摘要:

ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 1 Analytical Viewpoint ~~ The following is a member of a continuing series of articles providing either a personal view of part of one discipline in analytical chemistry (its present state, where it may be leading, etc.), or a philosophical look at a topic of relevance to chemists in general or analytical chemists in particular. These contributions need not have been the subject of papers at Analytical Division Meetings. Persons wishing to provide an article for publication in this series are invited t o contact the editor of Analytical Proceedings, who will be pleased to receive manuscripts or to discuss outline ideas with prospective authors. ~~ ~ Coprecipitation of Silver From Sea-water With Mercury(l1) Sulfide and Determination by Electrothermal Atomic Absorption Spectrophotometry Michael N.Quigley" and Frederick Vernon Department of Chemistry and Applied Chemistry, University of Salford, Salford M5 4 WT The coprecipitation of trace metals in fresh waters with sulfides is a popular method of concentration prior to analysis.' A survey of the literature has revealed, however, that sulfides have not been widely used in the trace metal analysis of sea- water, although their extreme insolubility makes them ideal for coprecipitation methods. A more popular gathering agent is hydrated iron(II1) oxide, which is effective for concentrating many divalent cations from sea-water. It has been shown, however, that silver cannot be collected by this m e t h ~ d . ~ - ~ Recently, tetrahydroborate reductive pre~ipitation,~ solvent extraction with dithizone ,5 and chelating ion exchange6 have been shown to be effective for the preconcentration of silver from sea-water prior to its determination by atomic absorption spectrophotometry .All of these techniques are labour inten- sive, however, so the relative ease with which silver can be coprecipitated with mercury(I1) sulfide should be of interest to those workers desiring a rapid and quantitative recovery of silver prior to analysis by electrothermal atomic absorption spectrophotome try. Matsuzaki and Zeitlin made a number of recommendations relating to the use of mercury(I1) ~ u l f i d e . ~ These included adding mercury(I1) chloride solution to the sample before the sulfide reagent to achieve a final concentration of 240 mg 1-' of Hg2+.A concentration of 250 mg 1-1 of Hg2+ was adopted for much of the present work, having first established that higher concentrations did not significantly improve the recovery of silver from solution. A lower concentration of mercury in solution heated to 70 "C results in significant improvements in recovery for certain other metals.2 In addition, the pH should be controlled so that it does not exceed pH 10, otherwise precipitation of Mg(OH)* occurs. Magnesium hydroxide can be used itself as an internal carrier, but filter clogging problems may be come apparent. Thiourea was chosen to act as precipitant for the following experiments. Addition of thiourea to a solution of mercury(I1) chloride results in the formation of a fine white precipitate of mercury thiochloride after a few minutes stirring.The colour changes to yellow, then yellowish-brown, due to the inter- mediate formation of a mixed crystal, mercury sulfide chloride. The transformation to black mercury(I1) sulfide is * Present address: Department of Chemistry, Chevron Science Center, University of Pittsburgh, Pittsburgh, PA 15260, USA. complete when excess sulfide reagent is used. After the precipitate has settled, options for its separation include filtration,*,' flotation7 and decantation. In this work, mem- brane filters were used. Flame atomic absorption analysis showed that >99% mercury could be recovered by this means.* On addition of 250 mg I-' mercury(I1) reagent, less than 1 pg 1-' of silver contained in sea-water was to be concentrated by a factor of 10 times with a corresponding increase in the mercury concentration. By use of an Instrumentation Labora- tory 351 atomic absorption spectrophotometer, an IL 555 graphite furnace and pyrolytic graphite cuvettes, the highest sensitivities for silver were obtained using the six stage temperature programme shown in Table 1.Instrument con- Table 1 Temperature programme used for analysis of silver. Nitrogen flow rate = 7.5 1 min-' Dry Ash Atomize Time/s 20 25 15 15 0 5 TemperaturePC 75 100 250 300 1800 - * * Start of signal integration. ditions for the IL 351 were set as follows: 328.1 nm wave- length, 5 mA lamp current, 1 nm bandpass. The double stage ash step was performed at a relatively low temperature (250- 300 "C) to ensure that mercury was removed with no covolatili- zation of silver prior to atomization.Ten microlitres of 2 pg 1-' silver(1) solution, in the presence of 250 mg 1-' of mercury, were injected into the furnace and analysed by using the method of standard additions. The sensitivity to silver was calculated to be 0.50 pg, which was the same as that obtainable by solution in 0.1 mol 1-' nitric acid.2 The silver concentration was calculated to be 2.32 pg l-', representing an accuracy of 16.0%. The precision for five analyses was calculated to be 2.6% relative standard deviation. Coprecipitation of Silver in Sodium Nitrate Solution In order to gain information on the reproducibility of the coprecipitation technique, three 1 pg 1-' Ag+ spiked solutions2 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 of 0.5 mol 1-' sodium nitrate and two blank (non-spiked) solutions were prepared according to a double precipitation technique.The following procedure was followed using analytical grade reagents: to 500 ml of 0.5 mol 1-' sodium nitrate solution 1 yg 1-' Ag+ and 250 mg 1-' Hg2+ were added; next 12 ml of 0.5 mol 1-1 thiourea solution were inserted, and the pH adjusted to 9 with ammonia solution. After heating to 70°C, and standing overnight, the solution was filtered through a 0.45 ym membrane filter. The filtrate was subjected to the precipitation procedure again. Then, after washing, the precipitates from the two preparations were dissolved with a 2+1 mixture of concentrated sulphuric and nitric acids, separately in one exercise and combined in another, to ascertain any benefit from sequential precipitation.The resulting solutions were diluted to 50 ml with distilled water. It was expected that most of the silver would be coprecipitated during the first precipitation of mercury(I1) sulfide, and that the second precipitation would coprecipitate negligible amounts of silver. The concentration step for mercury for each precipitation was ~ 1 0 , so that the actual concentration should have been 2500 mg 1-' of Hg2+ in separate solutions or double that in the solution containing the combined dissolved precipitate. The concentration step for silver was also x10, so the actual concentration could have reached 10 yg 1-1 of Ag+, assuming 100% coprecipitation and quantitative recovery. The mercury concentration in a solution repared from a single precipitation of HgS would be 1.5 x 10 times in excess of the theoretical silver concentration.A similar procedure was performed to prepare the blank solution. Some 2.5 + 7.5 dilutions were prepared for the determination of silver using electrothermal atomic absorption spectrometry, and the method of standard additions was employed (10 pl sample injection size). The results given in Table 2 show that an average 79% of silver was T: Table 2 Percentage recovery of 1 pg 1-' of silver in 0.5 mol I-' sodium nitrate solution by coprecipitation with mercury(I1) sulfide Duplicate Precipitation of HgS Blank A B 1st precipitation - 77.6 80.4 2nd precipitation - 0.0 2.4 Combined - 76.0 78.8 recovered from 0.5 mol 1-' sodium nitrate solution with a single precipitation of mercury(I1) sulfide.A further precipi- tation recovered a negligible amount of silver remaining. This was reflected in the analysis of the combined precipitates, which showed that an average 77% of Ag+ was recovered. In conclusion, a double precipitation technique would appear to be unnecessary. Coprecipitation of Silver in Stripped Sea-water Duplicate 11 batches of sea-water, previously stripped of metals using H+ form polyhydroxamic acid resin and NH4+ form Chelex-100 resin, were spiked with silver in order to obtain a concentration of 0.1 yg 1-' of Ag+. This concen- tration approximates to that found in the open ocean. Mercury(I1) solution was added to give a final concentration of 250 mg 1-1 of Hg2+, then 24 ml of 0.5 mol 1-l thiourea solution were added and the pH adjusted to 9 with ammonia solution.After heating to 70°C, and standing overnight, the solution was filtered through a 0.45 pm membrane filter. After washing, the precipitate was dissolved with a 2 + 1 mixture of sulphuric and nitric acids, and the resulting solution diluted to 50 ml with distilled water. The concentration step for both mercury and silver was x20, so the actual concentration should have been 5000 mg 1-' of mercury, and up to 2.0 yg 1-' of silver. The mercury concentration would be 2.5 x 106 times in excess of the maximum silver concentration. A similar procedure was performed to prepare the blank solution. Final solutions were analysed by the method of standard additions. Duplicate recoveries were 72.5 and 78.0%.Determination of Silver Concentration in Coastal Sea-water Sea-water was collected in acid washed, 20 1 polypropylene containers on a rainless day from the shore at Llanddulas (East and West beaches) and Abergele, North Wales. The method of Harvey," recommended by Martin," was used to determine the salinity. The figure of 33.15 parts per thousand obtained suggests that there was little influence by estuarial or meteoro- logical dilution. In addition, the pH was found to be 8.1. Before storage and subsequent silver determination, the sea- water was filtered through a 0.45 ym membrane filter and acidified to pH 2 with hydrochloric acid solution.12 The following single precipitation technique was duplicated by using analytical-grade reagents: 2.5 ml of 100 000 mg 1-' Hg2+ solution were pipetted into a beaker containing 1 1 of sea- water, stirred, and 24 ml of 0.5 mol l-' thiourea solution added. Ammonia solution was added to adjust the pH to 9.This solution was heated to 70 "C, and then left overnight. The final mercury concentration was 244 mg 1-l. The precipitate was filtered off by using a 0.45 pm membrane filter, and the HgS loaded membrane transferred to a 100 ml beaker, Next, 3 ml of a 2 + 1 mixture of concentrated sulfuric and nitric acids were added to dissolve the precipitate. This solution was finally diluted to 50 ml in a calibrated flask. The concentration step for mercury and co-precipitated silver was ~ 2 0 . In order to take account of any contamination during the addition of the mercury reagent and ammonia solution, blank solutions of the reagents in distilled water were also prepared.Solutions were analysed to determine silver by using the method of standard additions. Results corrected to take account of the 77% recovery of silver by mercury(I1) sulfide previously recorded are given in Table 3. Table 3 Concentrations of silver found in north Wales coastal sea- water (pg l-') Duplicate Sampling site A B Abergele 0.36 0.34 E. Llanddulas 0.32 0.29 W. Llanddulas 0.29 0.27 Conclusions The figures shown in Table 3 indicate a mean concentration of 0.31 pg 1-I of Ag+ in North Wales coastal sea-water. This value is an order of magnitude higher than those quoted by other workers for silver concentration in the same region. Kawabuchi and Riley used Deacidite FF-IP anion exchanger in the C1- form to preconcentrate silver from an unspecified area of the Irish Sea prior to neutron activation ana1y~is.l~ They obtained a figure of 0.04 yg 1-1 Ag+.Preston et al. reported the same concentration, found along the shoreline of the East Irish Sea during the 1970-71 MAFF survey.14 Interestingly, they noted that 'shoreline waters in the Irish Sea [had] . . . significantly higher concentrations [of trace metals] than offshore waters in the same area at the same time'. These figures agree with those obtained by the authors from a series of experiments involving passage of North Wales coastal sea- water through a column of NH4+ form Chelex-100. In this instance, silver was determined as being of concentration 0.053+0.009 pg However, such low values may not beANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 3 entirely accurate as the resin may suffer saturation by alkali and alkaline earth metals, and may also be dependent on other factors.l5 Riley et al. commented on the impracticability of pre- concentrating silver by using chelating ion exchange resins when they observed that although it could be quantitatively extracted, it was not possible to elute it quantitative1y.l6 This is in accordance with Riley and Taylor’s observation that 100% silver is retained by H+ form Chelex-100, but a maximum of 90% is eluted with 20 ml of 2 mol 1-1 nitric acid solution.” However, using Na+ form Chelex-100, Davey et al. found only 33% extraction of silver from artificial and natural sea-water.l8 Co-precipitation of silver with mercury(I1) sulfide obviates the difficulties encountered with such chelating resins, and is capable of providing an accurate figure for silver concentration in sea-water if used carefully. Editing and typing of the manuscript by Lisa A. Alzo is greatly appreciated. References Riley, J. P., Robertson, D. E., Dutton, J. W. R., Mitchell, N. T., and Williams, P. J. le B., in Chemical Oceanography, ed. Riley, J. P., and Skirrow, G., Academic Press, London, 2nd edn., 1975, vol. 3 , ch. 19, p. 281. Authors’ unpublished results. Nakashima, S., Sturgeon, R. E., Willie, S. N., and Berman, S. S., Anal. Chim. Acta, 1988, 207, 291. 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Mizuike, A., Enrichment Techniques for Inorganic Trace Analysis, Springer Verlag, New York, USA, 1983.Shijo, Y., Shimizu, T., andTsunoda, T., Anal. Sci., 1989,5,65. Samara, C., and Kouimtzis, T. A., Fresenius 2. Anal Chem., 1987, 327, 509. Matsuzaki, C., and Zeitlin, H., Sep. Sci., 1973, 8, 185. Erdey, L., Gravimetric Analysis Part 2, International Series of Monographs on Analytical Chemistry, Pergamon Press, 1965, pp. 57-62. Vassiliades, C. V., and Vasilikiotis, G. S., Microchem. J., 1969, 14, 7. Harvey, H. W., The Chemistry and Fertility of Sea Waters, Cambridge University Press, 2nd edn., London, 1957. Martin, D. F., Marine Chemistry, M. Dekker, New York, USA, 2nd edn., 1972, vol. 1, p. 89. Jones, K. C., Peterson, P. J., andDavies, B. E., Znt. J. Environ. Anal. Chem., 1985, 20, 247. Kawabuchi, K., and Riley, J. P., Anal. Chim.Acta, 1973, 65, 271. Preston, A., Jeffries, D. F., Dutton, J. W. R., Harvey, B. R., and Steele, A. K., Environ. Pollut., 1972, 3, 69. Paulson, A. J., Anal. Chem., 1986, 58, 183. Riley, J. P., Robertson, D. E., Dutton, J. W. R., Mitchell, N. T., and Williams, P. J. le B . , in Chemical Oceanography, ed. Riley, J. P., and Skirrow, G., Academic Press, London, 2nd edn., 1975, vol. 3, ch. 19, pp. 193-514. Riley, J. P., and Taylor, D., Anal. Chim. Acta, 1968, 40, 479. Davey, E. W., Gentile, J. H., Erickson, S. J., and Betzer, P., Limnol. Oceanogr., 1970, 15, 486. Gordon F. Kirkbright Bursary Fund This fund was established in 1985 as a memorial to Gordon Kirkbright and his contribution to analytical spectroscopy and to analytical science in general. The fund is administered by the Committee of the Association of British Spectroscopists and the ABS Trust; it aims to enable promising young scientists of any nation ( e . g . , postgraduate students or those in their first postdoctoral position) to visit a recognized scientific meeting or place or learning. In 1991, bursaries were awarded to H. Tan, a research student in Professor Montaser’s research group at George Washington University, and to Philip Riby, a postdoctoral research associate working in the US Department of Agriculture, BHNRC, Maryland. Both attended the XXVII CSI in Bergen and presented papers there. Applications are invited for the award of Gordon F. Kirkbright bursaries for 1992. Full details and application forms can be obtained from Professor W. 0. George, The Polytechnic of Wales, Pontypridd, Mid-Glamorgan CF37 lDL, United Kingdom. Telephone 0443-480480; Fax 0443-480558 (International: Phone +44-443-480480; Fax +44-443- 480558). Completed forms must be received not later than February 29th, 1992.

ISSN:0144-557X    

DOI:10.1039/AP9922900001

出版商:RSC    

年代:1992

数据来源: RSC

摘要:

ANPRDI 29(1) 1-40 (1992) Proceedings of the Analytical Division of The Royal Society of Chemistry Analytical Proceedings CONTENTS 1 Analytical Viewpoint 1 ‘Coprecipitation of Silver From Sea-water With Mercury(l1) Sulphide and Determination by E lectrot her ma I Atomic Absorption S pectrop hotometry’ by Michael N . Quigley and Frederick Vernon 4 SUMMARIES OF PAPERS 4 Recent Developments and Applications in Liquid Scintillation Counting 4 ’Recent Advances and Environmental Applications in Liquid Scintillation Spectrometry’ by Gordon T. Cook 7 Developments in Near Infrared Spectroscopy 7 8 ’Understanding Spectra of Highly Excited Vibrational States’ by Ian M. Mills ‘Qualitative Analysis in the NIR Region: a Whole Spectrum Approach’ by Gerard Downey, Paul Robert and Dominique Bertrand 10 Research and Development Topics in Analytical Chemistry 10 12 13 16 19 21 23 25 27 30 31 ’Peroxyoxa late C hemi I u m i nescence Detection in Liquid Chromatography’ by Simon W.Lewis and Paul J. Worsfold ’Ultramicroelectrodes: Their Use in Highly Resistive Systems’ by C. M. Lawrence and J. Slater ‘Fingerprinting Microbial Siderophore Production by High-performance Liquid Chromatography with Visible and Fluorescence Detection’ by C. Ruangviriyachai, J. D. Glennon, Fergal O‘Gara and P. M. Stephens ’Spreadsheet Computing in the Analysis of Metal Complex Equilibria’ by M. P. Ryan and J. D. Glennon ’Chromatographic Determination of Metal Ions Using Amino Acid Hydroxamates as Model Siderophore Reagents’ by G.A. Kearney, S. Srijaranai and J. D. Glennon ‘Trace Metal Preconcentration in Ion Chromatography Using Biochelating Silicas’ by N. Ryan and J. D. Glennon ’Analysis of Inorganic Solids by Laser Ablation Inductively Coupled Plasma ’Development of Polishable Electrocatalytic Electrode for Glucose Detection’ by ’Stripping Voltammetry With a Polymeric Calixarene Modified Carbon Paste Spectrometry’ by Jeff Franks, John Marshall, Irene Brown and Louise Garden Dona1 Leech, Joseph Wang and Malcolm R. Smyth Electrode’ by Damien W. M. Arrigan, Gyula Svehla, Stephen J. Harris and M. Anthony McKervey ’Fuel Cell Methodology for Determining Petrol Adulteration with Kerosene’ by M. Sahru Bahari, W. J. Criddle and J. D. R. Thomas ’Supercritical Fluid Extraction as a Sample Preparation Technique for Chromatography and Spectroscopy’ by Mark Kane, John R. Dean, S. M. Hitchen, C. Dowle and R. Tranter 34 Equipment News 37 Prize in Analytical Chemistry for Universities, Polytechnics and Colleges 37 Publications Received 38 Conferences and Meetings 39 Courses 40 Analytical Division Diary Typeset and printed by Black Bear Press Limited, Cambridge, England I I1 0144-557XC199211-A January 1992

ISSN:0144-557X    

DOI:10.1039/AP99229BX003

出版商:RSC    

年代:1992

数据来源: RSC

摘要:

