摘要:

ANPRDI 28( 11 ) 357-396 (1 991 ) ISSN 0144-557X President J. D. R. Thomas Publication of Analytical Proceedings is the responsibility of the Analytical Editorial Board: Editorial Secretary Claire Harris Analytical Proceedings Proceedings of The Analytical Division of The Royal Society of Chemistry Analytical Division Officers: Hon. Secretary C. A. Watson Analytical Division Secretary Miss P. E. Hutchinson Editorial Manager, Analytical Journals Judith Egan "H. M. Frey D. E. Games S. J. Hill D. L. Miles Senior Assistant Editor Paul Delaney A. G. Fogg (Chairman) K. D. Bartle D. Betteridge "J. Egan Hon. Assistant Secretary F. W. Sweeting All editorial matter should be addressed to The Editor, Analytical Proceedings, The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK.Telephone 0223 420066. Telex 818293 ROYAL. Analytical Proceedings (ISSN 0144-557)o is published monthly by The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF. England. All orders, accompanied by payment, should be sent to The Royal Society of Chemistry, Turpin Transactions Ltd., Blackhorse Road, Letchworth, Herts. SG6 IHN, England. 1991 Annual Subscription price if purchased on its own: EC €110.00, Rest of World f126.00, US $258.00, including air speeded delivery. Customers should make payments by cheque in sterling payable on a UK clearing bank or in US dollars payable on a US clearing bank. Air freight and mailing in the USA by Publications Expediting Inc., 200 Meacham Avenue, Elmont, N.Y.11003. USA Postmaster: Send address changes to: Analytical Proceedings, Publications Expediting Inc., 200 Meacharn Avenue, Elmont, N.Y. 11003. Second class postage paid at Jamaica, N.Y. 11431. All other despatches outside the UK by Bulk Airmail within Europe, Accelerated Surface Post outside Europe. PRINTED IN THE UK. Nb: Turpin Transactions Ltd., distributors, is wholly owned by the Royal Society of Chemistry. 0 The Royal Society of Chemistry 1991. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form, or by any means, electronic, mechanical, photographic, recording, or otherwise, without the prior permission of the publishers.R. M. Miller B. L. Sharp *Ex officio mem bers ANALYTICAL JOURNALS 1991 The Analyst ISSN 0003-2654 12 issues per annum plus index EC f246.00 USA $580.00 Rest of World f283.00 Analytical Proceedings ISSN 0144-557X 12 issues per annum plus index EC fllO.OO USA $258.00 Rest of World f126.00 ORDERING: Published by the Royal Sociew of Chemistry Journal of Analytical Atomic Spectrometry (JAAS) ISSN 0267-9477 8 issues per annum (including two special issues) plus index EC f309.00 USA $728.00 Rest of World f355.00 Analytical Abstracts ISSN 0003-2689 12 issues per annum EC f380.00 USA $765.00 Rest of World f420.00 The Analyst, Analytical Abstracts and Analytical Proceedings Journal Ref.No. 0000-0124 EC f648.00 USA $1527.00 Rest of World f745.00 The Analyst and Analytical Abstracts Journal Ref. No. ooocM132 EC f551.00 USA $1299.00 Rest of World E634.00 The Analyst and Analytical Proceedings Journal Ref. No. 0000-0140 EC f313.00 USA $738.00 Rest of World i360.00 SOCIETYOF SPECIAL PACKAGES (Non-RSC Members only) Non-RSC Members should send their orders to: The Royal Society of Chemistry, Turpin Transactions Ltd, Blackhorse Road, Letchworth, Hens SG6 lHN, UK. RSC Members should obtain members prices and send their orders to: Membership Affairs, The Royal Society of Chcmistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK. Turpin Transactions Ltd, distnbutors, IS wholly owned by The Royal Society of Chemistry Hon. Publicity Secretary Dr. J. D. Green, BP Chemicals Ltd., Research and Development Department, Hull Laboratories, Saltend, Hull HU12 8DS Editor, Analytical Proceedings Roger A. Young November 1991 Hon. Treasurer T. B. Pierce ROYAL CHEMISTRY Information Services

ISSN:0144-557X    

DOI:10.1039/AP99128FX041

出版商:RSC    

年代:1991

数据来源: RSC

ISSN:0144-557X    

DOI:10.1039/AP99128BX043

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 357 Achievements and New Directions in Analytical Chemistry: Luminescence and Optical Sensors The following are summaries of five of the papers presented at the Analytical Division Symposium at the Annual Chemical Congress of the RSC held on April 8th-I2th, 1991, in I m peria I College, London. From Fluorescent Probes to Optical Sensors Otto S. Wolfbeis Institute of Organic Chemistry, Karl-Franzens University, A-80 I0 Graz, Austria In the past 20 years, fluorescence spectroscopy has become a technique that has moved away from physics into other fields such as analytical, physical , and clinical chemistry, biophysics, diagnosis, physiology, cytology and molecular biology, but also a number of other highly diversified applications. This is mainly due to the versatility of this type of spectroscopy.Typical parameters that are measured in an experiment involving the measurement of emission of light include one or more of the following: intensity, spectral maximum, decay time, efficiency of energy transfer and polarization of light. Most of these optical parameters are strongly influenced by external per- turbers such as solvent polarity, temperature, viscosity of the solvent, mobility of the fluorophore, pH, oxygen (and other quenchers) and even the concentration of the fluorophore itself. It is little wonder that there has been such a reluctance to accept fluorescence spectroscopy as a reliable tool for analyti- cal, physico-chemical or biomedical sciences. In fact, a number of papers are still appearing in which proper attention is not being paid to the effects of the external perturbers described above.Notwithstanding this caveat, fluorescence spectroscopy has become highly popular in numerous fields of science for the following reasons: it is extremely sensitive, can be fairly selective, allows measurements down to the cellular and even molecular level and is extremely versatile. More than any other component, the laser has contributed to the increase in the use of fluorescence spectroscopy. However, there are some limitations in practice. When real samples (i.e., not the usual distilled water solutions investigated in the laboratory) are studied, a substantial background is evident when working in the 200450 nm excitation range. Also, there are no inexpen- sive laser or LED light sources available in this spectral range.Finally, fibre optics (see below) have a poor transmission at wavelengths below 450 nm. Therefore, one of our primary aims in the early 1980s was to shift the wavelengths of fluorescent probes to longer wave- length ranges. This was systematically carried out for many years and has resulted in a number of new probes with favourable absorption and emission properties (see, for example, reference 1). These probes have proved to be most useful for optical assay of pH, oxygen, enzyme activities, enzyme inhibitors (such as pesticides) and detergents. Many of the probes thus developed are now commercially available. Also, in the early 1980s, optical fibres of acceptable quality became accessible.Given the experience in the field of fluorescent probes, the obvious development was to couple these probes to optical fibres. However, a few problems have to be overcome. In order to obtain a sensor, the indicator must be immobilized on the fibre so that it is not washed out by the passage of the sample. Secondly, the dyes used must have a fairly high photostability so that photobleaching does not compromise the long-term performance of the fibre sensor. Finally, new materials have to be found that are compatible with: (a) the fibre material; ( b ) the species to be analysed; (c) the analyte; and ( d ) the fluorescent probe. Some of these problems have been overcome and have resulted in (fibre) optical sensor schemes for pH, oxygen and C02.24 These are the species of most interest. The technique and materials are now being used in the Cardiovascular Devices/3M Healthcare fibre optic instrumentation for sensin blood pH, oxygen and Some of the sensors described above have been coupled to enzymic reactions in order to obtain biosensors.More specifi- cally, oxygen sensors have been applied to the determination of glucose, cholesterol and lactate (using oxygen-consuming enzymes); pH sensors have been used in glucose and urea sensing (where protons are produced or consumed during enzymic action); C02 sensors have been used as transducers when determining glutamate and other carboxylates (using C02-producing enzymes); and ammonium sensors have been used to determine urea and creatinine (with enzymes produc- ing ammonium ion at near neutral PH).~'' The general philosophy in the research performed in the past five years has been to develop absorbing or emitting chromo- phores so as to produce sensor materials that are fully compatible with small solid-state light sources and detectors. Recently, new dyes have been found which can be excited at 520-550 nm (i.e. , by a green LED or the 520 nm semiconductor laser). In addition, multi-colour chemistries have been develo ed in order to apply a single fibre to multi-analyte sensing.33P2 We started the work on multi-analyte chemistry in 1985 in order to minimize space requirements. Two approaches were con- sidered. The first was to place different dye chemistries at the fibre end which could provide independent signals because their spectroscopic properties would be entirely different.The second was to extract more than one piece of information from one dye. Certain pH indicators, for example, display a strongly pH-dependent fluorescence intensity, but their fluorescence lifetimes remain unaffected by pH within a broad range. However, their lifetimes can be affected by oxygen. Therefore, such dyes are suitable, in principle, for the determination of two parameters simultaneously: PH (or C02) through inten- sity, oxygen through lifetime.' Recently, attempts have been made to discriminate, by using fairly specific optical sensors having a transducer chemistry (rather than by olarimetry), between the ( R ) and (S) forms of optical isomer^!^.'^ The sensing scheme introduced consists of C02 during cardiopulmonary bypass.!358 ANALYTICAL PROCEEDINGS, NOVEMBER 1991 , VOL 28 ( a ) specific recognition of one isomer of an optically active ammonium ion such as the @-blocker propranolol by an enantioselective carrier; and ( b ) coupling the process to a proton transport reaction in a PVC membrane. The approach is both sensitive and fairly enantioselective. All of the optical fibre chemical sensors described here, and many others described elsewhere,16 are based on an analyte- selective recognition process using some type of dye sensor material. It can be stated, however, that while there are a number of transduction methods available, the limiting step in optical and other sensing is still the specific recognition of the analyte from among a plethora of other species.Hence the area in which the most substantial progress is required in the future is in the improvement of the selectivity and sensitivity of the recognition process. References 1 Wolfbeis, 0. S . , and Koller, E., Anal. Biochem., 1983, 129, 365. 