摘要:

Proceedingsof the Analytical Division ofThe Chemical Society11344374242434446CONTENTSAnalyst Publications CommitteeSociety for Analytical ChemistryGold MedalSociety for Analytical ChemistrySilver MedalSummaries of Papers'Research and Development Topicsin Analytical Chemistry'Pesticide Residue AnalysisAnalytical Chemistry Trust FundPublications ReceivedMeetingsCoursesAnalytical Division DiaryVolume 16 No 1 Pages 1-46 January 197PADSDZ 16(1)1-46(1979)ISSN 0306-1 396The University of Bristol, April 3rd-5th, 1979PROCEEDINGSOF THEJanuary 1979ANALYTICAL DIVISION OF THE CHEMICAL SOCIETYOfficers of the Analytical Divisionof The Chemical SocietyPresidentR. BelcherHon. SecretaryP. G . W. CobbHon. Treasurer Hon.Assistant SecretariesJ. K. Foreman D. I. Coomber, O.B.E.; D. C. M. Squirrel1Secretary Hon. Publicity and Public Relations Officer Editor, ProceedingsDr. A. Townshend, Department of Chemistry,University of Birmingham, Birmingham, B15 2TTMiss P. E. Hutchinson P. C. WestonProceedings is published by The Chemical Society.Editorial: The Director of Publications, The Chemical Society, Burlington House, London, W1 V OBN.Telephone 01 -734 9864. Telex 268001.Subscriptions (non-members): The Chemical Society, Distribution Centre, Blackhorse Road,Letchwonh, Hens., SG6 1 HN.Nonmembers can only be supplied with Proceedings as part ot a combined subscription with The Anslysfand Analytical Abstracts.0 The Chemical Society 1979// 11 CHEMICAL SOCIETY/ROYAL INSTITUTE OF CHEMISTRYANNUAL CONGRESSThe Analytical Division will arrange two symposia. At the first, "lmmuno andCoupled Enzyme Assays," the speakers will be Professor Vincent MarksDr. Alister Voller, Dr. David Gofdie, Dr. John Whicher, Mr. B. Jovce, Dr. J. N.Miller, Dr. D. I. Chapman and Dr. A. C. Moffat.The second Symposium will be on the subject "The Influence of SpaceExploration on Analytical Instrumentation" and those speaking will be Dr. JamesMartin, Dr. Benton C. Clark, Professor Klaus Biemann, Dr. C. T. Pillinger andMr. R. J. Granger.In addition, the eighth Theophilus Redwood Lecture, entitled "Analysis in Non-segmented Flowing Systems," will be given by Professor E. Pungor.For further information contact Dr. J. F. Gibson, The Chemical Society,Burlington House, Piccadilly, London, W1 V OBN

ISSN:0306-1396    

DOI:10.1039/AD97916FX001

出版商:RSC    

年代:1979

数据来源: RSC

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January, 1979 ANALYTICAL DIVISION DIARY 45Analytical Division Diary, continuedFebruavy, continued“:\nalytical Chemistry and the ChemicalIndustry : Courtship and Marriage,” byC. lihalley.Department of Chemistry, University ofXberdeen, Meston Walk, Old Xberdeen.Tuesday, 20th, 4.15 p.m. : LoughboroughMidlands Region, jointly with the Lough-borough University of Technology Chemi-cal Society.“Optoacoustic Spectrometry and its Applica-tion to the Examination of Solid and LiquidSamples,” by G. F. Kirkbright.Lecture Theatre J O O l , University of Tech-nology, Loughborough, Leics.Wednesday, 21st, 2 p.m.: LondonMicvochemical Methods Gvoup: Meeting ofthe Elemental -4nalyser User Forum on“Determination of Low Levels of Carbonand Kitrogen.”Speakers : E.Hall and D. Mealor.Royal School of Mines, Prince Consort Road,London, S.W.7.Friday, 23rd, 9 a.m.: EdinburghScottish Region, Chvomatogvaphy and Electvo-plzovesis and Joint Pharmaceutical AnalysisGvoups, jointly with the Association ofClinical Biochemists and the Chromato-graphy Discussion Group on “High-performance Liquid Chromatography inClinical and Biological Chemistry.”“Recent Developments in Post-columnReactors for HPLC,” by Professor Ii. l V .Frei.“HPLC -Analysis of Drugs of .ibuse,” by-4. C. Moffatt.“Hl’LC AAnalysis of *Antidepressants on SilicaGel,” by I. I). Watson.“The Contribution of HPLC in Cases ofAcute Poisoning,” by M. J . Stewart.“HPLC in Clinical and PharmacologicalStudies of Analgesic Drugs,” by L. F.I’rescott.“Clinical ,inalysis of Steroids by HPLC,”by P.I?. Dixon.“The Development of HPLC Methods forthe Estimation of Enzymes of the HaemBiosynthetic Pathway,” by C. K. Lim.Department of Chemistry, The University,\Test Mains Road, Edinburgh.Tuesday, 27th, 4.30 p.m.: Swansea1Yestevn Region, jointly with the South West\Vales Section of the CSjRIC.“Nuclear Microprobes : *A Xew Technique forMaterials Examination,” by T. B. Pierce.Chemistry Department, University College,Swansea.CHEMICAL SOCIETY, ANALYTICAL DIVISIONMIDLANDS REGIONA Meeting onFLOW INJECTION TECHNIQUESatThe University of Aston in Birmingham24th April, 1979The speakers will include Dr. J. Ruzicka and Dr. D. Betteridge. Presentationsare invited for this meeting, and these may take the form of short papers, postersor table-top demonstrations.Summaries of proposed contributions should be sent to Dr.J. N. Miller,Department of Chemistry, Loughborough University of Technology, Lough-borough, Leicestershire, LEI 1 3TU, before February 28th, 1979Analytical DivisionJANUARYTuesday, 16th, 6 p.m.: LondonSouth East Region : Annual General Meeting,“Present and Future Role of Public Analysts,”Linnean Society, Burlington House, Picca-followed by an Ordinary Meeting.by A. J . Harrison.dilly, London, W. 1.Wednesday, 17th, 2.30 p.m. : Sheffieldand District Section of CS/KIC.Analysis,” by J . B. Headridge.North East Region, jointly with the Sheffield“A Century of Achievemerlt in MetallurgicalCity Polytechnic, Sheffield.Special Techniques Group on “Analytical Useof Semiconductors as Transducers.”Further details of this meeting may be ob-tained from Dr. I<.Mounce, British Gas,London Research Station, Michael Road,London, SW6 2AD.Lecture Theatre C, Old Chemistry Building,Imperial College, South Kensington,London, S.W.7.Wednesday, 17th, 2 p.m.: LondonThursday, lSth, 12 noon: LondonJoint Pharmaceutical Analysis Group : AnnualGeneral Meeting; 12 noon.IXscussion Meeting on “Analytical ProblemsAssociated with Specialised Dosage Forms” ;2 p.m.Pharmaceutical Society of Great Britain, 1Lambeth High Street, London, SE1 7JN.North West Region : Annual General Meeting,followed by the retiring Chairman’sAddress.“Analysis -An Industrial Viewpoint,” byJ .W. Ogleby.Training Centre, Laporte Industries Ltd.,Warrington.Friday, 19th, 6.30 p.m. : WarringtonTuesday, 23rd, 4 p.m.: BelfastNorthern Ireland Sub-Committee.“Catalytic Methods in Analytical Chemistry,”Queen’s University, Belfast.Wednesday, 24th, 7 p.m.: BathWestern Region.“What Price Analysis,” by F. Sweeting.Chemistry Department, The University, Bath.North East Region : Annual General Meeting,“Opium-Analysis and Anecdotes,” by C. A.Europa Lodge Hotel, Darlington.by G. Svehla.Wednesday, 24th, 7.15 p.m. : Darlingtonfollowed by a lecture.Johnson.DiaryThursday, 25th, 2 p.m.: Burton-on-TrentMidlands Region.“Analysis and the Brewing Industry,” byP. A. Martin.“The Examination of Wines and Spirits €orExcise Purposes,” by G.C. Hands.Reception Centre, Allied Breweries (Produc-tion) Ltd., Station Street, Bnrton-on-Trent.FEBRUARYWednesday, 7th, 2.30 p.m.: LondonAnalytical Division on “Affinity Chromato-“Affinity Chromatography on lmmobilised“Some Alternatives in the Design of AffinityThe meeting will also include poster presenta-Scientific Societies Lecture Theatre, 23graphy. ”Nucleotides,” by C. R. Lowe.Systems,” by 1’. I>. G. Dean.tions.Savile Row, London, Mi’. 1.Thursday, Sth, 10 a.m.: LondonMicrochemzcal Methods, Atomic Spectroscopyand Rndiochemical Methods Groups on“The Determination of Heavy Metals.”“The Evolution of Spectrochemical Tech-niques,” by G. F. Lewis and R. P. Farrow.“Electrochemical Methods for the Deter-mination of Heavy Metals,” by R. C.Rooney.“Activation and X-ray Methods,” by J. S.Hislop.“Water Analysis,” by K. C. Thompson.“Heavy Metals in Food and Drink,” byW. €€. Hill.“Trace Metals in Agriculture-EssentialityVersus Toxicity,” by D. S. Kirkwood.“Heavy Metals in Forensic Science,” byD. A. Hickman.Laboratory of the Government Chemist,Cornwall House, Stamford Street, London,SE1 9NQ. (Please enter the building bythe Waterloo Bridge entrance.)Thursday, 8th, 8 p.m.: ChesterNorth West Region, jointly with the SouthCheshire Branch of the PharmaceuticalSociety, on “Biological Values and theInfluence of Drugs.”Speakers: J. Barnes and A . Stott.Queens Hotel, Chester.Scottish Region, jointly with the Aberdeenand North of Scotland Section of the CS/RIC and the Aberdeen University ChemicalSociety.[continued inside back coverMonday, 12th, 4.15 p.m.: Old AberdeenPrinted by Heffers Printers Ltd Cambridge Englan

