摘要:

Pro C of the Society for Analytical Chemistry Analytical Division Chemical Society CONTENTS Reports of Meetings . . . 259 Euroanalysis I . . . . . . 260 Joint Pharmaceutical Analysis Group.. . . .. . . 262 Coprecipitation and Adsorp- tion Rules . . . . . . 264 Summaries of Papers “Selectivity in Trace Analysis” 266 Obituary . . . . . . 303 Notices .. .. .. . . 303 Forthcoming Meetings Back Cover Proc. SOC. Analyt. Chern. Vol. 9 No. 12 Pages 259-304 December 1972 PAYCAL Vol. 9. No. 12 December 1972 PROCEED I N G S THE SOCIETY FOR ANALYTICAL CHEMISTRY ANALYTICAL DIVISION CHEMICAL SOCIETY OF Hon. Secretory W. H. C. Shaw Officers of The Society for Analytical Chemistry and the Analytical Division of The Chemical Society President C. Whalley Hon. Treasurer Hon. Assistant Secretaries G.W. C. Milner D. I. Coomber O.B.E.; D. W. Wilson Secretary Miss P. E. Hutchinson 9/10 SAVILE ROW LONDON WIX IAF Telephone 01-734 9864 Editor J. B. Attrill Assistant Editor P. C. Weston Proceedings i s published by The Society for Analytical Chemistry and distributed to all members of the Analytical Division and t o subscribers with The Analyst; subscriptions cannot be accepted for Proceedings alone. Single copies can be obtained direct from The Chemical Society Publications Sales Office Blackhorse Road Letchworth Herts. SG6 I HN (NOT through Trade Agents) price 25p. post free. Remittances MUST accompany orders. 0 The Society for Analytical Chemistry SOCIETY FOR ANALYTICAL CHEMISTRY AND CHEMICAL SOCIETY ANALYTICAL DIVISION TIE A TIE bearing the Coat of Arms of the Society for ,4nalytical Chemistry is now on sale to members of the SAC/Analytical Division. The tie which carries a simplified version of the Coat of Arms woven in red silver and gold as a single motif is available in three different background colours-dark blue dark green and maroon. The tie is manufactured in a Crimplene - Terylene mixture. The price of the tie is El-00 including postage and it is being distributed from the Society’s Offices. Orders accompanied by the appropriate remittance should be sent to The Secretary Society for Analytical Chemistry 9/10 Savile Row London WlX 1AF. Please make cheques payable to The Society for Analytical Chemistry and ensure that the background colour required on the tie is stated.

ISSN:0037-9697    

DOI:10.1039/SA97209FX047

出版商:RSC    

年代:1972

数据来源: RSC

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SOCIETY FOR ANALYTICAL CHEMISTRY ANALYTICAL DIVISIOK CHEMICAL SOCIETY January \\oTednesday 10th PRESTOX Thursday 1 l t h BATH Tuesday 16th BIRMINGHAM Saturday 20th SALFORU Tuesday 23rd EDINBURGH IVednesday 24th 31 ID DLE s - BROUGH Il-ednesday 24th LONDOK Forthcoming Meetings SORTH WEST REGION. “Thermometric Analysis,” by L. S. Bark. Harris College Preston ; 7.30 p.m. WESTERN IIEGION h n u a l General &leeting followed by a Social and Film Films of America will be introduced by T. G. Morris. Chemistry Department The University of Technology Claverton Down Bath ; MIDLANDS REGIOK Elwell Award Meeting. “Computerised Interpretation of SMR Spectra Part I First-order Spectra,” by R. T. Jones. “Determination of Trace Quantities of Barium in Calcium Carbonate by *\toniic Absorption Syectrophotometry,” by F.J . Bano. “Analytical Uses of Insolubilised Enzyme Systcms as Illustrated by Horse- radish Peroxidase Covalently Bound to Polystyrene Beads,” by B. F. Iiocks “The Effect of Surfactants on the Colorimetric Determination of Tin,” by -\. Ashton. lioom 203 Haworth Building The University Edgbaston Birmingham 15 ; 6.30 p.m. XORTH WEST IIEGION i4nnual General Meeting followed by the &Address of tlw Retiring Chairman G. F. Longman. The University Salford ; 2.30 p.m. SCOTTISH REGION jointly with the Edinburgh and South East of Scotland “Analysis and Archaeology,” by H. McKerrell. Xational Museum of Antiquities of Scotland Edinburgh ; 5 p.m. NORTH EAST REGION Annual General Meeting. “An Assessment of the Analytical Techniques of ;Itoniic Spectrometry,” by Teesside Polytechnic Borough Road Middlesbrough ; 7 p.m. MICROCHEMICAL R’IETHODS GROUP London Discussion Meeting. Discussion on “Specifications for Reference Substances and Reagents,” intro- Imperial College London S.VV.7; 6.30 p.m. Even in g . 6 p.m. Section of the CS. Professor T. S. West. duced by E. Bishop. Printed by W Heffer & Sons Ltd Cambridge England

ISSN:0037-9697    

DOI:10.1039/SA97209BX049

出版商:RSC    

年代:1972

数据来源: RSC

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December I972 PROCEEDINGS OF THE SOCIETY Vol. 9 No. 12 FOR ANALYTICAL CHEMISTRY ANALYTICAL DIVISION CHEMICAL SOCIETY Reports of Meetings ORDINARY MEETING -4s Ordinary Meeting of the SAC/Analytical Division was held at 4 p-m. on Wednesday December 6th 1972 at the Scientific Societies Lecture Theatre 23 Savile Row London \f7.1. A lecture on “Analytical Applications of Molecular Complexes” was given by A. Townshend. The Chair was taken by the President Mr. C. Whalley. NORTH WEST REGION -4 JOIXT Meeting of the North West Region with the Carlett Park Chemical and Physical Society was held at 6.30 p.m. on Wednesday November 15th 1972 a t the West Cheshire Central College of Further Education Carlett Park Eastham. The Chair was taken by the Chairman of the North West Region Mr. G. I;. Longman.A lecture on “Myths and Legends in Analytical Chemistry” was given by Professor R. Belcher. WESTERN REGION -4s Ordinary Meeting of the Region was held at 2.30 p.m. on Friday November loth 1972 in the Chemistry Department; University College of Swansea Singleton Park Swansea. The Chair was taken by the Chairman of the Region Dr. J. D. R. Thomas. A lecture on “Analytical Aspects of Photoelectron Spectroscopy” was given by D. Bet teridge. MIDLANDS REGION L4s Ordinary Meeting of the Region was held at 2.30 p m . on Wednesday November 22nd 1972 in the Edward Herbert Building University of Technology Loughborough. The Chair was taken by the Vice-chairman of the Region Dr. D. Thorburn Burns. A lecture on “Enhancement of Chemical Measurement Techniques Using On-line Digital Computers” was given by Professor S.P. Perone. NORTH EAST REGION Ax Ordinary Meeting of the Region was held at 7 p.m. on Wednesday November 8th 1972 at the Royal County Hotel Old Elvet Durham City. The Chair was taken by the Chair- man of the Region Mr. A. E. Heron. A discussion on “Precision and Accuracy in Chemical Analysis” was introduced by K. A. Chalmers and A. A. Greenfield. .AN Ordinary Meeting of the Region was held a t 2 p.m. on Tuesday December 5th 1972 a t the Marton Hotel and Country Club Stokesley Road Marton Teesside. The Chair was taken by the Chairman of the Region Mr. A. E. Heron. The subject of the meeting was “The Analysis of Gaseous Effluents” and the following papers were presented and discussed “It’s in the Air,” by B. T. Leadbeater; “Field Methods for the Determination of Airborne Toxic Contaminants,” by E.C. Hunt; “Sampling and ,4nalysis of Airborne Contaminants to Assess the Effect on Health,” by B. T. Commins. 259 260 EUROANALYSIS I Proc. SOC. Analyt. Chenz. EAST ANGLIA REGION THE fifth Annual General Meeting of the Region was held at 3 p.m. on Thursday October 5th 1972 a t Spillers Ltd. Research and Technology Centre Station Road Cambridge. The Chair was taken by the Chairman of the Region Mr. N. R. Jones. The following office bearers were elected for the forthcoming year Chairman-Mr. J. S. Leahy. Vice-Chairman Mr. A. W. Hartley. Honorary Secretary and Treasurer-Mrs. D. Simpson Bakelite Xylonite Ltd. Research and Development Lawford Place Manningtree Essex C011 2NA. LWembe?f.s of Committee-Mr. A. G. Croft Dr. R. M. Dagnall Mr. N. K. Jones Rlr. N. Kirby and Rlr. J . I;. Sheridan. Mr. C. E. Waterhouse and Dr. A. N. Worden were appointed as Honorary Auditors. The Annual General Meeting was followed by an Ordinary Meeting of the Region at which the Chair was taken by the new Chairman Mr. J. S. Leahy. A lecture on “Forensic- Analysis in the Equine Field” was given by M. S. Moss. JOINT PHARMACEUTICAL ANALYSIS GROUP Ordinary Meeting of the Group was held at 2.30 p.m. on Wednesday Kovember 29tl1 1972 at the University of IVales Institute of Science and Technology Cathays Park Cardiff. The Chair was taken by the Chairman of the Group Dr. B. A. ivills. The meeting took the form of an open forum on “Questions and Answers in Pharma- ceutical Analysis.” The Panel members were C. A. Johnson L. E. Coles L. 11. Xtherden M. Ogden and J. Chissell.

ISSN:0037-9697    

DOI:10.1039/SA9720900259

出版商:RSC    

年代:1972

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260 EUROANALYSIS I -Proc. SOC. Analyt. Chenz. Euroanalysis I Heidelberg August 28th to September lst 1972 A T a time when European harmonisation has reached a stage of earnest endeavour at political and economic levels analytical chemistry took a significant step in this direction with the staging of the Euroanalysis I Conference at Heidelberg which was organised jointly by the -4nalytical Chemistry Division of the German Chemical Society the Section for Analytical Chemistry of the Royal Dutch Chemical Society and the Society for Ahalytical Chemistry the on-the-spot arrangements being the responsibility of the German Chemical Society. Subsequent to the setting up of the Joint Committee the Federation of European Chemical Societies came into being and it was then agreed that Euroanalysis I should be the first of a series of Conferences planned to be held at three-yearly intervals at various centres under the sponsorship of the Federation.In terms of European co-operation it represents a logical extension of the two highly successful joint meetings with the Royal Dutch Chemical Society held at Enschede in 1968 and London in 1970. Almost 450 delegates representing more than 20 nations assembled in the Physical Chemistry Building on the new science campus of the University of Heidelberg in the northern suburbs of the ancient city for a scientific programme compiled from submitted papers and specialist plenary lectures. Forty-six delegates were from the United Kingdom which contributed twenty eight of the one hundred and eighteen scientific discussion papers and three of the eight plenary lectures these being given by Professor R.Belcher Professor H. M. N. H. Irving and Dr. H. A. Willis. In addition to discussion papers that reported scientific advances over a wide front one session was devoted to the teaching of analytical chemistry in universities in which a plenary lecture and five papers were presented four of these being from the United Kingdom. Both in this dis- cussion and in the main body of the Conference simultaneous translation would have enhanced the value of the meeting and despite the obvious additional expense should be seriously considered for future Euroanalysis gatherings. The papers were followed by an open discussion. December 19721 EUROANALYSIS I 261 British delegates at the Oberbuvgeruneistev’s reception (L-R) Mr.D. W . Wilson iMr. R. Goulden Dr. I . L. M a w M Y . C . A . Johnson MY. S. Bance Professor R. Belcher Professov H . M . N . H . Irving Mv. C . Whalley (President) Pvofessov T . S . West MY. J . K . Foreman and Dr. D. Bettevidge The meeting was .marked by two formal functions a reception by the Oberburgermeister and a banquet at the Molkenkur restaurant high above the castle and overlooking the old city and the river Neckar. At the former the Presidents of the participating Societies were presented to the Oberburgermeister and each received a presentation volume of photographs of Heidelberg. At the banquet Dr. Kienitz spoke on behalf of the Organising Committee Dr. Visser on behalf of the Royal Dutch Chemical Society and Mr. Whalley President of the SAC proposed a toast to the hosts a t Heidelberg coupled with the name of Dr.Kienitz. That Euroanalysis I should be held at Heidelberg is entirely appropriate as its university is Germany’s oldest and is rich in academic tradition. Some instrumentally minded delegates will have been reminded of the birth of their profession on reading the plaque in the Haupt- strasse commemorating the discovery of spectroscopy by Bunsen assisted by Kirchhoff. Heidelberg and the Neckar valley also offer history and natural beauty in good measure and a varied social programme was arranged to take advantage of both. Dv. J . Visser (FAR LEFT) of the Royal Dutch Chemical Society in conversation with (L-R) MY. C. Whalley MY. D. TY. LYilson and MY. C. A . Johnson 262 JOINT PHARMACEUTICAL ANALYSIS GROUP [PYOC. SOC. AnaZyt. Clzem.Organised tours ranged from short tours of the historical parts of Heidelberg and visits to the local beauty spots to the more distant attractions of the Rhine and the Lorelei from which happily all delegates returned safely. On some days the more energetic delegates were to be seen rowing up (or was it down) the Neckar while others were taken by coach to various castles in the Neckar valley. Other items were a Mozart concert in Heidelberg Castle performed by the Heidelberg Kammerorchester and for the more scientifically disposed a visit to the analytical laboratories of B.A.S.F. at Ludwigshafen. The microchemical and physical instrument analysis laboratories were shown to the visitors who were afterwards entertained to lunch by B.A.S.F. The final day’s social programme was the already mentioned boat trip on the Rhine and on their return to Heidelberg delegates found that a grand firework display had apparently been laid on for their delight. Whether this was to speed their departure was never really ascertained but it certainly made a splendid finale to the week’s activities. Professor T. S. West with the President and Dr. D. Betteridge As an international forum and analytical conference Euroanalysis I was an undoubted success and the concept of European co-operation in analytical chemistry was fully estab- lished. During the meeting Budapest was selected as the venue for Euroanalysis I1 in 1975 where the consolidation of the achievements of Euroanalysis I can be anticipated with con- fidence.

ISSN:0037-9697    

DOI:10.1039/SA9720900260

出版商:RSC    

年代:1972

数据来源: RSC

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262 JOINT PHARMACEUTICAL ANALYSIS GROUP [PYOC. SOC. AnaZyt. Clzem. Joint Pharmaceutical Analysis Group THE Joint Pharmaceutical Analysis Group arose out of the informal Discussion Meetings held by the Department of Pharmaceutical Sciences of the Pharniaceutical Society of Great Britain. The Meetings were devoted to instrumental techniques and arranged in detail by the Science Committee (Pharmaceutical Analysis) now known as the Committee on Pharma- ceutical Analysis under its Chairman Dr. D. C. Garratt. The subsequent success of the Group was largely due to the vision and guidance of Dr. Garratt. Attendance at these Discussion Meetings was by invitation extended to senior pharma- ceutical analysts in Industry and Schools of Pharmacy. From the keenness to attend and the enthusiasm shown it became apparent that there was a need for a forum to be pro- vided specially for pharmaceutical analysts where they could discuss all aspects of their problems.At a discussion meeting held in October 1968 there was a unanimous decision from the ninety members present that action should be taken to explore how such a forum could be provided and in subsequent discussion there was equal preference for asking the Pharmaceu- tical Society to sponsor a scheme or for the Pharmaceutical Society and the Society for Analytical Chemistry to support a joint venture between them. A formal motion that “Representatives of the Pharmaceutical Society and SAC be asked to explore the setting up of an organisation to forward the interests of pharmaceutical analysts and to promote all aspects of quality control” was carried with a large majority.December 19721 JOINT PHARMACEUTICAL ANALYSIS GROUP 263 At a subsequent meeting of the Science Committee it was reported that the Royal Institute of Chemistry would be interested in such a group in view of its association with the Pharmaceutical Society through the Joint Diploma and Mastership in Pharmaceutical Analysis. The agreement to set up a Pharmaceutical Analysis Group sponsored jointly by the Pharmaceutical Society The Royal Institute of Chemistry and the Society for Analytical Chemistry was published in the Pharmaceutical Journal in June 1969. The Science Committee (Pharmaceutical Analysis) of the Pharmaceutical Society con- stituted a Steering Committee to initiate the group and prepared the original Group Rules which were finally approved by the individual Councils of the sponsoring bodies.The Group was inaugurated on January lst 1970 under the sponsorship of the Pharma- ceutical Society of Great Britain the Royal Institute of Chemistry and the Society for Analytical Chemistry. The registered membership on January lst 1970 was 380 the Royal Institute of Cheni- istry corporate members numbered 280 the Society for Analytical Chemistry 175 and the Pharmaceutical Society 102. The Committee of Management for the first 12 months was Mr. D. C. M. Adamson (Chairman) Mr. J. C. Deavin (Secretary) Dr. D. C. Garratt Dr. F. J. Bryant Mr. B. A. Forder Mr. C. A. Johnson Mr. G. F. Phillips Mr. R. Sinar and Dr. B. A. Wills. Dr. Bryant was nominated by the Society for Analytical Chemistry Mr. Forder by the Royal Institute of Chemistry and Mr.Johnson by the Pharmaceutical Society. The inaugural meeting was held on January 29th 1970 at B.M.A. House Tavistock Square London W.C.l and the title chosen for the meeting was “The R61e of the Analyst in Pharmaceutical Control.” Subjects for other meetings during the first year included “Microbial Contamingtion,” “Code of Good Manufacturing Practice” and “Analytical Ap- proaches to New Drug Substances.” It was agreed by the Committee of Management that at least one meeting each year should be held in centres other than London. ABOVE (L-R) aizd Dv. 1;. J . Bryant ( S A C representative). BELOW (L-R) Dv. B . A . Wills (Chairman) MY. J . C. Deavin (Honoravy Secvetavy) MY. D. C. M. Adamson and Dr. D. C. Gavvatt The Royal Institute of Chemistry withdrew at the end of 1971 and the Joint Pharma- ceutical Analysis Group is now jointly sponsored by the Pharmaceutical Society and the SAC/Analytical Division Chemical Society.264 COPRECIPITATION AKD ADSORPTIOK RULES [Proc. SOC. A nalyt. Chem. Registered membership on January lst 1972 was 465; average attendance a t Group Meetings is of the order of 120 a very encouraging figure. The officers for the current year are Dr. R. A. %’ills (Chairman) and Jlr. J. C. Deavin (Hon. Secretary). A new feature of the year’s programme is a forum at the British Pliarniaceutical Con- ference devoted to Pharmaceutical Analysis topics. The first such forum was held at Stoke- on-Trent in 1972 on the subject “The training of the analyst-what do we need and what are we getting?” The objects of the Joint Pharmaceutical Analysis Group are to encourage assist and extend the knowledge and study of Pharmaceutical Analysis and Quality Control by the holding of periodic meetings by the establishment and promotion of lectures demonstrations discussions or by any other means consistent with the aims and objects of the sponsoring bodies.Much importance is attached by the Committee of Management to arranging programmes of topical interest to members rather than formal programmes too far in advance and hence several of the meetings during the past 2 years have been devoted to repercussions of the Medicines Act on quality control matters. At the same time the educational r6le of the Group is recognised and meetings on instrumental techniques t q . high-pressure cliroma- tograpliy are held.Encouragement is given to young pharmaceutical analysts by pro- viding a meeting each year for the presentation or original papers; sutnmaries of papers presented are published in Proceedings. Considerable importance is also attached by the Committee to maintain the spontaneitj- and lively discussions of the earlier meetings. All meetings have been in the form of half-day sessions with three or four speakers at the most. Members have also taken part in meetings arranged by Regions or specialist Groups of the SAC/Analytical Division Chemical Society. The Group was fortunate to welcome Mr. A. G. Fishburn (Principal Inspector Medicines Inspectorate) to address the first Annual General Meeting on “The State as a Custodian of Drug Quality,” and Mr. H. S. Grainger (Secretary European Pharmacopoeia Commission) on the “European Pharmacopoeia” at the second Annual General Meeting. As well as a Chairman and Honorary Secretary the Group currently has a Committee of six elected members one member nominated by each of the sponsoring bodies and two co-opted members the latter being Dr. D. C. Garratt (founder member) and Ilk. B. A. Forder (formerly a member nominated by the Royal Institute of Chemistry). Membership is steadily increasing and the Group Committee confidently looks forward to the continued enthusiasm reflected by the high polls in each of the elections for the Group C om in i t t ee .