2 Offenbacher, H., Wolfbeis, 0. S . , and Furlinger, E., Sens. Actuators, 1986, 9, 73. 3 Wolfbeis, 0. S . , Weis, L., Leiner, M. J. P., and Ziegler, W., Anal. Chem., 1988,60, 2028. 4 Wolfbeis, 0. S., Pure Appl. Chem., 1987, 59, 663. 5 6 7 8 9 10 11 12 13 14 15 16 Clark, C. L., O’Brien, J . , McCulloch, J., Webster, M., and Gehrich, J., J. Extra-Corpor. Technol., 1986, 18, 185. Trettnak, W., Leiner, M. J. P., and Wolfbeis, 0. S., Biosensors, 1989, 4, 15. Trettnak, W., and Wolfbeis, 0. S . , Anal. Lett., 1989,22,2191.Trettnak, W., and Wolfbeis, 0. S . , Anal. Biochem., 1990, 184, 124. Schaffar, B. P. H., and Wolfbeis, 0. S . , Biosens. Bioelectron., 1990, 6, 137. Wolfbeis, 0. S . , Anal. Chim. Acta, 1991, 250, in the press. Wolfbeis, 0. S . , in Novel Techniques and Materials for Fiber Optic Chemical Sensing, eds. Arditty, H. J., Dakin, J. P., and Kersten, R. Th. , Springer Proc. Physics, Springer-Verlag, Heidelberg, 1989, vol. 44, pp. 416-424. Wolfbeis, 0. S . , Proc. SPIE, Int. SOC. Opt. Eng. , 1990, 1368, 218. Lippitsch, M. E., Pusterhofer, J., Leiner, M. J. P., and Wolfbeis, 0. S . , Anal. Chim. Acta, 1988, 205, 1. He, H., Uray, G., and Wolfbeis, 0. S . , Proc. SPIE, Int. SOC. Opt. Eng., 1990, 1368, 175. He, H., Uray, G., and Wolfbeis, 0. S . , Anal. Chim.Acta, 1991, 246, 251. Fibre Optic Chemical Sensors and Biosensors, ed. Wolfbeis, 0. S., CRC Press, Boca Raton, FL, 1991, vols. 1 and 2. Bioluminescent Sensors Pierre R. Coulet and Loic J. Blum Laboratoire de Genie Enzymatique, CNRS-Universite Claude Bernard L yon I , 43 Boulevard du I I Novembre 1918, 69622 Villeurbanne Cedex, France Many workers are involved in the design of chemical sensors. These systems associate a transducer and a sensing layer in which a sensitive element is embedded in a gel or membrane. When a large molecule is recognized by the sensing layer, a change occurs which is converted by the transducer into an electrical signal related to the concentration of the target analyte. Of particular interest are the biosensors which incorporate a biological element in their sensing layer, usually an enzyme, known to present a specific affinity for a molecule to be monitored in a complex mixture.Several types of transducers can be associated with such bioactive layers provided the type of signal generated by the biological element and the properties of the transducer for optimum functioning are compatible. Literature on the subject is fairly abundant, owing to intensive efforts in this field in the past decade, and updated reviews or books are regularly Our work has been oriented towards the design of amperometric enzyme electrodes and associated instrumentation based on oxidase reactions for practical use in real sample^.^ More recently, among the different types of chemical or biosensors, those associating an optical transduction appear even more promis- ing’ and we focused our efforts on this novel type of transduction.An original type of biosensor based on the use of light emitting enzyme systems was developed in this laboratory and the different steps of its conception will be summarized here. Chemiluminescent and bioluminescent reactions occur when energy from a chemical or biochemical source which has been transferred to a molecule is released, leading to the emission of light. Chemiluminescence reactions involving luminol and requiring hydrogen peroxide are particularly interesting as they can be enzymically catalysed by peroxidase and because many oxidases lead to hydrogen peroxide as a product. The use of these oxidases as auxiliary enzymes extends the analytical potentialities of the system to numerous analytes.Two main types of bioluminescence enzyme systems have been investi- gated: the first concerns the firefly luciferase reaction which catalyses the oxidation of luciferin in the presence of ATP. Emission of light occurs at 560 nm, the intensity of which is directly related to the concentration of ATP according to the over-all reaction: Firefly luciferase ATP + LH2 + 0 2 AMP + PPi + oxyluciferin + C02 + hv The second system is bienzymic and originates from marine bacteria (Vibrio harveyi and Vibrio fischeri) . Oxidoreductase and luciferase work sequentially as shown below Oxidoreductase NAD(P)H + FMN NAD(P)+ + FMNH2 Bacterial luciferase FMNHZ + RCHO + 0 2 > FMN + RCOOH + H20 + hv NAD(P)H is oxidized in the presence of FMN which in its reduced state, FMNH2, is a substrate for the bacterial luciferase, requiring also a long-chain aldehyde as co-sub- strate.Under limiting conditions, the light emitted at 490 nm is directly proportional to the NAD(P)H concentration. From our experience with enzyme electrodes, it was obvious that the characteristics of the bioactive membrane would be the determining factor for the performance of the resulting biosensor and initial experiments were devoted to the immo- bilization of the luminescence enzyme systems. Collagen membranes were first used for enzyme immobilization by using the acyl-azide procedure previously developed in this labora- tory.6 By using this procedure, the immobilization of firefly luciferase from Photinus pyrulis could be achieved on collagenANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 359 strips which were used for the internal coating of cylindrical cuvettes regularly used in conventional l~minometers.~ As the enzyme reaction proceeded under heterogeneous conditions, stirring was necessary and measurements of ATP could be performed in the range from 1 x lo-'' to 3 x low6 mol dm-3 with good reproducibility (RSD = 3%).It must be pointed out that atypical kinetics were observed after immobilization' with, in particular, a longer time for reaching the steady state and a noticeable influence of the nature of the saturating substrate initially in contact with the bound enzyme. In parallel, the immobilization of the bacterial bienzyme system was achieved and NADH determined in the range from 1 X Although collagen provided a stabilizing environment for the immobilized enzymes, the characteristics of membranes can vary from batch to batch.This drawback could be circumvented by using a new type of membrane supplied in a pre-activated form for immunodiagnostic uses by Pall (USA). Conditions for the immobilization were adapted in this laboratory to the design of bioactive membranes for tailor- made biosensors, '' and horseradish peroxidase immobilized on this membrane enabled hydrogen eroxide to be detected in the range from 1 x lo-' to 1 x 10- mol dmW3." based on the different luminescence enzyme systems immobilized on such membranes after adapting the experimental conditions. The main part of the biosensor consists of a glass-fibre bundle connected at one end by a screw cap and this sensing tip is connected to a light-proof reaction vessel into which samples are injected through a septum.Depending on the type of enzyme bound onto the membrane, h drogen peroxide could be measured in the range from 2 x lo-' to 2 x low5 mol dm-3, ATP in the range from 2 x lo-'' to 1 X mol dm-3 and NADH from 1 x to 3 x lod6 mol dm-3. Particular attention was devoted to improving stability, both operational and on storage, of the immobilized bacterial enzyme The ability of the biosensor to recognize other target analytes could be realized by co-immobilizing other enzymes involving hydrogen peroxide, ATP or NADH in their reactions. Assays of sorbitol, ethanol and oxaloacetate could be performed by co-immobilizing the appropriate dehydrogen- ase.I6 The alternate determination of ATP and NADH could also be carried out by co-immobilizing the bioluminescent systems from both the firefly and bacteria on the same membrane and varying sequentially the composition of the reaction medium.I7 In order to reduce the dependence of the biosensor on complex reaction media, including the different co-substrates, experiments were conducted recently with FMN to 2 X mol dm-3 with a precision of 5 y 0 .~ r A novel optical biosensor was then embedded and released in the immediate vicinity of the active enzyme. l8 In conclusion, this new type of biosensor appears to be highly sensitive and specific with possible extension to a variety of analytes through associated auxiliary enzymes. It does not require light sources and sophisticated electronics. Finally, such a biosensor combined with flow injection might lead to an extremely powerful analytical system and this is currently under investigation. l9 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 References Turner, A.P. F., Karube, I., and Wilson, G. S., Biosensors, Oxford University Press, New York, 1987. Janata, J., and Bezegh, A., Anal. Chem., 1988, 60, 62R. Blum, L. J., and Coulet, P. R., Biosensor Principles and Applications, Marcel Dekker, New York, 1991. Coulet, P. R., in Biosensors International Workshop 1987, GBF Monographs, eds. Schmid, R. D., Guilbault, G. G., Karube, I., Schmidt, H.-L., and Wingard, L. B., Jr., VCH, Weinheim, Wolfbeis, 0. S . , Fiberoptic Chemical Sensors and Biosensors, CRC Press, Boca Raton, FL, 1991, vols.1 and 2. Coulet, P. R., Julliard, J. H., and Gautheron, D. C., Biotechnol. Bioeng., 1974, 16, 1055. Blum, L. J., Coulet, P. R., and Gautheron, D. C., Biotechnol. Bioeng., 1985, 27, 232. Blum, L. J., and Coulet, P. R., Biotechnol. Bioeng., 1986, 28, 1154. Blum, L. J., and Coulet, P. R., Anal. Chim. Acta, 1984, 161, 355. Assolant-Vinet, C. H., and Coulet, P. R., Anal. Lett., 1986,19, 875. Blum, L. J., Plaza, J.-M., and Coulet, P. R., Anal. Lett., 1987, 20, 317. Blum, L. J., Gautier, S. M., and Coulet, P. R., Anal. Lett., 1988, 21, 717. Blum, L. J., Gautier, S. M., and Coulet, P. R., J. Biolumin. Chemilumin., 1989, 4, 543. Gautier, S. M., Blum, L. J., and Coulet, P. R., Biosensors, 1989, 4, 181. Blum, L. J., Gautier, S.M., and Coulet, P. R., Anal. Lett., 1989, 22, 2211. Gautier, S. M., Blum, L. J., and Coulet, P. R., J. Biolumin. Chemilumin., 1990, 5 , 57. Gautier, S. M., Blum, L. J., Coulet, P. R., Anal. Chim. Acta, 1990, 235, 243. Gautier, S. M., Blum, L. J., and Coulet, P. R., Anal. Chim. Acta, 1991, 243, 149. Blum, L. J., Gautier, S. M., and Coulet, P. R., Anal. Chim. Actu, 1989, 226, 331. 1987, V O ~ . 