ISSN:0306-1396    

DOI:10.1039/AD97916BX003

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

4 RESEARCH AND DEVELOPMEWT TOPICS Proc. AnaZyt. Div. Chewz. SOC. Research and Development Topics in Analytical Chemistry The following are summaries of twelve of the papers presented at the Research and Develop- ment Topics in Analytical Chemistry meeting of the Analytical Division held on June 28th and 29th, 1978, at the University of Wales Institute of Science and Technology, Cardiff. Studies in Flow Injection Analysis B.Fields Department of Chernistvy, Univevsity College of Swawsea, Si9agleton Park, Swansea, SA2 8PP Unsegmented continuous-flow analysis or flow injection analysis (FIA) has been developed during the last 4 years as an automatic method of analysis that is simple, accurate and rapid, typical sampling rates being 120 per h o ~ r . l - ~ In all such systems, a stream of reagent or other carrier flows through a small-bore tube, the flow-rate being maintained by a constant-pressure or a constant-volume pump. At a point along the length of the tube an injection mechanism allows the sample to be injected into the stream and as the sample bolus passes down the tube it may react with reagent in the stream or undergo other reactions with the stream solution.Situated downstream from the injection point is a sensor that measures the extent of these reactions. As the sample is injected directly into the carrier stream it follows that there is an inter- facial region between the sample plug and the carrier and that during the course of mixing concentration gradients are established across the interface if the initial concentrations in the carrier and sample are different.Thus, if we have a system in which the sample solution is a mixture of metal ions at a given pH and the carrier is at a different pH and is a solution of a reagent that reacts with the metal ions, we would expect a well defined sequence of colour-forming reactions to take place across the interfacial region as the reagent and metal ions reacted and the pH ~ h a n g e d .~Jniiitnry, 1979 RESEARCH AND DEVELOPMENT TOPICS 5 To test the feasibility of this approach a crucial experiment is suggested by the pH - absorbance graphs of the lead and vanadium chelates of 4- (2-pyridylazo)resorcinol (PAR) obtained under static conditions. At pH 9, only the lead will react with PAR whereas at pH 2 only the vanadium forms a colour.If the carrier is a solution of PAR at pH 9 and the sample is a solution of lead(I1) and vanadium(V) a t pH 2, the pH across the bolus - carrier interface will vary between 9 and 2. Hence the peak obtained by measuring the absorbance downstream from the injection point will not have the Gaussian shape that is obtained when the sample solution contains only a single metal ion, and it might contain enough information for the two ions to be determined.Experimental The reagent stream, Typical peak profiles are shown in Fig. 1. M PAR solution, was buffered with ammonia at pH 9.9 and The outer peaks arise from the reaction of samples were injected as solutions of 2.5 x PAR with lead and the inner peak is due to vanadium. M hydrochloric acid.B i A C' Time Fig. 1. Peaks obtained from one sample containing a mixture of Pb(I1) and V(V) injected into a solution of PAR. (A) General shape of curve; (B) increasing concentration of V(V) while that of Pb(I1) is held constant; and (C) increasing concentration of Pb(I1) while that of V(V) is held constant. -4 straight-line calibration graph is obtained for lead in the presence of a constant or varying amount of vanadium, all of the peak heights being within the expected precision limits of a single sample (standard deviation 1-2%).I t is therefore simple to determine lead selectivity in the presence of vanadium. The resolution of the lead and vanadium peaks is greatest when the vanadium concentra- tion is reasonably high. This puts the range of concentration over which determinations of vanadium can be made close to that of the reagent concentration and hence the slope of the calibration graph is small.If the lead concentration is constant it is possible to determine vanadium with limited precision, but if the lead concentration is varied i t is difficult t o determine the base of the vanadium peak and, coupled with the small slope, this leads to calibration graphs that have not proved useful in the absence of a sophisticated method of peak analysis.lye believe, however, that these results demonstrate the feasibility of using unsegmented continuous-flow systems to obtain a range of conditions (pH gradient, masking gradient, etc.) over a single sample bolus so that resolution of absorbing species in multi-element determinations can be achieved.It seems certain from the results presented and difficulties highlighted that some computing power will be required for peak resolution and more precise determination of peak characteristics. The successful extension of the method to more complex systems depends on the ability to choose suitable combinations of reagents, pH, masking agents and metal ions, on the ability to process results rapidly and on the development of a satisfactory theory of FIA.6 RESEARCH AND DEVELOPMENT TOPICS Proc.Analyt. Div. Chern. SOC. Novel Phototransducer for Improved Peak Detection in FIA A significant development that enhances the sensitivity of the method and hence ultimately the precision of the determination of peak characteristics has been the introduction of a novel type of phototransducer designed specifically for use in FIA.5 Although simple, physically small and inexpensive, it allows sampling rates of up to 300 per hour and is capable of a lower detection limit of less than The light components are extremely cheap and robust and offer a long life, typically 20 000- 100 000 h.Interchangeable units permit most of the visible and near-infrared spectrum to be covered.g of ions in solution. With the associated electronics the total materials cost is about Q O . Design of Transducer Cell The cell is constructed from a Perspex block through which a central hole is drilled as the light path. The light components are glued into either end and two further holes are drilled, perpendicular to the light path and as close as possible to the light components, in order to connect the cell into the stream.A gallium phosphide light-emitting diode (LED) and a silicon phototransistor act as a light source and sensor, respectively. After assembly the transducer cell and flow tubes are lacquered black in order to exclude ambient light. In operation, the output current from the phototransducer is converted into voltage by a simple current to voltage converter circuit before connection to a chart recorder or oscilloscope.Spectral Considerations The spectral emission of a gallium phosphide LED centres on 565 nm with a band width of 30nm. The absorption maxima of transition metal chelates with PAR are in the region of 500-550 nm, but the overlap of the curves is shown in practice to give reasonable results.As the molar absorptivities of the various metal chelates a t 565 nm differ, it follows that the sensitivity of the transducer is different for each metal. Results and Discussion Calibration graphs have been obtained for the transducer response to injected samples of cobalt(I1) in the concentration ranges 0-100 p.p.b.(parts per lo9) and 0-0.5 p.p.m., plotting the mean peak height of two samples. The degree of linearity is good in view of the spectral range of the light source and the graphs are of equal quality and similar linearity (linear regression coefficients typically 0.998) to those obtained using a flow cell in a spectrophoto- meter as a detector, but the sensitivity and resolution are greatly increased.These increases are due to the high stability of the LED used as a light source. For cobalt concentrations of 100 p.p.b. and greater the relative standard deviation in the result is about 1%. Refractometry By virtue of the cell design and its optical configuration the transducer is sensitive under dynamic conditions to changes in the refractive index of colourless samples.The form of the peaks obtained is illustrated in Fig. 2 and the distance from the base line to the first peak is a measure of refractive index under conditions of medium or high flow-rate. Principle of Operation The principle of measurement of refractive index is based on the formation of a refractive index gradient between the sample and a standard stream solution, the magnitude of which is a measure of the original refractive index of the sample.The high sensitivity of the system is due to the physical shape of this gradient. If a solution of high salt content and hence high refractive index is injected upstream from the transducer into a stream of distilled water, when the sample passes through the transducer it will do so such that the lines of equal salt concentration (isohalines) are parabolic in shape due to wall drag, and according to the theory of flow in tubes under laminar conditions.Each isohaline will have a different refractive index to that adjacent to it. The system can be regarded as a series of liquid lenses that focus or diverge light in a direction and of a magnitude dependent on the dimensions of the parabola, the aspect of the parabola with respect to incident light, the direction of the refractive index gradient and the magnitude of the refractive index gradient.RESEARCH AND DEVELOPMEST TOPICS c D i E E E E Fig.2 . Typical peak profiles for refractive index responscs for sodium chloride solutions: (&I) 1 ; (B) 2 ; (C) 3 ; (D) 4; and (E) 5 g 1-I.Carrier stream, distilled water. The refractometric responses are temperature dependent and at low flow-rates diff usivity At medium to high flow-rates the relative standard deviation is about 1% and dependent. the detection limit about 0.010/, m/m of solute. References 1. 2 . 3. 4. 5 . RGiitka, J . , and Hanscn, E. H., --1na!j,tica Chim. Acta, 1975, 78, 146. RiiiiEka, J , and Stewart, J .IT. B., Analytica Chinz. ,?eta, 1975, 79, 79. Stewart, I<. I<., Beecher, G. R., and Hare, P. E., dnalyt. Biochem., 1976, 70, 167. Betteridge, D., and Fields, B., ,4?zalyt. Chem., 1978, 50, 654. Retteridge, D., Dagless, E. L., Fields, B., and Graves, N. F., ,4izalyst, 1978, 103, 897. Cyanoethylation Reactions in Catalytic Thermometric Titrimetry L. Dajer de Torrijos and E.J. Greenhow Departnteizt of Clz Pnzistvy, Chelsea College, L1!Tawresa Road, Loudmi, Sit-3 6LX Xcrylonitrile is used as an indicator reagent in the determination of very weak to strong acids by catalytic thermometric titrimetry.l The temperature rise marking the end-point of the titration is caused by exothermic indicator reactions catalysed by a small excess of the basic titrant.At the end-point, two reactions can occur, anionic polymerisation of the acrylonitrile (reaction 1) and cyanoethylation, if a suitable substrate is present (reaction 2) : nCH,=CHCN 1-+A(CH,CH,CN),CH,CHCN . . . . ( 2 ) ~ - I CH,=CHCN -f- A- -+ ACH,CHCN - ! KH l+ACH,CH,CN + R-; R- + CH,=CHCN -+ RCH,CHCN; RCH,CHCN + RH -+ RCH,CH,CN + R- (2) where A- is the catalyst and RH is the substrate.Recently, we have shown by gas - liquid chromatography that cyanoethylation products are major constituents of the final titration solution when primary or secondary alkanols are present as solvents in the titrant or titrand.* The titrant-catalyst is usually an alkoxide or a hydroxide ion.8 PYOC. A Ptalyt. Div. Clzewc. SOC. A4s cyanoethylation makes a significant contribution to the indicator process, it was decided to investigate its influence on the shape of the thermometric titration curves by evaluating the combined effect of using different substrates, in varying amounts, in the sample solvent with different titrant systems. The solvent mixtures alone, in addition to solutions of benzoic acid in them, have been titrated because previous experience has shown3 that the effects on the titration curves brought about by changes in the composition of the solvent system and titrant are often indicated more clearly in the “blank” titrations. The titration curves for acrylonitrile alone were much sharper when potassium hydroxide in methanol, potassium n-butoxide in butan-1-01 and potassium tert-butoxide in tert-butanol were the titrants than when secondary alkoxides in secondary alkanols were used.This suggests that indicator reactions involving secondary alkanols are much slower than those involving primary and tertiary alkanols. Primary alkanols are known to be cyanoethylated more readily than secondary alkanols and the shapes of the titration curves reflect this fact. However, tertiary alkanols do not undergo cyanoethylation to a significant extent at ambient temperatures, and it must be assumed, therefore, that polymerisation, but not cyanoethyla- tion, occurs with the tert-butoxide titrant.The titration curves for the solution of benzoic acid in acrylonitrile did not differ markedly in shape, but that obtained by using the n- butoxide reagent had the sharpest end-point inflection.When the tert-butoxide titrant was used for titrations of mixtures of acrylonitrile with different alcohols, the titration curves confirmed that the least sharp curve is obtained with a secondary alkanol, sec-butanol. Sharp end-point inflections were achieved by using, as the co-solvents with acrylonitrile, butan-1-01, benzyl alcohol and diphenylmethanol. The last compound is a secondary alcohol and it would seem that the aryl substituents influence its reactivity towards acrylonitrile.A poor titration curve, in terms of end-point sharpness, was obtained with triphenylmethanol as a co-solvent, but this tert-alkanol is an unusual alcohol in the ease with which it forms triphenylmethyl anions. When the content of sec- butanol in the solvent system was varied, the sharpness of the end-point inflection deteriorated and the rate of temperature rise decreased with the increase in sec-butanol content. In all of these titrations, sharper inflections were obtained by adding the dipolar aprotic solvent dimethylformamide to the mixture of acrylonitrile and the alcohols.Earlier studies3 have shown that the presence of this solvent causes the rate of the anionic polymerisation of acrylonitrile to increase because it facilitates the dissociation, and therefore the reactivity, of the alkoxide titrants.The addition of a small amount of butan-1-01 to a solvent mixture consisting of acrylonitrile and dimethylformamide improved the sharpness of the end-point inflection in titrations with the potassium tert-butoxide - tert-butanol reagent.This suggests that some cyanoethylation or chain-transfer polymerisation, involving the butan-1-01, can be beneficial in increasing the rate of the indicator reaction after the end-point. Solvents other than dimethylformamide have been examined ; none was more beneficial with respect to end-point sharpness, and the least satisfactory was toluene, which markedly reduced the rate of the polymerisation and/or cyanoethylation reactions.Vl’hen various potassium alkoxide and hydroxide reagents were used to titrate a mixture of acrylonitrile and sec-butanol, containing a high proportion (75%) of the latter, the titration curves were almost identical. This is to be expected because, when equilibrium is attained in the titrand, the titrant anion will exist mainly as sec-butoxide in all instances.The molarity of the titrant was found to affect the sharpness of the end-point when a solution of benzoic acid in acrylonitrile -pyridine (2 + 2) was titrated with potassium hydroxide in propan-2-01. Poor end-points were obtained with 1.0 and 0.5 M titrants, apparently because cyanoethylation occurred before the expected end-point , while a sharp inflection was achieved by using the 0.1 M titrant.In contrast, the use of a 0.5 M potassium tert-butoxide - tert-butanol titrant, which does not give rise to cyanoethylation, led to a satisfactory end-point inflection. An interesting phenomenon was observed when pyridine was used as a co-solvent and 0.025 M tetramethylammonium hydroxide was used as the titrant.The temperature rise at the end-point was only about one quarter of that observed with the other solvent - titrant systems, but if propan-2-01 was added to the solution after the end-point inflection had occurred the rise in temperature increased markedly. The usual temperature rise was obtained by including propan-2-01 in the original sample RESEARCH AND DEVELOPMENT TOPICSJ Q IZ iiary, 19 79 RESEARCH AND DEVELOPMEST TOPICS 9 solution.Apparently, inhibition of the indicator reaction by pyridine is prevented by the presence of an excess of an alkanol. When primary or secondary amines are included in the sample solution or solvent system cyanoethylation occurs readily at ambient temperatures, without requiring the excess of titrant, and results in a temperature rise before the end-point of the titration.The magni- tude of the temperature rise depends on the content of the amine undergoing cyanoethylation. However, provided that not all of the acrylonitrile has been consumed when the end-point is reached, a sharp end-point inflection is still observed and there is no objection to using these amines as co-solvents.In addition to the alkanol and amine solvents, the acid samples have labile hydrogen and are, theoretically, capable of cyanoethylation. Fortunately, carboxylic acids and phenols do not undergo cyanoethylation under the titration conditions. Acidic thiol groups are readily cyanoethylated and alkyl and simple aryl thiols cannot be titrated.4 The thiol group of 2-mercaptobenzothiazole can be titrated although the group is readily cyanoethylated. \Ye found that both cyanoethylated 2-mercaptobenzothiazole and also O-cyanoethylated phenol are titrated as monofunctional acids by the catalytic thermometric method.Apparently, the cyanoethylation reaction is completely reversible for these compounds under the titration conditions. In earlier ~ t u d i e s , ~ the different titration values obtained when different solvents and different titrants were used in the determination of sulphanilamide were attributed to the latter being cyanoethylated to varying extents when the indicator reaction was initiated.This hypothesis has now been supported by the results obtained when samples of dicyanoethylated sulphanilamide are titrated ; the titration values were found to be dependent on the nature of the solvent system.The aim of this investigation has been to establish the optimum conditions for which the reactivity of the indicator reagents before the theoretical end-point is at a minimum and after the end-point is at a maximum. The information obtained has been used to devise suitable solvent and titrant systems for use with the acrylonitrile indicator reagent in the determination of weak acids.Two combinations are recommended. (i) An acrylonitrile - dimethylformamide (4 + 2) solvent system with 0.1 M potassium n-butoxide in butan-1-01 as the titrant. (ii) An acrylonitrile - dimethylformamide - butan-1-01 (3 + 2 + 1) solvent system with 0.5 M potassium tert-butoxide in tert-butanol as the titrant.Many of the effects of the titrants and sample solvents on the rates of polymerisation and cyanoethylation can be explained in terms of solvation of: (a) the alkoxide or hydroxide ions of the titrant; ( b ) the acrylonitrile; and (c) other solvents, e.g., dimethylformamide. In (a), solvation by alkanols reduces the reactivity of the alkoxide ions, and hence the rate of cyanoethylation ; in (b) , solvation of acrylonitrile by alkanols increases the electrophilicity and, consequently, the reactivity of the P-carbon of the acrylonitrile : s- ROH ...... 