ISSN:0037-9697    

DOI:10.1039/SA9720900262

出版商:RSC    

年代:1972

数据来源: RSC

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264 COPRECIPITATION AKD ADSORPTIOK RULES [Proc. Soc. A nalyt. Chem. Coprecipitation and Adsorption Rules COPRISCIPITATION has long been an important procedure for the separation of radioactive materials and reference was made to the contribution of the late Otto Hahn to our under- standing of the underlying principles in a lecture presented to the Radiochemical Methods Group in November 1970 which appeared in the September 1971 issue of Pyoccedings.l Professor Icasimir Fajans* has since pointed out in a letter to the writer that the terms “Pre- cipitation Law” and “Adsorption Law” which appeared in Hahn’s book “Applied Radio- chemistry”2 and which were mentioned in the lecture constitute an incorrect use of the term “law” and that these so-called laws are in any event incorrect. I t is possible as indeed Fajans has implied that the word “law” crept into the text of “Applied Radiochemistry” owing to an inaccuracy in translation since Hahn in his original paper3 used the term “Satz” “Professor Emeritus Kasimir Fajans well known for his work i n connection \\+ith the Fajans - Soddy displacement laws (1913) and for his contributions to the theory of chemical bonding now resides in ,Ann Zrbor JZichigan 1J.S.A.December 19721 COPRECIPITATION AND ADSORPTION RULES 265 with the meaning “rule” or “principle” rather than “law.” Nevertheless it seems that lie believed for a time that his “laws” applied without exception. \!’hen it became evident that there were exceptions Hahn broadened the discussion of principles in his book but continued to use the terms “Hahn’s Precipitation Law” and “Hahn’s Adsorption Law.”2 The first “precipitation rule” was put forward by Fajans and Beer4 in 1913 and a siniilar “adsorption rule” by Paneth and Horowitz5 in 1915.The latter referred specifically to adsorption on pre-formed precipitates and the two were afterwards combined as the Fajans - Paneth “precipitation and adsorption rule” “adsorption of a particular ion by an ionic lattice is favoured when it forms a compound with the oppositely charged component of the lattice which is of low solubility,” to which Fajans and von Beckerath6 added a reference to the important influence of the charge on the precipitate. On the other hand Hahn and his coworkers showed that there are numerous instances in which a radioactive cation forms a compound of low solubility with the anion of the precipitate and is not coprecipitated.Their investigations in which single crystals of precipitates were examined radiographically led Hahn to identify true coprecipitation with the formation of mixed crystals. It seemed to him that phenomena of this type were sufficiently definable to be described by a new “pre- cipitation law.” Thus “when the separation of the unweighable amounts takes place within the precipitate and is practically independent of the conditions of precipitation- such as speed and excess of precipitate-the process is called a true coprecipitation with the mass of the precipitate and is accompanied by the formation of mixed crystals or of systems resembling mixed crystals.” This was the “precipitation law.” If however “the separation depends markedly upon the external conditions that influence the formation of the precipitate if the separation can be readily induced or repressed then the process is an adsorption deposition accompanied by the formation of more or less rever- sible adsorption compounds” and the following “adsorption law” would apply “an ion a t any desired dilution will be adsorbed by a precipitate if that precipitate has acquired a surface charge opposite in sign to the charge on the ion to be adsorbed and if the adsorbed compound is only slightly soluble in the solvent involved.” The wording of the “adsorption law” is not very different from the Fajans - Paneth - von Reckerath statements,6 but Hahn felt that his formulation represented a marked advance by defining the mixed crystal pheno- mena separately and by giving “clear recognition of the influence of surface extent and surface charge upon adsorption processes.” Fajansi pointed out however that ThB2+ is precipitated with silver chloride owing to adsorption rather than to mixed crystal formation and is adsorbed by silver iodate when the surface of the latter bears a positive charge and that the same happens with anions of certain dyes e.g.erythrosin anions are adsorbed by a negatively charged precipitate of silver halide. Other exceptions to the “adsorption law” were found by Hahn’s own co-workers and he came to the conclusion that it “has not the general applicability originally claimed for it” and then went on to set out the factors de- termining adsorption of different ions by a particular lattice taken from the paper of Fajans and Erdey-Gr6zi “(a) The solubility of the adsorption compound-The less the solubility the more readily do the ions become attached to the crystal lattice.(b) The size of the ions-The larger the ions to be adsorbed the more noticeable is the repulsion by similarly charged lattice ions and the less the adsorption. (c) The polarisation phenomena-The tendency towards adsorption increases with increasing polarising influence of the ions that are being adsorbed upon the oppositely charged ions of the lattice. To sum up when the adsorption compounds are very slightly soluble and when the ions involved have strong polarisation the foreign ions can be adsorbed even when the resulting precipitate has a charge of the same sign so that the Adsorption Law does not hold in such cases. ” Fajans for his part did not see the necessity for the Hahn laws and put forward insteadi an improved version of the earlier Fajans - Paneth Rule “(a) An ion in aqueous solution is readily adsorbed on the uncharged surface of a salt (aquivalent Korper) only if it forms a compound of low solubility or weak disso- ciability with the oppositely charged ion of the lattice.266 SELECTIVITY IN TRACE ANALYSIS [Pvoc. soc. Analyt. Chem. ( b ) The adsorption of a cation (anion) is increased (decreased) in the presence of adsorbed anions i.e. by a negative charge on the surface and decreased (increased) in the presence of other adsorbed cations i.e. by a positive charge on the surface. In either case the effect is greater the greater the adsorption of other ions.” The extensive investigations of Fajans and of Hahn and their collaborators were supple- mented in later years by the work of Khlopin and others,8 which confirmed that several factors are operative and this can lead in particular instances to behaviour that is contrary to that which would be expected from the coprecipitation and adsorption “rules.” In many instances coprecipitation involves isomorphic replacement by the ion of the niicrocomponent and incorporation into the host lattice usually by means of an ion-exchange meclianisni.For what is probably the majority of instances however coprecipitation occurs through surface adsorption. It would seem therefore that whilst Hahn was justified in drawing attention to the special mechanism of mixed crystal formation his “adsorption law” was rather unsatisfactory and that the adsorption phenomena were more adequately described by the rules of Fajans and Erdey-Gr~z. REFERENCES 1. 2 . 3. 4. 6. 7. 8. -3 . Spence K. P’YOC. Soc. Ayzalyt. Chew. 1971 8 182. Hahn O. “Applied Radiochemistry,” Cornell University I’rc‘ss lthaca X.Y. 1936. Hahn O. Rer. dt. chem. Ges. 1926 59 2014. Fajans K. and Beer P. Ibid. 1913 46 3486. Horowitz K. and Paneth F. Z . fihys. Chem. 1915 89 513. Fajans K. and von Beckerath K. Ibid. 1921 97 478. Fajans K. and Erdey-Grdz T. I b i d . 1932 A-158 97. Starik I. E. “Principles of Radiocheniistry,” Publishing House of the hcademy of Sciences (The quota- tions in the text which are attributed to Hahn are taken from this hook.) of the U.S.S.K. Moscow and Leningrad 1959.

ISSN:0037-9697    

DOI:10.1039/SA9720900264

出版商:RSC    

年代:1972

数据来源: RSC

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266 SELECTIVITY IN TRACE ANALYSIS [Pvoc. SOC. Analyt. Chem. Selectivity in Trace Analysis The following are summaries of fifteen of the papers presented at a Joint Meeting of the niorth West Scottish and North East Regions and the hlicrochemical Methods Atomic Spectroscopy Chromatography and Electrophoresis and Radiochemical Methods Groups held a t the University of Stirling on June 21st to 23rd 1972 and first reported in the July issue of Pjfoccediizgs (p. 145). Determination of Small Amounts of Aluminium in Steel by Atomic-absorption Spectroscopy BY R. H. JENKINS AND C. P. JOKES (Bi4isla Steel Covpovation Stvip M i l l s Division Research C c d v e Povt Talbot Glatiaovganslzive) AL~-MINIUM is normally added to mild steel for the purpose of deoxidation stabilisation against strain-ageing or both.Levels of aluminium found in such “killed” steels range up to about 0.1 per cent. the amount remaining soluble being normally in excess of 0.01 per cent. In contrast certain classes of electrical steel require controlled total aluminium contents below about 0.005 per cent. The distribution of aluminium between its soluble and insoluble forms is also important. The method described was designed specifically for the analysis of such electrical steels which are essentially iron - silicon alloys containing about 3 per cent. of silicon. Titrimetric polarographic and photometric methods suitable for normal killed steels were not sensitive enough for our purpose. However the mercury cathode - erioclirome cyanine R method of Scholes and Smith (now a British Standard Met1iud)l gave good results down to an aluminium content of about 0.002 per cent.when applied very carefully. Direct atomic-absorption spectroscopic methods also lacked the necessary sensitivity. On most instruments about 0.01 per cent. was the lowest limit obtainable when using a 2 per cent. steel solution although some workers have reported lower limits when using very large The method is applicable however to pure irons and many mild steels. December 19721 SELECTIVITY I N TRACE ANALYSIS ‘67 scale expansion facilities. It was therefore necessary to consider a pre-concentration step. The aim was to keep the number of chemical operations to a minimum taking full advantage of the selectivity of atomic-absorption spectroscopy. A method was developed for acid-soluble and insoluble aluminium to cover the range 0.0002 to 0.01 per cent.I t can be summzrised as follows. YI E TH o D- Dissolve 5 g of sample in hydrochloric acid and oxidise it with nitric acid. Evaporate the solution to dryness and dissolve the residue in hydrochloric acid. Filter the solution on a paper pad washing with hydrochloric acid and water to give a volume of 90 ml approximately 9 M in hydrochloric acid. Add 150ml of isobutyl acetate and extract once washing the organic laver with hydrochloric acid. Add 5 ml of standard iron solution (= 0.15 g of iron). Soluble aluminium-Add 0.5 g of potassium hydrogen sulphate evaporate the solution and dilute to 25 ml. Total aluminium-Ignite the pad and residue. Volatilise silica by adding 2 ml of hydro- fluoric acid and 0-5 ml of sulphuric acid and heating the mixture under an infrared heater.Fuse the residue with 0-5 g of potassium hydrogen sulphate dissolve the mixture in 10 ml of dilute hydrochloric acid and add the solution to the original filtrate. Evaporate the mixture and dilute to 25 ml. Prepare a reagent blank omitting the sample. Measure the absorbances of the solutions. Lamp current 11 mA Auxiliary lamp current 400 mA Wavelength 309.3 nm Damping “B” Spectral band width 0.33 nm Burner height 7 mm below optical axis Calibrate by using 0.25 g of pure iron in hydrochloric acid with added standard aluminium Suitable conditions with the Techtron AA4 instrument were- Solution uptake 5-2 ml min-l Nitrous oxide 18 p.s.i. Scale expansion 10 x (absorbance) solutions diluted to 25 ml. DISCUSSION- Solvent extraction was chosen as the simplest and fastest means of removing the bulk of iron from a steel solution.Experiments using 5-g samples of pure iron established optimum conditions for a single extraction; 0.05 to 0.15 g of iron remained in the extracted solutions. Enhancement of aluminium absorption by iron in a nitrous oxide - acetylene flame has been reported by several workers. Variable amounts of residual iron would be expected to lead to variable enhancement and consequent loss of precision. Scholes2 had shown that with his equipment the enhancement became constant when an iron concentration of about 1 per cent. m/V was reached. The effect was examined under our own conditions of nebulisation by using synthetic solutions. The results showed that enhancement increased with increasing levels of iron until a plateau was reached in the range 0.125 to 0.375 g of iron per 25 ml.Accordingly a fixed addition of 0.15 g of iron (in solution form) was introduced into the method after extraction to bring the iron content on to this plateau. Later a change of nebuliser showed that the flat enhancement plateau was not always obtained and experiments with a forced feed to the nebuliser showed that the viscosity of the solution was affecting its performance. This result underlines the need to check such effects whenever a change of conditions or transfer of a method to another instrument takes place. Contamination in the laboratory is a serious problem at these low levels of aluminium. Initially unacceptably high blank values (about 90 pg of aluminium) were obtained. The contribution of each stage of the procedure was isolated and quantified.The blank was finally reduced to a consistent value of 35pg of aluminium by reserving batches of liigh- purity hydrochloric acid using the minimum volume (2 ml) of high-purity hydrofluoric acid storing filter discs in hydrochloric acid until immediately before use and reserving glassware for this work only. Aluminium recovery tests were carried out on the complete procedure by using high- purity iron and additions of aluminium equivalent to 0.005 per cent. Recoveries of 100 to 102 per cent. were obtained. 268 SELECTIVITY I N TRACE ANALI-SIS IProc. SOC. Analyt. Chettz. The performance of the method can be expressed as follows. Solublc aluminium per cent. r 7 7 i - - 7 Mean of 12 Standard Mean of 12 Standard Sample determinations deviation detcrniinations deviation Insoluble aluminium per cent A 3 O silicon steel (B.C.S.317) 0.00036 0.000036 0.0022 0*00022 Plain carbon steel 0.00253 0.00015 Reproducibility of blank- Mean of 6 determinations . . . . . . 0.00075 per cent. of aluminium Standard deviation . . . . . . . . 0.00003 per cent. of aluminium COXCLUSIONS- The determination of trace amounts of aluminium in steel has traditionally been one of the most difficult analytical exercises calling for extreme care and patience on the part of the analyst. Complicated and painstaking separations have been required to obtain the necessary selectivity. ,Itomic-absorption spectroscopy has simplified the determination although it is still necessary to carry out some chemical operations before instrumental measurement. However a procedure which works well in practice has been produced to cover the range 0.0002 to 0.01 per cent.of aluminium in 3 per cent. silicon - iron alloys and pure iron. The method is used to standardise samples for calibration of spectrographs and for the analysis of thin sheets that cannot be accepted by the spectrograph. REFERENCES 1. British Standard Handbook No. 19 Aluminium Method No. 2 British Standards Institution 2. London 1970. Scholes P. H. Proceedings of 21st BISRA Chemists Conference 1968 pp. 7-15. The Use of Separation Procedures for Atomic-absorption Spectroscopy in Clinical Chemistry BY H. T. DELVES (The Hospital f o v Sack Chaldren Great Ovnzoizd Street Londo12 W.C. I ) ,ALTHOUGH the inherent selectivity of atomic-absorption spectroscopy is sufficient for most clinical analyses certain applications require the use of separation procedures.For example solvent extraction procedures are used for the determination of trace amounts of metals in biological samples to eliminate interferences and to concentrate the analyte whereas ultra- filtration and electrophoresis can be used to provide more detailed information by separating the various metal-containing species in a sample and these species are then determined separately. Some examples of the use of these separation procedures are discussed below. SOLVEKT EXTRACTION- The atomic-absorption determination of chromium in ashed samples of whole blood is subject to severe interference from the relatively high concentration of iron in the sample. The depression of the chromium signal by iron in an air - acetylene flame can be readily removed by the addition of releasing agents such as ammonium chloride1 or by using a fuel- lean flame.2 Both techniques result in some loss of sensitivity the first due to dilution of the sample by the addition of the reagent and the second to the use of non-reducing flame con- ditions.As the normal concentration of chromium in blood about 0.05 pg ml-l is near to the atomic-absorption detection limit any losses in sensitivity should be avoided. Iron(II1) can be selectively extracted from chromium(II1) in 2 N hydrochloric acid solutions by using cupferron and isobutyl methyl k e t ~ n e . ~ The chromium(II1) oxinate can then be formed by heating with 8-hydro~yquinoline~ and the complex extracted into isobutyl methyl ketone. The increase in sensitivity due to the organic solvent effect is 3.9 times that obtained in aqueous solutions and further increases are obtained by concentrating the complex into small volumes of solvent.December 1972; SELECTIVITY I N TRACE ANALYSIS 269 Selective solvent extraction can be used for the multi-metal analysis of small samples of By using a six-stage extraction scheme twelve metals can be determined in 2-nil samples of blood with sensitivities some 5 times that obtained by direct analysis of (larger volumes of) aqueous solutions. ULTRAFILTRATIOK- The procedures mentioned above only give information about the gross metal concen- trations in the blood sample whereas certain clinical investigations require knowledge of the concentrations of various metal-containing species in the sample.For example calcium is present in blood in three forms that are in equilibrium ionised calcium complexed calcium and protein-bound calcium. Recently Putman5 has investigated the concentrations of all t h e e species in samples of plasma taken from young children with congenital heart defects who were undergoing cardiopulmonary bypass surgery. She separated the ionised and complex species from the protein-bound calcium by ultrafiltration. Atomic-absorption spectroscopy was used to determine the total calcium in the plasma and in tlie ultrafiltrate. The ionised calcium in the ultrafiltrate was determined by solution spectrophotometry by using ammonium tetramethyl murexide. The concentration of protein-bound species w a h calculated by difference between the concentrations of total ultrafilterable and the total plasma calcium.The concentration of the complexed species was determined by difference between the concentrations of the total ultrafilterable and the ionic species. Putman found significantly increased concentrations of ionised calcium in samples taken from the young cardiac patients compared with samples taken from a control group of children. These increased concentrations were not related to the total calcium concentrations which empha- sises the importance of studying the concentrations of the various species rather than the gross concentrations of tlie metal. ELECTROPHORESIS- Another example of the analysis of different metal-containing species in a given sample is the determination of metals in the various protein fractions in samples of plasma taken from cliildren with leukaemia.It has been observed that in childhood leukaemia before treatment the gross plasma concentrations of copper were significantly higher than normal whereas those of zinc were lower and that the concentrations of both metals returned to normal values when the children were on treatment and in remission.6 The copper to zinc ratio discriminated well between the untreated and treated patients. I t was decided to investigate the concentrations of these metals in more detail and to determine their concentrations in the xwious protein fractions in plasma. Electrophoresis on cellulose acetate has been used t o separate the various protein fractions (albumin al- a,- p- and y-globulins) and atoniic- absorption spectroscopy was used for the determination of the metal.The various protein fractions were cut from the cellulose acetate strip and placed into a carbon-tube furnace tlirough an 8 x l-mm rectangular slot cut in the tube. The organic material was ashed at a low power dissipation (4 V a t 150 A) and the metal atomised at high power (8 V at 300 A). The preliminary results indicated that large increases in copper are found in the a2- p- and y-globulin fractions of the untreated leukaemic patients. As copper is reportedly carried by caeruloplasmin which is an a,-macroglobulin further work is necessary to confirm these results. Future investigations of the changes in the concentrations of metals in disease states will include tlie determination of the various metal-containing species present in body fluids and tissues and not simply the determination of the gross concentration of the metal in whole samples.Such investigations can be carried out with very small samples by atomic- absorption spectroscopy because of the high sensitivity of flameless atomisation systems. The information that these investigations would yield will provide clinical chemists with a greater understanding of the biochemistry of those diseases associated with changes in the trace concentrations of metals. REFERENCES 1 . 2 3. 1. 5. ti. Barnes L. Analyt. Chew. 1966 38 1083. Price W. J . “Analytical Atomic Spectroscopy,” Heyden & Son Ltd. London 19i2 p. 89. DellTes H. T. Shepherd G. and Vinter P. Analyst 19i1 95 260. Moeller T. Ind. Engng Chern. Analyt. E d n 1943 15 316. Putman J . M. M.Phzl. Thesis University of London 1971. Delves IT.T. Alexander F. W. and Lay H. BY. J . Haewaat. in the press. 270 SELECTIVITY IN TRACE ANALYSIS LProc. SOC. ,4 ?zaZyt. Chewz. Some Factors Governing Limits of Detection in Separation Systems BY R. R. GOODALL (Analytical Development Section Pharmaceutical Department Imperial Chemical Ivldtistvirs Limited Pharmaceuticals Division Macclesfield Cheshire) THE distribution of a solute between two liquid phases is a basic concept that can be expressed in terms of distribution isotherms as shown in Fig. 1. This figure was first published in 1954,l and the graphs are now relevant to separations on thin-layer chromatograms or on high- pressure liquid chromatograms. (a 1 Linear I 0 ) r 8 0 8 0 Ii 0 c = Concentration in solvent (i.e. the flowing phase) - c = Concentration in flowing phase -+ Fig.1. (a) Distribution isotherms of a solute between flowing and static phases as in a chromatographic column and ( b ) the corresponding shape of the chromatographic bands Three forms of distribution isotherm can be distinguished-linear Q = kC ; Langmuir Q=- klC * and Freundlich Q = kCn. Q is defined here as concentration on the sorbent 1 + k,C' but the isotherms are generally applicable e g . to equilibria between non-miscible phases such as an aqueous buffer in contact with an extracting solvent. Before considering a mixture of solutes it is desirable to establish the isotherm of each component over the appropriate range. From these it can be concluded that solutes following linear isotherms present no complications as in admixture the distribution ratios do not alter with changes of concentration so that the separation factor K,/K, etc.does not change. Fortunately many of the substances chromatographed have followed or have been made to follow this rule by suppression of ionisation etc. Solutes that follow Langmuir or Freundlich isotherms tend to be distributed more towards the static phase at lower concentration. Thus the relative distribution ratios of A and B can vary according to the concentration of each present and the separation may become difficult especially for Freundlich-type distributions. Those who have to design chromatograms try to establish conditions for linear distribu- tions. For example the addition of excess of sulphuric acid suppresses the tailing of carboxylic acids in partition chromatography.2 Strongly ionised compounds such as sulphonates or quaternary ammonium salts are not amenable to this subterfuge.The lower half of Fig. 1 shows the shape of the chromatographic band (or counter-current distribution) corresponding to each type of isotherm. The Langmuir type extends back for some distance and the Freundlich type tails back exponentially towards the origin. December 19721 SELECTIVITY I N TRACE ANALYSIS 27 1 The prognosis for the separation of mixtures should now be understandable by reference to the isotherms representing each component. Assuming that no interactions occur a yeparation by thin-layer or high-pressure liquid chromatography of all proportions of A from admixture with B would be predicted under the linear behaviour if K,/K is greater than 1.1 to 1.2. In those mixtures of A and B that show the Langmuir and Freundlich isotherms separa- i ions are likely only if the isotherms are very widely separated.The separation of trace amounts of A from B or B from A would seem to be quite unpromising by the usual technique. Tiselius3y4 proposed a very elegant method for the chromatographic fractionation of mixtures that show Freundlich distribution isotherms termed displacement development. The mixture on the column is developed not by a solvent but with a solute D in solution. D is chosen so that it has a higher affinity for the static (Q) phase than any of the components A B or C of the mixture. The continuous advance of D displaces the mixture from the static phase. Fig. 2 illustrates the use of distribution isotherms for the design of a hypothetical dis- placement chromatogram.A suitable developing solute D is chosen such that a line from some part of the D isotherm to the origin intersects the B and C isotherms. Tiselius demon- strated that in a column B and C will be displaced by developing with D in solution and that they will travel a t the same rate as the advance of D. In order to reach this equilibrium the distribution ratios of B and C have to adjust themselves so as to be identical with that of D. B and C naturally achieve this by suitable changes of concentration in the two phases. A travels too fast down the column to fall under the influence of D and makes a rapid exit. In Fig. 3 the histogram of concentration against distance down the column shows A ahead and B and C as a contiguous pair having taken up the characteristic equilibrium concen- trations dictated by CD.Concentration in flowing phase CB CC cD Concentration in flowing phase Fig. 2 . The use of distribution isotherms Fig. 3. Idealised shape of a for the-design of a displacement chromatogram. The intercept of the line joining the developer D (QDCU) to the origin cuts the isotherms of B and C a t CB and CC which define the equilibrium concentrations reached by these components in the chromatogram (Fig. 3). h does not come under the influence of the developer D displacement chromatogram- obtain- able by using the developer concentra- tion CD as illustrated in Fig. 2 The elegance of the method lies in the predictability of separation conditions and in the capability of resolving a mixture of closely related compounds such as isomers that both follow Freundlich isotherms and where the separation factor is less than 1.05 1.The method has been rarely used on columns in the past because a very high standard of technique is 272 SELECTIVITY IN TRACE ANALYSIS [Proc. SOC. Analyt. Chem required. Now that this is available in high-pressure liquid chromatography engineering further developments may follow. For a further discussion of displacement development see reference 5. It is not always necessary to set up the isotherms when the analyst can envisage a series of rapid trial and error chromatograms as in microscope-slide thin-layer chromatography. From the appearance of the results the changes that are required in C may be inferred as in the following example. Three foodstuff colours amaranth azogeranine and guinea green have been selected because as salts they would not be expected to follow linear isotherms.These were readily tested on 3 x 3-inch silica gel G plates which might be regarded as a trace analysis in the context of the present symposium. Fig. 4 shows that when developed with ethanol amaranth stays at the origin azogeranine tails back to the origin and guinea green shows three different types of behaviour. Fig. 4. Foodstuff colours. Left to right-amaranth azogeranine guinea green amaranth azogeranine guinea green. Loads 2 pl M 2pg on silica gel G. Chromatogram developed with ethanol Fig. 6. Chromatogram as in Fig. 4 but developed with 0.1 per cent. methane- sulphonic acid in ethanol Fig. 5. Chromatograms as i n Fig. 4 but developed with 1 per cent. methane- sulphonic acid in ethanol Fig.7. Limits of detection of fluorescent spots. Volumes of 1 5 and 10 p1 a t concentrations of 1 and 10 ng p1-1 were applied to silica gel G and photographed under 366-nm irradiation. Q = quinine hydrochloride M = mepacrine hydrochloride and F = sodium fluorescein I)ecember 1972 SELECTIVITY I N TRACE ANALYSIS 273 From the author’s experience of displacement techniques in columns sulphuric acid or niethanesulphonic acid seemed to be likely developers and so both were tried at two different levels of concentration in ethanol i.e. 1 and 0.1 per cent. Sulphuric acid was unpromising. I t can be seen in Fig. 5 that the 1 per cent. methanesulphonic acid development gives asatis- factory displacement with each different colour driven ahead of the developer front and shows contiguous bands presumably of secondary impurities.The fact that the level of concentration C, is critical is confirmed in Fig. ci where the 0-1 per cent. methanesulphonic acid developer displaces guinea green but not the others. The developer front is at the level where the indicator streaks (i,i) change colour. The discussion of limits of detection in continuously monitored systems cannot be dealt with adequately in this paper but has been covered in an excellent paper by Heiftje.6 Some consideration of the factors that govern limits of detection by visual methods is appropriate. In colour-forming sprays on to thin-layer chromatographic plates the limit for less cliromogenic reactions such as the iron( 111) hydroxamate complex of penicillin is probably r)f the order of g. 1 he very sensitive ninhydrin reaction of amino-acids may attain the lo-’ g level.These estimates are based on the use of spot diameters of from 2 to 3 mm on 250-pm layers. The sensitivity of detection can be raised by a factor of from 2 to 5 simply by viewing tlie spots by transmitted as opposed to reflected light. This is the so-called “hyperchromic effect,” in which the absorbing path length is extended by light scattering. The detection of coloured substances depends on the specific absorbtivity which again is subject to wide variation. The loads of the foodstuff colours discussed above were 2 p g in 2 pl and probably 0.2 pg could be detected on the author’s 3 x 3-inch thin-layer cliromato- grapkic plates. The limits of detection of fluorescent spots have been tested as shown in Fig. i although these have not been subjected to spreading bv chromatographic development.The three fluorescent compounds quinine hydrochloride (Q) mepacrine hydrochloride (M) and sodium fluorescein (F) are shown a t loads of g in a l-p1 volume and these can readily be seen by illumination at 366 nm. Thus it is possible to detect fluorescence at about two orders of sensitivity higher than colour. The effect of varying the volume of the load from 1 to 5 to lop1 is also demonstrated. Such comparisons are easy to perform so that the analyst can select conditions to suit his own equipment but he must be careful to minimise diffusion. ,. and REFERENCES 1. 2. 3 4. - Endeavour 1952 11 No. 41 8. 5 6 Goodall R. R. J l R. Inst. Cheun. 1954 466. Isherwood F. A. Biochevn. J . 1946 40 688. Tiselius ,4 A r k . Kern. iWzneval. Geol 1943 16A No 18 20. Strouts C. R. N. Edztor “Analytical Chemistry The Working Tools,” Volume 11 Clarendon Press Heiftje G. M. Aizalyt. Chein. 1972 44 91.2. Oxford pp. 992-995.

