH concentration the signals were coming from impurities of the HCl or really from the formation of ArCl. To correct for the differences in the natural abundance of 35Cl and 37Cl (35C1:37C1=3.08) the intensities for m/z 77 are multiplied by 3.08 to correct for this difference. While the intensities at m/z 75 show a significant increase with increasing concentration of C1 the corrected count rate at m/z 77 is only slightly increased. If there were significant formation of ArCl the intensities of both masses should behave in a similar manner. However the observations indicate that the contribution to the As signal results more from impurities of As in the HC1 used for this study rather than from formation of ArCl.The equivalent As concentration found in 3% v/v HCl is 0.029 ,ug 1-I. In general HC1 also gives higher blank values for Hg. Vollkopf et aL3* and G i i n ~ e l ~ ~ have shown that HN03 can be used instead of HCl as carrier solution. A concentration of 3% v/v HN03 results in good sensitivity during the hydride-forming process. Nitrates in the measurement solution can cause some interferences in the hydride-forming process for Se. If the samples have to be pre-reduced by boiling with 6 mol 1 - I hydrochloric acid nitrites can be formed which can significantly interfere with the determination of Se.33934 In this case the samples must be treated with sulfanilamide or sulfamic acid. 0.6 0.7 0.8 0.9 1.0 1.05 1.1 1.2 Purge gas flow rate/l min-' Fig.4 Dependence of vapour generation signal intensities on purge gas flow A Te; B As; C Sb; D Hg and E Bi. Note the scale has been expanded between 1.0 and 1.1 1 min-' in order to show the real maximum more clearly Sodium Tetrahydroborate The rate of formation of volatile vapour greatly depends on the concentration of the NaBH solution. An experiment was carried out during which the concentration of NaBH was increased stepwise from 0.00002 to 2.0% m/v while the concentration of HN03 carrier was held constant. The signal intensities of As and Hg were monitored during this study. For As the best signal to noise ratio (S/N) was achieved using an NaBH concentration of 2.0% m/v. A further increase of the concentration of NaBH produced higher signal intensities but also higher background.There was also a greater risk of the generation of foam in the gas-liquid separator. Foam bubbles can enter the PTFE tubing leading to the gas torch and cause problems when entering the plasma without passing through a spray chamber. With decreasing concentrations of the NaBH solution As sensitivity falls and reaches background levels at 0.02% m/v (see Fig. 3). However Hg shows exactly the opposite behaviour. With a more dilute solution of NaBH signal intensity is improved for this element reaching a maximum intensity at concentrations of 0.002-0.0002% m/v NaBH (see Fig. 3). As compromise conditions an NaBH concentration of 0.2% m/v was employed for all subsequent measurements which gave in general good signal intensities for all elements investigated.For single element determinations of Hg where maximum detection power is required a 0.0002% m/v NaBH reductant solution should be used as this results in maximum sensitivity and the lowest contamination risk from the NaBH solution. Purge Gas Flow Rate The optimization of the purge gas flow rate was performed with a multi-element solution containing 2 pg 1-1 of Sb and Bi and 5 ,ug 1-' of As Te and Hg. The flow rate of the purge gas was increased in 0.1 1 min-l increments from 0.6 up to 1. I 1 min-l. The maximum sensitivity was achieved for all elements at a flow rate of between 1 .O and 1.1 1 min-I as Table 3 Influence of purge gas flow on S/N Element Flow rate/l min-' Element ng ml-I 0.6 0.7 0.8 0.9 1 1.05 1.1 As 5 3.7 8 8.3 31 57 52 42 Sb 2 1 1 21 8.6 37 69 67 53 Bi 2 45 1 1 1 193 714 784 672 359 Hg 5 35 69 69 148 252 232 137 concent rat ion/ .38 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL.8 c c - I i c) - 4 ) - - 1 - 1 I 1 0.95 ' 1 I I I I I 0 0.5 1 .o 0.5 2.0 2.5 3.0 Concentration NaCl (?h mlm) Fig. 6 Matrix effects of NaCl on the hydride-forming process for A Bi and B As and vapour generation for C Hg 150 I 1 C .- a .