ISSN:0144-557X    

DOI:10.1039/AP99128FX009

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANPRDI 28(3) 57-96 (1991) Proceedings of the Analytical Division of The Royal Society of Chemistry 57 Reports of Meetings 57 Obituary 58 SUMMARIES OF PAPERS 58 Electroanalysis and Chemometrics of Speciation of Natural Waters 58 59 61 63 'Reality of Metal Speciation Measurements in Natural Waters' by C. M. G. van den Berg 'Voltammetric Determination of Inorganic Sulphur Species in Natural Waters' by William Davison 'Performance of Metal-Ligand Titration Techniques' by Jill Ravenscroft and Mike Gardner 'Voltammetric Investigation of Natural Waters Using Microelectrodes' by Raymond 0. Ansell, Helen McAleer, Arthur McNaughtan and John R. Pugh 'Electrochemical Modelling of Ion Channel Transport: Thallium Voltammetry at Phospholipid Monolayer Coated Mercury Electrodes Modified With Gramicidin' by Andrew Nelson 'Stripping Voltammetry of Metal Complexes With Macromolecular Ligands: Some Fundamental Aspects' by Herman P.van Leeuwen 'Determination of Chromium Speciation in Sea-water' by Marc Boussemart and Constant M. G. van den Berg 'Electroanalysis of Metal Speciation and Its Relevance to Ecotoxicology' by Gregory M. Morrison and Chen Wei 'Speciation of Iron in Antarctic Lake Water by Adsorptive Cathodic Stripping Voltammetry' by Ornella Abollino, Edoardo Mentasti, Corrado Sarzanini, Valerio Porta and Constant M. G. van den Berg 'Problems with the Estimation of the Complexation Characteristics of Dissolved Organonickel Complexes' by Loes J. A. Gerringa 'In Situ Voltammetric Measurements in Natural Waters: The Advantages of Microelectrodes' by R.R. De Vitre, M.-L. Tercier and J. Buffle 'Lead Speciation in the Antarctic Ocean' by Gabriele Capodaglio, Giuseppe Scarponi and Paolo Cescon 'Reduction of Copper(ii) in the Presence of Monoamines a t the Ionic Strength of Sea-water' by Margarida M. C. Santos and M. Lurdes Simdes Gonqalves 'Investigation of Organometallics in the Marine Ecosystem by High-performance Liquid Chromatography With Inductively Coupled Plasma Atomic Emission Spectrometric and Electrochemical Detection' by Ambrogio Mazzucotelli, Aldo Viarengo, Laura Canesi, Fabio De Paz and Enrica Ponzano 'Speciation of Cobalt and Nickel in the North Sea' by Hao Zhang and Roland Wollast 64 66 68 70 72 73 74 76 77 79 80 82 Research and Development Topics in Analytical Chemistry 82 'Investigation of a Cation Exchange Separation Method for the Determination of Transition Metal Ions in Anaerobic Sealants' by Philip O'Dea, Marian Deacon, Malcolm R. Smyth and Raymond G. Leonard Typeset and printed by Black Bear Press Limited, Cambridge, England March 1991 Analytical Proceedings CONTENTS continued inside back cover

ISSN:0144-557X    

DOI:10.1039/AP99128BX011

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 57 Obituary Herbert Joseph (Joe) Cluley Dr. H. J . Cluley died suddenly on November 16th, 1990. Joe Cluley was born in 1920 and spent his early life in the Birmingham area. He was educated at Wolverhampton Grammar School, from which he joined the glass makers Chance Brothers in 1937. He worked in their analytical laboratory and at the same time obtained qualifications by part-time study. By 1941 he had graduated and in 1944 he qualified as an Associate of the Royal Institute of Chemistry. He also became a Fellow of the Chemical Society and a Member of the Society for Analy- tical Chemistry. At the end of 1945 he left Chance Brothers and joined the General Electric Company to work in their Research Laboratories at Wembley. He continued his part-time studies at the Sir John Cass Institute and obtained his MSc in 1950 and then his PhD in 1955.These were awarded for work on the extraction of germanium from flue dusts and the determination of potassium in glasses. In parallel with the work at Sir John Cass for his higher degrees Joe was also busy in other areas of analytical chemistry. He published a number of papers, mostly in The Analyst, which covered a wide range of subjects. These included work on the determinations of boron, iron, chro- mium, copper and water as well as work on glass analysis and investigations into the graphite-C02 interaction using 14C. The year 1969 saw him take over the leadership of the chemical and materials work at Wembley, a post that he held until his retirement from GEC in 1983.During his time at GEC great changes occurred in methods of chemical analysis and Joe played a large part in the intro- duction of modern instrumental methods into the analytical laboratories at Wem- bley. Throughout his later years he lec- tured at many meetings and conferences on the applications of analysis to industry and the need for feedback from industrial experience into the composition of courses in analytical chemistry. As well as his work with GEC, Joe was also involved in the professional aspects of analytical chemistry. This involved him with the Society for Glass Technology and the British Ceramic Research Association as well as the Society for Analytical Chemistry (SAC), which eventually became the Analytical Division (AD) of the Royal Society of Chemistry. He served on the Council of both the SAC and the AD and was Chairman, at differ- ent times, of the Analytical Abstracts Editorial Committee and of the Analy- tical Editorial Committee. He held the latter position during the change from SAC to AD. In 1970 Joe became Vice- President of the SAC and in 1982 received the Analytical Division’s Distinguished Service Award. His work for the Royal Society of Chemistry continued after his. retirement from GEC and up to the time of his death. Joe Cluley was not just a chemist. He was also a keen gardener and was interested in literature, photography, wine making and sport. He will be remembered by his ex-colleagues both at GEC and in the Analytical Division as a kind and gentle person who helped lead them through times of change. They would also like to express their sympathy to his widow Beryl and their family following the shock of his sudden death.