ISSN:0037-9697    

DOI:10.1039/SA9720900266

出版商:RSC    

年代:1972

数据来源: RSC

摘要:

Ikcember 1972 SELECTIVITY I N TRACE ANALYSIS 273 2-Methylated 2-Methyl-8-quinolinols as Solvent-extraction Agents BY F. R. HAB.4 G. H. I ' h Z I A ~ D D. A. PAXTOKY (Dspnvlment of Metalluvgy Imperial College of Science and Technology Lcndon SW7 2BP) SOME 15 years ago a solvent-extraction technique involving the use of 2-methyl-8-quinolinol as a clielatiiig agent for the second metal was devised in these laboratories (D. A. Pantony and I;. L. Selfe unpublished work) to carry out the analyses of binary aluminium alloys deposited in approximately 50-pg films on glass slides. Nickel copper magnesium or beryllium was quantitatively extracted under suitable pH conditions into a second phase of chloroform or chloroform containing methyl Cellosolve by means of the reagent and then with 8quinolino1 the aluminium was similarly extracted.Even when using appreciable excesses of sequestering agents such as tartaric acid the results proved to be accurate and by direct spectrophoto- metry precisions as standard deviations were about -+0.2 pg which with correctly chosen sample and spectrophotometric parameters gave coefficients of variation as low as k0.3 per cent. Such good reproducibilities are in keeping with those generally obtained with solutions of chelates of 8-quinolinols in many organic solvents that obey the Beer - Lambert law 274 SELECTIVITY IN TRACE ANALYSIS [PYOC. Soc. A?zaZ_vt. Chem. remarkably closely over a wide range of absorbances.]j2 An informative example of the quality of the method was the demonstration that the aluminium - magnesium “alloy” was exactly A1 - MgO as might be expected from thermodynamics applied to the deposition conditions.It would obviously be desirable to extend such a rapid elegant and precise method to the determination of aluminium in samples of greater commercial interest to the metallurgist. However the application of the method to ferrous and non-ferrous ores and alloys invariably gave extremely high results for aluminium for reasons that were not immediately obvious except that the pre-extraction of a large bulk of other elements was not efficient under the wide range of conditions that were investigated. An extensive investigation* of the increasingly methylated series 8-quinolino1 2-methyl- 2-ethyl- 2-isopropyl- and 2-t-butyl-8-quinolinol was commenced- OH where R =-H -CH, -CH,CH, -CH(CH,) or -C(CH,),.I t was argued that the increasing inductive effect along the series would slightly enhance the affinity of the reagents towards protons and metal ions but that steric hindrance would increase sharply for ions of small ionic radius at the insertion of the 2-methyl and 2-t-butyl groups. Owing to free rotation the 2-ethyl and 2-isopropyl compounds would behave sterically in a manner essentially similar to the 2-methyl homologue which as is well known does not form insoluble octahedral complexes with aluminium( 111). These effects can be demonstrated in a highly diagrammatic manner as shown in Fig. 1. The general idea of this scheme received confirmation from scale atomic models of chelates from dissociation and protonation constants of the reagents and from dissociation constants of certain metal chelates obtained from solvent-extraction studies.3~4 Of several possible synthetic methods only two proved to be of any real \ d u e particu- larly for the higher homologues.The first,3 involving the synthesis of the unsaturated aldehyde followed by a Doebner - von Miller coupling with o-aminophenol was unequivocal but over-all yields were low- HCI ~ a + H?O R CH ‘R NH2 OH However it provided reference compounds up to the isopropyl homologue for the second method,* which involved direct and 30 to 35 per cent. efficient 2-alkylations of 8-quinolinol with lithium alkyls. The site of the alkylation and the identity of the compounds were further confirmed physically especially by proton magnetic resonance used in an elegant quantitative and qualit at ive diagnosis. The physical chemistry of the extraction processes will be reported elsewhere but possible analytical applications in aluminium determinations are demonstrated by the results on the alloy B.C.S.233 (A1 6.98 Fe 51.15 Ni 11.22 Co 23.72 Cu 5-09 Ti 0.79 Mn 0-24 per cent.) performed under similar conditions- Reagent 2-Pl’lethyl-8-quinolinol 2-Ethyl-8-quinolinol 2-Isoprop yl-8-quinolinol Aluminium per cent. 7.84 7-52 6.95 In these extractions it does appear that the reagent to metal and sequestering agent to metal concentration ratios are critical in achieving quantitative results. Large excesses of * \Vith financial aid from the United States Air Force under Contract F61052 67 C. December 19721 SELECTIVITY I N TRACE AKALYSIS 275 e.g. tartaric acid and the use of exclusively perchlorate media cause marked reductions of extraction especially of iron( 111) ions for both thermodynamic and kinetic reasons.Un- doubtedly the experimental conditions could be improved still further and it is possible that the lower homologues can give the quantitative results obtained with 2-isopropyl-8-quinolinol under the as yet undiscovered correct conditions. In any event it is important to realise that with the critical nature of the tartaric acid to metal concentration ratio the first equilibration and nieclianical separation of the two phases must be made as efficient as possible and little is gained by successive extractions in which by removal of metal ions from the aqueous phase the ratio becomes so high that extractions become inefficient. I \\ Inductive + Steric -7 \ '.\. Steric \ -7 1 I I I I 0 1 2 3 4 Number of C-atoms in 2-substituent Fig. 1 . Diagrammatic representation of the variation oi inductive and steric effects with the number of carbon atoms in the 2-substituent of 2-alkyl-S-quinolinols The 2-t-butyl homologue is undergoing investigation of its extremely interesting proper- ties which will be reported elsewhere. Early observations however show that ( a ) it forms stoicheiometric insoluble chelates with only divalent ions i.e. with planar configuration while the octahedral chelates of trivalent ions are not formed ( b ) extractability veysus pH graphs are significantly shifted to higher pH values and (c) the kinetics of ligand exchange are slower. \Yith this reagent it may be possible to selectively extract at least iron (ionic radius 0464 nm) as well as aluminium (ionic radius 0.05 nm) owing to the large steric effect of the bulky 2-t- hutyl group.REFERENCES 1. i. > 3. 4. Blair A. J. and Pantony D. .I. Analytica Claim. A d a 1956 14 545 Haba F. R. P h B . Thesis University of London 1966. Iiazi G. H. Ph.D. Thesis University of London 1971. ~ _ _ - JZ R. Sch. Mines 1955 4 6. 276 SELECTIVITY IN TRACE ANALYSIS Auto-oxidation of Stilbenes BY P. R. A. SPAHR AND E. V. TRUTER [Proc. SOC. Aizaljlt. Chcvz. (Textile Chemistry Labovatory Leeds Univevsity Lecds LS2 9 J T ) FLUORESCENT whitening agents for textiles are based mainly on 4,4’-diaminostill)eiie. Their function is to eliminate the yellow tint of “white” fabrics but eventually tliey fail to function properly because they undergo slow oxidation to yield yellow substances.The clieniical pathway of the auto-oxidative process and some related chemical reactions have been elucidated by a study of 4,4’-diacetamidostilbene. Chrom~~tograpliy was performed in the dark in lined tanks. The adsorbent was alumina G F and tlie main eluerits were solvent A 1,2-dichloroethane - benzene - acetic acid (4 + 1 + l) and sol\-cnt B perchloroethylene - benzene - acetic acid (4 + 1 + 1). 4,4’-Diacetamidostilbene exists in czs and tifmzs forms which are readily resolved by solvent B. On examination of freshly prepared chromatograms in long-wavelengtli ultra- violet light (366 nm) the ti/mzs form is visible as a fluorescent spot on a dark background; the cis form is not visible. In short-wavelength ultraviolet light (254 nm) the cis form is visible as a dark spot on a fluorescent background; the t v m s form is not visible.After being irradiated for a few seconds both forms are converted into mixtures so that both component5 lwcome detectable in radiation of both wavelengths. For confirming that a substance i\ able to undergo pliotoisomerisation a sample containing both isomers is chromatographed in the dark in solvent B; the chromatogram is then irradiated for 10 minutes with ultraviolet light and the clironiatogram is eluted in the dark in the second dimension vith the same solvent. On the resultant chromatogram isomerisable compounds show a characteristic square of four spots. Detailed examination of samples of acetylated 4,4’-dianiinosti!bene which liad been prepared by different methods revealed that the expected diacetyl derivative wa\ often contaminated with hyperacetyl derivatives.Examination of a sample for which tlie analysis indicated 3.25 acetyl groups per molecule by the method designed to detect photoisonierisa- tion showed that it contained the t y a m and cis forms of the diacetyl derivative (Fig. 1 A4 and B) the tvaizs and cis triacetyl derivatives (C and D) and the tvnus and cis tetraacetj.1 deriva- tives (E and 1;). The hyperacetyl derivatives are unstable to irradiation with ultraviolet energy; they are relatively stable to recrystallisation. Their infrared spectra show that tliey are enol-acetates and not AT-diacetyl derivatives. A sample of 4,4’-diacetamidostilbene adsorbed on filter-paper was exposed in the Xenotest apparatus for 100 hours. After the oxidised sample had been extracted with methanol it was examined chromatographically.In solvent A it was resolved into eight components and a long fluorescent streak (Fig. 2 sample 3). Component G corresponded to authentic 4-acetamidobenzoic acid (sample 5) ; component D corresponded to authentic 4-acetamidobenzaldehyde (sample 2) ; component E was unchanged starting material (sample 4). The oxidised sample did not contain 4-acetamidobenzyl alcoliol (sample 1). Components G and D were isolated by preparative thin-layer chromatography and each gave satisfactory analyses (m.p. and mixed m.p. elemental analyses infrared spectra) for kxetamidobenzoic acid and 4-acetamidobenzaldehyde. Component C was obtained in good yield from 4-acetamidobenzaldehyde. I t proved to be the aldehyde Schiff’s base which is formed by condensation of two molecules of acetamido- benzaldehyde with the elimination of acetic acid.Further condensation leads to a series of Schiff’s polybases having aldehydic and through subsequent oxidation carboxylic acid end- groups. The series of polybases form the fluorescent streak (Fig. 2) which changes in hue from blue to yellow on passing from front to origin. In daylight tlie colours of the Schiff’s bases range from yellow to dark brown as their extent of polymerisation increases. Components F and H have not been fully identified but they are likely to be the mono- and the di-Schiff’s bases with carboxylic acid end-groups. Schiff ’s bases are easily distinguished from stilbene derivatives having the same hue of fluorescence because the former do not undergo photo- isomerisat ion. Components A and B were found to be artefacts that had been generated during the recovery of the oxidised sample from the filter-paper with methanol.They proved to be the methylacetals of the mono-Schiff’s base aldehyde and of acetamidobenzaldehyde respectively. With other alcohols the expected acetals were formed. Thin-layer chromatography was the main analytical technique used. Tlecember 19721 SELECTIVITY I Y TRACE ANALYSIS 277 Photo-oxidation of 4,4'-diacetamidostilbene first yields 4-acetamidobenzaldehyde ; most of the aldehyde is oxidised to 4-acetamidobenzoic acid which is not oxidised further but some of it undergoes condensation polymerisation to yield Schiff's polybases which become pro- gressively darker as their relative molecular masses increase. The photo-oxidative pathway is exactly the same in solution in acetone.In the dark liowever stilbene derivatives are stable at 60 "C for up to 18 niontlis. Hence the formation of yellow substances is exclusively a photo-oxidative process. Fig. 1 . Chromatogram of di- tri- and tetra- acetyl derivatives of 4,4'-diaminostilbene I X 5 Fig. 2. Chromatograni o f photo-oxidised diacetaniido- stilbene and reference com- pounds. Open areas represcnt fluorescent components shadctl areas represent dark com- ponents; for details see text 4,4'-Diacetamidostilbene-2,2'-disulphonic acid and Leucoplior (a ditriazinylstilbene- disulphonic acid) undergo photo-oxidation by the same route as diacet amidostilbene and they yield the corresponding products. Thus the former yields 4-acet amidobenzaldehyde-2- sulphonic acid 4-acetamidobenzoic acid-2-sulphonic acid and a series of sulphonated Scliiff's bases.REFERENCE Of these the first product has recently been identified.1 1. Seiber P. K. and Needles H. L. Chew.. Cornrnuvz. 1972 209. 258 SELECTIVITY IX TRACE ANALYSIS LYvoc. SOC. Aizalyt. Chem. Selectivity in the Application of Activation Techniques Based on the Measurement of Prompt Radiation Emitted During Charged-particle Irradiation BY T. R. PIERCE (.4 nalytacal Sciences Diviszon Atomic E+zevgy Research Establishment Harwell Dzdcot Bevkshzw) THE most familiar of the analytical techniques based on the use of accelerated positive ions is probably that of conventional charged-particle activation analysis which exploits the measure- ment of the induced radioactivity produced as a result of reaction of the charged-particles with the constituents of the sample.The half-lives of the active species formed are generally sufficiently long to permit the emitted radiation to be counted after the completion of the irradiation often after chemical processing of the sample. During charged-particle irradiation however other radiations are produced very rapidly after interaction of the charged particles which can ofler the basis of analytical measurement but these so-called prompt radiations must be measured while the irradiation is in progress in the presence of machine background and chemistry cannot be used to isolate the required activity from all others produced in the sample between irradiation and counting. Although prompt-radiation techniques have not so far received much attention from analysts they do offer a more extensive range of analytical techniques than is available solely by measurement of induced radioactivity and different methods can be selected to match the needs of specific analytical problems.Prompt radiations measured are ( a ) y-radiation ( b ) charged particles and neutrons from nuclear reactions (c) elastically scattered particles and (d) X-rays. Techniques were initially devised to provide gross information about the elemental content of the sample irradiated but more refined methods have since been developed that permit (i) information to be obtained from small volumes of sample by irradiating with small-diameter ion beams (ii) examination of sub- surface element profiles by using resonance and other effects that can be made depth sensitive and (iii) structures of some single crystals to be investigated by making use of the effect of channelling.Prompt y-radiation can result from the de-excitation of excited nuclcar states produced by a variety of nuclear reactions and as the energies of tlie y-rays are characteristic of the transitions that occur emitting nuclei can be identified by examination of the accumulated spectra; established methods of y-ray spectroscopy can often be used to calculate the contribu- tions of several lines from different sources to complex spectra. Absorption of y-rays is likely to be less troublesome than for X-rays and inter-element effects are absent. The excited y-lines will depend upon the irradiating particle and energy so that carbon has been deter- mined by the following reaction~-~~C(p,y)l~N (2-3) 12C(p,p’)12C (4.43) 12C(d,p)13C (3.09) Met.There is therefore some scope for designing experiments to give the most acceptable combination of y-lines from a particular sample. Most of the light elements have been determined by measurement of prompt y-radiation and techniques have been extended to a few heavier elements. Charged particles and neutrons resulting from nuclear reactions also have characteristic energies and can be counted to provide the basis for analytical determination but charged- particle measurement has been favoured because of the simpler methods that are available for energj- analysis and detection. A major attraction of particle group measurement is the low natural particle background which permits very sensitive techniques to be developed.Again light elements have primarily been determined measuring particles from reactions such as loB (d p) l1 B 2C (d p) 13C 15N (p a ) 12C 160 (d p) 1 7 0 19F (p a ) 160. The energy of an elastically scattered ion depends upon the mass of tlie scatterer at a constant scattering angle so that energy analysis of the scattered particles can provide information about target composition and as mass resolution is better at large scattering angles backscattering geometry is usually chosen for analytical measurements. Elastic scattering is best applied to the determination of thin films of heavy elements present on lighter substrates as the particle scattered from the film will be more easily counted if there is 110 energy overlap with those scattered from the substrate. Analytical techniques based on the measurement of X-radiation have an established place in research and industrial usage but normally exploit X-ray or electron excitation.Charged- particle excitation offers the advantage of low bremsstrahlung background leading to good 12c (;H 3 ,p)14N (1.64) the figures in parentheses giving the energy of the detected y-line in December 19721 SELECTIVITY IN TRACE AKALYSIS 279 signal to background ratios and an operational attraction in that high X-ray yields are achieved at particle energies used €or other prompt radiation measurements. Detection of X and other radiations can therefore often be combined in the same experiment provided that appropriate detector target and data acquisition systems are available thus reducing demand on accelerator time.X-ray measurement to some extent complements other prompt radiation techniques which tend to be biased towards the determination of light elements because although high X-ray yields can be generated from light elements characteristic X-rays can also be produced from elements of high atomic number. The techniques described above have been extended to provide more selective informat- tion about sample composition. Ion beams with diameters down to about 3 p m can be produced by means of a special quadrupole focusing assembly and offer a means of irradiating small volumes of sample. Beam scanning permits the ion beam to be moved relative to the sample enabling spatial variations of elemental composition to be followed. Depth profiles can be examined by measuring the radiation from nuclear reactions exhibiting resonances a t sharply defined incident ion energies; the ion energy is varied so that reaction occurs at different depths below the sample surface.Depth resolution depends not only on resonance width and straggling at the depth a t which reaction takes place but also on the cl-iarac- teristics of the experimental system; resolutions of the order of 10 nm have been achieved in favourable circumstances. Depth distribution can also be derived from elastic scattering and particle group experiments. When the target is not amorphous but is a single crystal a decrease in reaction yield may occur when a carefully collimated incident ion beam is aligned with particular crystal axis. This phenomenon of channelling enables the structure of single crystals to be investigated and information to be derived about interstitial or substitutional impurity atoms.The Analysis of Impurities in Inorganic Matrices by Flameless Atomic-absorption Spectrophotometry BY C. W. FULLER ( Tioxide International L t d . Billingham Tcesside) FLAMELESS atomic-absorption spectrophotonietry (taken here to mean the use of a Perkin- Elmer HGA70 graphite furnace) has three major advantages over conventional flame atomic- absorption spectropliotometry- This is an advantage if only small amounts of material are available otherwise it can be a disadvantage as it is possible that problems of sampling from an inhomogeneous sample matrix will occur. In the determination of impurities in organic matrices for example milk blood and oils this has already proved to be a most important feature of the technique.While significantly greater sensitivity is not obtained for all elements it is still obviously a major factor in most trace-element determinations. One of the problems and limiting factors in the analysis of trace elements in inorganic materials is the dissolution of the sample in a suitable solvent. For this reason flameless atomic-absorption spectrophotometry was investigated as a technique for the direct analysis of trace elements in refractory materials. For the following reasons however direct sampling of these types of material was rejected- ( a ) The process of weighing out 1-mg amounts of sample is time consuming particularly if repeat analyses are required. (b) At the trace level impurities are often not homogeneously distributed through the sample.This could therefore become a major problem when the amount of sample being taken is 1 mg or less. (i) Small amounts of sample can be used. (ii) Sample pre-treatment can be carried out itz situ e.g. ashing. (izi) Greater sensitivity is given for most elements. 280 SELECTIVITY IN TRACE ANALYSIS ~PYOC. SOC. Analyt. Chew. (c) During pre-atomisation heating cycles the refractory matrix remains unaffected and irrespective of how finely the sample has been ground the matrix still remains particulate in nature. Hence when the temperature of the furnace is raised to 2500 "C these particles tend to sputter out of the furnace before they have completely broken down and released the impurity elements from the matrix for determination in the normal way. The advantages of the alternative approach that is solubilisation of a large amount of material followed by sampling of the resulting solution with a micropipette are as follows- ( a ) Weighings are simplified and several determinations can be made on the one sample weighing.( b ) With larger amounts of samples inliomogeneity ceases to be a major problem. (c) After the solvent has been evaporated in the graphite furnace the sample is left as a thin and fairly uniform layer on the inside of the graphite tube so that volatilisation of the sample is easier. ( d ) Separation and pre-concentration methods can be used once the sample is in solution. The disadvantage of dissolving the sample is that impurities from the solvents are intro- duced ; this is an important consideration for determinations at very low concentration levels.The determination of impurities in titanium dioxide pigments demonstrates the use of the higli sensitivity of the flameless atomic-absorption spectrophotometric technique. Iron copper and manganese at the 1 pg g-l level in titanium dioxide can be determined by atomic- absorption spectrophotometry only after a fairly lengthy separation procedure. By dissolving 0.3 g of sample in 50 ml of solution iron copper and manganese can be determined directly on tlie resulting solution by flameless atomic-absorption spectrophotometry. This work can be further extended to the determination of these metal impurities in small amounts of thin paint films after pre-ashing and dissolution of the sample. The determination of iron and copper in high-purity silica down to levels of 0.01 pg g-l presents many problems when using colorimetry or atomic-absorption spectrophotometry.The methods require separation techniques and careful analytical procedures taking up to 5 or 6 hours for completion. By using the advantages of sensitivity and sample pre-treatment within tlie graphite furnace a simple flameless atomic-absorption spectrophotometric procedure has been deve1oped.l The silica is dissolved in the minimum volume of hydrofluoric acid and an aliquot of the resulting solution is injected directly into the graphite furnace. The instrument can be programmed to evaporate off the silicon tetrafluoride which is formed in the solution stage and the excess of hydrofluoric acid so that iron and copper can then be determined in the normal way. Ethyl silicate used to prepare the high-purity silica mentioned above can also be monitored for iron and copper contamination by diluting the sample 1 + 1 with acetone followed by direct flameless atomic-absorption spectrophotometric determination.More lengthy procedures can be used for the determination of impurities in refractory-type materials involving the use of separations into organic solvents. While the basic methods are similar to those used in atomic-absorption spectrophotometry they have the advantage that the final volume of the organic solvent can be much smaller to give even lower determination limits or so that smaller amounts of sample can be analysed to determine several elements. This approach has been successfully used for the determination of impurities in glasses. While flameless atomic-absorption spectrophotometry has a high potential as an analytical technique in the trace-element field there are still many problems to be investigated.One of these which has received very little attention up to now is the loss of elements during pre- atomisation heating cycles. Copper and nickel2 and manganese have been shown to lose 50 per cent. of their initial concentration after heating at 1100 "C for 30 200 and 300 s respectively. Losses from 1 per cent. solutions of hydrochloric nitric phosphoric and sulphuric acids were investigated. It was found that for copper the losses were independent of the acid present while for nickel and manganese the losses were about halved in the presence of sulphuric and phosphoric acids compared with those obtained in the presence of hydrochloric and nitric acids.REFERENCES 1 . 2. Fuller C. W. Analytica Chim. Acta in the press. ___ Ibid. in the press. December 19721 SELECTIVITY I N TRACE AN.4LYSIS 281 Combined Electrolysis and Atomic Absorption for the Determination of Metals in Biological Materials BY T. F. HARTLEX- AKD D. J. ELLIS (Department of Medical Physics Leeds Zlnivevsity Leedc LS2 9 J T ) THE feasibility of the electrolytic extraction of ionic copper zinc magnesium mercury or lead from biological fluids prior to their determination by atoniic-absorption spectroscopy has been investigated. APPAR.-lTL-s- I t consists of a 2-ml plastic haniple cup mounted in a slowly rotating holder that can be raised and lowered. In its raised position two iridium wires mounted at the ends of pivoted arms dip into the sample cup.During electrolysis these wires act as the electrodes. After electrolysis the sample cup is lowered and the electrodes are rotated into an air - hydrogen flame which vaporises the deposit into an electrically heated Nimonic tube mounted horizontally on the absorption path of an atomic-absorption spxtrometer. This tube acts as an atom reservoir for the pulse of atomic rapour. The absorption due to this vapour is displayed as a peak on a fast-response pen recorder. The apparatus has been described in detail elsewhere.1*2 1-1 SPF R I 31 I< S TS - liapid and efficient atomisation of deposited metal from the cathode wire was essential for the metliod to be successful. In preliminary experiments small volumes (about 4 p1) of pure aqueous solutions of a metal salt were evaporated to dryness on this wire prior to vaporisation into the Kimonic tube.Linear relationships between signals and increasing concentrations were obtained for each metal and the derived sensitivities are given in Table I line 2. The wnsiti\-ities u.;ing the conventional aspiration technique3 are shown in Table I line 1. TABLE I EXPERIMENTAL RESULTS Element r A I Parameter z I1 c u Hg P b % Sensitivity using conventional aspiration into a flame .il)sorbance per pg rn-1 0-30 0.044 0.00044 0.0058 0.63 Sensitivity when solutions were placed directly Sensitivity when solutions a t pH 2 were electro- lysed absorbance per current pulse per pg ml-1 0-041 0.031 0.0049 Degree of autodeposition from solutions a t pH 9 absorbance per pg ml-f s-1 0.30 0.018 0.0021 Electrode potential of the metal in acidic solution/V -0-76 $0.36 +0*85 Potential difference between the electrodes/V 3.0 1.5 4.0 Detection limit (pg ml-l) in serum electrolytes equivalent solution a t pH - 2 and passing 100 current pulses 0.005 0.005 30-0 on thc nire absorbance per pg 115 33.3 1.0 (0.002)* (0*006)* (0*5)* * Detection limits (pg nil-l) by conventional aspiration techniques.Detectable amounts of metal adhered to the electrodes after these 18.7 43 0.0035 0.0013 0.0028 0.0165 -0.13 - 2.37 4.0 3.0 0.16 0.1 (043) * (O.OO03) * had been dipped into pure aqueous inorganic solutions. The amount adhering was pH-dependen t and generally increased with pH. In Fig. 1 this effect and its relation to solution composition are illustrated for zinc. The corresponding results for the other metals are summarised in Table I line 4.The conclusion from all these observations was that the metals were being autodeposited on the electrodes by a pH-sensitive but otherwise unknown mechanism that was not related to the position of the metal in the electrochemical series (Table I line 5). In order to rninimise this effect the subsequent electrolysis studies were carried out in acidic solutions. 