0- N = *r\ C.CHF CH,S+ thereby increasing the rate of cyanoethylation.These two solvation effects are clearly in opposition, and the outcome will depend on the nature and concentration of the solvating alkanols.In (c), solvation of dimethylformamide by the alkanols will reduce the effective concentration of the latter, thus increasing the reactivity of the titrant anion and reducing the solvation of the acrylonitrile; this will tend to promote the polymerisation reaction in preference t o cyanoethylation. Further, dimethyl- formamide will solvate the cation of the titrant and release the anion from the ion pair, thus increasing its catalytic powers.In the titrations of benzoic acid, catalysis before the end-point can occur only by the weakly basic benzoate ion, if the stirring during titration is efficient. References 1. Greenhow, E. J., and Spencer, L. E., Analyst, 1973, 98, 90.10 RESEARCH AND DEVELOPMENT TOPICS Proc. Annlyt. Div. Chem. SOC.2 . 3. 4. 5. Greenhow, E. J., Nadjafi, .I., and Dajer de Torrijos, L., Analyst, 1978, 103, 411. Greenhow, E. J., and Shafi, A. A., Analyst, 1976, 101, 421. Greenhow, E. J., and Loo, L. H., Analyst, 1974, 99, 360. Greenhow, E. J., and Spencer, L. E., Analyt. Clzem., 1975, 47, 1384. Application of Carbon-skeleton Gas Chromatography to the Analysis of Polychlorinated Compounds Aileen M.Prescott and Michael Cooke School of Ckemistvy, Uniuevsity of Bvistal, Bvistol, BS8 1TS Polychlorinated biphenyls (PCBs) have been prepared industrially since 1929 by chlorination of biphenyl with anhydrous chlorine using either iron filings or iron(II1) chloride as a catalyst. The product obtained is a complicated mixture of several PCBs. In the UK, PCRs are marketed as Arochlors by Monsanto.All Arochlors are characterkd by a four-digit number ; the first two digits represent the type of molecule (e.g., 12 represents biphenyl, 54 terphenyl and 25 and 44 are mixtures of biphenyl and terphenyl) ; the last two digits give the percentage by mass of chlorine, e.g., Arochlor 1260 is a 12-carbon system with 60% mjm of chlorine. Commercially, polychlorinated naphthalenes (PCNs) are manufactured as Halowases, Nibren waxes, Seekay waxes and Clonacire waxes.The three major types of Nibren waxes are D88, Dll6N and D130, and all contain between 50 and 60% mjm of chlorine. I t is thought that the amount of PCNs produced industrially is about 10% that of PCBs. PCBs together with $9'-dichlorophenyldichloroethylene (DDE) are now the most abundant of chlorinated aromatic pollutants in the ecosystem and have been identified in many species of British wildlife, rainwater and sewage sludge.They are present because they are very stable and fat soluble. The possible paths by which they could be dispersed are as wastes into rivers and lakes, as industrial smoke, and via direct contamination of foodstuffs. PCRs can enter the body directly through the skin, by inhalation as vapours, or by ingestion in food. In the past, the analysis of environmental samples containing residues of organochlorine pesticides (OCPs), PCBs and PCNs has proved difficult as these compounds are essentially very similar.Many different procedures have been tried, most of which have involved three stages, viz., extraction, clean-up and detection. Two main extraction techniques have been employed, Soxhlet extraction and washing, i.e., solvent partitioning with solvents such as hexane or acetone. For the clean-up stage adsorption chromatography, liquid - liquid partitioning, gel-permeation chromatography and volatilisation have all been used to separate the three classes of compounds.These procedures have been only partially successful as certain pesticides, aldrin, heptachlor and $$'-DDE in particular, have tended to remain in the PCB fraction and they then interfere in the detection and quantification stage.Normally gas - liquid chromatography with an electron-capture detector has been used for quantitation as it is very sensitive to the electronegative chlorine atoms of the PCBs and PCNs.As there are a larg? number of components in each YCB mixture, the gas - liquid chromatographic trace is very complicated. Normally quantification has been based on the areas of one or more selected peaks, total peak areas or heights of selected peaks. However, these methods tend to be inaccurate because not only do environmental samples contain complex mixtures of PCBs and PCNs but in the environment there is weathering and preferential biodegradation of certain PCB isomers. To overcome this, perchlorination of the PCB residue to decachloro- biphenyl has also been used.In 1972 Flotard and Veith used it in the analysis of sediments. Recoveries of about 85% for Arochlors were obtained by refluxing acidified sediments for 4 h. Separation is achieved as the vapour pressures of many pesticides and industrial chemicals are greater than those of water-soluble chemicals. The principle of carbon-skeleton gas chromatography is embodied in the work of Thompson, who showed that sulphur, nitrogen, oxygen and halogens in organic compounds can be replaced by hydrogen, and unsaturated bonds can be saturated by passing the compounds over a heated catalyst in a stream of hydrogen. In humans they cause cliloracne and liver disease.Steam distillation has commonly been used in flavour and drug analysis.Jnizicuy, 1979 RESEARCH AND DEVELOPMENT TOPICS 11 Method In this work either a neutral 37; palladium catalyst or a 5q4, platinum catalyst was used. Both were conditioned under a stream of hydrogen at 120 "C for 30 min, 210 "C for 30 min and then a t 310 "C for 6 h.A normal Pj7e 104 gas chromatograph fitted with dual flame- ionisation detectors was employed. The catalyst was packed into the part of the column that passed through the injection point heater and was thus maintained at the required temperature. Products were identified by a mass spectrometer coupled to the gas chromatograph.As the tempera- ture of the catalyst was increased from 140 to 305 "C there was a progressive decrease in the formation of bicyclohexyl and phenylcyclohexyl and an increase in the yield of biphenyl. At 305 "C biphenyl was the only product from the ,4rochlors used. I t is likely that at low temperatures loss of chlorine is followed by or coupled with hydrogenation of the aromatic rings.At higher temperatures a secondary reaction involving the dehydrogenation of the cj-clic system is also present. At catalyst temperatures less than 280 "C hydrogenation of the rings was less pronounced although gas chromatographic - mass spectrometric studies indicated that s o n e tetrahydronaphthalene was present. Using this technique, polychlorinated terphenyls (PCTs) were converted into a mixture of 0- wz- and p-terphenyl at 305 "C.At 205 OC naphthalene gave two compounds, which, from mass-spxtrometric studies, were suggested to be tetra- and decahydronaphthalene. As the temperature was increased the peak heights decreased and at 305 "C no peaks remained; presumably the naphthalene skeleton was completelj? destroyed at this temperature. The results for PCNs were similar to those for naphthalene.At 280 "C small amounts of bicyclo- hex\-1, phenylcyclohexyl and biphenyl were eluted. As the temperature was decreased the amount of bicyclohexyl increased. At 180 "C conversion into bicyclohexyl was quantitative, and PCNs were converted only into decahydronaphthalene. Initially a 5y0 SE-30 column was used to separate the biphenyl and naphthalene after catalysis.Later gas - solid chromatography with a rubidium chloride column was employed, as inorganic salts have been found to give excellent separations of hydrocarbons and also very good reproducibility over a long period of time. Hydrogen was used as the carrier gas. At low temperatures hydrogenation of the aromatic rings tended to occur. Dechlorination of PCXs was much easier.At 305 "C PCNs were quantitatively converted into naphthalene. LTsing the 5% platinum catalyst, convzrsion of PCNs was poor. PCBs were also completely destroyed at 305 "C. Analysis of Environmental Samples Samples were taken from three areas of the Severn estuary-Aust, Sharpness and Arlingham. From the first two sites, sediment from an area of 0.09 m2 and a depth of about 5 CM was taken.At Arlingham there were two very different samples-a sandy sediment and coal particles. These samples were separated bj- washing with doubly distilled water. The coal appeared as an upper layer and was removed for separate analysis, as carbon has strong absorbing qualities and it was likely that any contaminants would be partitioned unequally.The samples were extracted by blending with doubly distilled water and then steam distilling for 2 h. After steam distillation the sample was removed and dried to a constant mass. The unit was washed with hexane and the combined extract and washings were concentrated to 2 cm3. For carbon-skeleton gas chromatography a 376 palladium catalyst was used together with a 2% rubidium chloride column.Temperature programming was used to obtain good separation. Xmong the compounds identified were a range of polynuclear aromatic hydrocarbons including naphthalene , met hylnap h t halene, biphenyl, dimet h ylnapht halene, phenant hrene / anthracene, methylphenanthrene, fluoroanthene, pyrene and chrysene. Only trace amounts of diphenylet hane, formed by dechlorination of DDT and related compounds, were found. This suggests that only trace amounts of these particular compounds were present. Biphenyl and naphthalene were found in the samples before catalysis and so biphenyl and naphthalene levels before and after catalysis were measured.Additional biphenyl or naphthalene was assumed to arise from declilorination of PCBs or PCXs. The contaminants were extracted into 20 cm3 of hexane.12 RESEARCH AND DEVELOPMENT TOPICS Proc.Analyt. Div. Chew. SOC. The possibility that other species such as hydroxybiphenyls may contribute has not been precluded, but as yet we have been unable to catalyse hydroxybiphenyl to biphenyl. The amounts of PCBs and PCNs found in the samples are given in Table I. TABLE I PCBS AND PCNS FOUND I N SEDIMENTS Values are given in parts per billion ( lop9 g g - l ) dry mass.Total Satural Total li’atural -1roc;hlor Site biphenyl biphenyl naphthalene naphthalene 1260 Xust . . .. . . . . 791 81.4 177 163 1689 Sharpness . . .. . . 589 118 269 266 1 120 (low carbon content) . . 46.0 10.1 ND* XD” 71 (high carbon content) . . 1120 144 1143 1021 2 322 Xrlingham ,Wingham * ND = not detected.These preliminary results suggest that extraction by steam distillation followed by carbon- skeleton gas Chromatography with either a flame-ionisation or mass-spectrometric detector is a practical alternative method for the determination of organochlorines in the environ- ment. Some Aspects of Quantitative Thin-layer Chromatography Samuel J. Lyle and M. Saber Tehrani The Chemical Laboratories, The University of Kent at Cantevbwvy, Kent, C T 2 7NH Thin-layer chromatography (TLC) often provides the means whereby complex mixtures can be separated into their constituent components without resort to expensive or elaborate equipment.However, quantitative determination1+’ of the amount of a separated com- ponent is not as readily accomplished as, for example, in gas - liquid or liquid - liquid chromatography.In general, for TLC in which conventional plates are used, quantitative methods are either based on in situ measurements or determinations in solution following elution of the resolved components from the chromatogram. The in situ determination is commonly performed by a scanning method making use of some physical property such as the reflectance or transmission of light, fluorescent emission or radioactivity. A component eluted from the chromatogram can be determined by any one of several conventional solution techniques.The component to be determined, together with a fixed mass of thin-layer adsorbent, is removed from the plate, mixed thoroughly and a single optical reflectance measurement made on it relative to pure adsorbent preferably also taken from the dried plate.A method based on this technique was suggested3 about 15 years ago but does not appear to have acquired much popularity. Results are compared with those obtained by application of (1) the elution procedure with a spectrophotometric finish and (2) a conventional light-scanning (densito- metric) method. A Pye Unicam SP500 spectrophotometer with reflectance attachment was used for reff ectance measurements. For densitometric determinations the Chromoscan (Joyce, Loebl & Co.), a one-dimensional scanner, was used.Preliminary studies were carried out on the 2,4-dinitrophenylhydrazones of formaldehyde and n-butyraldehyde ; later work related to some red water-soluble dyes. TLC was performed on silica gel G layers supported on glass.For reflectance measurements the variable depth depressions in the Pye Unicani sample holder required excessively large samples for present purposes even when used at minimum In the work described here a different type of technique is examined.J m i i a y , 1979 RESEARCH ASD DEVELOPMEK f TOPICS 13 depth (2 mm) settings. An aluminium insert was therefore constructed, reducing the sample diameter from 24 to 14 mm and the depth to 1 mm; this has the effect of reducing the amount of diluent to less than one fifth, making it possible to load each depression with about 100 mg of silica gel G adsorbent.In calibrations and determinations, known amounts of component applied to thin-layer plates were removed and “diluted” with pure adsorbent to a constant mass, thoroughly mixed and reflectance readings taken.Some tests were made by direct weighing of adsorbent (200 mg was chosen), but to reduce the time required for a measurement a simple apparatus was constructed to enable a constant area of adsorbent containing and surrounding the spot to be removed for mixing and measurement. This layer-removal apparatus con- sisted of a hollow metal thin-walled tube (i.d.3.9 cm), which can be pushed through the adsorbent layer to make contact with the glass backing. A sharp blade attached to a shaft passes down the inside of the tube. The blade is fixed at right angles to the shaft and is of a width that just allows clearance from the walls of the tube. IVhen the shaft is rotated the blade detaches the confined layer from the glass backing.Inversion of the plate over a watch-glass transfers the required mass of sample, provided that the layer is of constant thickness and composition. The uniformity of thickness of the layer is partly dependent on the variability in thickness of the glass backing. I t was found that for the usual layer thickness of 0.25 mm, window glass was an unsatisfactory backing as its thickness could \Tary by as much as the supported