- c g z 30 60 90 Time/min 50 o Fig. 7 Long-term precision of vapour generation for 200 replicate injections of 5 pg 1-I Hg shown in Fig. 4. A calculation of S/N carried out for each of the elements studied during the experiments on purge gas flow rates showed that the best ratios were obtained using a flow rate of 1.0 1 min-l.This flow rate was therefore used for all further measurements on all elements. The results of the S/N calculations are summarized in Table 3. Injection Volume The dependence of element signal intensities on the sample loop volume is shown in Fig. 5. The aim of this experiment was to minimize reagent and sample consumption without losing too much sensitivity for the analysis of the vapour- forming elements at ultratrace levels. Flow rates of carrier acid and NaBH solution were kept constant. Maximum peak height signal intensities were achieved with a sample loop volume of 800 pl. A further increase of the sample loop volume does not result in higher signals. A slight increase of the peak area intensities is indicated by a small amount of peak broadening.No steady-state signal was observed with increasing loop volumes so it seems probable that chemical saturation during the vapour-formation process is reached when a certain volume of sample is mixed with the adjusted NaBH and acid carrier flow rates. Since approximately 90% of the maximum possible signal intensity was reached with a sample loop volume of 500 pl this volume of sample loop was used for all further measurements leading to sufficient sensitivity and low sample consumption. Influence of Sample Matrix on Vapour Generation Signal and Internal Standardization The possibility of C1 vapour generation leading to a contribution to the As intensities caused by the formation of ArCl was discussed earlier. For the analysis of sea-water samples it is also very important to estimate the influence of increasing sample matrix on the vapour generation process for the different elements.Synthetic NaCl solutions from 0.1 to 3.0% m/v have been prepared and spiked with a 1 pg 1-l of Bi and a 10 pg 1-l of Hg and As standard solution. The recoveries found for these solutions expressed as relative concentrations compared with the matrix free calibration solution are shown in Fig. 6. All three elements show a similar pattern in these solutions and the inaccuracy is as low as 1-7%. This implies that the use of Bi as internal standard will lead to better precision and accuracy for the analysis of these types of samples. For different sample types e.g. biological and clinical materials Bi is not useful because it is part of the sample composition.Even in small amounts it will result in incorrect concentration values because of its tremendous sensitivity for the vapour formation process. There is no other suitable candidate as an internal standard for the analysis of such samples. Therefore use of an internal standard is not recommended. For the investigation of the stability during extended operation without the use of internal standardization a standard solution was prepared containing 5 pg 1-l of Hg. Mercury was used for this test with regard to two different analytical questions namely stability of signals and drift for Hg caused by contamination or carryover when analys- ing this element over long time periods. Two hundred replicate injections (loop volume 500 pl) were performed for 31 s each leading to a total measurement time of approximately 90 min.The precision of the particular injection without internal standardization is presented normalized to the first injection in Fig. 7. The calculated relative standard deviation (RSD O/o) for the 200 replicate injections is 1.67%. Precision and Accuracy The precision of the vapour generation process was evalu- ated using a mixed standard solution containing 5 pg 1-* of Hg As Se and Te and 2 pg 1-I of Bi and Sb. The SDs and RSDs were calculated for each element from five replicate sample injections with a loop volume of 500 pl. The results of the calculations are summarized in Table 4. Bismuth gave the best precision 0.5% RSD while the RSDs for the other elements determined at the same time were between 0.9 and 1.6%. To establish the accuracy of the method four interna- tional water standards (National Research Council of Canada NRCC) were analysed two Riverine Waters SLRS-1 and SLRS-2 Coastal Seawater CASS-2 and Open Ocean Seawater NASS-3.Five replicates of each sample were prepared using the sample preparation procedure Table 4 Precision of FI-ICP-MS vapour generation for five sample injections. Loop volume 500 pl Mean value Concentration/ of intensity/ SD/ RSD Element 1-I counts s-l counts s-I (Oh) As 2 17 