10, pp. 75-80. Laser Fluorimetric Detection in Capillary Electrophoresis Michael J. Sepaniak Department of Chemistry, University of Tennessee, Knoxville, TN 37996- 1600, USA The commercial availability of narrow-bore (< 100 pm i .d.), fused-silica capillaries, with their intrinsic ability to dissipate electrophoretically generated heat, has engendered the devel- opment of two highly efficient, ultra-low volume, separation techniques.Capillary zone electrophoresis (CZE) has been used to separate charged solutes ranging in size from small inorganic ions to large proteins and oligonucleotides. Often limited in efficiency only by axial diffusion, plate counts as high as lo6 m-l are obtained by injecting low nanolitre volumes of sample onto the capillary. Charged micelles can be included in the CZE buffer, creating a secondary phase that migrates electrophoretically , thereby imparting a chromatographic par- titioning mechanism to the technique. Micellar electrokinetic capillary chromatography (MECC), as we have called this form of CZE, can be used to separate relatively polar neutral solutes based on their differential association with the micelles.Micelles formed from sodium dodecyl sulphate are most commonly employed; however, cationic, mixed and even chiral surfactant systems have been used in MECC. Usually the electrophoretic migration of the micelles opposes the electro- osmotic flow of the buffer, but is smaller in magnitude, creating chromatograms that exhibit a unique 'elution window'. As in360 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 conventional liquid chromatography, various forms of resis- tance to mass transfer limit efficiency. Nevertheless, plate counts in excess of 10’ m-l are easily achieved. Despite exceptional separation power, the impact of the CZE/MECC techniques in chemical analysis is considerably reduced by the lack of compatible detectors. Most signifi- cantly, the diminutive capillaries produce solute band volumes that are minute and must be detected ‘on-column’ (in a short section of the capillary near its outlet), if high separation efficiency is to be maintained.For example, a 75 cm x 50 pm i.d. capillary exhibiting an efficiency of 10’ plates would yield a band volume for an unretained solute of less than 10 nl. Detection in CZE/MECC is generally accomplished by adapt- ing the spectrophotometric and fluorimetric detection schemes normally employed in liquid chromatography. Short optical pathlengths (usually approximately the capillary i.d.), low throughput and excessive stray radiation are common prob- lems that limit detectability with that approach. These problems are largely circumvented by using laser fluorimetric detection. The high intensity and tight focusing capabilities of laser outputs render this form of detection both sensitive and compatible with on-column detection. The outputs of most lasers can be focused to low micrometre spot sizes, producing effective flow-cell volumes in the picolitre range.While fluorimetry is pathlength-dependent , the high power densities that are possible (routinely greater than 1 MW m-2) produce large signals and, in fact, it is sometimes necessary to attenuate the laser output to prevent photobleach- ing of the sample and/or damage to the capillary. It is possible to detect low femtogram injected amounts of strong fluoro- phores by using CZE/MECC with laser fluorimetric detection. The influence of buffer components and surfactants on spectrofluorimetric characteristics (e.g. , heavy atom quenching and micelle enhancement of fluorescence signals) has been studied. Multiwavelength detection using photodiode arrays enhances analytical selectivity and can be performed rapidly, such that the integrity of narrow CZE/MECC solute bands is maintained. Pre-column and unique on-column derivatization techniques extend the applications of this mode of detection to include metal ions (via on-column formation of fluorescent complexes using the ligand 8-hydroxyquinoline-5-sulphonic acid) and proteins and detergents (via on-column solvophobic formation of fluorescent adducts using the probe 2-p-tolu- idinylnaphthalene-6-sulphonate) . Time-resolved Lanthanide(ii1) Electroluminescence and Its Analytical Feasibility K.Haapakka, J. Kankare and S. Kulmala Department of Chemistry, University of Turku, SF-20500 Turku, Finland The surface of an aluminium electrode in aqueous solution is covered by an oxide layer and can be regarded as a diprotic acid: k-A1OH2+ t--$ F-A1OH + H+ F-AlOH ++ k-AlO- + H+ where k- designates a surface species; the surface acidity constants are pK, * = 7.9 and pKa2* = 9.1. The low-voltage cathodic polarizatfon of this oxide-covered electrode surface in neutral and slightly alkaline electrolytes generally induces a relatively weak sub-bandgap electroluminescence (EL) of the electrode, i.e., the cathodic background EL. In addition to the sub-bandgap EL, the cathodic polarization of the electrode-electrolyte interface in the presence of strong oxidizing agents and fluorescent compounds can induce an intense EL with a characteristic spectrum.The steady-state response of this cathodic EL can be utilized for the determi- nation of electroluminophores at trace levels in aqueous and non-aqueous solutions. Lanthanide(II1) cations are also electroluminescent at an oxide-covered aluminium cathode and their EL spectra show the well-known lanthanide(II1) peak emissions. The terbium- (111) cation, particularly when chelated with the heptadentate ligand 2,6-bis[N, N-bis( carboxymethyl)aminomethyl]-4-ben- zoylphenol, is capable of generating an intense cathodic EL that is sufficiently long-lived to allow discrimination against the short-lived background EL on a time-resolved basis using an instrumentally simple gated detection technique.This time- resolved method of measurement substantially improves the signal-to-noise ratio in cathodic terbium(II1) electrolumino- metry and makes possible the determination of sub-picomolar levels of terbium(II1) in aqueous solution. Experimental No commercial EL apparatus is currently available; we have planned and constructed three different types of EL cells based on the use of an oxide-covered aluminium electrode as the I I 1 400 500 600 700 Wavelengthhm Fig. 1 (a) Cathodically induced background EL and (b) cathodically induced terbium(II1) EL. Conditions: 0.10 mol dmP3 sodium acetate adjusted to pH 6.7,l.O x loP3 mol dmP3 hydrogen peroxide and 1.0 x mol dmV3 terbium(II1); the solutions were de-aerated with nitrogen. Pulse amplitude and pulse duration of the symmetrical double step potential, 5.5 V and 2.0 ms, respectively; rotation rate of the electrode, 210 rev sP1 working electrode: (i) a cell which uses a rotating disc electrode and makes possible the recording of an EL spectrum;’’2 (ii) a cell which uses a stationary disc electrode on a disposable basis;3 and (iii) an EL detector for the flow analysis of electroluminescent compound^.^ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 361 The EL systems described in the present paper have been discussed in detail previously."' Results and Discussion An oxide layer at an aluminium electrode surface becomes cathodically conductive when the electrode is polarized with a potential more cathodic than approximately -4 V; the result- ing high-density cathodic current initiates the weak sub- bandgap EL with a peak maximum at about 570 nm (see Fig.1) and with a lifetime of 0.006 ms (see Fig. 2). The sub-bandgap EL is obviously caused by the impurities in the electrode oxide layer and its intensity and spectrum are to some extent dependent on the excitation conditions. Excitation potential pulse 1 -0v I u - l o " 1 0.40 ms 'f 0 2 4 6 8 Delay time/rns Fig. 2 Decay curves of cathodically induced EL at an oxide-covered aluminium electrode. A, Background EL; and B, EL of 1:l chelated terbium(rr1). For curve B, the scale has been reduced by a factor of 10. Conditions: 0.30 rnol dm-3 sodium sulphate adjusted to pH 10.0, 5.0 x mol dm-3 Tris, 1.0 x mol dm-3 potassium peroxydisul- phate, 1.0 X mol dmW3 2,6-bis[N, N-bis(carboxymethyl)aminomethyl]-4-benzoylphenol mol dmP3 terbium(n1) and 1.0 x A variety of inorganic cation^,^ organic compounds6 and micelle-encapsulated polycyclic aromatic hydrocarbons4 can, under these cathodic excitation conditions, be elevated to their excited levels, the relaxations of which generate characteristic electroluminophore emissions: e.g., copper(I1) EL at 630 nm, lead(I1) EL at 585 nm and mercury(1r) EL at 420 nm, 2- hydroxybenzoic acid EL at 405 nm, fluorescein EL at 545 nm and 6,7-dihydroxy-4-methylcoumarin EL at 510 nm and, finally, micelle-encapsulated 9,lO-diphenylanthracene EL at 425 nm, micelle-encapsulated pyrene EL at 400 nm and micelle-encapsulated perylene EL at 465 nm.The cathodic steady-state EL response is feasible for analytical purposes and as an example the cathodic 2-hydroxybenzoic acid EL responds linearly to this electroluminophore in the concentration range from 1 x lo-' to 1 x loW4 mol dmP3 with a relative standard deviation of 6% at 5 x mol drnp3.These cathodically induced emissions are, however, short-lived and their time- resolved detection at the oxide-covered aluminium electrode is not possible. The lowest excited singlet states of lanthanide(II1) cations are efficiently shielded from the interactions, leading to a rapid loss of electronic energy and, therefore, they can exhibit excep- tionally long-lived excited-state lifetimes. On the basis of the experiments conducted to date, europium(111) and sam- a r i u m ( ~ ~ ~ ) in the presence of nitrate7 and terbium(1Ir) in the presence of hydrogen peroxide or peroxydisulphate' are electroluminescent at an oxide-covered aluminium cathode in aqueous solution and show EL spectra consisting of well- characterized peak emissions; as an example, Fig. 1 displays the spectrum of the cathodic terbium(1rr) EL.From the spectrum it can be concluded that the terbium(ii1) EL is induced by the transitions from the lowest excited singlet state 5D4 to the ground states 7F6 (488 nm), 7 F ~ (546 nm), 7F4 (585 nm) and 7F3 (624 nm). According to our measurements, the lifetimes of the cathodically induced EL of hydrated lanthanide(rr1) cations at the oxide-covered aluminium electrode are 0.15 ms for euro- pium(m), <0.006 ms for samarium(Ir1) and 0.48 ms for ter- bium(m). Because it has the longest lifetime, the terbium(1Ir) EL provides the most appropriate basis for experiments to evaluate the improvement of the signal-to-noise ratio by time- resolved EL detection.Terbium(II1) forms stable 1 : l and 1:2 chelates with the heptadentate ligand 2,6-bis[N, N-bis(carboxy- methyl) aminome th yl] -4- benzo y lphenol (L) m3+ + 2 ~ ~ - - T ~ L ~ ~ - with the stability constants logpll = 23.6 and log612 = 29.8. The chelation efficiently removes coordinated water molecules from the terbium(rr1) solvation sphere, which, in turn, makes the cathodically induced terbium(u1) EL even longer-lived; depending on the number of water molecules remaining in the cation solvation sphere, the EL lifetime was found to range from 1.7 ms (1:l chelate) to 2.1 ms (1:2 chelate). In addition, the 1:2 chelate was capable of inducing an approximately ten times more intense cathodic terbium(m) EL than the 1:l chelate.The EL decay curves presented in Fig. 2 point out that the cathodically