adsorbent layer.Glass supplied by Gallenkamp & Co. was found to be sufficiently uniform for the purpose. A comparison of masses of adsorbent removed by the layer-removal apparatus gave the following results : using home-made silica gel G plates (20 x 20 cm plates; 88 CR glass from Gallenkamp) the mean mass (25 measure- ments) was 129.1 mg (standard deviation 10.0 mg), and using Xerck pre-coated silica gel 60 plates the mean mass was 146.7 mg with a standard deviation of 3.2 mg.The larger standard deviation with the home-made plates is thought to be partly due to inhomogeneity within the thin layer and partly to variation in the thickness of the glass.An approximate maximum loading of the thin layer with the 2,4-dinitrophenylhdrazones was 40 pg per spot. Typical calibration graphs for the reflectance and densitometric scanning methods are given in Fig. 1. The quantity (1 - R)2/2R, where R is the ratio of the intensity 150 100 50 0 20 40 Mass of component/pg Fig. 1. Calibration graphs for ( a ) reflectance and ( b ) densito- metric methods.The 2,4-dinitrophenylhydrazone of formalde- hyde on silica gel G is represented. The wavelength of measurement in (a) was 348 nin and in ( b ) a Violet 405 filter was used in the Chromoscan. of light scattered from the sample surface to that from the reference substance, is a function of the concentration of light-absorbing species in the system under consideration. For low concentrations (less than 10 pg of component per sample in this instance) it is insensitive to concentration changes, and only approximates to the direct proportionality with concentra- tion expected from theoretical considerations* at the upper end of the range and beyond in Fig.1. In the densitometric method the instrument response becomes relatively insensitive to concentration change a t hydrazone loadings above 25 pg.Hence, the two methods are complementary with regard to amount of component to be determined in the sample. Benzene and acetone were used in determinations by elution and spectrophotometry. Only14 RESEARCH ASD DEVELOPMEKT TOPICS Proc. Analyt. Dic. Cbzcm. SOC. the latter solvent eluted the hydrazone derivatives quantitatively in 10 ml of solvent, although the former eluted a constant fraction and could be used.Absorbances were in the range 0.05-0.35 for 5 4 0 pg per 10-ml sample. Table I summarises results obtained by the different methods for the formaldehyde and n-butyraldehyde derivatives chromatographed in admixture on silica gel G plates. When compared with the component masses taken, TABLE I SOME RESULTS FOR THE 2,4-I)Ir\'ITROPHEN~LHY-DRAZONES OF FORMALDEHYDE AKD n-BUTYRALDEHYDE SEPARATED ON SILICA GEL G PLATES DEVELOPED GSISG BENZENE - LIGROIN (B.P.60-80 "C) (3 + 1 VjV) AT 25 "C Formaldehyde clcri\ati\-c -7 Mass of sample Mean mass Method taken/pg found/pg Elution method . . . . . . 10.5 10.9 20.0 20.9 Reflectance method (mass adjustment) . . . . . . 10.5 10.2 removal apparatus) .. . . 9.5 10.0 Scanning method .. . . 9.0 10.4 21.0 21.6 Reflectance method (using layer- 20.5 21.2 17.0 18.0 Rutyraldehyde derivati\-c 7- i - 7 No. of lllass of ineasiiremen ts sample Mean mass per mean mass t ken / pg f ou 17 d ,us recordccl 10.5 11.1 7 20.0 I9.G 10.5 11.2 12 21.0 20.2 9.5 9.8 12 9.0 8.6 10 20.5 20.4 17.0 17.9 good agreement is obtained with the means of several determinations by each of the methods.The spread of values about the mean within each group of results was about &2-30;6 for elution, 5% for reflectance and 5-10yo for the densitometric measurements. The agreement between values expected and found when using the scanning method is poorer in comparison with the other two methods; this can be attributed largely to variation in (1) layer thickness and composition and (2) spot size and shape.lq4 Three red water-soluble dyes were separated by TLC and determined by the three methods.Relevant properties and results of the determinations are recorded in Tables I1 and 111. TABLE I1 SOME PHI'SICAL PROPERTIES A S D K , VALUES FOR THREE W.4TER-SOLUBLE DYES (9 + 2: + 1 v/v) AS DEVELOPING SOLVENT SYSTEM SEPARATED ON SILICA GEL G AT 25 "C USING ETHAXOI, - BLJTAN-~-OL - WATER AIolar extinction Colour coefficient * / Index No. 1 mol-l c n r l \\'avclength~/nm Amaranth (F, D and C Red No.2) ~ . IS 186 20 100 522 0.10 Erythrosinc B (F, D and C Red S o . 3) . . 45 430 68 000 522 0.95 Rhodainine B . . . . . . . . 45170 85 800 552 0.45 * In SOYo V / V ethanol - water. t Of maximum absorption in SOO,/, V / V ethanol - water.It can be seen that good agreement is obtained between expected and ohserved amounts, particularly for the reflectance and scanning methods. The scanning method was more successful here than in the measurements of the hydrazones, probably because the spot sizes and shapes were more reproducible. The elution method gave low results, which can be attributed to incomplete removal of the dyes from the silica gel by the eluting solvent.From the results, it can be concluded that the reflectance method examined is able to complement a scanning method such as that used here, regarding component mass range. To obtain a mean value in a determination within about 5% of the "true" value it was deduced that at least five replicate measurements by the elution method and ten by each of the others were required.I t was estimated that, starting with the dried developed plates,Jmz itavy, 1979 RESEARCH ,4KD DEVELOPMEXT TOPICS 15 TABLE I11 SEPARATION OF THREE RED DYES ON SILICA GEL G USING ETHANOL - BUTAN-~-OL - WATER (9 + 2 + 1 VjV) AS DEVELOPING SOLVENT AT 25 “C AND THEIR QUANTITATIVE DETERMINATIONS Mass of each -1mount of dye recoveredlpg s o .of J. dye in I separations and Method admixture/pg _\maranth Erythrosine Rhodamine measurements Elution* , . . . 9.7 Keflectance . . 9.6 Scanning . . . . 9.1 8.9 9.3 9.0 9.2 9.0 10 9.6 9.2 10 s.9 9.4 10 * IZ‘ith 80’6 T7/17 ethanol - water and absorbance measurement a t the wavelengths listed in Table 11. the times required were 45 min (elution), 40 min (reflectance using the layer-removal apparatus) and 20 min (scanning). Reliable determinations by the elution and reflectance methods therefore take similar times.Silica gel and alumina are satisfactory but Kieselguhr less so for reflectance determinations. References 1 . 2. 3 . 4. Shellard, E. J ., Editov, “Quantitative Paper and Thin-Layer Chromatography,” Academic Press, Perry, S.G., *\mas, R., and Brewer, P. I., “Practical Liquid Chromatography,” Plenuni Press, Ne\!- Frodyma, 31. M., Frei, R. \Y., and \Villiams, D. J., J . Clzvomat., 1964, 13, 61. Goodall, R. R., J . Clavomat., 1976, 123, 5. London, 1968. York, 1972. Some Analytical Problems in the Determination of Mercury in Biological Materials by a Cold Vapour Technique P.J. Barlow and D. R. Crump Depavtment of Coiastvztction and En-civonme?ztal Health, Univevsity of -4 stoqz iY1 Bivmiwgham, Bivminghain, 134 7ET A. K. Khera and D. G. Wibberley Depavtnzeitt of Pharnzacjr, Cnivessity of A stoiz i n Biwninghanz, Bivnzinglzam, B4 7E T Most mercury occurs in nature as a red crystalline sulphide called cinnabar. Until fairly recently, mercury has been used widely in medicine, but the toxic properties of mercury and its compounds have been recognised since ancient times.The mechanism of mercury toxicity is related to the strong affinity between mercury compounds and sulphydryl (SH) groups in biological materials, particularly in enzymes.lY2 Industrial use of mercury, estimated3 at about 10000 tonnes per annum, may cause pollution problems because it creates high levels of mercury in very limited locations.Therefore, it is most important to reduce the emission of mercury to the environment and it is the task of the analytical chemist to measure low levels of mercury accurately, so that even small changes in mercury concentrations can be detected. There are a large number of analytical techniques that can be used for the determination of mercury, including mass spectrometry, gas - liquid chromatography, atomic-absorption spectrometry with electrothermal atomisation, neutron activation analysis, colorimetric analysis and cold vapour atomic-a bsorption spectrometry.Cold Vapour Technique The method utilises the fact that mercury is the only element (other than inert gases) that has an appreciable vapour pressure at room temperature and of which the vapour is almost wholly monoatomic.Mercury has a low affinity for oxygen; a relatively high con-16 RESEARCH AND DEVELOPMEKT TOPICS Proc. A nalyt. Dkl. Chenz. Soc. centration of mercury atomic vapour can be maintained in air at room temperature. The relatively high vapour pressure also means that no thermal energy is required for vaporisa- tion and atomisation of elemental mercury.A cold vapour mercury atomic-absorption system consists basically of a light source emitting mercury resonance lines, an absorption cell and a detector system. In the work reported in this paper a Perkin-Elmer mercury analysis system fitted to a Model 360 atomic-absorption spectrophotometer was used.Determination of mercury in biological materials by the cold vapour technique involves two distinct stages : destruction of organic matter and sample preparation, and measure- ment of the mercury in the absorption cell. Once a sample has been digested, the procedure for mercury analysis is basically the same regardless of the biological material to be tested. The digested sample is diluted to 100 ml with distilled water and treated with nitric and sulphuric acids in the presence of potassium permanganate in order to oxidise all of the mercury present to the mercury(I1) form (Hg2+).The excess of permanganate is reduced with hydroxylammonium chloride and the mercury is reduced to metallic mercury with tin(I1) chloride. An aerator is placed in the sample solution and a circulation pump moves the air trapped in the system through the solution, thus evaporating the mercury and carrying the vapour through the absorption cell.Mercury vapour in atomic form absorbs the 253.7-nm radiation emitted from the light source. The change in energy is then detected and read out in the usual way on the atomic-absorption spectrophotometer. Standard solutions were prepared on the day of analysis from a 1000 pg ml-1 mercury stock solution. The standards were prepared in the range 0.1-1.0 pg of mercury and a rectilinear graph was obtained.Sample Preparations Human Hair Samples London). for 60 min at 140 "C. Hair samples were prepared using Digby decomposition vessels (Digby Chemical Services, A 100-mg amount of hair was digested with 3 ml of concentrated nitric acid The solutions were then diluted to 100 ml with water.Soil Samples acid for 1Q h. filtrate diluted to 100 ml with water.) Soil samples were prepared by digesting 1 g of dry soil with 20 ml of concentrated nitric The samples were gently heated on an electric hot-plate, filtered and the Plant Samples These samples were prepared in the same way as soil samples.Milk Samples concentrated nitric acid at 110 "C for 60 min in the Digby decomposition vessels. The milk samples were prepared by digesting 2 ml of pasteurised milk with -5 ml of Placental Samples were weighed after removing excess of blood. added and the samples were placed in a water-bath at 55 "C for 2 4 11. almost dissolved after this time. approximately 100 "C for 5 min.Deep-frozen placental samples were defrosted and approximately 4.0 g of the material Concentrated nitric acid (20 ml) was then The samples were To complete the digestion the samples were heated to These solutions were then diluted to 100 ml with water. Roman Bone and Soil Samples A considerable amount of Roman bones and soils have been collected from a Roman cemetery in the South of England; in order to estimate and compare the levels of a number of heavy metals with those in present-day samples.To date only a small number have been examined. The bone samples were prepared by crushing approximately 1.5 g of bone and placing it in 20 ml of concentrated nitric acid. The mixture was heated in a water-bath at 55 "C forJnrlltnvy, 1979 RESEARCH AND DEVELOPMENT TOPICS 17 2-4 h, which resulted in complete digestion, and the solutions were then diluted to 100 ml with water.Roman soil samples were prepared in the same way as described for soil samples. Teeth Samples There is a possibility that some of this mercury could be released into the digestive system, particularly when foods of low pH are consumed. To examine this possibility, teeth samples with and with- out mercury fillings were kept for 24 h in solutions of pH 4 and 7 and the resulting mercury released was then determined.Mercury is commonly used in the amalgam used in teeth fillings. Results and Discussion The results of the determination of mercury in soils, hair, placentae and bones aregiven in Tables I and 11. TABLE I MERCURY LEVELS IN SOILS Samples No.of samples Rangelng 8-l RIean/ng g-l .&gricultural soils (Cheshire) . . 9 33-1 3 1 51 Rural soils (Birmingham) . . 4 19-30 26 Roman soils . . .. .. 6 29-88 50 Yrban soils (Birmingham) . . 9 30-180 99 TABLE I1 MERCURY LEVELS IN HUMAN HAIR, PLACENTAE AND BONES Hair .. .. .. 10 330-5 200 110 Placentae . . . . . . 4 6.80-14.70 9.80 Bones (Roman) . . . . 6 33.6-151.0 81.9 Sample No.of samples Rangelng g-l Meaning 8-l The mercury levels given in Tables I and I1 are in close agreement with those reported b!~ other workers. Mercury was also determined in nine grass samples, and was found to range between 37 and 88 ng g-l dry mass with a mean of 64 ng 8-l. Mercury levels in milk were below the detection level of 0.01 pgml-l. When a known amount of mercury in solution was added to placental, soil and hair samples before wet digestion, the recoveries were 86, 90 and 95% respectively; therefore, only a small amount of the mercury present in solution was lost during the digestion and preparation of samples.Mercury in Teeth values are given in Table 111. teeth with fillings than without fillings. Mercury levels extracted from teeth samples with and without fillings at various pH The results indicate that mercury levels are higher from TABLE I11 MERCURY LEVELS EXTRACTED FROM TEETH Filling present pH Mercury level/ng No 7 20 No 4 40 Yes 7 44 Yes 4 162 Yes 7 29 Yes 4 191 Problems with the Analytical Method and the laboratory environment. The most significant analytical problems were contamination from glassware, reagents18 RESEARCH AND DEVELOPMENT TOPICS Proc.APzaZyt. Div. Cheriz. SOC. The precautions taken to Drevent contamination were as follows : 1. 2. 3. 4. 5. 6. The glassware : (i) (ii) (iii) (iv) (v) (vi) X reagent blank must be run in order to verify the purity of the reagents. When complex sample preparation is necessary, recovery studies should be made and standards should be carried through the same digestion procedure.Actual operation of the system should be preceded by completion of all sample preparation require- ments. All precautions should be taken to avoid mercury contamination from the laboratory. A large volume (up to 100mI) of distilled water is used and therefore it is necessary always to test the water before carrying out any analysis, as even slight contamination can have a large effect.Also, an acid wash of the B.O.D. bottle between each deter- mination was found to be essential. During wet digestion all samples should be completely digested. It is most important to exclude water vapour from the absorption cell by the use of a desiccant tube. all glass equipment was soaked in 2% Decon 90 concentrate overnight; rinsed twice with hot tap water; washed with concentrated nitric acid ; again rinsed twice with hot tap water; rinsed twice with distilled water and allowed to drain; all glassware were then covered during storage.Conclusion The cold vapour technique for the determination of low levels of mercury in biological materials gives results that compare well with literature values; good recoveries of mercury are obtained and it is a fairly rapid method for use as a routine analytical procedure.References 1 . 2. 