282 SELECTIVITY I N TRACE ANALYSIS [Pim. SOC. Aiznlyt. Chcm. 0.20 a C m 2 2 n 0.10 0 5 PH 10 Fig. 1 . Effcct of pH on the deposition of zinc on to an iridium wire by autodeposition. Deposition tinie - 40 s for all solutions. 1 0.01 pg nil-1 zinc; 2 0.01 pg ink1 zinc 111 fifty times diluted serum clectroll-tes equivalent solution ; and 3 serum diluted ten times Optimum electrode potentials for the deposition of the metals from a solution similar in inorganic content to normal plasma were determined.These potentials are presented in Table I line 6 and the corresponding currents ranged between 0.1 and 1 mA according to the total ionic content of the solution or sample. Polarisation of the electrodes during electrolysis was reduced by using a pulse electrolysis technique. The depositing current pulse lasted for 0.2 s and was followed by a 2-s recovery period. Under these conditions there was a linear increase of absorbance wit11 increasing numbers of current pulses and this is illustrated for copperin Fig. 2 graph ( a ) . I t was found that the amount of element deposited per pulse per unit concentration (pg ml-l) decrea5ed with decreasing concentration of the metal ions in solution and the results for copper are shown in Fig.2 graph (b). This phenomenon suggested that at low concentrations (10-8 g nil-1 and less) the rate of deposition was comparable with that of dissolution of deposited material. This is probably the main reason why the detection limits by this method as shown in Table I line 7 were no improvement on conventional aspiration techniques. The two methods were com- parable only for copper and zinc. The electrolytic extraction method has been applied to a study of the binding of copper in plasma. In these experiments small volumes of 5 31 hydrochloric acid were added sequentially to a plasma sample and the ionic copper concentration was measured after each addition. The graph of ionic copper concentration versws pH was sigmoid with a small rate of increase from pH 7 to pH 5 followed by a rapid increase from pH 5 to pH 2 and a plateau below pH 2 .The plateau value of copper (1.5 pg ml-l) corresponded to the total copper content of the sample measured by direct aspiration. These changes in copper concentration were interpreted as being due to the release of copper from various complexes in the plasma. Wlien an aliquot of the same plasma to which had been added an additional 0.1 pg ml-l of copper was progres- sively acidified its response graph showed that all the added copper had been released bv pH 4.4. During the previous experiment 14 per cent. of the total copper had been released at this December 19721 SELECTIVITY I N TRACE ANALYSIS 283 pH. These observations require closer investigation and correlation with the amounts of the various copper-binding proteins known to exist in plasma.If such correlations can be estab- lished then this technique may well prove to be a useful additional tool for the study of 0 5 10 Number of current pulses 1.5 10-6 10 9 Copper concentratiodg mI ’ Fig. 2 . Dependence of deposition of copper on ( a ) the number of current pulses (copper concentra- tion = 1 pg ml-l) and ( 0 ) the concentration of copper i n the solution COXCLCSIOXS- The amount of metal electrodeposited from various solutions could be conveniently measured by using atomic-absorption spectroscopy and there was a linear relationship between absorbance and the solution concentrations within the range 0.001 to 1-0 pg inl-l. The relative sensitivities for the metals studied were zinc > copper > mercury > lead > magnesium.The technique gave no improvement over conventional methods for measuring the total element contents and only copper and zinc could be extracted from serum. Pro- gressive acidification of plasma with hydrochloric acid released copper and zinc bound in complexes and the concentration of these ions could be measured after each acidification by using the combined electrolysis and atomic-absorption method. \Ye thank the Medical Research Council for its support of this work as part of a study of trace-clement metabolism. REFERENCES 1 . 2. 3. LI’alker B. E. Dawson J . B. and Ellis D. J . Abstracts of Papers 2nd International Conference on Ellis D. J . Hartley T. F. and Dawson J. B. Proceedings of3rd International Conference on .4tonzzc “Analytical Methods for Atomic Spectrophotometry,” Perkin-Elmer Norwalk 1971.Atomic Spectroscopy Shefield G.2 1969. Spectroscopy Paris 1971 p. 607 (in the press). Selectivity in Trace Analysis-The Detection and Determination of Compounds Plenary Lecture BY HAROLD EGAX (Departnzent of Trade and Industry Laboratory of the Government Clzemist Cornwall House Stani ford Street London SE1 9NQ) THE preface of the current edition of the Methods Book of the Association of Official Analytical Chemists1 refers to “the challenge of multiresidue multiproduct methods.” Chromatographic methods in particular have in recent years revolutionised trace analysis in that they have given access to sensitivity levels which hitherto were barely approachable by other techniques and at the sanie time have offered degrees of selectivity which earlier had been regarded as impossible.284 SELECTIVITY I N TRACE AKALYSIS [Pilot. SOC. Aunl_z)t. Clmw. All of the techniques represented by the Groups participating in this Joint Meeting-atomic spectroscopy chromatography electrophoresis and radiocliemistry-have had a share in this revolution but gas - liquid and thin-layer chromatography have made particular contributions insofar as compounds (as opposed to elements) are concerned. The term “selectivity” does not appear in the indexes to tlie first 21 volumes of ,11inl_ttticnl Abstvncts. Nor for that matter does the term “specificity,” the distinction being perhaps one of degree although this is by no means established either by convention or usage. Specificity has been defined as the degree to which the mean measurcment obtained by a method under consideration is due to the substance to be determined and not to other substances n~liicli may also be present.2 Perhaps selectivity can be distinguished from specificit) in tlie senw that the former is applied to what today have been loosely called “multi-detection” systems of analysis in which conditions can to some extent be adjustcd to tune across a range of \pecificities selecting one of them.The concept can be illustrated by a typical example the detection and determination of traces of polychlorobiphenyls. A straightforward gas chromatograni oper- ated under the right conditions ~ o u l d show a number of peaks \vhich thenisel\~es fall within an enveloping peak; however the shape of the cnvelope will i n circumstance5 of expobure to tlie atmosphere change with time.The envelope will proba1)ly embrace peaks wliicli other trace substances of interest would if they were also present indicate for example DDT. There would be great interest in a detector selective for the polychlorobiphenyl pattern (especially if it could be tuned to simulate typical changes of tlie pattern Ivitli time) just as there ~vould also be a great interest in a detector specijc for $,fi’-DDT. There is no unified concept of selectivity that is applicable across tlie whole field of analytical chemistry. I t is more correct to speak of the selectivity of a reaction or process than of a reagent. Analytical chemistry today is a vastly different discipline to analytical chemistry 100 years ago. The wet methods of separation and assay which then together with various pyrochemical techniques basically constituted the subject have since been supple- mented by many quantitative instrumental methods based 011 a much wider range of electro- chemical spectrophotometric surface and other characteristic properties of the sulxtances (in solution or otherwise) concerned.It is as a consequence of tliis vast array of ~7aried tecliniques now represented in analytical chemistry that no simple unified concept of selectivity emerges although there have been attempts to set out systematic expressions of selectivity in individual fields of analysis. As long ago as 1933 Lundell3 recognised that there was no dearth of analyti- cal methods which are entirely satisfactory for the determination of elements where they occur alone or in simple combination but that since in reality things were otherwise methods of determination had to be judged on their individual selectiveness.\Vilson4 recognised that specificity in analytical methods today is not solely a matter of specific reactions or specific reagents. The art of chromatography for instance is to separate only the compounds that are to be determined and to set up the conditions for such a separation by the use of appropriate preliminary clean-up techniques. In order to set the terms trace aNaZysis and speciftcity into some kind of perspective- Widmarkj has discussed the vast increase in the number of different trace compounds which are theoretically possible as one passes into higher realms of sensitivity. Various assuniptions can be made as to the numerical distribution of these compounds in what he describcs as the “tracer cosmos” as one extends the level of detection downwards and he has discuswd those in relation to present-day problems of pollution analysis.In doing this it is necessary in the first place to simplify the situation by making some assumptions for example that the substances of interest have a relative molecular mass of (say) 60 and that the substrate is 99 per cent. pure. Assume also a uniform distribution of the various impurities by mass. In this case the im- purity could consist of 1 per cent. of another substance or 0.1 per cent. each of ten different impurities or 10 000 different compounds each at the 1 mg kg-l level. However a number of analyses today are of interest at the parts per thousand million level or even lower; if all the impurities were present at this level one might theoretically have to contend with a million or more different trace compounds.Other assumptions can be made for example that the 1 per cent. impurity is equally divided by mass at each successive decimal level of concentration giving 100 compounds present at the mg kg-1 level and 100000 at the pg kg-l level. If however the number of compounds is equally distributed at each of the decimal levels each level would contain some 2000 different compounds. Other distribution profiles that might be more characteristic of typical pollution samples have been described and whilst in some of these Indeed this same approach is used in other fields. December 19721 SELECTIVITY I N TRACE ANALYSIS 285 the number of compounds at each successive concentration range decreases below a particular level the total number of different impurities that theoretically can be present may still be enormous.The possibilities of sample contamination in trace analysis also begin to assume special proportions in this context. Apart from such theoretical aspects of the size of the problem of specificity i n trace analysis selectivity has itself been considered by a number of workers. Cheng6 in 1961 described the concept of a selectivity ratio which lie has suggested as an index for the evalua- tion of masking agents in analytical reactions. This was simply a mathematical expression of the ratio of tlie negative logarithm of the metal-ion concentration dissociated respectively from the metal - reagent complex and the metal - maslting agent complex.X similar although not identical concept of selectivity ratio has been described for ion-selective elec- trodes by Moody and tho ma^,^ who criticised the inconsistent approach to the presentation of data for this in manufacturers’ literature. On the grounds that there is no such t l h g as a specific reagent Belchers has proposed the idea of a selectivity index number in order to avoid the vagueness which otherwise accompanies the consideration of selectivity through tlie use of such terms as “highly selective,” “moderately selective” or “non-selective.” Focusing atten- tion on reactions in solution he suggested that when only one ionic species responds to a reagent the latter might be said to have a selectivity index number of I ; if only two ionic \pecies the selectivity index number might be I1 and if 3 to 5 ions 111; the maximum index number is perhaps VI or VII.Betteridge9 extended this concept to analvtical reactions rather than reagents for which the idea of a selectivity index has been developed. In this a. central symbol indicates the type of reaction itself for example G = gravimetric S = spectroplioto- metric T = titrimetric and N = nephelometric. This is then qualified by further subscripts or superscripts in a systematic manner indicative of the selectivity index number described above the reaction for which the reagent is being considered the pH and the presence (or otherwise) of masking agents. I t would be wrong to think of this as a scheme for quantifying selectivity except perhaps in the very broadest sense; it is basically a teaching tool and is not in day-to-day use in applied analysis.Belcher and BetteridgelO recognised the practical limitations of such an index especially when it is desired to express specificity with respect to a wide range of possible interfering species. This can be done diagrammatically and neatly at least for ionic species by a Periodic Table display as by Holbrook and Reinll for the determination of gold as the bromoaurato - trioctylphosphine oxide complex in which the mole ratios of diverse ions to gold which are tolerated without interference are shown in distinctive colours less than 10 10 to 100 100 to 1000 etc. The I.U.P.A.C. Analytical Chemistry Division’s Nomenclature Commission V.3 which meets in London later this year is in fact developing this theme and West (private communication) has described an index based on the ideas set out above together with its possible application to the selection of an absorptiometric reagent for a particular ion or to screening reagents for their value with respect to a range of ions using Periodic Table grids as appropriate.The chemistry of specific selective and sensitive reactions of interest to the analyst was reviewed in 1949 by Feigl,12 who indicated that specificity has to be actively pursued but that in seeking it findings which may be of interest in other fields of chemistry may well be encountered. West has described some of the practical considerations in the search for new reagents for absorptiometry with special reference to the lack of selectivity shown by many illustrated by the development of the Calcichrome cyclotris-7-( 1-azo-8-1iydroxynaphthalene)- 3,6-disulphonic acid for the determination of ~a1cium.l~ More recently atomic-absorption spectroscopy X-ray fluorescence spectroscopy and activation analysis techniques have offered elegant and highly specific approaches to many elements.However interferences of a chemical nature due to failure to break the bond between the element and its original compound can occur in atomic-absorption work in addition to matrix interferences ; these have been reviewed by Platt.14 Infra red15 and more recently microwave rotationaP spectrometry are each capable of affording a relatively high degree of selectivity indeed specificity ; the interpreta- tion for each is an art in itself and this is also true of mass spectrometry. Great advances in the availability and use of these methods for selectively approaching analytical problems have been made in the last 10 to 15 years.However nuclear magnetic resonance methods still require milligram samples. 286 SELECTIVITY IN TRACE ANALYSIS ,PYOC. SOC. Analyt. Chena. Selective electrodes are now well established for many inorganic ions and the possibility of extending these to organic systems by the use of immobilised enzyme systems has been described by Barker and T0~nshend.l~ Thus an ammonium-selective electrode can if covered with a layer of urease become responsive to urea.18 Other systems can be made to be responsive to glucose lactates and L-amino-acids. Such systems are unlikely to be more selective than the enzyme systems they involve of course. An organic-ion selective liquid membrane electrode with a high selectivity for acetylcholine over choline and inorganic ions is available commercially and has been described by Baum.lg A special aspect of the use of enzymes in trace analysis (and one not normally thought of as such) is the microbiological assay.Whilst neither strictly physical nor chemical the technique is nevertheless a very important one for the determination of biologically active compounds for example some of the vitamins of the R group I t has over the years been put on a sound practical laboratory basis as evidenced by the Biological Methods Group of the Society for Analytical Chemistry. i n use it relies on the measurement of the growth (or inhibition of growth) of a micro-organism in response to the substance being assayed compared with the response to known graded standard levels the measurement of growth itself being possible by a variety of physical or chemical means.By careful selection of the micro-organism and the conditions for its culture it is possible to achieve a substantial degree of selectivity for individual compounds or groups of compounds in the presence of many others the separation of which would otherwise be a very tedious process. The interest in specificity in trace analysis has been nowhere better demonstrated than in the field of pesticide residue studies a typical area of trace analysis today where one is trying to detect and measure a small amount of an individual and often complex organic compound in the presence of a large number of other such compounds which are both similar and dissimilar in character.Bowman Young and Barthe120 illustrated the point in 1965 by showing that what appeared to be $,$’-DDT (the major decomposition product of DDT) and heptachlor in soils kept in a sealed container since 1940 (before the advent of chlorinated insecticides in the United States) were artifacts due for example to elemental sulphur. Powerful although the present-day multi-detection methods are for the persistent organochlorine pesticides such as DDT and dieldrin for which they were first devised gas-chromatographic separation techniques may not always be sharp enough to separate the individual components. Sometimes impuri- ties that are ordinarily present in the technical pesticide or naturally occurring substances present in the extract prepared from the sample material may interfere in this way.Pre- liminary clean-up is part of selective analysis. Even when such a clean-up is used Egan21 has emphasised the desirability of confirming the identity of unknown residues by infrared or mass spectrometry since the physical bases underlying other methods in common use including y-ray spectrometry or gas - liquid chromatography and solvent partition $-values are very similar. Caro22 has described a simple sensitive and relatively inexpensive “fingerprint” technique for such residues based on the ultraviolet irradiation of a dry film followed bygas chromatography of the degradation products the pattern of which is quantitatively repro- ducible. A good practical example is the polychlorodibenzo-p-dioxins technical impurities of interest in connection with herbicides based on chlorinated phenols.For these Woolson and Thomas23 used three different quantitative gas-chromatographic columns each with a different detector solvent partition +-values and ultraviolet irradiation conversion pattern supplemented as necessary by thin-layer chromatography. Beroza and Bowman24 have set out a full list of methods for confirming the identity of terminal residues of organophosphorus pesticides. These include in addition to the technique mentioned above visual spectrophoto- metry nuclear magnetic resonance spectrometry polarography and bioassay (cholinesterase inhibition). The application of chromatographic methods to separation for purification (or clean-up) purposes and the integration of such techniques with sensitive methods of detection and measurement have revolutionised trace analysis in the last 20 years.The various types of chromatography involved have recently been reviewed by Done Kennedy and K n ~ x ~ ~ in the context of liquid chromatography (and in particular high-pressure liquid chromatography) who traced the evolution and application of this method from the original work of Tswett and its present-day development from liquid - liquid partition paper thin-layer and gas - liquid chromatography. The chromatographic separations which have been devised for application to trace analysis impart selectivity provided that sufficiently sensitive methods of detection are available. December 19721 SELECTIVITY I N TRACE ANALYSIS 287 Chromatographic methods have made a substantial contribution to selectivity in analyti- cal chemistry.There are few if any groups of compounds which are not or cannot be made to be amenable to chromatographic treatment. Carbohydrates amino-acids polypeptides alkaloids terpenes hydrocarbon oils synthetic colours preservatives antioxidants vitamins pharmaceuticals and pesticides are some examples. A very large number of variations have been introduced to the basic techniques to this end. The conditions of separation in column paper and thin-layer chromatography can and have been varied almost to an infinite degree from simple operations such as two-dimensional reversed-phase or displacenient paper chromatography to wedge-layer multi-bend and derivative layer chromatography ring-oven techniques high-pressure liquid chromatography temperature-programmed pyrolysis and multicolumn gas - liquid chromatography and combinations of these.The field is not without its dangerous traps for the selectivity hunter ; gas-chromatographic columns have themselves been known to isomerise the sample for example. These are the basic methods of separation; but this is only the beginning of chromatographic selectivity. The methods of detection have themselves been the subject of considerable attention and in many cases also impart substantial selectivity over and above that achieved chromatographically. They range from a wide variety of colorimetric (including ultraviolet sensitive) so-called “visualising” agent used in column and particularly paper and layer chromatography to the specialised detectors that have been developed for gas chromatography.Examples of the latter are the nitrogen and phosphorus-sensitive flame-ionisation detectors that have been widely used in trace for example for pesticide residues or nitrosamines. The specialist detectors are not merely limited to these however. In the name of selectivity they can extend to conventional physical methods of analytical instrumentation such as refractive index or infrared spectro- photometry and are now in particular exemplified by a widespread interest in the combination of gas chromatography with mass spectrometry. Such applications do not come about casually; the development of this combination has a literature of its own. In all of these cases there is need for a critical interpretation of the results in order that the true degree of selec- tivity can be recognised.The unexpected result should not be rejected but it should not be accepted without this critical judgment. To take a current example a number of workers examining extracts of natural food products for trace constituents by combined gas chromato- graphy and mass spectrometry have identified chloroform. for milk and cream and of Stevens Bomben Lee and McFadden28 for grapes relate mainly to a large number of other more conventional constituents. Schormuller and K o ~ l i m a n n ~ ~ have also detected chloroform in the volatile products from tomatoes. Trace amounts of chloroform were almost certainly present in all of these samples (the origin of such traces is a different cluestion) but confirmation of this by gas chromatography coupled with high-resolution inass spectrometry is necessary before a final judgment is made.The whole subject of what is called the positive identification of unknown (that is not deliberately introduced) traces or residues has to a large extent dominated the field of selectivity in trace compound analysis in recent years. Indeed the Analytical Methods Committee is at present discussing jointly with the Association of Official Analytical Chemists the problem of an acceptable method for measuring the proportion of residual mercury in marine fish which is bound as methylmercury compounds. Widmark has devoted a lot of thought and practical energy to the problem of positive identification. His flow-chart of the separation and identification processes involved begins with the clean-up of the sample in the original and in derivative forms by thin-layer and gas - liquid chromatography and concludes with detection by nuclear magnetic resonance infrared and ultraviolet spectrophotometry electron-capture and flame-ionisation detection and mass ~pectrometry.~ Apart from mass spectrometry none of these detectors should be used to give the sole indication of the achievement of selectivity; nor is it in practice profitable to use them (mass spectrometry included) without the additional selectivity imparted by the preliminary clean-up processes.But by using the correct combinations of techniques almost complete specificity is possible. The need for specificity arises in compositional as well as trace analysis a good example of current interest in the field of food analysis being in the determination of foreign proteins (including regenerated vegetable proteins and those of microbial origin) in meat and meat products.Trace analysis is also used for identification purposes for example the trace analysis for compounds (in this case called “congeners”) present in whisky and other spirits. In this The results of 288 SELECTIVITY I N TRACE ANALYSIS ‘Yifoc. SOC. Aualyt. Chew. particular field the palate is still highly regarded and is still by many reckoned to be the final arbiter. I t is of interest here however that traditional colorimetric tests for diagnostic trace compounds such as higher alcohols esters and aldehydes are now being supplemented by gas chroniatographic met hods. Conclusions in a field so ill-defined as specificity are bound to be tenuous but it is worth recording that the modern extremely sensitive and often multi-detection methods of trace analysis today are capable of high resolution between individual compounds.They can with skill be used in a highly selective manner but for the purposes of practical (and indeed theoretical) interpretation need to be backed up by a degree of specificity that is not usually easy to achieve. It is necessary to ask the question posed by L ~ n d e l l ~ who wrote of heaven as including a shelf on which there were 92 reagents No. 26 of which was a sure shot for iron- why are chemical analyses made ? Trace analyses (as with compositional analyses) are some- times made for the purposes of quality control and today more often made for the assessment of risk to health or environmental quality. These aspects call for a critical approach it is all too easy to indulge in expensive trace analysis firstly detecting and secondly seeking to confirm the identity of an individual complex substance in a substrate containing 100 000 other trace substances.Selectivity in analytical chemistry can usually be secured at a price it is necessary to consider whether the price is appropriate to the value obtained. 1 . 2. 3. 4. 5. 6. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. I . REFERENCES “Official Methods of Analysis of the Association of Official Analytical Chemists,” 1 l t h Edition A\nastassiadis P. X. and Common R. H. Analyt. Biochem. 1968 22 409. Lundell G. E. F. I n d . Engng Chenz. Analyt. E d n 1933 5 221. Wilson H. N. Analyst 1960 85 540. Widmark G. Adv. Chem. Ser.1971 No. 104 1. Cheng K. L. Analyt. Chevn. 1961 33 783. Moody G. J. and Thomas J. D. R. Talanta 1971 18 1251. Relcher R. Ibid. 1965 12 129. Retteridge W. H. Ibid. 1965 12 129. Belcher R. and Betteridgc W. H. Ibzd. 1966 13 535. Holbrook W. B. and Rcin J . E. Analyt. Chem. 1964 36 2451. Fcigl F. Ibid. 1949 21 1298. Fiest T. S. Analyst 1962 87 630. Platt P. Sel. A . Rev. Analyt. Sci. 1971 1 177. Philpotts A. R. and Maddams W. F. Proc. I n t . Synzp. J4wochem. 1958 1959 373. Cuthbert J. and Denney E. J. PYOC. Inst. Petrol. Symp. Molec. Spectrosc. 1971 243. Barker S. A. and Townshend X. Chem. Process. 1972 May 9. Guilbault G. G. and Montalvo J . G. J . Amer. Chem. Soc. 1969 91 2164. Bauni G. Analyt. Lett. 1970 3 105. Bowman M. C. Young H. C. and Barthel W. G. J . Econ. Ent. 1965 58 896. Egan H. J . A s s . 08. Analyt. Chem. 1967 50 1067. Caro J . H. Proc. 2nd I n t . I U P A C Congr. Pestic. Chem. 1971 4 457. Woolson E. A. and Thomas R. F Ibzd. 477. Beroza M. and Bowman M. C. “Pesticide Terminal Residues,” Butterworths T-ondon 1972 Done J . N. Kennedy G. J . and Knox J . H. Natuve 1972 237 77. Ruzicka J . H. *4. Thomson J . and Wheals B. B. J . Chromat. 1968 34 14. Wong N. P. J . Dairy Sci. 1963 46 571. Stevens K. L. Bomben J . Lee A. and McFadden W. H. J . Agric. Fd Chem. 1966 14 249 Schormuller J . and Kochmann 13. J. Z . Lebensmittelunters. u. -Fovsch. 1969 141 1 . Association of Official Analytical Chemists Washington D.C. 1971. pp. 79-92.