4 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 Recent Developments and Applications in Liquid Scintillation Counting The following is a summary of the paper presented at a Meeting of the Scottish Region held on April 4th, 1991, in the University of Strathclyde, Glasgow. Recent Advances and Environmental Applications in Liquid Scintillation Spectrometry Gordon T. Cook Scottish Universities Research and Reactor Centre, East Kilbride G75 OQU Liquid scintillation counting is today probably the most widely used technique for the measurement of radioactive decay emissions. It is applicable to alpha and beta particles, electron capture and gamma photons, although, traditionally, the technique is mostly applied to CJ-emitting radionuclides such as 14C, 3H, 32P and 35S. In its most primitive form, the scintillation counter consists of a single photomultiplier tube (PMT), a high voltage supply, an amplifier and a scaler for registering the events.However, this system suffers from two distinct disadvantages: firstly, generation of noise pulses within the PMT; and secondly, the amplitude of the PMT pulse depends on the location of the event within the vial. With only a single exception, this one PMT system has been virtually redundant since the 1950s. The first commercial scintillation counter was developed by Lyle Packard, the founder of the Packard Instrument Company. The basic limitations of the single PMT system were overcome by the introduction of coincidence circuitry and the use of two diametrically opposed PMT tubes. A decay event occurring within a vial produces a number of photons which will stimulate both PMTs simultaneously; however, noise pulses are pro- duced randomly and at a sufficiently low rate that unless both PMTs are stimulated within the resolving time of the circuit (usually approximately 20 ns) then the pulses are ignored.This has the effect of dramatically reducing background count rates. The second disadvantage is overcome by the introduction of a summation circuit. The output pulses of the individual PMT tubes are summed, thereby making pulse amplitude indepen- dent of location. Nevertheless, by today’s standards, these instruments still had relatively high background count rates and were of limited use for the measurement of radionuclides at environmental concentrations.The next quarter of a century saw a number of advances in the technique, such as improved PMT tubes, the development of more efficient fluors and improved vial design and materials. However, the most significant advances have probably taken place within the last decade with the introduction of multi-channel analyzer tech- nology (MCA) and the new generation of ’low level’ counters specifically designed for environmental applications. The first two commercially available instruments with these features were the LKB-Wallac 1220 Quantulus (now LKB-Pharmacia) and the Packard 2000CNLL. The Packard counters are those which are used in the SURRC laboratory and will therefore form the major part of this discussion. LKB-Pharmacia Quantulus The Quantulus was designed at the instigation of Henry Polach of the Australian National University, originally as an instru- ment primarily for radiocarbon dating.It incorporates a number of features designed to reduce background count rates. These are as follows: firstly, much enhanced passive shielding (630 kg primarily of lead but also containing cadmium and copper linings) to reduce environmental gamma radiations and soft cosmic rays; secondly, an active coincidence guard counter consisting of a liquid scintillator (which surrounds the counting chamber) and a second pair of PMT tubes which act in anti- coincidence with the sample PMT tubes, i.e., events that stimulate a simultaneous response in both pairs of PMT tubes are disregarded, which acts to reduce background further, primarily the hard cosmic component; thirdly, a pulse ampli- tude comparator, which is needed when the individual PMT pulses are outside a defined ratio, because they are likely to be caused by optical cross-talk which can be suppressed by the comparator; fourthly, a high or low coincidence threshold because with 14C, the higher energy enables a higher coinci- dence threshold or bias to be employed so that low energy noise pulses will not trigger the coincidence circuit; and fifthly, high purity Teflon vials.In addition to these features, the Quantulus also has pulse shape analysis circuitry which enables QC activity to be distinguished from (3 and y activity. New Generation Packard Instrument Company Scintillation Counters The new generation of Packard scintillation counters ( e .g . , Models 200OCA/LL, 2250CA, 2550CA) employs none of the background reduction features found in the Quantulus. A feature termed ‘burst counting circuitry’ is used to differentiate true events from background events on the basis of pulse shape/duration analysis. The majority of background events (non-quenchable com- ponent) have a prompt pulse of approximately 2 ns duration followed by a number of randomly spaced after-pulses of much smaller energy, i.e., amplitudes similar to photoelectrons. In contrast, a pulse produced by a true (3 event consists of a similar duration prompt pulse followed by a very few or no trailing after-pulses. Advantage is therefore taken of this difference in after- ulsing characteristics to reduce background count rates! An additional feature incorporated into the ModelANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 5 2260XL is that of a modified detector assembly consisting of a slow scintillating plastic, which almost completely surrounds the sample when it is in position in the counting chamber.This acts as a quasi-active guard counter by increasing the number of photons in the trailing burst from background radiation. Vial holders constructed from the same plastic are available for use with 7 ml vials and enable a further reduction in background to be made. The complexity in these instruments lies not in optimizing the coincidence threshold and pulse amplitude comparator settings but rather in the selection of both the type and concentration of scintillant required to maximize perfor- mance and ensure stability of response. For example, Polach et aL2 demonstrated when using butyl-PBD as the scintillant for I4C measurement that background count rates decreased significantly; however, efficiency was also markedly reduced compared with counters with conventional circuitry.In con- trast, Cook, Harkness and Anderson3 were able to regain much of this loss in efficiency by the addition of the secondary scintillant bis-MSB. It was proposed that this enhancement in efficiency was due to a sharpening of pulse widths or a suppression of after-pulsing , rather than the traditional role of bis-MSB as a wavelength shifter, since the effect was not observed to any marked extent with other secondary scintil- lants such as POPOP and dimethyl-POPOP.In addition to this influence of scintillant type, they also observed that changes in scintillant concentration were accompanied by measurable changes in efficiency. In contrast, a much more stable efficiency response was observed with the burst counting circuit disabled. Again, however, through careful observations of response, Anderson and Cook4 devised cocktails for I4C measurement whereby moderate variations in both the butyl- PBD and bis-MSB had a negligible influence on response. Similarly, for 241Pu measurements, Cook and Andersons have demonstrated that di-isopropyl naphthalene (DIPN) based cocktails bring about a large reduction in efficiency. It has been proposed that the DIPN produces a broad-tailed pulse which is incompatible with the thresholds in the burst counting cir- cuitry.It is well established that naphthalene produces such pulse shapes.6 A relatively recent innovation in certain mdoels is that of further pulse shape analysis circuitry to distinguish a from fi and y activity. In this instance, it is important to use a DIPN based scintillant to maximize the discrimination. This would also apply to the Quantulus. ORDELA Model 8100 AB Perals Spectrometer The Perals spectrometer (Photon Electron Rejecting Alpha Liquid Scintillation) was designed at Oak Ridge by McDowell and co-workers and represents a very interesting concept in liquid scintillation spectrometry. Although it had been known since the 1940s that alpha particles could be measured by liquid scintillation,' the technique suffered from several problems, namely, poor resolution, interference from fily activity and quenching and variable scintillator response.Horrocks' demonstrated much improved resolution using a single PMT system with the sample between the PMT and a reflector with oil providing the optical coupling; however, the second and third remained somewhat unsolved. The work of McDowell and c o - w o r k e r ~ ~ . ~ ~ has brought about enormous advances in solving these problems. The interfering @/y activity is separated from the a activity by pulse-shape analysis, while the problem of quenching and variable scintillator response has been resolved by the use of solvents used in liquid-liquid extraction being added to scintillators to produce an 'extractive scintil- lator'. Several of these are now available commercially, each having different ion selectivities.Resolutions of 230 keV full width at half maximum (FWHM) are achievable by using this system, which is much improved compared with conventional systems (FWHM >500 keV); however, it should be remem- bered that this system is for a determinations only. In a sense, Table 1 Comparison of two instruments Optimum Volume/ efficiency Background/ Instrument ml (%) counts min-' E'V'IB Packard 2.3 71.7 0.71 38 300 Quantulus 2.0 65.0 0.44 38 400 therefore, the technique has turned a full circle, returning here to a commercially available single PMT system. Environmental Applications In terms of environmental applications, the low background instruments now available have generally improved limits of detection and precision.In radiocarbon dating, for example, the applied time scale has certainly been pushed back towards 60 000 years. As an example of relative performance, Table 1 compares the Quantulus used by the NERC Radiocarbon Laboratory and the Packard 2260XL used by the SURRC Radiocarbon Laboratory. For the Packard, this data was obtained by using standard Packard 7 ml glass vials and the slow scintillating vial holders. For the Quantulus, the same vial type was used but with high density polythene vial holders (Quantulus cannot accept 7 ml vials otherwise) masked to reduce cross-talk further between the PMT tubes. It should be pointed out that the Teflon vials would significantly reduce this background count rate; how- ever, they are not routinely used and do suffer from certain disadvantages.In a similar manner, groundwater dating using 'H has benefited enormously from the reduction in back- ground. Recently, we have developed a method for 234Th analysis at SURRC which has several advantages over traditional methods. The one spectroscopic disadvantage is that the 234mPa, with which the 234Th is in equilibrium, overlaps the peak from the a-emitting 230Th yield tracer, thus necessitat- ing overlap corrections in calculations. Preliminary results with the Packard 2250 a/@ counter suggest that the alfi option may enable this to be overcome by se aration of the 234Th/234mPa beta/gamma activity from the 2'Th alpha activity into the separate MCA's by pulse shape analysis. In addition, liquid scintillation spectrometry is now widely used by the nuclear industry for environmental monitoring of 9oSrpoY, 241Pu, 3sS, 99Tc, etc., while the a/fi options open up possibilities of single count gross a and gross fi determinations commonly employed for screening.The a/fi option also lends itself to other specific determinations similar to the 234Th application described above where the isotopes of interest are a mix of both a and (3 emitters. Relatively recently, Packard Instruments have introduced a method for 222Rn measure- ments in offices or domestic premises using a scintillation vial containing a small charcoal cartridge. 1 2 3 4 5 6 7 8 9 10 References Noakes, J. E., De Fillippis, S. J., and Valenta, R. J . , in International Seminar for Liquid Scintillation Analysis, Tokyo, Japan, 5-42, 1988.Polach, H., Calf, C-., Harkness, D. D., Hogg, A . , Kaiohola, L., and Robertson, S . , Nucl. Geophys., 1988, 2, 75. Cook, G. T., Harkness, D. D . , and Anderson, R., Radiocar- bon, 1989, 31, 352. Anderson, R., and Cook, G. T., Radiocarbon, 1991, 33, 1. Cook, G. T., and Anderson, R., J . Radioanal. Nucl. Chem. (Lett.), 1991, submitted for publication. Birks, J. B., in Solutes and Solvents for Liquid Scintillation Counting, Koch-Light, Colnbrook, 1975. Broser, I., and Kallmann, H. P., 2. Naturforschg., 1947, 2A, 642. Horrocks, D. L., Rev. Sci. Instrum., 1964, 35, 334. Bouwer, E. J . , McKlveen, J . W., and McDowell, W. J., Nucl. Techno[., 1979, 42, 102. McDowell, W. J., and McDowell, B. J., in international Conference on New Trends in Liquid Scintillation Counting and6 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 Organic Scintillators, 2-5 October, Gatlinburg, Tennessee, D.D., in International Conference on New Trends in Liquid 1989, eds. Ross, H., Noakes, J. E . , andspaulding, J. D., Lewis Scintillation Counting and Organic Scintillators, 2-5 October, Publishers, MI, USA, 1991. 1989, Gatlinburg, Tennessee, eds. Ross, H., Noakes, J. E., and 11 Anderson, R., Cook, G. T., MacKenzie, A. B . , andHarkness, Spaulding, J. D., Lewis Publishers, MI, USA, 1991. BIRKBECK ANALYTICAL LECTURES 1992 These advanced-topic lectures are given by visiting lecturers who are leaders in their fields. Interested scientists from industry or the public service are encouraged to attend without formality. All sessions start at 14.00 and terminate at about 17.00. The venue is the Chemistry Lecture Theatre, Christopher lngold Laboratories, 20 Gordon Street, London WC1 H OJA.February 26: Environmental Analysis Trace Elements, Geochemistry and Health: Professor lain Thornton, Chairman, Global Environment Research Centre, Imperial College, London. Strategic Factors in Environmental Analysis: Dr. Daniel Osborn, The Institute of Terrestrial Ecology (NERC), Monks Wood. Running an Environmental Laboratory for Local Government: Dr. Sheila van Dorst, Laboratory Manager, London Borough of Lambeth. March 4: Clinical Analysis In-vivo Sensors-Problems and Prospects: Dr. John M. Thompson, Head of Biomedical Engineering, Queen Elizabeth Hospital, Birmingham. Using NMR Spectroscopy and Pattern Recognition Methods to Probe Drug Metabolism and Toxicology: Dr. Jeremy K. Nicholson, Reader in Biological Chemistry, Birkbeck College. 'Good Enough for Clinical Purposes?'-The Quality Assessment of Clinical Laboratories: Dr. David G. Bullock, Director of the Wolfson EQA Laboratory, Queen Elizabeth Hospital, Birmingham. March 11 : Special Topics Forensic Chemistry-Fit for the Purpose? Dr. Bill Wilson, Deputy Director, Metropolitan Police Forensic Science Laboratory. Analytical Requirements in the Petroleum Industry: Dr. James Crighton, Senior Scientist, BP Research I nter nat i ona 1, Sun bu ry. Reference Materials and Chemical Traceability: Dr. Ron Walker, Head of Reference Materials, Laboratory of the Government Chemist. The lectures are organized by the Centre for Analytical Science, Birkbeck College, Gordon House, 29 Gordon Square, London WC1 H OPP. Telephone: 071 -380-7466; Fax: 071 -380-7464.

ISSN:0144-557X    

DOI:10.1039/AP9922900004

出版商:RSC    

年代:1992

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 Developments in Near Infrared Spectroscopy 7 The following are summaries of two of the papers presented a t a Meeting of the Molecular Spectroscopy Group held on November 7th, 1990, in the Zoological Society of London. Understanding Spectra of Highly Excited Vibrational States Ian M. Mills Department of Chemistry, University of Reading, Reading RG6 2AD Vibrational spectroscopy at high excitation is an important research frontier for two reasons. Firstly, the near infrared is proving to be an important area for the analytical applications of spectroscopy, and we would therefore like to understand how the spectra we observe relate to the molecular structure of the absorbing species. Secondly, there is a fundamental interest in understanding molecular dynamics and energy flow within a polyatomic molecule at high excitation, because this is the boundary between spectroscopy and chemistry through which we try to understand the details of a chemical reaction. In this presentation I shall survey recent progress in this field.Experimentally we may observe direct absorption from the ground (or low vibrationally excited) states, or we may observe emission from electronically excited states. I shall cover only absorption spectra in this paper, but emission spectra (using laser techniques such as stimulated emission pumping) have the advantage that the Franck-Condon selection rules allow us to sample different regions of coordinate space and thus access different vibrational levels. Absorption spectra are weak, and require the use of long path lengths with Fourier transform spectroscopy, or special detection techniques such as photo- acoustic spectroscopy. There is interest in both the intensities of high overtone spectra and the positions of the bands in the spectrum, although the intensities are little understood at present.One simple statement about the intensities is that the most intense overtone bands (and thus the most frequently observed bands) are always the overtones of H-stretching vibrations. The combination of all methods only allows us to observe a minute fraction of the total density of states for a polyatomic molecule at high energy. Relating the patterns observed to the potential energy surface and to the molecular dynamics requires the development of the theory of anharmonic vibrations, local modes and variational methods of calculating the spectrum.At sufficiently high energy, when all pattern is lost, one speaks of chaos, although there is some doubt that this is ever appropriate to a quantized vibrational spectrum. Resonances in the eigenstate spectrum, more or less localized, become increasingly important at high energy. They often mix an allowed transition (called a 'window' state) with a forbidden transition or transitions. Fermi resonances, in particular, become more important than ever in the overtone region, so that each H-stretching overtone is usually accom- panied by a surrounding group of neighbouring bands all borrowing intensity from the H-stretching overtone. Res- onances can be analysed by means of high resolution spec- troscopy.They play a key role in understanding the molecular dynamics of energy flow within a molecule: in a dynamic description they relate to the rates of relaxation; weak resonances (about 0.1 cm-') relate to slow relaxation pro- cesses (100 ps to 1 ns), and strong resonances (about 50 cm-') to fast processes (100 fs). In the dynamic description, when only two states are in resonance, the wavefunction oscillates between the two states (with a period determined above), but when a window state is mixed with many background states, the window state wavefunction relaxes into a combination of the background states (at a rate determined above) and never recurs. This is equivalent to the dynamic description of a chemical reaction.Many of these concepts will be illustrated by the excited vibrational state spectrum of the monofluoroacetylene mol- ecule, HCCF, which we have been studying extensively over the past 2 years. This molecule has just five normal modes, three parallel bands (ul, CH stretch at 3367 cm-*; 212, C=C stretch at 2239 cm-'; and 'u3, CF stretch at 1061 cm-') and two degenerate perpendicular bands v4, CH bend at 584 cm-'; and u5, k C - F bend at 336 cm- ). By persisting in our study of weak overtone bands we have now observed and assigned about 250 bands in the overtone spectrum (observed by FTIR up to 10 000 cm-' and by laser photoacoustic spectroscopy on up to 18 000 cm-'). They show a complex pattern of Fermi resonances, since u1 resonates with u2 + v3, 212 with 2213, and 'u3 with 2v4.Although these resonances are weak at low energy, they grow in strength with increasing energy, and they lead to Fermi polyads of rapidly growing dimension in the overtone spectrum. In the 10 000 cm-' region there are over 100 vibrational states interacting in a single Fermi polyad. We have also rotationally analysed many of the overtone bands. Rotational analysis gives further information on anhar- monicity, as rotational constants are a sensitive measure of the nature of the vibrational wavefunction. Finally, we have observed many weak rotational resonances, some of which have been completely assigned. These spectra provide bench- mark data to test the relationship of the vibrational spectrum to the potential surface, and our results will be compared with the ab initio calculations of Handy and co-workers.i8 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 Qualitative Analysis in the NIR Region: a Whole Spectrum Approach Gerard Downey The National Food Centre, Castleknock, Dublin 15, Ireland Paul Robert and Dominique Bertrand INRA, LTAN, Rue de la Geraudiere, 44072 Nantes, France Near infrared reflectance (NIR) spectroscopy is well estab- lished as a reliable technique for the quantitative analysis of industrial raw materials. A major challenge now facing the technique is to develop methods for qualitative analysis. A number of successful approaches have been reported. Mark and Tunnel’ used Mahalanobis distances to categorize chemi- cal products while Dardenne and Biston’ have applied multiple discriminant techniques to the identification of wheat varieties.However, these procedures utilize only a limited amount of the spectral data. Devaux et aL3 described the possibility of using complete spectral data by applying discriminant analysis to the factorial coordinates obtained following principal component analysis of near-infrared specta. This summary reports the application of this approach to the heat classification of skim milk powders. The Problem Skim milk powder is produced by holding liquid milk at one of a number of temperatures for a short period of time before spray-drying; three temperatures are commonly used in producing skim milk powders, referred to in the industry as high heat, medium heat and low heat. These products are all white, amorphous powders, but they possess quite distinct functional properties such as cold-water solubility and water- holding capacity. The dairy industry uses a series of chemical procedures to confirm the identity of such powders but these are time consuming and not generally used on each batch produced.Most industrial powder users do not possess either the skilled staff or the premises needed to carry out confirma- tory analyses on incoming batches. A need therefore exists for a rapid, accurate and simple technique for the unambiguous identification of skim milk powders. Experimental Sixty-six samples of commercially-produced skim milk samples were obtained from a number of creameries in the Republic of Ireland. Twenty-one of these were classified as high-heat, 25 as medium-heat and 20 as low-heat powders.Samples in each group originated from more than one creamery and were produced between June, 1987, and October, 1988. To facilitate discrimination between the three heat classes, a new variable called ‘class’ was introduced; low-heat samples were arbitrarily ascribed a value of 1, medium heat a value of 2 and high-heat samples the value 3. The sample collection was divided into a calibration development set ( n = 34) and a prediction set ( n = 32 samples) (Table 1). Table 1 Composition of sample sets Sample set heat heat heat Total Evaluation 10 13 9 32 High Medium Low Development 11 12 11 34 To minimize any potential complication from moisture variations between samples, all were exposed to the atmos- phere at room temperature for 48 h prior to recording sample spectra.All samples were manually mixed a number of times during this equilibration period. Reflectance spectra were recorded with a Technicon InfraAlyzer 500C instrument in the range 1100-2500 nm at 4-nm intervals. Each recorded spec- trum was the mean of duplicate scans on one sample without re-packing of the sample cell. Data were recorded on a HPlOOOL computer and transferred to an IBM personal computer. Data Treatment After transfer, spectra were normalized according to the following formula: i normalized Normalized spectra were subject to principal component analysis using wavelengths as principal variables and ‘class’ values as supplementary variables; calibration samples and prediction samples were principal and supplementary obser- vations, respectively.Principal component space was created by using principal observations and variables. Results Twenty principal components were developed, with the first five explaining 99% of the total variance of the variables input into the analysis. Correlations obtained between individual components and the variable ‘class’ are shown in Table 2. Table 2 Principal component correlations with ‘class’ Component PC 2 PC 3 PC 9 PC 7 PC 6 Correlation coefficient 0.62 0.38 0.33 0.21 0.20 These data suggest that principal components alone would not be able to model the variable ‘class’. Factorial coordinates for each of the 66 samples were plotted using PCs 2 and 3; a moderate separation between the low-heat treated powders and the others was achieved but the medium- and high-heat products were not separated at all. Factorial Discriminant Analysis Principal component analysis of a data set condenses the original data into a small number of variables.Each sample is located in multi-dimensional space by its factorial coordinates; these were used in a discriminant analysis procedure to maximize the distance between the observed groups. Initially, a stepwise discriminant procedure was used to ascertain the number of components needed to achieve discrimination. Twenty principal components were used at the outset but only 10 were needed to classify all the samples in the calibration setANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 9 correctly while 91% of the prediction set were correctly ciassified.These 10 PCs (PCs 1-9 and 13) were then input into a factorial discriminant procedure to generate two discriminant functions which produced almost perfect discrimination between the two sample groups. The first discriminant function described 55.1% of the variance input, with the second explaining 44.9%. The classification obtained for all powder samples using these discriminant functions is shown in Table 3. Table 3 Classification table for milk powder samples L M H Calibration set L 11 0 0 M 0 12 0 H 0 0 11 Prediction set L 9 0 0 M 0 10 3 H 0 0 10 Of the 32 samples in the prediction set, all ten of class 3 (High) and all nine of class 1 (Low) were correctly identified. Three of the 13 samples in class 2 (Medium) were mis-classified as class 2 (Medium). The separation achieved can be seen on a discriminant map (Fig.1). Discriminant function 1 is separat- ing the samples in group 1 (Low) from the others while function 2 effects the discrimination between groups 2 (Medium) and 3 (High). Ascription of bands in NIR spectra or spectral patterns remains difficult and no definitive identification of molecular species underlying the discriminant patterns developed in this model was possible. Conclusion On the basis of this very limited sample size, it appears that it is possible to identify unknown batches of skimmed milk powder. Axis 2 Fig. 1 Discriminant map of powder samples. Samples in parentheses are wrongly classified. 0, Gravity centre of group The techniques of principal component analysis and factorial discriminant analysis permit the use of complete spectral information.The technique is sufficiently rapid to be of use in an industrial environment. References 1 2 Mark, H. L., and Tunnell, D., Anal. Chem., 1985, 57, 1449. Dardenne, P., and Biston, R., ‘Attempt to Recognize Wheat Species by Discriminant Analysis’, in International NIRIT Spectroscopy Conference, Budapest, Hungary, 1986, The Central Food Research Institute, Budapest, Hungary, 1986. Devaux, M. F., Bertrand, D., Robert, P., and Qannari, M., Appl. Spectrosc., 1988, 42, 1015. 3 THE ROYAL SOCIETY OF CHEMISTRY: ANALYTICAL DIVISION The Annual Meeting on RESEARCH AND DEVELOPMENT TOPICS IN ANALYTICAL CHEMISTRY will be held at the University of Birmingham on July 7th and 8th, 1992 The 1992 Meeting will be the twenty-ninth in the series. Papers and poster presentations are invited describing work carried out by postgraduate research students in universities and colleges and by young research workers in industrial and other establishments. Oral contributions are to be presented by the student or his industrial counterpart in 20-minute lectures. The number of oral contributions is limited in order to balance the over-all programme. Titles of oral papers or posters with the name(s) of the author(s) and a summary of 100-1 50 words should be sent by February 28th, 1992, to the Secretary, Analytical Division, The Royal Society of Chemistry, Burlington House, Piccadilly, London WIV OBN. A limited number of bursaries will be available to the presenters.