3. Westermark, T., and Lunggren, K., “Mercury Contamination of Man and His Environment,” Hughes, ?V. L., Anit. N . Y . Acad. Sci., 1957, 65, 454. Passow, H., Rothstein, A., and Clarkson, T. W., Pharm. Rev., 1961, 13, 185. Proceedings of IAEA Symposium, International Atomic Energy Agency, Vienna, 1972.Application of lon-selective Electrodes to Environmental Pollution Problems in the Steel Industry D. S. Macintyre, B. G. Cooksey and J. M. Ottaway Depavtment of Ptcvc and Applied ChemistJy, Uwivevsit-v of Strathclyde, Cathedval Street, Glasgow, GI 1 X I - Strict legislation governing the discharge of industrial effluents into the environment gives rise to a need for continuous monitoring of a variety of different substances.Ion-selective electrodes are ideally suited to continuous monitoring but, like most analytical techniques, they suffer from interference effects.l The steel industry, like many other heavy industries, produces large amounts of some- times potentially toxic waste and it is often useful to know whether substances such as fluoride or cyanide, for example, are being discharged into the environment in complexed or ionised forms, as the toxicities of the two forms frequently differ.2 The lanthanum fluoride ion-selective electrode was used to measure fluoride in a variety of steelworks effluents and natural water samples.Tests showed that the electrode was not susceptible to any direct interference effects other than from hydroxyl ions, which restricted the operating pH to not greater than 7.0 at a fluoride concentration of 0.1 p.p.m.Com- plexation of fluoride with hydrogen ions also restricted the operating pH to not less than 4. Aluminium and iron gave low fluoride recoveries when present in fluoride standard solutions owing to the formation of soluble metal - fluoride complexes.Atomic-absorption spectro- metry showed that Ravenscraig Steelworks effluents contained only very low concentrationsJanuary, 1979 RESEARCH AND DEVELOPMEKT TOPICS 19 of aluminium (less than 2.0 p.p.m.), but other British Steel Corporation effluents are known to contain more than 25 p.p.m. of aluminium. Tests were carried out to establish whether fluoride recoveries in the presence of aluminium could be improved by the addition of various decomplexing agents.EDTA solutions at pH 6.0 gave poor fluoride recoveries (of the order of loo,/, at 50 p.p.m. of aluminium). This is presumably because metal ion - EDTA4 com- plexes are strongly pH dependent. The best decomplexing buffer was found to be a mixture of 0.1 M sodium acetate and 0.1 M sodium citrate at pH 6.0.However, only 70% fluoride recoveries were obtained in the presence of 50 p.p.m. of aluminium. Fluoride recoveries of greater than 90% could be obtained when 5 g of sodium citrate were added to 100-ml samples, which were boiled and cooled before the addition of the previously mentioned citrate - acetate buffer. However, this type of system is not acceptable for continuous on-line analysis and so attention was turned to automated techniques.-4 Technicon AutoAnalyzer TI fitted with an automatic distillation module was used with an Orion combination fluoride electrode fitted with a continuous flow cell to measure auto- matically total fluoride concentrations. An EIL 7050 expanded-scale pH meter and a Honeywell 195 chart recorder were used to measure and record the electrode potentials.Fig. 1 shows the apparatus. ,Analysis of 40 effluent and natural water samples for fluoride by this technique showed good agreement with similar analyses carried out colorimetrically. A regression line of y = 0.01 + 0.99% was obtained with 95% confidence limits on b of 0.95 and 1.03. Analysis of the same samples by the fluoride electrode without distillation also compared favourably, giving a regression line of y = 0.03 + 1.01% with 95% confidence limits on b of 0.98 and 1.04.This illustrated that a good measure of total fluoride concentrations in the samples could be obtained simply by mixing solutions with citrate - acetate buffer and analysing them directly by the fluoride ion-selective electrode. Effluents containing high concentrations of aluminium would require the automatic distillation procedure, which ga1.e fluoride recoveries of greater than 90% in the presence of 50 p.p.m.of aluminium. The determination of cyanide presents more problems than the determination of fluoride. T'ery low concentrations of free cyanide are extremely toxic to fish.Thiocyanates and complex cyanides are considerably less toxic, but variations in temperature, pH and the amount of sunlight may give rise to variable amounts of cyanide pollution downstream of any discharge point. It is therefore useful to be able to measure free cyanide, thiocyanate and complexed cyanide concentrations independently. However, most techniques available do not distinguish between cyanide and thiocyanate and delicate separation techniques are often required in order to measure complexed cyanide concentrations.Ion-selective electrodes for the direct determination of both thiocyanate and free cyanide are aL7ailable commercially, but both types of electrode suffer from problems of insensitivity and unacceptable interference effects.Free cyanide, however, can be determined indirectly by using a silver ion-selective electrode and a potassium silver cyanide 'KAg(CN),] indicator solution. Frant et aL3 reported a detection limit of less than 0.02 p.p.m. of cyanide for this technique, which should not suffer from serious thiocyanate interference because the solubility product is not exceeded. One major interference in this technique is sulphide.Tests showed that as little as 0.08 p.p.m. of sulphide gave readings of 0.1 p.p.m. of cyanide when no cyanide was in fact present. The interference results from destruction of the potassium silver cyanide indicator solution. Calibration graphs were plotted for cyanide in the presence of 0.05 M lead nitrate with and without sulphide present. These results showed that 100% removal of sulphide interference was not possible by this method, and conse- quently sulphide was found to interfere in cyanide determinations in the range 0.01-0.1 p.p.m.of cyanide. The finite amount of sulphide expected to remain in solution owing to tlie partial solubility of lead sulphide was negligible and cannot explain this interference. The colorimetric technique for the determination of cyanide showed considerably less sulphide interference, but sample pre-treatment stages such as distillation or dialysis were essential in the analysis of steelworks effluents, owing to highly coloured and turbid samples.Further problems arise from the fact that reactions such as the pyridine bipyrazalone colori- metric reaction are also sensitive to thiocyanate, and when solutions containing thiocyanate are distilled an apparent recovery for cyanide in excess of 25% is recorded.This effect can, of course, be corrected for by independently measuring the thiocyanate concentrations, for example by using the iron(II1) nitrate colour reaction. However, considerable errors can20 RESEARCH AND DEVELOPMENT TOPICS R o c . Analyt.Dia. Chew. SOC. arise when this technique is applied to steelworks effluents, as thiocyanate concentrations are frequently higher than cyanide concentrations by a factor of 10. An apparatus similar to that shown in Fig. 1 was used to distil cyanide-containing samples and to determine the cyanide content with the silver ion-selective electrode. Cyanide recoveries of only 2-3% were obtained when thiocyanate solutions in the range 0-3 p.p.m.were analysed by this technique. This indicates that about 22% of the thiocyanate distils over. /c--7\ 31 Sampler I V Heating bath with distillation coil Distillation solution Waste -1 Buffer Orion pH meter combination and recorder fluoride electrode Fig. 1 . Simplified diagram of apparatus used for the determination of total fluoride concentrations.It was also found that recoveries of free cyanide of about 98% were obtained when iron- complexed cyanides were distilled and analysed by this technique. Atomic-absorption analyses showed that the concentration of metal ions that form very stable metal - cyanide complexes, for example, cobalt and nickel, were negligible in steelworks effluents at Ravens- Craig Works. Samples that were exposed to ultraviolet radiation before distillation gave a I I I 0.1 1 .o 10 100 200 0.01 Cyanide concentration, p.p.m.Fig. 2. Cyanide calibration graphs obtained by automatic distillation and analysis with a silver sulphide electrode : (A) potassium cyanide ; (B) iron-complexed cyanide : (D) thiocyanate; and (C) thiocyanate after automatic treatment with ultra- violet radiation, before distillation.Jar z 21 m y , 19 79 RESEARCH AND DEVELOPMENT TOPICS 21 constant recovery of about 45% of cyanide from thiocyanate. This was carried out using a Technicon automatic ultraviolet digestor and the results are shown in Fig.2. By using this technique, it is possible to obtain measurements of free cyanide, complexed iron cyanide and thiocyanate using automated ion-selective electrodes.Free cyanide measurements are made by analysing samples mixed with potassium silver cyanide, free cyanide plus complexed iron cyanides are measured with an ion-selective electrode after auto- matic distillation (an approximately 30-fold excess of thiocyanate can be tolerated) and free cyanide plus complexed cyanide and thiocyanate can be measured by treatment with ultraviolet radiation followed by distillation.This work illustrates the ever increasing importance of ion-selective electrodes in analvtical chemistry. The authors thank the Ravenscraig Laboratory of the British Steel Corporation for providing facilities to carry out this work. References 1. 2 . 3. Orion Research, “_lnalytical Methods Guide,” Orion Research Inc., Cambridge, Mass., 1975.Erichson Jones, J . R., “Fish and River Pollution,” Butterworths, London, 1964. Frant, 31. S., Ross, J . \T., Jr., and Riseman, J. H., .4iznZyt. Chein., 1972, 44, 2227. Some Studies in Inductively Coupled Plasma Emission Spectroscopy J. F. Alder, R. M. Bombelka and G. F. Kirkbright The high-frequency inductively-coupled argon plasma (ICP) has become established during the past decade as a versatile tool for emission spectrochemical analysis, offering the analytical chemist a stable, high-temperature source and high sensitivity for the determination of a wide range of e1ements.l Analytical growth graphs are commonly found to be linear over a concentration range of 4 or 5 orders of magnitude from the detection limit to the onset of self-absorption, and inter-element effects are small or absent owing to the high gas and electron temperatures encountered in the analyte emission zone.2 In order to characterise this zone, we have measured excitation and ionisation temperatures and studied the role of water vapour on various parameters in the ICP.The criterion for the existence of local thermal equilibrium (LTE) in a plasma is that bound states should have at least a 10-fold higher probability of de-excitation by collision than by emission of radiation ; when this occurs at sufficiently high electron densities (about 2 x 1022m-3 for argon) the gas temperature, T,, electron temperature, Te, excitation temperature, Tex, and ionisation temperature, Tion, are found to be ~ i m i l a r .~ Deviations from LTE will result in a disparity between these temperatures with Te rising and T , falling below the equilibrium value, and consequent over- and under-populations of various energy levels. Fe I was chosen for the determination of the electronic excitation temperature in the ICP and Ca, Ra, Zn, Cd, Fe, Mg and Ti for the determination of the ionisation tempera- ture via the Saha equation.The electron density was determined from the Stark half-width of the Stark broadened line Hp (486.1 nm) after deconvolution of the Doppler component and the instrumental function. The instrumental system employed in this work consisted of a 2-kW, crystal-controlled, radiofrequency generator operating at 27 MHz (International Plasma Corp., Model 120-27) with a manual matching network, a three-tube demountable silica torch, a concentric glass nebuliser (Meinhard Associates, Model T-230-A2) and a l-m scanning monochromator (Rank Hilger, Monospek 1000) fitted with an EN1 6256 B photomultiplier tube and a plane diffrac- tion grating blazed at 330 nm.The radiofrequency forward power was set at 1 200 13’ and the argon coolant gas flow-rate was 12.8 1 min-l; no plasma gas was employed.Measure- ments were performed at two injector gas flow-rates, 0.9 and 1.3 1 min-1, and the internal22 RESEARCH AND DEVELOPMENT TOPICS Proc. Analyt. Div. Chem. SOC. diameter of the injector tube, an important parameter that determines the axial velocity of the sample, was 1.60 mm. Fe I was chosen for the determination of the excitation temperature, and 20 emission lines were selected with upper energy levels, E,, in the range 26 875-55 754 cm-l.Boltzmann plots of Ix3/gf against E, were constructed at three different viewing heights, 10, 20 and 30 mm, in the tail flame above the top of the load coil. The excitation temperature in each instance calculated from low-energy lines was found to be substantially lower (about 1500 K) than that calculated from high-energy Fe I lines.In addition, the ionisation temperatures obtained from atom and ion line intensities of the seven elements studied were found to be similar in magnitude and to correspond more closely to the values of the excitation tempera- ture obtained from the high-energy Fe I lines.Radial intensities calculated via the Abel inversion of lateral data also showed a non-linearity of the Boltzmann plot, and hence the non-LTE properties of this excitation source were demonstrated. The non-linearity of the Fe I Boltzmann plot can be explained in terms of an over-population of the lower energy levels with respect to higher energy levels owing to radiative de-excitation from the upper levels that is not balanced by the inversz absorption process.Hence, care should be taken in equating the electron temperature to the excitation temperature derived from low-energy lines for this two-temperature non-LTE plasma. On pneumatic nebulisation of aqueous solutions into the ICP, a substantial amount of water vapour enters the source. At 6 000 K, water is almost entirely present as H and 0 atoms, with a small percentage of other species (H+, Of, 02+, e, OH, H,O, H, and 0,).5 The presence of water might be expected to modify the conditions in the analyte zone.A small U-tube containing dry coarse silica gel was mounted between the nebuliser chamber and the plasma torch. The silica gel served to remove water from the aerosol while still permitting a small amount of sample particles to enter the plasma, without affecting the argon flow-rate.The amount of water removed was determined from the increase in mass of the U-tube. It was found that both the electron density and cadmium ionisation tempera- ture decreased as water was progressively removed. The continuum emission intensity, being a sensitive function of the electron density, was also found to decrease. To show this effect conclusively, electron densities, cadmium ionisation temperatures and the Fe I excita- tion temperature were measured at different viewing h3ights in the plasma both with water and with most of the water removed. Again, a significant reduction in each parameter was observed when the aerosol was dried substantially. It can therefore be concluded that the presence of small amounts of water vapour in the ICP increases the excitation parameters. An increase in the electron density would be expected with water present, as under the actual conditions the degrees of ionisation of both hydrogen and oxygen are expected to be about 5 times higher than that of argon. When ultrasonic nebulisation rather than pneu- matic nebulisation is employed, far higher rates of water transport to the plasma are obtained. In this instance lower temperatures might result if a large fraction of the energy available was used to dissociate the substantial amount of water present. Sample excitation and ionisation in the ICP is most likely to be the result of direct electron collisions in a stepwise fashion, with excitation of high levels occurring by excitation from intermediate energy levels, the probability of such a process increasing as the physical size of an excited atom increases. Although Penning ionisation of analyte atoms with excited argon atoms may play a part in excitation and ionisation (collisional lifetimes of all four 4s Ar I levels are extremely short in the ICP and thus the distinction between metastable and other excited argon atoms should not be made in the ICP), a two-temperature plasma with an electron temperature 1 000-2 000 K higher than the gas temperature, where elec- trons alone are principally responsible for analyte excitation and ionisation, is to be favoured. ,4 series of studies to measure spatially resolved gas temperatures in the ICP from Doppler half-widths using a piezoelectric scanning Fabry - Yerot interferometer has been initiated in this department. Using this technique, we hope to obtain in the near future reasonably accurate spatial values of Tg, which would then serve as absolute minimum values of Te. Knowledge of these parameters, together with n e , is essential to an understanding of the excitation mechanism in the ICP, and to explain why ion lines are more intense than commonly expected. Whilst Mermet and Trassy6 and Roumans and De Boers favour a As the transition probabilities of Fe I are known to be accurate to aboutJa?iuary, I979 RESEARCH AND DEVELOPMENT TOPICS 23 mechanism involving Penning ionisation to explain these observations, we feel that a moderately high electron temperature, closer to the value obtained from the high-energy Fe I lines, can explain this effect equally well. References 1. 2. 3. 1. 5. 6. 7. Fassel, V. .1., and Kniseley, R. N., Analyt. Chem., 1974, 46, 1110*1 and 1155.1. Kornblum, G. R., and De Galan, L., Spectrochim. .4cta, 1977, 32B, 455. Bacri, J., Gomes, A\. >I., and Benzaid, S., ,I. Phjvs. D , .4ppl. Ph?is., 1976, 9, 1743. Bridges, J . &I., and Kornblith, R. L., A s t v o p h ~ ~ s . J . , 1974, 192, 793. Rurhorn, F., and Wienecke, R., Z. Phys. Chem., 1960, 215, 285. Mermet, J. M., and Trassy, C., Rm. Phj)s. AppZ., 1977, 12, 1219. Roumans, 1’. W. J . M., and de Boer, F. J . , Spectrochim. Actn, 1977, 32B, 365.