ISSN:0037-9697    

DOI:10.1039/SA9720900273

出版商:RSC    

年代:1972

数据来源: RSC

摘要:

288 SELECTIVITY I N TRACE ANALYSIS ‘Yifoc. SOC. Aualyt. Chew. Some Sources of Contamination in Trace Analysis BY R. 0. SCOTT AND A. &.I. URE (The Macaulay Institute for Soil Research Craigiebuckler Abevdeen AB9 2Q J Scotlaxd) THE progressive lowering of trace-element detection limits and the increasing number of elements known to be of significance in biological and industrial fields has emphasised the necessity of ensuring that samples are not contaminated by these elements from extraneous sources prior to and during the analytical determination. Fluctuating contamination especially can produce spurious results that may invalidate the experiment. December 19721 SELECTIVITY I N TRACE ANALYSIS 289 Problems that have been encountered in the analyses of biological or related samples have been considered in several p~blications.l-~ I t should be emphasised however that elementswhich might be acceptable as contaminants in industrial samples might not be accept- able in agricultural and biological analyses and vice zlema.The process of contamination can conveniently be considered in three phases (1) at the experimental or manufacturing stage (2) during sampling and packaging and (3) in the analytical procedure. The analyst should be able to reject samples that are obviously contaminated as their analysis would seldom be justified. COXTAMINATION DURING THE EXPERIMENTAL OR MANUFACTUKING STAGE- Whatever the nature of the material being sampled it inevitably exists in an environ- ment by which it may be contaminated. For example O’Sullivan,* in the course of investiga- tions on zinc deficiency in plants grown in pots contaminated his samples with zinc from white plastic labels inserted in the soil.I t is essential therefore to design every experiment so that this intrinsic contamination is minimised controlled or at least monitored. Con- structional materials must form part of the environment of any experiment (and must also be used in the analytical stage) and these may be inorganic for strength or rigidity-metals or alloys brick mortar stone cement plaster and glass or organic for corrosion resistance- rubber plastics and wood. Some contamination may have to be accepted at this stage and when metals are necessary the two least objectionable in biological work are probably alumin- ium and mild or carbon steel. Even these metals should be carefully chosen as some a h - niinium alloys contain copper with zinc or cadmium surface treatments while free-cutting mild steels often contain lead or selenium.Stainless steels and high-temperature alloy steels should be used with caution. The former can contain large amounts of chromium manganese molybdenum and nickel and the latter in addition cobalt vanadium and tung- sten. Copper alloys are generally undesirable while plated materials can introduce cadmium chromium copper nickel phosphorus or zinc contamination. Metals bricks concrete and plaster used in construction are often painted so as to prevent corrosion and dust formation. Suitable paints should be carefully chosen as the coinmor? pigments are the oxides of lead titanium zinc or aluminium with antimony(II1) oxide often being added to the latter as a whitener while cobalt or other heavy-metal complexes are used as hardeners.In the dust from an old wooden greenhouse,j for example there were present 4000 to 5000 p.p.m. of lead and titanium 1000 to 1500 p.p.m. of barium and zinc 400 p.p.m. of antimony and 25 p.p.m. of cobalt and these elements were almost certainly derived from deteriorating layers of paint. Similar lead and zinc contents have been found in the dust from a domestic furnace air filter.g Organic constructional materials can introduce more contamination than is generally appreciated. Rubber often has a high zinc content while many synthetic plastics contain heavy metals. Ritchie Critchley and Hilllo described compounds of barium calcium cadmium phosphorus lead and zinc used as stabilisers of phosphorus and sulphur as anti- oxidants and ultraviolet absorbers along with fillers of asbestos glass fibre talc clay barium sulphate calcium carbonate calcium fluoride antimony(II1) oxide titanium dioxide zirconium dioxide molybdenum disulphide aluminium aluminium oxide copper and bronze.It is therefore obvious that synthetic plastics should always be tested prior to use. Table I indicates some of the elements found in various plastics tested at the Macaulay Institute but the same products from other manufacturers could differ in their trace-element contents. Three levels of contents are given high (greater than 1 per cent. in the ash) medium and low (less than 100 p.p.m.). From an analyst’s point of view the total content may not be as important as the soluble contents which will be discussed later but contamination could be introduced by abrasion during the experimental sampling or packaging stages when for example in animal studies the cages or food troughs can be licked or gnawed.The choice of a suitable plastic for trace-element experiments may be restricted by the requirements of rigidity flexibility or transparency but of those listed the most acceptable are probably polythene polypropylene nylon Perspex Fluon and silicone rubber. Although the most expensive Fluon and silicone rubber are the best from the contamination point of view. Polythene prepared by the high-pressure process is usually preferable to the more rigid metal-catalysed high-density variety. Stainless steels may also have selenium or titanium surface treatments. 290 SELECTIVITY IN TRACE ANALYSIS [Proc.SOC. Analyt. Chem. TABLE I SOME ELEMENTS PRESENT I N THE ASH OF VARIOUS SYNTHETIC PLASTIC MATERIALS THE CONTENT REIXG SHOWN AS HIGH (PROBABLY OFTEN UKACCEPTABLE) MEDICPII AND LOW (POSSIBLY ACCEPTABLE) Element content I A \ Plastic material P o lyt 1i c11 r- High pressure natural" . . High pressure natural* . . High density yellow . . High density black . . High density white . . Expanded foam white Expanded foam black . . Polj~/wopyle>ze- Tube natural . . . . Sheet natural . . . . Poly(vi?zyl chloride) ( P V C ) - Sheet grey . . . . Tube clear? . . . . Tube natural . . . . Tape white . . . . DletJzyl methacrylate (Peyspex)- Clear . . .. .. White . . .. . . Black . . . . .. Polysty~ene- Clear . . . I . . Expanded foam white . . Expanded foam yellow Polyamide (Nylon)- Rod natural .. . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. .. .. . . . . . . . . High Ti Ba Zn Cd Ti Ti Ti Zn Na Cd Ti Ti Cr Cu Zn Pol~~tefm~~uovoethylene (Fluon Teflon PTFE)- Rod natural . . . . . . Aerosol spray . . . . . . Ti Phenolic Yesin (Bakelite TufPzol Paxalin etc.)- Black . . . . . . . . Ti Ba Mn Zn Asbestos based green . . . . Mg Si Paper based brown . . . . Silicone yubbey- Tube natural . . . . . . Si A4dlicsive tapes- Cellulose based clear . . . . Ba Cd Mg Embossing tape red . . . . Cr Mo Pb Embossing tape green . . . . Cr Cu Pb Embossing tape blue . . . . Ti Ba Cu * Different suppliers. + Cadmium and tin water-soluble. Tin water-soluble. Medium Si Mg hIg l.'c Ti Fe Ca Fe Si Mg Si Mg Si Jlg Fe Si Mg Fe Si Mg Ti Si Mg Si Mg Fe Si Mg 211 Mg Si Mg K Na Si Mg Na Cr Cu Mg Cr Ca Fe Mg Mn Zn Cu Mg Cr h-i Zn Ti Sr Ba S a Ba Na Mn Na Low Cr Cu Cr Cd Cr Cu Cr Cu Mn C,r IIn Ni Cu c u Cd c u Cd Ba Sn Zr Pb Cu Cr Sn Pb Cu Pb Mo Cu Sn Sr Cd Ra Sr Pb Ah Cu Ni Cr Mn Cu Sr Cu Cd Sn Cd Sn Sr SAMPLING AND PACKAGING- The next stages during which contamination may arise are the sampling and packaging stages neither of which may be under the analyst's control.The sampling should of course be representative of the experiment and the materials used for the sampling process should be December 19721 SELECTIVITY I N TRACE ANALYSIS 291 carefully chosen. For example in the determination of trace elements in peats the corrosion- resistant stainless-steel corer with brazed fittings commonly used at the Macaulay Institute which could introduce chromium copper nickel and zinc contamination has been replaced by a corer made of welded carbon steel.Polythene bags or boxes or glass-stoppered bottles are generally suitable as sample containers. Metal boxes or containers with metal screw-tops should never be used. Yoly- styrene tubes and jars should be used with caution as lubricants such as zinc stearate are often used in the moulding process. Erown paper bags and boxes may contain a volatile boron compound.11912 Mitchell,12 for example found that a ground plant material with a boron content of 3-5 p.p.m. contained 31.0 p.p.m. of boron after storage for 15 weeks in a greaseproof paper-lined brown paper bag. Adhesive tapes and labels could also cause contamination. Table I shows that clear cellulose tape contains cadmium and zinc as well as other metals while embossing tape can contain chromium copper molybdenum and lead.One example of a self-adhesive label although not shown in the table contained 1-2 per cent. of extractable barium as well as small amounts of copper manganese and zinc. The identi- fying label should not be enclosed in contact with the sample as inks such as the red and green inks in glass-fibre pens contain copper and sodium and in black felt pens titanium zinc and trace amounts of other metals in a d d i t i ~ n . ~ The elements extracted from various materials by dilute nitric acid (material left overnight in cold dilute nitric acid) are given in Table 11. Table I1 shows for example that some packaging materials such as phenolic resin screw-on tops of glass bottles and associated cardboard liners could introduce several elements of biological importance such as copper iron manganese and zinc while brown paper bags contain extractable barium copper and manganese.ANALYTICAL PROCEDURE- The sub-sampling of a soil is usually most safely carried out by manual coning and quartering as commercial rifflers are often made of objectionable metals. A biological material must first be dried and for the determination of most elements this drying is most conveniently carried out in an aluminium-lined oven at 80 “C. Thereafter the material is ground either in a steel hammer- mill or some type of agate mortar or ball-mill. Some iron and silicon contamination might have to be accepted at this stage but that of chromium copper nickel and zinc can be avoided by replacing any plated stainless-steel or brass parts with aluminium or plastic fittings.Tungsten carbide grinding vessels and cutting tools should generally be avoided because cobalt metal is used as a binder. For multi-element determinations in biological materials dry-ashing at 450 “C in a silica-lined furnace is preferable to wet-ashing. Even by this dry-ashing technique Williams and Vlamis13 found boron contamination while silver contamination arising from the thermal fuse in the furnace has been observed by Parle and Wet-ashing may be suitable for the determination of single or small groups of elements for which the acids used can be selected for purity. Mitchell2 and Scott Mitchell Purves and Voss15 have described many of the contamination problems that can arise during the laboratory procedure.The sources can broadly be divided into contamination from atmospheric dust unsuitable equipment and the reagents used. Pinta3 showed that nitric acid evaporated in air instead of in a vacuum picked up large amounts of aluminium calcium iron and magnesium as well as copper manganese and nickel. The possibility of contamination of samples by volatile elements such as mercury should also be considered. The concentration of mercury found in the atmosphere of one of the Macaulay Institute’s laboratories in which metallic mercury was occasionally used was 2000 ng m-3 compared with 1300 ng m-3 in an adjacent laboratory and with only 190 and less than 80 ng m-3 in a laboratory office and outside air respectively. The design of the trace-element laboratory and some of the equipment used at the llacaulay Institute have been described by Mitchell.2912 In recent years the use of plastics for laboratory fittings and apparatus has increased and in Table I1 an indication is given of some of the elements that are extracted by the mild acidic treatment comprising leaving 1 g of shredded sample overnight in 100 ml of cold 0.1 M nitric acid.In most instances the samples were the same as those for which the total contents are given in Table I but a com- parison of Tables I and I1 shows that often it is not the elements that are listed as “liigli” in This phase begins with the preparation of the sample for analysis. SOME ELEMENTS EXTRACTED FROM Material I? a Bottle lid black . . . . 50 Phenolic Yeszn (Bakelite Tufnol etc.)- Paper based brown . . . . <5 Caydboard- Brown paper- Bottle lid liner .. . . .. 30 Bag . . . . . . . . 40 Greaseproof lined bag . . . . 123 Bag . . . . . . . . < 6 Tubing . . . . . . . . 35 Sample tube . . . . . . <5 Expanded foam black . . 31 Pol-ythene- Expanded foam white . . (5 Poly $ropy lene- Tube . . . . . . . . 11 Sheet . . . . . . . . 19 PoZy(vinyZ chlovide) (PVC)- Sheet grey . . . . . / 5 Tubing natural . . . . 25 Clear . . . . . . . . <:5 White . . . . . . . . 400 Black . . . . . . . . 10 Methyl methacrylate (Pevspex)- Po/ysty?ene- Polyavnide (LYj~Z~n)- Expanded foam whitc . . 70 liod natural . . . . .. 21 Cd <0*1 <0*1 (0.1 i o . 1 <0*1 <0*1 <0.1 <0.1 <0.1 <0*1 (0.1 ec0.1 <0.1 <0.1 0 . 1 -,0.1 co.1 6 (0.1 PolytetvafiuovoethyIene (Fluogt ; Tefion; Silicone nibbey- 13 itbbev- l i b o d e - Papey- liocl natural .. . . . . Tube natural . . . . . . Glove . . . . . . . . nrown . . . . . . . . Filter low grade . . . . Filter high grade . . .. Tissue laboratory grade . . 10 i o . 1 15 -co.1 ( 5 -:0-1 11 <0*1 7 .:0*1 110 ,0.1 VAR I 0 U S co < 0.3 17 ( 0 . 3 < 0.3 < 0.3 < 0.3 <0*3 < 0.3 < 0.3 (0.3 < 0.3 (0.3 < 0-3 < 0.3 < 0.3 < 0.3 < 0.3 < 0.3 0.3 < 0.3 (0.3 (0.3 1 <0.3 < 0.3 -<0*3 TABLE I1 MATERIALS BY Cr C U <0.1 <0.1 42 17 (0.1 9 <o-1 6 <0.1 11 2 (0.1 <0*1 <0.1 1 (0.1 1 2 4 (0.1 1 2 1 1 1 1 1 6 7 1% <0*1 ci 1 1 t 0 . 1 c0.1 1 2 <0*1 5 2 14 <0.1 5 <0*1 < @ I <0*1 2 DILUTE NITRIC ACID (p.p.m. IK ORIGINAL SAMPLE) Fe <5 1920 70 ( 5 69 26 20 <5 <5 36 < 5 < 6 6 <5 66 = 5 <5 <5 (5 25 33 <5 122 49 57 77 Hg < 0.0 1 <0.01 y.0-01 .< 0.0 1 < 0.01 (0.01 <0.01 (0.01 <0.01 <0.01 0.04 0.03 < 0.0 1 t 0 .0 1 (0.01 0.01 0.02 <0.01 (0.01 0.01 <0*01 (0.01 <0.01 <0*01 (0.01 <0.01 M 11 < 0.2 116 10 11 39 1 < 0.2 (0.2 1 1 (0.2 < 0.2 1 < 0.2 :0.2 < 0.2 < 0.2 I- 0.2 .:0.2 1 -, 0.2 1 2 1 < 0.2 3 Ni < 0.3 390 X 0 . 3 <0*3 < 0.3 (0.3 < 0.3 <0.3 < 0.3 < 0.3 <0.3 < 0-3 < 0.3 < 0.3 y 0.3 0.5 0.5 < 0.3 3 0.5 ’0.3 -< 0.3 0.5 < 0-3 < 0.3 < 0.3 l’b <0.5 < 0.5 <0*5 < 0.5 < 0.6 <0.5 .< 0.5 < 0.5 < 0.5 ( 0 . 5 < 0.5 < 0.5 1 <0.5 < 0.5 < 0.6 J 0.5 ./ 0.5 < 0.5 / 0 . 5 < 0.5 <0.5 6 <:0*5 <0.5 < 0.5 Ti < 0.8 < 0.3 1.3 0.5 1.6 1.3 (0.3 < 0.3 <0.3 < 0.3 1-5 1.8 < 0.3 < 0.3 0.8 2.0 0.5 <0.3 < 0.3 c.0.3 0.3 -1 0.3 1 < 0.3 < 0.3 < 0.3 V < 0-3 < 0.3 < 0.3 < 0.3 1.0 <0.3 0.5 < 0.3 < 0.3 < 0.3 < 0.3 < 0.3 < 0.3 < 0.3 < 0-3 < 0.3 < 0.3 < 0.3 < 0.3 < 0.3 < 0.3 (0.3 1 < 0.3 < 0.3 < 0.3 Zn 34 7 3 2 4 1 <0.01 <0-01 2 4 2 1 3 <0,01 1 50 6 5 1 0.01 0.5 50 120 2 0.5 120 December 19721 SELECTIVITY I N TRACE ANALYSIS 293 Table 1 that are extractable. The sample of PVC tubing (Table 11) shows barium as the only nitric acid extractable element although an earlier sample showed water-soluble tin (Table I ) . ‘The elements that are extractable from most of the materials considered are barium copper iron manganese and zinc although the iron in some instances may be caused by laboratory contamination.Many of the materials contain trace amounts of mercury (ebonite 70 p.p.m. ; black polythene expanded foam 0.3 p.p.m.) but in most instances the mercury present appears to be insoluble. Tables I and I1 emphasise the necessity of ensuring that any material used cannot introduce into the sample the elements that are being determined. Tlie reagents used can usually be selected for purity when only a few elements are being determined. Mitchel116 and Scott Xitchell Purves and Voss15 described methods for the preparation or purification of reagents such as acetic nitric and hydrochloric acids ammonia solution sodium and calcium carbonates and iron and aluminium chlorides and oxides.For multi-element analysis it may be necessary to purify them. The authors thank Messrs. Churchill Livingstone Edinburgh for permission to reprint T Table 1. 3 . 4. 3.. 6 . 7 . 8. !I. 10. 11. 12. 13. 14. 1.5. 16. ? d . REFERENCES Hamilton E. I. and Minski M. J. Enviv. Lett. 1972 3 53. JIitchell R. L. J . Scz. Fd Agric. 1960 11 553. Pinta M. Colloyues X a t n . Cent. Watn. Rech. Scient. 1970 S o . 923 25. Robertson D. E. Analj)t. Chew. 1968 40 1067. Scott K. O. in Mills C . F. Editov “Trace Element Metabolism in ;Inimals,” Churchill Livingstone l’hiei-s R. E. Me!h. Riochem. ,4nalysis 1957 5 273. Zief M. and Rlichelotti I;. W. Clin. Chew. 1971 17 833. O’Sullivan M. .J. Sci. Fd Agvzc. 