ISSN:0144-557X    

DOI:10.1039/AP991280057b

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

58 ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 Electroanalysis and Chemometrics of Speciation of Natural Waters The following are summaries of fifteen of the papers presented at a Joint Meeting of the Electroanalytical and Chemometrics Groups held on July gth-loth, 1990, in Liverpool University. Reality of Metal Speciation Measurements in Natural Waters C. M. G. van den Berg Oceanography Laboratory, University of Liverpool, Liverpool L69 38X The geochemistry and bioavailability of trace metals are affected by their chemical speciation. Estuarine studies, for instance, have shown that the dissolved concentrations of copper and zinc both vary with the concentration of organic complexing ligands which bind with these metals,' whereas the relationship between the free, uncomplexed, metal concentra- tion and its toxicity to aqueous micro-organisms is well known.* Studies of organic complexation of trace metals in natural waters have revealed consistently that a large proportion of several trace metals occurs complexed by dissolved organic material, but the fraction observed to be complexed differs between studies and metals as shown in Table 1.It is to be expected that differences in complexation occur between metals and samples from different waters. However, sea-water tends to have a rather constant composition; hence very large differences in the degree of complexation of individual metal ions in samples from comparable origin (surface waters, deep waters) are not to be expected. For this reason the spread of values for conditional stability constants for complexes with copper over several orders of magnitude is rather surprising.Table 1 Literature data for (YML as a function of the detection window of the analytical technique used to detect the speciation. D is the centre of the detection window. The data can be fitted by linear regression to an equation of the form log OLML = dog L) + b with the slope being equal to a = 0.98 f 0.10 and the y-axis intercept equal to b = 0.3 f 0.8 Metalltechnique Log D Log (YML Reference ZdCSV 1.1 2.81 3 ZdASV 1.3 2.08 4 Zn/Mn02 2.2 1.24 5 CdASV 2.6 2.50 6 CdASV 2.6 2.55 7 CdASV 2.6 1.90 8 CuIASV 2.6 2.15 9 CdASV 2.6 2.50 10 CdMn02 2.6 3.20 10 CdMn02 3.6 3.20 11 CdCSV 3.9 4.00 12 CdCSV 3.3 4.00 10 CdCSV 4.3 5.30 3 c01csv 6.3 7.23 13 Ni/CSV 9.2 9.00 14 One possible cause of the apparent spread in the data is an operational effect caused by the analytical techniques having a specific detection window and hence detecting only particular complexing ligands in a solution containing ligands of a broad range of complexation abilities.The detection window of voltammetric techniques can be calculated from the limit of detection and the standard deviation of individual measure- ments in anodic stripping voltammetry (ASV) and from the complexing ability of the added ligand in adsorptive cathodic stripping voltammetry (CSV) .3 Hence the detection windows of the methods used for the data shown in Table 1 have been calculated and are shown in the same table. It can be seen in Fig. 1 that a linear relationship exists between the detection windows of the analytical techniques used and the detected a-coefficients (aML) of organic complex- ation.A linear relationship holds for copper on its own, and for several metals combined, indicating that an operational effect related to the detection window of the techniques used is affecting the speciation detected. This effect can be explained by the presence of many complexing ligands forming com- plexes of greatly varying stabilities;3 in this scenario the organic complexation detected is only a small fraction of the large range of complexing material present in the samples. 10 9 8 7 d 6 J 0, 3 5 4 3 2 CUICSV / -Zn/CSV Cu1Mn02 Cu/MnOz - ZnlASV /- ,":;;:," c c u / c s v A u / c s v [/inlMnOFUIAsv I I 1 I I 1 2 3 4 5 6 7 8 9 1 0 Log (detection window) Fig.1 Relationship between the detection window of the analytical techniques used to measure metal complexation in natural waters and the detected values for (YML. The data are given in Table 1. Slope, 0.98 f 0.1 In order to verify whether this relationship is true for individual samples, the organic complexation of copper was determined by using CSV while varying the detection window by using several complexing ligands as adsorptive electroactive ligands, and by varying the concentration of the added ligand (AL).3 It can be seen in Fig. 2 that the detected a-coefficient of complexation increases with the detection window when this is varied for individual samples, suggesting that a large range of complexing ligands is indeed present in these samples [in this instance the samples originated from the North Sea and the Plymouth Sound (south-west UK) but there is no reason toANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 3 - 2 59 - 1 I I I I 9 sufficient to carry out a single complexing capacity titration, but rather that it is necessary to investigate the metal speciation over a broad range of complex stabilities by varying the analytical detection window.This range has to include the strong complexing ligands present at concentrations similar to that of the trace metal studied. The technique of cathodic stripping voltammetry is eminently suitable for this type of analysis as the detection window can be varied readily by increasing or decreasing the concentration of the added surface-active ligand or by selecting a different ligand for different detection windows.assume that the same would not be true for samples from other origins]. The concentration of the complexing ligands decreases with increasing complex stability; hence the influ- ence on the calculated metal complexation will become minimal when the concentration of the strongest complexing ligands is lower than that of the trace metal. The findings that a large series of ligands forming complexes of greatly varying strength are present in sea-water, and that the detection of the ligands depends on the detection window of the analytical technique used, have important implications for the study of metal complexation in natural waters. The data indicate that natural waters contain a mixture of ligands rather than a single ligand.Further, the data show that in order to investigate the metal complexation completely it is not 1 2 3 4 5 6 7 8 9 10 11 12 13 14 References van den Berg, C. M. G., Merks, A. G., and Duursma, E. K.. Estuarine, Coastal Shelf Sci., 1987, 24, 785. Brand, L. E., Sunda, W. G., and Guillard, R. R. L., J. Exp. Mar. Biol. Ecol., 1986,96, 225. van den Berg, C. M. G., Nimmo, M., Daly, P., and Turner, D. R., Anal. Chim. Acta, 1990. 232, 149. Bruland, K. W., Limnol. Oceanogr.. 1989,34, 269. van den Berg, C. M. G., and Dharmvanij. S . , Limnol. Oceanogr., 1984,29, 1025. Kramer, C. J . M., Mar. Chem., 1986, 18, 335. Seritti, A., Pellegini, D., Morelli, E., Barghigiani, C., and Ferrara, R., Mar. Chem., 1986, 18, 351. Hanson, A. K.. Jr., Sakamoto-Arnold, C. M., Huizenga, D.L., and Kester, D., Mar. Chem., 1988,23, 181. Coale, K. H.. and Bruland, K. W., Limnol. Oceanogr., 1988, 33, 1084. Buckley, P. J . M., and van den Berg, C. M. G.. Mar. Chem., 1986, 19, 281. van den Berg, C. M. G., Mar. Chern., 1984, 14, 201. van den Berg. C. M. G., and de Luca Rebello, A., Sci. Total Environ., 1986,58, 37. Zhang, H., van den Berg, C. M. G., and Wollast, R., Mar. Chem., 1990, 28, 285. van den Berg, C. M. G., and Nimmo, M., Sci. Total Environ., 1987, 60, 185. Voltammetric Determination of Inorganic Sulphur Species in Natural Waters William Davison" lnstitute of Freshwater Ecology, Windermere laboratory, Far Sawrey, Ambleside, Cumbria LA22 OLP The application of voltammetric procedures to natural waters has concentrated on the measurement and speciation of metals, even though many non-metal inorganic species can be determined voltammetrically.Most sulphur species, apart from sulphate, are electroactive and therefore amenable to measurement. This paper describes the species which exist in various natural environments and outlines how they can be measured. It then provides case examples of the application of such measurements to natural waters. Sulphur Species In completely reducing environments which are devoid of oxygen, sulphur exists predominantly in the form of sulphide, as H2S or HS- H2S + HS- + H+; pK = 7 HS- + S2- + H+; pK = 17.3 Hydrogen sulphide is a fairly insoluble gas and hence in neutral or acid waters, where it is present in appreciable concentra- tions, it is easily lost from solution by volatilization.At higher pH values (>lo), the H2S contribution is small and hence solutions are fairly stable. In all natural waters the contribution of the S2- species is negligible. Elemental sulphur dissolves in sulphide solutions to form polysulphides of various chain lengths [equation (l)] nSO + HS- += S,S2- + H+ (1) Rearrangement to other chain lengths proceeds rapidly by reactions of the type given in equation (2)' (n-1)SnS2- + HS- + nS,-lS*- + H+ (2) The total concentration of sulphur at zero oxidation state is given by summing the polysulphide species of various chain lengths, n, and various ionic forms [equation (3)] [ S o l T + C n [S,S2--] + C n [HS,S-] + C n [H2SnS] (3) * Present address: Institute of Environmental and Biological Scienccs, Lancaster University, Lancaster LA1 4TQ.The total concentration of sulphide species is given by summing60 ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 all the polysulphide species and also H2S and HS- [equation (411 [ S ' - ] T - X [S,S2-] + C [HS,S-] + C [H2SnS] + H2S + HS- (4) Equilibrium calculations suggest that polysulphide might be important in sea-water at pH >8, but unimportant in fresh- water at pH <7.2 Under completely oxidizing conditions the stable sulphur species is sulphate, but in partially reducing environments, such as close to a redox boundary or where the oxygen tension is low, there might be a range of partially oxidized sulphur species. Sulphite (SO32-), thiosulphate (S2032-) and tetra- thionate (S4062-) are the most common, but several other oxyanions are known.They are intermediates in the complete oxidation to sulphate, but depending on the redox conditions of the local environment and their rate of supply, they might have appreciable steady-state concentrations. Voltammetric Measurement At positive potentials, sulphide reacts with a mercury surface to form a film of mercury(i1) sulphide' [equation ( 5 ) ] Hg + HS- + HgSad, + H+ + 2e- ( 5 ) The half-wave potential for this reaction, which has been used extensively for the determination of sulphide, is -0.68 V [versus saturated calomel electrode (SCE)] (pH 10-12). It has long been recognized4 that the analytical response might not be simple, owing to the formation of insoluble films of HgS at the mercury surface. If the reaction only proceeds to a limited extent, however, less than a monolayer of sulphide is formed and a good analytical signal is obtained.With a stationary ~~ 0 0.5 1 .o 1.5 - E N versus SCE Fig. 1 Differential-pulse polarogram of anoxic water from the bottom of Esthwaite Water, showing peaks attributable to thiosulphate, total soluble sulphide, an iron sulphide dimer, labile Fez+ ions and labile Mn2+ ions electrode it is possible to scan anodically, starting at a negative potential where there is no reaction. A rapid scan also limits film formation.3 Moreover, the use of a dropping mercury electrode limits the formation of sulphide to the life of the drop. If there is still a problem, normal pulse polarography can be used.5 By using a negative starting potential where there is no reaction with sulphide, and pulsing to more positive potentials, film formation is restricted to the duration of the pulse, which is measured in milliseconds.The anodic reaction of polysulphides, v i z . , S,S2- + Hg + HgS + nSO + 2e- (6) is indistinguishable from the reactions of sulphide species; therefore, the signal with a half-wave potential of -0.68 V (versus SCE) provides a measurement of the sum of all of the sulphidic sulphur, [?+IT, whether it be polysulphide or not, and independent of the polysulphide chain length.6 There is also a cathodic reaction with the same half-wave potential,6 where polysulphide sulphur is reduced to sulphide [equation (711 S,S2- + 2ne- + ( n + 1)H20 .+ (n + 1)OH- + (n + 1)HS- (7) In a simple solution of a single polysulphide, the ratio of the cathodic to anodic signal provides a measure of the poly- sulphide chain length. In a nitrate-hydrogen carbonate solu- tion at pH 9.5, a good cathodic signal is obtained, but in more neutral solution HS- ions reacting at the electrode surface lower the current.Polysulphides have been alternatively measured by reacting them with sulphite to produce thiosul- phate [equation (S)]. Voltammetric measurement of the loss of sulphite or gain of thiosulphate is proportional to the number of sulphur atoms of zero oxidation state. 2 h, 60°C H 2 0 + S,S2- + nS032- - HS- + nS2032- + OH- (8) Both sulphite [equation (9)] and thiosulphate [equation (lo)] undergo electrode reactions analogous to that for sulphide.3~6 In an acetate buffer at pH 5 all three reactions can be clearly distinguished.' Tetrathionate can also be measured.It is reduced to thiosulphate at a half-wave potential of -0.32 V (versus SCE) in a saline solution3,6 Hg + 2S032- + [Hg(S03)2]2- + 2e- -0.60 V (versus SCE), 0.6 mol dm-3 NaCl (9) Hg + 2S2032- -+ [Hg(S203)2]2- + 2e- -0.12 V (versus SCE), 0.6 mol dm-3 NaCl (10) Applications The deep waters of productive lakes can become devoid of oxygen, allowing the accumulation of sulphide and other reduced ions. Sulphide species have been measured in such waters using various polarographic techniques,g and simul- taneous measurement of the concentration of Fell by polaro- graphy has been used to demonstrate that the concentration of sulphide may be controlled by equilibrium with freshly formed amorphous iron(i1) sulphide.9 It was first observed in anoxic lake water10 that when Fez+ and S2- ions are simultaneously present in a solution, there might be an additional signal at about -1.1 V (versus SCE).This is now thought to be due to a soluble Fe2S2 species which can be reduced at the mercury electrode. 11,12 Generally, Fe2S2 does not account for a significant fraction of the Fe" or S-11 unless one element is in extreme excess over the other, in which instance Fe2S2 represents an appreciable fraction of the element at lower concentration. Four species present in anoxic lake water, S-11, Fell, Mn" and the presumed Fe2S2, can readily be measured by a single scan using differential-pulse polarography (Fig. 1) .3 There is also a small peak at about -0.4 V (versus SCE).This rather broad peak is also observed in well oxygenated surface waters (Fig. 2). It closely corresponds to the potential of the thiosulphate reaction (Fig. 2), suggesting that thiosulphate might be responsible for at least part of this broad signal. Preliminary experiments have shown that bubbling through C 0 2 to lower the pH causes a small cathodic shift (20 mV) and a reversible reduction in peak height for both the lake water signal and the solution spiked with thiosulphate. In a seasonally anoxic lake the signal at -0.4 V was higher in the anoxic bottom waters (Fig. 3). When the signal was measured in the surface waters of several lakes it was systematically larger in those lakes with a higher biological productivity. These results are consistent with the signal being due to an algal degradation product which might be thiosulphate.Measurements of dis-ANALYTICAL PROCEEDINGS, MARCH 1991. VOL 28 9 - 10 E 1 1 - 0" . 5 Q 12 13 14 15 16 61 0 0 - 0 0 0 0 - 0 0 - 0 0 - 0 0 - 0 I I 1 0 0 0.2 0.4 0.6 - E N versus SCE Fig. 2 Differential-pulse polarogram of a surface water sample from Esthwaite Water after purging with an Ar-CO2 gas mixture (pH about 7) (1). Also shown are spiked additions of Na2S203 to concentrations of 200 (2); 400 ( 3 ) ; and 600 nmol 1-1 (4) solved organic carbon in the biologically productive lake Esthwaite Water indicate that about 1.5 mg 1-1 of C might be associated with algal decomposition. 13 This represents about 125 ymol 1-1 of C, which would contain about 1 ymol I-1 of S, about ten times the observed concentration of thiosulphate (Fig.3). In surface waters, the thiosulphate is likely to be continuously removed by oxidation, but in anoxic waters it might be stable, thus accounting for the increase in concentra- tion with depth (Fig. 3). Voltammetric measurements of [s2-]T, [SOIT, S2032- and S032- in sub-tidal marine sediments6 have produced a range of concentrations; [s2-]T is always the most dominant form. Polysulphides become progressively less important as the depth within the sediment increases. In salt marshes, which are partially oxidizing owing to the tidal flow and the vegetation providing an oxygen pump, [s2-]T is less dominant, with polysulphides sometimes representing 50% of the sulphidic sulphur. Thiosulphate can also be present in appreciable concentrations.The adsorption of sulphide on to mercury has recently been exploited by using cathodic stripping square wave voltammetry to measure a signal in anoxic sea-water which has been attributed to sulphide.14 It appears to be present in all sea-water at concentrations of 0.2-2.0 nmol 1-1 and is tentatively suggested to be due to sulphide covalently bonded to a metal. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 References Shea, D., and Helz, G. R., Geochim. Cosmochim. Acta, 1988, 52, 1815. Boulegue, J., and Michard, G., in Chemical Modelling in Aqueous Systems, ed. Jenne, E. A., A CS Symposium Series 93, American Chemical Society, Washington, DC, 1979, pp. 25-50. Davison, W., Buffle, J., and De Vitre, R., Pure Appl. Chem., 1988, 60, 1535. Canterford, D.R., Anal. Chem.. 1973,45, 2414. Canterford, D. R., J . Electroanal. Chem., 1974, 52, 144. Luther, G. W., Giblin, A. E.. and Varsolona, R., Limnol. Oceanogr.. 1985, 30,727. Renard, J. J., Kubes, G., and Bolker, H. I., Anal. Chem., 1975, 47, 1347. Davison, W., and Gabbutt, C. D., J . Electroanal. Chem., 1979, 99, 311. Davison, W., and Heaney, S. I., Limnol. Oceanogr., 1978,23, 1194. Davison, W., Limnol. Oceanogr., 1977, 22, 746. Buffle, J., De Vitre, R. R., Perret, D., and Leppard, G. G., in Metal Speciation: Theory, Analysis and Application, eds. Kramer, J. R., and Allen, H. E., Lewis, Chelsea, 1988, pp. Buffle, J., Zali, O., Zumstein, J., and De Vitre, R., Sci. Total Environ., 1987. 64, 41. Tipping, E., Hilton, J., and James, E., Freshwater Biol., 1988, 19, 371. Luther, G.W., and Tsamakis, E., Mar. Chem., 1989,27, 165. 99-1 24. Performance of Metal-Ligand Titration Techniques Jill Ravenscroft and Mike Gardner Water Research Centre, Medmenham Laboratory, P.O. Box 76, Henley Road, Medmenham, Marlow SL7 2HD The term metal-ligand titration refers to a technique widely used to examine the interaction between trace metals and complexing substances in natural waters. * J It has been established that complexation by naturally occurring organic ligands can reduce the toxicity of important trace metals to aquatic life.3 The importance of dissolved phase speciation has been acknowledged in the way European Community water quality standards are defined. For example, higher levels of copper arc permitted where organic complexation is present .4 There is a need for a better understanding of complexation in order ( a ) to know if existing metal levels pose a threat to the environment, and ( b ) to be able to predict the effect of any changes in the future.The two parameters of interest in investigating metal speciation are the total ligand concentration, [L], often referred to as the complexing capacity, and the conditional stability constant, K ' , for the metal-ligand equilibrium in the natural water matrix, where K' = [ML]/[L][M]. Knowledge of62 ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 the complexing capacity and stability constant for a metal complex allows the calculation of the relative proportions of the different forms of the metal, specifically the free metal ion, inorganic forms of the metal and organic complexes.This, in turn, will give a guide to the behaviour and toxicity of the metal.5 The basic approach in studying complexation is to take portions of the sample under examination and to add increas- ing amounts of the trace metal of interest. As the metal concentration is increased, any free organic ligand present in the sample becomes associated with the metal until the capacity for complexation is exhausted. Application of a measurement technique (or measurement/separation technique) which can distinguish between the “free” and complexed metal produces a titration curve of the form shown in Fig. 1. Beyond the equivalence point, the titration curve (B) becomes linear. The shape of the titration curve indicates the extent and nature of complexation in the sample.The displacement of the curve from that obtained in the absence of complexation (A) is taken as a measure of the ligand concentration, [L]; the shape of the curve is a guide to the strength of the metal-ligand complex, expressed in terms of K’. t s :: 0 U Performance Characteristics of Titrations It is important, in order to interpret the results of a metal-ligand titration, to understand the limitations of its performance. Knowledge of the precision with which K’ and [L] can be measured is required to be able to assign significance to changes in these parameters or to decide whether or not complexation has been detected. Determination of measure- ment precision by repetition of titrations is prohibitively time-consuming. Computer simulation of the titration, incor- porating the components of random measurement error derived from preliminary practical investigations, can provide a way of determining precision.9 A series of individual titration observations, each subject to the variability associated with the measurement technique under investigation, can be generated as illustrated in Fig.2. 4 t 0, C 0 Q v) U Metal concentration - Fig. 2 Generation of a series of individual titration observations. e, Theoretical response; f , imposed random error; and +, simulated measurement These simulated measurements can then be processed to arrive at estimates of K’ and [L]. Repetition of this provides a means of assessing the likely variability of real measurements. Metal concentration - Fig.1 and B, response with complexation present Titration curves. A, Response in the absence of complexation; Practical Approaches Ideally, any experimental technique used to assess metal complexation in natural waters should possess the following characteristics: ( a ) it should be sufficiently sensitive to be used directly at natural metal concentrations; ( b ) the type of ligand (or range of types) detected should be clearly defined, to allow unambiguous interpretation of the results; and (c) the depen- dence of the results on experimental or instrumental par- ameters should be minimized to allow comparison of results obtained on different occasions or by different workers. No existing technique meets these criteria entirely. The low metal levels involved and the need for multiple measurements in order to define complexation parameters tend to make speciation techniques time consuming and technically demand- ing.The methods used most widely at present are based on voltammetry, either anodic stripping voltammetry (ASV) or adsorptive/cathodic stripping voltammetry (CSV).6,7 With ASV, it is uncertain exactly which species are detected, owing to the possibility of complex dissociation during measurement. Current applications of CSV8 are less subject to this shortcom- ing as they involve equilibration of the naturally occurring ligands with an added competitor ligand and the determination of the position of the resulting equilibrium. Values for [L] can be obtained directly from the titration curve. Knowledge of the concentration of the added ligand and its affinity for the metal of interest can be used to estimate K’ for the metal-natural ligand complex. Results Apte et al.9 have investigated the effects of random measure- ment error on the accuracy of complexation titrations using ASV and CSV.The implications for the estimation of K’ and [L] are slightly different. For stability constant measurements, simulation techniques indicate that a titration carried out under a given set of experimental conditions has the capability to determine accurately the stability constant of complexes within a rela- tively narrow range or window of K’ values. Complexes of strength below a critical value are not detected; they tend to be dissociated during measurement. This sets a lower limit to the window of K’ values which are accessible to the technique. The upper boundary of the window arises from the fact that complexes above a certain strength are too strong to interact with the measurement technique, hence their K’ value cannot be assessed accurately.