ISSN:0306-1396    

DOI:10.1039/AD9791600004

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

RESEARCH AND DEVELOPMENT TOPICS 23 Microprocessor-controlled Laser Remote Sensing System A. R. Morrisson and B. L. Sharp Allocaiday Iszstitute f o r Soil Research, Crazgiebucltler, A berdeua, d B9 2QJ There has been growing concern during the last decade about the protection and conserva- tion of the environment. Modern industrial processes and urbanisation produce vast amounts of waste products, many of which are toxic, adversely affecting animal life either directly or through the food cycle.The most widespread pollutants are those which are emitted directly into the atmosphere. Sulphur dioxide, produced mainly by the combustion of fossil fuels, is a prime example and its effect on soil acidity and plant growth rate are subjects of current research and discussion.There has been much controversy in recent years concerning the emission of sulphur dioxide by the industrialised countries of Western Europe and the effect of this pollution on tree growth in the forests of Scandinavia. Yearly all of the analytical techniques currently employed use point sampling methods. A sampling unit is located at some point and the sample collected over a pzriod by filling a plastic bag with the gas or pumping the gas through a suitable absorber. A variety of analytical methods can then be employed in the laboratory to measure the concentration.The disadvantages of these methods are that they yield average values of the concentration with poor spatial and temporal resolution and have little or 110 ability to track the path of the pollutant.In addition, no information can be obtained about pollutant concentrations at inaccessible points. Laser Remote Sensing Developments in laser technology have yielded a variety of coherent optical sources having outputs whose wavelengths range from the ultraviolet to microwave regions of the spectrum. Continuously tunable lasers are now available covering the ranges 280-340 nm, 400-690 nm and various selected ranges in the infrared region.The high power density and collimation of laser beams enables them to be transmitted over considerable distances and still yield measurable power levels at a receiver point. These factors have led to their use in rernote sensing of the atmosphere, whereby a combination of laser transmitter and adjacent optical receiver are used to detect and determine the concentration of molecules at a location remote from the observation point.The analogy with RADAR techniques has resulted in the term LIDAR (light detection and ranging) being applied to such methods. -1 \.ariety of spectroscopic phenomena can be employed in the detection scheme, for example Raman and resonance Raman scattering, electronic absorption and fluorescence, and rotational and vibrational absorption.Because of the high quenching rate of excited states in air, absorption is the most sensitive technique for the in sit% measurement of sulphur dioxide. Two types of measurement are possible, of which the simpler is long path absorption. The laser beam is tuned to an absorbing wavelength and is attenuated over an absorbing path of several kilometres, according to Beer’s law.Although this technique has the advantages of simplicity and low24 RESEARCH AND DEVELOPMENT TOPICS Proc. Analyt. Din. Chenz. SOC. source power requirement, it has the serious limitation that it is necessary to place a receiver a t the far end of the absorption path or a retro-reflector to return radiation to a local receiver.This is not practical when measurements a t finite elevation or over difficult terrain are required; also, no range information is obtained as the laser light has to pass through the entire absorbing path before reaching the detector. A further difficulty exists in stabilising the relative positions of the transmitter and receiver as small angular shifts in either (e.g., 1 mrad) produce linear displacements of several metres when subtended by a range of several kilometres.An alternative method is that of differential LIDAR, in which the atmosphere is used as a distributed reflector (Fig. 1). Two sequential pulses are transmitted, one at the peak of the absorption band and one at an adjacent non-absorbing wavelength (for sulphur dioxide, 300.1 and 299.5 nm, respectively).The backscattered intensities are then ratioed to give a measure of the sample absorbance and, from a knowledge of the absorption cross-section and the path length, the concentration can be calculated. The range from which back- scattered signals can be detected is limited by the cross-section for Rayleigh and Mie scattering from atmospheric gas and particulates, and the transfer function of the receiver - detector system.The selected sampling range is defined by the overlap of the laser beam with the telescope field of view (Fig. 1) and the timing of the transmitting and receix-ing cycles. The detection limit is determined by the ability of the detector to discriminate small differences in the intensities of the two beams (about 1% absorption is normally detectable).The laser pulse duration is 1 ps and therefore the range resolution (given by CT/2 where T is the pulse length1) is 150 m. Fig. 1. The differential absorption LID_IK technique. Instrumental System The source is a modified Electro-Photonics, Model 23, flash-lamp pumped tunable dye laser using Rhodamine 6G dye. The light from two high-pressure xenon flash lamps is focused on to the dye cell and the laser cavity is formed by two 100yo reflecting mirrors.Tuning to 600 nrn is accomplished by an intra-cavity voltage-controlled interferometric filter. The light is polarised, intra-cavity, by a Glan - I’homson polariser and focused on to a frequency-doubling crystal, which halves the wavelength of the output to the required ultraviolet value.The phase-matching angle for the crystal is selected by rotation of a stepper motor. The output mirror has a low reflectivity at 300nm, which allows the frequency-doubled light to pass out of the cavity and through a beam expander to yield aJanizaiy, 1.979 RESEARCH A%XD DEVELOPhlENT TOPICS 25 transmitted beam with a diameter of about 25mm. Beam steering is accomplished with two adjustable mirrors.The laser is operated a t about 1 Hz and produces a 0.1-mJ pulse a t 300 nm with a beam divergence of 2 mrad. The laser power is monitored by focusing the small fraction of light that passes through one of the beam-steering mirrors on to a photodiode. There is a shot to shot variation in the output power of about 10% and this measurement allows the collected data to be normalised.The laser is mounted beside a 0.5m diameter Cassegrain telescope on a mechanically rigid table. The transmitted ultraviolet laser light is fired in the desired direction and the backscattered light collected by the telescope. The collected light is first filtered to reduce the background radiation by the use of a 5 nm band pass, 12y4 transmission interference filter with centre wavelength at 299.8 nm.It then passes on to an EM1 9789QB photo- multiplier tube whose signal is pre-amplified and digitised using a Tektronix R7912 transient digitiser, which records the temporal variation in backscattered intensity. The operating functions and data handling in the system are controlled by an Intel SBC 80-10 microcomputer.The on-board computer memory is augmented with an 8 kbyte random-access memory expansion built in the laboratory. A 250 kbyte floppy disk drive is linked to the computer for bulk data storage. The programmed experimental sequence consists of tuning the laser, firing the laser pulse, acquiring the digitised backscattered waveform from the transient digitiser and measuring the transmitted pulse energy.This sequence is then repeated at the two wavelengths alternately and the normalised data from several hundred shots are averaged. Signal averaging is necessary in order to enhance the signal to noise ratio and hence to improve the measurement precision. The LIDAR system should not pose an eye hazard to the general public, both because of the transmission path used and as the beam expanded pulse yields an energy flux below the maximum permissible exposure for direct ocular viewing.2 In the event of an emergency the operator can activate the computer interrupt system, which suspends the experimental sequence.Thereafter, the experiment can be continued or terminated by entry of a character on the keyboard. The prototype differential LIDAR system has been built and preliminary testing is under- way.Theoretical studies3 indicate that a wide range of concentrations of sulphur dioxide down to 10 p.p.b. (parts per lo9) can be measured at ranges of several kilometres. This compares with a sensitivity of about 3 p.p.b. for the best point sampling instruments. Future work will include extension of the system for the measurement of nitrogen dioxide and ozone.References 1. 2. 3. Hinkley, E. D., Edztor, “Topics in -$pplied Physics,” Yolume 14, Springer-Verlag, Berlin, 1976, I3ritish Standards Institution, “Draft Guide to the Protection of Personnel against Hazards from Xdrain, R. S., Brassington, D. J., Sutton, S., Tozer, B. A,, and \‘are)-, R. H., Central Electricity pp. 76-78, Laser Radiation,” BS 4803, Document 76/31221 DC.Kesearch Laboratories Laboratory Note Xo. RU/L/N 120/77‘, 197’7. Problems in the Analysis of Chromite Ores: Precision Spectrophotometric Determination of Total Iron M. E. M. Abdel Aziz and D. Thorburn Burns Depni,tiizriit of Chenzistvj~, The Queen’s Uizivrvsity of Belfast, Belfast, BTS L 4 G The long established method for the determination of total iron in chromite ores is by dichromate titration of reduced solutions of the ores1 Recently, the British Standards Institution has adopted a spectrophotometric method for iron2 as a major constituent in chrome-bearing materials using 1,lO-phenanthroline, a reagent that is normally used for trace-level determinations.Following the success of earlier work on the determination of chromium in chromite ores,3 precision spectrophotometry has now been applied to the determination of total iron based on the absorbance of the iron(II1) chloro complex at 342 nm.Problems were encountered in the development of the method a t the ore decomposition and filtration stages and in selecting the chromogenic species for final spectrophotometric26 RESEARCH AND DEVELOPMENT TOPICS Proc.Analyt. Div. Chem. SOC. measurement. It was not possible to use an iron(I1) species as was the original intent. The optimised conditions are as follows. A 0.45-g amount of finely powdered chromite ore, intimately mixed with 5 g of sodium peroxide, is sintered for 3 h at 510 10 “C in a zirconium crucible. The sintered mass is leached with 50 ml of distilled water and filtered by gentle suction through a Whatman GF/C glass fibre filter-paper.The residue is washed with hot distilled water and then dissolved in 250 ml of concentrated hydrochloric acid and diluted to 500 ml with distilled water in a calibrated flask. The final concentration of hydrochloric acid should be about 6.0 M; previous workers4 have shown that this is the least critical concentration for variation of absorbance with acidity.The solution is mixed, thermostated at 25.0 “C, made up to volume and its absorbance measured at 342 nm using a thermostated cell holder in a Pye Unicam SP 3000 spectrophotometer. The iron contents are calculated from the pre-determined specific absorptivity of the iron( 111) chloro com- plex; Beer’s law holds up to 1.5 absorbance units.Sample masses are chosen so as to give absorbaaces in the range 0.700-1.200 using 0.2-cm cells. The results except for sample 49gG show acceptable accuracy and precision. Sample 49gG was analysed by the British Standards Institution method2; the figure obtained, 14.43 & 0.04% of FeO, is in agreement with the chloro complex determination. The cause of the apparent discrepancy is being investigated. Results are shown in Table I for the analysis of standard samples.TABLE I DETERMINATION OF TOTAL IRON -4s FeO IN STANDARD REFERENCE CHROME ORES Sample Certificate value, ()& Result, BCS 308 . . . . .. .. 15.3 15.38 + 0.07 Student’s sample 49f . . .. 15.3 15.40 & 0.05 Student’s sample 49gG . . .. 15.2 14.63 & 0.02 We thank the Pye Unicam Company for the gift of the SP 3000 spectrophotometer and the Industrial Research and Consultancy Institute, Khartoum, Sudan, for leave of absence and financial assistance for one of us (M.E.M.A.) References I .2. 3. 4. Brearlcy, H., and Ibbotson, F., “The XnaIysis of Steei-Works Materials,” Longmans, London, 1902. HS 1907 : P a r t 2C : 1974. 4bdel Aziz, M.E. M., and Thorburn Burns, D., unpublished results. Desesa, M. A,, and Rogers, L. R., Awzlytica Chim. Acta, 1952, 6, 534. Development of Fluorescence lmmunoassay Methods of Drug Analysis G. Handley and J. N. Miller Department of Clzernistry, University of Technology, Loughborough, Leicestershire, LE11 3T U and J. W. Bridges Uepavtmeizt of Biochemistry, Univevsity of S u ~ r e ~ y , Guildford, Surrey Fluorescence immunoassay methods for drug analysis are being developed in an attempt to overcome some of the disadvantages of radioimmunoassay (RIA).The intention is to produce assays that are rapid, homogeneous (i.e., do not require a separation step) and do not involve the use of hazardous materials or expensive equipment. One such method for the analysis of thyroxine (T4) involves the phenomenon of fluorescence enhancement.It has been found that when T, is labelled with a fluorescent moiety, such as fluorescamine (4-phenylspiro [f uran-2 (3) - 1 ’-pht halan] -3,3-dione) or MD PF [2-me thoxy-2,4-diphenyl-3 (2H) - furanone], the fluorescence of the complex is greatly increased on binding with anti-T, antibodies. This report describes how this effect of fluorescence enhancement can be utilised in a fluorescence immunoassay.January, 19 79 RESEARCH AND DEVELOPMENT TOPICS Thyroxine (T4) Fluorescent derivative o f fluorescarnine R \ Fluorescent derivative of MDPF 27 Experimental The first involved the rapid addition of 0.5 ml of a 0.03:/, solution of the label in acetonel to 2 ml of a 10 pg ml-1 solution of T, in phosphate buffer (0.1 M, pH 8.0) that was being mixed on a vortex mixer.The second technique involved the incorporation of the label into a cycloheptaamylose complex, after the method of Nakaya et aZ.2 The resultant stable solid was added in excess to a solution of T, in phosphate buffer and incubated for 30 min at 37 "C. Residual cycloheptaamylose was removed by centrifugation.No further purification was deemed necessary as neither the labels nor their hydrolysis products are fluorescent. The latter technique was the preferred method of labelling and fluorescamine the preferred label as it is commercially available and MDPk. is not. Both fluorescarnine and MDPF were obtained from Roche, anti-T, serum from Calbiochem and cycloheptaamylose from Sigma.A11 dilutions were carried out in barbital buffer (0.075 ni, pH 8.6) and a Raird Atomic Fluoricord spectrophotometer with excitation and emission wavelengths set at 390 and 490 nm, respectively, was used for all fluorescence measurements. An antibody dilution graph was constructed by the addition of a series of 1-ml antiserum dilutions to 1 ml of fluorescarnine-labelled T, solution (10 ng ml-l).After incubation at room temperature for 15 min the fluorescence of each mixture was measured. In order to correct for the background contribution of the antiserum, the fluorescence of the anti- serum dilutions was also measured separately in the absence of T,. A standard graph was constructed using 0.5-ml aliquots of known T, dilution. These were added to 0.5 ml of labelled T, (20 ng ml-l), followed by 0.5 ml of anti-T, serum.The antiserum was used in an initial dilution of 1 : 200 (1 : 600 final dilution) on the basis of information gained from the antibody dilution graph. After incubation at room temperature for 15 min the fluorescence of the mixtures was measured and corrected for the fluorescence of the antiserum. Therefore, a series of T, solutions of known concentration were prepared in pooled T,/T,-depleted serum.Aliquots (0.25 ml) of these solutions were diluted to 0.5 ml with barbital buffer and 0.5 ml of labelled T, solution and 0.5 ml of anti-T, serum added as before, in order to construct a standard graph. The high background signal produced by serum could be caused by either scattering of light or the fluorescence of species present in the serum.In order to investigate the possi- bility that scattered light was responsible a horizontal polarising film was inserted into the excitation beam and another standard graph constructed. A standard graph of T, in serum was also constructed using MDPF as the fluorescent label, using the same procedure as that used for the fluorescamine label.Thyroxine was labelled by one of two methods. I t is, however, normal to wish to measure T, concentrations in serum.28 RESEARCH ASD DEVELOPMEST TOPICS P V O C . A%L~J$. D i V . Chem. SOC. Results From the antibody dilution graph (Fig. 1) it can be seen that the fluorescence of labelled T, is enhanced on binding with antibod!.. The data obtained from this graph allow the antiserum dilution for the standard graph to be determined.The standard graph of T, in barbital buffer (Fig. a), which summarises the pooled results of several experiments, shows that unlabelled T, competes for antibody binding sites, causing a decrease in observed fluorescence with increasing concentration of added T,. co +J ._ 2. P -fi 40 a- m 35 z P +-’ 3 - ; 1 5 # 30 “I 10 1 : l O O 1 1 000 1:10000 I nit i a I antiserum d i I II tion \ +\ Fig. 1.Antibody dilution graph. Fig. 2. Standard graph of fluorescence enhance- The results of the standard graph in serum (Fig. 3 line A) show that the effect is still present, but do not indicate the high background signal obtained, which is several times greater than the fluorescence due to fluorescamine. ment of T, in buffer.I I 100 1000 Initial thyroxine concentrationhg ml-’ Fig. 3. Standard graphs of fluorescence enhancement assay of T, in serum, (A) using fluorescamine-labelled T,, (B) using fluo- rescamine-labelled T, and a horizontally polari- sed excitation beam and (C) using MDPF- labelled T,. The presence of a horizontal polariser in the excitation beam (Fig. 3 line B) produced no When MDPF was used as the fluorescent label in the construction of a standard graph Therefore, improvement in the standard graph and reduced the background only slightly.(Fig. 3 line C) the results were comparable to those obtained using fluorescamine.Jizir iinvy, 1979 RESEA4RCH ASD DEVELOPMEKT TOPICS 29 the only advantage of using MDPF would be that its derivatives are slightly more stable than the derivatives of fluorescamine.Discussion Iodine is well known for its quenching of fluorescence by the “heavy atom e f f e ~ t . ” ~ Therefore, it is possible that the fluorescence of labelled T, is normally quenched by the iodine atoms of the iodothyronine moiety of T,. If so, the enhancement of fluorescence on binding with antibody might be explained in terms of inhibition of this quenching.This possibility is still being investigated. Horizontally polarised light has been shown to reduce the effect of scattered light,, improving the sensitivity of standard fluorescence graphs. However, as no improvement of the standard graph was obtained and the background was reduced only slightly it appears that the high background signal was due mainly to the fluorescence of species present in serum, The enhancement of fluorescence on binding of labelled T, by antibody and the reduction of the effect when unlabelled T, is presznt, results which compare favourably with those obtained by Smith,j using fluorescein isothiocyanate-labelled T,, indicate that it would be possible to assay serum T, by a fluorimetric immunoassay technique.This assay would be rapid as there is only a 15-min incubation period, homogeneous as no separation step is required and cheap as the assay is followed by conventional fluorimetry. Unfortunately, serum has a high intrinsic fluorescence that will vary from sample to sample. It would therefore be advantageous to use a label that fluoresces at a wavelength outside the fluorescent spectrum of serum.Such a compound is rhodamine, with an emission maximum at 595 nm; work is currently being carried out to determine if the quenching effect of the iodothyronine moiety of T, will apply to rhodamine. References 1. 2. 3. 4. 5. Bohlcn, P., Stein, S., Dariman, \Y., and Udenfriend, S., Arch. Biochem. Biophys., 1973, 155, 213. Xakaya, I<., Yabuta, M., Iinuma, F., Kinoshita, T., and Nakamura, Y., Biochem.Biophys. Res. Wehry, E. L., in Guilbault, G. G., Editor, “Practical Fluorcscence,” Marcel Dekker, New York, r i m , C. S., Miller, J . N., and Bridges, J . \V., -4nnlytica Chiwz. .-lcta, in the press. Smith, D. S., FERS Lett., 1977, 77, 2 5 . Commun., 1975, 67, 760. 