1969 20 259. Schwarz I<. in. Mills C . I;. Editov op cit.p. 25. Kitchie P. D. Critchley S. \fr. and Hill X. Editovs “Plasticisers Stabilisers and Fillers,” Iliffe \f7insor H. W. Soil Sci. 1957 84 389. Jlitchell R. L. zvz “Analytical Chemistry. \Villiams D. E. and Vlamis J . So22 ScZ. 1961 92 161. l’arle P. J . and Fleming G. A Analjlst 1972 97 19.5. Scott R . O. Mitchell R. J2. Purves D. and VOSS R. C. Biill. c‘omz/fI. C o n m . L)e?l. Spectvogv. Wk Mitchell R. L. Tech. Covnm. C O W 2 ~ O n ? Y J . BUY. Soils Havpenden 1864 No. 44X. Edinburgh and London 1970 p. 497. London 1972. Proceedings of the Feigl Xniiiversary Symposium Birmingham 1962,” Elsevier Amsterdam 1963 p. 314. iVIucaulay Inst. Abevdeen 1971 NO. 2. Programmed Elution Thin-layer Chromatography as a Technique in the Selective Analyses of Phenols BY JOHN M. PHJLP (Glenochil Reseavch Statiox Distillem Co.L t d . Menstvie Clackmannanshire FK11 7ES) THIS-L~I-ER chromatography has now been in common use for about 10 years and has changed little during this period. It is still generally considered to be a simple technique requiring only a glass plate coated with an adsorbent a glass tank and a suitable solvent. On the whole this concept works well on simple mixtures of components. If however the mixtures are more complex and contain components of both similar and widely differing polarities as is often found in samples of natural origin then preliminary fractionation is usually required followed by multiple-elution or gradient-elution analyses by thin-layer chromatography in order to achieve the required resolution of the components. These are time-consuming procedures and there is therefore an obvious case for the automation of the thin-layer chromatographic process.In addition the introduction of automation removes the time factor from the analyses and slower moving less polar solvents may then be used with a corresponding increase in resolution. Tlie traditional thin-layer chromatographic tank with the solvent and solvent vapour a t equilibrium is not amenable to automation. We must therefore examine the r6le of the solvent 294 SELECTIVITY I N TRACE ANALYSIS LYroc. SOC. ,4 nnlyt. C'hcm. vapour in the thin-layer chromatographic process and determine the advantages and dis- advantages if any of maintaining the solvent vapour at equilibrium during the whole of the development process. The two basic vapour states are ( a ) saturated which by definition means that the solvent must be added to the tank a t least 1 hour before the addition of the plate and (b) unsaturated which again by definition means that the solvent and the plate are added simultaneously to the dry tank.Traditionally and largely due to the application of paper chromatography theory to thin-layer chromatography it has been assumed that an unsatur- ated vapour state would have an adverse affect on both the resolution and the reproducibility of the RF values. However Von Arx and Neher,l and more recently Jones and Heathcote,2 have reported a better separation of amino-acids under unsaturated vapour conditions. In addition de Zeeuw and Feitsma3 found that hypnotics could best be separated by using an unsaturated chamber. Subsequent investigations by de Zeeuw4 demonstrated conclusively that the r81e of the solvent vapour is very important and that with multi-component solvents the best separations are not necessarily associated with saturated tanks.A contributing factor was undoubtedly the preferential adsorption on to the silica gel of one of the components in the solvent vapour thus creating a polarity gradient on the adsor- bent. Vapour not originating from the solvent could also influence the resolution of com- ponents in the mixture. For example the activated silica gel plate could be treated with ether vapour to establish a polarity gradient prior to development in chloroform. These observa- tions led to the development of vapour-programmed thin-layer chromatography by de Zeeuwj and the subsequent application of this technique in the separation and identification of pharmaceutical sulphonamides.In further studies by de Zeeuw,6 involving the use of a single solvent benzene and silica gel layers in both saturated and unsaturated tanks it was also observed that the unsaturated vapour state produced better resolutions. This unexpected result was inexplicable in terms of de Zeeuw's previous theory and is still unexplained. Development work by Philp7,s on the use of saturated and unsaturated vapour conditions for the separation of monohydric dihydric and trihydric phenols was carried out at approxi- mately the same time as and independently of the work of de Zeeuw. I t was concluded that saturated vapour conditions were not an essential prerequisite for the satisfactory resolution of these phenols and that the resolution could often be improved by using unsaturated vapour conditions.From these preliminary investigations a manual programmed elution thin-layer chroma- tograph was ~ o n s t r u c t e d ~ ~ ~ which was then developed into an entirely automatic programmed elution thin-layer chr~matograph.~ The thin-layer chromatographic plates are activated and the spots applied in the normal manner. The programmed elution under either unsaturated or saturated vapour conditions is then entirely automatic. The pre-selected solvent is added to the solvent trough in the thin-layer chromatographic tank by gravity and the plate developed with or without vapour saturation in the normal way. The solvent is then drained and pumped back to the original solvent reservoir. The plate is dried in.sit% with nitrogen or air at constant pressure for a pre- set time. This process may be repeated indefinitely with any number of pre-selected solvents in order to achieve the desired solvent-polarity programme. The latter is achieved by incorporation of a 90" turn of the plate at an appropriate time in the development programme. A third mode of operation step-programmed development is also possible. In this mode the adsorbent on the plate is cut into four discrete strips diminishing in length in pre-determined steps from right to left. Each strip of adsorbent is spotted with both the mixture under analysis and a suitable reference mixture. By lowering the level of the solvent relative to the plate any strip or strips may be developed a t will. Consequently the effective length of the plate is increased four-fold without a corresponding increase in diffusion of the spots.A linear presentation of the spots rather than a two-dimensional presentation is also desirable for quantitative analyses by linear-scan densitometry. Solvents of increasing polarity may be applied to each plate mode as a simple multiple development with one solvent or as part of a pre-selected step-wise solvent polarity gradient. The turning of the plate in the two-dimensional mode and the control of the solvent level in the step-programmed mode is facilitated by incorporating automatic raising and lowering of the solvent trough The basic concept is simple. The solvent flow on the plate may be either one-dimensional or two-dimensional. December 19721 SELECTIVITY I N TRACE ANALYSIS 295 during these development programmes.All operations are controlled automatically from a twelve-position punched tape and twenty digital pre-selectors. Pro- grammes that could resolve amixture of twenty-five model phenols by both the two-dimensional and the step-programmed mode were also presented. The order of elution is principally governed by the number of hydroxyl groups which are then modified in polarity by the other functional groups present in the molecule. As a result a definite elution sequence is predict- able. Functional group analyses with conventional sprays and reagents can then be carried out in the usual way. I t is therefore concluded that automatic programnied elution thin-layer chromatography is a useful convenient and time-saving technique for the analyses of complex mixtures of phenols and that these new concepts in both the theory and practice of thin-layer chromato- graphy should be applicable to the solution of diverse analytical problems.Examples of typical solvent programmes for each plate mode were presented. 1 . 2. 3. 4. 5. 6. 8. 9. 1 . REFERENCES 1'011 Llrx E. and Neher K. J . Chrounat. 1963 12 329. Jones K. and Ileathcote J . C. Ibid. 1966 24 106. de Zeeuw R. A. and Feitsma M. T. Pharm. Weekbl. Ned. 1966 101 957. de Zeeuw R. A. J . Chrorvlat. 1968 32 43. - Ibid. 1970 47 382. Philp J . M. PYOG. Soc. Analyt. Cheun. 1969 6 77. -- Ph.D. Thesis Heriot-Watt University 197 1 . - British Patent Application No. 09642/71. - l b i d . 1970 48 27. Problems in the Measurement of Drug Availability BY J . P. GLYNN (Stevlzng- Winthrofi Reseavch and Development Fawdon Newcastle upon Tyne h'E3 3 T T ) THE clinical cffect of a drug can be altered dramatically by both the rate of absorption of the drug into the body and by the amount absorbed.There is a good deal of evidence that indicates that the absorption characteristics of a drug and so its therapeutic action can be greatlv altered by the various materials and processes used in preparing the dosage form or formulation. The formulation may contain several other materials besides the active drug which are biologically inactive themselves and are included for a variety of reasons such as to reduce the disintegration time of a tablet to prevent bacterial growth in a suspension or to mask tlie taste of the drug. Until recently it was considered that these excipients played little or no part in drug abqorption and so far as the oral dose forms were concerned if a compressed tablet had a satisfactory disintegration time it could be biologically equivalent to other tablets of similar disintegration times.Studies on the effect of dosage form on drug absorption have been made necessary because o f tlie possibility of improving drug absorption by altering the formulation. Conversely the risk of increasing the toxicity of a drug unintentionally by changing the formulation is becom- ing more apparent. The problem therefore is to devise ways of testing changes in drug formulations in vizm before they reach the clinic or chemist. In other words a form of bio- logical quality control is required. The first proof of the availability of a drug from a particular formulation is the size and duration of the drug's biological action.Unfortunately this is very difficult to quantify for most drugs. The second proof could be the concentration of the drug at the sites of action. This is virtually impossible to quantify so in practice the appearance of the drug and its metabolites in the blood urine and tissues is accepted as proof of availability. This approach is based on the assumption that the drug concentration in the blood reflects tlie concentration at the site of action. Availability studies therefore are concerned primarily with measuring the rate of appearance concentration and duration of the drug and its metabolites in the blood stream. This is not now accepted. 296 SELECTIVITY IN TRACE ANALYSIS PYOC. SOC. A izalyt. Chrm.These studies are not carried out in hospitalised patients but in normal healthy young subjects. This may appear anomalous as drugs are usually destined for sick patients and not healthy subjects. However such studies are designed to assess the variability of the formula- tion preferably before the drug reaches the market. Of course sick patients could be used and formulation differences detected by clinical failures. Clinical studies are rather imprecise and insensitive however and are of little value in the routine assessment of formulation differences. In operation an availability study would consist in various test and standard drug formulations being administered to between ten and twenty subjects according to established designs. The concentration of the drug in the blood or urine could be determined by a suitable specific analytical method.If the measurement of the drug level in blood is not possible alternative sources can be used. These include urine saliva and even perspiration. The basic quantitative measurements made in such a study are the maximum blood drug concentration (Cmax.) the time needed to achieve this (tmax.) and the area under tlie blood drug concentration zleYsz.1.s time curve ( A UC). The biological availability of a test formula- tion is related to that of a standard (usually solution) formulation by comparing tlie respec- tive A UC Cmax. and t,,,. values. The basic assumption made in this relationship are that first-order or experimental processes of drug metabolism and excretion operate. This relationship cannot be applied indiscriminately to drugs that are excreted by complex order processes nor can it be applied to drugs if the metabolising enzymes are saturatable.In these instances tlie relationship becomes more complicated. If a particular drug is extensively metabolised in the body then oral absorption differs from other routes in one important respect. When given orally the drug must pass tlirough the stomach or intestinal wall and then the liver before reaching the general blood pool. The net result is that even though all the drug is absorbed the proportion of unchanged drug that reaches the general circulation is less than that after intravenous administration when the drug does not pass totally through the liver immediately after administration. This “first- pass effect” rules out the comparison of oral rectal intramuscular and intravenous administra- tion of highly metabolised drugs on the basis of the corresponding areas Cmax.and tmax. I t is essential therefore that such drug formulations are compared by the use of the same route of administration. (This “first-pass effect” explains the 1000 1 comparative potency of some drugs when the drug is given intravenously or orally in equal amounts. When given orally the drug is decimated by liver and gut enzymes and reduced to its inactive metabolite.) When biological availability studies are used in conjunction with kinetic studies of the drug in man they can provide the basis for rational drug therapy. They can also alert pharmaceutical scientists and clinicians to the fact that formulation effects can and do occur and must be considered as one of the possible causes of therapeutic drug failure.A New Gas Chromatography Detector Tunable to a Wide Range of Elements BY W. R. MCLEAN D. L. STANTON and G. E. PENKETH (Inzpevial Chemical Industries Limited Petvochernicals Division Research and Development Dcpartmrnt Billingham Teesside TS23 1 JB) IN 1965 McCormack Tong and Cookel described an element-selective detector for gas chromatography in which argon used as the carrier gas passed from the chromatograph outlet through a gas discharge or plasma sustained by microwaves. As organic molecules entered the plasma they decomposed into atomic fragments. In turn these fragments were excited by the energy of this plasma and added their emission spectra to that of the carrier gas. On viewing selected parts of the emission spectra by means of a tunable monochromator a degree of element selectivity was obtained.Later Bache and Lisk2 showed that substitution of argon by helium gave a more energetic plasma that enabled atomic-emission lines to be used (e.g. S a t 545.3 nm) in place of diatomic band heads (e.g. CS at 257.6 nm). An argon plasma could be operated at atmospheric pressure but with helium a reduced pressure (1 to 10 torr) was necessary. Our early attempts to repeat the results of Bache and Lisk were unsatisfactory owing to a persistent deposition of carbon within the plasma tube. This deposition had disastrous December 19721 SELECTIVITY I N TRACE ANALYSIS 297 effects on the emission characteristics of the plasma and even interfered with tlie tuning of the microwave cavity.It was found that these difficulties were avoided by introducing a per- manent bleed of air oxygen or nitrogen into the plasnia to act as a carbon scavenger. This led to a dramatic improvement in the stability of the plasma during analysis. Further tests showed that element selectivity was improved and that the atomic emission detected was directly and linearly proportional to the amount of elements originally present in the organic compounds issuing from the gas-chromatographic column. All of the elements normally found in organic compounds could be selectively detected and quantitatively determined. To make effective use of the qualitative and quantitative character of the atomic emission a dual detection system was then devised. A separate supply of carrier gas was used to maintain the column system exit at a pressure above atmospheric.After mixing with the column outflow the combined flow was then split equally into two streams across specially designed flow restrictors to a non-selective flame-ionisation detector and the element-selective detector. The flame-ionisation detector signal acted as a reference for the quality of the gas-chromatographic separation as a relative measure of sample size and as a basis upon which to interpret the element-selective results. To a first approximation the flame-ionisation detector signal corresponded to that obtained from the element-selective detector channel when tuned to carbon (247.8 nm). Thus if the element- selective detector were tuned to hydrogen (656.2 nm) it was for example an easy matter to distinguish aromatic compounds (hydrogen-lean) from aliphatic compounds (hydrogen-rich) .The rapid visual information on elemental composition derived from the two simultaneous detectors was demonstrated on a synthetic test sample. For example of all the fourteen components indicated by the flame-ionisation detector only two contained chlorine and of these one had twice as much chlorine per carbon atom as the other (see Fig. l a ) . Of the two bromo compounds one had slightly less (six-sevenths) bromine per carbon atom than the other (see 1;ig. lb). The selectivity of detection with respect to a hydrocarbon matrix varied from element to element but was typically of the order of lo3 1 which is adequate for the un- ambiguous identification of tlie various elements. This dual system had many advantages.1 1 1 I i I I I J L M.P.D. channel chlorine 479.454 nm 12 I L ~~~~~ M.P.D. channel bromine 470.486 nm F.I.D. channel F i g . 1. Sclcctive detection of ( a ) chloro compounds and ( h ) h o m o co1npo1111(1~. 