(Another way of looking at it is that the ligands of very high K’ value reduce the free metal concentra- tion below the limit of detection of the measurement tech- nique, leading to poor precision.) This means that whenever ligands of K’ higher than the upper boundary of the detection window are present, the estimate of K’ from the titration will be unreliable. The detection window is usually about 1-2 orders of magnitude in width. The estimation of [L] is limited by measurement error only in that the complex must be of sufficient strength not to be dissociated during measurement: only the lower edge of the window applies.Hence, all ligands of K’ higher than the lower edge of the window can be observed; the measured value of [L] is the sum of the concentrations of ligands of different stability constants greater than the threshold represented by the lower boundary of detection. 10ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 63 For a total ligand concentration of 1 X 10-7 mol dm-3, simulation of the performance of the CSV titration of copper in sea-water samples gives a detection window for K‘ of between 1 x 10-*0 and 1 x 10-1*. This assumes that observations are affected by realistic random errors, approximately 5% relative standard devaition (RSD) on individual measurements of labile copper.Interestingly, it appears that there is little scope for widening the K ’ window by improving the precision of measurement. Simulations employing a notional measurement RSD of 1% or lower (far better than could be achieved in practice) only result in a widening of the window by one order of magnitude to K‘ values of from 1 X 10+ to 1 X lo-”. The concentration of the ligand also has a small effect on the position of the detection window. Not surprisingly, if it is just possible to detect a small amount of a relatively strongly complexing ligand, it will also be possible to measure the effects of a larger amount of a weaker ligand. Simulations confirm this as shown in Table 1. This shows the position of the centre of the K’ window for simulations involving a single ligand at various concentrations.The experimental parameters are typical of those in common use. In each instance the width of the window remains at about two orders of magnitude. _ _ _ _ _ ~ ~ ~~ ~ ~ ~ Table 1 Position of detection window for different ligand con- centrations True [L]/nmol dm-3 20 50 100 500 Centre of log K ’ window rcvcalcd by simulation 11.5 10.0 9.8 9.5 Product K’ [L] 6324 500 631 1581 The product k”[L] has been suggested7 as a means of defining the position of the detection window, with values of about 600 applying for the most commonly used experimental conditions. This is confirmed for ligand concentrations in the range 50-100 nmol dm-3 which appears to be typical for many river and estuary samples. Conclusions The application of different measurement techniques to metal-ligand titrations has been observed to give different values for K’ and [L] in the same types of water.This has been attributed to the different powers of the techniques concerned to dissociate natural complexes and is thought to indicate a range of complexes of different strengths in natural waters. This conclusion is undoubtedly correct,lO.11 but has been reached, in some instances, for possibly the wrong reasons. The choice of analytical technique will tend to fix a lower boundary of complex strength which is accessible; the aggreg- ate concentrations of all ligands above this boundary will then be determined. However, the values observed for stability constants, when different techniques are used, will not necessarily reflect the ranges of K’ for ligands in the sample.The value of K’ which is obtained tends to be determined by a combination of the competitive power of the technique and the random error associated with the titration. Simulations suggest that the importance of the second factor can easily be underestimated. 1 2 3 4 5 6 7 8 9 10 11 References Ruzic. I., Anal. Chim. Acta, 1982, 140, 99. Neubecker, T. A., and Allen. H. E., Water Res., 1983, 17. 1. Allen. H. E., Hall, T. A., and Brisbin, T. D . , Enwiron. Sci. Technol., 1980. 14,441. Gardiner, J., and Mance. G., United Kingdom Water Quality Standards Arising From European Community Directives, Water Research Report, TR 204, Water Research Council, Medmenham, 1984. Borgmann. U.. in Aquatic Toxicology, ed. Nriagu, J.0.. Wiley, New York, 1983, pp. 47-72. Coale, K. H., and Bruland, K. W.. Limnol. Oceanogr., 1988, 33, 1084. Buckley, P. J . M., and van den Berg, C . M. G., Mar. Chem., 1986, 19, 281. van den Berg, C. M. G., Mar. Chem., 1984. 15. 1. Apte. S. C., Gardner, M. J., and Ravenscroft, J. E., Anal. Chim. Acta, 1988, 212, 1. Apte. S. C., Gardner, M. J.. and Ravenscroft, J. E., Anal. Chim. Acta, 1990, 235.287. van den Berg, C. M. G., Nimmo, M., and Daly, P., Anal. Chim. Acfu, 1990. 232, 149. Voltammetric Investigation of Natural Waters Using Microelectrodes Raymond 0. Ansell, Helen McAleer, Arthur McNaughtan and John R. Pugh Department of Physical Sciences, Glasgow College, Cowcaddens Road, Glasgow G4 OBA The ability of a microelectrode to sustain a steady-state current as a result of spherical rather than linear diffusion has led to its application in a wide variety of techniques including anodic stripping voltammetry. 1 4 The microelectrode allows a stable deposition current without stirring or rotation3 and is particu- larly suitable for trace metal ion determination in natural waters including lakes and rivers.4 The concentration of metal ions is lower than that of other ions in solution and the other ions act as a supporting electrolyte, allowing the electrodeposi- tion of the ion of interest.The capacitance of the electrode and ohmic drop effects within the solution are minimized as a result of the small size of the electrode. The work described here includes measurements made with direct voltammetry on a model system, viz., that of the oxidation of potassium hexacyanoferrate(i1).This has allowed the determination of the important parameters of the measurement system prior to the anodic stripping experiments. Although measurements are often made with mercury thin films, it is known that results on platinum electrodes can be irreproducible and this was also found for initial studies on the mercury film coated platinum microelectrode. Consequently, the results reported here were obtained by using a 0.005 mm diameter platinum microelec- trode and by direct deposition on the platinum electrode surface. The usefulness of the microelectrode technique in an64 ANALYTlCAL PROCEEDINGS, MARCH 1991, VOL 28 unsupported electrolyte has been illustrated by the determina- tion of the lead level in Glasgow rain water, without the addition of a supporting electrolyte.Experimental The electrodes used were made by using 0.05 and 0.025 mm diameter platinum wire (Goodfellow Metals, Cambridge, UK) sealed into glass tubes and polished on silicon carbide paper. The procedure for making the 0.005 mm glass electrodes was similar to that described by Rolison.1 These platinum elec- trodes were made using Wollaston wire which consists of 0.005 mm platinum wire encased in 0.1 mm silver wire. The wire was soldered to a piece of copper-covered board and a glass capillary tube fed over it. The wire was then etched in 50% nitric acid to remove the outer silver coating near the tip and rinsed in ultrapure water (Barnstead Nanopure system).The glass capillary was fixed to the copper-covered board using Araldite epoxy resin. After this had dried the electrode tip was sealed into the glass by using a butane microburner. A two-terminal cell was used with a Perspex lid which held the microelectrode and a saturated calomel reference electrode (SCE). The cell contained 10 cm3 of solution and was de-aerated by using white-spot nitrogen introduced through a hole in the lid by means of a Pasteur pipette. This was adjusted so that the nitrogen could flow over the solution to out-gas it initially and above it after out-gassing. Voltammetric measurements were made using a voltage scan unit (Oxford Electrodes) which applied the potential across the two-termi- nal cell and a series measuring resistor. The measuring resistor was chosen to be 1 MB as this developed a measurable voltage which, nevertheless, was negligible compared with the voltage applied.The potential was also applied to the x-terminal of the x-y recorder. The current flowing through the cell was measured as the potential drop across the series resistor, which was amplified by a Princeton Applied Research (PAR) 113 voltage pre-amplifier before being fed to the y-terminal of the x-y recorder. The anodic stripping curves were recorded on the x-y recorder; the potential was first held at the required value for sufficient time for deposition to occur, time periods ranging from 1 to 40 min, then the anodic scan followed at SO-200 mV s-1. Impedance measurements for the microelectrode were made using a Solarton 1255 HF frequency response analyser which was connected to the cell by a specially constructed interface.Results The impedance data were used to investigate the processes occurring at the electrode surface. This was carried out by plotting the real and imaginary parts of the impedance in the normal way.5 The impedance curve for the microelectrode is in the form of a semicircle passing through the origin of the graph with its own origin below the x-axis on a line at 45" below the x-axis. This type of curve is expected for an electrode where spherical diffusion is the controlling electrode process, and the low frequency intercept for the 0.005 mm microelectrode in a 1.67 X 10-3 mol dm-3 solution was 8.5 MQ. This compares with a value of 9.2 MQ calculated using the theory developed by Fleischmann and Pons.' At smaller electrode sizes the complex plane impedance plots are closer to normal semicircles centred on the x-axis; the reasons for this are currently under investigation.The voltammetric curve shows a well defined wave of height 3.6 pA for a 0.025 mm electrode at a concentration of 1 x 10-6 mol dm-3. Considering the diffusion coefficient of potassium hexacyanoferrate(n1) of 7 x 10-6 cm2 s-*,6 the current for this concentration would be 3.4 pA based on the theoretical treatment of the microelectrode.' It is possible that direct voltammetric measurements could be made at lower concen- trations and this is currently under investigation. In order to obtain results at the concentration levels in natural waters, a stripping technique had to be employed.For a sample of rain water collected in Glasgow, voltammetric peak currents of 400 pA for lead and 238 pA for copper were obtained during an anodic scan at 200 mV s-1 after a deposition time of 40 min at -0.7 V versus SCE. The lead peak occurred at -0.45 V versus SCE and the copper peak at +0.06 V versus SCE. By the addition of standard samples of lead and copper it was possible to determine the lead concentration as 6 ppb and the copper concentration as 7 ppb. There was some concern over the high value for copper as this was not expected and could have arisen from sample contamination; this will be the subject of further investigation. References Rolison, D. R., in Ultramicroelectrodes, eds. Fleischmann, M., Pons, S . , Rolison, D.R., and Schmidt, P. P., Datatech Systems, Morganton, NC, 1987, pp. 65-106. Wang, J., and Zadeii, J . M . , J . Electroanal. Chem., 1988, 246, 297. Wehmeyer, K. R., and Wightman, R. M., Anal. Chem., 1985, 57, 1989. Wang, J., Tuzhi, P., and Zadeii, J., Anal. Chem., 1987,59,2119. Sluyters-Rehbach, M., and Sluyters, J., in Comprehensive Treatise of Electrochemistry, eds. Yeager. E., Bockris, J. O'M.. Conway, B. E., and Sarangapani, S . , Plenum Press, New York and London. 1984. vol. 9. p. 177. Zhaohui, L., Zhenbin, J . . and Dengping, G., J . Electroanal. Chem., 1989,259, 39. Electrochemical Modelling of Ion Channel Transport: Thallium Voltammetry at Phospholipid Monolayer Coated Mercury Electrodes Modified With Gramicidin Andrew Nelson Marine Biological Association, Citadel Hill, Plymouth The gramicidin A channel has always received a great deal of interest as a model for ion channels in biological and model membranes.' The precise structure, and the chemical and physical properties, have been reported2 and the various mechanisms of ion transfer have been discussed at great length.3 Recently, a membrane model of a phospholipid monolayer adsorbed on a mercury electrode has been de- veloped4 and it seemed pertinent therefore to investigate the effect of gramicidin on the ionic permeability of this adsorbed monolayer.This has resulted in the development of a novel approach, summarized here, in which ion channel transport is driven electrochemically. The system involves the reductionANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 65 and oxidation of thallium at a gramicidin-modified dioleoyl lecithin (di-0-PC) monolayer coated mercury electrode.The experimental methods, the results and their quantitative analysis are reported in full elsewhere.5 I D -0.3 -0.5 -0.7 E N Fig. 1 Cyclic voltammograms of 4 x mol dm- TI* (A, B, D, E and F) and 4 X mol dm-3 CdI1 (C) at a di-0-PC coated electrode. The 1 pAscaleappliestoA,B, CandD. A,Scanrate0.2Vs-l,in0.55 rnol dmp3 KNO,; B. scan rate 0.2 V s - l , in 0.55 mol dm-3 KCI; C, scan rate 0.2 V s-', in 0.55 mol dm-3 KN03 with 1.3 X mol dm-3 gramicidin; D. scan rate 0.2 V s - l , in 0.55 mol dm-3 KN03 (solid line) and 0.55 rnol dm-3 KCI (broken line), both with 1.3 x mol dm-3 gramicidin; E, scan rate 2 V s- l , in 0.55 mol dm-3 KN03 with 1.3 x lo-' rnol dmP3 gramicidin; and F, scan rate 20 V s-l, in 0.55 mol dm-3 KNO3 with 1.3 X lop7 mol dm-3 gramicidin Phospholipid monolayers were deposited on the electrode as described previ~usly.~ Thallium was used as a probe to study the permeability of gramicidin-modified phospholipid layers as it undergoes a reversible redox reaction at a clean mercury electrode .6 The influence of the electrolyte solution composi- tion on the electrochemistry of TI was studied.In the low pH electrolyte, the pH was decreased by the addition of small amounts of HCI. Gramicidin A channels were introduced into the monolayer by adding microlitre volumes of a methanolic solution of commercial gramicidin (Fluka) to 50 cm3 of electrolyte, giving a final concentration of 1.3 x 10-7 mol dm-3 gramicidin.Almost instantaneously the gramicidin partitions into the lipid layer and the monolayer properties are changed. Subsequently, the gramicidin-modified monolayer at the air- water interface is repeatedly deposited on to fresh mercury drop electrodes for each electrochemical experiment. Cyclic voltammetry was the technique employed and in the voltam- mograms all potentials are quoted versus an Ag-AgC1,3.5 rnol dm -3 KCI, reference electrode. Fig. 1 shows that the unmodified adsorbed phospholipid layers inhibit the reduction of TI1. However, by introducing gramicidin into the layers, the reduction current increases markedly. This is in contrast to the lack of effect of gramicidin on the monolayer-blocked reduction of Cd". Hence it can be concluded that as the metal ion reduction is inhibited by the impermeability of the metal ion in the unmodified layer, the gramicidin channel is permeable to T11 but impermeable to Cd".The influence of scan rate on the voltammograms shows that the reduction current of T11 at the gramicidin-modified lipid coated electrode tends to a constant value at high scan rates which is limited by the permeability of the modified monolayer to TI'. 2.0 0 2 4 0 2 4 v-1N-l s+ Fig. 2 Cyclic voltammetry of 4 x rnol dm-3 TI' at a di-0-PC coated electrode in electrolyte with 1.3 x mol dm-3 added gramicidin: reciprocal peak reduction current versus the reciprocal of the square root of the scan rate. ( a ) A, in 0.55 mol dm-3 MgC1,; 0 in 0.55 mol dm-3 KCl; and W, in 0.55 mol dm-3 KN03. (b) A, in 0.55 rnol dm-3 KCI, pH 2.3; A, in 1.1 mol dm-3 KCI; and 0, in 0.55 mol dm-3 Mg(N03)2 Fig.2 displays reciprocal peak reduction current (ip-l) versus reciprocal square root scan rate (d) plots for the reduction of TI' at the modified coated electrode. The reciprocal limiting current (ik-l), which is inversely propor- tional to the monolayer permeability to TI', can be estimated by extrapolation of the plots to v-i = 0. It is observed that i k - 1 in nitrate electrolyte is lower than in chloride electrolyte. Note also the inhibitory effect of chloride on TI1 transport across the modified layer in more concentrated KCI solutions and the lack of a simple i,-1 versus Y-l relationship in this system. The suppressive effect of the chloride anion and other more strongly complexing TI1 species such as pyrophosphate and phosphate7 on the voltammograms for TI can be seen in Figs.1 T A lUAl c -0.3 -0.5 EN -0.7 Fig. 3 Cyclic voltammograms of 4 x mol dm-3 TI1 at a di-0-PC coated electrode in electrolyte with 1.3 X 10-7 mol dm-3 gramicidin at a scan rate of 0.2 V s-l. A, In 1.1 mol dm-3 KCI; B, in 0.1 mol dm-3 Na4P207; and C, in 0.55 rnol dm-3 Na3P0466 ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 and 3. Hence, complexing agents in the electrolyte inhibit TI1 transport by gramicidin. It is also seen in Fig. 2 that the TI' flux across the modified monolayer is increased in the presence of MgII. The influence of Mg2+ and H+ on the slope of the i-1 versus v-h plots is noted and might be correlated with the binding of these ions to the lipid layer.4 The occurrence of significant Tll transport across the channel-modified mono- layer in low pH solutions shows that binding of T1* inside the channel is not important in its transport.At low pH values, oxygenated sites inside the channel will be protonated and not available for binding. In conclusion, TI1 ions can be reduced at a mercury electrode covered with a phospholipid monolayer provided that the latter contains gramicidin. Hence the gramicidin, presumably present as a monomer in an adsorbed phospholipid monolayer, behaves like the bimolecular gramicidin channel in a free- standing lipid bilayer and a biological membrane. Accordingly, it is selective to univalent cations ( e . g . , TI+) compared with both divalent cations ( e . g . , Cd'+) and complexed TI' species.The results further establish the validity of the electrode- adsorbed lipid monolayer as a relevant biological membrane model. With respect to analytical applications, it is also evident that these coated electrodes could be developed as selective sensors for heavy metal ions. This work forms part of the Fellowship Programme of the Marine Biological Association of the UK. References Hladky, S. B., andHaydon, D. A., Curr. Top. Membr. Tramp., 1984, 21, 327. Koeppe, R. E.. 11, Hodgson. K. 0.. and Stryer, L. J., J. Mol. Biol., 1978, 121, 41. Finkelstein. A., and Andersen. 0. S., J. Membr. Biol., 1981, 59, 155. Nelson, A., and Auffret, N., J. Electroanal. Chem., 1988, 244, 99. Nelson, A., J. Electroanal. Chem., in the press. Bond, A. M., Modern Polarographic Methods in Analytical Chemistry.Marcel Dekker, New York, 1980, p. 302. Manners, J. P., Morallee, K. G., and Williams, R. J. P., J . Inorg. Nucl. Chem., 1971, 33, 2085. Stripping Voltammetry of Metal Complexes With Macromolecular Ligands: Some Fundamental Aspects Herman P. van Leeuwen Department of Physical and Colloid Chemistry, Wageningen Agricultural University, Dreijenplein 6, 6703 H B Wag en ing en, The Netherlands The electroanalytical chemistry of metal complexes is a classical subject. The basic voltammetric effects of association of the reactant with an electroinactive component in solution were described in the early days of polarography.1 More recently, macromolecular ligands have become important and this has called for consideration of some new aspects, including different diffusion coefficients of various metal species and unconventional metal binding characteristics.The simul- taneous effects of different diffusion coefficients and limited associatiorddissociation rates have been analysed in some detail24 for the simplest complexation scheme Lability Criteria As a by-product of these theoretical studies, the criterion of lability of such a complex system could be defined as a special limit of the dynamic regime for the case of excess ligand over total metal: where E = DML/DM ( D being the diffusion coefficient), K' = kacL*/kd (cL* being the bulk ligand concentration) and t is the effective time of the dynamic experiment. On the same basis, a lability criterion can be derived for the steady-state situation that holds for the usual stripping voltam- metric conditions.The expression parallel to eqn. 2 is:s-6 >> 1 (3) 6 D&2K'ka' - 112 where 8 is the thickness of the diffusion layer, which is a function of D M ~ , and k,' = kacL*. For the case of an RDE and under conditions that EK' >> 1, the Levich equation7 can be used: (4) 6 = 1.610113 co-112~116 ML with co being the angular rotation frequency and Y the kinematic viscosity of the solution. In many practical situa- tions, however, exact expressions for 6 are not available. For an HMDE in a conventional cell with stirring effected by a rotating bar or rod, the relationship between 6 and D is not very well known. Estimates of 6 can be made, but the exact functionality with respect to DML is uncertain and in any case will vary with the precise stirring conditions.This aspect is rather crucial because more often than not the relation between the measured current and the effective diffusion coefficient is the only basis of stripping voltammetric specia- tion. An exact treatment of the coupled convective diffusion of M and ML should start from their conservation equations with the relevant expression for the liquid velocity as a function of distance from the electrode surface. For many practical conditions with HMDE cells it is only possible to simulate responses by solving the transport equations for some guessed velocity profiles. Alternatively, one could, on a more opera- tional level, try to fit the experimentally observed response to some postulated fu2ctionality with respect to the mean diffusion coefficient D.Let us first recall that where cT = cM + cML, and let us further introduce CD as the ratio between the stripping voltammetric (SV) peak current of the complex system and the one obtained in the absence of ligands (where cM would be cT). Now, one could postulate that for labile systems @ = (D/D,)P (6) and try to fit this expression to experimental data. For someANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 67 model metal-polyelectrolyte systems, the results of the fitting are most reasonable over the whole relevant range of cL* values. Values for p usually lie between % and */3.8,9 Results Before applying a procedure such as that outlined above to a given complex system, definite proof of its lability on the effective time scale of the SV experiment should be obtained.For a number of metal-polyelectrolyte systems such proof is available. For example, the zinc(r1)-polyacrylate (PAA) and zinc(I1)-polymethacrylate (PMA) systems show the following features: the pulse polarographic limiting current depends linearly on pulse duration; different voltammetric experiments show a finite potential shift that systematically varies with ligand concentration and is independent of the effective time scale; and stabilities computed from the current parameter @ compare well with those evaluated from potential shifts. l o , l l For Zn"-humic acids (HA) systems, the stripping voltammetry gives clear indications of lability: there is a systematic shift of the peak potential for a sufficiently large excess of ligands (i.e., large enough to overcome the metal concentration enhance- ment); and the peak current approaches a certain plateau value with ever increasing excess of ligands, whereas it would decrease to zero in the instance of non-lability.12 Fig.1 gives a typical example of experimentally obtained SV complexation curves for the ZnIl-HA system, the humic acids being obtained from Fluka material as outlined previously.13 I should add here that the quantitative interpretation of SV peak potential shifts may be a tricky matter,14 especially in the range where the ligand concentrations are not large enough to maintain the excess condition after the accumulation. Still, the appearance of a potential shift, at some stage, which systematically increases with increasing ligand concentration, is a strong indication of lability.Stripping voltammetry complexation curves for Zn-HA systems are regular in appearance, which is typical for labile systems. The family of curves in Fig. 1 is for 10-7 mol dm-3 ZnlI and effectively spans a metal to ligand ratio range of about 0.8 ri I * O 0 ' I I I I C: x 104/m01 1-1 0.5 1 .o 1.5 Fig. 1 Stripping voltammetry complexation curves for the Zn-HA system for different KN03 concentrations. [Zn] = 10-7 mol dm-3; a, = 0.8. 