ISSN:0144-557X    

DOI:10.1039/AP9922900007

出版商:RSC    

年代:1992

数据来源: RSC

摘要:

10 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 Research and Development Topics in Analytical Chemistry The following are summaries of eleven of the papers and posters presented at a Meeting of the Analytical Division held on July gth-loth, 1991, in the University of Aberdeen. Peroxyoxalate C hem il u m i nescence Detect ion in Liquid Chromatography Simon W. Lewis and Paul J. Worsfold* Department of Environmental Sciences, Polytechnic South West, Drake Circus, Plymouth PL4 8AA Luminescence is the emission of ultraviolet, visible or infrared radiation from a molecule or an atom resulting from the transition of an electron from an excited state to a lower energy state (usually the ground state). When the excited state is produced by a chemical reaction the emission is termed chemiluminescence (CL) .Chemiluminescence reactions occur in the solid, liquid and gaseous states. Such reactions, when used analytically, have the attractions of excellent limits of detection (owing to the absence of source noise and scatter), wide linear ranges and the use of simple, inexpensive instrumentation. Direct analysis can be achieved with CL, but is more often used as a post-column reaction and detection system for liquid chromatography (LC). The most common reactions are the aqueous luminol reaction, used for determining metal ions and hydrogen peroxide, and the peroxyoxalate reaction which is best used in non-aqueous media. Peroxyoxalate Reaction Peroxyoxalate CL, which was first reported in 1967 by Rauhut et ul.,' involves the hydrogen peroxide induced oxidation of aryl oxalate esters in the presence of a suitable fluorescent species (sensitizer).The emission profile is characteristic of the sensitizer present rather than the CL reagent. A simplified reaction scheme is outlined in Fig. 1. (I) + F - F" + 2C02 -t F + Light Fig. 1 Reaction scheme for the peroxyoxalate reaction. F = Fluorescent species The most widely used aryl oxalates have been bis(2,4- dinitrophenyl) oxalate (DNPO) and bis(2,4,6-trichlorophenyl) oxalate (TCPO), although alternative aryl oxalates have been investigated.* Bis(2,4,6-trichlorophenyl) oxalate has an opti- mum pH of 7.5, is easy to synthesize and is relatively stable (giving a lower background signal), whereas DNPO can be used down to pH 3.5 and has faster reaction kinetics.Aryl oxalates are best used in non-aqueous media as they are relatively insoluble and unstable in the presence of water, * To whom correspondence should be addressed. although the DNPO reaction can be used with a water content as high as 20% v/v, making it compatible with reversed-phase LC. The first analytical application of the reaction was as a detection method for thin-layer chromatography ;3 since then, it has been used as a reaction and detection system for LC and flow injection (FI). Molecules with native fluorescence and derivatized species can be determined by energy transfer to the peroxyoxalate system, with detection limits often much lower than with spectrofluorimetry ; for example, amines have been determined after fluorogenic derivatization, with detection limits in the low femtomole range, a 100-fold improvement on fluorescence d e t e ~ t i o n .~ Peroxyoxalate CL is most efficient for easily oxidized sensitizers, making it more selective than fluorescence and hence giving less complex chromatograms. Ultimately, the detection limits are controlled by the weak background emission from the aryl oxalate, which is present even in the absence of the sensitizer. Analytical Applications Chemiluminescence detection has mainly been applied to clinical analysis and the peroxyoxalate reaction is no exception. It has been used to determine directly the fluorescent drugs dipyridamole and benzydamine in plasma, with detection limits of 345 pmol and 147 nmol respectively.' Direct analysis is limited to analytes with native fluorescence.The usual approach is derivatization of the species of interest with a fluorescent label, including for example, dansyl, coumarin or fluorescamine groups. Dansylation is a popular fluorogenic derivatization pro- cedure and it has also been widely used for CL analysis. For example, dansyl chloride has been used to label amphetamine- related compounds in urine,6 primary alkylamines from butylamine to decylamine (with detection limits of 0.8-14 f m ~ l ) ~ and estradiol in serum (with a detection limit of 50 pg).* Steroids in blood plasma have been determined, with a detection limit of 7.5 pg after derivatization with dansyl hydrazine .9 Coumarins have been used for the determination of amines, with separation being achieved by both normal- and reversed- phase LC.The detection limits for pentylamine were 1 fmol with the normal-phase system and 6 fmol with the reversed- phase ~ y s t e m . ~ Other species determined with a coumarin label include fluoropyrimidines" and carboxylic acids. l1 The cate- cholamines norepinephrine and dopamine have been deter- mined in urine after derivatization with a fluorescarnine group. l2 Another approach to utilizing the peroxyoxalate CL reaction for clinical analysis is to determine the analyte by detecting theANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 Mobile phase MeCN-H20 (80 + 20) 0.5 11 1 ODS2-5 ml min-1 20 pl n 1 Single piston pump 0.5 DNPO 2 mmol dm-3 in MeCN Pulse I I damDers 0.5 H 2 0 2 220 mmol dm-3 in MeCN Peristaltic pump Laminar flow cell 3 v Waste 1 Recorder 1 Fig.2. LC-CL manifold for the determination of carboxylic acids in non-aqueous media hydrogen peroxide generated from a reaction between the analyte and enzymes, the post-column reagents being the aryl oxalate and a fluorophore. For example, acetylcholine and choline have been determined by the detection of hydrogen peroxide generated using acetylcholine esterase and choline oxidase immobilized on a column. With perylene as the fluorophore, the detection limit for both cholines was 1 pmol. l3 Peroxyoxalate CL has been used to determine species of environmental importance. Mixtures of polycyclic aromatic hydrocarbons (PAHs) have been separated and determined, with the detection limits for some species being better than those determined by fluorescence; for example, the detection limit for perylene with fluorescence detection was 80 pg, whereas with CL detection it was 0.77 . The method was used to identify PAHs in coal tar extracts.’FAmino-PAHs have been determined in shale oil, coal oil and coal gasifier tar, with a detection limit of 0.11 pg for 1-aminoperylene.” This method has been extended to nitro-PAHs in carbon black extracts by use of an on-line zinc reductor column to reduce the nitro- PAHs to the corresponding amino-PAHs.l6 The PAHs released during the combustion of biomass fuels have been separated and quantified using DNPO as the aryl oxalate. It was found that 707 pg kg-‘ of PAHs were produced during combustion. l7 A selective pre-column spectrofluorimetric derivatization procedure for carboxylic acids in non-aqueous media with separation by reversed-phase LC and peroxyoxalate CL detection has been used to monitor carboxylic acids in oxidized petroleum-based lubricating oils.l7 A schematic diagram of the LC-CL manifold is shown in Fig. 2. The acids (C2-CZo) were derivatized with a fluorescent species, 9-anthracenemethanol, in a heptane matrix using dicyclohexylcarbodiimide as a coupling agent. Bis(2,4-dinitrophenyl) oxalate was used as the post-column reagent owing to its rapid reaction kinetics, which lead to a ‘chemical band narrowing’ effect that allows the use of large detector cells. l8 Liquid chromatography with peroxyoxalate CL detection has been shown to be a useful combination owing to the excellent selectivity and sensitivity that can be achieved.Future developments are likely to include the use of new selective pre-column fluorescence derivatization procedures, solid-state reagent reactors, detailed mechanistic studies of the reaction and research into novel, for example, water-soluble, aryl oxalates. The authors thank Shell Research Ltd., Thornton Research Centre, for financial support of this work. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 References Rauhut, M. M., Bollyky,, L. J . , Roberts, B. G., Loy, M., Whitman, R. H . , Iannotta, A. V., Semsel, A. M., and Clarke, R. A., J. Am. Chem. SOC., 1967, 89, 6515. Honda, K., Miyaguchi, K., and Imai, K . , Anal. Chim. Acta, 1985, 177, 103. Curtis, T. G., and Seitz, W. R., J. Chromatogr., 1977,134,343. Tod, M., Prevot, M., Poulou, M., Farionotti, R., Chalom, J., and Mahuzier, G., Anal.Chim. Acta, 1989, 223, 309. Nishitani, A., Tsukamoto, Y., Kanda, S . , and Imai, K., Anal. Chim. Acta, 1991, 251, 247. Hayakawa, K., Hasagawa, K . , Imaizumi, N., Wong, 0. S., and Miyazaki, M., J. Chromatogr., 1989,464, 343. Melbin, G., and Smith, B. E. F., J. Chromatogr., 1984, 312, 203. Nozaki, O., Ohba, Y., and Imai, K., Anal. Chim. Acta, 1988, 205, 255. Kozoli, T., Grayeski, M. L., and Weinberger, R., J . Chroma- togr., 1984, 317, 355. Yoshida, S., Urakami, K., Kito, M., Takeshima, S . , and Hirose, S . , Anal. Chim. Acta, 1990, 239, 181. Grayeski, M. L . , and DeVasto, J. K., Anal. Chem., 1987, 59, 1203. Kobayashi, S . , Sekino, J., Honda, K., and Imai, K., Anal. Biochem., 1981, 112, 99. Honda, K., Miyaguchi, K., Nishino, H., Tanaka, H., Yao, T ., and Imai, K., Anal. Biochem., 1986, 153, 50. Sigvardson, K. W., and Birks, J. W., Anal. Chem., 1983, 55, 432. Sigvardson, K. W., Kennish, J. M., and Birks, J . W., Anal. Chem., 1984, 56, 1096. Sigvardson, K. W., andBirks, J. W., J. Chromatogr., 1984,316, 507. Yan, B., Lewis, S. W., Worsfold, P. J., Lancaster, J . S., and Gachanja, A., Anal. Chim. Acta, 1991, 250, 145. de Jong, G. J., Lammers, N., Spruit, F. J . , Brinkman, U. A. Th., and Frei, R. W., Chromatographia, 1984, 18, 129.12 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 Ultramicroelectrodes: Their Use in Highly Resistive Systems C. M. Lawrence and Jonathan M. Slater" Analytical Group, Chemistry Department, Birkbeck College, Gordon House, 29 Gordon Square, London WC7H OPP Ultramicroelectrodes (UMEs) are usually defined as elec- trodes with one dimension of less than 25 pm.Ultramicroelec- trodes have been constructed as microdiscs' (diameter ranges of 25 to less than 0.5 pm) and microbands2 (1-5 pm x 1-5 mm). The particular attraction of these electrodes is that the small dimensions confer some specific properties, which allow otherwise inaccessible measurements to be carried out. Our particular interest is in the measurement of analytes in highly resistive media, such as oils. Ultramicroelectrodes were originally developed for the investigation of diffusion coefficient^,^ where the steady-state current is rapidly established owing to the fast response times of the electrodes, allowing the rapid evaluation of diffusion coefficients.Other advantages of UMEs were rapidly realized and facilitated their use in other areas of study. (1) The fast response time, caused by the lack of signal distortion by charging currents, has led to UMEs being used to measure fast heterogeneous electron-transfer reaction rates4 and in electrochemical detection, where scanning of a range of potentials very rapidly would be an advantage, as in high- performance liquid chromatographic, gas chromatographics and liquid chromatographic6 detection. (2) The extremely small currents associated with these electrodes give rise to a very small iR drop7 across the solution/ electrode interface and a decrease in the extent of polarization of the electrode. The very small current can also pass through the reference electrode without causing polarization and obviates the need for an auxiliary electrode,' thus removing the requirement for a three-electrode potentiostat and hence reducing the amount of noise in the system.(3) Ultramicroelectrodes can be used in highly resistive solutions,' such as oils, without the need for a supporting electrolyte because autoprotolysis of the solvent and impurities produce sufficient numbers of ions and dipoles to charge the double electric layer of the electrode and allow the small faradaic currents to flow through the solution. There has been a requirement to determine directly a number of analytes in highly resistive solutions, such as oils where the oxidation products need to be monitored. Many properties exhibited by UMEs appear to be ideal for an on-line electrochemical detection system in the oil itself.We have carried out preliminary experiments using a commercial UME to investigate a series of systems in which the amount of electrolyte added to the oil mixtures was varied. In each instance the analyte was ferrocene, which gives a well documented response at gold electrodes. These results will be used as the basis for determining more intractable analytes such as furaldehydes. Experimental Measurements were carried out using an E G & G Princeton Applied Research UME; this is a gold microdisc electrode of 10 pm diameter (+2 pm), which is encased in thick glass to facilitate polishing. Electrodes were polished before each experiment in order to remove residues and prepare a reproducible surface. Even a small amount of contamination on the UME caused a significant loss of signal; hence, in order * To whom correspondence should be addressed.to obtain reproducible results it was necessary to ensure the surface was perfectly clean. The electrode was hand-polished on a rotating disc mineral polisher. Progressively finer grades of diamond paste were used, reducing to 0.25 pm. For these studies, the UME was part of a three-electrode arrangement with the auxiliary electrode positioned near to the working electrode (>1 mm) to reduce the solution resistance. The auxiliary electrode was a platinum wire (macro) sealed in a glass capillary. The reference electrode used throughout was a Gallenkamp silver-silver chloride electrode. A two-electrode system could be used; however, the results presented here were obtained with a three-electrode system, mainly for compati- bility with the Amel potentiostat, although the very high solution resistances might have produced problems of polariz- ation at the reference electrode.The potentiostat used was an Amel 433, a dropping mercury electrode apparatus which can be used to drive an external cell. Cyclic voltammograms and differential-pulse voltammograms were generated. The current signals observed were close to the limit of detection of the potentiostat; hence particular precautions had to be taken to ensure that the signals were not obscured by the background noise. Therefore, the whole of the electrolytic cell was placed in a Faraday Cage, which was constructed from a die cast metal box with ports for each of the electrodes. Results The cyclic voltammograms for ferrocene (Fig.1) were obtained for a mixture of oil and acetonitrile (50 + 50). The relatively low scan rate of 1 V s-l caused considerable distortion of the expected sigmoidal response. A higher scan rate would have almost completely obscured the signal. The differential-pulse voltammograms (Fig. 2 ) produced a much clearer response than the corresponding cyclic voltam- mogram. Curve B is the response obtained from 1 mmol dm-3 ferrocene in acetonitrile without a supporting electrolyte at a scan rate of 10 mV s-l and clearly shows the characteristic ferrocene oxidation peak. The smallest curve (A) is the re- sponse from an oil and acetonitrile mixture (SO + 50); here, the -2.4 t -0.8 P .c) C 0.8 0 2.4 4.0 I I I I 1 .o 0.8 0.6 0.4 0.2 PotentialN Fig. 1 Cyclic voltammograms of 1 mmol dm-' ferrocene in aceto- nitrile, in the absence of a supporting electrolyte. Scan rate: A, 10; B, 100; and C, 1000 mV s-'ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 13 0.0 I l A I 2.5 1 E N versus Ag-AgCI Fig. 2 Differential-pulse voltammograms of 1 mmol dm-3 ferrocene. A, Oil-acetonitrile (50 + 50) 10 mV s-'; B, acetonitrile with no supporting electrolyte, scan rate 10 mV s-l; C, oil-acetonitrile (50 + 50) with 0.1 mol dmP3 TBAPFs, 10 mV s-l; and D, oil-acetonitrile (50 + 50) with supporting electrolyte, 100 mV s-l signal is much less pronounced and the position of the peak has shifted to a much more positive potential. The lower curves (C and D) are from an identical mixture but with an added electrolyte [O.1 mol dm-3 tetrabutylammonium hexafluoro- phosphate (TBAPF6)]. Here the response has increased markedly from less than 0.3 nA above the baseline to greater than 3 nA. These curves also show the 'electrolyte window'" where the breakdown of the added electrolyte masks the other signals present; for the electrolyte used, TBAPF6, this window occurs at potentials higher than 0.8 V versus Ag-AgC1. For applications such as the detection of organic species, it is advantageous to be able to monitor the widest possible range of potentials. Ultramicro- electrodes and their use in non-electrolytic solutions have obvious applications in this area. Ultramicroelectrode Arrays For On-line Measurements Great interest in arrays of UMEs has been generated by the theoretical implications that such arrays," if suitably arranged, would not lose the special characteristics found in individual UMEs and would offer a number of additional advantages. The signals from these individual electrodes can be com- bined in order to amplify the signal from the system.Another advanta e of an array of microelectrodes has been demon- applications in flow-through cell detection. Our approach had been to prepare an array of gold microdiscs by encapsulating gold microwires. The wires were bonded together with epoxy resin in a strong glass capillary for polishing. Both ends were plane-polished using a rotating disc with various grades of diamond paste. Examination of the electrode array stubs by optical microscopy indicated that a number of fine disc UME arrays had been produced.Work is curently underway to integrate there arrays into a flow measurement system. stratedl F by showing the flow independence of an array, and its References 1 Fitch, A,, and Evans, D. H., J. Electroanal. Chem., 1986,202, 83. 2 Cranston, D. H., Jones, C. P., and Williams, D. E., Talanta, 1991, 38, 17. 3 Wightmann, R. M., Anal. Chem., 1981, 53, 1125A. 4 Wipf, D. O., Kristensen, E. W., Deakin, M. R., and Wightmann, R. M., Anal. Chem., 1988, 60, 306. 5 Brina, R., Pons, S . , and Fleischmann, M., J. Electroanal. Chem., 1988, 244, 81. 6 White, J. G., and Jorgenson, J. W., Anal. Chem., 1986, 58, 2992. 7 Wipf, D. O., and Wightmann, R. M., Anal. Chem., 1988, 60, 2460. 8 Bond, A. M., Fleischmann, M., and Robinson, J., J.Electro- anal. Chem., 1984, 168,299. 9 Wang, S., J. Electrochem. SOC., 1989, 136, No. 3. 10 Cassidy, J., Khoo, S. B., and Pons, S . , J. Phys. Chem., 1985, 89, 3933. 11 Reller, H., Kirowa-eisner, E., and Gileadi, E., J. Electroanal. Chem., 1982, 138, 65. 12 Caudill, W. L., Howell, J. O., and Wightmann, R. M., Anal. Chem. , 1982, 54, 2532. Fingerprinting Microbial Siderophore Production by High- performance Liquid Chromatography with Visible and Fluorescence Detection Chalerm Ruangviriyachai and Jeremy D. Glennon" Ch em is try De pa rtmen t, University Co lleg e Cork, Cork, lrelan d Fergal O'Gara and Peter M. Stephens Microbiology Department, University College Cork, Cork, Ireland Under iron-limiting growth conditions, many micro-organisms produce powerful iron-sequestering compounds of low relative molecular mass, termed siderophores.These siderophores complex iron and transport it into the cells by a high-affinity iron transport system. Microbial siderophores are an import- ant class of naturally occurring metal-sequestering agent, with a number of uses in biology, agriculture, clinical medicine, biotechnology , industry and chemical analy~is.~-~ Functional groups particularly responsible for the high selectivity of these agents towards Fe'" include the hydroxamate and catecholate groups. Models of naturally occuring siderophores have been synthesized as analytical reagents and their Fe'" binding properties examined by potentiometry ."* ~ ~ - _ _ _ _ * To whom correspondence should be addressed.Whether synthesized or biosynthesized, there is an increas- ing need for efficient methods of analysis of these agents. Reversed-phase high-performance liquid chromatography (HPLC) has the potential to be the method of choice for the analysis of siderophores. Methods for the analysis of the complexed and uncomplexed forms of the chelation therapy drug desferrioxamine have been A procedure has also been reported for the determination of desferrioxa- mine and ferrioxamine in biological fluids using a method of pre-enrichment from serum sample on a reversed-phase pre-column. l1 The production under controlled growth conditions of yellow-green , fluorescent, water-soluble siderophores is a characteristic property of some Pseudomonas sp .I2 The structure of one such siderophore called pseudobactin, isolatedANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 ~ Complex J 300 t 350 400 450 Wavelengthlnrn 400 500 600 Wavelengthh m Fig.1 (a) Absorption spectrum and ( b ) fluorescence emission spectrum of filtered supernatant of Pseudomonas sp. strain M114 (pH 7.0) from Pseudomonas B10, has been determined. l3 It contains a dihydroxyquinoline moiety responsible for the fluorescence, which is attached to a hexapeptide containing a terminal N- hydroxyornithine. In addition, Philson and Llinas14 described a similar structure for a siderophore produced by P. fluorescens strain ATCC 13525. An assay method with the ability to distinguish between siderophores produced by different strains or species of microbes would be of benefit in this area.This work examines the chromatographic behaviour of siderophores from different strains of Pseudomonas sp. using reversed-phase HPLC. The technique is particularly powerful when dual visible and fluorescence detection is applied for monitoring and fingerprinting the siderophores produced in Iiquid media. Experimental Apparatus The metal-free HPLC system consisted of a Dionex analytical pump and an inert high-pressure injection valve and a Dionex RPIC-C18 (particle size, 10 pm) analytical column (250 x 6 mm i.d.). The injection volume was 48 1.11 with a flow rate of 1.0 ml min-l. Visible detection was carried out using a Waters Lambda-Max Model 481 LC variable-wavelength detector at 405 nm, in series with fluorescence detection using a Model 2000 fluorescence spectrometer (Perkin-Elmer) equipped with a 1 mm pathlength flow-through cell.Fluorescence emission was measured at 480 nm after excitation at 399 nm. Note that the visible detector is placed prior to and in series with the fluorescence detector. Bacterial Strains and Culture Conditions Pseudomonas sp. designated M114, 1/31 NC3, 1/33 and F121 were chosen for study. These strains were isolated from the roots of sugar beet and produce yellow-green, water-soluble, fluorescent siderophores on SA media. The strains were maintained on minimal asparagine liquid media consisting of I, & o 10 20 0 10 20 0 10 20 30 0 10 20 30 Time/mi n Fig. 2 Chromatograms of filtered supernatant from Pseudomonas sp. strain M114 with visible [(a) and (c and fluorescence [(b) and (d)] Fe"' in the media.HPLC conditions: flow rate, 1 ml min-'; mobile phase, 0.015 mol dmP3 acetate buffer (pH 5.0) with 8% MeOH; 48 pl injections detection. (a) and (b), No added Fe' II in the media: (c) and (d), added 0 10 20 30 Ti me/rn i n Fig. 3 Chromatograms of Pseudornonas sp. strain M114 supernatant (a) with no Fe"' and ( b ) added Fe"', with visible detection (4Q5 nm)ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 15 20 g of sucrose, 2 g of L-asparagine, 1 g of KZHP04 and 15 g of agar in 1 1 of de-ionized water. Liquid media contain all the above constituents except for agar. Glassware was washed with 6 mol dm-3 HC1 in all experiments to remove trace metals. The medium described contains no added source of iron and no attempt was made to remove traces of iron from the medium.All media were sterilized by autoclaving at 121 "C (103.4 kPa) for 15 min. The 10% MgS04-7H20 was autoclaved separately and then added to the other media constituents. Single colonies from the Pseudomonas sp. agar plates were transferred to 10 ml of liquid media, and the liquid cultures were grown overnight at 28 "C, being aerated by shaking. Overnight cultures were than used to inoculate 250 ml volumes of sterile media in 1 1 Erlenmeyer flasks. These liquid cultures were grown at 28 "C for 48 h with aeration. After 48 h, bacterial cultures showed a yellow-green fluorescent pigment. The supernatant from each strain was collected and filtered, prior to injection into the HPLC system. Results and Discussion Spectrophotometric analysis of siderophores, isolated from strains such as P.jluorescens B 1613, P. aeruginosa ATCC (bl i I 1 0 10 20 15692 and Pseudomonas B10, revealed characteristic broad and intense absorption bands with absorption maxima between 400 and 405 nm, similar to Pseudomonas sp. strain M114 shown in Fig. l(a). Following excitation at 399 nm, fluorescence emission spectra showed maxima at 480 nm for the supernatant solutions [Fig. l(b)]. These optical characteristics allow for dual visible and fluorescence detection following chromato- graphic separation at the selected wavelengths of 405 and 480 nm, respectively. HPLC Profiles and Biological Activity For the purposes of this work, the strain M114 can be considered to be a reference Pseudomonas sp. in that it produces a characteristic yellow-green solution over a period of 48 h when grown in liquid culture.Further, the retention behaviour of its yellow-green components on octadecylsilica has previously been studied in this laboratory. This earlier work indicated that an amount of organic modifier in the range 8-10% was suitable for adequate resolution of the contributing siderophore components. By using visible and fluorescence detection, two main siderophore peaks are evident as shown in Fig. 2. The relative peak heights of the siderophore peaks 0 10 I ( d k I 0 10 0 10 20 I 0 10 20 0 10 20 0 10 0 10 0 10 20 Tirnehnin Fig. 4 Chromatographic analysis of filtered supernatant of Pseudornonas sp. strain M114 [(a) and (f)],1/31 [(b) and (g)], NC3 [(c) and ( h ) ] , 1/33 [(d) and (i)] and F121 [(e) and (j)].HPLC conditions as in Fig. 2. (a)-(e) Visible detection (405 nm) in series with 0-0 fluorescence detection (480 nm)16 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 change depending on the harvesting time and pH of the supernatant solution and the longest retained fluorescent component is generally considered to be the most important or main siderophore. Further evidence that these peaks are siderophores is provided by their absence when the Pseudo- monas sp. is grown in Fe"*-containing media [see Fig. 2(c) and The antifungal activity of these bacterial strains is mediated by the siderophores produced, which deprive the fungi of vital Fel'* ions. Under iron-rich conditions, the siderophores are not produced as shown by the chromatograms and no inhibition of fungal growth is observed.Detection of Fe'"4iderophore Complex Results from previous work with Pseudomonas sp. strain M114 and those obtained here on the addition of Fe'" to the siderophore supernatant (Fig. 3) show that the Fe"' complex is retained longer than the main siderophore component. The metal-free HPLC system was chosen in order to eliminate any contamination by Fe"' from the system and in general only minor indications of Fel"-siderophore peaks were observed in the chromatograms obtained in these studies. The majority of siderphore peaks have some shoulders or tailing at longer retention which is caused by Fe"' complexation. Note that supernatant samples would be expected to have a certain amount of the complexed siderophore present and that it is difficult to ensure totally Fe'"-free chromatographic conditions when the separation column is silica based.Fingerprinting Siderophores by HPLC The results of the chromatographic analysis of the supernatant samples from several different strains of Pseudomonas sp. are given in Fig. 4. Non-fluorescent early eluting bands are caused by media constituents such as sucrose. As shown, dual detection with visible and fluorescence detectors pinpoints the free siderophore bands. These chromatograms can be used to identify and distinguish different strains of Pseudomonas sp. From Fig. 4, it is clear that the strains M114 and 1/31 are similar with respect to the number of components and their retention behaviour. As the chromatographic profiles for strains NC3, 1/ 33 and F121 are different from those of strains M114 and 1/31, it is possible that there are structural variations in the siderophores produced by these strains. It is probable that the siderophores produced by each strain share the same chromo- phore but with different peptide or functional groups attached.In particular, strains NC3, 1/33 and F121 could contain fluorescent siderophores which are less hydrophobic than those of strains M114 and 1/31, judging from their lower retention times on octadecylsilica. However, in the absence of isolated products, these profiles can be used as 'fingerprintings' of the siderophore components produced in liquid media and are (41. particularly valuable when taken together with results of biological assays. Conclusion In this work, reversed-phase HPLC using a metal-free HPLC system has been applied successfully to the analysis of naturally occurring metal-chelating agents from different strains of Pseudomonas sp.It is apparent that reversed-phase HPLC is an effective method of separation and characterization of siderophores. Fluorescence detection in conjuction with visible detection has proved to be very powerful in providing good sensitivity and selectivity. Fluorescence detection can differen- tiate between compounds that are simply media constituents, or by-products and the actual fluorescent siderophores. The use of reversed-phase HPLC as a rapid means of examining siderophores without their purification is possible. Hence a means of 'fingerprinting' siderophores from various species of bacteria and fungi has been developed.A comparison of the chromatograms obtained in this work revealed that different strains of the same Pseudomonas sp. can produce chromato- graphically different siderophore profiles. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 References Neilands, J. B., Ann. Rev. Biochem., 1981, 50, 715. Avdeef, A., Sofen, S. R., Bregntj, T. L., andRaymond, K. N., J. Am. Chem. Soc., 1978, 100, 5362. Senior, A. T., and Glennon, J. D., Anal. Chim. Acta, 1987, 196, 333, Raymond, K. N., and Carror, C. J., Ace. Chem. Res., 1979,12, 183. Wong, G. B., Kappel, M. J., Raymond, K. N., Matzanke, B. F., and Winkelmann, G., J. Am. Chem. SOC., 1983, 105, 810. Brown, D. A., Geraty, R., Glennon, J. D., and Ni Choileain, N., Inorg. Chem., 1986, 25, 3792.McMahon, R., Ni Choileain, N., and Glennon, J. D., Anal. Chim. Acta, 1987, 196, 329. Ruangviriyachai, C., Mills, D., and Glennon, J. D., Proc. R . Ir. Acad., Sect. B, 1989, 89, 471. Cramer, S. M., Nathanael, B., and Horvath, C., J. Chroma- togr., 1984, 295, 405. Glennon, J. D., and Senior, A. T., J. Chromatogr., 1990, 527, 481. van de Horst, A., De Goede, P. N. F. C., Willems, M. J. J. and van Loenen, A. C., J. Chromatogr., 1986, 381, 185. Strainier, R. Y., Palleroni, N. J., and Doudoroff, M., J. Gen. Microbiol., 1966, 43, 159. Teintze, M., Hossain, M. B., Barnes, C. L., Leong, J., andvan der Helm, D., Biochemistry, 1981, 20, 6446. Philson, S. B., and Llinas, M., J. Biol. Chem., 1982,257,8086. Spreadsheet Computing in the Analysis of Metal Complex Equilibria Martina P.Ryan and Jeremy D. Glennon" Department of Chemistry, University College Cork, Cork, Ireland Spreadsheet computing is becoming increasingly important as a tool for the analysis and display of chemical data. In analytical chemistry, the uses can be extended to the steps in the analytical process that include sampling, real time interac- tion and data ac uisition from instruments, and data reduction and reporting. ' The growth of instrumental methods of trace analysis based on flow injection (FI) , high-performance liquid ~ ~ ~ ~ ~ ~ ---- * To whom correspondence should be addressed. chromatography (HPLC) and sensor technology has placed a fresh demand on the supply of novel selective and sensitive reagents. Whatever the source, the selection of a reagent is assisted by the ready availability of information of the nature and stability of metal complexation.Spreadsheets, such as SuperCalcS, add graphic features that, together with facilities for creating tables of data and perform- ing intricate calculations, make them powerful tools for the analysis of metal complex equilibria. The analysis of the complex equilibria involved between the FI reagent, aceto-ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 17 hydroxamic acid and Fe111,778 and between the HPLC reagent, L-aspartic acid (3-hydroxamate' and Cu", utilizing poten- tiometry and spreadsheet computing, is described here (Fig. 1) .The numerical method involves the calculation of formation 0 OH II I H&-C-N-H Fig. 1 aspartic acid P-hydroxamate ( a ) Structure of acetohydroxamic acid.( b ) Structure of L- curves for metal complexation from pH titration curves as described by Irving and Rossotti. Tedious equations relating to the calculation of iiH, i i , pL and the logarithm of the stability constants are applied using macro programming language , which is written within SuperCalc5. The calculated L : M ratio for the Cu'I-L-aspartic acid (3-hydroxamate system is verified using ultraviolet-visible spectrophotometry. Experimental L-Aspartic acid P-hydroxamate and acetohydroxamic acid were obtained from Sigma. The 1.015 mol dmP3 sodium hydroxide solution used was standardized against weighted amounts of dried potassium hydrogen phthalate. A solution of 1.005 mol dmP3 nitric acid was standardized a ainst the base.Separate stock solutions of 0.050 mol dm-' iron(m) nitrate nonahydrate (AnalaR) and 0.050 mol dmP3 copper(I1) nitrate trihydrate (AnalaR) were prepared in 0.020 mol dmW3 nitric acid. The stock acid and salt solution used was 0.020 mol dm-3 nitric acid in 0.150 mol dm-3 sodium nitrate. The potentiometric method involved recording three ti- tration curves for each of the two systems investigated: Fe"' with acetohydroxamic acid (cFe = 1.001 mmol dm-3, cL = 5.163 mmol dm-3; and Cu" with L-aspartic acid P-hydroxa- mate (ccu = 1.057 mmol dmP3, cL = 5.1124 mmol dmP3). An excess of ligand over metal was used to allow complete metal coordination and to prevent metal precipitation. The Radi- ometer automatic titrimeter used consisted of a PHM84 pH meter, an ABU80 autoburette, a TTT80 titrator and a REC80 recorder.The titration vessel was thermostated at 25 k 0.05 "C. A computer interface to a BBC microcomputer was constructed to facilitate automatic data acquisition at every 0.1 pH interval. A digital DECstation 200 PC was used to process the titration data. The program was written in SuperCalc Version 5 .OOA. Visible light spectra were recorded using a Shimadzu UV- 260 spectrophotometer. Ligand and metal concentrations were increased by a factor of 10 from previous titrations to obtain sufficiently coloured solutions for visible light analysis. The investigation of complexation as a function of pH was carried out on a 10 ml solution of Cu" (cM = 10.356 mmol dm-3) and L-aspartic acid (3-hydroxamate (cL = 50.034 mmol dmP3). The pH of the resulting solution was adjusted by the addition of microlitre volumes of NaOH and spectra were obtained at 0.2 pH intervals in the range 900-300 nm.The molar ratio study was carried out on a 10 ml solution of Cu" (cM = 5.178 mmol dmP3) and L-aspartic acid P-hydroxamate. A solution of the ligand in water was prepared such that 25 yl additions increased [L]T/[M]T by increments of 0.1. Spectra were obtained at pH 5.5. Evaluation of Metal Complex Equilibria The evaluation of stability constants and ligand pK, values by graphical methods is based on the early work of Bjerrum, and Irving and Rossotti.' This treatment involves the determi- nation of the pH-dependent quantities AH (the average number of protons bound to the ligand), ii (the average number of ligands bound to the metal) and pL (the negative logarithm of the free ligand concentration). Simplified formation functions can be used when monomeric stepwise complexation and well separated associations are involved.The logarithm of the stability constant values can be determined as follows: [ i i l 1-ii Log K = -' + pL In order to assist calculation and graphical display of data, a progam was written in SuperCalc with extensive use of macro programming language. Spreadsheets A spreadsheet is a rectangular array of cells identified by column and row numbers, e.g., cell B5 is the intersection of the second column with the fifth row. Each cell is a discrete region that can contain data, alphanumeric labels, equations or labelled instructions (i. e., macros). SuperCalc is controlled by a menu system which is accessed by pressing the '/' key.Hence in the macro '\metalconc' (Fig. 2), a sequence of keystrokes such as '/ncmetal-J15-' representing Name Create metal <ret> J15 <ret>, has the effect of naming cell J15 as 'metal'. A macro is therefore created by placing such a sequence of keystrokes into labelled cell(s) and is activated by pressing ALT and F5 followed by the macro label. All of these keystrokes are processes without further intervention by the user. This concept becomes much more powerful when combined with command keywords such as: GETNUMBER, e.g., (GETNUMBER 'Input conc. of metal', J15); IF, which allows a decision to be made in a macro; BRANCH, which passes control of the macro to another cell address or macro.User-defined menus can also be generated with macros which allow the user to interact with the program [see '\editdata' (Fig. 2)]. Hence macro language is a programming language in its own right, allowing controlled looping, conditional testing, file system access and input/output control. In this program, extensive use was made of macros to operate the entire model, \metalconc {LET A15 "Concentration of Metal . . . . . . . . . . . . 1 {MESSAGE "Range 0.0005 < = Metal conc < = 0.01 M") {GETNUMBER "Input conc. of Metal", J15) /ncrnetal-J15- {IF (AND (0.0005 < = metal, 0.01 > = metal))){RETURN) {BEEP I } /bJ 15- {BRANCH \metalconc} \editdata {MENU} ADD DELETE EDIT CONTINUE Add points Delete Points Edit Point Begin Calculations { BRANCH\addp { BRANCH\delet { \BRANCH\edit { BRANCH\work} Fig.2 Sample macros from the program18 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 Set up headings prompting the user for data as necessary and generating the final report (Fig. 3). Read constants- Names of metal and ligand, [acid], [base], [ligandl, [metal], initial volume, No. of dissociable protons For each pH value, read also corresponding volume for each of three titration curves I Read data- 1 Calculate fiH and i, Check No. of dissociable protons 1 2 3 Calculate: Calculate: Calculate: PKa PKa1 PKa, mean pKa mean pKa, mean pKal PL ~Ka2 ~Ka2 Log Kl mean pKa, mean pKa2 Log K2 PL ~Ka3 Log K3 Log Kl mean pKa3 Log K2 Log K3 Log Kl Log K2 Log K3 Set b- up and print graphs Print data table Save data file Fig. 3 Program structure Applications The applications of the spreadsheet program to the analysis of metal complex equilibria are illustrated in the following two examples.The complexation of iron(1rr) in aqueous solution by the monohydroxamate, acetohydroxamic acid [Fig. l(a)], repre- sents classical simple stepwise complexation. l1 The ligand itself is monoprotic and bidentate and liberates one mole of proton per mole of complexed ligand. The spreadsheet-generated input and output data for this metal-ligand system are shown in Fig. 4. Experimental data from these titration curves are included and the data are rapidly processed to yield the species- dependent quantities, tiH, ti, pKa and the logarithm of the stability constant values. For the determination of the pK, value of the ligand, the best set of calculated values can be easily chosen and averaged to yield the pK, value.The variation of riH values as a function of pH can be readily displayed and an approximate pKa value obtained for the half- fiH method (Fig. 5). Further, the extent and pattern of metal complexation can be seen from the A values as a function of pH, either tabulated (Fig. 4) or displayed graphically (Fig. 6). In Fig. 6, it is clear that complexation is well advanced in the acidic pH region with the complexation advancing to 1:2 and 1:3 complexation by pH 6. The second example chosen is a copper(I1)-L-aspartic acid p- hydroxamate [Fig. l(b)] aqueous complex solution. The ligand is triprotic as illustrated in Fig. 5 with iiH values ranging from 3.0 to 0.The plot of ri versus pH shown in Fig. 6 indicates that complexation in this system is consistent with the formation of a 1:l M-L complex, with fi reaching a value of 1.0 at pH 5. Molar ratio studies at pH 5.5 also indicate that this complex corresponds to [L]T/[M]T = 1, i.e., a 1:l M-L complex. From these examples, it is clear that the spreadsheet program provides an attractive, efficient and informative means of examining metal complex equilibria, and offers an alternative to conventional, linear programming in a language ANALYSIS OF METAL COMPLEX EQUILIBRIA Calculation of pKa and stability constant values Background electrolyte Temperature Name of metal Name of ligand Concentration of base Concentration of mineral acid Concentration of ligand Concentration of metal Initial volume No.of ionizable protons on ligand No. of data points Average pKa PH 2.1 2.4 2.8 3.4 4.0 4.5 5.0 5.5 6.0 6.5 7.5 8.5 9.3 9.4 9.5 9.6 Vol 1 0.467 0.71 2 0.877 0.959 0.979 0.981 0.983 0.983 0.985 0.985 0.985 0.985 0.985 0.985 0.988 0.990 Vol2 0.467 0.712 0.877 0.959 0.985 0.989 0.989 0.989 0.991 0.991 0.996 1.013 1.089 1.105 1.121 1.135 Vol3 0.542 0.792 0.964 1.057 1.092 1.109 1.122 1.130 1.136 1.136 1.141 1.157 1.207 1.21 6 1.226 1.232 fiH 1 .ooo 1 .ooo 1 .ooo 1 .ooo 0.977 0.970 0.977 0.977 0.977 0.977 0.959 0.894 0.608 0.548 0.499 0.453 n 1.534 1.628 1.765 2.217 2.505 2.755 2.921 3.004 3.004 3.063 3.260 3.930 1.985 PKa 5.635 6.007 6.635 7.135 7.635 8.135 8.864 9.428 9.490 9.483 9.497 9.51 9 PL Log& 9.81 9.52 9.14 8.57 8.00 7.54 7.08 6.61 6.12 5.62 4.64 3.72 3.26 3.26 3.26 3.24 NaN03, 0.15 mol dm-3 25 "C Iron Acetohydroxamic acid 1.01 5 0.020 0.005 0.001 50 1 96 9.49 Log K2 Log K3 9.869 9.751 9.654 10.389 7.442 7.551 7.570 7.675 Fig.4 Sample input/output from the programANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 19 " 2 4 6 8 10 12 PH Fig. 5 fiH data as a function of pH. A, Acetohydroxamic acid; and B, L-aspartic acid (3-hydroxamate I I I I I 2 3 4 5 6 7 8 9 PH Fig. 6 Degree of formation fi as a function of pH. A, Iron- acetohydroxamic acid; and B, copper-L-aspartic acid (3-hydroxamate such as BASIC. With relatively little hands-on experience, a PC- based solution was developed which could be easily understood and used. Calculations are fast, even for calculation-intensive methods such as analytical potentiometry: a typical data matrix of 200 elements requiring a total of 450 equation evaluations takes less than 5 min to process. Changing a single input value results in rapid and automatic recalculation of the entire spreadsheet, reducing the time for 'what if.. .' types of analysis to seconds. Powerful graphing facilities allow graphical rep- resentations to be easily and rapidly obtained and formating output, perhaps one of the most difficult parts of conventional programming, is automatically carried out. To the experienced worker or teacher, the errors and inconsistency in the data can be seen when tabulated or displayed graphically. At present, the slowest step in using this model involves data input to the spreadsheet. Work is currently in progress to speed up data transfer and to eliminate data transfer errors by allowing the PC to interact directly with the titrimeter.1 2 3 4 5 6 7 8 9 10 11 References Rosenburg, R. M., J. Chem. Educ., 1985, 62, 140. Coe, D. A., J. Chem. Educ., 1987, 64, 137. Henderson, J., J . Chem. Educ., 1988, 65, A150. Salit, M. L., Anal. Chem., 1988, 60, 731A. Allars, A., Znt. Biotechnol. Lab., 1988, June, 38. Reich, L. S., and Patel, S . H., Znt, Lab., 1987, November, 20. Glennon, J. D., Wolfe, M. R., Senior, A. T,, and Ni Choileain, N., Anal. Chem., 1989, 61, 1474. Senior, A. T., and Glennon, J. D., Anal. Chim. Acta, 1987, 196, 333. Srijaranai, S . , Kearney, G. A., and Glennon, J. D., unpub- lished work. Irving, H. M., and Rossotti, H. S . , J , Chem. SOC., 1954, 2904. Brown, D.A., Chidambaram, M. V., Clarke, J. J., and McAleese, D. M., Bioinorg. Chem., 1987, 9, 255. Chromatographic Determination of Metal Ions Using Amino Acid Hydroxamates as Model Siderophore Reagents Gary A. Kearney, Supalax Srijaranai and Jeremy D. Glennon" Department of Chemistry, University College Cork, Cork, Ireland One approach commonly adopted in the high-performance liquid chromatographic analysis of trace metal ions involves the pre-column formation of metal chelates. Previous reports on the separation of metal chelates have described the use of mainly normal-phase chromatography, with a variety of ligands successfully used includin dithizone ,1,2 substituted and unsubstituted dithiocarbamate~?-~ @-diketone: semicarba- zone and hydra~one.~ More recently, a shift has occurred towards the use of reversed-phase chromatography.Among the most extensively used water-soluble chelates are the metal complexes of dithiocarbamates, 1 ,lo-phenanthroline, ethyl- enediaminetetraacetic acid bipyridines, crown ethers and porphyrins.*-" Valenty and Behnken" were the first to demonstrate the possibility of using ion-pair reversed-phase liquid chromatography for the analysis of charged metal chelates. 4-(2-Pyridylazo)resorcinol (PAR) and its derivatives have been widely used for metal ion determination using the ion-pairing approach. 12,13 Shijo and Sakai14 reported the separation of 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfo- * To whom correspondence should be addressed. pro y1amino)phenol (5-Br-PAPS) chelates of Cu", Co", Ni", Cr' and Vv at ppb levels on a LiChrosorb RP-18 column using a mobile phase containing 0.1 mol dm-3 LiC1.Fritz and co- workers have demonstrated the use of ion-paired chelates of bis(2-hydroxye thyl) dithiocarbamate (HEDC) l5 and N-me th- ylfurohydroxamic acid (NMFHA)16 for trace metal analysis. Apart from the latter work, very little work had been carried out on the use of hydroxamic acids and reagents for the liquid chromatographic analysis of metal ions. Hydroxamic acids form stable chelates with a large number of metal ions, generally through bidentate chelation at the [--C(O)-N(0H)-] group. They are important Fe'" trans- port agents in microbial systems (where they are termed siderophores) and have been used as reagents in analytical chemistry for gravimetric, spectroph~tometric,~~ flow injec- tion" and solid-phase extraction.19-*' The purpose of this work was to examine the use of two water-soluble amino acid hydroxamates, aspartic acid p- hydroxamate (ASPHA) [Fig. l ( a ) ] and a-glutamic acid y- monohydroxamate (GLUHA) [Fig. l(b)] for the pre-column formation and separation of the metal chelates of A1*", Co", R20 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 OH \ ASPHA "HZ GLUHA NH2 Fig. 1 Structure of a-glutamic acid y-monohydroxamate (GLUHA) (a) Structure of aspartic acid 6-hydroxamate (ASPHA). (b) 0 1 2 3 4 5 6 [TBAP]/mmol dm-3 Fig. 2 Effect of variation of concentration of TBAP on retention of various ASPHA metal chelates. A, MeV'; B, Cu"; C, AI"'; D, Vv; E, Co": and F, Fe"' 1 2 3 4 5 [TBAPl/mmol dm-3 Fig.3 Effect of variation of concentration of TBAP on retention of various GLUHA metal chelates. A, MeV'; B, Cu"; C, Al1Ir; D, Co"; E, FeI'I; and F, Vv Cu'', Fe'" and MeV'. These reagents are models of naturally occurring siderophores, many of which contain amino acid and hydroxamate functional groups. Experimental The chromatographic behaviour of metal ions was investigated by injecting their pre-complexed solutions. For calibration graphs, an aqueous eluent containing 2% CH3CN, 5 mmol dm-3 ASPHA or 5 mmol dmP3 GLUHA, 1 mmol dm-3 acetate buffer and 5 mmol dmP3 tetrabutylammonium per- chlorate (TBAP) at pH 7 was used. The eluent flow rate was 1 ml min-l, with detection at 313 nm. The influence of pairing ion concentration on the chromato- graphic behaviour of the ASPHA and GLUHA chelates of t - m 0 v) .- Fig.4 a) cu I 1 Mo I I 1 1 0 2 6 10 b) co I I A t 1 Mo I Time/rnin rypical separation of various ASPHA metal chelates Fig. 5 Typical Al a) I I 1 1 10 6 2 0 ?' Fe ( b) I I I 14 10 6 2 0 Timelmin ieparation of various GLUHA metal chelates AlIII, Co'', CdI, Fe"' and MoV' was examined by using an eluent of 2% CH3CN and 1 mmol dm-3 acetate buffer at pH 7 , in the presence (Figs. 2 and 3) and absence of ligand. Other studies involving the variation of buffer concentration and percentage of or anic modifier were carried out with an eluent of 5 mmol dm-'ASPHA and 5 mmol dm-3 TBAP at pH 7. Quantitative analysis of the ASPHA and GLUHA chelates ofANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 21 Al"', Co", Cu", Fe"' and MoV' was studied for mixed metal chelate solutions by using an eluent of 2% CH3CN in 1 mmol dm-3 acetate buffer of pH 7 containing 5 mmol dm-3 ligand and 5 mmol dm-3 TBAP for ASPHA and 2 mmol dm-3 TBAP for GLUHA (Figs.4 and 5 ) . Results and Discussion In order to obtain the optimum conditions for the separation of metal-ASPHA and metal-GLUHA chelates, the eluent para- meters including pH, pairing ion, buffer concentration and organic modifier were studied. It was observed for ASPHA that there is a reduction in the retention of the metal chelates when the pH, buffer concentration or percentage of organic modifier is increased. In an aqueous solution of pH 7, the a- carboxyl of the amino acid hydroxamates should be completely deprotonated, giving a net negatively charged complex.Hence TBAP was chosen for ion pairing. The main focus here is on the effect of varying the concentration of this counter ion on the chromatographic retention of metal chelates. The perchlorate anion was chosen as the co-ion. In the absence of TBAP, little or no retention of metal- ASPHNGLUHA chelates is observed. A sharp rise in retention is evident in the TBAP concentration range 0 4 . 1 mmol dmP3. A maximum is reached at a concentration of 2 X lop4 mol dm-3 TBAP, after which the retention starts to drop as the concentration of the pairing ion increases (Figs. 2 and 3). The increase in retention is consistent with the increasing hydrophobicity of the Al''', Co", CuI', Fe"' and MoV' chelates on ion-pair formation. The parabolic behaviour or bell-shaped curve for the dependence of retention on the pairing ion concentration was also observed by previous workers.Several mechanisms have been proposed to explain this behaviour, including the formation of micelles or compounds that are retained to a lesser extent. However, a competition by the co- ion or counter ion of the pairing ion has also been suggested. The need for pre-complexation of metal ions before injection on to the high-performance liquid chromatography column has also been recognized. Typically, a 5-fold excess of ligand is recommended. The advantages of the presence of a ligand in the mobile phase have been well established, including the enhancement of the stability of complexes and the promotion of re-formation of the complexes if dissociation takes place.However, for kinetically inert complexes, the addition of a ligand to the mobile phase is ~nnecessary.'~ In this work, a mobile phase containing 5 mmol dm-3 ASPHA or GLUHA was compared with a mobile phase with no added ligand and the chromatographic behaviour of the metal-ASPHA and metal-GLUHA chelates examined. With no ligand in the mobile phase, MoV1 was not detected, whereas Fe"' was detected with very poor reproducibility. The chromatographic behaviour of the other chelates, i.e., Al"', Co" and Cu", was not affected by the removal of the ligand from the mobile phase. These results are consistent with dissociation of the Mo"' and Fe"' hydroxamate chelates and the suggestion that the other metal ions form kinetically inert chelates. It should also be noted that GLUHA metal chelates showed much shorter retention times than ASPHA metal chelates, resulting in a considerably reduced selectivity for metal ions using 5 mmol dm-3 TBAP.1 2 3 4 5 6 7 8 9 12 11 12 13 14 15 16 17 18 19 20 21 References O'Laughlin, J. W., and O'Brien, T. P., Anal Lett., 1978, 11, 829. Henderson, D. E., Chaffee, R., and Novak, F. P., J. Chromatogr. Sci., 1981, 19, 79. Uden, P. C., and Bigley, I. E., Anal. Chim. Acta, 1977,94,29. Liska, O., Lehotay, J., Brandsteterova, E., Guiochon, G., and Colin, H., J. Chromatogr., 1979, 172, 384. Moriyasu, M., Hashimoto, Y., Anal. Lett., Part A , 1978, 11, 593. Tollinche, C. A., and Risby, T. H., J. Chromatogr. Sci., 1978, 16, 448. Heizmann, P., and Ballschmiter, K., J. Chromatogr., 1977,137, 153.Willeford, B. R., and Veening, H., J. Chromatogr., 1986, 251, 61. O'Laughlin, J. W., J. Liq. Chromatogr., 1984, 7, 127. Steinbrech, B., J. Liq. Chromatogr., 1987, 10, 1. Valenty, S. J., andBehnken, P. E., Anal. Chem., 1978,50,834. Hoshino, H., and Yotsuyanagi, T., Anal. Chem., 1985,57,625. Yamada, H., and Hattori, T., J. Chromatogr., 1986,361, 331. Shijo, Y., and Sakai, K., J . Chromatogr., 1985, 333, 133. Palmeri, M. D., and Fritz, J. S., Anal. Chem., 1987, 59, 2226. King, J. N., and Fritz, J. S . , Anal. Chem., 1987, 59, 703. Agrawal, Y. K., and Patel, S. A., Rev. Anal. Chem., 1980, IV(4), 237. Senior, A. T., and Glennon, J. D., Anal. Chim. Acta, 1987, 196, 333. Shah, A., and Devi, S., Analyst, 1985, 110, 1501. Fadeeva, V. I., Tikhomirova, T. I., Yuferova, I.B., and Kudryavtsev, G. V., Anal. Chim. Acta, 1989, 219, 201. Glennon, J. D., and Srijaranai, S., Analyst, 1990, 115, 627. Trace Metal Preconcentration in Ion Chromatography Using Biochelating Silicas Noel Ryan and Jeremy D. Glennon" Department of Chemistry, University College Cork, Cork, Ireland Solid-phase extraction for organic and inorganic analytes has been marketed mainly as an off-line sample pre-treatment technique for trace enrichment and sample clean-up. Major attributes of this approach are the amenability to automation and the availability of a large number of solid phases, many of which are established chromatographic stationary phases. Application areas include clinical , pharmaceutical and en- vironmental analysis. Indeed, a survey of the most significant developments in the determination of trace metals in waters and effluents has highlighted the increasing use of preconcen- tration columns in sample treatment. ' Although traditional * To whom correspondence should be addressed.approaches to trace metal preconcentration based on che- lation-solvent extraction, ion exchange and coprecipitation are widely used, high preconcentration factors and selectivity have been obtained by using chelating solid phases such as silica- immobilized 8-hydroxyquinoline , It is recognized that the sensitivity of ion-chromatographic analysis can be improved by the use of pre-columns for trace analyte preconcentration. The simplest approach involves the loading and back-flushing of a pre-column incorporated in the loop of a single high-pressure switching valve.This and other approaches have been applied in ion chromatography for the preconcentration of anions such as phosphate, sulfate and oxalate of low and high ionic strength.* Less attention has been paid to the on-line22 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 Cartridge e Injection valve Waste Fig. 1 Instrumental configuration for the ion chelation chromato- graphic technique 0 1 2 3 Volume of metal ions loadedhl U 4 Fig. 2 Volume uptake studies for 1-4 ml of metal ion mixture on chelating dextran-coated silica. A, Ni2+; B, Cu2+; C, CdZ+; D, Co2+; and E, Zn2+ A u) c.’ .- 5 300 0 200 400 600 800 1000 Concentration of loaded sample (ppb) Fig. 3 Calibration graphs for A, Zn2’; B, Cu2+; C, Ni2+; and D, Co2+ preconcentrated on chelating dextran-coated silica preconcentration of trace metals in ion chromatography, in spite of the challenge presented in the determination of trace metals in complex matrices such as high ionic strength media.However, a technique termed chelation ion chromatography has been described, which utilizes an iminodiacetic acid resin prior to the analytical column; the technique has been successfully applied to trace metal determination in concen- trated brines and sea-water sample^.^ The solid-phase extrac- tion properties of a silica-based chelating phase using immobi- lized ligands of biological origin have also recently been de~cribed.~ This biochelating phase contains immobilized hydroxamic acid functional groups, which play an important role in the natural transportation of Fe3+ in the microbial world.A trace metal cartridge utilizing this biochelating silica shows good stability, preconcentration and elution properties for a number of metals. This paper presents results obtained from the use of this biochelating material and of dextran- coated silica materials also with hydroxamic functional groups in the ion-chromatographic analysis of environmental water samples. Experimental Materials Chelating solid-phase materials based on silica particles (40 pm) and dextran-coated silica particles were prepared as described previ~usly.~ Hydroxylammonium chloride, potas- C c o 1 1 I I ’b 1 16 12 8 4 0 t/min Fig. 4 Metal ion separation for Pb2+ ( 5 pprn), Cu2+ (1 ppm), Cd2+ (3 ppm), Co2+ (1 ppm), Zn2+ (1 ppm) and Ni2+ (1 ppm) preconcentrated on chelating dextran-coated silica sium hydroxide and sodium hydroxide were obtained from Merck (Poole, Dorset, UK).Lead nitrate [Pb(N03)2], cad- mium nitrate tetrahydrate [Cd(N03)2-4H20] and cobalt chloride hexahydrate (CoC126H20) were also obtained from Merck. Standard ZnC12, CuC12 and NiC12 solutions were purchased from Merck (Darmstadt , Germany). (a) 10.05 A 20 10 0 20 10 0 tlmin Fig. 5 Comparison of ( a ) direct injection of 25 p1 of tap water with (b) preconcentration of 1 ml of tap water on the chelating dextran-coated silica. A = absorbanceANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 23 Solutions Stock solutions of metals (1000 ppm) were used in all instances, from which standards with concentrations ranging from 10 ppb to 5 pprn were prepared.Solution pH values were adjusted to 8.0 prior to injection. De-ionized water from an Elgastat spectrum water purification unit, with a resistivity of 16 MQ cm or better, was used throughout. Tap water and sea-water were collected from the laboratory and in the local area. Metal ion separations were carried out by using a mobile phase of 0.05 mol dmA3 oxalic acid and 0.095 mol dm-3 LiOH. Instrumentation A schematic diagram of the instrumentation used is shown in Fig. 1. The chelating materials were packed in 5 X 0.4 cm Tefzel cartridge columns. A Dionex 4500i ion-chromato- graphic system was used. A solution of 4-(2-pyridylazo)resorci- no1 (PAR) was used as a post-column derivatization reagent. The wavelength chosen for metal detection was 520 nm. Analytical (CS5 and NS1) columns were used for metal separation. Results and Discussion By using post-column derivatization with PAR and visible detection, a standard metal mixture of Pb2+, Cu2+, Cd2+, Co2+, Zn2+ and Ni2+ in the concentration ratio of 5: 1 :3: 1 : 1 : 1 (ppm) was used to study the chromatographic responses obtained as a function of injection volume over the volume range 0.1-4.0 ml. The pH of all the injected solutions was adjusted to 8.0. The results are shown in Fig. 2 for the chelating dextran-coated silica. Further studies were carried out by using an injection volume of 1.0 ml, as higher values led to loss of resolution and poor peak shape. Standard metal ion solutions in the concentration range 0.01-5.0 ppm were used to construct calibration graphs, which yielded correlation coefficients in the range 0.9970-0.9998. Typical plots obtained for the chelating dextran-coated silica are shown in Fig. 3. Limits of detection were assigned to metal ion concentrations producing chro- matographic responses three times greater than the back- ground noise and were found to be between 5 and 10 p b for Cd2+ when these ions were part of a metal mixture. Further studies were carried out on Pb2+ and Cd2+ individually and the detection limits were found to be <20 and <30 ppb, respectively. A typical chromatogram obtained for a standard mixture of Pb2+ (5 ppm), Cu2+ (1 pprn), Cd2+ (3 pprn), Co2+ (1 pprn), Zn2+ (1 ppm) and Ni i- (1 ppm) by using the technique of on-line preconcentration in ion chromatography is shown in Fig. 4. The improvement in sensitivity obtained by using this technique is shown in Fig. 5, in which the chromatogram obtained for a direct injection of 25 pI of laboratory tap water is compared with that obtained for a 1.0 ml injection using pre-column trace enrichment on a chelating dextran-coated silica. Cu2+, Co2+, Zn2+ and Ni2+ but were >lo0 ppb for Pb p+ and References 1 Cresser, M. S., Ebdon, L. C., McLeod, C. W., and Burridge, J. C., J. Anal. At. Spectrom., 1986, 1 , 1R. 2 Jackson, P. E., and Haddad, P. R., J. Chromatogr., 1988,439, 37. 3 Siriraks, A., Kingston, H. M., and Riviello, J. M., Anal. Chem., 1990, 62, 1185. 4 Glennon, J. D., and Srijaranai, S., Analyst, 1990, 115, 627.