1 o-Dichloro- benzcwe ; 2 chlorocyclohcxanc ; 3 o-bromotoluene; and 4 bromobcnzenc 298 SELECTIVITY IN TRACE ANALYSIS [Proc. SOC. AnaZyt. Chcm. The quantitative nature of the element-selective responses can be used to determine the atomic ratio of pairs of atoms in various molecules and thereby to build up empirical formulae. By referring to the behaviour of ethylbenzene hydrogen carbon atomic ratios for paraffinic olefinic naphthenic and aromatic hydrocarbons were determined to within i-2 per cent. of theoretical values. For molecules containing carbon and chlorine the relative emission intensities accurately and linearly reflected stoicheiometries of C.Cl,.down to C.Cl,.,,,. In mono-oxygenated compounds such as ketones epoxides and alcohols the intensity ratio of carbon oxygen was directly proportional to the number of carbon atoms in the molecule. The least sensitive elements are oxygen nitrogen hydrogen and carbon because they are the most persistent contaminants of the helium carrier gas and the sensitivity of the tech- nique has an apparent dependence on the levels of spectral backgrounds at the element- selective wavelengths. Typical limits of detection have been in the range 0.03 to 0-09 ng s-l. Oxygen and nitrogen are exceptions and the best limits so far found have each been 3.0 ng s-l. Interference effects occur when the linear emission characteristics of the plasma are over- loaded with too much scavenger or organic material.This can instantly be recognised from the appearance of the plasma and the magnitude of the flame-ionisation detector response. Fluorine and to a lesser extent chlorine give rise to phantom oxygen signals as a result of the corrosion effect on the quartz plasma tube and the subsequent release of oxygen into the gas 1)hase. Inter-element effects are negligible for example the same hydrogen carbon intensity ratios are observed for chloroform and benzene. The detection technique has much to offer in problems concerning the analysis and identification of volatile organic compounds and gases. Work is in progress on the construc- tion of a multi-channel element-selective detector which it is hoped will lead to a rapid quantitative elemental analysis of organic compounds as they are sequentially delivered to the plasma by a gas-chromatographic column system.REFERENCES 1. 2 . McCormack A. J. Tong S . S. C. and Cooke W. D. AnaZyt. Chem. 1965 37 1470. Rache C. A. and Lisk A. J. Ibid. 1967 39 786. Spark-source Mass Spectrometry BY K. B. WRIGLEY (Analytical Control Section RISRA-The Covpovate Labovatovies oj the Bvztisli Steel Corpovation Hoyle Street Shefield S3 7 E Y ) SPARK-SOURCE mass spectrometry has not been widely adopted by the steel industry as it has been considered to be a slow inaccurate and expensive technique of dubious accuracy. However the instrumentation and techniques involved have radically changed over the past few years as have the British Steel Corporation’s trace analysis requirements.The Corporate T,aboratories of the British Steel Corporation have been investigating some of the newer aspects of the technique to determine its usefulness as a routine and research analytical tool in the steel industry. This paper outlined some of these developments together with some of the problems that were currently restricting application. An example was given of how the technique might be used for the improvement of steel quality. After briefly explaining the principles of double-focusing mass spectrometers the elec- trical detection facilities now available for spark-source mass spectrometers were described and the advantages (higher precision greater sensitivity increased sample throughput) to be derived from the use of such a system were discussed.However spark-source mass spectro- metry is still dogged by certain problems. Some of these problems were described with particular emphasis on sample inhomogeneity (and its effect on precision) and the difficulties experienced in establishing reliable relative sensitivity coefficients for quantitative analysis. The various ways of predicting or minimising the effects of these problems were also discussed the contributions in this field of Nichols,l Morrison and Rothenberg,2 Jackson Whitehead and \Tossen,3 Evans Guidoboni and Leipziger4 and Oblas5 being cited as particularly noteworthy . Finally the results were presented of some work carried out on the analysis of the rare earth elements lanthanum cerium praseodymium and neodymium in steels and steelmaking materials. December 19721 SELECTIVITY IN TRACE ANALYSIS 299 In recent years rare earth metals in the form of mischmetall have increasingly been used as additives to improve the physical properties of steels intended for oil and natural gas pipelines.The extent to which the properties are improved is critically dependent on the rare carth content of the steel; rare earths also act as powerful deoxidants and can be lost to a c.ertain extent from the melt so that it is important to have reliable analytical data on the rare earth content of the steel. The analysis of the rare earths is well known to be difficult. However X-ray fluorescence techniques have been used extensively for the determination of the element cerium alone. As cerium is present as about 50 per cent. of mischmetall it has become expedient to measure the cerium content of the steel and to double this to find the total rare earth content.This practice makes three assumptions that required verification-(a) that there is 50 per cent. cerium in mischmetall; (b) that the manufacturers’ supplies are of consistent cerium content; and (c) that there is no preferential loss of one or other of the rare earths lanthanum cerium praseodymium and neodymium during steelmaking. Spark-source mass spectrometry was thought to be a suitable technique as the rare earth region of the mass spectrum is relatively uncomplicated. As any differences in sample com- Iwsition were expected to be small the high precision peak switching technique was used. The analysis of five mischmetall samples produced few surprises typical compositions being approximately cerium 54 per cent.lanthanum 20 per cent. praseodymium 7 per cent. and neodymium 17 per cent. However one sample did show an exceptionally high cerium figure of about 67 per cent. which suggests that there might be variations in the product from at least one supplier. The analysis of the rare earth content of steels compared with mischmetall produced the results shown in Fig. 1 which indicates that the proportions of the individual rare earths appear to be changed in the addition process. Lanthanum and neodymium are lost in preference to cerium and praseodymium. Fig. 1 . Proportions of rare earth elements in steel (unshaded areas) and mischmetall (shaded areas) The effect of this phenomenon on a steel analysis is shown in Fig. 2. I t can be seen that cerium might constitute 65 per cent.of the total rare earths in the steel. For a typical steel containing 150 p.p.m. of cerium the total rare earth content of the steel would be calculated to be 300 p.p.m. by using the “50 per cent. cerium” assumption. However as the proportions of the rare earths are changed in the addition process the true rare earth content is substantially less about 230 p.p.m. 300 50 w C 8 40- 1 a Q .- 30- u aJ 20 SELECTIVITY IN TRACE AXALI-SIS Proc. Soc. ,4 IzaLyt. Chrw. - - 70 Steel 6 0 1 Mischmetall 50% 65% Fig. 2. Effect of the “50 per cent. cerium” assumption on thc total rare earth content of steel The example presented demonstrates just one of the features of the spark-source technique -the ability to perform relatively easily what would normally be considered a difficult analysis.There are other features of the technique that it is hoped to exploit in the future particularly the rapid scanning technique,6 which can reveal all elements present in a sample with liigh sensitivity. The application of this technique to the analysis of water and air particulate pollutants may offer a further example of how spark-source mass spectrometry can help to improve not only product quality but also the quality of some of the steel industry’s undesirable by-products. REFERENCES 1. 2 . 3. 4. 5. ti. Nichols G. D. Pvoc. BY. Ceram. Soc. 1970 April 85. Morrison G. H. and Kothenberg A. XI. Analyt. Chem. 1972 44 3. Jackson P. F. S. Whitehead J. and Vossen P. G. T. I b i d . 1967 39 14. Evans C. A, Guidoboni R. J . and Leipziger F. D. A p p l .Spectvosc. 1970 24 1 Oblas D. W. Ibid. 1971 25 3. Ringham R. A. and Elliott R. M. Analyt. Chem. 1971 43 1. Some Applications of Heteropoly Acids for Amplification Procedures in Atomic- absorption Spectroscopy BY H. N. JOHNSON G F. KIRKBRIGHT AND T. S. IVEST (Chemistvy Department Imperial College of Science and Techizology London S. 17*.7) DESPITE the wide applicability of atomic-absorption spectroscopy to tlie rapid and selective determination of trace concentrations of elements in solution there remain a number of elements that cannot be directly determined. These elements have their principal resonance lines in the far ultraviolet region or are difficult to atomise so that they can be determined with only poor sensitivity. The sensitivity (for 1 per cent. absorption) that can be attained depends principally on the oscillator strength for the line used the degree of atomisation in the atom cell and the efficiency of tlie nebulisation process by which the sample is introduced into the atom cell.To overcome these limitations indirect methods have been devised for many e1ements.l The basis of some of these methods involves the formation of a stoicheiometric compound between the analyte element and one or more other species and tlie subsequent determination of the equivalent concentration of this Any of these may be the cause of poor sensitivity. December 19721 SELECTIVITY I N TRACE ANALYSIS 301 other species in the compound. Molybdenum for example as molybdate forms binary heteropoly compounds with some thirty five elements,2 and other elements also form ternary complexes with molybdate and phosphate.In either case the analyte element may fre- quently form a heteropoly complex which can be extracted with a water-immiscible solvent. Phosphorus arsenic germanium and silicon can be determined by this general method via the formation of their respective binary heteropoly acids. The general method involves the addition of molybdate to an aqueous solution of the anionic analyte species adjustment of the acidity to the optimum value and extraction of the binary complex with a single volumeof organic solvent. The organic solvent is washed with dilute acid to remove traces of molybdate that are mechanically transferred or extracted into the solvent and is then nebulised into the flame for determination of the equivalent molybdenum in the extracted species.The molybdenum in the heteropoly acid is determined by atomic-absorption spectroscopy at 313-2 nm in an air - acetylene or nitrous oxide - acetylene flame. Phosphorus has been determined as orthophosphate by using various acidities and organic solvents. The latter include isobutyl acetate,3 n-butyl acetate,4 isobutyl methyl ketone5y6 and octan-2-01.~-~ The indirect method has been used for the determination of phosphorus in urine,3 milk product^,^ blood serum,57s plasma,G?s bone biological tissues and enzyme-containing reaction mixtures? and fresh water and seawater.9 In each case dodecamolybdophosphoric acid is formed. Boltz and co-workers have reported indirect methods for the determination of arsenic,l0 germaniumll and silicon12 singly. The molybdoarsenic acid is extracted with isobutyl methyl ketone and is then back-extracted into an ammonia - ammonium chloride buffer with decomposition of the heteropoly species.The molybdate in the aqueous layer is then determined by atomic-absorption spectroscopy in an air - acetylene flame at 313-2 nm. Molybdogermanic acid is extracted after formation at pH 1.5 with a 1 + 4 V/V mixture of pentan-1-01 - diethyl ether.ll The molybdogermanic acid is again back-extracted into a basic buffer to decompose the complex and the molybdate is determined by atomic-absorption spectroscopy. Molybdosilicic acid formed at pH 1.3 is extracted from 2 M hydrochloric acid with a 1 + 5 V/V mixture of pentan-1-01 - diethyl ether.12 Decomposi- tion and back-extraction is accomplished with 0.1 M ammonia solution. The aqueous layer is not immediately nebulised but a known excess of lead(I1) is added to precipitate lead molyb- date.The lead remaining in the supernatant solution is measured at 217.1 nm in an air - acetylene flame. Sequential methods have been developed for phosphorus arsenic and silicon,l3 phos- phorus and arsenic,14 and phosphorus and silicon.15>16 All rely on selective extraction. After the formation of molybdophosphoric molybdoarsenic and molybdosilicic acids in nitric acid at pH 0.7 the molybdophosphoric acid is extracted with isobutyl acetate and the associated molybdenum determined by atomic-absorption spectroscopy. The molybdoarsenic acid is extracted with a 1 + 1 + 2 V/V mixture of ethyl acetate - butanol - isopentyl acetate and the associated molybdenum again determined by atomic-absorption spectroscopy.The molybdo- silicic acid remaining in solution is then extracted into isobutyl methyl ketone in the presence of citrate. Of forty ions tested only titanium(1V) and zirconium( IV) interfere in the determination of phosphorus and germaniuni(1V) is the only ion that interferes in the determination of silicon. No ions were found to interfere in the determination of arsenic. Devoto14 determined arsenic in urine as molybdoarsenic acid by extracting with cyclohexane after first removing phosphate as molybdophosphoric acid with isobutyl acetate. Kirkbright Smith and Westl5 first determined phosphorus and silicon sequentially in the same aliquot of solution via the respective heteropoly acids. The molybdophosphoric and molybdosilicic acids are formed in 0.96 M hydrochloric acid from which molybdophosphoric acid is extracted with isobutyl acetate and the associated molybdenum determined in a nitrous oxide - acetylene flame.After adjusting the acidity to 0.15 M hydrochloric acid the molybdosilicic acid is extracted with butanol and the molybdenum measured at 313-2 nm in a nitrous oxide - acetyl- ene flame. Hurford and Boltz16 used diethyl ether to extract the molybdophosphoric acid and a 1 + 5 V/V mixture of pentan-1-01 - diethyl ether for the extraction of molybdosilicic acid. In both instances the heteropoly acids are back-extracted and decomposed with a basic buffer before the molybdenum is measured in an air - acetylene flame. As all the binary heteropoly acids have a molybdenum to element combining ratio of 12 1 good sensitivity is obtained (see Table I).Ternary heteropoly acids have been used for the determination of niobium,l7 thorium,ls Ten minutes is normally sufficient for formation of the complex. 302 SELECTIVITY IN TRACE ANALYSIS ~PVOC. SOC. Analyt. Chem. TABLE I INDIRECT ATOMIC-ABSORPTION SPECTROSCOPIC METHODS BASED ON THE FORMATION OF MOLYBDOHETEROPOLY CORIPOUNDS Sensi tivi ty * Element P As Ge Si V Nb Th Ti Indirect 0.003 0.025 0.05 0.008 0.01 1 0.015 0.063 0.013 Direct7 250 0.25 3.5 2.0 1-5 20 - 2.0 1 Range (Indirect) pg/ml-l Reference 0.04-2 7 0.2-2 13 0-1.6 11 0.08-1 -2 15 0,2-2 21 0.22-2.2 17 1-6 18 0.3-3 19 * Concentration in p g ml-I for 1 per cent. absorption. t From Perkin-Elmer Methods Book. titaniumlg and vanadium.20*21 Excess of phosphate and molybdate is added to a solution of the metal ion and the acidity adjusted to the optimum value.As the phosphate and molyb- date are present in excess molybdophosphoric acid is always formed simultaneously and its prior selective extraction is necessary. In the niobium1’ and thorium18 procedures isobutyl acetate is used to remove the excess of molybdophosphoric acid followed by butanol to extract the complex. With the thorium complex the butanol probably extracts only the molybdo- phosphoric acid associated with the complex.22 A 1 + 4 V/V mixture of butanol- chloroform is used to selectively extract the excess of molybdophosphoric acid in the titaniumlg and vanadium21 procedures. Again butanol is used to extract the complex and as with the niobium and thorium procedures the associated molybdenum is determined in the organic solvent in a nitrous oxide - acetylene flame.Calibration solutions for niobium and titanium are prepared by dissolution of the metal in hydrofluoric acid. Aluminium(II1) is added to prevent the interference of fluoride in the titanium determination. A mixture of 1 + 4 V/V pentan-l-ol- diethyl ether may be used to extract the vanadium heteropoly complex after the excess of molybdophosphoric acid is removed with diethyl ether.20 Back-extraction of the complex into a basic buffer is then required before the niolybdenuni is determined in an air - acetylene flame. Because the molybdenum to element combining ratios are 11 1 or 11 2 with titanium good sensitivity is achieved (Table I). The indirect heteropoly acid method for vanadium has been applied to the determination of vanadium in aluminium.21 Although the indirect methods described are of necessity more time consuming than direct methods an enhancement in sensitivity of up to two orders of magnitude can frequently be obtained without significant loss of selectivity for particular analyses.1. 2. 3. 4. 5. 6. 7. 8. 9. 20. 11. 12. 13. 14. 15. 16. 17. IS. 19. 20. 21. 22. REFERENCES Kirkbright G. F. and Johnson H. N. Talanta ifi the press. Cotton F. A. and Wilkinson G. “Advanced Inorganic Chemistry,” Second Edition Interscience Devoto G. Boll. SOC. Ital. Biol. Sper. 1968 44 424. Kumamaru T. Otani Y. and Yamamoto Y. Bull. Chem. SOC. Japan 1967 40 429. Linden G. Turk S. and Tarodo de la Fuente B. Chemia Analit. 1971 53 244. Parsons J . A. Dawson B. Callahan E. and Potts J . T. jun. Biochem. J. 1970 119. 791.Zaugg W. S. and Knox R. J. Analyt. Chem. 1966 38 1759. - Analyt. Biochem. 1967 20 282. Zaugg W. S. Atomic Absorption Newsletter 1967 6 63. Danchik R. S. and Boltz D. F. Analyt. Lett. 1968 1 901. Jakubiec R. J. and Boltz D. F. Analyt. Chem. 1969 41 78. Trudell L. A. and Boltz D. F. Mikrochim. Acta 1970 1220. Ramakrishna T. V. Robinson J. W. and West P. W.. Analytica Chirn. Acta 1969 45 43. Devoto G. Boll. SOC. Ital. Biol. Sper. 1968 44 425. Kirkbright G. F. Smith A. M. and West T. S. Analyst 1967 92 411. Hurford T. R. and Boltz D. F. Analyt. Chem. 1968 40 379. Kirkbright G. F. Smith A. M. and West T. S. Analyst 1968 93 292. Kirkbright G. F. Rao A. P. and West T. S. Spectrosc. Lett. 1969 2 69. Kirkbright G. F. Smith A. M. West T. S. and Wood R. Analyst 1969 94. 754. Jakubiec R. J. and Boltz D. F. Analyt. Lett. 1968 1 347. Johnson H. N. Kirkbright G. F. and West T. S. Analyst 1972 97 696. Barkovskii V. F. and Velikanova T. V. Russ. J . Inorg. Chem.. 1970. 15. 829. London 1966 p. 941. NOTICES 303 Obituary NORMAN EVERS \\-E deeply regret to announce the death of Dr. Norman Evers formerly Editor of ,4~zalyticnl ,lhstractsJ on October 25thJ 1972. A full obituary will be published in a later issue of Pro- ctwlings.