350 319 1.6 Sb 1 76 384 951 1.1 2916 0.5 Bi 1 477 697 Hg 2 214 544 3057 1.3 82Se 2 27 369 484 1.6 78Se 2 65 157 678 0.9 Te 2 287 785 5096 1.6JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY FEBRUARY 1993 VOL. 8 39 Table 5 Results for the determination of As Sb and Hg in reference water samples.Recovery (O/O) was estimated by spiking samples with 1 pg g-' of Sb and 2 pg 1-I of As and Hg Certified value/ FI-ICP-MS Element Pg I-' SD /pg I-' SD Recovery (O/O) SLRS-I- As 0.55 0.08 0.50 0.03 98.5 Sb 0.63 0.05 0.69 0.04 113 Hg NC* - 0.5 0.1 108.5 SLRS-2- As 0.77 0.09 0.8 0.06 112 Sb 0.26 0.05 0.33 0.02 1 1 1 Hg NC - (0.04) - 101.5 CASS-2- As 1.01 0.07 1.08 0.04 102 Sb NC - 0.3 0.01 96 Hg NC - 0.5 0.07 95 NASS-3- As 1.65 0.19 1.74 0.04 105 Sb NC - 0.189 0.008 97 Hg NC - 1.36 0.2 93 *NC = Not certified. Table 6 Detection limits of FI-ICP-MS vapour generation with and without sample pre-reduction Detection limiting 1-I Element Without pre-reduction Pre-reduction with KI As 26 78Se 16 82Se 7 Sb 4 Te 1 Hg 4 Bi 0.5 6 - - 1.3 43.I* 0.6 - * Hg detection limit degraded due to reagent contamination. outlined previously. External calibration was performed using a blank and two aqueous standard solutions contain- ing 1 and 2.5 pg 1-' for Sb and 2 and 5 pg 1-' for As and Hg. All solutions were prepared in the same way as the samples and 2 pg 1-l of Bi were added as internal standard. Because Se and Te are reduced to the elemental state during the reduction step they could not be detected together with the other elements. The results for As Sb and Hg are presented in Table 5. Mean values are shown for three replicate measurements of the five individual sample preparations of the reference material. The calibration graphs for As Sb and Hg were all linear with correlation coefficients varying between 0.997 and 0.999.The results for As and Sb show excellent agreement with the certified values. The concen- trations of Hg are not certified in these reference water samples. To confirm the results for this element recovery tests were performed. The samples were spiked with 1 pg 1-l of Sb and 2 pg 1-I of As and Hg and re-analysed. The results are shown in Table 5 and satisfactory recoveries of the order of 93- 1 13% were found. The reproducibility of the quantitative results was calcu- lated based on three replicate measurements of five indivi- dual sample preparations of the water reference samples. The RSDs of the measurements varied between 2.8 and 7.5% for Sb and As and is somewhat poorer (14-20%) for the very low concentrations of Hg in all four samples (see Table 5).Detection Limits The detection limits summarized in Table 6 were estimated for multi-element determinations with the standard solu- tions used for the determination of precision. Detection limits were calculated based on 30 using blank solutions ( 18 Mi2 de-ionized water) which were pre-reduced in exactly the same way as the samples and without pre-reduction prior to analysis. Lower detection limits were achieved for As and Sb when the samples were pre-reduced prior to measurement since higher signal intensities are found for these two elements when they are in oxidation state +3. The pre-reduction procedure has no beneficial effect on the detection limits for Bi and the detection limit for Hg is worse after the pre-reduction procedure. This is due to slight contamination of the reagents used for pre-reduction.The detection limits for Hg could be improved by using reagents of higher purity. Conclusions Flow injection vapour generation in conjunction with ICP- MS is a very powerful technique that enhances considerably the analytical capabilities of ICP-MS for volatile vapour- forming elements thus allowing multi-elemental determi- nations of those analytes at ultratrace levels in environmen- tal samples with very good accuracy and precision. Vapour generation offers several advantages over continuous solu- tion aspiration for several vapour-forming elements. The advantages of increased sensitivity and avoidance of spec- tral interferences caused by a high salt matrix are high- lighted. The sensitivity precision and accuracy of the technique for fresh and ocean waters are demonstrated by the analysis of certified reference materials. References 1 Doherty W.and Van der Voet A. Can. J. 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ISSN:0267-9477    

DOI:10.1039/JA9930800035

出版商:RSC    

年代:1993

数据来源: RSC