ISSN:0144-557X    

DOI:10.1039/AP9922900010

出版商:RSC    

年代:1992

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 23 Analysis of Inorganic Solids by Laser Ablation Inductively Coupled Plasma Spectrometry Jeff Franks, John Marshall and Irene Brown ICI plc, Wilton Materials Research Centre, P. 0. Box 90, Wilton, Middlesbrough, Cleveland TS6 8JE Louise Garden ICI Advanced Materials, P. 0. Box 90, Wilton, Middlesbrough, Cleveland TS6 8JE Silicate-containing materials are not easy to prepare for elemental analysis by inductively coupled plasma techniques, as complex mixtures of acids or fusion fluxes are required to effect complete dissolution. Tatro et al.‘ described a method for dissolution of zeolites in a sealed PFA vessel, enabling silicon and other elements to be determined in the same solution. Zurhaar and Mulling2 described a dissolution procedure of the characterization of forensic glass samples by inductively coupled plasma mass spectrometry (ICP-MS) involving the measurement of 48 isotopes. The method was used to distinguish between window glass samples from Australia and the USA.examined the possibility of introducing zeolite powder in the form of a slurry into inductively coupled plasmas, and obtained results that were in good agreement with those of a conventional dissolution method. Laser ablation has been used in conjunction with inductively coupled plasma atomic emission spectrometry (ICP-AES) for the direct analysis of solids. This technique has been applied to the determination of elements in geological samples with varying degress of success, involving lithium metaborate fusion4 and pelleting’ for sample preparation.Previous work in this laboratory6 has shown the feasibility of using laser ablation inductively coupled plasma mass spec- trometry (LA-ICP-MS) for the analysis of polymeric materials. Williams er al. Relative standard deviations of about 10% were achieved. In the present work, laser ablation was used to provide a direct solid sampling method of quantifying elements in silicate matrices by ICP-MS. It is shown that significantly better repeatability can be obtained for the inorganic matrices examined. In the first application, major elements were determined in zeolites by using a wide range of certified refractory materials as calibration standards. In the second application, minor and trace elements were determined in glass fibres from different suppliers, with the aim of improving quality control.Experimental Zeolites Zeolites fused in a 1 + 1 lithium carbonate-lithium metaborate mixture were quantitatively analysed for silicon and aluminium using LA-ICP-MS. The instrument used was a VG Plasma- Quad 2 Plus with the VG Laserlab accessory (Nd:YAG laser). British Chemical Standard and Euronorm Certified Reference Materials from the ceramics, minerals and cement section were used to calibrate the system. Results were compared with those obtained by hydrochloric-hydrofluoric acid dissolution followed by ICP-AES.24 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 The fusion conditions were: 0.1 g of sample, 2.0 g of lithium carbonate and 2.0 g of lithium metaborate in a platinum-gold crucible at 1100 "C. The laser ablation conditions used for optimum precision involved continuously sampling at a fixed site with a Q-switched laser beam focused on the sample surface. The flashlamp voltage was set at 700 V, with a repetition rate of 7 Hz. The sample was pre-ablated for 3 min prior to five replicate acquisitions.Glass Fibres Glass fibres from three different suppliers were examined using LA-ICP-MS. The fibres were fused into a solid mass in a platinum-gold crucible prior to continuous sampling with the Q-switched laser beam focused on to the sample surface. The flashlamp was set at 850 V, with a repetition rate of 10 Hz. The same batches of glass fibre were analysed by inductively coupled plasma optical emission spectrometry following diges- tion with cold hydrochloric-hydrofluoric acid for 48-72 h.Concentrations of strontium derived by ICP-OES were used to improve the accuracy of the semiquantitative LA-ICP-MS glass identification routine. Quantitative analysis of the glasses was carried out following calibration of the ICP-MS instrument with certified elements in the National Institute of Standards and Technology (NIST) glass series 610-616. The effect of using different internal standard elements on the accuracy and precision of the method was also studied. Results and Discussion Analysis of Zeolites It has been suspected that low silicon results might be obtained from the dissolution of refractory materials in hydrochloric- hydrofluoric acid solution in open vessels, even in the cold. This was verified for the reference materials with silicon recoveries of about 80-90%, whereas aluminium recoveries were 9&95% and iron recoveries 95% and above.The fusion method described was therefore adopted in order to improve the recovery of silicon. A single isotopic mass was monitored with respect to time while continuously ablating the sample surface. A fairly sharp rise in signal was obtained, followed by a decay to a relatively steady-state level. This profile was the same for all of the isotopes monitored (6Li, log, 27Al, 28Si, 48Ti and 56Fe) with approximately 90 s required to reach the steady state. Relative standard deviations for five replicate acquisitions at the same site were typically about 5% following pre-ablation for 3 min. There was little or no improvement in precision by ratioing to the minor isotopes of lithium or boron.Matrix interferences arising from the presence of the light element fusion flux used were expected and were found, the most serious of which was caused by LiO at mlz 23, which prevented measurement of sodium at the levels which can be present in some zeolites. The species BC would also interfere with sodium. Polyatomic combinations of B and 0 might be expected to interfere with aluminium and silicon at mlz 27,28, 29 and polyatomic combinations of C and 0 might be expected to interfere with silicon at mlz 28, 29, 30. Nevertheless, good calibrations were achieved for alumin- ium, silicon, titanium and iron. By using three reference materials (BCS 267, BCS 395 and ECRM 776-1) good results were achieved for zeolite-type materials.Titanium and iron were not present in measurable amounts in the samples. It can be calculated that the ratio of ICP-OES to LA-ICP-MS for silicon is about 0.82 and for aluminium about 0.92. These figures are very similar to the recoveries achieved by dissolu- tion-ICP-OES of the reference materials, indicating that the LA-ICP-MS results are more accurate. Incorporation of seven reference materials in the calibration routine produced good calibrations, but instrumental drift was apparent for silicon on the following eight samples. Aluminium did not drift over the same period. The speckled appearance of the fused bead suggested the possibility of sample inhomogeneity. This was tested by measuring silicon and aluminium at ten different sites on each of two samples.The relative standard deviations found for silicon were no worse than those found earlier for a single site, whereas for aluminium the relative standard deviation was found to be about 14% for the level present in one of the zeolites and about 5% in the reference material, It is probable that drift arises from deposition and vaporization of lithium salts at the sampler and skimmer cones, affecting ion trans- mission rather than bead inhomogeneity . Bracketing samples and standards might reduce drift, while use of a single fusion compound (lithium metaborate) would reduce interferences on silicon and any attendant inhomogeneity . Analysis of Glass Fibres It was found that results obtained with the dissolution-ICP- OES method for glass fibres could be used to identify the supplier and for the purpose of quality control.A major disadvantage was the time required (48-72 h) to effect the dissolution. A more rapid method was then developed based on LA-ICP-MS. Fusion of the fibres into a mass, as described under Experimental, followed by semiquantitative analysis by LA-ICP-MS, was found to provide more elemental infor- mation, and in a much shorter time scale (less than 2 h). It was also shown that short mass range scans over 4 min enabled elements to be detected at levels of less than 10 ng g-' in glass. For quantitative analysis by LA-ICP-MS, it was found that the relative standard deviations for NIST reference glasses were much improved if 42Ca were used as an internal standard, typically from 5% (no internal standard) to 1% with 42Ca) for a nominal analyte concentration of 500 pgg-'.At nominal concentrations of 1 pg g-', the relative standard deviations were acceptable at about 5%. There was a deterioration in repeatability when 30Si was used as an internal standard. As calcium levels in the samples were different to the level in NIST base glass it was necessary to use the mean calcium result for each glass type (previously determined by ICP-OES) to correct the quantitative results. By using this protocol, good agree- ment was obtained between ICP-OES, semiquantitative and quantitative LA-ICP-MS for most elements. Consequently, LA-ICP-MS is recommended for problems involving identifi- cation, whereas the quantitative approach is more suitable for quality control purposes.Conclusions Laser ablation ICP-MS is a viable technique for the direct analysis of solid materials that are silicate based. Further work is required to reduce instrumental drift; however, relative standard deviations of less than 5% have been achieved for the determination of trace elements in glass, indicating that laser stability is not the limiting factor. Research is underway to establish appropriate methodology for the direct analysis of powders, which would alleviate the necessity of the fusion step used for the preparation of the zeolite samples in this work. The authors thank ICI plc for permission to submit this paper for publication. References 1 Tatro, M. E., Elabd, A., and Kassa, P., ZCP Znf. Newsl., 1990, 15, 665. I . 2 Zurhaar, A., and Mullings, L., J.Anal. At. Spectrom., 1990, 5 , 611. 3 Williams, J. G., Gray, A. L., Norman, P., and Ebdon, L., J . Anal. At. Spectrom., 1987, 2 , 469. 4 Thompson, M., Goulter, J. E., and Sieper, F., Analyst, 1981, 106, 32. 5 Lin, S. and Peng, C., J . Anal. At. Spectrom., 1990, 5 , 509. 6 Marshall, J., Franks, J., Abell, I., and Tye, C., 1. Anal. At. Spectrom., 1991, 6, 145.ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 25 Development of Polishable Electrocatalytic Electrode for Glucose Detection Dona1 Leech* and Joseph Wangt Department of Chemistry, New Mexico State University, Las Cruces, NM 88003, USA Malcolm R. Smytht School of Chemical Sciences, Dublin City University, Dublin 9, Ireland Owing to the clinical and industrial significance of monitoring glucose levels, the development of sensors for glucose detec- tion continues to attract considerable interest.Amperometric, non-enzymic sensors for glucose are generally developed so that the analyte is oxidized directly at solid electrode surfaces. The voltammetric response for glucose at carbon electrodes is limited by the rather large overvoltage associated with its oxidation at these electrode surfaces. Various other electrode materials have therefore been investigated for their application in this area. The most relevant electrode materials used for the direct electrochemical detection of glucose are gold and platinum. Oxidation of glucose at these electrodes results, however, in the poisoning of the electrode surface. Hence, a stable response at these electrodes is only obtained if appropriate potential cycles are utilized to clean and condition the electrodes between sensing intervals.This usually involves the use of a dual- or triple-pulse potential waveform involving oxidative cleaning of adsorbed material with subsequent reductive removal of the oxide layer. The use of electrocata- lytic chemically modified electrodes for the detection of glucose has also been described. Santos and Baldwin' have utilized a cobalt phthalocyanine modified carbon paste elec- trode for the detection of picomolar levels of carbohydrates. This electrode requires a pulsed potential waveform similar to that of the gold and platinum electrodes in order to obtain reproducible signals. Nickel or copper electrodess-l3 are also capable of oxidizing glucose at low potentials and have been used for the direct electrochemical detection of glucose and other carbohydrates using a constant-potential waveform. A recent promising alternative modified electrode for carbohydrate detection has been described.14-16 A carbon paste electrode modified with ruthenium dioxide (Ru02) was utilized for fixed-potential flow injection detection of various carbohydrates, alcohols and selected antibiotics. The enhanced stability and applicability of this modifier, on incorporation in a graphite-epoxy electrode matrix, was also demonstrated. l5>l6 The aim of the present study was to illustrate the application of polishable Ru02-modified graphite-epoxy electrodes to the detection of glucose. Attempts to lower the NaOH concen- tration, and pH, as required for the electrocatalytic reaction to occur, are also described. Selective detection of glucose at these modified electrodes was also attempted by the appli- cation of various polymer films to the electrode surface. Experimental Apparatus Cyclic voltammetry and batch amperometry were performed using an EG & G Princeton Applied Research Model 264A voltammetric analyser, in conjunction with a Houston Omni- scribe x-y recorder.A Bioanalytical Systems (BAS) Model VC-2 electrochemical cell (10 ml volume) was employed in these experiments with the working electrode, reference * Permanent address: School of Chemical Sciences, Dublin City t To whom correspondence should be addressed. University, Dublin 9, Ireland. 0.6 0.2 -0.2 PotentialN Fig.1 Cyclic voltammograms at the 20% m/m Ru02-modified electrode. Broken line represents the blank, 0.5 mol dm-3 NaOH solution, response. Solid line represents the voltammetric response on addition of 2.5 mmol dmP3 glucose to the cell. Scan rate, 20 mV s-' electrode (Ag-AgC1, Model RE-1, BAS) and platinum wire auxiliary electrode inserted into the cell through holes in its Teflon cover. Reagents and Procedures The Ru02-modified graphite-epoxy electrode was prepared by mixing equal amounts of the epoxy-bonded graphite (Dylon) resin and accelerator components, with the subsequent addi- tion of the required amount of Ru02 (usually 80 : 20 graphite- epoxy: Ru02) to the graphite paste. Portions of the resulting paste were then packed into the end of a glass tube (3 mm i.d.) and allowed to cure at room temperature for 48-72 h.The hardened electrode surface was then polished with wet and dry emery paper (1200 grade), rinsed with de-ionized water, polished with a 0.05 pm alumina slurry, rinsed with water again, and finally ultrasonicated for 3 min to remove any residual alumina. All solutions were prepared from doubly distilled, de- ionized water. Standard solutions of glucose (Sigma) were prepared fresh daily in the 0.5 mol dm-3 NaOH (Baker) electrolyte. Results and Discussion Voltammetry Preliminary experiments, confirming the retention of the electrocatalytic activity of the RuOz-modified graphite-epoxy electrodes, were performed using cyclic voltammetry. Typical cyclic voltammograms obtained with the Ru02-modified electrodes, in 0.5 mol dm-3 NaOH electrolyte, both with and without added glucose (solid and broken lines, respectively) are shown in Fig.1. Profiles similar to those seen for lucose oxidation at an Ru02-modified carbon paste electrodeg4 were observed; peak potentials of +0.04 V (anodic) and +0.35 V (cathodic) were obtained for the ruthenate-peruthenate transi- tion, in this electrolyte. The RuO2-modified electrodes exhi- bited classic electrocatalytic behaviour, with an increase in26 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 4- 2 3 0 2 min H 0 10 20 Ru02 (% m/m) Time Fig. 2 (a) Effect of Ru02 loading in the raphite-epoxy electrode matrix on the batch addition of 1 mmol dm- glucose levels to A, 5 ; B, 10; and C , 20% m/m Ru02-modified electrodes.(b) Plot of current versus loadin Constant-potential detection at +0.35 V. Stirring rate, 400 rev min-'f and electrolyte, 0.5 mol dm-3 NaOH B anodic and a decrease in cathodic peak currents, on addition of glucose to the cell. These currents were extremely stable with no apparent decrease on extended cycling over a 60 min period, illustrating the highly stable nature of both the modifying matrix and modifier. Amperometry The effect of the Ru02 'loading' within the graphite-epoxy matrix on the response to glucose was investigated by constant- potential (+0.35 V) measurements of 1 mmol dm-3 glucose increments. The current-time profiles observed at the 5 (A), 10 (B) and 20% m/m (C) RuO2-modified graphite-epoxy elec- trodes are shown in Fig. 2. Also shown (6) is the corresponding current-loading curve determined for these modified elec- trodes.A similar, linear correlation between response and Ru02 loading in the electrode matrix was observed at Ru02- modified carbon paste electrodes14 used for the electro- oxidation of carbohydrates. An RuOZ loading of 20% m/m was selected for further investigations in order to achieve the highest electrocatalytic response while minimizing the higher background currents associated with even higher loadings (not shown). A hydrodynamic voltammogram similar to those obtained for the oxidation of some antibiotics at Ru02-modified graphite-epoxy electrodes16 was obtained for glucose oxi- dation. A monitoring potential of +0.35 V was selected for subsequent investigations in order to minimize interferences at the higher potentials and to maintain lower background currents.Attempts to lower the relatively high NaOH concentrations and pH levels required for the electrocatalytic reaction to occur proved unsuccessful. The currents obtained in low (<0.1 mol dm-3) NaOH concentrations, on addition of glu- cose to the cell, were negligible but rose sharply to a plateau on increasing the NaOH concentration, reaching maximum levels at approximately 0.5 mol dm-3 NaOH concentration. Experi- ments conducted in 0.05 mol dm-3 phosphate buffer, using NaOH for adjustment of pH, showed that negligible currents were obtained on addition of glucose to the cell, below a pH of 10. Above this pH, a sharp rise in current was observed for glucose additions, related to the increase in NaOH concen- 4- 2 3 0 'a) 1 2 3 Concentration/ mmol dm-3 B i Time I Fig.3 ( a ) Current-time recording obtained at A, the 20% m/m RuOrmodified and B , the unmodified graphite-epoxy electrodes on the batch addition of glucose in 0.5 mmol dm-3 increments to the stirred (400 rev min-') cell. Other conditions as in Fig. 2. ( b ) Corresponding current-concentration calibration graph tration. This dependence of response on base concentration can be attributed to the availability of the adsorbed radical species OHads, which is thought to participate in the electro- oxidation of alcohols and carbohydrates at Ru02-based electrode^,'^>^^ and/or to the requirement of high pH for the formation of the higher valency ruthenium-oxy species known to be the catalytically active surface component^.^^ An NaOH concentration of 0.5 rnol dm-3 was selected for subsequent investigations.This high pH level precluded the addition of a modifying polymer layer on to the surface of the Ru02- modified graphite-epoxy electrode, which would be required in order to exclude interferences such as proteins and other biological entities, All the polymers investigated for this purpose (Nafion, cellulose acetate, PVP, AQ55-D and AQ29- D) proved to be unstable on the electrode surface in this electrolyte. The response at the 20% m/m Ru02-modified graphite- epoxy electrode to the repeated addition of 0.5 mmol dm-3 levels of Flucose is depicted in Fig. 3. A slope of 1.06 pA dm mmol-' (correlation coefficient: 0.999) was obtained, with the electrode displaying linearity over the 0.5- 5 mmol dm-3 concentration range.All of the 20% m/m Ru02- modified electrodes prepared functioned in a similar manner, yielding calibration graphs with slopes of approximately 1 pA dm3 mmol-' (+lo%) over the linear range. The success of this electrode fabrication technique (100% success rate for the 15 electrodes prepared) compares favourably with other techniques for the incorporation of modifiers in polishable, robust electrode^.^'-^^ The stability and precision associated with the detection of glucose using these Ru02-modified electrodes are demon- strated in Fig. 4. Fig. 4(a) illustrates the precision of the electrode response from surface-to-surface, with the electrode being polished for 30 s with a 0.05 pm alumina slurry between additions. For the series of eight determinations shown, a mean current of 1.98 FA, with a relative standard deviation of 3.75%, was obtained for the addition of 2.5 mmol dm-3 glucose to the cell.Fig. 4(b) shows the repeated addition of 2.5 mmol dmP3 glucose to the cell, with the electrode being rinsed with distilled water between experiments. A mean current of 1.72 pA with a relative standard deviation of 2.1% was obtained for this series. These results, taken together, illustrate the extremely good stability and reproducibility that can be achieved with inorganic modifiers of graphite-epoxy electrodes.ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 27 c c ? 3 0 I a) 8 7 6 5 4 3 2 1 2 min [ b ) H 8 7 6 5 4 3 2 1 Time Fig. 4 Precision experiments for the 20% m/m Ru02-modified electrode on addition of 2.5 mmol dm-3 glucose.(a) Surface-to- surface precision; polishing with 0.05 pm alumina slurry for 30 s and rinsing with distilled water. ( b ) Precision obtained for one electrode surface: rinsing with distilled water between additions. Other con- ditions as in Fig. 2 Conclusion It has been shown that the Ru02-modified graphite-epoxy electrodes are capable of glucose detection, yielding stable, reproducible and renewable responses for millimolar levels of glucose. Attempts to reduce the high pH level and NaOH concentration required for the electrocatalytic oxidation of glucose were unsuccessful, however, as were attempts to modify the electrode surface with polymer films to confer a degree of selectivity on these modified electrodes.It would appear, therefore, that the practical application of these modified electrodes will be in the non-selective detection of hydroxyl-containing species (alcohols, carbohydrates and selected pharmaceuticals) following chromatographic separ- ation. It is envisaged that the Ru02-modified graphite-epoxy electrodes might offer viable alternatives to the commercially available pulsed amperometric detection systems for carbo- hydrate detection. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 References Hughes, S . , Meschi, P. L., and Johnson, D. C., Anal. Chim. Acta, 1982, 132, 1. Hughes, S . , and Johnson, D. C., Anal. Chim. Acta, 1982,132, 11. Hughes, S., and Johnson, D. C., Anal. Chim. Acta, 1983, 149, 1. Neuberger, G.G., and Johnson, D. C., Anal. Chem., 1987,59, 203. Neuberger, G. G., and Johnson, D. C., Anal. Chem., 1987,59, 150. Bindra, D. S . , and Wilson, G. S . , Anal. Chem., 1989,61,2566. Santos, L. M., and Baldwin, R. P., Anal. Chem., 1987, 59, 1766. Fleischmann, M., Korinek, K., and Pletcher, D., J. Electro- anal. Chem., 1971, 31, 39. Schick, K. G., Magearu, V. G., andHuber, C. O., Clin. Chem. ( Winston-Salem, N . C. ), 1978, 24, 448. Morrison, T. N., Schick, K. G., and Huber, C. O., Anal. Chim. Acta, 1980, 120, 75. Reim, R. E., and Van Effen, R. M., Anal. Chem., 1986, 58, 3203. Prahbu, S . V., and Baldwin, R. P., Anal. Chem., 1989,61,852. Prahbu, S. V., and Baldwin, R. P., Anal. Chem., 1989, 61, 2258. Wang, J., and Taha, Z., Anal. Chem., 1990, 62, 1413. Leech, D., Wang, J., and Smyth, M.R., Electroanalysis, 1991, 3, 37. Leech, D., Wang, J., and Smyth, M. R., Analyst, 1990, 115, 1447. Burke, L. D., and Murphy, 0. J., J. Electroanal. Chem., 1979, 101, 351. Watanabe, M., and Motoo, S . , J. Electroanal. Chem., 1975,60, 267. Lam, K. W., Johnson, K. E., and Lee, D. G., J. Electrochem. SOC., 1978, 125, 1069. Cox, J. A., and Kulkarni, K. R., Talanta, 1986, 33, 911. Shaw, B. R., and Creasy, K. E., J. Electroanal. Chem., 1988, 243, 209. Shaw, B. R., and Creasy, K. E., Anal. Chem., 1988,60,1241. Park, J., and Shaw, B. R., Anal. Chem., 1989, 61, 848. Stripping Voltammetry with a Polymeric Calixarene Modified Carbon Paste Electrode Damien W. M. Arrigan and Gyula Svehla" Department of Chemistry, University College, Cork, Ireland Stephen J.Harris Research and Development, Loctite (Ireland) Ltd., Whitestown Industrial Estate, Tallaght, Dublin 24, Ireland M. Anthony McKervey School of Chemistry, Queen's University, Belfast BT9 5AG The use of stripping voltammetry' for trace measurements of inorganic and organic analytes in complex matrices is well established. It is based on a two-step procedure: firstly, the analyte of interest is accumulated at the working electrode and secondly, the accumulated analyte is stripped from the working electrode by applying a voltammetric waveform; the resulting voltammogram provides a measure of the analyte accumu- lated. The combination of the accumulation step, which serves to preconcentrate the analyte, with advanced voltammetric waveforms such as differential-pulse or square-wave voltam- _ _ _ _ _ ~ _ _ _ _ _ _ _ ~ - * To whom correspondence should be addressed.metry, allows a low limit of detection for many analytes of interest. Electrolytic accumulation (amalgam formation) at hanging mercury drop and mercury film electrodes is used for anodic stripping voltammmetry of metals. However, the determination of some metals cannot be achieved at mercury- based electrodes, e.g., if the electrode potential of the metal of interest is more positive than that of mercury then the anodic response for mercury will mask the response for the analyte. Similarly, analytes that are not amenable to electrolytic deposition at mercury can only be determined with difficulty. Hence the search for non-electrolytic preconcentration schemes and alternative electrodes has intensified.28 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 A range of new electrodes has been developed.2 Of these, chemically modified electrodes ( CMES)~,~ have been utilized for non-electrolytic accumulation by ion-exchange , com- plexation and covalent reactions. By attaching a reagent with desirable properties to an electrode surface, the electrode takes on the properties of that reagent.Various reagents have been used for electrode modification with application in stripping voltammetric schemes. We have studied calixarenes for electrode modification. Calixarenes' are macrocyclic phe- nol-formaldehyde condensates that exhibit interesting ion- bindin characteristics when modified at the phenolic oxygen selective electrode^^^^ and here their use in another branch of electroanalysis is illustrated. The calixarene used for electrode modification is a linear polymeric calix[4]arene, as shown in Fig.1. The preparation of this polymer has been el~ewhere.