induced emission of chelated terbium( 111) is sufficiently long-lived for an efficient time-resolved discrimi- nation against the 0.006 ms background EL. By using a 0.10 ms delay time from the falling edge of the cathodic excitation pulse and a differentially gated count mode A-B, where A is the count period from 0.10 to 5.10 ms and B the count period from 5.10 to 10.10 ms, the time-resolved ter- bium(rn) EL response at a peak wavelength of 546 nm was found to be linear with respect to the terbium(Ir1) concentration in the range from approximately to lop6 mol dmP3 under the conditions given in Fig.2. Ten sequential EL measurements using a terbium(rI1) concentration of 1.0 x mol dm-3 gave a relative standard deviation of 4%. In conclusion, this new time-resolved detection approach of electrochemically generated terbium(111) luminescence is still in its early stages; however, the results currently available clearly demonstrate its feasibility for the determination of trace amounts of terbium(rr1) in aqueous solution. t--, TbL2- n 3 + + Ls- References Haapakka, K., and Kankare, J., Anal. Chim. Acta, 1982, 138, 253. Pihlajamaki, S . , and Kankare, J . , Anal. Instrum., 1986, 15, 171. Kankare, J . , FaldCn, K., Kulmala, S . , and Haapakka, K., submitted for publication. Haapakka, K., Kankare, J., and Lipiainen, K., Anal.Chim. Acta, 1990, 233, 199. Haapakka, K., Kankare, J., and Kulmala, S . , Anal. Chim. Acta, 1985, 171, 259. Haapakka, K., Kankare, J., and Puhakka, O., Anal. Chim. Acta, 1988, 207, 195. Haapakka, K., Kankare, J., and Kulmala, S., Anal. Chim. Acta, 1988, 209, 165. Kulmala, S., Kankare, J . , and Haapakka, K., Anal. Chim. Acta, in the press.362 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 Robert Boyle (1627-1691): A Foundation Stone of Analytical Chemistry in the British Isles. Part Vl.* Contributions to the Early Study of Luminescence D. Thorburn Burns Department of Analytical Chemistry, The Queen‘s University of Belfast, Belfast BT9 5AG, Northern Ireland Luminous phenomena were of great interest in the early days of the Royal Society.’ Robert Boyle was one of the most outstanding experimentalists in this field in the 17th century.Although he never wrote a general account of lumines- cence, there is much on luminescence throughout his works.233 Boyle was prob- ably the first to describe phosphor- escence, thermoluminescence, electro- luminescence and triboluminescence in a single substance, a diamond. He also studied phosphorescence, chemilumi- nescence, bioluminescence and fluor- escence. Boyle’s contributions have been put in perspective within a ‘History of Luminescence, from the Earliest Times Until 1900’4 and earlier by E. Newton Harvey. The account is brought up to date by O’Haver’s discussion ‘The Development of Luminescence Spectro- photometry as an Analytical Tool’7 with its useful concise account of instrumentation.For convenience Boyle’s contributions to the study of luminescence are outlined in four sections: examination of solu- tions - the first fluorescent acid-base indi- cator; luminescence studies of solids- diamonds, shining wood, fish and flesh and glow worms; phosphorus-manufac- ture and properties; and the Golden Phoenix, at one time assumed to be Boyle’s laboratory. Analysis of Solutions - the First Flu- orescent Acid-Base Indicator Boyle made considerable contributions to the examination of solutions, developing many selective reactions for iron, cop er, salt, etc., giving their detection limits.’He also made advances in the examination of acids, bases and distinguished neutral salts as such. Much of this work is described in his text Experiments and Contributions Touching C o l o u r ~ ~ ~ ’ ~ and Mineral Waters.l1 ,12 * For Part I, see Anal. Proc., 1982, 19, 222; Part 11, Anal. Proc., 1982, 19, 288; Part 111, Anal. Proc., 1985, 22, 253; Part IV, Anal. Proc., 1986,23,75; Part V, Anal. Proc., 1986, 23,349. Boyle was the first to describe a fluor- escent acid-base indicator, extract of Lignum nephriticum. This extract had been used since pre-Columbian days in the treatment of kidney and bladder infections and as a diuretic. The manu- script history of the wood has been reviewed in detail by Partingt~n.’~ In the 16th and 17th centuries the wood was imported into Europe from the New World and attracted attention on account of its apparent medical virtues and for the unusual yellow colour and pronounced blue fluorescence in its infusion with water.The section in Boyle’s C o l o u r ~ , ~ ~ ~ ~ Experiments 10 and 11 in Part 111, is quite detailed and comprises 20 pages.loa The effect of concentration, acidity and angle of viewing are described. The earliest account known to Boyle was that of Monardes;14 he also cited the work of the great Jesuit encyclopaedist, Kircher. l5 Boyle was particularly fond of using extract of Lignum nephriticum and refers to it in Sceptical C h e m i ~ t , ’ ~ ? ~ ~ ~ Experi- menta Observationes Phy~icae,~’~’~” A n Essay on the Porousness of Solid Bodies,20921a Icy N o c t i l u ~ a , ~ ~ ’ ~ ~ ~ and in Mineral Waters. 11~12a Robert Boyle’s examination of mineral waters was more detailed and a consider- able advance on those of earlier workers, contemporaries and most later workers up to the time of His account is brief and fragmentary yet it gives a clear insight into Boyle’s experimental approach and his knowledge of the limi- tations of the various experiments.A set of suggested geographical and mineral- ogical observations (heads or titles 1-17) are followed by the physico-chemical part (titles 1-30). This later section is ampli- fied in sections on ‘Experimental Remarks’ followed by ‘Marginal Notes’. The book concludes with consideration of mineral water as a medicine. In general few details are given, it being assumed that the reader is fully familiar with Boyle’s earlier works. For example, title 16 of the physico-chemical part reads ‘How to examine, without evaporation, whether the Mineral Water have any acidity, tho’ it be but very little’.The marginal notes concerning the sixteenth title extend to two pages, in which he states ‘The circumstances, that made this way of examining so critical, will cost me too many words to set down here, and I have done it in another Paper expressly written, of the way of discovering the Qualities of divers Bodies, by changes of colour made in or with them: And there- fore I shall here but briefly tell you, that I discover the Acidity of Liquors by their operations upon the colours of an Infu- sion of Lignum Nephriticum made in Lympid Water (and order’d after a certain manner) . . .’ He then discusses his results with selected mineral waters including imported German Spaw Water. By the mid-18th century the wood had become rare in Europe and its botanical origin was lost.Safford2’ positively identi- fied the material used by Boyle as Eysen- hardtia polystachya. The principal fluor- escent acid-base indicator component of the heart wood has been established as 7-hydrox -2’ ,-4’ ,-5’ ,-trimethoxyiso- flavone. 2: Luminescence Studies of Solids Boyle’s principal luminescence studies of solids began with diamonds, extended to shining wood, fish and flesh, and ended with the element phosphorus. Luminous Diamonds Belief in luminous stones seems to have been widespread in mediaeval times. Gesner in the first text, L ~ n a r i a e , ~ ~ on luminescence, reported on a stone in a ring owned by Catherine of Aragon (1485-1536) which luminesced at night. As noted by Boyle, Cellini, the celebrated Italian jeweller, told of a diamond which shone after exposure to light.28 Boyle’s experiments show the truth of the matter; the account is annexed to Colours9 (see Fig.1). They were carried out on October 27th, 1663, using Mr. Clayton’s diamond. The account was well referenced includ- ing de Boot’s Gemmarium ,29 although the latest account known to Boyle was that of Olaus Worimus’ M u ~ a e u m . ~ ~ The diamond had to be gently rubbed before itANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 363 A S H O R T ACCOUNT’ O F S O M E OBSERVATIONS Fidt cnclokd in a Letter written cc a Friend, Light and Colottrs. Fig. 1 Title page to An account about a diamond that shines in the dark (1664) shone in the dark, it also shone if gently warmed. Boyle examined a series of precious stones-rubies, sapphires, emeralds, etc., but only some diamonds shone in the dark.Bioluminescence-Shining Wood, Fish and Flesh and Glow Worms Boyle made numerous studies of shining wood, fish and flesh with his air pump, aided b his laboratory assistant Robert Hooke.” The experiments were made on October 29th and following nights and December 6th, 1667.32 From the later series we note Boyle worked a seven day week ‘. . . so that I caused the Receiver to be exhausted once more, but that it being a Sunday night, I was unwilling to scan- dalize any, by putting my servants upon a laborious, and not necessary work’. Both the shining wood and fish lost their light when air was removed which was restored when air was readmitted. He then pub- lished observations and trials about the resemblances and differences between a burning coal and shining wood.33 Boyle noted five resemblances: both were lumi- naries, the light resided in them, both needed air to continue shining and re- covered after lack of air, could be quenched by water and air temperature was not important. Six differences were noted: a live coal was extinguished by compression (not so for shining wood); once a coal was totally extinguished, it did not recover on admitting air, unlike shining wood; shining wood needed air, gave no smoke, did not waste so fast and was not even lukewarm.Further experiments were February 15th 1671/2 on the flesh of a pullet and of Boyle noted that spirit of wine quenched the light after fifteen minutes but water did not at least within one hour.Although Boyle did not know that luminous bacteria were responsible for the shining fish and flesh or that mycelia of a luminous fungus caused the wood to shine, we must credit him with recogniz- ing the fundamental similarity of the two phenomena and with demonstrating the necessity of some latent property of air (oxygen) to maintain the luminescence. These are the first important experiments on luminescence. At the time Boyle had studied the effects of air on shining wood and flesh he had wished to examine glow worms but none was available. A few years later an experiment was carried out and the results appeared in Tracts Touching the Relation Betwixt Flame and Ai?5936 (see Fig. 2). 1 C A L D i h u t f e oc- ions’ of Dr. &ry More atmn< of Ncw Expcruncnts of thcfc Tr&s : To which Spring on Bodies undcr Ptcfiire of Hcasy S+ .