1973, pp. 87-91. Determination of Atmospheric Pollutants by Gas Phase Auger Electron Spectrometry G.N. Killoran and J. F. Tyson Chemistry Department, University of Technology, Loughbovough, Leicestevshire, LE11 3T U The potential of Auger electron spectrometry (AES) as an analytical technique for gases and vapours has been under study a t Loughborough University of Technology for the past few years. These studies have concentrated on the molecular spectra and the qualitative aspects of AES.ly2 Applications of AES in general and with reference to gases have recently been reviewed.3 In this paper some of the more recent studies conducted at Loughborough are described.The good resolution and high counting rates available, together with unique molecular and sensitive elemental identification, make AES a potentially powerful analytical tool., The analytical system chosen to continue the study of the analytical possibilities of AES for gases was the determination of the common pollutant gases found in air.The gases studied in- cluded carbon monoxide, carbon dioxide, hydrogen sulphide, sulphur dioxide, nitrogen oxide, nitrogen dioxide and ammonia, as well as oxygen, nitrogen and argon. These gases were studied as pure gases or in simple mixtures.The Auger spectra of the individual gases were obtained under similar conditions, so that they could be more easily compared. *4s AES is an elemental identification method the30 RESEARCH AND DEVELOPMENT TOPICS Proc. AnaZyt. Diu. Chenz. SOC. compounds were studied in groups having a common element: for example, sulphur dioxide, hydrogen sulphide ; carbon monoxide, carbon dioxide ; nitrogen oxide, nitrogen dioxide, ammonia.In order to assess the quantitative analytical potential the sensitivity, limit of detection and analytical calibration graph were determined for each gas in a binary mixture. Analytical Basis of Auger Electron Spectrometry AES is related to both X-ray fluorescence spectrometry (XFS) and X-ray photoelectron spectrometry (XPS), as shown in Fig.1 , in that they all depend on the ionisation of an inner shell, X, of an element. The energy of the ejected inner-shell electron is the basis of SPS. The inner shell vacancy is filled by an electron falling from level Y; this results in either the creation of an X-ray photon or the release of an Auger electron from level Z.The measure- ment of the energy and intensity of these electrons forms the basis of Auger electron spectro- metry. A e- Auger electron i L, 1 2 p ” * I \ \ Excitation e I ec tron s, X-ray Fig. 1. The Auger proccss. The Auger electron ejected is designated an XYZ electron. For the elements studied the Auger spectra are the KLL spectra for the first row elements and LMM for the second row elements. The energy of the XYZ electron can be calculated from the following equation: E X Y ~ = Ex - (Er + Ez) where Ex,, is the calculated Auger energy.Ex is the energy of the level where the initial vacancy occurs and Ey and EZ are the binding energies of the levels from where the “down” and Auger electrons originate, respectively. Also, E , is the binding energy of an electron in the shell of an ion having a single vacancy in the Y level.The Auger energy depends chiefly on the energy of the initially ionised level, which is characteristic for a given element, so that elemental identification is possible by AES as well as by XPS and XFS. The Auger spectra are complex and difficult to interpret. However, they are also characteristic of a given free molecule, hence molecular identification is possible.Under a given set of spectrometer operating conditions the intensity of a selected Auger peak will be proportional to the partial pressure of that component in the gas mixture, and thus AES is capable of quantitative analysis. The spectrometer used was a Vacuum Generators AFM2 and it is described in reference 1 .The excitation source was an electron gun operated at a beam energy of 5 kV. The other parameters were set for maximum signal to background ratio for qualitative analysis and for maximum figure of merit ( 2/Ip - l / l b ) for quantitative analysis, where I, and I b are the peak and background intensity, respectively.~~n1lllnYy, 1979 RESEARCH AND DEVELOPMEKT TOPICS 31 Results and Discussion Qualitative Analysis The Auger spectrum of each pure gas obtained could be easily distinguished from other spectra. In an equal concentration mixture of sulphur dioxide, carbon tetrachloride, carbon dioxide, argon and nitrogen, each element was easilv identifiable in the spectruni (Fig.2 ) . 2 I I 1 I 1 uc) 200 300 1 Electron kinetic energy/eV 0 Fig. 2 . Auger spectrum of a gas mixture.Problems of inolecular identification arise when gases in the mixture contain the same ele- ments, such as carbon and oxygen. Changes in the chemical environment of an atom can cause Auger peak shifts, intensity changes and changes in shape. The spectra of the elements common to each set of compounds were therefore compared to determine the possibilities of determining each compound in a mixture.The carbon and oxygen spectra for carbon mono- oxide, carbon dioxide and a mixture of the two gases are shown in Figs. 3 and 4. It can be seen that the carbon Auger peaks of carbon monoxide at 251 and 154 eV enable it to be identi- fied, whereas the oxygen peaks of carbon dioxide a t 494 and 503 el’ makes its presence distinguishable. J!q co/co, 1 I 1 ! 1 2 50 260 Electron kinetic energylell Fig.3 . Carbon Auger spectra of CO, CO, and a CO - CO, mixture. I I I I I ! 490 500 Electron kinetic energyfev Fig. 4. Oxygen huger spectra of CO, CO, and a CO - CO, mixture.32 RESEARCH AND DEVELOPMENT TOPICS Proc. Analyt. Div. Chew. Soc. Thus, a compound without elemental spectral interference can be determined qualitativelj. in a mixture, whereas compounds with common elements are more difficult to determine simultaneously, unless of course, they contained other elements, for example a sulphur dioxide - hydrogen sulpliide mixture in which only sulphur dioxide contains oxygea.For mixtures such as carbon monoxide - carbon doxide, if the spectral profile was known for each element in each component it might be possible to determine small amounts of one in the other by spectral deconvolution. Quantitative Analysis The sensitivity, limit of detection and analytical calibration graph were obtained for each compound studied.A series of binary mixtures of each compound in either argon or nitrogen were prepared, with concentrations ranging from 0 to 20 mole percent of the analyte.The sensitivity (counts per second per mole yo) ranged from 65 (for carbon dioxide oxygen) to 3 800 (for argon). The limits of detection were calculated from the formula: Limit of detection = 3 Ib S T 21- where S is the sensitivity, Ib the background intensity and T the counting time (100 s). These limits ranged from 0.24 (for carbon dioxide carbon) to 0.012 (for argon) mole :;, or 2 400 to 120 v.p.m. (see Table I).Most analytical calibration graphs were linear over the range from 0 to 20 mole :$. TABLE I Eleineii t C C 0 0 S S -1r SESSITIVITIES AND LIMITS OF DETECTION Sensitivity1 count s-l Limit of detection, Compound mol ? L - l v.p.m. co 340 950 co 66 1700 H,S 1 7 0 0 360 SOL 920 700 Xr 3 800 120 co, 140 2 400 co, 65 1 900 In addition to the well known problem of the high secondary-electron background ( I b ) , these studies revealed an instability in the electron gun’s output (owing to interaction between certain gases and theheated filament) and therefore also in the Auger electronintensity.Detec- tion limits could be improved by increasing the sensitivity and/or reducing the background. The stability could be improved by keeping the electron gun more isolated from the sample.References 1 . 2 , 3. 4. Thompson, M., Hewitt, P. X., and Wooliscroft, D. S., Analyt. Chrm., 1976, 48, 1336. Thompson, M,, Hewitt, P. X., and Wooliscroft, D. S., .4na?yt. Chewa., 1978, 50, 690. Thompson, M., Talanta, 1977, 24, 399. Carlson, T. A,, “Photoelectron and Auger Spectroscopy,” Plenum Press, London, 1975. Selectivity Rating of Calcium Ion-selective Electrodes G.J. Moody, N. S. Nassory and J. D. R. Thomas Chemistyy Department, Universzty of Wales Instatute of Science and Technology, Cavda ff, CF1 3 S C’ Interference Equations proposal^^-^ for rating selectivities of calcium ion-selective electrodes include the widely used selectivity coefficient, k::;, a selectivity parameter, K,, which is derived from a consideration of interference potentials, and a more arbitrary parameter, Ki.The origin of hF:i5, recommended in IUPAC nomenclature recommendation^,^ lies in the following form of the Nicolsky e q u a t i ~ n ~ , ~ : E = constant -t- . . . .Janiiavy, 1979 RESEARCH AND DEVELOPMENT TOPICS 33 where E is the emf of the calcium ion-selective electrode coupled to a reference electrode, a,, and a, are the activities of calcium ions and interferent B ions, respectively, and z, is the valence of the B ions.By measuring the emf, El, of a solution containing only calcium ions and the emf, E,, o: a solution containing calcium ions at the same activity and interfering ions, it is possible to deduce kF;k from R, T and F have their normal significance.. by plotting eAf:?”/RT against . ~ This corresponds to the Srinivasan and Rechnitzs (a,) 2’2n (%a) method for high k::; values (Method IIC of references 9 and 10). Another such potential, E,, has been defined in terms of the difference between an Eidea, and an E,, representing the theoretical and experimental difference between the emf of a pure calcium chloride solution and that of a mixed calcium chloride - interferent chloride solution, respec- tively.2 The two solutions are of equal ionic strength.For the theoretical case, Eidea, assumes that there is no interference and also that the single-ion activity coefficient of Ca2+ depends only on the total ionic strength, but not on composition. The results for E , ob- tained in this way for calcium chloride solutions plus sodium chloride or lithium chloride at a total ionic strength of less than 0.6 have been shown2 to fit The AE term of equation (2) can be regarded as an interference p~teni-ial.~ E , = - ~ In 1 + K , - ] .. . . . . RT F [ (a,,)‘ ,411 arbitrary relationship for calculating selectivity arises from misgivings3 concerning the power term in equation (1) : E , - E - - In 1 + ~ i 51... . . . . . - RT 2F [ a,, (4) Here, the selectivity parameter, Ki, is based3 on a principle of equal affinity whereby an electrode “has an equal affinity for a primary ion and an interfering ion if the same measured potential is obtained for solutions of the primary ion and the interfering ion which have the same activities, regardless of the charges on the ions.” Critique of Interference Equations The definitive basis of equation (4) demands an intersection between the calibration line for primary calcium ions and that for interfering B ions, when Ki = 1 .M’hen the calcium ion calibration line is at a more positive emf than that for the interfering ions Ki is less than 1; a t more negative emfs Ki is greater than 1. For calibration graphs of calcium and interfering ions, respectively, that are of equal slope, the condition of equal affinity holds at all points for superposable calibrations and Ki = 1 over the complete calibration.This situation occurs for calcium - magnesium or “water hardness” electrodes based on calcium dialkylphosphate as sensor with decan-1-01 solvent as mediator.lY1l However, when calibrations of equal slope are not superposable the definitive requirement of equation (4) cannot be fulfilled; nevertheless, Ki can still be calculated and will be less than 1 for calcium ion calibrations that lie at more positive emfs than those for interferents and more than 1 for calibrations with more negative emfs.Misgivings concerning the power, 2/zu of aB in equation (1) have arisen3 because of k,t& values of greater than 1 for electrodes that demonstrate selectivity of calcium ions over sodium ions.’These occurrences need cause no concern as the relationship . . . . - (5) a,, = kE& (aNa)2 . . . . used for calculating k:::, by the mixed solution Method IIA of references 9 and 10 shows that when a,, is less than 1 electrodes can usefully be used for calcium ion determinations,34 RESEARCH AND DEVELOPMENT TOPICS Proc.Aaalyt. Div. Chcm. SOC. even for apparently high kgka values.12 For example, when RzJa = 46, determined in the presence of a 10-2 M sodium ion background, the calcium ion selective electrode still responds down to about a 4.6 x M concentration of calcium ions with little interference from the background sodium ions.I2 In fact, the useful calcium ion range will be even better because the true activity of sodium will be less than 1 0 - 2 ~ .Any misgivings concerning the significance of the power term in equation (1) need to be of a more fundamental origin, particularly because the calibration graphs obtained by use of an electrode for interfering ions, B, frequently do not match that expected from the charge on B and are frequently sub-Nernstian or hyper-Nernstian.Furthermore, the graphs may be curved, as with magnesium ions for the first PVC-matrix membrane calcium ion selective electrode based on calcium bisdidecylphosphate sensor with dioctyl phenylphosphonate solvent,l3 where the slope gradually increased from 14.2 to 23.6 mV decade-l. Because no allowance is made for such features, variations occur in the selectivity coefficient, k:::, and while their significance is relatively unimportant in the recommendati~n~~~~ for quoting the background level of interferent in relation to k::: values, there are problems when applying graphical-type relationships like equations (1)-(4) over extended ranges.15 Any fundamental physicochemical deductions made from such equations need to be cognisant of slope changes that must be related to rather more complicated features of membrane - solution interface ion-exchange and membrane diffusion processes than would be the case for constant calibra- tion slopes.Some Practical Considerations Because of the likelihood of non-Nemstian slopes or curvatures in calibration graphs of ion- selective electrod3s for interEering ions, linear graphs emanating from equations (2) and (3) are frequently just a coincidence rather than a regular feature.15 This phenomenon presents difficulties in conveying helpful data.In any case, the nature of kp,t is such that its values for B ions of different valencies are not comparable and, of course, it is of paramount import- ance for kyi data to be accompanied by information on how they were obtained.14 Despite the difficulties of theoretical interpretation, such background information on kE data en- hances their utility in assessing the practical scope of ion-selective electrodes.Improved Calcium Ion Sensors Selectivity coefficient data derived by the mixed solution method (Method IIA of references 9 and 10) and accompanied by the actual background level of interferent59l4 constitute a conven- ient way of conveying information on the selectivity of ion-selective electrodes.Thus, the lower k:$ values for a calcium ion selective electrode based on calcium bis[di(p-1,1,3,3- tetramethylbutylphenyl)phosphate] as sensor and dioctyl phenylphosphonate solvent as mediator confirm greater selectivity towards calcium ions than is obtained by use of an electrode based on Orion 92-20-02 calcium liquid ion exchanger (Table I).Tripentyl phos- phate is a good alternative to dioctyl phenylph~sphonatel~ (Table I). Table I establishes calcium bis[di(#-l,l,3,3-tetram~thylbutylphenyl)phosphate] as a superior calcium ion sensor, like its octyl isomer.16 It can be even better than is indicated in Table I, TABLE I SELECTIVITY DATA FOR PVC MATRIX MEMBRANE CALCIUM ION-SELECTIVE ELECTRODE+ k;:; for various interferents, B I 1 Membrane components Na* K* Mgt Srt Bat Mnt Cut Nit Znt Orion 92-20-02 liquid ion-exchanger 0.045 0.062 0.13 0.14 0.058 0.23 0.16 0.96 $ Calcium bis[di(p-l,1,3,3-tetramethyl- butylphenyl) phosphate] plus dioctyl phenyl- phosphonate 0.017 0.018 0.021 0.041 0.000 0.040 0.014 0.013 0.30 Calcium bis [di(p-l,1,3,3-tetramethylbutyl- phenyl)phosphate] plus tripentyl phosphate 0.021 0.022 0.062 0.091 0.043 0.22 0.086 0.082 0.48 * B ion level = 5 x M.t B ion level = 5 x M. 1 Calibration graph for Ca2+ in the presence of zinc ions did not, a t any stage, coincide with the normal Ca*+ calibration.January, 1979 RESEARCH AND DEVELOPMENT TOPICS 35 and Table I1 presents k;c data, obtained in various studie~~~J5@J9 and compared with those for a neutral carrier sensor,17 that were obtained for a lower level of background sodium ion interferent.These factors all point to a similar low interference from sodium ions for (~-1,1,3,3-tetramethylbutylphenyl)phosphate sensor for the various electrodes to that for the neutral carrier system, although the phosphate is synthetically more accessible.20 TABLE I1 k,Pit,, DATA FOR CALCIUM ION-SELECTIVE ELECTRODES BASED ON CALCIUM BIS[DI($-1,1,3,3- TETRAMETHYLBUTYLPHENYL)PHOSPHATE] SENSOR Sensor DTMBPP + DOPP* Limit of useful Ca2+ Pot Na+ level/M range from eqn./M Reference kcam 0.017 4.3 x 10-5 11 2.5 x 10-5 15 0’01 0.001 } 0.05 2.5 x 18 t 4.6 x 19 o-nitrophenyl octyl ether 0.01 0.01 1.0 x 10-6 17 Neutral carrier sensors + * DTMBPP, di@- 1,1,3,3-tetramethylbutylphenyl)phosphate ; DOPP, dioctyl.phenylphosphonate. t Sodium interference not measurable. ’+ Calibration limit. § Neutral carrier ssnsor = The relative freedom from sodium ion interference when using (@-1,1,3,3-tetrarnethylbut~+ pheny1)phosphate sensor can be seen from the “at a glance” graphs of Fig.1 (curves B and C compared with E and F). Such at a glance graphs emphasise the utility of k,Pi\ because for interferents at any single level and of the same charge, the lowest k::: values yield the longest interference-free calibration ranges with respect to calcium ions (compare curve B with E, and C with F, in Fig.1). For any one interferent, it frequently occurs that k,P;L is greater for low levels of B than for higher levels. This stresses the importance of quoting the interferent level alongside k , E and also the usefulness of equation ( 5 ) , as the higher k;;; values give the more extensive range with respect to calcium ions (compare curve B with C, and E with F, in Fig. 1). Studies on Di[p-( 1,1,3,3-tetramethylbutyl)-o-nitrophenyl]phosphate Sensor Effect of Zinc Interference Continuation of the studylg of the behaviour of a calcium ion-selective electrode with a more electrophilic octylphenyl group in the phosphate sensor, as with the calcium salt of di[$- (1,1,3,3-tetramethylbutyl)-o-nitrophenyl]phosphate, has shown an interesting aspect concern- ing zinc interference.15 A long recovery time is normally required by calcium ion-selective electrodes based on dialkylphosphate sensors after exposure to zinc.13 This is not the case with the nitrated sensor but unfortunately its calibration range is shorter.Also, calcium electrodes made from the nitrated sensor with dioctyl phenylphosphonate solvent mediator exhibit less interference than the non-nitrated sensor when only low levels of zinc are present (Fig.2).36 > E > u! c! 3 h c m - 5 RESEARCH AND DEVELOPMENT TOPICS R o c . Analyt. Div. Chem. SOC. F E D B A I I I I I l l I I I 6 5 4 3/16 5 4 3 PCa Fig. 1. Calibration of calcium ion-selective electrodes containing (I) calcium bis [di(p-1,1,3,3-tetramethylbutylphenyl)phosphate] sensor with dioctyl phenyl- phosphonate solvent mediator and (11) Orion 92-20-02 calcium liquid ion exchanger trapped in a PVC matrix membrane.15 A and D, Calibration with calcium chloride standards; B, C, E and F, calibration with calcium chloride standards in background sodium chloride solutions containing 0.05 M (B and E) (hgka = 0.01 and 0.11, respectively) and 0.15 M (C and F) = 0.002 8 and 0.050, respectively) sodium chloride. pH Interferences In an alternative mixed solution method for expressing interferences (Method IIB of refer- ences 9 and lo), the primary ion level is kept constant while the interferent level, say pH, is varied.Normally with calcium dialkylphosphate sensors and dioctyl phenylphosphonate solvent mediator a dip appears in the pH interference curve which, with the more electro- philic di(p-octylpheny1)phosphate sensors, occurs at lower pH values.This dip was not observed for PVC matrix membrane electrodes based on calcium di(@-nitropheny1)phosphate sensor with dioctyl (m-nitropheny1)phosphonate solvent mediatorlg or with the same mediator in conjunction with di [@- (1,1,3,3-tetramethylbut yl) +nit rophenyl] phosphat e ~ens0r.l~ I I I / 11 I I 5 4 3 '5 4 3 P Ca Fig. 2.Calibration of calcium ion-selective electrodes containing (I) calcium bis [di( p - 1, 1 ,3,3-tetramethylbutylphenyl) phosphate] with dioctyl- phenylphosphonate solvent mediator and (11) calcium bis {di[P-l,1,3,3- tetramethylbutyl(o-nitro)phenyl]phosphate} with dioctyl phenylphosphonate solvent mediator trapped in a PVC matrix membrane.15 A, Calibration with calcium chloride standards ; B-D, calibration with calcium chloride standards in background zinc chloride solutions containing 0.000 5 M (B), 0.005 M ( C ) and 0.05 M (D) zinc chloride. The slight dip in the pH curve with the lower permittivity mediators like dioctyl phenyl- phosphate or tripentyl phosphate in conjunction with the nitrated sensor becomes moreJuiiiiary, 1979 PESTICIDE RESIDUE AN4LTiSIS 37 prominent with the non-nitrated di[p-( 1,1,3,3-tetramethylbutyl)phenyl]phosphate sensor.Such trends seem to suggest that the existence of a dip in the pH interference curves for the phosphate ester type sensors of calcium ion-selective electrodes are related to the acid strength of the diester. Thus, the sensors of high pK,, with their strong affinity for protons, exhibit dips in the pH interference curves, while the sensors of low pK, are less likely to do so, particu- larly with solvent mediators of sufficiently high permittivity such as dioctyl (m-nitropheny1)- phosphonatr .Conclusion The selectivity coefficient, k::;, associated with the level of interferent at wh‘ch it is determined is a satisfactory parameter for expressing the practical scope of calcium ion selective electrodes.The best electrode is based on calcium dire-( 1,1,3,3-tetramethylbutyl)- phenyl] phosphate as sensor plus dioctyl phenylphosphonate as solvent mediator for reasons of convenience of fabrication and freedom from interference. The nitrated form of the sensor, although appearing to give greater freedom from low level zinc interference and also from pH interference when used in conjunction with dioctyl (9%-nitrophenyl)phosphate, does not offer a sufficient additional advantage over its non-nitrated counterpart to compensate for the loss of calcium calibration range. The authors are grateful to the University of Technology, Baghdad, Iraq, for financial support (to XSN). 1 . ? -. 3. 4. 8 . 6. -3 8 . 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. References Koss, J . U’., in Durst, K. A, Editov, “Ion-Selective Electrodes,” Special Publication 314, National Bagg, J . , Nicholson, O., and Vinen, R., J . Phys. Chem., 1971, 75, 2138. Cattrall, K. W., and Drew, D. M., Analytica Chim. Acta, 1975, 77, 9. Moody, G. J., Nassory, N. S., and Thomas, J. D. R., Hung. Sci. Instvum., 1977, 41, 23. IIJPAC, “Recommendations for Nomenclature of Ion-Selective Electrodes,” Puvp A p p l . C h e w , 1976, Nicolsky, B. P., and Schultz, M. M., Zh. Fix. Khim., 1962, 36, 704. Nicolskq-, B. P., Schultz, M. M., Belijustin, A. A., and Lev, A. A,, in Eisenman, G., Editor, “Glass Srinivasan, K., and Rechnitz, G. A., ,4nalyt. Chem., 1969, 41, 1203. Moody, G. J . , and Thomas, J. D. R., Lab. Pvact., 1971, 20, 307. Moody, G. J . , and Thomas, J. D. R., “Selective Ion Sensitive Electrodes,” Merrow, \Vatford, 1971. Moody, G. J., Nassory, N. S., and Thomas, J . D. R., Analyst, 1978, 103, 68. Craggs, X., Keil, L., Moody, G. J., and Thomas, J . D. R., Talanta, 1975, 22, 907. Moody, G. J , Oke, R. B., and Thomas, J. D. R., Analyst, 1970, 95, 910. Moody, G. J . , and Thomas, J . D. R., Talanta, 1971, 18, 1251. Moody, G. J., -?;assory, S. S., and Thomas, J . D. R., t o be published. KbEiCka, J., Hansen, E. H., and Tjell, J . Chr., ilnaZ&a Chzm. Acta, 1973, 67, 155. Amman, D., Bissig, R., Guggi, M., Pretsch, E., Simon, W., Borowitz, I. J., and Weiss, L., Helv. Chim. Acta, 1975, 58, 1535. Birch, B., Craggs, A,, Moody, G. J . , and Thomas, J. D. R., i n Pungor, E., and Buzas, I., Editors, “Ion-Selective Electrodes,” Akademiai Kiadb, Budapest, 1978, p. 335. Iieil, L., Moody, G. J . , and Thomas, J . D. K., Analytica Chirn. Acta, 1978, 96, 171. Craggs, Bureau of Standards, Washington, D.C., 1969, p. 57. 48, 127. Electrodes for Hydrogen and Other Cations,” Marcel Dekker, New York, 1967. Delduca, P. G., Keil, L., Key, B. J . , Moody, G. J . , and Thomas, J . D. R., J . Inovg. Xucl. Chem., 1978, 40, 1483.