0, 0.01 mol dm-3; A , 0.03 mol dm-3; 0, 0.10 mol dm-3 10-1-10-3 (the ligand concentration being given by the volume concentration of deprotonated groups on the HA molecules). Typical qualities of fitting these data sets to eqn. 6 are given by values of r2 of about 0.9.Plateau values indicate diffusion coefficients for the humic entities of the order of 0.05 DZn (with Dz, being near 7 x 10-10 m2 s-1 under the experimental conditions). The values for the stability K (= k,lkd), as obtained from the @,cL* data, are in the range between 3 x 104 and 105 1 mol-1 for the salt concentration range studied. Discussion Comparison of the Zn-HA results with the complexation characteristics of the synthetic polyacids PAA and PMA shows that for HA the dependence of K on salt concentration is much weaker. This must mean that the interaction of the humate polyanion with K+ counter ions is much weaker, a finding which is in accordance with conductimetric counterion binding data,13 which show that K+ ions remain practically unbound.Apparently, the density of charges on the humate polyion is not high enough to cause appreciable condensation of mono- valent counter ions. Considering that the equivalent molar mass (i.e., the mass per single binding site) would be near 300 for the HA used, the mean separation between sites is unlikely to be less than 1 nm. This is well above the Bjerrum length (about 0.7 nm under our experimental conditions) and explains the absence of electrostatic K+ binding. Considering the above results, SV should permit the measurement of K as a function of the ratio between bound zinc and total ligand and this would allow a test of the data in terms of purely chemical polyfunctionality. Also, it should be possible to measure K as f([salt]) with alkaline earth salts (Ca, Ba), which would show whether exchange of Znl1 with divalent counterions occurs.Stripping voltammetry will be an almost indispensable tool again, because it can be applied to such low metal ion concentration levels that the condition cmetal << Cligand << cSalt is obeyed over a broad range of cSalt values. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 References Heyrovsky, J., Polarographie, Springer, Wien, 1941. de Jong, H. G., van Leeuwen. H. P., and Holub, K., J. Electroanal. Chem.. 1987. 234, 1, 17. de Jong, H. G., and van Leeuwen, H. P., J. Electroanal. Chem., 1987, 235, 1. van Leeuwen, H. P., de Jong, H. G.. and Holub, K., J. Electroanal. Chem., 1989, 260, 213. Davison. W.. J. Electroanal. Chem., 1978.87. 395. van Leeuwen, H. P., Sci. Total Environ., 1987, 60, 45.Levich, V. G., Physicochemical Hydrodynamics, Prentice-Hall, Englewood Cliffs, NJ, USA, 1962. Esteban, M., de Jong, H. G., and van Leeuwen, H. P., Znt. 1. Environ. Anal. Chem., 1990, 38, 75. van den Hoop, M. A. G. T.. Leus, F. M. R. and van Leeuwen, H. P., Collect. Czech. Chem. Commun., in the press. Cleven, R. F. M. J., de Jong, H. G., and van Leeuwen, H. P., J. Electroanal. Chem., 1986, 202, 57. Esteban, M., Casassas, E.. de Jong, H. G., and van Leeuwen, H. P.. Anal. Chim. Acta. 1990, 229.93. van den Hoop, M. A. G. T., and van Leeuwen, H. P., to be published. van den Hoop, M. A. G. T., van Leeuwen, H. P.. and Cleven, R. F. M. J., Anal. Chim. Acta, 1990, 232, 141. Buffle, J., Complexation Reactions in Aquatic Systems; A n Analytical Approach, Ellis Horwood, Chichester, 1988, Ch.9.68 ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 Determination of Chromium Speciation in Sea-water Marc Boussemart and Constant M. G. van den Berg Oceanography Laboratory, The University, Liverpool L69 3BX Chromium occurs naturally in two oxidation states, viz., CrVI in the form of the chromate ion(Cr042-), and Cr"' in the form of Cr(OH)3, the hydrolysis product of the Cr3+ ion [more probably Cr(OH)2+ .4H20]. In sea-water, the relative propor- tions of both species could be governed by thermodynamic parameters such as pH, pE and temperature but the actual proportions are affected by kinetic stabilization of the CrIII species (hydration), which hinders the oxidation of Cr'11 to CrVI. Previous data suggest that the marine geochemistry of Cr is governed by the following features: in oxidizing surface waters, the main dissolved form is CrVI and scavenging is performed by the vertical particle fluxes on which CrIrl is adsorbed.The role of manganese dioxide colloids also appears to be of interest as they can easily adsorb and convert CrIII into CrVI.1 In anoxic waters, CrIII might be more abundant. The toxicity of CrVI species, and also the complexity of the processes that govern Cr speciation, justify further investiga- tion and the elaboration of reliable analytical methods. The usual technique involves a concentration step by selective coprecipitation of Cr species by iron hydroxides, and the use of graphic furnace atomic absorption spectrometry.* A voltammetric method [cathodic stripping voltammetry (CSV)] has been used to measure directly the total Cr content of natural waters.3 This method has been optimized for the analysis of sea-water and adapted to the study of Cr speciation.Experimental Voltammograms were recorded with an Autolab polarograph connected to a Metrohm 663 hanging mercury drop electrode (HMDE) (drop surface area, 0.38 mm2) controlled by an AT 80286 IBM-compatible personal computer. The following parameters were generally used: accumulation potential, - 1 V (versus an Ag-AgC1, 3 mol dm-3 KCI reference electrode); accumulation time, 60 s; differential pulse mode, with a pulse rate of 10 s-1; pulse amplitude, 25 mV; and scan rate, 20 mV s-1. De-ionized water was supplied by a quartz double distillation unit or a Nanopure ion-exchange resin unit.Die thylene triaminepen taace tic acid (DTPA) was obtained from Sigma; all the other reagents were obtained from BDH. The reagent used for the determination of Cr was a mixture of DTPA (1.97 g), sodium nitrate (85 g) and sodium acetate trihydrate (13.6 g) in 200 ml of de-ionized water adjusted to pH 5.1 with Aristar HCI and ammonia. A 1 ml volume of this solution in 10 ml of sea-water gives the required pH and reagent concentrations (see under Methods). Ultraviolet irradiation was carried out for 4 h by using a 1 kW mercury vapour lamp. Methods Chromium(1Ir) forms a complex with the ligand DTPA with log K = 15.3. Under appropriate conditions, this complex is adsorbed on to a HMDE and a cathodic scan reveals a peak at -1.275 V, which corresponds to the reduction of Cr"1-L to Cr".A catalytic effect caused by the nitrate ions enhances the measured signal. Chromium(vr), which is reduced electro- chemically to Crl" on the drop when the potential is more negative than -0.05 V, gives rise to the same peak. The following conditions allow the determination of total Cr in fresh waters down to a concentration of a few ng 1-1:3 DTPA, 10 mmol dm-3; pH, 6.2; and NO3-, 0.5 mol dm-3. Unfortunately, the sensitivity proved to be 20 times lower in sea-water. This was shown to be caused by the high levels of Mg2+ and Ca2+ ions in sea-water, which are known to form complexes with DTPA [log K = 9.3 (Mg); and 10.7 (Ca)]. Similar effects have been observed for both Mg (Fig. 1) and Ca (not shown). A decrease in the sensitivity and a peak shift towards a more positive potential confirmed that there was competition between these cations and Cr for DTPA.- 1230 - 1240 > -1250 - m m +- .- -1260 +- E u 20 a Q 0 5 10 15 20 25 30 35 Mg*+/mmol dm-3 Fig. 1 Influence of Mg'f concentration on the sensitivity and peak potential of the Cr peak (2 nmol dm-3 or CrVI in ultraviolet-irradiated de-ionized water; DTPA = 5 mmol dm-3) Various comparative experiments showed that better results are obtained by using the following conditions: pH, 5 (with an acetate buffer); DTPA, 2.5 mmol dm-3; and NO3-, 0.5 mol dm-3. The analysis of sea-water reveals a peak at -1180 mV which increases linearly with the Cr concentration up to 20 nmol dm-3 after an accumulation time of 1 min. For a Cr concentration of 6 nmol dm-3, which corresponds to the concentration of coastal sea-water, the signal is proportional to the accumulation time up to 4 min.As CSV involves a surface adsorption process, surfactants are known to interfere strongly with this technique. The influence of the concentration of Triton X-100 on the sensitivity is shown in Fig. 2 in order to illustrate the strong interference by such surfactants. The interferences caused by other metals were found to be negligible. The following metals were tested: Co ( 5 ) , Ni (50), Zn (loo), Ti (loo), Mn (100) and Fe (1000 nmol dm-3). Hydrogen peroxide and nitrites cause a noisy response. Neither is normally found in natural samples but nitrites, for instance, are easily formed during the ultraviolet irradiation of nitrates ( e .g . , a sample that has been acidified with nitric acid) 0 0.1 0.2 0.3 0:4 0.5 Triton X-100 (ppm) Fig. 2 Influence of the surfactant Triton X-100 concentration on the sensitivity for two different accumulation times (6 nmol dm-3 of CrV1 in ultraviolet-irradiated sea-water; DTPA = 2.5 mmol dm-3). Accumu- lation time: A, 1; and B, 2 minANALYTICAL PROCEEDINGS, MARCH 1991. VOL 28 69 and hydrogen peroxide is sometimes used to assist the ultraviolet photolysis of natural organics. The sensitivity of the CSV procedure is very high, owing to the catalytic process, and is about 5.8 nA dm3 nmol-I min-l for CrVl and 3.3 nA dm3 nmol-1 min-1 for CrflI (in ultraviolet- irradiated sea-water). The detection limit, defined as the lowest concentration that can be measured confidently, is about 0.1 nmol dm-3 for an accumulation time of 3 min.The standard deviation for a concentration of about 6 nmol dm-3 is 3%. The reagents had to be purified in order to lower the reagent blank. Coprccipitation with iron(i1) hydroxide followed by a filtration step was found to give a reagent blank below 0.05 nmol dm--3. ~~ Table 1. CSV peak height (Yo) for Crl" and CrV' remaining after equilibration of DTPA with sea-water for 10 min as a function of pH CrI" CrVI PH remaining (%) remaining (%) 5.0 75 98 6.0 35 99 6.7 7 100 7.0 5 100 Speciation Measurements Dissolved Cr in sea-water can be assumed to occur in the following chemical forms: inorganic CrVf, inorganic Cr111 and organic CrIl1. Photolysis of the organic material using an ultraviolet lamp at natural pH converts all the Cr into free CrVI.The recovery of both CrV1 and Crl11, as CrVI, is almost 100%. Hence, the total Cr concentration can be determined. The next measurement can be performed owing to an important feature of the electrochemical method when applied to CrII1. Surprisingly, this has not been reported by Golimowki et al.3 The determination of this species gives an unstable peak, the intensity of which decreases rapidly with time regardless of the experimental conditions employed. Some measurements performed using atomic absorption spectrometry showed that this decrease was not caused by adsorption and that the Cr1I1 remained in solution, although it could not be detected by using CSV. The following process might explain this effect: Cr111, in solution, is first weakly complexed by DTPA to give CrIll-DTPA, which is electroactive and can be reduced to CrI1 as described previously.Subsequently, a second CrI1I-DTPA complex is formed, which is not electroactive, and therefore undetectable. Chromium(il1) is known to react slowly in aqueous solutions. The stability of the signals due to both CrlI1 and CrV1, as a function of the pH, is shown in Table 1. The signal due to Cr"1 is very unstable, particularly at higher pH values. Note that there is a slight decrease in the CrVI peak with time for the lower pH values. This could result from the reduction of CrVl to Cr1" followed by masking of Cr111 by the 4- Time -t Fig. 3 and CrV1 Evolution of the peak height with time for a mixture of CrlI1 process described above.It should be noted that metallic mercury is able to reduce CrV1.4 Comparative experiments showed that the much smaller mercury drops of the Metrohm 663 VA electrode produced a smaller decrease in the peak height for CrVI than the large mercury drops of the Princeton Applied Research 303 electrode. The signal, for a mixture of CrV1 and CrIIl, decays with time as shown in Fig. 3. The remaining signal is due to CrVI, which can be determined subsequently. The current that has been lost is due to electrolabile Cr"1. The initial Cr"' concentration can then be evaluated from a standard addition of Cr111. However, the CrIII level in sea-water is very low (often less than 10% of total Cr). We are, therefore, currently testing various pro- cedures in order to pre-concentrate Cr-111 from sea-water prior to analysis by CSV. Preliminary Results The preliminary method described above was applied to the determination of Cr species in several sea-water samples stored in our laboratory. The results are reported in Table 2.In order that the speciation was not affected, the samples were not acidified. Our data compared well with published data (first entry in Table 2). A more systematic study is necessary in order to demonstrate the interesting environmental features. For some samples from the Mediterranean, measurements of CrVI were also carried out on-board ship, a few hours after collection. It is clear that the storage method (freezing) was inadequate for preserving the natural concentrations of CrVI. Chromium(ii1) was already known to adsorb strongly on to the container walls, but the losses of CrVI were also high.Reduction of CrVI by the organic matter during the freezing process (heterogeneous freezing) might have occurred. We performed Cr measurements on-board ship during the Cybele Cruise (Eros Project) in April 1990. Data for labile CrV1 and Cr111 were collected at different depths and stations situated in the north-western part of the Mediterranean (Golfe du Lion). Fig. 4 shows data corresponding to a station located Table 2. Effect of sample storage on the detected Cr speciation in sea-water. The data for the Eastern Pacific are taken from reference 1 CrV' determined Sample origin Storage conditions CrV1 Total Cr Cr"' on-board ship Eastern Pacific None 2-6 Mediterranean Natural pH, fridge, 3.40 polyethylene bottle glass bottle polyethylene bottle North Sea Natural pH, fridge, 2.00 Atlantic Natural pH, fridge, 2.40 Mediterranean Natural pH, freezer, - polyethylene bottle 2.10 1 .50 - - - 3.60 2.80 2.40 2.80 3.60 4.20 2.60 3.50 0-1 - 0.20 - 0.80 - 0 - - 4.90 1.50 5.80 2.70 5.10 - 5.00 - 4.4070 ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 m I 0 0 E - 'E ..0 .- .I- F * C 0 0 0 't 3 1 * B I A " 0 50 100 150 200 Depth/ m Fig. 4 Profile of labile CrV1 and Cr"' concentrations in sea-water from the north-west Mediterranean (April 1990; 20 nautical miles off Marseille, France). A, CrVI; and B, CrrlI 20 nautical miles off Marseille (France). The quantification of Cr111 was not very accurate because our procedures had not been fully optimized. Nevertheless, the fairly constant CrVl profile confirms the vertical mixing of the water column in this area at this time of the year.The mean concentration of labile CrvI in open sea-water from the Mediterranean was found to be about 5 nmol dm-3. References Murray, J . W., Spell, B., and Paul, B., in Trace Metals in Sea Water, eds. Wong, C. S . , Boyle, E., Bruland, K. W., Burton, J . D.. and Goldberg, E. D., Plenum Press, New York and London, 1983, pp. 643-669. Cranston, R. E., and Murray, J . W., Anal. Chirn. Acta, 1978.99. 275. Golimowski, J . , Valenta, P., and Nurnberg, H. W., Fresenius Z . Anal. Chem., 1985, 322, 315. Crossmun, S. T . , and Mueller, T. R., Anal. Chirn. Acra, 1975, 75, 199. Electroanalysis of Metal Speciation and Its Relevance to Ecotoxicology Gregory M.Morrison and Chen Wei Department of Sanitary Engineering, Chalmers University of Technolog y, S-4 12 96 Goteborg, Sweden Metal Speciation Analysis Undoubtedly metal speciation analysis is an essential step in the study of the significance of priority metal pollutants during discharge, mobilization or transformation in natural water. 1 It is known that certain forms of metals, for example ionic copper or methylmercury, are more toxic than complementary forms of the same metals, for example copper bound to fulvic acid and inorganic mercury. Electroanalysis, usually involving anodic stripping voltam- metry (ASV), is frequently used because of its intrinsic capability in separating ionic metal species from electroinactive forms and its estimate of the potential metal detoxification capacity of the water sample, viz., complexation capacity.* Consequently, attempts have been made to compare metal speciation and toxicity in water samples and to relate further the results to in-stream ecology.These ideas are illustrated for an urban discharge in Fig. 1. Metal Speciation and Toxicity Laboratory comparisons of the interactions between model ligands, such as fulvic acid and NTA (nitrilotriacetic acid), and metals, have shown consistencies in the metal detected by bioassay and ASV (Table 1). It should be stressed that lability depends on the experimental conditions at the mercury electrode.3 The flexibility of these speciation measurements was en- hanced by the introduction of mercury electrodes coated with Nafion (perfluorosulphonate) and cellulose acetate.These allow the separation of metal complexes which are negatively charged and have low molecular size, respectively.4 The empirical comparisons of bioassay with electrochemical analysis might be satisfactory in laboratory studies with a controlled sample matrix, but difficulties arise in water samples where surfactants significantly affect the transport of ionic metal to the mercury electrode. By a combination of medium exchange and controlled acid additions it has been possible to estimate that the interference of surfactants amounts to a 60-100% decrease in metal lability in water samples.5 Clearly, as surfactants in natural or polluted waters are the dominant factor in the decrease of ASV lability and at the same time do not decrease metal toxicity to aquatic test organisms, then ASV will seriously underestimate the toxic fraction. This difficulty can be overcome by the use of the acidification procedure outlined in Table 2. The measurement required for toxicity studies (i.e., the effect of complexing agents on deposition) is [lo0 - (2) + (l)] where the values are in per cent. of the total metal. Lability values in natural waters Table 1. Speciation and toxicity of copper to algae Copper toxicity or lability (%) ~~~~~ ~ ~ Bioassay ASV Nitzschiu Chlorella closterium pyrenoidosa HMDE* MFET NMFES Fulvic acid 8 60 21 8 36 Fe-humic colloid 60 109 36 4 78 NTA 20 NDIS 67 ND§ 3 * HMDE = Hanging mercury drop electrode. t MFE = Mercury film electrode. + NMFE = Non-mercury film electrode. Q ND = Not detected.ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 71 metal speciation ___c Fig. 1 Relationship between metal speciation, toxicology and ecotoxicology Table 2. Effects of complexing agents and surfactants on the deposition and stripping steps of ASV Complexing agents Surfact ants ASV technique Deposition Stripping Deposition Stripping ( I ) Deposition, pH 7.0 (2) Deposition. pH 7.0 Stripping, pH 1.9 Yes No Yes Yes Stripping, pH 1.9 No No Yes Yes increase significantly owing to the absence of surfactant effects. That this is a correct value is confirmed by medium exchange during stripping, which also gives an increase in lability owing to surfactant removal.' Metal Speciation and Ecotoxicology It might be the case that metal speciation procedures, which have been verified under controlled laboratory conditions and in parallel with toxicity studies, will require further verification in order to determine their ecological significance. Fig. 1 illustrates the latter relationship and identifies the problem of deciding whether toxic metal species are likely to cause ecotoxicological effects. It does appear that complexation capacity and toxic metal species analysis might profitably be combined with ecotoxico- logical methodology. Bioaccumulation of metals in transferred or in situ popula- tions and community diversity indices are notoriously difficult to relate to metal speciation measurements.6 However, metal speciation analysis appears to be relevant to the enzyme activity of the in situ sedimentary microbial community.7 The tolerance of the periphyton community8 and metallothionein accumulation and avoidance behaviour in fish populations might also prove promising. These developments provide a challenge for analytical chemists to develop metal speciation methods that have ecotoxicological relevance. References 1 Morrison, G. M. P.. Batley, G. E., and Florence, T. M., Chem. Br., 1989, 791. 2 Florence, T. M . , Analyst, 1986, 111, 489. 3 Morrison, G. M. P., and Florence, T. M., Anal. Chim. Acla, 1988, 209, 97. 4 Morrison. G. M. P . , and Florence, T. M., Electroanalysis, 1989, 1, 485. 5 Morrison, G. M. P., Florence, T. M., and Stauber, J . L., Electroanalysis, 1990, 2, 9. 6 Luoma, S. N.. Sci. Total Environ.. 1983, 28, 1. 7 Morrison, G. M. P., and Chen, W.. Hydrubiolugia, in the press. 8 Blanck, H.. and Wangberg, S . , Can. J. Fish. Aquat. Sci., 1988, 45, 1816.