~ atom. (F They have previously been used as ionophores in ion- was chosen for further work because of its non-complexing nature and in view of the potential analytes to be studied. Each measurement cycle consisted of three steps, as follows: 1. Preconcentration Mn+ + calixarene (M"+calixarene) (M"+calixarene) + ne- + (M'calixarene) (M'calixarene) --+ M"+ + calixarene + ne- Of the metals examined, lead(II), mercury(I1) and copper(I1) were readily accumulated under open-circuit conditions (step 1 above). For lead, application of -1.0 V for step 2 and a subsequent anodic-going (step 3) differential-pulse waveform produces the voltammograms depicted in Fig.2. These 2. Reduction 3. Stripping voltammetry OCH2COCH2CH3 OCH2COCH2CH20CCCH3 II I II 0 OCH2 II 0 Fig. 1 Linear polymer of a tetrameric calixarene used for electrode modification; n = 3-7 t Experimental Chemically modified carbon paste electrodes (CMCPEs) were prepared by dissolving 10 mg of the polymeric calix[4]arene in 5 ml of chloroform; 190 mg of graphite powder were then added and the mixture was stirred constantly until the solvent had evaporated. The paste was then prepared by thoroughly mixing 120 mg of Nujol with the graphite-calixarene mixture and was packed into an electrode body (a glass tube fitted with a nylon top having a 3 mm diameter well with a copper disc at the bottom for electrical contact) to yield the CMCPE.Preconcentration took place from 10 ml of solution at open circuit; the CMCPE was then transferred into the voltammetric cell and the surface-bound metal reduced by application of an appropriate potential. The measurement step was an anodic voltammetric scan. Differential-pulse voltammetry was carried out (pulse amplitude, 50 mV) on either a Metrohm 626 Polarecord or an EG & G Princeton Applied Research 174A polarographic analyser in conjunction with an RE0074 x-y recorder. The three-electrode cell consisted of the CMCPE working electrode, a platinum wire counter electrode and a saturated calomel reference electrode (SCE) . The electrolyte was 0.1 mol dmP3 HN03. Results and Discussion A variety of electrolytes were investigated for use in stripping voltammetry. The best electrolytes were those that had a pH of less than 5 , with HN03 and HC1 being the optimum.Nitric acid w c -0.6 -0.5 -0.4 -0.3 -0.2 2 (3 I ( b ) .2 yA I I I I I -0.6 -0.5 -0.4 -0.3 -0.2 , E N versus SCE Fig. 2 Differential-pulse stripping voltammograms for various pre- concentration times at the CMCPE. (a) [Pb2'] = 1 x mol dm-3; preconcentration time: A, 1; B, 2; and C, 3 min. (6) [Pb"] = 1 x lop6 mol dm-3; preconcentration time: A, 1; B, 2; C, 3; and D, 5 min voltammograms were obtained after different preconcen- tration times; the peak current increases with preconcentration time up to 5 min after which the response levels off, owing to an equilibrium between the CMCPE surface and the solution.Similar results were obtained for mercury and copper, Figs. 3 and 4, respectively. These results indicate that preconcen- tration under open-circuit conditions with this calixarene CMCPE for periods of time of up to 5 min should allow the detection of micromolar levels of these three analytes. Indeed this is so: 0.2 pmol dm-3 lead, 5 pmol dm-3 mercury and 1ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 29 2.0 1.5 ; 1.0 ._ 0.5 0 5 10 P reco ncentration ti rn e/m i n Fig. 3 the CMPE. [Hg2+]: A, 1 x lo-’; B, 1 x lo-‘; and C, 1 X mol dmP3 Effect of preconcentration time on peak current for Hg” at I 0.4 0.3 % . .-a 0.2 0.1 C n B X A V I I 0 2 4 6 8 10 Preconcentration tirnelmin Fig. 4 Effect of preconcentration time on peak current for Cu2+ at the CMCPE. [Cu”]: A, 1 x and C, 1 x lO-‘mol dm-3 B, 1 x ymol dm-3 copper are detectable with these short preconcen- tration times.Simultaneous preconcentration of the three metals would be advantageous, allowing their measurement in mixtures. Pre- concentration-voltammetry of an equimolar mixture yielded two main peaks, corresponding to lead and mercury. Even when copper is present in a 10-fold excess, only a very small response is obtained for this metal. These results indicate that the polymeric calixarene used for electrode modification has a selectivity for lead and mercury over copper. Fig. 5 shows a stripping voltammogram for a mixture of the three metals after accumulation for 5 min, illustrating that at higher levels of copper the three metals can be detected.Tetrameric calixarenes have been found to show selectivity for sodium when incorporated in ion-selective electrode^.^ Therefore, additional information on the selectivity of the electrode was obtained by studying the response of the CMCPE to lead in the presence of sodium ions. It was found that for 1 x mol dmP3 lead in the presence of different concentrations of sodium, the lead response decreased with increasing sodium concentration (Table 1). This decrease is caused by the excess of sodium competing with the lead for the calixarene binding sites on the electrode surface. Hence the use of this CMCPE would require prior removal of such ions from a sample before trace metal analysis could be carried out. I I I -0.5 0.0 +0.5 EN versus SCE Fig.5 Differential-pulse stripping voltammogram for a mixture of three metals at the CMCPE. [Pb2+] = 1 X lop6 mol dm-3; [Cu2+] = 1 x lop4 mol dm-3; and [Hg-+] = 1 x lo-‘ mol dmP3. Preconcen- tration time, 5 min Table 1 Effect of sodium on the CMCPE response to 1 X mol dm-3 Pb2+ Response in the absence of Na+ [Na+]/mol dm-3 (Yo 1 0 100 1 x 98 1 x 43 1 x lo-’ 36 The work reported here illustrates an additional application of calixarenes in electroanalysis. Studies are underway to examine calixarenes having nitrogen and sulfur donor atoms within the ion-binding portion of the macrocycle, in the hope that selectivity for the heavy metals over Group 1 metals will be improved. 1 2 3 4 5 6 7 8 9 References Wang, J., Stripping Analysis: Principles, Instrumentation and Applications, VCH, Deerfield Beach, FL, 1985.Bond, A. M., and Scholz, F., 2. Chem., 1990, 30, 117. Murray, R. W., in Electroanalytical Chemistry, ed. Bard, A. J., Marcel Dekker, New York, 1984, vol. 13. Dong, S . , and Wang, Y., Electroanalysis, 1989, 1, 99. Gutsche, C. D., Calixarenes, Monographs in Supramolecular Chemistry, Royal Society of Chemistry, Cambridge, 1989. Arnaud-Neu, F., Collins, E. M., Deasy, M., Ferguson, G., Harris. S. J.. Kaitner, B., Lough, A. J . , McKervey, M. A , , Marques, E., Ruhl, B. L., Schwing-Weill, M. J . , and Seward, E. M., J . Am. Chem. SOC., 1989, 111, 8681. Diamond, D., Svehla, G., McKervey, M. A., and Seward, E. M., Anal. Chim. Acta, 1988, 204, 223. Cadogan, A . , Diamond, D., Smyth, M. R., Svehla, G., McKervey, M. A., Seward, E.M., and Harris, S. J., Analyst, 1990, 115, 1207. Loctite (Ireland) Ltd., Irish Pat. Appl., 3986/89, December 1989.30 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 L. 2 5 90 lQ a, - 85 0. v) 2 CI) 80 4 Fuel Cell Methodology for Determining Petrol Adulteration with Kerosene - - - M. Shahru Bahari, W. J. Criddle" and J. D. R. Thomas School of Chemistry and Applied Chemistry, University of Wales College of Cardiff, P.O. Box 912, Cardiff CFI 3TB The total or partial reduction in the use of lead additives in petrol has led to an increase in the use of oxygenates (alcohol and ethers)' to enhance the octane rating of petrol. These can be active in fuel cells, thus offering a route for analytical determinations. Owing to its relatively low importance as a fuel compared with petrol, non-aviation kerosene (a high-boiling fraction in petroleum refining) lacks these additives and its addition to petrol will lower the octane rating of the motor vehicle fuel.The dilution effect caused by the addition of kerosene to petrol will lower the concentration of those potentially fuel cell active materials initially present and will reduce the partial pressure of such additives in the headspace of the fuel investigated. This paper discusses the correlation between the level of adulteration of petrol with kerosene and fuel cell responses of adulterated petrol headspace. The fuel cell instrumentation used consists of commercially available fuel 100 , I z I _ 5 95 22 75 0 4 8 12 16 20 Kerosene in petrol (% v/v) Fig. 1 AE-D3 instrument response for petrol samples adulterated with kerosene.[Regression equation: y = 95.17 - 0.87~; correlation coefficient (Y) = 0.9941 140 v) c w .- ; i 20 2 e ; 100 w .- v) c 0 a W 80 60 I 1 1.8 I I _ _ . .- 10 20 30 40 10 20 30 40 Temperature/"C Fig. 2 Typical temperature correlation data for Lion AE-D3 instru- ment response for mixtures of petrol in hexane (100 cm3) * To whom correspondence should be addresses. Table 1 Data for plots of log(AE-D3 response) versus temperature (see Fig. 2) at different concentrations of petrol in hexane Petrol in hexane Correlation (Yo v/v) Slope coefficient (Y) 5.0 0.0115 0.991 10.0 0.0110 0.997 15.5 0.0127 0.997 20.0 0.0114 0.985 25.0 0.0123 0.989 Mean: 0.0118 k 0.0006 v) Y .- 5 5.0 L- 2 e % 4.5 !? CI .- I 0 Q v) 7 I I I I 0 4 8 12 16 20 Kerosene in petrol (% v/v) ' 4.0 ' Fig.3 Calibration data for adulterated petrol samples using the Lion DA-1 Drinks Analyzer. Regression analyses: A, Brand 3, y = 5.004 - O.O49x, r = 0.998; B, Brand 1, y = 5.058 - O.O48x, Y = 0.996; and C, Brand 2. y = 5.073 - O.O47x, Y = 0.998 cell based instruments, namely, the Lion AE-D3 Alcolmeter and DA-1 Drinks Analyzer.2 Experimental Premium (4-Star) petrol samples (BP, Esso and Texaco) and kerosene (Texaco, the only available source) were used as received. Hexane (General Purpose Reagent, Merck, Poole, Dorset, UK) was used as solvent in order to dilute the concentrations of the oxygenated materials present in petrol. This is necessary as both types of fuel cell instrument used can only take limited concentrations of fuel cell active materials within their (linear working) capability range.The Lion AE-D3 Alcolmeter was first used to study the fundamental behaviour of petrol samples, namely, their fuel cell responses, signal reproducibility, optimum concentrations and a fuel cell fatiguing phenomenon characteristic of petrol- hexane mixtures. The Lion DA-1 Drinks Analyzer, which is fully automated and more suitable for use in the field, was used for the subsequent calibration studies and analysis. The mode of operation of both of these units has been described elsewhere .3-4 Results and Discussion It was shown that fuel cell fatiguing is a strong feature of the petrol-hexane system compared with the aqueous ethanolicANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 31 system.The fuel cell requires extensive conditioning prior to taking analytical data; this is achieved by successive sampling of the headspace of the petrol-hexane mixture (six times), followed in each instance by repeated sampling with air to clear the fuel cell after each sample. This process takes up to 30 min; however, subsequent samplings can be performed as soon as a green instrument indicator light shows ( 5 min). The change in the AE-D3 instrument response with respect to percentage of kerosene adulteration (0-20% v/v; 2% increments) is shown in Fig. 1. The linearity of response, albeit with modest precision, indicates good prospects for the investigation. The effect of temperature on the AE-D3 instrument response is logarithmic (Fig. 2) with a reduced slope (0.0118) (Table 1) compared with the aqueous ethanolic system (0.0281) which was incorporated in the DA-1 instrument software.' Modification of the DA-1 data for the petrol system was carried out in order to compensate for the difference in the slope of the temperature correlation curve.Owing to the fuel cell fatiguing effect, observed for the Lion AE-D3 instrument, fuel cell conditioning of the DA-1 instru- ment was performed by carrying out three automatic analyses (six samplings) on a 10% v/v petrol-hexane control mixture. The DA-1 instrument was then recalibrated and set to read five analyses for each sample at the 5% level. Calibration data for DA-1 analyses are shown in Fig. 3. Conclusion The linearity, identical slopes and the small differences between brands shown by the fully automated Lion DA-1 instrument are promising features with respect to application of the approach to in-the-field analysis for adulteration screening.However, as petrol components vary with season, locality and refinery, it is imperative that reference petrols of the same brand or even the same batch be available as samples, although brand/batch differences, as exemplified in Fig. 3, might not be sufficiently marked to prevent the approach being used for screening purposes. References 1 Lang, G. J., and Palmer, F. F., in Gasoline and Diesel Fuel Additives, ed. Owen, K., Wiley, Chichester, 1989, p. 133. 2 Instrument Leaflets, Lion AE-D3 Alcolmeter and DA-1 Drinks Analyzer, Lion Laboratories, Barry, South Glamorgan. 3 Criddle, W. J . , Parry, K.W., and Jones, T. P., J . Am. SOC. Brew. Chem., 1989, 47, 1. 4 Criddle, W. J., Parry, K. W., and Jones, T. P., Analyst, 1986, 111, 507. Supercritical Fluid Extraction as a Sample Preparation Technique for Chromatography and Spectroscopy M. Kane, J. R. Dean and S. M. Hitchen Department of Chemical and Life Sciences, Newcastle upon Tyne Polytechnic, Ellison Building, Newcastle upon Tyne NEI 8ST C. J. Dowle ICI plc, Wilton Materials Research Centre, P.O. Box No. 90, Wilton, Middlesbrough, Cleveland TS6 8JE R. L. Tranter Glaxo Manufacturing Services Ltd., Harmire Road, Barnard Castle, Co. Durham DL 12 8DT Supercritical fluid extraction (SFE)''2 is emerging as a viable sample preparation technique for analytical chemistry. This is because of the need to speed up the analytical sample preparation protocol. It has been reported that two-thirds of the analysis time in an industrial laboratory is spent on sample p r e p a r a t i ~ n .~ Potential advantages of SFE are: speed of operation, selectivity of extraction, minimal solvent handling, ease of automation, capabilites for off- or on-line analysis and reproducible extractions. These advantages are being achieved because of beneficial properties of supercritical fluids, which include high diffusion rates, variable solvent strength and low viscosity. Carbon dioxide has emerged as the most amenable supercritical fluid4 owing to its low critical temperature, moderate critical pressure, relative inertness, non-toxicity and its ready availability in high purity at low cost.This paper will describe the use of a commercial SFE instrument and its application for off-line sample preparation in analytical chemistry. Experimental The Hewlett-Packard 7680A SFE was used for the extractions. This instrument is an automated, PC based, dedicated extraction unit. Supercritical fluid chromatography (SFC) grade carbon dioxide (Air Products Ltd., Sunderland), fitted with a diptube and carrying a certified purity of 99.995%, is used. Fig. 1 is a schematic representation of the extraction instrumentation. The pumping system is a twin piston pump :: Sample vessel Analyte collection High pressure Pump ii - Rinse solvent Pump Fig. 1 Diagram of HP 7680A extractor which allows control over flow rates between 1 and 4 ml min-' and at pressures up to 365 bar.In addition, a second cylinder of carbon dioxide (Air Products Ltd., Sunderland), fitted with a diptube and having a water content of <100 ppm, is used for the cryogenic cooling of the pump head, sample vessel and column trap. The use of the cryogenic cooling system allows almost instantaneous operation and temperature control. The sample vessel (1 or 7 ml available) is a stainless steel tube with PEEK caps fitted with 10 pm frits at either end. The caps are screwed finger tight, enabling the rapid change over of samples. The vessel is inserted in a sample well which is then raised under computer control to form a high pressure seal. Solid and semi-solid samples can be simply weighed into the32 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 vessel, whereas liquid samples must be placed on a inert medium, such as celite, prior to extraction.Two methods of extraction can be used, dynamic and static. In dynamic extraction the fluid is continually flowing through the vessel, relying on the diffusion characteristics to sweep the analytes from the sample matrix. Alternatively static extrac- tion can be used to ‘soak’ the sample in the fluid. It is thought that the solvating properties of the fluid are more prominent here. It is often advantageous to use both static and dynamic flow in the one extraction to effect the maximum recovery. Pressure within the system is regulated by the use of an electronically controlled variable restrictor. The restrictor allows for complete independent control over the flow and pressure of the system, while preventing blocking as the system depressurizes. The restrictor is thermostatically temperature controlled by using a heating block.As the system depressurises extracted components are collected on to a chromatographic support material and the carbon dioxide is vented to waste. The choice of support material is dependent on the nature of the analyte. Typically, Hypersil ODS (30 pm) has been employed for the collection of non-polar analytes. The final step involves the elution of the analytes from the support material by selecting an appropriate solvent. The system retains two solvents for column rinsing. Methanol and hexane are the most commonly used. The eluted analytes are collected in 2 ml sample vials located in a fraction collector prior to analysis.The samples studied were analysed by using a Carlo Erba (Fisons Instruments Ltd., Crawley) SFC 3000 series chromato- graph. Ultraviolet-visible spectrophotometry measurements were made using a Kontron Uvicon 860 instrument with silica sample cells. Results and Discussion Design of an Extraction Three stages of an extraction procedure can be identified. Stage 1 involves consideration of the sample type. Liquid samples or solids with low melting-points can be extruded through the transfer line. In this case it is essential to absorb the sample on to a solid support material. Solid samples with a non- porous matrix can be freeze dried and ground to present a larger surface area for extraction. Stage 2 involves the selection and use of an appropriate chromatographic packing material for retention of the extracted analytes.Typically, the use of a stainless steel packing material is advisable when non-volatile analytes are to be retained. In contrast, ODS can be used to retain non-polar analytes. However, careful control of the column trap temperature and restrictor is essential for reten- tion of the analytes. During the final stage (Stage 3) the appropriate rinse solvent must be chosen, not only to remove the analytes from the trap but also to be compatible with the subsequent method of analysis. Density and Temperature During SFE the two main parameters which affect good separation of the analytes from the bulk matrix are the fluid’s density and temperature. There is a complex relationship between these two parameters and the solubility of analytes in the fluidq5 The more involatile and polar the analyte the less soluble it will be in pure carbon dioxide.For higher relative molecular mass compounds with olar groups high densities of temperatures may also aid extraction, particularly for polymer samples. fluid (possibly with modification 8 ) should be used. Increased Effect of Varying Carbon Dioxide Density A major advantage of SFE over other extraction techniques is the solvent strength selectivity. This is clearly demonstrated by the extraction of a chromophore from plant material (Fig. 2). By increasing the density of the carbon dioxide used for 0.3 a, c 4 0.15 n 2 a 0.0 350 480 600 Wavelength/nrn Fig. 2 Extraction of plant material extraction in a stepwise manner the chromophore is solubilized to a greater extent.This is a degree of selectivity which cannot be achieved by classical extraction techniques. The PC software allows the programming of stepwise extraction and deposition of analyte fractions in separate sample vials. Extraction of Phthalate from Polyester Resin The extraction of polymer additives is a constant source of concern to polymer manufacturers. Quality assurance and possible migrational effects are two areas in which SFE can be very useful. The example in Fig. 3 demonstrates how the Di octy I p h t h a late 30.97 r- 1 I 1 20.0 30.0 40.0 I I I I I 10.0 20.0 30.0 40.0 50.0 Timehi n Fig. 3 and ( b ) , impure dioctyl phthalate extracted from PVC sample Capillary SFC chromatogram: ( a ) dioctyl phthalate standard; phthalate plasticizer from a commercial freeze-ground PVC sample can be extracted to the same levels as attained by traditional Soxhlet extraction.However, the time scale is an order of magnitude less for SFE.ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 33 Conclusions This paper has demonstrated the potential of SFE as a sample preparation technique for chromatography and spectroscopy. Selected examples highlight the controllable solvent strength and versatility of SFE in analytical chemistry. The speed and reproducibility of extraction will contribute to the growth and acceptance of SFE as a viable alternative to existing sample preparation techniques. We acknowledge the financial support of ICI plc., Wilton Materials Research Centre (Dr. W.C. Campbell), Glaxo Manufacturing Services Ltd. (Mr. K. Leiper) and Hewlett- Packard (UK) Ltd. for the loan of the HP 7680A instrument. References 1 Hawthorne, S. B., Anal. Chem., 1990, 62, 633A. 2 King, J. W., J. Chromatogr. Sci., 1989, 27, 355. 3 Majors, R. E., LCGC, 1991, 4, 10. 4 Larson, K. A., and King, M. L., Biotech. Progress, 1986,2,73. 5 McHugh, M. A., and Krukonis, V., Supercritical Fluid Extrac- tion, Principles and Practice, Butterworths, Boston MA, USA, 1986. 6 Dobbs, J. M., Wong, J. M., Lahiere, R. J., and Johnston, K. P., Ind. Eng. Chem. Res., 1987, 26, 56. ROYAL SOCIETY OF CHEMISTRY The COSHH Regulations: A Practical Guide Edited by: D. Simpson and W. G. Simpson, Principal Consultants, Analysis for Industry The COSHH (Control of Substances Hazardous to Health) Regulations are the most significant health and safety legislation since the Health and Safety at Work Act 1974. Chemists are one of the largest professional groups to be affected by these regulations and this new book provides a definitive guide to their implications and implementation. The Regulations apply to employers in every walk of life, as well as to the self-employed, and The COSHH Regulations: A Practical Guide warns of the penalties that will follow any harm to employees or the general public. It offers realistic help and advice on the steps to be taken to comply with the Regulations or prepare a defence if necessary. Based on the editors’ and contributors’ wide experience the book is immensely practical and provides examples of the application of the Regulations in many different fields of business and commercial life. It is one of the few independent publications available on the COSHH Regulations and is an essential addition to the bookshelf of anyone with an interest in or responsibility for safety. Hardcover Approx 208 pages 234 x 156 mm Price f45.00 ISBN 0 85186 189 X Autumn 1991 ~~ ~ ~ ~~~~ ROYAL SOCIETY OF 6 Royal Society of chemistry, Sales and Promotion Department, Thomas Graham House, Science Park, Milton Road, Information Services To Order, Please write to the: Royal Society of chemistry, Turpin Transactions Ltd, Blackhorse Road, Letchworth, Herts SG6 1 HN, UK. or telephone (0462) 672555 quoting your credit card details. We can now accept AccessNisalMasterCard/Eurocard. Turpin Transactions Ltd, distributors, is wholly owned by the Royal Society of Chemistry. For information on other books andjournals, please write to: Cambridge CB4 4WF, UK. RSC Members should obtain members prices and order from : The Membership Affairs Department at the Cambridge address above.