- L O N D O N , ’ * Printed for Kicbrrd DJvir,Book-fcllcr in O X ~ Fig. 2 Title page to Tracts containing New Experiments touching the Relation betwixt Flame and Air Boyle’s motive was to learn more about the ‘vital flame’ of animals in relation to air. He introduced the experiments as ‘For the sake of those learned men, that have thought the light of glow worms and other shining insects to be a kind of effulsion of the biolychnium, or vital flame, that nature has made more luminous in these little animals than in others . . . we took two glow worms . . . these we laid on a little plate, which we follows:36a included in a small receiver of finer glass than ordinary .. . and as we expected, upon the first exsuction there began to be very manifest diminution of the light, which grew dimmer and dimmer, as the air was more and more withdrawn until at length it disap- peared, though there were young eyes among the assistants. This darkness having suffered to continue a long while in the receiver we let the air in again, whose presence as we look for, restored at least as much light as its absence deprived us of.’ To test the possibility that the disappear- ance of the light might be caused by some reaction of the whole animal, Boyle repeated the whole experiment with a tail of a dead glow worm and found its luminescence also disappeared on removal of air and that returning air restored the light. These experiments served to establish the similarity of the light of shining wood, fish flesh and insects.They supplemented his obser- vations that flames cannot exist in a vacuum, that the light of burning sulphur, camphor or alcohol quickly went out in a closed space and that animals die when deprived of air. These experiments were an early demonstration of the necessity of something in air for bodies to live, mater- ial to burn and clearly placed lumines- cence of organisms in the same category. Phosphorus The term phosphorus (Greek, phos-light, phero-I bear) was applied in the 17th century to an substance that luminesced in the Ignited nature barium sulphate was known as Bolognian phos- phor or phosphor~s.~~” Boyle received samples of this material from Robert Southwell in Florence according to a letter dated October loth, 1660.39 The early history of phosphorus has been reviewed by Partingt~n.~’ In 1667 there arrived in London a certain Johann Daniel &aft4’ who showed Boyle and his friends a small amount of ‘kaltes Feuer’ he had obtained from its discoverer, Hennig Brand of Hamburg.Brand was a merchant who became wealthy by mar- riage and spent his days in the laboratory seeking to amass a fortune through alchemy. He turned his attention to urine probably because of the doctrine of signa- t u r e ~ ~ ~ which was widely believed at that time. Nature was supposed to help man- kind by giving clues, a plant’s shape, for example, indicated which organ it might affect. Natural objects of a golden colour were supposed to contain gold.Although urine did not give Brand gold directly it did so indirectly. It yielded him a waxy easily melted inflammable substance which luminesced in the dark. Brand sold the secret to Dr. Kraft of Dresden for 200 Thalers, who then exhibited das kalte Feuer at many courts in Europe.364 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 The account of Kraft’s demonstration, on September 15th, 1677, in London at Boyle’s home, was given by Boyle in Hooke’s Lectures and collection^^^ in 1678. Boyle obtained a hint of its manu- facture38b ‘his phosphorus belonged to the body of a man’ and set about trying to make the material. He encountered diffi- culties which were solved for him by ‘AG MD’ who is almost certainly Ambrose Godfrey Hanckwitz. 4434s Boyle wrote up the properties of the material in two works.Firstly, in the Aerial Noctiluca (1680)37,38 (see Fig. 3) . . , :.. T H E .. . . . _ . - . . .. . * . . ’ ., . . ’ O R - - . . . . . .... . A Fa&kkious Self-hini<g Subfiance. (1 riiied by ~ J O . Snowden, a’nd are t o be fold by Nafb. Raxcur, h k f e l l e r in St. P a d s Church-Yard. 1680. . Fig. 3 Title page to The Aerial Notiluca (1680) and secondly in experiments on the Icy N o c t i l u ~ a . ~ ~ , ~ ~ He, however, kept the preparation secret in a sealed paper deposited on October 14th, 1680, with the Secretaries of the Royal Society. This sealed paper was opened after Boyle’s death and published in Phil. Trans. in 1693.46 The first preparations did not contain much solid phosphorus but above the liquid the vapour glowed, hence the name ‘aerial night light’.Later, solid waxy material, i. e., elemental phosphorus in a reasonably pure state, was prepared. Boyle studied the vapour, solution and solid forms of phosphorus and noted the effects of air on all three, including the periodic nature23b of some of the emis- sions. He observed the red and waxy (yellow) forms,23c prepared the pentaox- ide and phosphoric acid, which he tested with lignum n e p h r i t i ~ u m . ~ ~ ~ As with other studies of reactions Boyle was interested in detection limits and recorded ‘that one part of the noctiluca, first being dissolved in alcohol of wine, and afterwards being briskly shaken with a convenient quantity of water, rendered luminous as much Fig. 4 Bill head of Godfrey and Cooke (dated 1830) liquor as upon calculation amounted to four hundred thousand times its weight’.23d Boyle’s assistant noted that phosphorus burns were more painful and slower to heal than ordinary Boyle was not without humour, and untroubled by COSHH regulations, when he wrote: ‘The same laborant, who was very helpful to me varying the preparation of the phosphorus, had a worse mis- adventure not long after (earlier his hair had caught fire in an experiment with gunpowder and phosphorus), for bringing me some newly distilled grains of noctiluca, covered with some of the shining water, that came over with it, he unluckily broke the glass in his pocket, whereupon the heat of his body, increased by the motion of his long walk had put into it, did so excite the matter, that was fallen out of the broken phial, that it burned two or three great holes in his breeches, before he could come to me and relate his misfortune, the recent effects of which I could not look upon without some wonder as well as smiles’.23f The glow and drama of phosphorus prep- aration has attracted at least one artist. It is the subject of the fine painting by Joseph Wright (1734-1797) of Derby, entitled ‘The Alchymist in Search of the Philosopher’s Stone discovers Phos- phorus and prays for the Successful Con- clusion of His Operation, as was the Custom of the Ancient Chymical Astrologers’. 47 The Golden Phoenix Probably the first commercial manufac- ture of phosphorus was carried out at the laboratory in Maiden Lane, Covent Gar- den, London, known as the ‘Golden Phoenix’. It has commonly been assumed to be Boyle’s l a b ~ r a t o r y .~ ~ ’ ~ ~ - ~ ~ It was, however, set up b Boyle’s operator Hanckwitz in 1707,ak despite the date 1680 carved under the golden Phoenix which stood on the front of the building. The date 1680 refers to the discovery of phosphorus, the production of which was a landmark in Hanckwitz’s career. With the passage of time this would seem to have been interpreted as the date of foundation of the business and as such appeared in the bill heads of Godfrey and Cooke (see Fig. 4) in the nineteenth century. Maddison’s biography of B ~ y l e ~ ~ reproduces three illustrations tradition- ally regarded as representing the interior of the ‘Golden Phoenix’ in the early days. Pilcher’l adds a fourth published in 1769.Hanckwitz eventually set up as a manu- facturing, analytical and consulting chemist and had a monopoly in making phosphorus because of his mastery of the technical requirements of the process. He was proud of being able to produce seven or eight ounces at one distillation. Ambrose Godfrey Hanckwitz’s two sons, Ambrose and Boyle, dropped the name Hanckwitz. The business passed in 1756 to a nephew, Ambrose Godfrey, son of Boyle, who took as a partner Charles Gomand Cooke around 1795.& The busi- ness of Godfrey and Cooke became more pharmaceutical in character but remained on the site until 1862, when it moved to the West End. The old laboratory was ultimately demolished to provide the site for the Roman Catholic Church of Corpus Christi which opened in 1874.The busi- ness ran down over the years and was acquired by Savory and Moore Ltd., 143 New Bond Street, in 1916. Thus, we have a direct line back to practical chemistry of the seventeenth century from a close associate of Boyle, in principle, if not on the original site. References Goliniski, J. V., ‘A Noble Spectacle. Phosphorus and the Public Lectures of Science in the Early Royal Society’, Isis, 1981, 80, 11. The Works of the Honorable Robert Boyle. In Five Volumes. To which is prefixed a Life of the Author, A. Millar, London, 1744. The Works of the Honorable Robert Boyle. In Six Volumes. To which is prefixed a Life of the Author. A New Edition, J. and F. Rivington et GI., London, 1772. (References to indi- vidual works and pages are given to this edition.) Harvey, E.N., A History of Lumines- cence. From the Earliest Times until 1900, American Philosophical Society, Philadelphia, USA, 1957. Harvey, E. N., The Nature of Animal Light, J. B. Lippincott, Philadelphia and London, 1920.ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 365 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Harvey, E. N., Living Light, Princeton University Press, Princeton, NJ, USA, 1940. O’Haver, T. C., ‘The Development of Luminescence Spectrometry as an Ana- lytical Tool’, J . Chem. Ed., 1978, 55, 423. Thorburn Burns, D., Anal. Proc., 1982, 19, 288; 1986, 23, 75. Boyle, R., Experiments and Consider- ations Touching Colours . . ., H. Her- ringman, Anchor, New Exchange, Lon- don, 1664. Reprinted by Johnson Reprint Corporation, New York, 1964; 2nd ed.H. Herringman, 1670. The Works of the Honorable Robert Boyle, J. and F. Rivington et al., Lon- don 1772, Vol. I, pp. 662-788; a, Vol. I, Boyle, R., Short Memoirs for the Natural Experimental History of Mineral Waters . . ., S. Smith, Prince’s Arms, St. Paul’s Church Yard, London, 168415. The Works of the Honorable Robert Boyle, J . and F. Rivington et al., Lon- don, 1772, Vol. IV, pp. 794-821; a, Vol. IV, p. 814. Partington, J. R. ‘Lignum Nephriti- cum’, Ann. Sci., 1955, 11, 1. Monardis, N. , De Simplicibvs Medica- mentis ex Occidentali India delatis . . ., Clvsio, C., Plantin, Antwerp, 1574. Kircher, A., Ars Magna Iucis et umbrae in decem Libros digesta, L. Grignan for H. Scheus, Rome, 1646. Boyle, R., The Sceptical Chemist . . ., J. Caldwell for .I.Crooke, London, 1661. [The second edition, Oxford, was printed by H. Hall for R. Davies and B. Took at the Ship in St. Paul’s Church Yard, London, 1680 (was however printed in 1679).] The Works of the Honorable Robert Boyle, J. and F. Rivington et al., Lon- don, 1772, Vol. I, pp. 458-661; a, Vol. I, p. 519. Boyle, R., Experimenta & Observa- tiones Physicae . . . to which is added a small collection of strange reports, J. Taylor and J. Watt, London, 1691. The Works o f the Honorable Robert Boyle, J. and F. Rivington et al., Lon- don, 1772, Vol. V, pp. 564-609; a, Vol. Boyle, R., Experiments and Consider- ations about the Porosity of Bodies, in two Essays, S. Smith, London, 1684. pp. 729-735. v , p. 579. 