ISSN:0144-557X    

DOI:10.1039/AP9912800058

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

72 ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 Speciation of Iron in Antarctic Lake Water by Adsorptive Cathodic Stripping Voltammetry Ornella Abollino, Edoardo Mentasti, Corrado Sarzanini and Valerio Porta Dipartimento di Chimica Analitica, Universita di Torino, Via Giuria, 5, Torino, Italy Constant M. G. van den Berg Department of Oceanograph y, University of Liverpool, Bedford Street North, Liverpool Finding speciation techniques for trace metal ions in natural waters is becoming increasingly important, as the toxicity of each element depends not only on its total concentration, but also on its distribution among different forms or oxidation states .I-3 The determination of a single metal species is generally not possible, but several speciation schemes have been devel- opedb7 based on the separation of the different forms of the element in fractions. Typical fractions are: particulate metal, total soluble metal, labile or inert metal.Anodic stripping voltammetry (ASV) is extensively used for speciation studies because it allows one to distinguish between ASV labile, i.e., free ions and weak complexes able to dissociate during the measurement, and inert or bound metal, i. e., electroinactive organic and inorganic complexes. Also, the use of adsorptive cathodic stripping voltammetry (ACSV)X-10 allows the determination of the total concentration of metal ions in natural waters and their separation in different fractions. In the prescnt work, ACSV was employed for the speciation of iron in lake water. The method used was discovered and developed by Dr.van den Berg and Dr. Nimmo (University of Liverpool) and further studied and optimized by Dr. Abollino (on leave from the University of Turin, Italy).11 The method, which detects combined Fell and Fell', is based on the complexation of dissolved iron with 1-nitroso-2-naphthol (1-N-2-N) and the adsorption of the complex onto a hanging mercury drop electrode. After adsorption, the potential is scanned in the negative direction, giving rise to a reduction current proportional to the amount of complexed metal. Experimental The samples were collected from Carezza Lake in Antarctica during the Italian Expedition completed under the 'Progetto Antartide'" and immediately frozen, Prior to analysis, the water was buffered to pH 6.9 with 0.01 mol dm-3 PIPES [piperazinyl-l,4-bis(ethanesulphonic acid)] ; the added ligand concentration was 2 x 10-5 mol dm-3.All treatments were performed under a class-100 laminar flow hood. The measurements were carried out with an Amel 433A, ~ 5 . 6 ~ polarograph. The adsorption potential was set to -0.2 V and the potential scan was performed in the linear sweep mode. Because of the high sensitivity of the method, a 20 s adsorption time without stirring was sufficient to evaluate the concentrations in the samples. Results and Discussion Speciation of Antarctic Lake Water The samples were analysed under four different sets of conditions: (a) as such; ( b ) after acidification to pH 1.6; (c) after filtration through a 0.45 pm membrane filter; and (d) after filtration and acidification.The analysis of the lake water at its natural pH gave an iron content of 7.1 k 0.7 x 10-8 rnol dm-3, with no significant differences before and after filtration: in both instances the method responds to free or weakly complexed iron. The highest value was found after acidification of the untiltered sample: 1.05 k 0.09 x 10-6 rnol dm-3. This is due to the contribution of the acid-exchangeable metal13 present in the dissolved and particulate phase to the previous values. If the sample is acidified after filtration, the iron content decreases to 3.52 k 0.11 X 10-7 rnol dm-3: this value represents the free or weakly complexed iron plus the fraction of colloidal and strongly bound iron released after acidification. From these data we can see that: (a) more than 60% of the total iron present in the sample is associated with particulate matter, as it is detected only after acidification of the unfiltered sample; and ( b ) nearly 80% of the dissolved iron is present in colloidal or strongly bound form, as it is released only after acid treatment.A peculiar feature of Carezza Lake water is that it is an example of a natural sample with no, or at least very low, contamination by human activities. It must be emphasized that the lake is a very small depth basin, where biological activities (algae, birds) contribute to element distribution between soil, sediment, particulate, algae, etc. One of the objects of the next Antarctica campaign will be the collection of samples of all the other components, so that it will be possible to investigate such dynamic equilibria. Characterization of the Analytical Method In order to investigate the response of the method to different species of iron, samples of lake water were spiked with various forms of the metal ion, and scans were recorded before and after the spike.On addition of 2.5 x 10-7mol dm-3 of free iron to a sample, the average increase in the peak height was 23.5 nA, corresponding to a sensitivity of 9.4 nA per lo-' mol dm-3. 0.0 -0.2 -0.4 -0.6 -0.8 PotentialN Fig. 1 Cathodic stripping scans of Carezza Lake water: A. before addition of Fe complexed with humic acid; B, soon after the spike; and C. 30 min later When the same amount of iron was added in the hydrous oxide form, the peak height increased very little immediately after the addition, but then increased with time. This means that 1-N-2-N slowly complexes colloidal iron: by extrapolation to zero time it should be possible to obtain an estimate of truly labile iron.ANALYTICAL PROCEEDINGS, MARCH 1991.VOL 28 73 After spiking the sample with the iron-humic acid complex, the peak potential was shifted to more negative values, probably because of the formation of a mixed iron-l-N-2-N- humic acid complex; the peak height increased slightly during the first scan, and increased with time, as shown in Fig. 1. This probably occurs because 1 -N-2-N gradually prevails over humic acid in the competition for the complexation of iron. No differences in peak potential and height were detected after the addition of iron complexed with ethylenediaminetetraacetic acid (EDTA), chosen to represent naturally occurring strong complexing agents.Moreover, the peak did not increase with time: this means that 1-N-2-N cannot displace iron from its complex with EDTA. If the solution was further spiked with free iron, no further increase in the peak height occurred: the added metal preferentially binds to EDTA. On the other hand the addition of EDTA to a solution already containing iron and 1-N-2-N in the concentration range 1 x 10-5-1 x 10-3 mol dm-3 did not affect the iron peak height, i.e., the ligand cannot complex iron if this is already bound to 1-N-2-N. From these observations, it can be concluded that in the interaction between iron and the two ligands studied, both thermodynamic and kinetic effects occur.1 2 3 4 5 6 7 8 9 10 11 12 13 References Trace Element Speciation: Analytical Methods and Problems, ed. Batley, G. E., CRC Press, Boca Raton, FL, 1989. The Determination of Trace Metals in Natural Waters, eds. West, T. S., and Nurnberg. H. W.. Blackwells. Oxford. 1988. Stumm, W., and Morgan, J. J . . Marine Chemistry, Wiley, New York, 1981. Florence, T. M., and Batley, G. E., Talanta, 1977, 24, 151. Figura, P., and McDuffie, B., Anal. Chem., 1980, 52, 1433. Hart, B. T., and Davies, S. H. R., Aust. J. Mar. Freshwater Res., 1981.32, 175. Laxen, D. P.. and Harrison, R. M.. Sci. Total Environ., 1981, 19, 59. van den Berg, C. M. G.. Sci. Total Environ.. 1986, 49. 89. van den Berg, C. M. G., and Nimmo, M., Sci. Total Environ., 1987, 60, 185. van den Berg. C. M. G., and Khan, S.H., Anal. Chim. Acta, 1990,231, 221. van den Berg, C. M. G., Nimmo, M.. Abollino, 0.. and Mentasti, E., in preparation. Ann. Chim. (Rome), 1989. 79, (11-12). Allen, H. E., Matson. W. R., and Mancy, K. H., J . Water Pollut. Control Fed., 1970, 42, 573. Problems with the Estimation of the Complexation Characteristics of Dissolved Organonickel Complexes Loes J. A. Gerringa Delta Institute for Hydrobiological Research, Vierstraat 28, 440 I €A Yerseke, The Netherlands Recently, van den Berg and co-workers'.' and Huynh-Ngoc et af.3 studied the complexation characteristics of organonickel complexes by means of cathodic stripping voltammetry using dimethylglyoxime (DMG) as the added ligand. The condi- tional stability constant of the Ni-DMG complex in sea-water is 10-17.1 The above mentioned workers found that the dissolved organic ligands in sea-water samples were saturated with respect to Ni.The exact value of the conditional stability constant could not be determined because titration of these ligands was not possible. However, the fact that DMG could only compete with the natural organic ligands to a very limited extent, indicated that the conditional stability constant of the dissolved organonickel complex must be high. van den Berg and Nimmol were unable to extract Ni from the natural organic ligands with MnO?, thus confirming this hypothesis. The estimation of the complexation characteristics of organ- ometallic complexes by the addition of a known ligand is based on the assumption that equilibrium is reached between the natural ligand, the added ligand and the metal.No conclusion concerning the complexation characteristics can be drawn if one is not certain that equilibrium has been reached. Experiments with continuously mixed sediment slurries resulted in considerably lower conditional stability constants for organonickel complexes.4 These experiments were conduc- ted at different air saturation values in order to study the exchange of metals between sediment and sea-water in relation to degradation of dissolved organic matter (DOM). Complexa- tion of Ni and Cu with dissolved organic ligands was determined during aerobic slurry experiments (100% air saturation). Determination of the complexation characteristics was carried out by using the Mn02 method of van den Competition between Cu and Ni for the same ligand sites was expected (Irving-William order and results in reference 4).This competition was checked by titration of the organic ligands with both metals at the same time. Degradation of DOM started immediately after the onset of the experiment. Dissolved organic carbon (DOC) decreased from 7 to 2 mmol dm-3 within 2 d, after which DOC remained more or less constant. The complexation characteristics of dissolved organocopper complexes could be estimated without any problem. The logarithm of the conditional stability constant of the organocopper complex was 11.1 (k0.3), while the ligand concentration decreased from 300 to 150 nequiv dm-3 owing to degradation of DOM. The organic ligand sites were saturated with respect to Ni, as was also found by van den Berg and Nimmol and Nimmo et a f .,2 except for the samples taken during the first 2 d of the experiment. The logarithm of the conditional stability constant of the dissolved organonickel complex could be estimated from these latter samples to be 10 (k0.8). As for Cu the ligand concentration decreased with time from 230 to 30 nequiv dm-3. Replacement of Ni in organic complexes by Cu was only observed in samples taken during the first day of the experiment. Moreover, this replacement of Ni by Cu did not seem to be a first-order reaction, because a decrease in the organonickel complex concentration was not observed after addition of low (50 nmol dm-3) Cu concentrations, but only after addition of higher Cu concentrations (>150 nmol dm-3).Other indications of competition between Cu and Ni for the same ligand sites were given by an experiment at 20% air saturation. The total dissolved Cu concentration was very low compared with the aerobic experiment, while the total dissolved Ni concentration was higher compared with the aerobic experiment. The total dissolved Ni concentration decreased simultaneously with that of DOC, as was the case during the aerobic experiment. Dissolved Ni was assumed to be organically complexed and its relatively high concentration was thought to be caused by the absence of competition from Cu. During an experiment at 0% air saturation, the dissolved Cu concentration was less than 5 nmol dm-3, while that of Ni decreased gradually from 85 to 20 nmol dm-3 within 4 d.The DOC concentration remained constant. The decrease of the dissolved Ni concentration was thought to be caused by precipitation as the sulphide. A calculation, using the solubility product of NiS obtained from the literature7 and using calculated sulphide concentrations, revealed that competition74 ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 between sulphide and a dissolved organic ligand could only result in precipitation of NiS if the logarithm of the conditional stability constant of the organonickel complex was below 12. Although it could not be measured directly it seems likely that Cu replaced Ni from the ligand sites in these slurry experiments and it is also probable that sulphides could compete with the dissolved organic ligands. The organonickel complex could probably dissociate within 2-4 d.Titration of organic complexes with Ni in order to obtain the conditional stability constant and the ligand concentration was performed with an equilibration time of 24 h.1J.4 It is possible that a period of 24 h is too short for equilibrium to be reached between the natural organic ligands, Ni and the added known ligand (DMG or Mn02). In conclusion, it can be stated that difficulties in determining the complexation characteristics of dissolved organonickel complexes can be explained in two ways: either the conditional stability constant of the organonickel complex is very high or the association and dissociation kinetics of the complex are slow. Evidence exists for both theories, but neither theory has been proven.Further investigation is therefore necessary. References van den Berg, C. M. G., and Nimmo, M.. Sci. Total Environ., 1987, 60, 185. Nimmo, M., van den Berg, C. M. G., and Brown, J., Estuarine, Coastal ShelfSci., 1989, 29, 57. Huynh-Ngoc, L., Whitehead, N. E., Boussemart. M.. and Calmet, D., Mar. Chem., 1989, 26, 119. Gerringa, L. J. A., PhD Thesis, University of Groningen, The Net herlands, 1990. van den Berg, C. M. G., Mar. Chem., 1982, 11,307. van den Berg, C. M. G., Mar. Chem., 1982, 11,322. Stumm, W., and Morgan. J. J., Aquatic Chemistry. Wiley. New York, 1981. ln Situ Voltammetric Measurements in Natural Waters: The Advantages of Microelectrodes R. R. De Vitre, M.-L. Tercier and J. Buffle Department of Inorganic, Analytical and Applied Chemistry, Sciences I/, 30 Quai E.Ansermet, 121 I Geneva 4, Switzerland Lakes, rivers and oceans are subject to an increasing load of toxic metals caused by industrial release, acidification and the leaching of waste landfills. In order to be able to understand the effects of this on natural aquatic media and to undertake remedial action it is necessary to be able to measure the concentration of toxic metals. Voltammetric stripping tech- niques such as differential-pulse adsorptive stripping vol tam- metry or square-wave ASV are very suitable for this purpose as they are capable of multi-element analysis, have high sensitiv- ity, are species discriminating and the instrumentation is relatively inexpensive and can be readily automated. During the last 10 years, a considerable amount of progress has been made1 in the measurement of trace metals by voltammetry; however, in all instances the measurements were performed on board a boat or, more often, on returning to the laboratory, after sampling, sample storage and sometimes separation.Because of the low concentration levels of trace metals found in natural systems, sampling and sample handling can lead to erroneous data owing to losses by adsorption and/or contami- nation. Further, speciation data might be lost because of chemical and physical changes (temperature, pressure, pH, pC02, pHZS, p02) in the sample prior to measurement. All of these problems can be solved if the measurement is performed in situ without any sample pre-treatment. In this paper, we briefly describe the characteristics of an in situ voltammetric probe, some of the results that have been obtained for the measurement of sub-nmol dm-3 metal concentrations in sea-water and the development of an iridium-based mercury film microelectrode for trace metal determinations in low ionic strength natural waters. Experimental The characteristics of the in situ voltammetric probe have been described in detail elsewhere.2 Briefly, however, it is com- posed of three sub-units: a flow-through voltammetric cell, a submersible housing and a control box and its communication cord.In situ measurements were performed by using a pressure-resistant Xerolyt reference electrode (Ingold No. 363-DXK-S7) with a double junction, and a palladium ring counter electrode surrounding the working electrode.The latter was either a sessile mercury drop electrode (SMDE) [Metrohm hanging mercury drop electrode (HMDE), No. 6.0335.0001 or a glassy carbon mercury film electrode (Bio- analytical Systems, No. MF 2012). Laboratory measurements in low ionic strength solutions were also carried out by using both iridium3 and platinum mercury-coated microelectrodes (Taccusel No. 437451) and the results compared with those obtained by using a mercury film electrode (MFE) and an HMDE. Procedures for the preparation of the MFE2 and iridium microelectrode3 have been described elsewhere. All voltammetric measurements were carried out by using a Bioanalytical Systems BAS-100 polarograph or an Amel 433 (Amel, Milan, Italy) instrument. Trace metals were deter- mined in situ in air-saturated sea-water2 by square-wave stripping voltammetry (SWSV) using the following conditions: deposition potential, -1400 mV; rest period, 5 s; amplitude, 25 mV; frequency, 50 Hz; and step amplitude, 2 mV.Laboratory tests were carried out by SWSV using the following conditions: deposition potential, -1200 mV; deposition time, 5 min; amplitude, 25 mV; frequency, 50 Hz; and step amplitude, 8 mV. I T t 1 p" I cu Pb A ~ -0.10 -0.50 -1.00 - 1.40 EN Fig. 1 In situ SWSV measurements of trace metals in air-saturated sea-water using an MFE. Metal concentrations: Cu, 4.7; Pb, 0.5; Cd, 0.04; and Zn, 3.8 nmol dm-3 Results and Discussion The in situ voltammetric probe has been successfully used to measure the concentration of Cu, Pb, Cd and Zn in sea-water directly (Fig. 1). The results obtained in the previous study2ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 75 clearly demonstrated the advantages of performing the deter- mination in situ.Trace metal concentrations as low as 3 X rnol dm-3 were determined in air-saturated sea-water ( 1 X 10-4 rnol dm-3 0,) by SWSV using a glassy carbon MFE. Contamination was found to be less of a problem than when the sample was collected, and because the system could be flushed prior to measurement with a large volume of sea-water. In order to extend the usefulness of the in situ voltammetric probe we have investigated the possibility of measuring low concentrations (sub-pmol dm-3) of trace metals in low ionic strength freshwaters. Reports in the literature4 suggested that the use of a classical sized MFE or an HMDE would have severe limitations.In particular, peak heights are decreased and broadened and peak potentials are shifted. These limita- tions were indeed encountered in experiments with both a glassy carbon MFE and an SMDE, when 1 x 10-6 rnol dm-3 Cd" and Pb" were determined by SWSV in de-gassed 1 x 10-3 rnol dm-3 NaC104 solutions, as shown in Fig. 2(a) and (b). It is known that the use of microelectrodes can solve this problem, owing to the lower ohmic drop associated with their use.5 For example, by comparing the voltammograms obtained with a Pt microelectrode [Fig. 2(c)] with those obtained in the same solutions with either an MFE or SMDE [Fig. 2(a) and (b)] it can be seen that for the Pt microelectrode the peak height and potential are not affected by a change in the ionic strength.-0.3 -0.5 -0.7 -0.9 B -0.3 -0.5 -0.7 -0.9 Pb I I I 1 I -0.3 -0.5 -0.7 -0.9 EN Fig. 2 SWSV curves obtained in A, 0.1; and B, 0.001 rnol dm-3 NaCIO4 at pH 4 and spiked with 1.0 pmol dm-3 Pb" and Cd". ( a ) Glassy carbon and MFE; ( b ) SMDE; and ( c ) Hg-coated Pt microelec- trode (diameter 10 pm) Unfortunately, however, for trace metal determination, the use of a mercury-coated Pt or Pt-Ir alloy microelectrode in such media is hampered by the solubility of Pt in Hg, which leads to the formation of intermetallic species,6 in particular for Cd and Zn. This effect explains the decrease in the Cd peak in Fig. 2(c), whereas for both the SMDE and MFE[Fig. 2(a) and (b)] no Cd suppression due to intermetallic interactions occurred.Kounaves and Buffle7 have shown that for the determination of trace metals, Ir can be used as a substrate for an MFE as it does not form intermetallic species because of the very low solubility of Ir in Hg (<10-6%). In order to be able to measure Cu, Pb, Cd and Zn in low ionic strength freshwaters, we have developed an Ir microelectrode3 which to our knowledge is the first of its type. In Fig. 3, typical examples of SWSV curves, obtained with a 12.5 pm diameter mercury- coated Ir microelectrode in a 0.1 mol dm-3 NaCIO4 solution and a lake-water sample, are given. In contrast to the result obtained with a Pt microelectrode [Fig. 2(c)], the Cd peak height is not suppressed by intermetallic interaction. Further, as expected, no significant effect of ionic strength was found because for both Pb and Cd the shape, height and peak potential are not significantly different when measured in spiked lake water or in a 0.1 rnol dm-3 solution of NaC104. Finally, linear calibration plots for Pb and Cd, in the pmol dm-3-nmol dm-3 concentration range, were obtained by using the Ir-based mercury-coated microelectrode in lake water.t c E 3 u 1 1 0 0 n A I I I I -0.3 -0.5 -0.7 -0.9 EN Fig. 3 SWSV curves obtained with an Hg-coated Ir-based microelec- trode (diameter 12.5 pm): 1.2 pmol dm-3 PblI and 1.1 pmol dm-3 Cd". ( a ) 0.1 rnol dm-3 NaC104, pH 4; and ( b ) lake water, filtered through a 0.2 pm filter, pH 8 In conclusion, our results have shown that although a classical sized MFE can be used for in situ measurements of trace metals in high ionic strength media such as sea-water, they cannot be used in freshwaters.The voltammetric determi- nation of trace metals in low ionic strength freshwaters requires the development of new electrodes: ( i ) in the micrometre size range in order to overcome the disadvantages linked to the ohmic drop in resistive solutions and (ii) to avoid the formation of intermetallic species in mercury films. Because of its unique properties the Ir-based mercury-coated microelectrode de- veloped here appears to have great promise in this respect. Financial support for this project from the Swiss National Foundation (FN No. 2000-5.512) is gratefully acknowledged. References 1 Nurnberg. H . W.. and Mart. L., in The Determination of Trace Metals in Natural Waters, eds.West, T. S., and Nurnberg, H. W., Blackwells. Oxford, 1988. 2 Tercier, M.-L., Buffle, J . , Zirino, A., and De Vitre. R. R., Anal. Chim. Acta, in the press. 3 De Vitre, R. R., Tercier, M.-L., and Buffle, J . , Anal. Chim. Acta, submitted for publication. 4 Wang. J . . and Zadeii. J . M., J. Electroanal. Chem.. 1988, 246, 297. 5 Fleischmann, M.. Pons, S., Rolison, D. R . , and Schmidt, P. P., Ultramicroelectrodes, Datatech Systems, 1987. 6 Wechter, C., and Osteryoung, J . , Anal. Chim. Acta, 1990,234, 275. 7 Kounaves, S. P., and Buffle, J . . J . Electroanal. Chem., 1987, 216, 53.ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 75 clearly demonstrated the advantages of performing the deter- mination in situ. Trace metal concentrations as low as 3 X rnol dm-3 were determined in air-saturated sea-water ( 1 X 10-4 rnol dm-3 0,) by SWSV using a glassy carbon MFE.Contamination was found to be less of a problem than when the sample was collected, and because the system could be flushed prior to measurement with a large volume of sea-water. In order to extend the usefulness of the in situ voltammetric probe we have investigated the possibility of measuring low concentrations (sub-pmol dm-3) of trace metals in low ionic strength freshwaters. Reports in the literature4 suggested that the use of a classical sized MFE or an HMDE would have severe limitations. In particular, peak heights are decreased and broadened and peak potentials are shifted. These limita- tions were indeed encountered in experiments with both a glassy carbon MFE and an SMDE, when 1 x 10-6 rnol dm-3 Cd" and Pb" were determined by SWSV in de-gassed 1 x 10-3 rnol dm-3 NaC104 solutions, as shown in Fig.2(a) and (b). It is known that the use of microelectrodes can solve this problem, owing to the lower ohmic drop associated with their use.5 For example, by comparing the voltammograms obtained with a Pt microelectrode [Fig. 2(c)] with those obtained in the same solutions with either an MFE or SMDE [Fig. 2(a) and (b)] it can be seen that for the Pt microelectrode the peak height and potential are not affected by a change in the ionic strength. -0.3 -0.5 -0.7 -0.9 B -0.3 -0.5 -0.7 -0.9 Pb I I I 1 I -0.3 -0.5 -0.7 -0.9 EN Fig. 2 SWSV curves obtained in A, 0.1; and B, 0.001 rnol dm-3 NaCIO4 at pH 4 and spiked with 1.0 pmol dm-3 Pb" and Cd".( a ) Glassy carbon and MFE; ( b ) SMDE; and ( c ) Hg-coated Pt microelec- trode (diameter 10 pm) Unfortunately, however, for trace metal determination, the use of a mercury-coated Pt or Pt-Ir alloy microelectrode in such media is hampered by the solubility of Pt in Hg, which leads to the formation of intermetallic species,6 in particular for Cd and Zn. This effect explains the decrease in the Cd peak in Fig. 2(c), whereas for both the SMDE and MFE[Fig. 2(a) and (b)] no Cd suppression due to intermetallic interactions occurred. Kounaves and Buffle7 have shown that for the determination of trace metals, Ir can be used as a substrate for an MFE as it does not form intermetallic species because of the very low solubility of Ir in Hg (<10-6%). In order to be able to measure Cu, Pb, Cd and Zn in low ionic strength freshwaters, we have developed an Ir microelectrode3 which to our knowledge is the first of its type.In Fig. 3, typical examples of SWSV curves, obtained with a 12.5 pm diameter mercury- coated Ir microelectrode in a 0.1 mol dm-3 NaCIO4 solution and a lake-water sample, are given. In contrast to the result obtained with a Pt microelectrode [Fig. 2(c)], the Cd peak height is not suppressed by intermetallic interaction. Further, as expected, no significant effect of ionic strength was found because for both Pb and Cd the shape, height and peak potential are not significantly different when measured in spiked lake water or in a 0.1 rnol dm-3 solution of NaC104. Finally, linear calibration plots for Pb and Cd, in the pmol dm-3-nmol dm-3 concentration range, were obtained by using the Ir-based mercury-coated microelectrode in lake water.t c E 3 u 1 1 0 0 n A I I I I -0.3 -0.5 -0.7 -0.9 EN Fig. 3 SWSV curves obtained with an Hg-coated Ir-based microelec- trode (diameter 12.5 pm): 1.2 pmol dm-3 PblI and 1.1 pmol dm-3 Cd". ( a ) 0.1 rnol dm-3 NaC104, pH 4; and ( b ) lake water, filtered through a 0.2 pm filter, pH 8 In conclusion, our results have shown that although a classical sized MFE can be used for in situ measurements of trace metals in high ionic strength media such as sea-water, they cannot be used in freshwaters. The voltammetric determi- nation of trace metals in low ionic strength freshwaters requires the development of new electrodes: ( i ) in the micrometre size range in order to overcome the disadvantages linked to the ohmic drop in resistive solutions and (ii) to avoid the formation of intermetallic species in mercury films.Because of its unique properties the Ir-based mercury-coated microelectrode de- veloped here appears to have great promise in this respect. Financial support for this project from the Swiss National Foundation (FN No. 2000-5.512) is gratefully acknowledged. References 1 Nurnberg. H . W.. and Mart. L., in The Determination of Trace Metals in Natural Waters, eds. West, T. S., and Nurnberg, H. W., Blackwells. Oxford, 1988. 