ISSN:0144-557X    

DOI:10.1039/AP9922900023

出版商:RSC    

年代:1992

数据来源: RSC

摘要:

34 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 Equipment News X-ray Fluorescence Spectrometers The 8400+ series and 8600+ series XRF spectrometers have evolved in appear- ance through the incorporation of the 8410 design philosophy, where the instru- ment power supply and electronics are built into one compact cabinet; cabinets are reduced from three to two. The convenient and ergonomic worktable for the computer-operator interface is now available on all the makers' XRF prod- ucts. The MoirC Fringe goniometer, avail- able on either system for sequential ope- ration, was improved last year to extend the range of analysis and to achieve higher performance. Applied Research Laboratories SA, En Vallaire Ouest C, CH-1024 Ecublens. Industrial Estate, High Wycombe, Buckinghamshire. Multiple Kinetic Assays The Uvikon 900 series of double-beam ultraviolet-visible spectrometers enables the analyst to measure the rate of up to 10 reactions simultaneously using a thermo- statted automatic cell changer.An electri- cally controlled heating system maintains the samples to within 0.1 "C; the tempera- ture of the cell content is displayed on the spectrometer. The progression of the reaction is displayed in real time on the built-in VDU and the kinetics software calculates the rate of up to 10 reactions. Kontron Instruments Ltd., Blackmoor Lane, Croxley Centre, Watford, Hert- fordshire WD1 SXQ. pH Probes for NMR Cells A specially designed pH probe has a total length of 22.8 cm and an outer diameter of 2.5 mm with a 5-15 s response time over the range 0-14 through the temperature range from -5 to 100 "C for measurement on samples with less than 1.5 mm immer- sion depth.V. A. Howe and Co. Ltd., Beaumont Close, Banbury, Oxfordshire OX16 7RG. FTIR Spectrometers Unicam has expanded its range of FTIR spectrometers with the Mattson Series, comprising the 1000 series for quality control or teaching applications, the 3000, 5000 and 7000 ranges and a sophisticated research model, the RS series. The last is an advanced range of instruments offering 0.25 cm-' resolution and the fastest scan speed of any FTIR currently available. A comprehensive software package oper- ating on a standard MS-DOS platform provides easy-to-use data handling tech- niques to solve the most complex research problems. By using this type of platform the software can be easily integrated with other PC-based software packages. Unicam Ltd., York Street, Cambridge CBl2PX.Measurement Device for Microlitre Samples The Ultra-Microcell is a device for measuring sample volumes as small as 2-5 pl. A typical example of its use is in the spectrophotometric measurement of absorbing species using the makers' DU Series spectrophotometer and employing a capillary format for simple DNA sample management. The cell can be effectively used for the measurement of DNA con- centration and purity and protein con- centrations. The Ultra-Microcell consists of an adapter and short path length, disposable, fused silica capillary tubes. Beckman, Progress Road, Sands Flame-ou t Detector A compact flame-out detector, compat- ible with the Autosystem GC and all the Perkin-Elmer 8000 Series gas chromato- graphs, improves laboratory productivity by protecting valuable samples.It detects FID failure by monitoring the associated drop in background signal and immedi- ately stops the chromatograph from entering 'Ready' status. Perkin-Elmer Ltd., Maxwell Road, Beaconsfield, Buckinghamshire HP9 1QA. Automated Pyrolysis System A Curie-point pyrolyser (CPP) coupled with an automatic sampling system for coupling to a gas chromatograph provides an effective method of characterizing a wide range of materials, especially syn- thetic polymers. The sampler can handle up to 20 samples for truly automated routine analysis. The system can be inter- faced to any manufacturer's gas chro- matograph, and extra versatility can be obtained in GC-MS and GC-IR.Applied Chromatography Systems Ltd., The Arsenal, Heapy Street, Macclesfield, Cheshire S K l l 7JB. High-performance Thin-layer Chro- matography Plates HPTLC plates are an ideal way of separ- ating nanogram or picogram samples rapidly, reproducibly and accurately. Each plate consists of an absorbent layer of 4.6 pm silica gel particles mixed with an inert binder and spread in a 200 pm layer on a smooth glass support plate. Plate size options are 5 x S,10 x 10 and 20 x 10 cm. Typically, up to 15 sample spots of less than SO 1.18 each could be run on a 10 x 10 cm plate. HPTLC plates are also available with a pre-adsorbent spotting area along the lower edge, allowing true HPTLC to be performed without the need for special spotting equipment or laborious spotting techniques.Other options are an added phosphor for fluorescence detection of samples and a pre-channelled format for running multiple samples. Whatman Scientific Ltd., Whatman House, St. Leonard's Road, 20120 Maid- stone, Kent ME16 OLS. Electrophoresis System The Minigel system allows as little as 15 ml gel to be used. Overlaid with buffer, a typical 75 x 100 mm gel run at 100 V takes approximately 30 min to develop. An ultraviolet transparent base allows gels to be viewed and photographed in situ with virtually no fluorescence background. A migration scale is etched on the unit, allowing direct measurement of migration rates and distances between bands. V. A. Howe and Co. Ltd., Beaumont Close, Banbury, Oxfordshire OX16 7RG.Gel Scan Accessory The DU Series 7000 gel scan accessory simplifies the analysis of samples prepared by gel electrophoresis. Avail- able as Tube Gel Holder and Film Holder, it works with gels as small as 3.8 x 3.8 cm and obtains data from audio- radiographs, dried slab gels, photo- graphs, transparencies, negatives or 35 mm slides. In addition, the gel scanner software features offer zoom-in and zoom-out, autoscale and peak editing via mouse. The accessory automatically and precisely moves the gel sample through the light beam. To maximize gel scanning resolution there is a range of slits with widths of 0.05, 0.1 and 0.2 mm. Slit lengths of 0.5, 1.0,2.0 and 4.0 mm can be set for each width to optimize resolution for specific needs. Beckman, Progress Road, Sands Industrial Estate, High Wycombe, Buckinghamshire. Blood Controls Improved convenience and greater cost effectiveness are the outstanding features of the new MBX-21 range of blood controls, introduced for use with the ARGOS 5-Diff, LMG and MINOS STX systems and replacing MBX-6 products.Stability is impressive, increasing to 6 months unopened and 21 d following first use. Roche Diagnostic Systems, P.O. Box 8, Welwyn Garden City, Hertfordshire AL7 3AY. Liquid Sample Handling Equipment The Beeline 3 is a totally automated, PC- driven sampler featuring single or twin probes of polymer or stainless steel and probe movement resolution of 0.25 mm in the X Y axis and 0.137 mm in the Z one.ANALYTICAL PROCEEDINGS. JANUARY 1992. VOL 29 35 The Series 4000 autosampler offers a wide range of format options: 40-place or 20- place sample carousel, 40 or 70 mm probe lift to cater for differing height containers, two or three digit timer, optional sample batch counter and a choice of manual, RS232 or TTL control.Other optional extras include a variable speed sample mixer, multiple sampler probes and a HPLC valve facility. The Compudil SR is a compact, single syringe instrument sup- plied with a choice of nine interchange- able syringes between 50 pl and 25 ml. Hook and Tucker Instruments Ltd., Vulcan Way, New Addington, Croydon CRO 9UG. Measurement of Weak Strength Materials The Rank Shearometer uses a shear wave pulse principle to measure accurately the strength of a wide range of food and non- food gels, creams, slurries, dispersions, suspensions and other viscoelastic ma- terials. It has no moving parts and can thus permit repeat tests of the same sample over a period of time without degradation of the material; this is invalu- able for charting the progress of setting, coagulation or cure.With a measurement range of 50-5 x lo5 N m-* the system will provide accurate readings for products from fresh animal blood to non-drip paints. It can even measure concrete and clay in their pre-set form. Stevens Advanced Weighing Systems Ltd., Oak Industrial Park, Chelmsford Road, Dunmow, Essex CM6 1XN. Instrument Rental Low-cost rental has been introduced as well as all-inclusive lease options on four instruments. Regular monthly, quarterly or annual payments will secure use of the Coulter Multisizer I1 and Coulter ZM particle size analysers, the Coulter Porometer pore size analyser and the Coulter LCM liquid condition monitor. Coulter Electronics Ltd., Northwell Drive, Luton, Bedfordshire LU3 3RH.Determination of Nitrogen in Steels Working closely with the American Iron and Steel Institute and with major Euro- pean steel producers, ARL has improved the performance of its optical emission spectrometers, measurements of ex- tremely low wavelengths now being poss- ible. Working with a modified ARL 3460 metals analyser and using the more sensi- tive 149.2 nm line, even the stringent demands of low alloy steel producers can be met. Limits of detection (3 sigma) of 10 ppm are now possible. A lecture tran- script, ‘Nitrogen by Optical Emission’, is available.Applied Research Laboratories SA, En Vallaire Ouest C, CH-1024 Ecublens. Polarime ter The Chiramonitor 2000 shows much enhanced sensitivity and stability over previous models, and the use of its 2 channel chiral software package allows automated calculation of specific rotation, enantiomeric purity and Cali- bration of data within an existing inte- gration package. The makers, ACS, have taken on the distributorship of the ABI range of ultraviolet-visible and diode array detectors and announce a new evaporative light scattering detector. Applied Chromatography Systems Ltd., The Arsenal, Heapy Street, Macclesfield, Cheshire SKll 7JB. Water Purifiers The Prestige reverse osmosis/deionizer range of laboratory water urifiers can provide from 50 to 4000 1 d- . The water quality available covers the full spectrum from reverse osmosis only (for still replacement) to reverse osmosis, organic removal ultrafiltration and nuclear ion exchange for tissue culture, molecular biology and critical analysis. Certain versions are ideal to feed automatic clini- cal analysers.Purite Ltd., Unit E, Bandet Way, Thame Industrial Estate, Chinnor Road, Thame, Oxfordshire OX9 3SJ. I: Quality Control Samples Manufactured under a co-operative research and development agreement between Supelco and the US Environ- mental Protection Agency’s Environmen- tal Monitoring Systems Laboratory in Cincinatti, a new range of quality control samples are direct equivalents to semi- volatile, volatile, pesticide and PCB quality control samples formerly supplied by the EPA’s Repository for Toxic and Hazardous Materials.They are used in EPA methods for drinking water, waste- water and groundwater analyses. A brochure is available. Supelchem UK Ltd., Shire Hill, Saffron Walden, Essex CBll 3AZ. Continuous Flow Analysers The Alternative Detector Interface (ADI) expands the range of methods available for the makers’ TrAAcs system by providing a link to alternative detec- tors, such as a flame photometer or ultraviolet spectrophotometer, thus permitting high speed sample analysis in a wide range of applications, for example, sodium and potassium in soil extracts and fertilisers. The TrAAcs 800 was the first instrument to introduce random access sampling, automatic reagent sequencing, automatic dilution and microflow hydraulics.Bran and Luebbe Analysing Tech- nologies, Beechwood, Chineham Business Park, Basingstoke, Hampshire RG24 OWA. Flow Injection Analysis Software SuperFlow EX is the third generation software for flow injection analysis. It makes possible the integration of the makers’ FIAstar 5010 system with vir- tually any type of flow-through detector. It is especially suitable for ultraviolet- visible, fluorescence and luminescence detectors. With the help of a powerful analog-to-digital board and a multi- purpose interface box, detectors with an output signal of up to 10 V are easily integrated into the FIA system. Litera- ture is available. Tecator AB, Box 70, S-263 21 Hoga- nas, Sweden. Sample Processing Software A software support package, Quatro Concerto, has been launched to comp- lement the makers’ range of Quatro 200 and 300 sample processors.It combines a new quatro controller and editor, WORKFORCE application program suite, WORKSAVER application library and a documentation support pack. New features include automatic calculation of reagent volumes, which decreases reagent addition time by up to 50%, an increased number of rack layouts and configur- ations and the facility to define circular racks for direct sampling to and from carousels. Quatro Biosystems, Broadoak Busi- ness Centre, Ashburton Road West, Trafford Park, Manchester M17 1RW. Syringe Filters The new range of 4 mm syringe filters provides the easiest way to maximize sample recovery from sample volumes of 2 ml or less. The filters consist of a polypropylene housing containing a filter of PVDF, polysulfone, polypropylene, PTFE or nylon 66 media in a choice of pore sizes, from 0.1 to 1.0 pm.Whatman Scientific Ltd., Whatman House, St. Leonard’s Road, 20/20 Maid- stone, Kent ME16 OLS. Filtration Membranes With their hydrophobic, PTFE mem- branes in strong polypropylene housings, TF microfiltration devices offer a versatile answer to many difficult filtration prob- lems. Chemically resistant PTFE is ideal for organic solvent filtration and, when pre-wetted with alcohol, will filter aggressive aqueous solutions. It is equally effective when used for venting and air- gas applications. Disposable Puradisc 25 TF, Polydisc TF and Polycap TF devices vary in their design and style of polypro- pylene housing. All are supplied ready for use and most are available in 0.1,0.2,0.45 and 1.0 pm porosities.Whatman Scientific Ltd., Whatman House, St. Leonards’ Road, 20/20 Maid- stone, Kent ME16 OLS.36 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 Membrane Cell The high pressure SEPA CF membrane cell is a patented membrane test unit capable of operation to 800 lb in-2 for high pressure reverse osmosis testing. It can accommodate any 7.5 X 5.5 in flat sheet membrane for reverse osmosis, nanofiltration, ultrafiltration or micro- filtration and simulates the flow dynamics of spiral-wound and tubular membrane elements. It also has a selection of mesh and tubular feed spacers to optimize separation performance. Osmonics Inc., 5951 Clearwater Drive, Minnetonka, Minnesota 55343, USA. Scales Flexibility is the outstanding feature of the new DT DigiTOL scales for trade.Depending on the weighing range, they can be used as bench or floor scales. They are also available in a certified version following OIML, class 111. Mettler-Toledo AG, CH-8606 Greifen- see, Switzerland. Centrifuges The 52 Series high speed centrifuges feature a unique friction reduction system (FRS) that maximizes throughput, helps to protect labile samples, reduces heat output, enhances instrument reliability and, when combined with an optional HEPA air filter, provides protection when working with biohazardous ma- terials. The J2-HS is the basic analogue version and there are two digital models, the J2-MC and J2-MI. Three high ca- pacity centrifuges have been introduced in the J6 Series: the J6-HC basic analogue and the microprocessor controlled J6-MC and J6-MI.All the J6 models feature rugged belt-drive systems that minimize heat output. Beckman, Progress Road, Sands Industrial Estate, High Wycombe, Buckinghamshire . Cooling Unit The innovative Coolosan unit converts any shape of insulated space into a portable, robust refrigerator for trans- port, boats or caravans and can be used for industrial condensation testing appli- cations. The Coolosan is able to cool any space up to 60 1 and operates on a standard 12 V car battery, using only 1-2 A h-l. A built-in thermostat is set to maintain the temperature between 5 and 7 "C. Jepson Bolton and Co. Ltd., 22 Con- duit Place, London W2 1HS. Laboratory Information Management System The statistical quality control of analytical methods is now a key feature of the high performance VAX-based ACCOMPLIS laboratory information management system.The new facility immediately alerts users to measurement errors, unex- pected results or adverse trends. It also maintains long-term records of measure- ment accuracy, enabling the reliability of results over a period of time to be demonstrated. Another feature of ACCOMPLIS is a fully data driven fa- cility for automatically handling second- ary analytes. Any number of levels of secondary analyte can be specified, allow- ing the derived results themselves to be used in further calculations. ICI Chemical and Polymers Ltd., P.O. Box No 1, Billingham, Cleveland TS23 1LB. Pharmacokinetic and Chemical Kin- etic Libraries The MINSQ pharmacokinetic and chemi- cal kinetic libraries are designed to aid users of MINSQ.Both include models for several types of reactions and both come with models, sample data sets of par- ameters for each model and a comprehen- sive manual which documents each model as an example problem. Both are avail- able in either 5.25 or 3.5 in formats. Upgrades are available for users of pre- vious releases. The Text Formatting Co., Suffield Works, 1 Suffield Road, London N15 5JX. Plastic Tubing The CPC range of plastic quick couplings and tubing includes a recently launched sub-miniature coupling design with shut- off valve, one-piece Softube connectors that need no hose clamps, a Tentube multiple coupling and an all-plastic hy- gienic connector with quick latch-release mechanism.The CPC range incorporates Delrin acetal versions with Buna-N seals for general use and polypropylene options with EPR seals for improved chemical resistance. Tom Parker (Hydraulics and Pneu- matics) Ltd., P.O. Box 36, Marsh Lane, Preston, Lancashire PR1 1HY. Beakers Two standard sizes of measuring beakers are available from stock, both manufac- tured in high clarity polypropylene and incorporating graduations on the side. The two sizes are 20 and 50 ml. Moss Plastic Parts Ltd., Langford Lane, Kidlington, Oxfordshire OX5 1HX. Hazardous Spill Response Kit The 3M Lab Kit is ideal for the fast containment and clean-up of both bench- top and floor spills. Able to absorb up to 5 1 of liquid, it contains 10 Powersorb universal sorbent sheets and 1 universal sorbent pillow.3M Occupational Health and Environ- mental Safety, Technology House, P.O. Box 90, Old Wokingham Road, Crow- thorne, Berkshire RGll 6PX. Mouse House The Mouse House is an acrylic stand to hold the keyboard above the desktop, inclined toward the user at an angle of 15", creating a clutter-free work surface below for the free operation of a mouse. Radleys, Shire Hill, Saffron Walden, Essex CBll 3AZ. Molecular Modelling Software The Chem-X molecular visualization, database and computational software has been ported to run on IBM 386 and 486 PCs under DOS. The visualization capa- bilities have been enriched by the devel- opment of dials and a low cost stereo- viewer which uses liquid crystal display glasses. Chemical Design Ltd., Unit 12, 7 West Way, Oxford OX2 OJB.Literature Brochures describe the TJA 181 optical emission spectrometer and the Smith- Hieftje 8000 automatic atomic absorption spectropho tome ter . Thermo Jarrel Ash Corporation, 8E Forge Parkway, Franklin, MA 02038- 3148, USA. A leaflet offers information on the MB series of FT-IR spectrometers. Bomen Inc., 32 Whirlow Road, Crewe, Cheshire CW2 6R5. A leaflet gives prices for replacement nebulisers for ICP instruments. Precision Glassblowing of Colorado, 14775 East Hinsdale Avenue, Engle- wood, Colorado 80112, USA. A brochure describes the Spectrolab product line for the analysis of metals. Spectro Analytical Instruments, Bosch- strasse 10, D-4190 Kleve, Germany. The 450 page sterling priced colour Supelco Chromatography Catalogue covers GC, capillary, HPLC, LC, SPE, filtration, adsorbents, chemical standards and accessories.Details of applications and trouble-shooting guides are included.ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 37 Supelchem UK Ltd., Shire Hall, Saffron Walden, Essex CBll 3AZ. GUMS Update is a new bimonthly series of current awareness bulletins containing extracts from the recent literature on gas chromatography-mass spectrometry methods, applications and techniques. There are two parallel publications: Section A covering environmental analy- sis and Section B dealing with clinical, biomedical and drugs analysis. HD Science Ltd., 4a Bessell Lane, Stapleford, Nottingham NG9 7BX. Literature is available on the Model 1505 and 1555 analysers for laboratory measurements of total organic carbon, purgeable organic carbon and total car- bon in water samples. Ionics UK Ltd., Carrington Business Park, Carrington, Urmston, Manchester M314DD. The International Food Information Service (IFIS) has joined the Life Science Network (LSN) as an Information Service Affiliate (ISA). IFIS is the producer of Food Science and Technology Abstracts. LSN is a computerized system providing access to international research infor- mation from more than 80 life sciences and related databases. IFIS has recently signed a contract with Cambridge Scien- tific Abstracts to participate in Human Nutrition CD-ROM. IFIS Publishing, Lane End House, Shinfield, Reading RG2 9BB. A leaflet give prices for various items of laboratory glassware: extractors, flasks, etc. Precision Glassblowing of Colorado, 14775 East Hinsdale Avenue, Engle- wood, Colorado 80112, USA. A catalogue describes Reflex, a quality supplies service for routine laboratory consumables. Unicam Ltd., York Street, Cambridge CB12PX. Silver Platter and the Royal Society of Chemistry announce that Analytical Ab- stracts (AA) is available on CD-ROM. Silver Platter Information Ltd., 10 Barley Mow Passage, Chiswick, London W4 4PH.