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 The Works of the Honorable Robert Boyle, J.and F. Rivington et al., Lon- don, 1772, Vol. IV, pp. 759-793; a, Vol. IV, p. 792. Boyle, R., New Experiments and Obser- vations made upon the Icy Notiluca . . ., R. E. for B. Tooke, London, 168112. The Works of the Honorable Robert Boyle, J. and F. Rivington et al., Lon- don, 1772, Vol. IV, pp. 469-505; a, Vol. IV, p. 490; b, Vol. IV, p. 473; c, Vol. IV, p. 475; d, Vol. IV, p. 483; e, Vol. IV, p. 488; f, Vol. IV, p. 489. Kirwan, R., A n Essay on the Analysis of Mineral Waters, J. W. Myers, London, 1799. Safford, W. E., Lignum Nephriticum- Its History and an Account of the Remarkable Fluorescence of its Infu- sion, Government Printing Office, Washington, DC, USA, 1916; Ann. Rep. Smithsonian Inst., 1915, p, 271. Burns, D. T., Delgarno, B.G., Gargan, P. E., and Grimshaw, J., ‘An Isoflavone and a Coumestan from Eysendardtia Polystachya - Robert Boyle’s Fluor- escent Acid-Base Indicator’, Phyto- chem., 1984, 13, 167. Gesneri, C., De raris et admirandis herbis quae sive quod noctu luceant, sive alias ob causas, Lunariae . . ., Andream & Lacobvm, Tiguri, 1555. Cellini, B., Due Trattati uno intorno alle Otto principali arti dell’ oreficeria . . . , V. Panizza & M. Peri, Florence, 1568. Boetius, A., ‘Gemmarium et lapidum historia’, Lugd. Bat., 1630. Worm, O., ‘Museum Wormianum seu Historia Rerum Rariorum . . .’, Lugd. Bat., 1655. Andrade, E. N. Da C., ‘Robert Hooke FRS (1635-1703)’, Notes Rec. R. Soc., 1960, 15, 137. Boyle, R., ‘New Experiments, to the Number 16, concerning the Relation between Light and Air (in Shining Wood and Fish) . . . I , Phil. Trans., 16671 8, 2, 605. Boyle, R., ‘Observations and Tryals about the Resemblances and Differ- ences between a Burning Coal and Shining Wood . . .’, Phil. Trans., 166718, 2, 605. Boyle, R., ‘Some Observations about Shining Flesh, both of Veal and of Pullet . . .’, Phil. Trans., 1671, 7, 5108. Boyle, R., Tracts containing New Experiments touching the Relation betwixt Flame and Air . . ., London, Printed for R. Davis, Oxford, 1672. 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 The Works of the Honorable Robert Boyle, J. and F. Rivington et al., Lon- don, 1772, Vol. 111, pp. 562-595; a, Vol. 111, p. 587. Boyle, R., The Aerial Noctiluca: or some New Phenomena . . ., Printed T. Snowden and sold by N. Ranew, Lon- don, 1680. The Works of the Honorable Robert Boyle, J. and F. Rivington et al., Lon- don, 1772, Vol. IV, pp. 379404; a, Vol. IV, p. 380; b, Vol. IV, p. 381. The Works of the Honorable Robert Boyle, J. and F. Rivington et al., Lon- don, 1772, Vol. VI, pp. 297-298. Partington, J. R., ‘The Early History of Phosphorus’, Sci. Prog. , 1936, 30, 402. Maddison, R. E. W., ‘Studies in the Life of Robert Boyle, FRS. Part I, Robert Boyle and some of his Foreign Visitors’, Notes Rec. R. SOC., 1951, 9, 29. Read, J., Prelude to Chemistry. A n Outline of Alchemy Its Literature and Relationships, G. Bell, London, 1939, 2nd edn., p. 96. Hooke, R., Lectures and Collections, J. Martyn, London, 1678. Maddison, R. E. W., ‘Studies in the Life of Robert Boyle FRS. Part V, Boyle’s Operator: Ambrose Godfrey Hanck- witz, FRS’, Notes Rec. R. SOC., 1954, 11, 159. Ince, J., ‘Ambrose Godfrey Hanckwitz 1660-1740’, Pharm. J . , 1858, 18, 126, 157 and 215. Boyle, R., Phil. Trans., 1693, 17, 583. In Derby Art Gallery, Derby. Repro- duced in black and white (ref. 1) and in colour in Powell, N., Alchemy the Ancient Science, Aldus Books, London, 1976. The painting was engraved in mezzotint, 1775, by William Pether (1731-1795) and shows the mirror image, reproduced in Read, J., The Alchemist in Life, Literature and Art, Nelson, London, 1947. Ince, J., ‘The Old Firm of Godfrey’, Pharm. J., 1896, 2, 116, 205, 215. Ince, J . , ‘On the Discovery of Phos- phorus,, Pharm. J. Trans., 1854, 13, 280. Gunther, R. T., Early Science in Oxford. Part I. Chemistry, Oxford University Press, Oxford, 1921, p. 21. Pilcher, R. B., ‘Boyle’s Laboratory’, Ambix, 1938, 2, 17. Maddison, R. E. W., The Life of the Honourable Robert Boyle FRS, Taylor and Francis, London, 1969.

ISSN:0144-557X    

DOI:10.1039/AP9912800357

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

366 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 New Electrochemical Sensors The following are summaries of eleven of the papers presented at the Joint Analytical/ Faraday Symposium at the Annual Chemical Congress of the RSC held on April 8th-I2th, 1991, in Imperial College, London. Solid-state Gas Sensors: Prospects for Selectivity David E. Williams Department of Chemistry, University College London, 20 Gordon Street, London WCI H OAJ Metal oxides, such as tin dioxide and zinc oxide, fabricated either in the form of thin (=lo0 nm) films or as thicker porous bodies, show an electrical conductivity at temperatures of about 300°C which is very sensitive to the presence of trace amounts (ppm level) of reactive gases (hydrocarbons, hydro- gen, carbon monoxide, methane, ammonia, oxides of sulphur and nitrogen, chlorine, hydrogen sulphide) in air.This phenomenon has been exploited for many years in warning devices. Most commercial elements utilize porous, thick (==lo0 pm) films of tin dioxide. Typically, the layer might be deposited onto the outside of a small alumina tube by successive dipping into a tin salt solution and thermal decomposition. A heater is threaded into the centre of the tube. These devices are simple, robust and inexpensive. They are, however, if anything, too sensitive to too many things, although a certain degree of selectivity can be obtained by control of the operating temperature. The question is, therefore, whether, by choice of oxide material or some other means, selectivity can be enhanced. 1,2 M~rrison,~ in discussing this question, has pointed out that although the gas sensing phenomenon appears to be intimately connected with the occurrence of a surface- catalysed combustion, the notion of selectivity in a gas sensor is different to that of the apparently related notion of selectivity in a catalyst: for a catalyst, selectivity means a bias in favour of a particular reaction product, whereas for a sensor it means a bias in favour of a particular reactant, often in a complex mixture of potential reactants.As far as the second part of the question is concerned, it has been pointed out' that the surface-catalysed combustion causes a gradient in the composition of reactant and product gases throughout a porous sensor structure, and that this can be used to build in a degree of selectivity based on the differing reactivity of different gases.Hence, in a sufficiently thick structure, the outer layers of the device act as a kind of filter, burning away the more reactive gases and leaving only the less reactive gases to affect the conductivity in the vicinity of electrodes buried within the structure. There seems to be plenty of scope for using this kind of idea, the alteration of relative response by alteration of the geometry of the sensor layer and of the measuring electrodes, to develop tailored devices. In order to address the first part of the question, an experimental programme was carried out2 to investigate the response of several hundred different oxides to a range of gases. Table 1 indicates the range of materials investigated; the gases studied were: hydrogen, carbon monoxide, methane, propane, ethene, ammonia, hydrogen sulphide, nitrogen dioxide, sulphur dioxide and chlorine, and changes in oxygen partial pressure.The first conclusion of this work was strikingly simple: most oxides respond to most gases. A few materials showed selectivity to some gases, most often ammonia and Table 1 Range of materials investigated Perovskite-type Pyrochlore-type compounds compounds of tin of tin Niobates Bronzes Al - ,B,Snl - .CXO3 - A Ca, Sr, Ba Specific examples: Examples: B Ca, Sr, Ba, CaCeSnzO7 A2 - ,B,Sn2 - xCx07 - Al - xBxNb206 CaSnTi207 A, B-Pb, Ba, Sr Pb Gd2Sn207 A6BxNblO - xo30 La, Y, Gd La2Sn207 Example: y2sn207 Bi6Fe4Nb6030 C Fe, Co Bi2Sn207 Ti, Zr, Ce Transition metal Fe, Co, Ni, Cu Tantalates compounds Specific examples: BaSn03 FeTa04 niobates BaSn0.5Ti0.503 CoTa206 BaSn0,9Zr0,103 NiTa206 BaSnO.8FeO.2 0 3 CUTa206 Ba0.9Gdo. 1Sn03 hydrogen s ~ l p h i d e , ~ but this was the exception rather than the rule. A second conclusion was that there was a clear rz-typelp- type classification of the oxides, even in the absence of a response to varying oxygen partial pressure, and correspond- ingly a classification of the gases into oxidizing and reducing agents. Exceptions to this classification stood out clearly: Table 2 shows a part of it, in which the response has been coded simply in terms of its sign. The interpretation is that, in general, the response of oxides to gases, being a change in the concentration of the charge carriers giving rise to the conduc- tivity, is controlled by the surface concentration of a single, reactive surface species, common to all oxides and presumed (following studies on tin dioxide and zinc to be an oxygen ion, 02-, 0-.Response mechanisms have been fully discussed elsewhere ,13235 and, indeed, a model simply rational- izing the exceptions in the classification can be constructed.6 The answer, therefore, to the first part of the question posed above is that very strong selectivity seems rather rare, being confined to a few materials and a few gases: if a generalization is required, in the study these were those gases (NH3, H2S) that could be considered to act as Lewis bases on materials in which it is presumed that oxygen surface species were unreactive at the measurement temperature.On the other hand, there was sufficient variation in the relative magnitude of the response of different materials to different gases to allow ample scope for the strategy of using arrays of differently responding sensors to resolve the composition of mixtures.ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 367 Table 2 Classification of materials and responses: the response is coded simply by the sign of the resistance change on exposure to the gas. Exceptions to the general n-typelp-type classification of materials, showing opposite sign of response to oxidizing and reducing gases stand out clearly. A plus sign indicates a resistance increase with respect to the value in air; a minus sign indicates a resistance decrease. In all atmospheres, except for the first listed, the gases are introduced as mixtures (1'70 except where stated) in air Low 0 2 C2H4 H2S Material (100PPm) cH4 co H2 (0.7%) NH3 so2 (0.1%) Cl2 NO2 2.Effectively p-type oxides- Sr( SrNb) 0 3 LiFeSn04 Y 2Ti20 BaTi03 SrTiO3 LaO.9CaO. lFe03 La6W012 NdzZ1-207 Y2BaZn05 + + + + + + + + + + + + + + + + + + - + - - + - + + + + References 1 Williams, D. E., in Solid State Gas Sensors, eds. Moseley, P. T., and Tofield, B. C., Adam Hilger, Bristol and Philadelphia, 1987, 2 Moseley, P. T., Stoneham, A. M., and Williams, D. E., Techniques and Mechanisms in Gas Sensing, eds. Moseley, P. T., Williams, D. E., and Norris, J. 0. W., Adam Hilger, Bristol and Philadelphia, 1991, ch. 4. pp. 71-123. 