2 Tercier, M.-L., Buffle, J . , Zirino, A., and De Vitre. R. R., Anal. Chim. Acta, in the press. 3 De Vitre, R. R., Tercier, M.-L., and Buffle, J . , Anal. Chim. Acta, submitted for publication.4 Wang. J . . and Zadeii. J . M., J. Electroanal. Chem.. 1988, 246, 297. 5 Fleischmann, M.. Pons, S., Rolison, D. R . , and Schmidt, P. P., Ultramicroelectrodes, Datatech Systems, 1987. 6 Wechter, C., and Osteryoung, J . , Anal. Chim. Acta, 1990,234, 275. 7 Kounaves, S. P., and Buffle, J . . J . Electroanal. Chem., 1987, 216, 53.ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 75 clearly demonstrated the advantages of performing the deter- mination in situ. Trace metal concentrations as low as 3 X rnol dm-3 were determined in air-saturated sea-water ( 1 X 10-4 rnol dm-3 0,) by SWSV using a glassy carbon MFE. Contamination was found to be less of a problem than when the sample was collected, and because the system could be flushed prior to measurement with a large volume of sea-water.In order to extend the usefulness of the in situ voltammetric probe we have investigated the possibility of measuring low concentrations (sub-pmol dm-3) of trace metals in low ionic strength freshwaters. Reports in the literature4 suggested that the use of a classical sized MFE or an HMDE would have severe limitations. In particular, peak heights are decreased and broadened and peak potentials are shifted. These limita- tions were indeed encountered in experiments with both a glassy carbon MFE and an SMDE, when 1 x 10-6 rnol dm-3 Cd" and Pb" were determined by SWSV in de-gassed 1 x 10-3 rnol dm-3 NaC104 solutions, as shown in Fig. 2(a) and (b). It is known that the use of microelectrodes can solve this problem, owing to the lower ohmic drop associated with their use.5 For example, by comparing the voltammograms obtained with a Pt microelectrode [Fig.2(c)] with those obtained in the same solutions with either an MFE or SMDE [Fig. 2(a) and (b)] it can be seen that for the Pt microelectrode the peak height and potential are not affected by a change in the ionic strength. -0.3 -0.5 -0.7 -0.9 B -0.3 -0.5 -0.7 -0.9 Pb I I I 1 I -0.3 -0.5 -0.7 -0.9 EN Fig. 2 SWSV curves obtained in A, 0.1; and B, 0.001 rnol dm-3 NaCIO4 at pH 4 and spiked with 1.0 pmol dm-3 Pb" and Cd". ( a ) Glassy carbon and MFE; ( b ) SMDE; and ( c ) Hg-coated Pt microelec- trode (diameter 10 pm) Unfortunately, however, for trace metal determination, the use of a mercury-coated Pt or Pt-Ir alloy microelectrode in such media is hampered by the solubility of Pt in Hg, which leads to the formation of intermetallic species,6 in particular for Cd and Zn.This effect explains the decrease in the Cd peak in Fig. 2(c), whereas for both the SMDE and MFE[Fig. 2(a) and (b)] no Cd suppression due to intermetallic interactions occurred. Kounaves and Buffle7 have shown that for the determination of trace metals, Ir can be used as a substrate for an MFE as it does not form intermetallic species because of the very low solubility of Ir in Hg (<10-6%). In order to be able to measure Cu, Pb, Cd and Zn in low ionic strength freshwaters, we have developed an Ir microelectrode3 which to our knowledge is the first of its type. In Fig. 3, typical examples of SWSV curves, obtained with a 12.5 pm diameter mercury- coated Ir microelectrode in a 0.1 mol dm-3 NaCIO4 solution and a lake-water sample, are given.In contrast to the result obtained with a Pt microelectrode [Fig. 2(c)], the Cd peak height is not suppressed by intermetallic interaction. Further, as expected, no significant effect of ionic strength was found because for both Pb and Cd the shape, height and peak potential are not significantly different when measured in spiked lake water or in a 0.1 rnol dm-3 solution of NaC104. Finally, linear calibration plots for Pb and Cd, in the pmol dm-3-nmol dm-3 concentration range, were obtained by using the Ir-based mercury-coated microelectrode in lake water. t c E 3 u 1 1 0 0 n A I I I I -0.3 -0.5 -0.7 -0.9 EN Fig. 3 SWSV curves obtained with an Hg-coated Ir-based microelec- trode (diameter 12.5 pm): 1.2 pmol dm-3 PblI and 1.1 pmol dm-3 Cd".( a ) 0.1 rnol dm-3 NaC104, pH 4; and ( b ) lake water, filtered through a 0.2 pm filter, pH 8 In conclusion, our results have shown that although a classical sized MFE can be used for in situ measurements of trace metals in high ionic strength media such as sea-water, they cannot be used in freshwaters. The voltammetric determi- nation of trace metals in low ionic strength freshwaters requires the development of new electrodes: ( i ) in the micrometre size range in order to overcome the disadvantages linked to the ohmic drop in resistive solutions and (ii) to avoid the formation of intermetallic species in mercury films. Because of its unique properties the Ir-based mercury-coated microelectrode de- veloped here appears to have great promise in this respect.Financial support for this project from the Swiss National Foundation (FN No. 2000-5.512) is gratefully acknowledged. References 1 Nurnberg. H . W.. and Mart. L., in The Determination of Trace Metals in Natural Waters, eds. West, T. S., and Nurnberg, H. W., Blackwells. Oxford, 1988. 2 Tercier, M.-L., Buffle, J . , Zirino, A., and De Vitre. R. R., Anal. Chim. Acta, in the press. 3 De Vitre, R. R., Tercier, M.-L., and Buffle, J . , Anal. Chim. Acta, submitted for publication. 4 Wang. J . . and Zadeii. J . M., J. Electroanal. Chem.. 1988, 246, 297. 5 Fleischmann, M.. Pons, S., Rolison, D. R . , and Schmidt, P. P., Ultramicroelectrodes, Datatech Systems, 1987. 6 Wechter, C., and Osteryoung, J ., Anal. Chim. Acta, 1990,234, 275. 7 Kounaves, S. P., and Buffle, J . . J . Electroanal. Chem., 1987, 216, 53.ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 75 clearly demonstrated the advantages of performing the deter- mination in situ. Trace metal concentrations as low as 3 X rnol dm-3 were determined in air-saturated sea-water ( 1 X 10-4 rnol dm-3 0,) by SWSV using a glassy carbon MFE. Contamination was found to be less of a problem than when the sample was collected, and because the system could be flushed prior to measurement with a large volume of sea-water. In order to extend the usefulness of the in situ voltammetric probe we have investigated the possibility of measuring low concentrations (sub-pmol dm-3) of trace metals in low ionic strength freshwaters.Reports in the literature4 suggested that the use of a classical sized MFE or an HMDE would have severe limitations. In particular, peak heights are decreased and broadened and peak potentials are shifted. These limita- tions were indeed encountered in experiments with both a glassy carbon MFE and an SMDE, when 1 x 10-6 rnol dm-3 Cd" and Pb" were determined by SWSV in de-gassed 1 x 10-3 rnol dm-3 NaC104 solutions, as shown in Fig. 2(a) and (b). It is known that the use of microelectrodes can solve this problem, owing to the lower ohmic drop associated with their use.5 For example, by comparing the voltammograms obtained with a Pt microelectrode [Fig. 2(c)] with those obtained in the same solutions with either an MFE or SMDE [Fig. 2(a) and (b)] it can be seen that for the Pt microelectrode the peak height and potential are not affected by a change in the ionic strength.-0.3 -0.5 -0.7 -0.9 B -0.3 -0.5 -0.7 -0.9 Pb I I I 1 I -0.3 -0.5 -0.7 -0.9 EN Fig. 2 SWSV curves obtained in A, 0.1; and B, 0.001 rnol dm-3 NaCIO4 at pH 4 and spiked with 1.0 pmol dm-3 Pb" and Cd". ( a ) Glassy carbon and MFE; ( b ) SMDE; and ( c ) Hg-coated Pt microelec- trode (diameter 10 pm) Unfortunately, however, for trace metal determination, the use of a mercury-coated Pt or Pt-Ir alloy microelectrode in such media is hampered by the solubility of Pt in Hg, which leads to the formation of intermetallic species,6 in particular for Cd and Zn. This effect explains the decrease in the Cd peak in Fig. 2(c), whereas for both the SMDE and MFE[Fig.2(a) and (b)] no Cd suppression due to intermetallic interactions occurred. Kounaves and Buffle7 have shown that for the determination of trace metals, Ir can be used as a substrate for an MFE as it does not form intermetallic species because of the very low solubility of Ir in Hg (<10-6%). In order to be able to measure Cu, Pb, Cd and Zn in low ionic strength freshwaters, we have developed an Ir microelectrode3 which to our knowledge is the first of its type. In Fig. 3, typical examples of SWSV curves, obtained with a 12.5 pm diameter mercury- coated Ir microelectrode in a 0.1 mol dm-3 NaCIO4 solution and a lake-water sample, are given. In contrast to the result obtained with a Pt microelectrode [Fig. 2(c)], the Cd peak height is not suppressed by intermetallic interaction.Further, as expected, no significant effect of ionic strength was found because for both Pb and Cd the shape, height and peak potential are not significantly different when measured in spiked lake water or in a 0.1 rnol dm-3 solution of NaC104. Finally, linear calibration plots for Pb and Cd, in the pmol dm-3-nmol dm-3 concentration range, were obtained by using the Ir-based mercury-coated microelectrode in lake water. t c E 3 u 1 1 0 0 n A I I I I -0.3 -0.5 -0.7 -0.9 EN Fig. 3 SWSV curves obtained with an Hg-coated Ir-based microelec- trode (diameter 12.5 pm): 1.2 pmol dm-3 PblI and 1.1 pmol dm-3 Cd". ( a ) 0.1 rnol dm-3 NaC104, pH 4; and ( b ) lake water, filtered through a 0.2 pm filter, pH 8 In conclusion, our results have shown that although a classical sized MFE can be used for in situ measurements of trace metals in high ionic strength media such as sea-water, they cannot be used in freshwaters. The voltammetric determi- nation of trace metals in low ionic strength freshwaters requires the development of new electrodes: ( i ) in the micrometre size range in order to overcome the disadvantages linked to the ohmic drop in resistive solutions and (ii) to avoid the formation of intermetallic species in mercury films.Because of its unique properties the Ir-based mercury-coated microelectrode de- veloped here appears to have great promise in this respect. Financial support for this project from the Swiss National Foundation (FN No. 2000-5.512) is gratefully acknowledged. References 1 Nurnberg.H . W.. and Mart. L., in The Determination of Trace Metals in Natural Waters, eds. West, T. S., and Nurnberg, H. W., Blackwells. Oxford, 1988. 2 Tercier, M.-L., Buffle, J . , Zirino, A., and De Vitre. R. R., Anal. Chim. Acta, in the press. 3 De Vitre, R. R., Tercier, M.-L., and Buffle, J . , Anal. Chim. Acta, submitted for publication. 4 Wang. J . . and Zadeii. J . M., J. Electroanal. Chem.. 1988, 246, 297. 5 Fleischmann, M.. Pons, S., Rolison, D. R . , and Schmidt, P. P., Ultramicroelectrodes, Datatech Systems, 1987. 6 Wechter, C., and Osteryoung, J . , Anal. Chim. Acta, 1990,234, 275. 7 Kounaves, S. P., and Buffle, J . . J . Electroanal. Chem., 1987, 216, 53.ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 75 clearly demonstrated the advantages of performing the deter- mination in situ.Trace metal concentrations as low as 3 X rnol dm-3 were determined in air-saturated sea-water ( 1 X 10-4 rnol dm-3 0,) by SWSV using a glassy carbon MFE. Contamination was found to be less of a problem than when the sample was collected, and because the system could be flushed prior to measurement with a large volume of sea-water. In order to extend the usefulness of the in situ voltammetric probe we have investigated the possibility of measuring low concentrations (sub-pmol dm-3) of trace metals in low ionic strength freshwaters. Reports in the literature4 suggested that the use of a classical sized MFE or an HMDE would have severe limitations. In particular, peak heights are decreased and broadened and peak potentials are shifted.These limita- tions were indeed encountered in experiments with both a glassy carbon MFE and an SMDE, when 1 x 10-6 rnol dm-3 Cd" and Pb" were determined by SWSV in de-gassed 1 x 10-3 rnol dm-3 NaC104 solutions, as shown in Fig. 2(a) and (b). It is known that the use of microelectrodes can solve this problem, owing to the lower ohmic drop associated with their use.5 For example, by comparing the voltammograms obtained with a Pt microelectrode [Fig. 2(c)] with those obtained in the same solutions with either an MFE or SMDE [Fig. 2(a) and (b)] it can be seen that for the Pt microelectrode the peak height and potential are not affected by a change in the ionic strength. -0.3 -0.5 -0.7 -0.9 B -0.3 -0.5 -0.7 -0.9 Pb I I I 1 I -0.3 -0.5 -0.7 -0.9 EN Fig. 2 SWSV curves obtained in A, 0.1; and B, 0.001 rnol dm-3 NaCIO4 at pH 4 and spiked with 1.0 pmol dm-3 Pb" and Cd".( a ) Glassy carbon and MFE; ( b ) SMDE; and ( c ) Hg-coated Pt microelec- trode (diameter 10 pm) Unfortunately, however, for trace metal determination, the use of a mercury-coated Pt or Pt-Ir alloy microelectrode in such media is hampered by the solubility of Pt in Hg, which leads to the formation of intermetallic species,6 in particular for Cd and Zn. This effect explains the decrease in the Cd peak in Fig. 2(c), whereas for both the SMDE and MFE[Fig. 2(a) and (b)] no Cd suppression due to intermetallic interactions occurred. Kounaves and Buffle7 have shown that for the determination of trace metals, Ir can be used as a substrate for an MFE as it does not form intermetallic species because of the very low solubility of Ir in Hg (<10-6%).In order to be able to measure Cu, Pb, Cd and Zn in low ionic strength freshwaters, we have developed an Ir microelectrode3 which to our knowledge is the first of its type. In Fig. 3, typical examples of SWSV curves, obtained with a 12.5 pm diameter mercury- coated Ir microelectrode in a 0.1 mol dm-3 NaCIO4 solution and a lake-water sample, are given. In contrast to the result obtained with a Pt microelectrode [Fig. 2(c)], the Cd peak height is not suppressed by intermetallic interaction. Further, as expected, no significant effect of ionic strength was found because for both Pb and Cd the shape, height and peak potential are not significantly different when measured in spiked lake water or in a 0.1 rnol dm-3 solution of NaC104.Finally, linear calibration plots for Pb and Cd, in the pmol dm-3-nmol dm-3 concentration range, were obtained by using the Ir-based mercury-coated microelectrode in lake water. t c E 3 u 1 1 0 0 n A I I I I -0.3 -0.5 -0.7 -0.9 EN Fig. 3 SWSV curves obtained with an Hg-coated Ir-based microelec- trode (diameter 12.5 pm): 1.2 pmol dm-3 PblI and 1.1 pmol dm-3 Cd". ( a ) 0.1 rnol dm-3 NaC104, pH 4; and ( b ) lake water, filtered through a 0.2 pm filter, pH 8 In conclusion, our results have shown that although a classical sized MFE can be used for in situ measurements of trace metals in high ionic strength media such as sea-water, they cannot be used in freshwaters. The voltammetric determi- nation of trace metals in low ionic strength freshwaters requires the development of new electrodes: ( i ) in the micrometre size range in order to overcome the disadvantages linked to the ohmic drop in resistive solutions and (ii) to avoid the formation of intermetallic species in mercury films.Because of its unique properties the Ir-based mercury-coated microelectrode de- veloped here appears to have great promise in this respect. Financial support for this project from the Swiss National Foundation (FN No. 2000-5.512) is gratefully acknowledged. References 1 Nurnberg. H . W.. and Mart. L., in The Determination of Trace Metals in Natural Waters, eds. West, T. S., and Nurnberg, H. W., Blackwells. Oxford, 1988. 2 Tercier, M.-L., Buffle, J . , Zirino, A., and De Vitre. R. R., Anal.Chim. Acta, in the press. 3 De Vitre, R. R., Tercier, M.-L., and Buffle, J . , Anal. Chim. Acta, submitted for publication. 4 Wang. J . . and Zadeii. J . M., J. Electroanal. Chem.. 1988, 246, 297. 5 Fleischmann, M.. Pons, S., Rolison, D. R . , and Schmidt, P. P., Ultramicroelectrodes, Datatech Systems, 1987. 6 Wechter, C., and Osteryoung, J . , Anal. Chim. Acta, 1990,234, 275. 7 Kounaves, S. P., and Buffle, J . . J . Electroanal. Chem., 1987, 216, 53.ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 75 clearly demonstrated the advantages of performing the deter- mination in situ. Trace metal concentrations as low as 3 X rnol dm-3 were determined in air-saturated sea-water ( 1 X 10-4 rnol dm-3 0,) by SWSV using a glassy carbon MFE. Contamination was found to be less of a problem than when the sample was collected, and because the system could be flushed prior to measurement with a large volume of sea-water.In order to extend the usefulness of the in situ voltammetric probe we have investigated the possibility of measuring low concentrations (sub-pmol dm-3) of trace metals in low ionic strength freshwaters. Reports in the literature4 suggested that the use of a classical sized MFE or an HMDE would have severe limitations. In particular, peak heights are decreased and broadened and peak potentials are shifted. These limita- tions were indeed encountered in experiments with both a glassy carbon MFE and an SMDE, when 1 x 10-6 rnol dm-3 Cd" and Pb" were determined by SWSV in de-gassed 1 x 10-3 rnol dm-3 NaC104 solutions, as shown in Fig.2(a) and (b). It is known that the use of microelectrodes can solve this problem, owing to the lower ohmic drop associated with their use.5 For example, by comparing the voltammograms obtained with a Pt microelectrode [Fig. 2(c)] with those obtained in the same solutions with either an MFE or SMDE [Fig. 2(a) and (b)] it can be seen that for the Pt microelectrode the peak height and potential are not affected by a change in the ionic strength. -0.3 -0.5 -0.7 -0.9 B -0.3 -0.5 -0.7 -0.9 Pb I I I 1 I -0.3 -0.5 -0.7 -0.9 EN Fig. 2 SWSV curves obtained in A, 0.1; and B, 0.001 rnol dm-3 NaCIO4 at pH 4 and spiked with 1.0 pmol dm-3 Pb" and Cd". ( a ) Glassy carbon and MFE; ( b ) SMDE; and ( c ) Hg-coated Pt microelec- trode (diameter 10 pm) Unfortunately, however, for trace metal determination, the use of a mercury-coated Pt or Pt-Ir alloy microelectrode in such media is hampered by the solubility of Pt in Hg, which leads to the formation of intermetallic species,6 in particular for Cd and Zn.This effect explains the decrease in the Cd peak in Fig. 2(c), whereas for both the SMDE and MFE[Fig. 2(a) and (b)] no Cd suppression due to intermetallic interactions occurred. Kounaves and Buffle7 have shown that for the determination of trace metals, Ir can be used as a substrate for an MFE as it does not form intermetallic species because of the very low solubility of Ir in Hg (<10-6%). In order to be able to measure Cu, Pb, Cd and Zn in low ionic strength freshwaters, we have developed an Ir microelectrode3 which to our knowledge is the first of its type.In Fig. 3, typical examples of SWSV curves, obtained with a 12.5 pm diameter mercury- coated Ir microelectrode in a 0.1 mol dm-3 NaCIO4 solution and a lake-water sample, are given. In contrast to the result obtained with a Pt microelectrode [Fig. 2(c)], the Cd peak height is not suppressed by intermetallic interaction. Further, as expected, no significant effect of ionic strength was found because for both Pb and Cd the shape, height and peak potential are not significantly different when measured in spiked lake water or in a 0.1 rnol dm-3 solution of NaC104. Finally, linear calibration plots for Pb and Cd, in the pmol dm-3-nmol dm-3 concentration range, were obtained by using the Ir-based mercury-coated microelectrode in lake water.t c E 3 u 1 1 0 0 n A I I I I -0.3 -0.5 -0.7 -0.9 EN Fig. 3 SWSV curves obtained with an Hg-coated Ir-based microelec- trode (diameter 12.5 pm): 1.2 pmol dm-3 PblI and 1.1 pmol dm-3 Cd". ( a ) 0.1 rnol dm-3 NaC104, pH 4; and ( b ) lake water, filtered through a 0.2 pm filter, pH 8 In conclusion, our results have shown that although a classical sized MFE can be used for in situ measurements of trace metals in high ionic strength media such as sea-water, they cannot be used in freshwaters. The voltammetric determi- nation of trace metals in low ionic strength freshwaters requires the development of new electrodes: ( i ) in the micrometre size range in order to overcome the disadvantages linked to the ohmic drop in resistive solutions and (ii) to avoid the formation of intermetallic species in mercury films.Because of its unique properties the Ir-based mercury-coated microelectrode de- veloped here appears to have great promise in this respect. Financial support for this project from the Swiss National Foundation (FN No. 2000-5.512) is gratefully acknowledged. References 1 Nurnberg. H . W.. and Mart. L., in The Determination of Trace Metals in Natural Waters, eds. West, T. S., and Nurnberg, H. W., Blackwells. Oxford, 1988. 2 Tercier, M.-L., Buffle, J . , Zirino, A., and De Vitre. R. R., Anal. Chim. Acta, in the press. 3 De Vitre, R. R., Tercier, M.-L., and Buffle, J . , Anal. Chim. Acta, submitted for publication. 4 Wang. J . . and Zadeii. J . M., J. Electroanal. Chem.. 1988, 246, 297. 5 Fleischmann, M.. Pons, S., Rolison, D.R . , and Schmidt, P. P., Ultramicroelectrodes, Datatech Systems, 1987. 6 Wechter, C., and Osteryoung, J . , Anal. Chim. Acta, 1990,234, 275. 7 Kounaves, S. P., and Buffle, J . . J . Electroanal. Chem., 1987, 216, 53.ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 75 clearly demonstrated the advantages of performing the deter- mination in situ. Trace metal concentrations as low as 3 X rnol dm-3 were determined in air-saturated sea-water ( 1 X 10-4 rnol dm-3 0,) by SWSV using a glassy carbon MFE. Contamination was found to be less of a problem than when the sample was collected, and because the system could be flushed prior to measurement with a large volume of sea-water. In order to extend the usefulness of the in situ voltammetric probe we have investigated the possibility of measuring low concentrations (sub-pmol dm-3) of trace metals in low ionic strength freshwaters.Reports in the literature4 suggested that the use of a classical sized MFE or an HMDE would have severe limitations. In particular, peak heights are decreased and broadened and peak potentials are shifted. These limita- tions were indeed encountered in experiments with both a glassy carbon MFE and an SMDE, when 1 x 10-6 rnol dm-3 Cd" and Pb" were determined by SWSV in de-gassed 1 x 10-3 rnol dm-3 NaC104 solutions, as shown in Fig. 2(a) and (b). It is known that the use of microelectrodes can solve this problem, owing to the lower ohmic drop associated with their use.5 For example, by comparing the voltammograms obtained with a Pt microelectrode [Fig.2(c)] with those obtained in the same solutions with either an MFE or SMDE [Fig. 2(a) and (b)] it can be seen that for the Pt microelectrode the peak height and potential are not affected by a change in the ionic strength. -0.3 -0.5 -0.7 -0.9 B -0.3 -0.5 -0.7 -0.9 Pb I I I 1 I -0.3 -0.5 -0.7 -0.9 EN Fig. 2 SWSV curves obtained in A, 0.1; and B, 0.001 rnol dm-3 NaCIO4 at pH 4 and spiked with 1.0 pmol dm-3 Pb" and Cd". ( a ) Glassy carbon and MFE; ( b ) SMDE; and ( c ) Hg-coated Pt microelec- trode (diameter 10 pm) Unfortunately, however, for trace metal determination, the use of a mercury-coated Pt or Pt-Ir alloy microelectrode in such media is hampered by the solubility of Pt in Hg, which leads to the formation of intermetallic species,6 in particular for Cd and Zn.This effect explains the decrease in the Cd peak in Fig. 2(c), whereas for both the SMDE and MFE[Fig. 2(a) and (b)] no Cd suppression due to intermetallic interactions occurred. Kounaves and Buffle7 have shown that for the determination of trace metals, Ir can be used as a substrate for an MFE as it does not form intermetallic species because of the very low solubility of Ir in Hg (<10-6%). In order to be able to measure Cu, Pb, Cd and Zn in low ionic strength freshwaters, we have developed an Ir microelectrode3 which to our knowledge is the first of its type. In Fig. 3, typical examples of SWSV curves, obtained with a 12.5 pm diameter mercury- coated Ir microelectrode in a 0.1 mol dm-3 NaCIO4 solution and a lake-water sample, are given. In contrast to the result obtained with a Pt microelectrode [Fig. 2(c)], the Cd peak height is not suppressed by intermetallic interaction. Further, as expected, no significant effect of ionic strength was found because for both Pb and Cd the shape, height and peak potential are not significantly different when measured in spiked lake water or in a 0.1 rnol dm-3 solution of NaC104. Finally, linear calibration plots for Pb and Cd, in the pmol dm-3-nmol dm-3 concentration range, were obtained by using the Ir-based mercury-coated microelectrode in lake water. t c E 3 u 1 1 0 0 n A I I I I -0.3 -0.5 -0.7 -0.9 EN Fig. 3 SWSV curves obtained with an Hg-coated Ir-based microelec- trode (diameter 12.5 pm): 1.2 pmol dm-3 PblI and 1.1 pmol dm-3 Cd". ( a ) 0.1 rnol dm-3 NaC104, pH 4; and ( b ) lake water, filtered through a 0.2 pm filter, pH 8 In conclusion, our results have shown that although a classical sized MFE can be used for in situ measurements of trace metals in high ionic strength media such as sea-water, they cannot be used in freshwaters. The voltammetric determi- nation of trace metals in low ionic strength freshwaters requires the development of new electrodes: ( i ) in the micrometre size range in order to overcome the disadvantages linked to the ohmic drop in resistive solutions and (ii) to avoid the formation of intermetallic species in mercury films. Because of its unique properties the Ir-based mercury-coated microelectrode de- veloped here appears to have great promise in this respect. Financial support for this project from the Swiss National Foundation (FN No. 2000-5.512) is gratefully acknowledged. References 1 Nurnberg. H . W.. and Mart. L., in The Determination of Trace Metals in Natural Waters, eds. West, T. S., and Nurnberg, H. W., Blackwells. Oxford, 1988. 2 Tercier, M.-L., Buffle, J . , Zirino, A., and De Vitre. R. R., Anal. Chim. Acta, in the press. 3 De Vitre, R. R., Tercier, M.-L., and Buffle, J . , Anal. Chim. Acta, submitted for publication. 4 Wang. J . . and Zadeii. J . M., J. Electroanal. Chem.. 1988, 246, 297. 5 Fleischmann, M.. Pons, S., Rolison, D. R . , and Schmidt, P. P., Ultramicroelectrodes, Datatech Systems, 1987. 6 Wechter, C., and Osteryoung, J . , Anal. Chim. Acta, 1990,234, 275. 7 Kounaves, S. P., and Buffle, J . . J . Electroanal. Chem., 1987, 216, 53.