ISSN:0144-557X    

DOI:10.1039/AP9922900034

出版商:RSC    

年代:1992

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 37 Publications Received Spectroscopic Properties of Inorganic and Sampling Encylopedia of Chemical Technology. Organometallic Compounds. Volume 24 By G.E. Baiulescu, Pmpilia Dumitrescu and Edited by Mary Howe-Grant. pp. xxxii + Senior Reporter E.G. Davidson. Specialist P. Gh. Zugravescu- Ellis Horwood Series in 1087. wiley. 1991. Price ~135.00. ISBN 0- Periodical Report. Pp. xiv + 492. Price Analytical Chemistry- PP. 184. Ellis Her- 471-52669-X. f149.50. Royal Society of Chemistry. 1991. wood. 1991. Price $45.50. ISBN 0-13- Fourth Edition. Volume 1: A to Alkaloids ISBN 0-85 186-223-3. 79 1021 -5. Physical Methods of Chemistry. Second Edition. Volume IV. Microscopy Edited by Bryant W. Rossiter and John F. Ha- Modern Methods of Polymer C k ~ a c - milton. Pp. x i + 539. Wiley. 1991. Price says Edited by Howard G. Barth and Jimmy W. Ilkka A. Hemmila. Volume 117 in Chemical Mays. Volume I13 in Chemical Analysis: A Analysis: A Series of Monographs on Analyti- Series of Monographs on Analytical Chem- Principles of Polarography cal Chemistry and Its Applications. Pp. xi + istry and Its Applications. Series Editor J.D. By R.C. Kapoor and B.S. Aggarwal. Pp. xi + 343. Wiley. 199 I . Price $67.00. ISBN 0-47 1 - Winefordner. Pp. x + 56 1. Wiley. 199 1. Price 185. Wiley. 199 1. Price C28.50. ISBN 0-470- Applications of Fluorescence in Immunoas- terization El 09.00. ISBN 0-47 1-08026-8. 5 109 1-2. f86.00. ISBN 0-47 1-828 14-9. 21 732-4.

ISSN:0144-557X    

DOI:10.1039/AP992290037b

出版商:RSC    

年代:1992

数据来源: RSC

摘要:

38 ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 Conferences and Meetings Analytical Instruments in Japan January 23, I992 , London A Seminar on Analytical Instruments in Japan, aimed at UK suppliers of analytical instrumentation and equipment, will be held at 86 Park Lane, London. The event will be a practical introduction for UK companies con- sidering developing business in Japan. It will report on the findings of the High Level Mission in Analytical Instrumentation which visited Japan in August and September, 199 1, and will highlight some of the key issues for UK exporters of instrumentation. Further details can be obtained from Mr. Colin Andrews, The GAMBICA Association Ltd., Leicester House, 8 Leicester Street, London WC2H 7BN. Edinburgh International Science Festival April 11-25, 1992, Edinburgh The Edinburgh International Science Festival is the only one of its kind in the world, and is now gearing up for its fourth year.With a programme of over 300 talks, walks, films, exhibitions, demonstrations and conferences, this extravaganza allows children, tourists and curious adults alike to rub shoulders with famous scientists and industry leaders as they explore the fascinating, multi-faceted sides of science upon which the 20th Century has been built and depends. Having adopted ‘The Universe’ as its theme for 1992, the fourth Edinburgh International Science Festi- val is taking a truly expansive look at the world with a programme of events that will provide visitors, whatever their age and back- ground, with a memorable experience, and one upon which they can build when they return home.For those who like to be informed and entertained, the 1992 Festival programme covers space research, the ocean depths, and genetic engineering. Wave power, crop circles, biomedical breakthroughs, stress, the physics of bagpipes and the hi-tech world of Grand Prix racing are just some of the topics explored in films, demonstrations and talks. There are also discussions and debates on in- tellectual property, biotechnology, chemicals in the environment, defence technology, tech- nology transfer and the Third World, plus major conferences and symposia on environ- mental health, stone cleaning technology, human genetics and what business has to learn from science. Enquiries should be addressed to the Edinburgh Science Festival Ltd., 1 Broughton Market, Edinburgh, EH3 6NU.ESEAC ’92 May 31-June 3, 1992, Noordwijkerhout, The Netherlands The 4th European Conference on ElectroA- nalysis will be held in Noordwijkerhout (The Netherlands). Under the auspices of the Eu- ropean Society for ElectroAnalytical Chem- istry, the Conference will be organized in the conference centre ‘De Leeuwenhorst’ in Noordwijkerhout. As before, ESEAC ‘92 is entirely devoted to modern electroanalytical subjects. The current status of electroanalyti- cal techniques, including theoretical develop- ments and instrumental applications, will be discussed. For further information contact W.P. van Bennekom, Utrecht University, Faculty of Pharmacy, Department of Pharmaceutical Analysis, P.O. Box 80.082, 3508 TB Utrecht, The Netherlands.1992 Food Structure Meeting May 9-14, 1992, Chicago, IL, USA The 1992 Food Structure meeting will be held at the McCormick Center Hotel in Chi- cago. General tutorials on Sunday, May 10, will be followed by a general session on Monday morning, May 11. Food structure sessions will be held from Monday afternoon, May 1 1 to Thursday morning, May 14. Those sessions will cover Dairy Products, Emulsifiers, Encapsulation, Food Processing, Image Analysis, Meat Foods, and Plant Rhe- ology, and a General Food Structure session will also be organized. Contributions are sol- icited for any of these programmes or for the general Food Structure sessions. The meet- ing will be held in conjunction with the an- nual Scanning Microscopy International meeting.For more information, contact Dr. Om Jo- hari, Scanning Microscopy International, P.O. Box 66507, Chicago (AMF O’Hare), IL, 60666-0507. USA. International Symposium on Hormone and Veterinary Drug Residue Analysis May 19-22, 1992, Ghent, Belgium The Symposium will attempt to continue the tradition of the two meetings held in Ghent in May, 1988, and May, 1990, under the title of the International Symposium on the Analysis of Anabolizing and Doping Agents in Bio- samples. The title of the Symposium has been widened in order to include all kinds of growth promoting agents. The 1992 Sympo- sium will review contemporary developments in the area of the analytical methodology for the detection of residues of hormones and ve- terinary drugs and growth promoting activity in various biosamples. The plenary lectures will be presented by R.J.Heitzman, J. He- nion, H.H.D. Meyer, w. Schanzer, R. Schilt and M.J. Shepherd. C. van Peteghem, Symposium Chairman, Faculty of Pharmaceutical Sciences, Univer- sity of Ghent, Harelbekestraat 72, 9000 Ghent, Belgium. Eurochem June 23-26, 1992, Birmingham The introduction of the Environmental Pro- tection Act earlier this year has prompted the chemical and process industries to re- examine their manufacturing processes. Whilst it appears that the major players are responding to the environmental challenge, the Government is urging smaller companies to keep pace with legislation in order to re- main profitable. At this year’s Eurochem ex- hibition (which will be held in the NEC, Birmingham) a group of 50 companies will be exhibiting the latest environmental tech- nology equipment and services under the banner of ‘Environmental Technology at Eu- rochem’.Specifically aimed at the chemical and process industries, the Group will pro- vide visitors with a window on the latest in- novations i n pollution control, water treatment, waste management and noise abatement equipment. For further information on Eurochem 92 contact Sara Binns, Reed Exhibitions, on 08 1-948-9940. Third International Conference on Nu- clear and Radiochemistry September 7-1 I, 1992, Vienna, Austria This conference will be organized by the Austrian Society of Environmental and Radiochemistry in collaboration with the Technical University of Vienna Atominstitute of the Austrian Universities.The topics considered in the conference will be Nuclear Reactions, Radioanalytical Chemistry, Radionuclide Production and La- belling, Radioactive Nuclides in the Environ- ment, Chemistry of the Nuclear Fuel Cycle, Cosmo- and Geochemistry, Mossbauer Ef- fect, Application of Short Lived Radionu- clides and Rapid Radiochemical Separations. The scientific program will consist of oral sessions and poster presentations. For further information contact Ms. Eva Haberl pa, Atominstitut der Osterr. Universi- taten, Schiittelstrasse 1 15, A- 1020 Wien, Aus- tria. Anabiotec ’92 September 21-23, 1992, Noordwijkerhout, The Netherlands Anabiotec ’92 will cover the rapidly develo- ping interdisciplinary field at the interface of biotechnology and analytical methodology, For further information contact Professor enable analytical chemists and biotechnolog-ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 39 ists to exchange information in order to de- velop a better understanding of analysis in biotechnology and integrate fundamental and applied research in this overlapping field of interest.The following topics are definitely planned: HPLC, GC preparative and dis- placement chromatography, sample prepara- tion; NMR, IR, MS; separation techniques such as capillary-zone electrophoresis and field flow fractionation; flow injection ana- lysis; hyphenated techniques; kinetic methods; new developments; biosensors; monoclonal antibodies and DNA/RNA probes; and glycobiology. Among the appli- cation areas will be: fermentation/production monitoring and process control; regulatory aspects and environmental control; protein engineering; animavplant cell biotechnology ; ticides/organochlorines and PCBs.Environ- and regulatory aspects of rDNA products. mental chemists, food chemists, analytical For more information contact the organiz- chemists, toxicologists and biologists will ing bureau. The address is Anabiotec '92, p/a discuss in an interdisciplinary way the rele- CAOS, WG Plein 475, 1054 SH Amsterdam, vant scientific problems. Emphasis will be The Netherlands. placed on: residue monitoring programmes, chemical and biological screening methods, 4th of Modern Pesticides and Related Pollu- F~~ Eastern E~~~~~~~ c o u n ~ e s enquiries tants should be sent to Dr. J. Hajslova, Department kia Chemical Technology, 166 28 Prague 6-Dej- vice, Suchbitarova 5 , Czechoslovakia. For Owing to the presence of significant environ- all other countries: IAEAC, M. Frei-Hausler, mental problems in Eastern Europe, the pre- P.O. Box 46, CH-4123 Allschwil 2, Switzer- vious topic, Modern Pesticides, has been land. expanded by addition of the withdrawn pes- On Chemistry and Fate quality control, toxicology and legislation. September 8-10, 1993, Prague, Czechoslova- of Food Chemistry and Analysis, Institute of

ISSN:0144-557X    

DOI:10.1039/AP9922900038

出版商:RSC    

年代:1992

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, JANUARY 1992, VOL 29 39 Courses Liquid Chromatography Beginners Train- ing Course Applied Chromatography Systems (Maccles- field) are continuing to run these highly suc- cessful and acclaimed basic training courses. The numbers on these courses are limited to 20 people to enable ‘hands-on’ experience for all participants. Outside lecturers are used who are experts in their relevant fields of chromatography. During the 3 days of the course, the par- ticipants will receive ‘hands-on’ practical ex- perience to emphasize the theoretical aspects. All day-time meals, a course dinner and full course notes are included in the price. The course will run on February 18-20, April 7- 9, June 16-1 8 and October 6-8. For full information contact Stephanie Edge, Course Administrator, ACS Ltd., The Arsenal, Heapy Street, Macclesfield, Che- shire SKI 1 7JB.Selective Delivery of Therapeutic Polypep- tides, Protein and Oligonucleotides March 2-4, 1992, Annecy, France For a full brochure on this course please con- tact Lucinda Middleton, IBC Technical Ser- vices, Gilmoora House, 57-61 Mortimer Street, London W 1 N 7TD. Safety Aspects of Laser Use Murch, 3 4 , I992, Loughborough The University Training Group at Loughbo- rough University of Technology is organizing a health and safety course on this subject. It will focus on the British Standard BS7192: 1989 which makes recommendations to manufacturers and users of laser products. Hazards of laser use and their control will be described and the course will include practi- cal demonstrations. Further details are available from Joyce Motyka, University Training Group, Univer- sity of Technology, Loughborough, Leices- tershire, LEI 1 3TU. Quality Strategic Management and High Performance Execution March 5-6, I992, Berlin, Germany For a full brochure on this course please con- tact Lucinda Middleton, IBC Technical Ser- vices, Gilmoora House, 57-6 1 Mortimer Street, London W 1 N 7TD.HPLC Beginners Training Course HPLC Technology announce the dates of their courses for 1992. These are: March 3- 5; April 28-30; June 23-25; September 8-10; and November 17- 19. Each course dedicates over 70% of its time to practical, hands-on use of HPLC instruments and components. Participants will learn about: The basics of HPLC-what is HPLC, who uses it and why?; What equipment is required and avail- able?; What do all the ‘Buff’ words really mean; Effects of changing stationary phases (Ci, C4, Cs, cis, C3w-the effect on separ- ation); Dead volume-how ‘bad’ HPLC can be avoided by understanding extra column effects; Use of ultraviolet fluorescence and conductivity detectors; Use of isocratic, gra- dient pumping systems; InternaUexternal standards, data captive using integrators and computers; Selecting the correct mobile phase by experiment and prediction using computers.Both lectures and practicals in- volve simple HPLC, allowing anyone with basic laboratory experience to benefit from the course. Send for a comprehensive leaflet and ap- plication form to Nikki Rathbone, HPLC Technology Ltd., Wellington House, Water- loo Street West, Macclesfield, Cheshire SKI 1 6PJ.ImDroving R&D Productivity Through Food Analysis and Food Examination April 7-1 0, 1992, Reading The Association Public Analysts, in conjunc- tion with the APA Educational Trust and the Royal Society of Chemistry Analytical Chemistry Trust, offers a four day residential traning course in the analysis and examin- ation of food, etc. The Course will be held at the University of Reading and is of particular interest to analysts and other scientific per- sonnel working in the enforcement, consult- ancy, industrial or government sectors. Topics included in the 1992 course cover practical entomology, practical microscopy, food microbiology, analytical toxicology, COSHH assessments, AQA, Food Packaging Testing, Heat Treatment of Food, Pesticides Residues, and the writing of Public Ana- lyst/Food Examiner certificates and reports. Whilst this Course is of special interest to those considering the Mastership in Chemical Analysis (MChemA) examination, the ma- terial will appeal to many other analysts and scientists wishing to broaden their under- standing of these subjects. Further information on this course, and a course brochure/enrolment form, can be ob- tained from: Mr. M.F. Godfray, APA Training Officer, 27 Burnbrae, Edinburgh EH12 SUB.

ISSN:0144-557X    

DOI:10.1039/AP9922900039

出版商:RSC    

年代:1992

数据来源: RSC