3 Morrison, S. R., Sens. Actuators, 1987, 12, 425.4 Moseley, P. T., and Williams, D. E., Sens. Actuators, 1990, B1, 113. 5 Heiland, G., and Kohl, D., in Chemical Sensor Technology, Volume I , ed. Seiyama, T., Kodansha and Elsevier, Tokyo and Amsterdam, 1988, pp. 15-38. 6 Williams, D. E., and Moseley, P. T., J. Muter. Chem., in the press. Semiconductor Gas Sensors and Selectivity Gary S. V. Coles Department of Electrical and Electronic Engineering, University of Wales, Swansea SA2 8PP The resistance of certain semiconductor materials has been known to change in the presence of reducing gases since the early 1950s. Gas sensors exploiting this observation, initially based on zinc oxide but now usually based on the n-type semiconductor tin dioxide, have been available commercially for some two decade^.^.^ Early sensors received a great deal of criticism as they tended to be irreproducible and have poor selectivity, responding to a wide range of reducing gases.It might also be true that industry and commerce expected too much of this type of sensor, despite the fact that they can possess many of the characteristics desirable in a gas sensing device, including high sensitivity, fast response speed, low power consumption and cost. However, it is the problem of selectivity that is addressed in this paper. Selectivity in Tin Dioxide Gas Sensors Early workers in this area discovered that operating tin dioxide sensors at different temperatures conferred a degree of ~electivity.~ For example, operating a sensor at =300 "C gave a device sensitive to the presence of carbon monoxide but 14 v) m $ 10 B 6 2 0 2 4 6 [Gas] (lo3 ppm) Fig.1 Variation of conductivity with gas concentration for a hydrogen-selective sensor in hydrogen and carbon monoxide368 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 0 5 10 25 0 5 10 0 [Gas] (lo2 ppm) 5 10 Fig. 2 three different operating temperatures: ( a ) 400; (b) 280; and (c) 175 "C Resistance versus contaminant gas concentration plots for a sensor fabricated from Sn02 pre-sintered at 1500 "C in air and maintained at insensitive to the presence of methane. Producing a sensor with the opposite selectivity required the addition of =l% platinum to the oxide and operation at a higher temperature of -600 "C. Initial work at Swansea produced two selective sensors.6 The first, prepared from tin dioxide, aluminium silicate and palladium chloride, gave a device sensitive to the presence of the lower hydrocarbons but insensitive to the presence of carbon monoxide. A second sensor, formed by the sintering of tin dioxide and bismuth oxide, gave a sensor with the opposite selectivity.The notable feature of these sensors is that the selectivity is observed throughout the viable operating temper- ature range (between =150 "C, below which resistances become excessively high and surface reactions too slow, and -700 "C, above which conductivity by thermal excitation obscures the changes produced by the presence of a contami- nant gas). A maximum sensitivity is observed at an operating temperature of =250"C. In an attempt to understand the properties exhibited by these sensors the carbon monoxide selective device was studied in more detail.Tin Dioxide-Bismuth Oxide System Tin dioxide itself exhibits conductance changes in the presence of many reducing gases. However, as bismuth oxide is added the response to methane rapidly diminishes, falling to zero at -15% m/m. The response to carbon monoxide remains unaltered. Above a concentration of =17% m/m Biz03 the response to CO also begins to fall and this reaches zero above -23% m/m. The optimum composition of this sensor is therefore 8345% m/m Sn02 : 1517% m/m Bi203. Although the term selective has been used, in reality these sensors, and many other types of sensor, will also respond to certain other gases, notably hydrogen. When the Bi203 content of these devices is increased above that at which the carbon monoxide response has fallen to zero, the response to hydrogen is observed to persist undiminished until this also begins to fall to zero above -25% m/m. It is therefore possible to produce a third sensor which is sensitive to the presence of hydrogen but shows no resistance changes in the presence of carbon monoxide or the lower hydrocarbon^.^ A remarkable feature of this sensor is its linear change in conductance with increasing gas concentration even up to several thousand ppm, as shown in Fig.1. Sensors of this type usually tend towards saturation at such high levels. In the production of these sensors the oxide mixture is fired at 800°C. It is known that bismuth oxide and tin dioxide undergo a solid-state reaction above -600 "C producing bismuth stannate, Bi2Sn207, which has a pyrochlore struc- ture.' In our sensors all of the bismuth oxide reacts and the final sensor element is composed of bismuth stannate and tin dioxide only.There are several other stannates of general formula M2Sn207 which also possess the pyrochlore structure .9 These were also studied in the hope that they would yield new selective sensors and further elucidate the properties exhibited by these devices. An immediate difference is the high temperatures required to produce these other stannates , being typically in the region of 1500 "C. Sensors produced from these materials in an analogous way to the tin dioxide-bismuth oxide sensors, but fired at higher temperatures, showed various degrees of selectivity and sensitivity but none compared favourably with the original devices.As a control, sensors were also produced from pure tin dioxide fired at 1500°C. These devices showed remarkable characteristics as shown in Fig. 2. At high operating temperatures ( ~ 4 0 0 "C) the sensor shows conventional decreases in resistance in the presence of all three gases as would be expected for this n-type material. At low operating temperatures (-175 "C) the device shows no re- sponse to carbon monoxide or methane but exhibits an increase in resistance in the presence of hydrogen as would be expected in a p-type material. At intermediate temperatures (-280 "C) no response is observed for methane; a conventional response is observed in the presence of hydrogen but a resistance increase is observed in the presence of carbon monoxide. Conclusions It is possible to produce tin dioxide based sensors with marked selectivity towards the common toxic and/or flammable gases methane, carbon monoxide and hydrogen.These sensors are selective throughout the viable operating temperature range. It is also possible to produce a single sensor in which the selectivity and mode of operation can be switched and tuned by modulation of the operating temperature. The exact reasons for these observations are as yet not fully understood but are currently being studied and will form the basis of a subsequent paper. References 1 Brattain, W. H., and Bardeen, J., Bell Syst. Tech. J., 1953,32,1. 2 Heiland, G., 2. Phys., 1954, 138, 459. 3 Seiyama, T., Kato, A., Fukiishi, K., and Nagatini, M., Anal.Chem., 1962, 34, 1502. 4 Taguchi, N., Br. Pat., 1280809, 1288009, 1282993, 1970. 5 Firth, J. G., Jones, A., and Jones, T. A., Environmental Sensors and Applications, IERE Conference Proceedings, 1974, p. 57. 6 Coles, G. S. V., Watson, J., and Gallagher, K. J., Sens. Actuators, 1985, 7, 89. 7 Coles, G. S. V., Williams, G., and Smith, B., Sens. Actuators, 1991, B3, 7. 8 Roth, J., J. Res. Natl. Bur. Stand., 1956, 56, 17. 9 Brisse, F., and Knop, O., Can. J. Chem., 1968, 46, 859.ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 Novel Solid-state Potentiometric Sensors 369 Michel Kleitz Laboratoire d’lonique et d’Electrochimie des Solides de Grenoble, LIESG/ENSEEG, Domaine Universitaire, BP 75, 38402 Saint Martin-d’Heres, France Solid-state potentiometric sensors can be described as being composed of sensitive surfaces and an electrolytic reference transmission line.’ These functions can be separated to a large extent which has not yet been fully explored. A good transmission line is composed of elements through which the electrolytic reference is constant and possibly interphases where the electrolytic reference steps are well defined by local chemical buffers.The differential zirconia sensor,2 the zirconia-tip sensor3 and the sulphate-zirconia contact4 illustrate the different behaviour of such interphases. Some of these interphases, such as the sulphate-zirconia interface can be used as sensing elements. This is also true of the conventional ion-sensitive electrodes and of the Nasicon membrane5 investigated for Na+ sensing.In order to be of interest, a sensitive surface must be ionically anchored to the electrolytic reference and must exhibit a redox reaction which equilibrates rapidly with the species to be analysed.6 Generally, this latter condition implies that the electron conduction associated with the redox system is not very high. Therefore, an additional potential-collecting com- pound must be suitably incorporated. Electrode reactions, in the conventional electrochemical sense, are the natural choice. As in aqueous electrolytes, an efficient ionic anchoring does not require that the counter ion of the species to be analysed be the predominant ionic ~ a r r i e r . ~ Catalysts known to be active for the species to be analysed can also be good candidates for the redox function.It has been demonstrated with 02*- and 02- that a catalysed partial redox reaction can give better sensor performance than a conventional complete reaction. At low temperatures, the transition to the peroxide reduction can result in shorter response times.8 References Kleitz, M., Siebert, E., Fabry, P., and Fouletier, J., in Chemical and Biochemical Sensors, eds. Gopel, W., Hesse, J., and Zemel, J. N., VCH Weinheim, 1991, in the press. Fouletier, J., Seinezia, H., and Kleitz, M., J . Appl. Electro- chem., 1975, 5 , 177. Fouletier, J . , Fabry, P., and Kleitz, M., J. Electrochem. SOC.. 1976, 123, 204. Kleitz, M., Pelloux, A., and Gauthier, M.. in Fast Ion Transport in Solids, eds. Vashishta, et al., Elsevier, Amsterdam, 1979, pp. Fabry, P., Gros, J.P., Million-Brodaz, J. F., and Kleitz, M., Sens. Actuators, 1988, 15, 33. Kleitz, M., and Siebert, E., in Chemical Sensor Technology, ed. Seiyama, T., Kodansha Elsevier, Tokyo and Amsterdam, 1989, Pelloux, A., Quessada, J. P., Fouletier, J . , Fabry, P.. and Kleitz, M., Solid State lonics, 1980, 1, 343. Siebert, E., Fouletier, J., and Kleitz, M., 1. Electrochem. Soc., 1987, 134, 1573. 