ISSN:0144-557X    

DOI:10.1039/AP9912800072

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

82 ANALYTICAL PROCEEDINGS, MARCH 1991. VOL 28 Research and Development Topics in Analytical Chemistry The following is a summary of one of the papers presented at a Meeting of the Analytical Division held on July 16th-I7th, 1990, in ICI C and P Ltd., Runcorn, Cheshire. Summaries of thirteen other papers and posters presented at the Meeting were published in the January (p. 8 ) and February (p. 37) issues. Investigation of a Cation Exchange Separation Method for the Determination of Transition Metal Ions in Anaerobic Sealants Philip O'Dea, Marian Deacon and Malcolm R. Smyth* School of Chemical Sciences, Dublin City University, Dublin 9, Ireland and Raymond G. Leonard Loctite (Ireland) Ltd., Whitestown Industrial Estate, Tallaght, Co. Dublin, Ireland The use of high-performance liquid chromatography (HPLC) for the simultaneous determination of transition metal ions has received much attention in the last decade.1-8 The modes of separation that have been developed include suppressed cation-exchange chromatography,' single-column cation- exchange chromatography, using a low capacity cation- exchange column with an eluent containing a complexing agent, e.g., an organic acid such as 2,3-dihydroxy-1,4-butan- dioic acid (tartaric acid) or 3-hydroxy-2-methylpropanoic a~id~2.3 reversed-phase chromatography with an eluent con- taining a ligand species, e.g., a dithiocarbamate4-6 or 8-hydroxyquinoline ,7 or reversed-phase chromatography using a dynamically coated CIS column.8 The use of a suppressed cation-exchange mechanism invol- ving conductivity detection is limited because of problems of precipitation of most polyvalent metal cations in the hydroxide form suppressor column.The use of reversed-phase separa- tions in which the metal ion is complexed to a ligand, either prior to injection or on-column, has been shown to be an excellent method for the determination of mixtures of transi- tion metal ions, but there is a limit to the number of metal ions which can be separated at any one time. The aim of this work was to develop a separation method for the simultaneous determination of eight metal ions, namely Fell, Fe111, Cull, Co", Ni", Mn", Zn" and C F , in typical anaerobic sealant formulations. Based on the literature it was decided to investigate the use of a low capacity ion-exchange column operating via a 'push-pull' mechanism, where the 'pushing effect' is provided by the ethylenediammonium (EDA) cation and the 'pulling' effect by a weakly complexing organic acid anion.3 This system was expected to offer the capability of multi-element separa- tion, the ability to speciate between Fell and Fell', and could be coupled to a detection system involving post-column derivati- sation with 4-(2-pyridylazo)resorcinol (PAR).This reagent has been shown to react qualitatively and quantitatively with a wide range of transition metal ions, and the resulting absor- bance of the complexes in the visible region of the spectrum can be used for sensitive detection purposes.9 * To whom correspondence should be addressed. Experimental Materials All chemicals used were of analytical-reagent grade.Raw materials used in adhesive sealant formulations were supplied by Loctite (Ireland) Ltd. Deionized water, which was obtained by passing distilled water through a Milli-Q water purification system, was used in the preparation of all aqueous solutions. Solutions of Cull, C011, Ni", Cr111 and Zn" were made up from chloride salts, while solutions of Mn", Fell and Fell' were prepared from sulphate, ammonium sulphate and nitrate salts, respectively. Both Fell and Fell1 stock solutions were stable for a period of a week if made up in sulphuric acid (10% mh). The colour-forming post-column reagent used for the detection of the metal ions was the monosodium salt of 4-(2-pyridylazo)resorcinol (PAR), which was supplied by Sigma Ltd. Silica and CI8 sample preparation cartridges (Sep-Pak) were obtained from Waters Associates.The Interac- tion Ion-210 metals column was supplied by Technicol Ltd. and was a 0.32 cm x 10 cm i.d. stainless-steel column containing Macronex MC-210 cation-exchange polymer with a capacity of approximately 500 pequiv g-1. The pulse dampener consisted of a stainless-steel column containing polystyrene beads and was supplied by Philips Analytical Ltd. An Interaction Ion-Guard GC-200 was employed to protect the analytical column. Apparatus Chromatography was performed by using a Waters Associates M-45 pump connected to 20 p1 Waters U6K injection port. The post-column reagent was delivered by a Waters Associates 6000 dual-piston pump to the mixing T, at the same flow rate as was used for the elution of the metal ions from the ion- exchange column.Detection was achieved using an Applied Chromatography Systems (ACS) Ltd. fixed wavelength (520 nm) detector in conjunction with a Philips 8251 single pen recorder. All pH measurements were made on a Corning 240 pH meter. Methods Extraction procedure ( I ) Extractions were performed by dissolving 5 ml of plasticizer [polyethylene glycol di(2-ethylhexanoate)], which had been spiked at the 10 ppm level with Fe", CU", Ni", Mn", Co" and Zn", in 5 ml of chloroform and extracting the metal ions withANALYTICAL PROCEEDINGS, MARCH 1991. VOL 28 83 an equal volume of 0.1 mol dm-3 hydrochloric acid. The acid extract was passed through a CI8 Sep Pak column prior to being injected on to the ion-exchange column.Extraction procedure (2) As for extraction procedure (l), 5 ml of plasticiser containing spiked metal ions was dissolved in chloroform. This was then passed through a silica Sep Pak column. The column was washed with 20 ml of chloroform and the retained metal ions were eluted with 2 ml of 3.9 mmol dm-3 EDA solution and 17 mmol dm-3 citric acid, i.e., the mobile phase employed in the separation of the transition metal ions on the ion-exchange column. Results and Discussion Optimisation of Post-column Derivatisation Reaction Based on the work of Wang et a!. ,9 it had been suggested that the optimum post-column reagent concentration was 2 x 10-4 rnol dm-3 PAR dissolved in 2 mol dm-3 ammonia solution and 1 rnol dm-3 ammonium acetate, the pH being approximately 11.In this study, the concentration of PAR was varied between 1 x 10-4 and 8 x 10-4 rnol dm-3, keeping the pH constant at approximately 10.2; the optimum concentration was found to be 3 x 10-4 rnol dm-3. Although an improved detector response (at 520 nm) was obtained at higher concentrations of PAR, the base line noise increased significantly at concentra- tions greater than 3 x 10-4 rnol dm-3 of PAR. As the PAR concentration increased, so did the difference in absorbance between the post-column reagent and the column eluent. Short term fluctuations in the flow of both streams caused short term changes in absorbance which, in turn, resulted in increased detector noise. By using a PAR concentration of 3 X 10-4 rnol dm-3, the pH of the reagent was varied from 8.01 to 10.9 by adjusting the volume of concentrated ammonia solution in 1 rnol dm-3 ammonium acetate.The actual pH at which the metal ions were complexed with the post-column reagent was determined by monitoring the pH of the eluent coming from the HPLC detector. The optimum pH was found to be 10.14 for the reagent being introduced into the system. The pH of the eluent resulting from this was found to be 10.02. Optimisation of Mobile Phase Composition In the optimization of the separation of the transition metal ions on the low capacity ion-exchange column, it was decided to adopt the following procedures. The choice of the ethylene- diammonium cation was based on the work of Sevenich and Fritz,3 and this compound was used throughout this study to provide the mass action 'pushing' effect in the separation process.A variety of organic acids were then investigated for their 'pulling' effect. These included citric, tartaric, lactic, oxalic, malonic, sulphosalicylic, fumaric and malic acids. In each instance the concentration of the EDA cation was first kept at 3.5 mmol dm-3 and the concentration of the organic acid varied between 5 and 20 mmol dm-3. When an optimum separation was reached in such a system, the concentration of the organic acid was kept constant and the concentration of the EDA cation varied between 2 and 4.5 mmol dm-3. The organic acid which gave rise to the best chromatographic separation was found to be citric acid, in agreement with the finding of the manufacturers of the Interaction column used in this work.10 This was at some variance with the work of Sevenich and Fritz,3 who advocated the use of tartaric acid.We found, however, that the use of tartaric acid as the complexing agent resulted in the co-elution of Nil1 and ZnIL, and that CoII and Fell were not adequately resolved. Increasing the tartaric acid concentration while keeping the EDA concentration constant at 3.5 mmol dm-3 improved the resolution between Co11 and Fe111. However, the separation of Nil1 from ZnlI never improved beyond forming a shoulder peak to the latter eluting cation. Neither lactic acid nor oxalic acid effected a good separation of the metal ions, and the adsorption of the metal ions on to the ion-exchange column became a significant problem when these complexing agents were employed in the mobile phase.Varying the ratio of the organic acid to EDA and reducing the concentration of the injected metal ion standards did not improve matters. Although good sensitivity and resolution were obtained between Fell' and Cull when malonic acid was used as the complexing agent, the remaining metal ions were not separated and eluted as one broad peak. Sulphosalicylic acid and fumaric acid exhibited no selectivity between the transition metal ions. However, malic acid (the cis-isomeric form of fumaric acid) showed reasonable selectivity between the metal ions and could separate five of the seven metal ions injected into the ion-exchange separation system. In a similar manner to tartaric acid, Nil1 co-eluted with Zn", but Fe" and Mn" were not separated and eluted as one peak.The optimum concentration of citric acid was found to be 17 mmol dm-3 (in the presence of 3.9 mmol dm-3 of EDA). During this study, the effect of pH was monitored by measuring the pH of the mobile phase. The optimum pH was found to be approximately 3.0, i.e., just below the first- pK, value of citric acid (pK,! = 3.13; pK,, = 4.76; pKa3 = 6.40 at 25 "C). The reason for this is that one only requires partial dissociation of the organic acid in order for it to perform the 'pulling effect'. At higher pH values, the citric acid complexed more strongly with the transition metal ions and the retention times decreased, with a consequent reduction in the resolution between the eluting ions. The best separation for Cull, Ni", Zn", Co11, Fell and Mn" is shown in Fig.1. 15 10 5 0 tlmin Fig. 1 Separation of: 1 . 110 ppm FeI"; 2, 10 pprn Fe"; 3.10 ppm NiII; 4, 10 pprn Z n l ; 5. 10 ppm Co"; 6, 10 ppm Fell; and 7, 10 pprn Mn" using a mobile phase of 3.9 mmol dm-3 EDA and 17 mmol dm-3 citric acid Chromium(n1) was not detected, because although it forms a complex with PAR, in highly alkaline media the molar absorptivity of the complex is very low.11 The optimized isocratic separation system was not suitable for the speciation of Fell and Fell'. The elution of Fell' within 1 min of the injection suggests that a gradient separation system would be more appropriate for the separation of Fell1 from the other transition metal ions. The poor detector response for FeI11, which could only be detected at the 110 pprn level, was in part84 ANALYTICAL PROCEEDINGS.MARCH 1991, VOL 28 due to the presence of this metal ion in the deionized water employed in this study. Linear calibration curves were obtained for Zn", Co", Fell and Mn" over the concentration range of 1.0-10 ppm and for CU" from 2 to 9 ppm. The limit of detection based on the peak height being greater than 3 times the base line noise was approximately 0.5 ppm for Zn", Co", Fe" and Mn" and 1 ppm for Cull. Development of Extraction Procedures A typical plasticizer used in an anaerobic sealant formulation manufactured by Loctite (Ireland) Ltd. is { poly(ethylene glycol di[2-ethylhexanoate])}. Studies were therefore directed to the efficient extraction of trace metal ions from this matrix. Extractions performed using extraction scheme (1) gave rise to recoveries from 88.4 to 99.8% for all the metal ions, except for Fell where only a 35.3% recovery was obtained.The loss of Fell in the procedure was thought to be due to the partial retention of the metal ion in the chloroform. When using extraction scheme (2) , similar extraction recoveries were obtained for the metal ions although there was a complete loss of Fe". Further investigation of the procedure showed that Fell was retained in both the chloroform layer and on the silica Sep Pak column, so that more work is required to find an alternative organic solvent to dissolve the plasticiser and investigate the retention of Fe" on the silica Sep Pak column. However, with regard to the other transition metal ions, the second extraction method was an improvement on the first procedure as it permitted a preconcentration of the metal ions present in the plasticiser.This extraction and preconcentration procedure was only limited by the availability of a large volume of sample and the capability of the silica Sep Pak column to preconcentrate trace metal ions from large volumes of plasti- ciser. Conclusion This preliminary investigation has shown the possible applica- tion of ion-exchange chromatography with detection by post-column derivatization for the determination of transition metal ions in anaerobic sealants. Further investigation will be required on the optimisation of the extraction of the trace metal ions from plasticisers a i d other more important constitu- ents in anaerobic adhesives, such as the monomers poly- ethylene glycol dimethacrylate (PEGMA) and triethylene glycol dimethacrylate (TRI-EGMA). 1 2 3 4 5 6 7 8 9 10 11 References Small, H ., Stevens. T. S . , and Buaman, W. C., Anal. Chem.. 197.5. 47, 1801. Cassidy, R. M., Elchuk, S. and McHugh, J . O., Anal. Chem.. 1982, 54, 727. Sevenich, G. J . , and Fritz, J . S . . Anal. Chem.. 1983, 55, 12. Uden, P. C., and Bigley, I. E., Anal. Chim. Acta, 1977,94,29. Schwedt, G., Chromatographia, 1978, 11. 14.5. Bond. A. M., and Wallace, G. G., Anal. Chem., 1981.53.1209. Mooncy. J . P.. Meaney. M., Srnyth. M. R., Leonard, R. G.. and Wallace, G. G., Analyst, 1987, 112, 1.555. Knight. C. H . , Cassidy, R. M., Recoskie. B. M.. and Green, L. W., Anal. Chem., 1984, 56,474. Wang, W.-N., Chen, Y.-J., and Wu, M.-T., Analyst, 1984,109, 281. McBlane, D., and Benson, J. R., Interaction Transition Metals Column Ion-210 Application Note, Interaction, Mountain View, CA, USA, 1985. Yotsuyanagi, T., Takcda. Y., Yamashita, R., and Aomura. K . , Anal. Chim. Acta. 1973. 67, 297. ROYAL SOCIETY OF CHEMISTRY: ANALYTICAL DIVISION THERMAL METHODS GROUP 10th THERMAL ANALYSIS SCHOOL April 22-26,1991 Manchester Materials Science Centre This residential course will be held in the University of Manchester and UMIST Materials Science Centre. It is intended for those who are new to thermoanalytical techniques. The lecturers will include Professor F. R. Sale, Professor E. L. Charsley, Dr. J. N. Hay, Dr. M. Reading, Mr. L. Holcroft, Mr. J. Leckenby, Dr. R. Marsh, Mr. P. J. Haines, Dr. J. Ford, Dr. D. J. Morgan, Dr. N. Lambert, Dr. R. S. Whitehouse, Dr. E. Gimzewski and Dr. J. H. Sharp. Details of the course are available from Mrs. 0. Richert, Manchester Materials Science Centre, University of Manchester and UMIST, Grosvenor Street, Manchester M1 7HS.

ISSN:0144-557X    

DOI:10.1039/AP9912800082

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 85 Equipment News Near-Infrared Photometer The Model 514 near-infrared photometer provides continuous on-line analysis of specific near-infrared absorbing com- pounds with an accuracy matching that obtained in the laboratory. This elimi- nates the time lag between sample collec- tion and analysis. One of the most fre- quent applications for the Model 514 is monitoring low ppm water at various stages of manufacturing and processing chemicals, for corrosion prevention and quality control. The Model 514 also moni- tors hydroxyl value, unreacted epoxides and other parameters in the manufacture of polyether polyols. Teledyne Analytical Instruments, The Harlequin Centre, Southall Lane, South- all, Middlesex UB2 5NH. Infrared Microspectroscopy System The Nic-Plan research-grade infrared microscope utilizes the View Thru Pro- jected Aperture Masking System, which permits the entire sample image to be viewed simultaneously while positioning the apertures for infrared sampling.This makes viewing, infrared analysis and photomicrography of the sample a logical, flowing process, since the apertures do not block the view of the surrounding Pulsed Electrochemical Detector The Dionex pulsed electrochemical detector (PED) combines superior con- ductivity and amperometry capability in one unit, making it a powerful detection scheme for non-chromophoric com- pounds. Compounds detected by PED with high sensitivity and specificity include inorganic anions and cations, organic acids, amines (including quater- naries), carbohydrates, oligosaccharides from glycoproteins, glycosidic drugs, alcohols, aldehydes, thiols and sulphides.For method development on any ion chromatograph or high-performance liquid chromatograph, PED complements UV to form a nearly universal detection scheme. In addition to pulsed conductiv- ity and amperometry modes, PED measurement capabilities include cyclic voltammetry, d.c. amperometry, pH and temperature. A brochure is available. Dionex Corporation, P.O. Box 3603, Sunnyvale, CA 94088-3603, USA. Amino Acid Analysis Module The module combines state of the art HPLC instrumentation with post-column ion-exchange amino acid analysis. It includes all hardware, columns, reagents and eluents needed to convert a commer- Nicolet Nic- Plan infrared microscope sample area.The Nic-Plan, interfaced with a high-performance Nicolet FTIR spectrometer, provides a system for com- bining microscopic imaging with infrared spectroscopy and chemical analysis. An optional Contour display processing package allows one to set up a mapping routine on the FTIR data station, collect the map set of spectra and then display and plot the processed data. Nicolet Instrument Corporation, Bud- brooke Road, Warwick CV34 5XH. cia1 HPLC system into an analyser specific for amino acids in protein and collagen hydrolysates, as well as complex samples such as cell culture media and fermenta- tion broths, and physiological fluids, including blood, urine and cerebrospinal fluid. The fully assembled module includes a post-column analysis module, temperature controller and post-column reactor, plus guard and analytical col- umns.Pickering Laboratories, 1951 Colony Street, Suite S, Mountain View, CA 94043, USA. Amino Acid Analyser The HP AminoQuant Series I1 analyser resolves all amino acids found in proteins along with two internal standards. Offer- ing a comprehensive guarantee on results, it is available both with computer con- troller and in a lower-priced version without computer but with the same separation performance. Hewlett-Packard SA, 150 Route du Nant-d’ Avril , CH- 12 17 Meyrin (GE) 2, Switzerland. Automatic DNA Sequencing Film Reader Autoreader, a new maximum throughput automated DNA sequencing film reader, is now exclusively available from Beck- man. Output generated by this instrument can be saved on floppy disk for use with sequence analysis software such as Beck- man’s MicroGenie and Amersham’s (the makers of Autoreader) Staden-Plus.(MicroGenie is a registered trademark of SciSoft Inc., and the sequence analysis program is licensed for exclusive distribu- tion by Beckman.) Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. Oxygen Analyser The Model 326R per cent. oxygen ana- lyser provides reliable on-line monitoring of a wide range of gases and gas mixtures. Full-scale measuring ranges are available from 0-1% to &loo%; for hyperbaric applications, ranges up to 10 bar oxygen partial pressure can be provided. The Model 326R is available in a weather resistant bulkhead mounted housing or in a panel mounted housing for use in general purpose (non-hazardous) areas.Explosion-proof and intrinsically safe ver- sions can also be provided; certain models feature CENELEC approval. Teledyne Analytical Instruments, The Harlequin Centre, Southall Lane, South- all, Middlesex UB2 5NH. Differential Amplifier for Titrations Non-aqueous titrations often suffer severe interference from static charges. With the Metrohm differential amplifier even these titrations can be run and evaluated faultlessly. The electronic cir- cuitry eliminates the disturbances of the indicator and reference electrode. The device is so small that it can be inserted in the electrode socket. It fits all sockets conforming to DIN 19 262.86 ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 V. A. Howe and Co.Ltd., Beaumont Close, Banbury, Oxfordshire OX16 7RG. Balances The range of FX balances has been extended by the inclusion of the FX400 and FX4000, which are extremely accu- rate and offer eleven measurement units, including grams, carats, pounds and ounces. Both balances are equipped with the makers’ ACAI counting function, which continuously re-establishes the average unit weight, while the percentage function makes ovedunder weighing a very simple process. The FX400 has a capacity of 410 g x 0.001 g and the FX4000 a capacity of 4100 g x 0.01 g. Salter Industrial Measurement Ltd. , George Street, West Bromwich, Birming- ham B70 6AD. Ultracentrifuge The Centrikon T-2100 ultracentrifuge’s data analysis and management system (DAMS) has versatile, fully separated software modules for remote control, centrifuge and rotor history data manage- ment, dynamic drive/rotor field testing and centrifugation run simulation and calculation.With the Centrikon reprodu- cibility is the keyword. For sharper sep- aration and better results it has an improved drive with inbuilt imbalance tolerance. It also features a slow start mode with automatic rate control for smooth acceleration. It will accept a variety of rotors, both continuous flow and zonal rotors as well as the new low mass carbon fibre vertical rotors, which give precise, rapid separations in biotech- nology applications. A water vapour purging vacuum system promotes high level reproducibility. Kontron Instruments Ltd., Blackmoor Lane, Croxley Centre, Watford, Hert- fordshire WD1 SXQ.Sample Recovery System The Gyrovap is a complete sample recovery system which improves concen- tration of samples from organic, aqueous, acidic or alkaline liquids. It comes com- plete with cold trap for vapour capture and vacuum pump. Many samples can be concentrated simultaneously and the system is suitable for protein, enzyme, DNA, insecticide, pesticide and salt recovery amongst other applications. It can recover up to 99% of sample with no cross-contamination. V. A. Howe and Co. Ltd., Beaumont Close, Banbury, Oxfordshire OX16 7RG. Sample Handling Facility An advanced sample handling facility designed with laboratory safety, cost sav- ings and efficiency in mind combines the benefits of primary tube sampling, LED bar-code scanning and Synchron Interlink System Director.Intended for use with new or upgraded Synchron AS, CX3, CX4 and CX5 clinical systems, it can streamline the laboratory’s sample input procedures and record keeping. The system handles up to four sizes of blood collection tube and recognizes the stan- dard versions of Code 39, Codabar, Code 128 and Interleaved 2 of 5 bar codes, Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. Autosampler The System Gold Model 502 autosampler is particularly suited to routine applica- tions. It features filled-loop injection vol- umes from 10 to 2000 p1 and can inject from 92 2 ml vials with four additional 2 ml vials used as needle-wash fluid con- tainers. When driven by a System Gold Sample Table, vials can be accessed directly for efficient calibration and analy- sis.Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. Glass Filter Housings Glass filter housings designed for filtra- tion applications requiring non-metallic contact of filtered fluids are fabricated entirely of transparent , tempered borosil- icate glass and are compatible with aggressive solutions. Two models are offered. The GPTX Series consists of a housing held together by a flange, allow- ing access to the filter element; it can be plumbed direct into existing conical glass pipelines. The GPTN Series consists of a Ceratrex controlled porosity ceramic ele- ment with a nipple end adaptor for suction hose connections. Osmonics Inc., 5951 Clearwater Drive, Minnetonka, MN 55343, USA. Microbiological Bunsen Burner The Flam-o-matic burner is ideal for the microbiologist. It operates without pilot light and the flame is provided only when required.Gas sensing electronics avoid gas leaks. A brochure is available. International PBI, Via Novara 89, 20153 Milan, Italy. Networking and Automation Capabilities for ChemStations The new ChemLAN software/hardware package integrates HP ChemStations (both Pascal and HP-UX series) into the HP Unified Laboratorv. Manv tvDes of analytical instrument can be incorporated into a network that uses the Pascal series HP ChemStation to acquire data that are processed by the HP-UX series HP ChemStation, automating many data handling routines to increase throughput and laboratory productivity. Hewlett-Packard SA, 150 Route du Nant-d’Avril, CH-1217 Meyrin (GE) 2, Switzerland.Laboratory Information Management Perkin-Elmer Ltd. has combined with BBN, Digital Equipment Co., SAS and Oracle to integrate the new P-E Nelson SQL*LIMS product with a range of third party software packages. Information from various sources can be integrated using Compound Document Architecture (CDA). Data can be imported from SQL*LIMS in report form, or directly from the underlying ORACLE tables, from chromatography data handling packages such as P-E Nelson’s ACCESS*CHROM, and as graphical images from SAS and RS/1. Use of the live-link facility allows the automatic update of any component. The final document combines varying types of information in an easily designed format which is simple to understand.Perkin-Elmer Ltd. , Maxwell Road , Beaconsfield , B uckinghamshire HP9 1QA. Optical Attenuator The Model 720 compact and lightweight optical attenuator unit provides both vari- able and stepped attenuation and is so designed that its inherently high accuracy is maintained during operation. It can be used at wavelengths of both 1300 and 1550 nm. Features include an I/O crosstalk of 70 dB, insertion loss not exceeding 3.5 dB, and an operational temperature range from 0 to +40°C. Hakuto International (UK) Ltd. , Eleanor House , 33-35 Eleanor Cross Road, Waltham Cross, Hertfordshire EN8 7LF. Containment Pack The Whatman Spill Containment Pack contains all that is needed to deal with most laboratory spillages: large porous sleeves containing sorbent material (booms) that will contain and absorb spreading liquids, compact booms and loose sorbent fibre that can be used for mopping up, plastic bags for safe disposal of all contaminated material, a scoop and a pair of nitrile gloves.Whatman Scientific Ltd. , Springfield Mill, Maidstone, Kent ME14 2LE. 3-D Molecular Graphics The IBM 386 PC is now supported as a 3-D graphics window for distributed molecular modelling. 3-D GKS windows have been develoDed for use with Chem-ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 87 ical Design’s Chem-X molecular model- ling software. All graphics calculations are offloaded to the IBM 386 PC, while computer-intensive calculations are per- formed on the VAX server or UNIX workstation. The system is ideal for small molecule modelling in drug design appli- cations, providing real-time 3-D manipu- lation of shaded structure displays and property plots.Chemical Design Ltd., Unit 12, 7 West Way, Oxford OX2 OJB. Molecular Modelling Oxford Molecular, which develops and markets computer software for the mol- ecular sciences, is the first company set up by the Oxford University technology trans- fer unit. It has now joined Sun Micro- systems’ Catalyst programme of third- party suppliers. Oxford Molecular’s pro- ducts available on Sun comprise: ASP, which identifies similarities between molecular structures and how they will interact with a receptor; COBRA, a 3-D structure predictive and conformational analysis package; and CONSTRICTOR, a distance geometry package for structu- ral analysis and docking. PIMMS, a graphical interface to these three pack- ages, will soon be available on Sun.Sun Microsystems Ltd., Watchmoor Park, Riverside Way, Camberley , Surrey GU15 3YL. Chemical Structures Database The chemical structures database, Phar- mastructures, is now available in a format compatible with Molecular Design Ltd.’s Chembase System, in addition to PSI- DOM software. Pharmastructures is a PC-based database with state of the art chemical structure search and display facilities. It contains approximately 4000 structures, is updated monthly and caters for anyone interested in the chemistry of drugs in research and development. Pharmaproducts Information Services, 18-20 Hill Rise, Richmond, Surrey TWlO 6UA. New Version of Pro-Search Software Pro-Search search-aid software is now available for the Macintosh, Version 1.1.Pro-Search is designed for easier and less expensive searching on DIALOG and is part of the makers’ complete line of desktop research products, which include Pro-Cite and Biblio-Links. Personal Bibliographic Software Inc., P.O. Box 4250, Ann Arbor, MI 48106- 4250, USA. Literature A new atomic spectroscopy supplies cata- logue briefly outlines different techniques and systems and covers all the accessories and supplies required. Perkin-Elmer Ltd., Maxwell Road, Beaconsfield, Buckinghamshire HP9 1QA. A brochure describes a wide range of products for environmental analysis. Among the topics covered are inorganic analysis using chemically suppressed ion chromatography, metals using IC and IC-ICP, and organics analysis by HPLC, IC and SFC.Also included is a discussion of improved extraction speed and effi- ciency using supercritical fluid extraction. Dionex Corporation, P.O. Box 3603, Sunnyvale, CA 94088-3603, USA. A brochure gives details of the lamps available for HPLC detectors. Deuterium, mercury, xenon, zinc, cad- mium and tungsten lamps are available for virtually all HPLC detectors used. HPLC Technology Ltd., Wellington House, Waterloo Street West, Maccles- field, Cheshire SKll 6PJ. A brochure describes a new gas-chroma- tography column designed to analyse optical isomers. It illustrates the separ- ating power of the Cyclodex-B column with chromatograms of ginger oil, synthetic apple essence, menthol and several other compounds. J and W Scientific, 91 Blue Ravine Road, Folsom, CA 95630, USA.An information bulletin from Metrohm, ‘New Opportunities in Ion Chromato- graphy’, gives details of the Ion Chroma- tograph 690, as well as applications and literature references. It also contains details of the 691 pH meter. V. A. Howe and Co. Ltd., Beaumont Close, Banbury, Oxfordshire OX16 7RG. The new Waters Chromatography Col- umns and Supplies price list includes applications and column selection guides as well as many new products. Waters Chromatography Division, Mil- lipore (UK) Ltd., The Boulevard, Black- moor Lane, Watford WDl SYW. A booklet gives details of techniques and applications of thermal desorption-gas chromatography systems. Applications presented include flavours and fragrance analysis, environmental monitoring of atmospheric pollution and monitoring of volatiles in water and sediment. Perkin-Elmer Ltd., Maxwell Road, Beaconsfield, Buckinghamshire HP9 1QA. Information is given on micropipettes, dispensers and accessories in a liquid handling products brochure. Camlab Ltd., Nuffield Road, Cam- bridge CB4 1TH. Designed as both a technical and sales reference guide, the Dage Clean Room catalogue provides information on a full range of clean room equipment. Dage (GB) Ltd., Rabans Lane, Ayles- bury, Buckinghamshire HP19 3RG. New notification and marking require- ments affecting sites on which hazardous substances are stored are outlined in a free Health and Safety Executive leaflet. The leaflet, in the form of a checklist, is a brief guide to the requirements of the Dangerous Substances (Notification and Marking of Sites) Regulations 1989. HSE Information Centres. A brochure catalogues imaging detector products and provides a detailed insight into imaging technology. Instrument Technology Ltd., 29 Castle- ham Road, St Leonards-on-Sea, East Sussex TN38 9NS. A range of high-performance ultrasonic baths is described in a brochure, which also gives details of accessories. Camlab Ltd., Nuffield Road, Cam- bridge CB4 1TH. A brochure, ‘Fishing for New Ideas?’, gives information on a range of US and European patent databases. Micropatent, Cambridge Place, Cam- bridge CB2 1NR.