ISSN:0037-9697    

DOI:10.1039/SA9720900288

出版商:RSC    

年代:1972

数据来源: RSC

摘要:

NOTICES 303 Notices INTERNATIONAL SYMPOSIUM ON SELECTIVE ION-SENSITIVE ELECTRODES APRIL 9TH TO 12TH 1973 CARDIFF THIS International Symposium will be held under the sponsorship of I.U.P.A.C. at the Uni- \-crsity of Wales Institute of Science and Technology in Cardiff. Plenary lectures will be given by Prof. E. Pungor Prof. G. A. Rechnitz Prof. W. Simon Prof. G. Bates and Dr. J. H. Riseman. About 50 contributed papers will be presented and discussed under the following subject headings 1 New electrodes including reference elec- trodes ; 2 Interference and mechanism studies ; 3 Activity - concentration problems ; 4 General applications ; 5 Applications to the study of chemical equilibria including stabilitj- constants; 6 Applications in the medical and biological fields; and 7 Application to on-line and general control of processes.Further details and application forms can be obtained from the Symposium Secretary Sliort Courses Section U.W.I.S.T. King Edward VII Avenue Cardiff CF1 3NU Wales. INTERNATIONAL SYMPOSIUM ON LIQUID SCINTILLATION COUNTING SEPTEMBER 3RD TO 6TH 1973 BRIGHTON FOLLOWING last year’s very successful venture the Radiochemical Methods Group propose to hold a second International Symposium on Liquid Scintillation Counting at the Hotel Metro- pole Brighton. An exhibition of scintillation counters scintillators and associated equipment will be held in conjunction with the scientific programme. Persons wishing to present a contribution to this symposium and firms wishing to take part in the exhibition should write to Mr. M. A. Crook Radiochemical Methods Group Society for ,4nalytical Chemistry 9/10 Savile Row London W1X 1AF.CHEMICAL SOCIETY “REVIEW SYRIPOSIA” THE Chemical Society is extending its educational programme for practising chemists by starting a series of short teaching courses. These will be two-day meetings with a strong iustrsictional element” and thus quite distinct f r o m the Society’s specialist research symposia. The basic aim of review symposia will be to cater for graduate chemists from many specialisms either by introducing new topics in chemistry that may be of direct or peripheral interest or hy updating them in fundamental areas of chemistry that have progressed very quickly since the chemist graduated. SYMPOSIUM 1 REVIEW SYMPOSIUM ON ‘(HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY” JULY 4TH TO 5TH 1973 UNIVERSITY OF SUSSEX There will be four lectures by renowned authorities who will deal with principles techniques of liquid - liquid partition and liquid - solid adsorption and with ion-exchange chromatography.Additionally there will be an extensive exhibition and a “brains trust’’ on the second day to deal with matters arising from lectures and from the equipment exhibited. SYMPOSIUM 2 REVIEW SYMPOSIUM ON ‘(ENZYMES’’ JULY 1 8 ~ ~ TO 1 9 ~ ~ 1973 UNIVERSITY OF EXETER The chemistry and biochemistry of enzymes is a rapidly growing and important field not only of research but also of practical applications. This Symposium is not intended for special- ists but primarily for graduates in chemistry with the object of giving them a general outline of the subject. There will be eleven lectures grouped under the general headings “What enzymes do,” ‘‘What enzymes are,” “How enzymes work” and “Application of enzymes.” Details and application forms for both Symposia 1 and 2 are available from Dr. M. D. Robinson Education Officer The Chemical Society Burlington House London W1V OBN.

ISSN:0037-9697    

DOI:10.1039/SA9720900303

出版商:RSC    

年代:1972

数据来源: RSC