ISSN:0306-1396    

DOI:10.1039/AD9791600023

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

PESTICIDE RESIDUE AN4LTiSIS 37 Pesticide Residue Analysis The following paper originated from a discussion at a meeting of the ad hoc Working Group on Methods of Analysis of the Codex Committee on Pesticide Residues in The Hague, Holland, 1977. I t was discussed in draft form a t the 1978 meeting of the Working Group and by the UK Committee on Analytical Methods for Pesticide Residues (CAM), and also at the meeting of the IUPAC Commission on Pesticide Residues Analysis in Deidesheim, West Germany, 1978.The author acknowledges the help given by many colleagues, including members of the above bodies, in producing these guidelines.38 PESTICIDE RESIDUE ANALYSIS Proc. Analyt. Div. Chem. SOC. Good Analytical Practice in Pesticide Residue Analysis G. M. Telling Unilever Research Laboratory, Colworth House, Shavnbvook, Bedfordshire, MK44 1LQ The Codex document Alinorm 76/24 Appendix IV (Report of the ad hoc Working Group on Methods of Analysis) contained the following statement.“It was considered that the ultimate goal in fair practice in international trade depended, among other things, on the reliability of analytical results. This in turn, particularly in pesti- cide residue analysis, depended not only on the availability of reliable analytical methods, but also on the experience of the analyst and on the maintenance of ‘good practice in the analysis of pesticides.’ ” This paper is an attempt to define such good analytical practice and may be considered in three inter-related parts: The Analyst Basic Resources The Analysis.The Analyst Residue analysis consists of a chain of procedures, most of which are known, or readily understood, by a trained chemist, but because the margin of error is smaller than in most other types of analysis and any mistake can invalidate the whole analysis, attention to detail in thes2 procedures is essential. There should be adequate overlap and continuity of staff and all need to be experienced in residue analysis over a period of years.Staff should be trained in the correct use of apparatus and basic laboratory skills and the basic principles of residue analysis. They must understand the purpose of each stage in the method being used and the importance of following the method exactly as described and of noting any enforced deviations.A clear understanding of the terminology involved is also essential. Ideally, when a laboratory for residue analysis is set up, the staff should spend some of their training period in a well established laboratory where experienced advice and training is available. If the laboratory is to be involved in the analysis for a wide range of pesticide residues it may be necessary for the staff to gain experience in more than one established laboratory.Basic Resources The Laboratory In ideal circumstances the laboratory and its fittings should be designed to allow tasks to be allocated to well defined areas with maximum safety and minimum chance of contamination of samples. Fittings should be of materials resistant to attack by chemicals likely to be used in the area.Thus, in such ideal conditions separate rooms would be available for sample re- ceipt and storage, for sample preparation, for extraction and clean-up and for instrumentation used in the determinative step. The area used for extraction and clean-up would meet solvent laboratory specifications and all fume extraction facilities would be of high quality. The minimum requirements for pesticide residue analysis are that the facilities are adequate to avoid contamination.Laboratory safety must also be considered in terms of necessary and preferable conditions as it must be recognised that the stringent working conditions enforced in residue laboratories in some parts of the world would be totally unrealistic in others. No smoking, eating, drink- ing or application of cosmetics should be permitted in the working area.Only small volumes of solvents should be held in the working area and the bulk of the solvents stored separately, away from the main working area. The use of toxic solvents and reagents must be avoided whenever possible. The main working area should be treated as a solvent laboratory and all equipment such as lights, macerators and refrigerators should be spark-free.Extractions, clean-up and con- centration steps should be carried out in a well ventilated area, preferably in fume cupboards or under fume hoods. All waste solvents should be stored safely and disposed of frequently.January, 1979 PESTICIDE RESIDUE ANALYSIS 39 Safety screens should be used when glassware is used under vacuum or pressure.There should be an ample supply of safety glasses, gloves and other protective clothing, emergency washing facilities and spillage treatment kit. All staff should be trained in the use of these facilities and in an appreciation of the hazards involved. Staff must be aware that many pesticides have toxic and/or carcinogenic properties and although little risk is attached to the handling of most samples, great care is necessary in the handling of standard reference com- pounds.Adequate fire fighting equipment must be provided. The staff should be given periodic medical checks. Equipment and Supplies Supplies The laboratory will require adequate supplies of electricity and water and various gases, either piped or from gas cylinders of proven quality. Adequate supplies of reagents, solvents, glassware, stationary phases, etc., are essential.Servicing facilities for gas chromatographs, balances, spectrophotometers, etc., will be required and will probably involve keeping some essential spare parts plus access to a good technical service. Adequate equipment Although, in an ideal situation, equipment should be regularly updated in order to keep up with developments, e.g., gas chromatography with microprocessor controls, the equipment only needs to be sophisticated enough to do the job required. Thus, the demands for monitor- ing commodities a t tolerance levels laid down in the Codex are much less stringent than those required in a research environment.All laboratories require an adequate range of standard pesticides of known and reasonably high purity.The range should cover all parent species for which the laboratory is moni- toring samples as well as their more common metabolites. The Analysis Avoidance of Contamination One of the major areas in which pesticide residue analysis differs significantly from macro- analysis is that of the problem of contamination. Trace amounts of contamination in the final samples used for the determination stage of the method can give rise to errors such as false positive results and to a loss of sensitivity that may prevent the residue analyst from achieving the necessary limits of determination. Contamination may arise from either the environment or the procedure.Contamination from the working environment Bench polish, barrier creams, soaps containing germicides, fly sprays, perfumes and cos- metics are all commodities that can give rise to laboratory contamination and are especially significant when an electron-capture detector is being used.There is no real solution to the problem other than to ban their use. Greases, plasticisers, rubber bungs and tubing, oil from air lines, extraction thimbles, filter-papers and cotton-wool can also all give rise to contamination of the final test solution.Pesticide reference standards should always be stored in a room separate from the main residue laboratory. Field samples, sample preparation and formulation analysis should also be kept separate from the main residue laboratory. Contamination from the procedure being used previous samples.then rinsed with the solvent to be used. pesticide residue work. contain components that interfere in the analysis. adsorbents by heating and it is generally necessary to use redistilled solvents. Contamination of glassware, syringes and gas-chromatographic columns can arise from All glassware should be cleaned with detergent, rinsed thoroughly and There must be a separate stock of glasswarefor Chemical reagents, adsorbents and general laboratory solvents may It may be necessary to purify reagents and De-ionised40 PESTICIDE RESIDUE ANALYSIS Proc.Analyt. Div. Chew. SOC. water is often suspect and redistilled water is preferable. In many instances tap water or well water may be satisfactory. Other materials containing plasticisers are suspect but PTFE and silicone rubbers are usually acceptable and others may be acceptable in certain circumstances.Sample storage containers can cause contamination and glass bottles with ground glass stoppers should always be used. Instru- mentation should always be housed in a separate room. The nature and importance of con- tamination can vary according to the type of determination technique used and the level of pesticide residue to be determined. These contamination problems, which are important with methods based on gas chromatography or HYLC, may well be less significant if a spectro- photometric finish is used, and vice versa.For relatively high levels of residues the background interference from solvents and other materials may be insignificant in comparison with the amount of residue present, while many problems can be solved by the use of specific detectors.Furthermore, if the contaminant does not interfere with the residue being sought, its presence may be acceptable. No apparatus containing PVC should be allowed in the residue laboratory. Avoidance of Losses Losses during storage In an ideal situation samples should be stored at chill temperature, away from direct sun- light, and analysed within a few days.However, in many instances samples can require storage for an extended period (6-9 months) before analysis and the following precautions should be observed. Storage temperature should be approximately -20 O C , when degradation of residues of pesticides by enzyme action is extremely slow.If any doubts exist, the samples should be compared with fortified samples stored under the same conditions. All samples should be re-homogenised after freezing as there is a tendency for water to distil out and to collect as ice crystals, which, if discarded, will affect the analytical result. Neither the containers used for storage nor their caps or stoppers should allow migration of the chemical being sought into the container.The containers must not leak. All samples should be labelled clearly with permanent labels and recorded in a sample book. Losses dutring the analysis The extracts and final test solutions should not be exposed to direct sunlight. Validation of Methods In a routine laboratory monitoring for compliance with Codex or national tolerances, standardised methods will be used in most instances and effort expended on validation of methods will be at a minimum.In all laboratories, regular checks will be made on the effects of variation in sources of supply of chemicals, solvents, etc. The performance of the method will have to be checked by, for example, the recovery of standards, added at appropriate levels, taken through the method both alone and in the pres- ence of each new substrate.The effects of light, storage at intermediate stages of the procedure, temperature, etc., on the stability of reagents and samples must be studied. The evaluation of detection/determination systems (e.g., in gas or liquid chromatography) for effects of flow-rate, temperature, etc., is important. In laboratories where method development and/or modification is undertaken other aspects that may be studied are the effect of variation in sample size, partition ratios, etc., theefficiency, resolution and column stability of gas- and liquid-chromatographic systems and variations in activity of various column clean-up systems.The amount of effort allocated to the validation of methods will vary considerably.Maintenance of Over-all Analytical Performance of the methods in use, both at the tolerance level and at the lower limit of determination. In all laboratories engaged in pesticide residue analysis there is a need for regular assessmentJ a m a r y , 1979 PESTICIDE RESIDUE ANALYSIS 41 Rwovery studies Recovery of pesticides from “spiked” samples is commonly used as a measure of efficiency of extraction, but it must be recognised that such studies are of limited value.More emphasis should be placed on checking recoveries where residues are in a “real” state, e.g., in aged samples. I t must also be recognised that a method that gives adequate recoveries from samples spiked with parent compounds may be inadequate for the measurement of significant metabolites produced during ageing of the substrate.Recoveries should be within the range ‘iO-llO(?b with a mean of greater than SOo,b after removal of outliers. Bluii k responses and interferences check that contamination is not occurring. Regular analyses of substrates known to be free of pesticide residues is necessary in order to Stubilitv of standards Regular injection of standards during the analysis of a series of samples allows the perform- ance of the determination step to be checked.In addition, care should be taken that standard solutions of pesticides are not decomposed by the effect of light or heat during storage or become more concentrated owing to solvent evaporation. Equal care must be taken to ensure t lie stability of reference standard compounds.-4 Irnljisis of check samples check samples at regular intervals. samples without any indication being given as to their special nature. ;ln excellent means of monitoring the performance of a method (or an analyst) is to introduce These check samples should be introduced as routine Participation in collaborative studieslring tests I’arious national and international organisations now organise collaborative studies on particular methods and/or ring tests on particular substrates.These present an ideal way for laboratories to assess their own performance. If possible, collaborative samples should be introduced as routine samples so that the analyst concerned does not attempt to “make a special effort,” which would invalidate the samples as a test of laboratory performance.Confirmatory Tests beforehand, confirmatory tests will not normally be necessary. the reliability of results need confirmatory tests be used. under a number of headings. Use of solvent partitioning effects such as P values. Use of multiple gas-chromatographic columns. Use of different chromatographic techniques. For routine control, where the range of resulting values is, at least to a certain extent, known Only if there are doubts as to Confirmatory tests can be considered Although this technique is widely used, its value is limited because, in all instances, the basic chromatographic technique is similar.In many instances confirmation of gas- chromatographic findings is best achieved by using thin-layer chromatography or high- Performance liquid chromatography.Both have considerable advantages over gas chromato- graphy in some circumstances, especially when dealing with substances that are not thermally stable. Whenever possible, confirmatory techniques should be carried out rather than placing complete reliance on gas-chromatographic columns as a method of identification. Use of different detector systems.I‘se of chemical derivatisation techniques. These are widely used techniques and a number of text books are available on the types of derivatisation that can be achieved. A closely linked technique is the use of, for example, ultraviolet light to change the chemical structure of the compound under examination. Gas chromatography - mass spectrometry is a technique widely used in laboratories with a high level of sophisticated instrumentation, although it is not available in the majority of pesticide residue laboratories.Pre-gas - liquid chromatographic separation techniques often give an indication of the identity of residues, as they are based on the properties of residues present.42 ANALYTICAL CHEMISTRY TRUST FUND Proc.Analyt. Div. Chem. sot. Reporting Results This aspect of pesticide residue analysis depends very much on the requirements of the organisation demanding the analytical information and it is difficult to lay down strict rules of reporting, or even on the accuracy required. I t is recommended that both analyst and user of the information fully appreciate the capability of the methods used and the interpretation to be placed upon data produced before the work is started. In all instances reports of results should indicate the method used in order to obtain those results. I acknowledge the help that I have received from numerous colleagues who were prepared to discuss what they thought such a document should contain. Bibliography Burke, J., and McMahon, B., “Analysis of Food for Residues of Pesticides,” FDA By-Lines, No. 4, January “Guidelines on Analytical Methodology for Pesticide Residue Monitoring,” Federal Working Group on Pest Sherma, J , , “Manual of Quality Control for Pesticides and Related Compounds in Human and Environ- “Pesticide Analytical Manual,” Volume 1 , U.S. Department of Health, Education and Welfare, Food and 1977. Management, Washington, D.C. 20460, June, 1975. mental Samples,” USA Environmental Protection Agency, EPA 600/1-76-017, February, 1976. Drug Administration.

ISSN:0306-1396    

DOI:10.1039/AD9791600037

出版商:RSC    

年代:1979

数据来源: RSC

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42 ANALYTICAL CHEMISTRY TRUST FUND Proc. Analyt. Div. Chem. SOC. Publications Received Transform Techniques in Chemistry. Edited by Peter I<. Griffiths. Pp. xxiv + 385. New York and London: Plenum. 1978. Price $47.40. Contemporary Topics in Analytical and Clinical Chemistry. Volume 2. Edited by David M. Hercules, Gary M. Hieftje, Lloyd R. Snyder and Merle A. Evenson. Pp. x +2S6. New York and London: Plenum.1978. Price $33.00. Structure Determination by X-Ray Crystal- lography. M. F. C. Ladd and R. A. Palmer. Pp. xxii +393. New York and London: Plenum. 1978. Price $17.70.J a w a r y , 1979 PUBLICATIONS RECEIVED 43 Ion Chromatographic Analysis of Environ- mental Pollutants. Edited by Eugene Sawicki, J . D. Mulik and E. Wittgenstein. Pp. vi + 210. Ann A4rbor, Mich. : Ann Arbor Science Publishers.Distri- buted by John Wiley, Chichester. 1978. Price ,517.65. Trace Metals in the Environment. Volume 3. Zirconium. Ivan C. Smith and Bonnie L. Carson. Pp. xviii + 406. Ann Arbor, Mich.: Ann Arbor Science Publishers. Distributed by John \\?ley, Chichester. 1978. Price L15.20. Trace Metals in the Environment. Volume 4. Palladium and Osmium.Ivan C. Smith, Bonnie L. Carson and Thomas L. Ferguson. Pp. xiv + 194. Ann Arbor, Mich. : Ann Arbor Science Publishers. Distributed by John Wiley, Chichester. 1978. Price k15.20. Analysis with Ion-selective Electrodes. J. Vesel9, D. Weiss and K. Stulik. Ellis Horwood Series in Analytical Chemistv-v. Pp. 245. Chichester : Ellis Horwood. Distributed by John Wiley. 1978. Price L16.Computer Applications in the Analysis of Chemical Data and Plants. Plenary and Main Lectures Presented at the Chemdata 77 held in Espoo Korpilampi, Finland, 9-10 June, 1977. Edited by J . Larinkari. Pp. 277. Princeton X.J.: Science Press. 1977. Price $20. The Chemical Analysis of Manganese. Roland S. Young. Pp. 32. Paris: The Man- ganese Centre. 1978. Gratis. The Study of Ionic Equilibria.An Intro- duction. Hazel Rossotti. Pp. xiv + 194. London and New York: Longman. 1978. Price L5.95. Nuclear Safeguards Analysis. Non- destructive and Analytical Chemical Tech- niques. E. Arnold Hakkila. A CS Symposium Series No. 79. Pp. x + 214. Washington, D.C.: American Chemical Society. Available in Great Britain from The Chemical Society. 1978. Price $22. Guide for the Perplexed Organic Experi- mentalist. H.J. E. Loewenthal. Pp. x + 174. London, Philadelphia and Rheine: Heyden. 1978. Price L4.80; $9.60; DM22. Resonance Raman Spectroscopy as an Analytical Tool. Edited by A. J. Melveger. 1977 Eastern Analytical Symposium Series. Pp. viii + 84. Philadelphia : Franklin Institute Press. 1978. Price $10.50. Thermal Methods in Polymer Analysis. Edited by S.W. Shalaby. 1977 Eastern Analytical Symposium Series. Pp. viii + 204. Philadelphia : Franklin Institute Press. 1978. Price $18.95. Atomic Absorption, Fluorescence and Flame Emission Spectroscopy. A Practi- cal Approach. Second Edition. K. C. Thompson and R. J . Reynolds. Pp. xii + 320. London and High Wycombe: Griffin. 1978. Price ,515. Blood Drugs and Other Analytical Chal- lenges.Edited by E. Reid. Methodological Surveys in Biochemistvy. Pp. xii + 356. Chichester: Ellis Horwood. Distributed by John Wiley, Chichester. 1978. Price L19.50. Colorimetric Determination of Nonmetals. Second Edition. Edited by David F. Boltz and James A. Howell. Chemical Analysis, Volume 8. Pp. xxviii + 544. New York, Chichester, Hrisbane and Toronto: John Wiley. 1978. Price L23.95; $45.30. Tropical Storage Abstracts. No. 1. Edited by J . R. 0. Humphries. Pp. 14. Slough : Tropical Stored Products Centre. 1978. A ATew Journal. Analiticheskaya Khimiya Elementov. Barii N. C. Frumina, N. N. Goryunova and S. N. Eremenko. Pp. 200. Moscow: Nauka. 1977. R1.80. P a ) *

ISSN:0306-1396    

DOI:10.1039/AD979160042b

出版商:RSC    

年代:1979

数据来源: RSC

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Jamary , 1979 PUBLICATIONS RECEIVED 43 Meetings CS Annual Chemical Congress The Annual Chemical Congress of the Chemical Society and the Royal Institute of Chemistry is to take place a t the University of Bristol. The subjects of the analytical symposia will be A p ~ i l 3-5, 1979, Byisto144 COURSES “The Influence of Space Exploration on Analytical Instrumentation” and “Immuno and Coupled Enzyme Assays.” The eighth Theo- philus Redwood Lecturer will be Professor E.Pungor. Further information, including application forms, can be obtained from I>r. John F. Gibson, The Chemical Society, Burlington House, I’iccadilly, London, W1V OBN. Third International Bioanalytical Forum September 4-7, 1979, Guildford The subject of this forum is to be “Aids to Trace-organic Analysis.” Topics covered will include the assay of environmental contamin- ants (sample-handling aspect) and o f drugs in blood (sample preparation and automatic handling, the usefulness of radioisotopes and enzymes and sources of error). For information contact Dr.E. Reid, IVolfson Bioanalytical Centre, University of Surrey, Guildford. GU2 5XH. Proc. Analyt. Div. Cheni. SOC.CHEMICAL SOCIETY, ANALYTICAL DIVISION SCOTTISH REGION A Symposium on HPLC IN CLINICAL AND BIOLOGICAL CHEMISTRY at the Wolfson Liquid Chromatography Unit, Department of Chemistry, University of Edinburgh Friday, 23rd February, 1979 A one-day Symposium on current developments in HPLC technology and its applications in clinical, biological and pharmaceutical analysis will be held a t the University of Edinburgh.The Chairmen for the two scientific sessions will be Professor J. H. Knox (University of Edinburgh) and Dr. S. S. Brown (MRC Clinical Research Centre, Harrow). Papers will be presented on "Post-column Reactors" (Professor R. W. Frei), "Drugs of Abuse" (A. C. Moffat), "Analgesics" (L. F. Prescott). "Acute Poisoning" (M. J. Stewart), "Antidepressants" (I. D. Watson), "Enzymes" (C. K. Lim) and "Steroids" (P. F. Dixon). For application forms and further details contact the Honorary Secretary of the Region: Mr. A. F. Fell, Department of Pharmacy, Heriot-Watt University, 79 Grassmarket, Edinburgh, EHI ZHJ, before Friday, 16th February, 1979.

ISSN:0306-1396    

DOI:10.1039/AD9791600043

出版商:RSC    

年代:1979

数据来源: RSC

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44 COURSES Proc, Analyt. Div. Cheni. SOC. Courses Immunology as an Analytical Tool Afiril 2-6, 1979, Guildford This course is intended for novices and the lectures and practical work will include brief coverage of radioimmunoassay and immuno- fluorescence. The intention is to gil-e an appreciation of the study of immunoactive substances in blood. For further details con- tact Dr. E. Reid, Wolfson Bioanalytical Centre, University of Surrey, Guildford, GU2 5XH. Introduction to Blood-drug Analysis August 28, 1979, Guildford This course, which is again intended for novices, will be run in conjunction with the Third Inter- national Bioanalytical Forum (starting Septem- ber 4th). The instruction is aimed especially a t recruits to drug-company laboratories. For further details contact Dr. E. Reid, TYolfson Bioanalytical Centre, University of Surrey, Guildford, GU2 5XH.

ISSN:0306-1396    

DOI:10.1039/AD9791600044

出版商:RSC    

年代:1979

数据来源: RSC