ISSN:0144-557X    

DOI:10.1039/AP9912800085

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 Analytical Division Distinguished Service Award 87 Nominations are invited for the Division's Division of The Royal Society of Distinguished Service Award, the Rules exceptional voluntary service over a Chemistry (including that to the for which are as follows: Society for Analytical Chemistry). 1. The aim of the Award is to recognize period of years to the Analytical88 ANALYTICAL PROCEEDINGS. MARCH 1991, VOL 28 2. The Award shall normally be in the form of an illuminated address which may be accompanied by such additional recognition as Council of the Division shall agree. invited annually from members of Council of the Division, and may be received from any member of the Division. They shall be made in 3. Nominations for the Award will be 4. writing, with supporting evidence, to the President of the Analytical Division, The Royal Society of Chemistry, Burlington House, London, W1V OBN. Nominations shall be considered by the Honours Committee of the Analytical Division, which shall recommend to Council of the Divi- sion ( a ) to whom an award should be made, ( b ) the nature of the award or (c) that no award should be made. 5. The Award shall be made by the Council of the Analytical Division, which must approve any alteration of these Rules. Nominations for the Award should be sent to the President of the Analytical Division before March 28th, 1991.

ISSN:0144-557X    

DOI:10.1039/AP9912800087

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

88 ANALYTICAL PROCEEDINGS. MARCH 1991, VOL 28 IUPAC Recommendations IUPAC has recently made available for terms. They have been harmonized with obtained on request from Dr. Alan public comment a document on nomen- other previously published IUPAC docu- McNaught, The Royal Society of clature of kinetic methods of analysis. The ments. Chemistry, Thomas Graham House, report lists, in alphabetical order, names IUPAC welcomes comments on these Science Park, Milton Road, Cambridge and definitions of the 41 terms most definitions prior to the production of a CB4 4WF. In order that comments may widely used. These include kinetic, dif- definitive version for publication in Pure be considered by IUPAC, they should be ferential-kinetic, catalytic and enzymic Appl. Chem. Copies of the text may be received by October 31st, 1991.

ISSN:0144-557X    

DOI:10.1039/AP991280088b

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 89 Conferences and Meetings 1991 International Symposium on Radon and Radon Reduction Technology April 2-5, 1991, Philadelphia, Pennsylvania, USA This Symposium is sponsored by the US En- vironmental Protection Agency, Air and En- ergy Engineering Research Laboratory, the US Environmental Protection Agency, Office of Radiation Programmes and the Conference of Radiation Control Programme Directors (CRCPD) Inc. The sessions will be on: Gov- ernment Programmes and Policies Relating to Radon; Radon Related Health Studies; Meas- urement Methods; Radon Reduction Meth- ods; Radon Entry Dynamics; Radon Surveys; State Programmes and Policies Relating to Radon; Radon Prevention in New Construc- tion; Radon Occurrence in the Natural Envi- ronment; and Radon in Schools and Large Buildings.For further information contact Pat Heightchew, CRCPD, 205 Capital Avenue, Frankfort, KY 4060 I , USA. 16th International Conference on Coal and Slurry Technologies April 22-25,1991, Clearwater, Florida, USA Current technological developments will be featured in ninety technical papers covering Atomization and Combustion, Coal Prepara- tion and Beneficiation, Demonstrations and Evaluations, Direct and Indirect Coal Lique- faction, Materials and Equipment, Pipeline Technology, Rheology, Characterization and Preparation and Small Scale Applications. In- dustry leaders from 11 countries (Australia, Bulgaria, Canada, France, Germany, Great Britain, Italy, Japan, People’s Republic of China, Soviet Union and United States) will offer presentations on the state of the art of coal and coal liquid technologies. Additional details can be obtained from the Coal and Slurry Technology Association, 1156 Fifteenth Street N.W., Suite 525, Wash- ington, DC 20005, USA.Control and Instrumentation Exhibition May 21-23,1991, Birmingham A comprehensive range of high technology products suitable for use in laboratories and research institutions and ranging from sen- sors to systems for measuring, monitoring or controlling liquids, gases, solids and all other physical variables will be well represented at this year’s Control and Instrumentation Ex- hibition at the National Exhibition Centre (NEC), Birmingham. Important themes at the exhibition will be the development of the automated laboratory and whether analysis should be carried out on-line or in the labora- tory.A conference on Environmental Protec- tion, Control and Monitoring, organised by the European Region of the Instrument So- ciety of America (ISA), will be another new attraction that will run alongside the 1991 C&I. Topics to be covered at the conference will include: EC environmental legislation, initiatives and programmes; challenges for industry of increased environmental aware- ness; the challenge of technology and future trends in markets; and technologies that will be created by an increasing environmental awareness. Further information about the Conference can be obtained from Alan Reeve on 08 1-3 16-3203. C&I is sponsored by the Institute of Measurement and Control, Britain’s interna- tionally-esteemed chartered professional body, and GAMBICA, the UK trade associ- ation for manufacturers of instrumentation, control and automation equipment.Further information can be obtained about C&I Ex- hibition from the Exhibition Manager, Tony Thompson, at MGB Exhibitions Ltd., Mar- lowe House, 109 Station Road, Sidcup, Kent DA15 7ET. Chemical, Biochemical and Environmental Fibre Sensors I11 September 3 6 , 1 9 9 1 , Boston, MA, USA The use of optical fibres for remote spectros- copy predates the use of fibres in communi- cations systems and continues to be an important technique in environmental, bio- medical, and process-control sensing. Recent progress in fibre optic chemical sensing, in- cluding the development of opt(r)odes, intrin- sically sensitive fibres, and sensors based on integrated optic devices, has greatly ex- panded the range of application of chemical and environmental fibre optic sensors, as has the use of such techniques as Raman and Fourier transform infrared (FTIR) in remote fibre spectroscopy.Fibre optic and planar waveguide sensors are now used in chemical analysis laboratories, environmental monitor- ing applications, the control of chemical pro- cesses, vehicles, critical medical applications, and industries ranging from heavy manufac- turing to food processing. The organizers wish to encourage submis- sions from chemical, biochemical and optical researchers and engineers in government, in- dustry and academia. Presentations in the form of 18 minute talks or posters will be considered.Papers addressing these topics will be solicited: fibre refractometry and spectroscopy (including Raman and FTIR); intrinsic and disturbed chemical sensors; inte- grated optic and planar waveguide sensors; chemical optrodes; evanescent- w ave fibre optic sensors; fibre optic gas sensors; and new materials and techniques for sensing. Typical application areas include: chemical process control; water and air quality moni- toring; building control and safety; process- control sensing for biotechnology; food pro- cessing and quality control; chemical sensors for aerospace applications. For further information contact SPIE, P.O. Box 10, Bellingham, Washington 98227- 0010, USA. First Congress of UK Biotechnology September 24-2 7,1991, Leeds The venue for both the technical sessions and the trade exhibition of this meeting will be centred on Leeds University’s new exhibition complex which is situated within easy walk- ing distance of the City Centre. Symposia will be held in the adjoining Playhouse theatre, and in the Medical and Dental lecture theatres.Rooms are available for other meet- ings and workshops. The provisional programme is divided up as follows. Symposium S l , Antibody Tech- nology: Catalytic Antibodies, Professor W.H. Stimson (University of Strathclyde); Immu- nosensors, Dr. S. Charles (Amersham Inter- national plc); Protein Engineering of Antibodies and Antibody Fragments, Profes- sor W.J. Harris (University of Aberdeen); Antibody Targeting, Dr. A. Epenetos (Ham- mersmith Hospital). Symposium S2, Animal Cell Technology: Culture Stress, Professor R.H.Burdon (University of Strathclyde); Genetic Engineering of Animal Cells, Dr. C. MacDonald (University of Strathclyde); Ani- mal Cell Bioreactors-Design and Perfor- mance, Dr. B.J. Griffiths (CAMR, Salisbury); Therapeutic Products from Mammalian Cells, Dr. J.R. Birch (Celltech Ltd., Slough). Sym- posium S3, Genetic Disease-Diagnosis and Gene Therapy: DNA-the Best Diagnostic Reagent?, Professor A.D.B. Malcolm (Char- ing Cross and Westminster Medical School); Genetic Disease: Diagnosis and Gene Ther- apy, Dr. K. Johnson (Charing Cross and Westminster Medical School); Diagnostic Gene Probes (Dr. N. Kalsheker (University of Wales); The Impact of Recombinant DNA Technology on Diagnosis and Management of Blood Diseases, Dr.L. Luzzatto (Hammer- smith, Hospital). Symposium S4, Glycosyl- ation and Recombinant Glycoproteins: Glycobiology: Concepts, Technology and the Future, Professor R. Dwek (University of Oxford); The Relevance of Glycosylation to the Production of Recombinant Glycopro- teins, Dr. R. Parekh (Oxford Glycosystems Ltd.); Glycosylation and Recombinant Gly- coproteins, Dr. G. Yarranton (Celltech); The Expression of Recominbinant ELAM Recep- tors, Dr. J.M. Devine (British Biotechnology Ltd., Oxford). Symposium S5, Protein En- gineering: Application of Protein Engineering to Insulin for Therapy, Professor G. Dodson (University of York); Crystallography in Pro- tein Engineering, Professor B.W. Matthews (University of Oregon, USA); Engineering of Chloramphenicol Acetyltransferase and its90 ANALYTICAL PROCEEDINGS, MARCH 1991, VOL 28 Substrates, Professor W.V.Shaw (University of Leicester); The Design of Proteins, Dr. J. Thornton (Birkbeck College, London). Sym- posium S6, Biosensors: Amperometric Biosensors, Professor I.J. Higgins (Cranfield Institute of Technology); Real-time Estima- tion of Microbial Biomass by Dielectric Spectroscopy, Dr. D.B. Kell (University of Wales); Enzyme-based Optical Biosensors, Dr. O.S. Wolbeis (University of Graz, Aus- tria); Bioelectronics-Techniques and Possi- bilities, Dr. P. Connolly (University of Glasgow). Symposium S7, Biotransforma- tions: Production of Novel Chiral Synthons by Industrial Biocatalysis, Dr. C.T. Evans (Enzymatix Ltd., Cambridge); Enzymes in Novel Carbohydrate Synthesis, Dr.N.J. Tur- ner (University of Exeter); Enzymes in Or- ganic Synthesis, To be announced; Biotransformations for the Flavour and Fra- grance Industry, Dr. P.S.J. Cheetham (Unilever Research, Bedford). Symposium S8, Food Bioprocessing: Food Biotechnol- ogy : the Engineering Challenge, Professor D.L. Pyle (Food Technology Centre, Univer- sity of Reading); Design Considerations for a Fermented, High-protein Beverage Process, Dr. J. Adler-Nissen (University of Lyngby, Denmark); Novel Bioconversions, Dr. B. Law (Institute of Food Research, Reading); The Biotechnology of Probiotics, Professor J. Smith (University of Strathclyde). Sympo- sium S9, Biodegradation of Industrial and Other Wastes: Organometallics, Heavy Me- tals and Radionuclides, Dr. G.M. Gadd (University of Aberdeen); 'Liquids' in Biode- gradation of Industrial and Other Wastes, Dr.J. Wyatt (Viridian Bioprocessing Ltd., Kent); Soils, Dr. J.F. Rees (Cardiff); The Degrada- tion of Organohalides, Dr. T. Marks (CAMR, Salisbury). Symposium S 10, Bioprocess Control: Feed-forward Control of Feed-batch Processes, Professor D.E. Brown (Cranfield Institute of Technology); Modelling Human Intelligence for Fermentation Supervision, Professor A. J. Morris (University of New- castle-upon-Tyne); Image Analysis for Con- trol of Fungal Fermentations, Dr. C.R. Thomas (University of Birmingham); State Variable Estimations, Dr. N. Thornhill (University College of London). Symposium S 11, Downstream Processing: Large Scale Chromatography Improving its Performance, Professor J.A. Howell (University of Bath); Developments in Affinity Chromatography, Dr.C.R. Lowe (University of Cambridge); Blood Plasma Fractionation, Dr. P.R. Foster (Protein Fractionation Centre, Edinburgh); The Control of Protein Purification Pro- cesses, Dr. M. Hoare (University College of London). Symposium S 12, Molecular Biol- ogy of Plasmid Vectors for Genetic Manipu- lation: Promiscuous Plasmids as Tools for Genetic Manipulation, Dr. C.M. Thomas (University of Birmingham); Biology of Plas- mid Vectors for Gram Positive Bacteria, Dr. S.D. Ehrlich (Institut de Biotechnologie, France); The Biology of Plasmid Vectors in Streptomyces, Dr. H. Richards (University College London); Molecular Biology of Yeast Plasmids (Dr. A. Cashmore (University of Leicester). Symposium S 13, Genetic Manipulation of Secondary Metabolic Pro- duction: Analysis and Manipulation of Genes for Polyketide Biosynthesis in Streptomyces, Professor D.A.Hopwood (John Innes Centre for Plant Research, Norwich); The Link be- tween P-Lactams and Other Peptide Anti- bodies, Dr. H. von Dohren (Technical University, Berlin); Mechanisms and Mole- cular Biology of Tetrapyrrole Biosynthesis in Escherichia Coli, Professor P.M. Jordan (University of London); Anthocyanin Pro- duction in Higher Plants, Dr. C. Martin (John Innes Centre for Plant Research, Norwich); Symposium S14, Genetic Manipulation of Crop Plants-Novel Approaches to Delete Existing Characters or Add New Ones: De- velopment of a Selection for Homologous Genetic Recombination in Plants, Dr. C. Lichtenstein (Imperial College of Science and Technology, London); Controlling Ethylene Synthesis and Ripening With Antisense Genes, Professor D.Grierson (University of Nottingham); Genetic Trans- formation to Confer Virus Resistance, Dr. R.N. Beachy (Washington University, St. Louis, USA); Manipulation for Pest and Dis- ease Resistance, Dr. V.A. Hilder (University of Durham). In order to register for the Congress or Poster Sessions, please complete an Applica- tion Form and send it together with your cheque to The Conference Department, SCI, 14/15 Belgrave Square, London SW 1 X 8PS. Inmedtec '91 September 24 - October I , 1991, Kiev, USSR NOWEA International will be organising IN- MEDTEC '91 in Kiev in collaboration with the Ukrainian Chamber of Trade and Com- merce, Ukrexpo, as well as the Ukrainian Health Ministry.The Health Fair INMED- TEC '91 caters especially to the requirements in the Ukraine, the second largest republic in the Soviet Union with 52 million inhabitants. It is being staged at the express wish of the Ukrainian Health Ministry which intends to give the event tremendous support. The specialist exhibition with interna- tional participation will showcase a wide range of products, embracing all areas con- cerning equipment for hospitals, nursing homes, and spas as well as the subject of oc- cupational health. At the Trade Fair complex in Kiev, the specialist audience will be given the opportunity to see electromedical devices and systems, medical instruments and sys- tems, room facilities for nursing homes, as well as supply and disposal devices. Please contact NOWEA International GmbH, Mr.Axel Steller, Tel. 021 1-4560-792. Thirteenth International Symposium on Polynuclear Aromatic Hydrocarbons October 14,1991, Bordeaux The Bordeaux meeting will be the first PAH Symposium which is being held in Europe. The first ten Symposia in the series were held at the Battelle Columbus Laboratories on an annual basis beginning in 1975. In 1987 it was decided that the meeting would be held on a biannual basis and that the headquarters would be moved to the National Institute of Standards and Technology. The Thirteenth International Symposium on Polynuclear Aromatic Hydrocarbons is being organized by the Groupe Francais Polyaromatiques and will be sponsored by the University of Bor- deaux I, the Centre National de la Recherche Scientifique, the commission of the European Communities, along with several private companies.The 1991 meeting will focus on intense disclosure of state-of-the-art research results on the chemical properties and biological ef- fects of polynuclear aromatic hydrocarbons. It will include presentations on parent PAH, PAH metabolites, heteroatomic species and PAH derivatives including amino, nitro and halogen substituted compounds. Further details are available from Dr. Ph. Garrigues, Universite de Bordeaux I, U.R.A. CNRS 348, 351, Cours de la Liberation, F 33405 Talence, France. 1991 FACSS/Pacific Conference October 6-11,1991, Anaheim. CA, USA The Eighteenth Annual Meeting of the Feder- ation of Analytical Chemistry and Spectros- copy Societies and The Thirteenth Pacific Conference on Chemistry and Spectrochem- istry will be held at the Disneyland Hotel and Convention Centre, Anaheim, California.This joint meeting will provide a programme of expanded technical coverage with an em- phasis on emerging technologies in analyti- cal, spectroscopic, chemical and biochemical sciences. Contributed papers are solicited in a number of subject areas. To contribute a presentation of original research, complete a title submission form and return it with a 100 word brief by March 15, 1991. Submitted papers will be given as either 20 minute talks or presented in poster sessions. Upon accept- ance of your submission, final abstract ma- terials and instructions will be sent to you prior to May 1, 1991.Final acceptance of your presentation is contingent upon receipt of your 250 word final camera ready abstract by June 1, 1991. The instrument exhibit is one of the most useful and exciting components of the con- ference and is designed to complement the scientific program. The 19 000 square foot exhibition area can accommodate 1 I5 booths and is also the primary gathering place for many of the social events associated with the conference. For forms and other information contact FACSS, P.O. Box 278, Manhattan, KS 66502, USA. 9th International Symposium on Prep- arative and Industrial Chromatography April 6 3 , 1 9 9 2 , Nancy. France The symposium, which will be in the PalaisANALYTICAL PROCEEDINGS. MARCH 1991. VOL 28 91 des Congres, Nancy, aims to reflect the most and optimization, including new stationary tions. An exhibit of modern instrumentation recent progress in Preparative and Industrial phase developments; process integration and will be organized. Chromatography with Gas, Liquid or Super- cost estimation; and applications and devel- For further information contact PREP 92 critical Eluents. Among the topics discussed opment case stories. The Symposium will Secretary, ENSIC-LPCI, 1 , rue Grandville, will be: modelling and simulation of the take place over 3 days. The programme will B.P. 45 1, F-54001 Nancy Cedex, France. physicochemical interactions between sta- include plenary lectures (45 min), oral com- tionary and mobile phases; equipment design munications (20 min) and poster communica-

ISSN:0144-557X    

DOI:10.1039/AP9912800089

出版商:RSC    

年代:1991

数据来源: RSC