69-73. V O ~ . 2, pp. 151-171. Design and Synthesis of Receptors for Sensor Use Joyce C. Lockhart Chemistry Department, The University of Newcastle upon Tyne, Newcastle upon Tyne NEI 7RU The availability of crystal structure information on biological receptor sites’ for metal ions has provided a blueprint for the design of synthetic receptor molecules, causing the deliberate synthesis of thousands of new molecules, many of which have provided analytical reagents for sensors.There is much less information available on the receptor sites for anions. Natural strategies for anions, as at present understood, involve two main types, one using sites of opposite charge (provided principally by the proximity of protonated Arg and Lys residues) with hydrogen bonding as a directional force, and hydrophobic interactions, the other apparently constructed without the obvious Coulombic interactions. In each instance the receptor site is a close fit to the contours of the anionic substrate, whether achieved by perfect size match or by induced fit. The first type is found in proteins which bind to DNA,’ and the second in the sulphate receptor protein2 of Salmonella typhimurium, for example.The synthetic approach to coordinating anions essentially turns the inorganic chemist’s ideas of coordination inside out. A straight comparison of the coordination of 18-crown-6 to potassium ions with the coordination of hexaprotonated l8-aza crown-6 to chloride ions indicates that the ion-dipole interac- tion of the crown molecule has no direct analogue in the second situation, as the directional force, in that instance hydrogen bonding, is unlikely to involve as many as six interactions to chloride simultaneously; if one N-H on each nitrogen points into the cavity of the ring, the other must point outwards. In fact the chloride binds exo3 to the ring, while the potassium goes into the ether cavity. Macrocycles which are oligomers of ethyleneimine also tend to have the nitrogens anti on each ethane segment and to have a large open cavity.It is also noteworthy that polyamines in which the linkers have three or more methylene links between nitrogens (such as the biological amines spermidine and putrescine) are much more basic than the ethylenediamine oligomers ubiquitous in inorganic chemistry, and thence more suitable for coordination to anions. In some crystal structures, anions are found inside the cavity of polyaza macro cycle^.^ Basic Design We used another approach with the intention of building a receptor site which would have an induced fit to anions of choice. Molecules containing two crown ether moieties, separated by a linking group, will sandwich potassium cations,370 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 X = polyaza Fig.1 Structural formula of bis(crowns) and it has been postulated that the linker between the two crown rings will form a p ~ c k e t . ~ It occurred to us that if the linker was formed from a polyamino residue, as for example formula (I) (Fig. l), then in hydroxylic solvents at neutral pH, it should be capable of complexing the counter ion of its potassium ‘filling’. Discussion Adenosine triphosphate (ATP) is a favourite anion for complexation studies. Suitable receptors for the phosphate residues have been detected previously by examining the time- averaged 31P NMR signals for the a,P,y phosphorus atoms, which are shifted relative to those of the free ATP in solutions containing receptor in a suitable mole ratio to the ATP.6,7 Molecular graphics studies indicated that diethylenetriamine in the extended, protonated conformation was an excellent sideways fit to the phosphates of a triphosphate chain, while a slightly longer chain, tetraethylenepentamine, likewise extended and protonated, could wrap simultaneously round the y and residues; small cyclic polyamines (four nitrogens) were more likely to interact with the terminal y phosphate only.The 31P shifts observed for 1 : 1 ratios of polyamine to ATP were shifted for these situations in accordance with this prediction. The size of cavity required to complex various anions from chloride to ATP was also estimated by using molecular graphics for the bis(crown) designs. The bis(crowns) (I) (Fig. 1) were shown by ‘H NMR to sandwich potassium ions.5 The Schori-Grodzinski NMR method8 of determining rates of exchange of quadrupolar nuclei between solvated and complexed environments was applied with limited success, to show that the coreceptor is clearly binding potassium ions plus counter ions simultaneously.A synthetic route, and the separation and characterization of the bis(crowns) (I) , the first multi-receptors to exhibit multiple binding to cation and counter ion simultaneously, will be described elsewhere. Further evaluation of the modified potential of the assembly for recognition and binding of anionic substrates in the presence of potassium ions is proceeding, prior to development of the new materials as anion sensors. Thanks are due to the SERC for financial support, and to Dr.N. P. Tompkinson, Dr. K. I. Kinnear, Dr. E. Arafa and D. P. Mousley for their help in this project. References Brookhaven Protein Data Bank, Bernstein, F. C., Koetzle, T. F., Williams, G. J. B., Meyer, E. F., Jr., Brice, M. D., Rodgers, J. R., Kennard, O., Shimanouchi, T., and Tasumi, M., J. MoI. Biol., 1977, 112, 535. Pflugrath, J. W., and Quiocho, F. A., Nature (London), 1985, 314, 257. Cullinane, J., Gelb, R. I., Margulis, T. N., and Zompa, L. Z., J. Am. Chem. SOC., 1982, 104, 3048. Lehn, J.-M., Meric, R., Vigneron, J.-P., Bkouche-Waksman, I., and Pascard, C., J. Chem. SOC., Chem. Commun., 1991, 62. Handyside, T. M., Lockhart, J. C., McDonnell, M. B., and Subba Rao, P. V., J. Chem. SOC., Dalton Trans., 1982, 2331. Hosseini, M. W., Lehn, J.-M., and Mertes, M.P., Helv. Chim. Acta, 1983, 66,2454. Hosseini, M. W, Lehn, J.-M., and Mertes, M. P., Helv. Chim. Acta, 1985, 68, 818. Shchori, E., Jagur-Grodzinski, J., Luz, Z., and Shporer, M., J. Am. Chem. SOC., 1971, 93, 7133. Control of Ion Transport Through Lipid Membranes Ulrich J. Krull, Dimitrios P. Nikolelis, John D. Brennan, R. Stephen Brown, Michael Thompson, Vida Ghaemmaghami and Krishna M. Kallury Chemical Sensors Group, Department of Chemistry, Erindale Campus, University of Toronto, 3359 Mississauga Road North, Mississauga, Ontario L5L IC6, Canada The perturbation of the structure of artificial lipid membranes can be monitored by electrochemical methods, and offers opportunities for development of chemically selective biosen- sors. An important advantage of such an electrochemical sensing system is the increased sensitivity which is derived from an intrinsic amplification process.A single selective binding event between a receptor and a target molecule can result in an increase of the transmembrane conduction that involves thousands of ions.’ A large number of biochemical reactions based on enzyme- substrate , antibody-antigen, lectin-saccharide , hormone- receptor and avidin-biotin interactions have been monitored by observation of the transmembrane ion current. A further extension of artificial lipid membranes for electrochemical sensing was the construction of ‘biomimetic ion-channel sensors’.* These devices were based on Langmuir-Blodgett deposition of multilayers of acidic lipid membranes on glassy carbon electrodes, More than three layers of lipid were necessary to block the permeation of Fe(CN)64-, which was used as a marker ion. In the presence of the stimulant Ca2+, a change in the alignment of the lipid occurred on the glassy carbon surface owing to electrostatic complexation of calcium ions with acidic phosphate head groups of the lipids, resulting in an increase of the marker ion penetration to the electrode.When ethylenediaminetetraacetic acid was added to the solution in slight excess of that required to complex the calciumANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 371 ions, the electrode signal for Ca2+ was eliminated. This indicates that a conductive zone can be opened reversibly by interaction of an analyte at a membrane in the absence of ion- channel proteins; however, the nature of such a conductive zone is poorly understood.Determination of the mechanism of ion permeation and establishment of control of the energetics associated with conductive pathways would permit optimization of the struc- ture of lipid membranes for biosensor development. Further development must include mechanical stabilization of a lipid membrane onto a solid electrode , where covalent linkages between the support and the lipidreceptor molecules are desirable. In order to avoid the effects caused by accumulation of ions on one side of such a stabilized membrane, the measurements must be made by driving the system with an a.c. voltage and by monitoring admittance with a phase-sensitive amplifier. Progress towards a surface-stabilized a.c.admittance modulation lipid membrane-based biosensor that operates on the basis of control of ion permeation by artificial ion channels is described. Control of Ion Permeability Through Planar Bilayer Lipid Membranes Ion conductivities through solvent-free planar bilayer lipid membranes (BLMs) formed from mixtures of egg phosphatidyl choline and dipalmitoylphosphatidic acid were evaluated to determine the effect of surface charge and phase domain formation on the process of ion translocation. Ion conductivity in a small d.c. voltage field was controlled by the surface distribution of potassium ions (0.1 mol dmP3 KC1 electrolyte) at the membrane-solution interface as predicted from electri- cal double layer theory. It was found that the conductivity of the membranes could be approximated as a linear function of the per cent.mass composition of the charged lipid. The conductivity was observed to alter drastically at a lipid composition containing a minimum of 25% phosphatidic acid as this component within the membrane was increased. This was attributed to the presence of a phase transition induced by the phosphatidic acid. At compositions of acid less than 25%, ion conduction occurred through zones that were enriched in the charged lipid. At concentrations of the acid above 25%, the average surface charge was the dominant factor which deter- mined the magnitude of ion conductivity. The adjustment of pH to control the degree of ionization of the phosphatidic acid had a similar effect to the variation of the amount of the acidic phospholipid within the membrane for experiments carried out at fixed pH.The ion conductivity could be used to measure accurately the pK, value associated with the acidic lipid within a planar BLM, and suggests a general method for evaluation of pK, for charged species in lipid membranes. Based on results of studies of cystic fibrosis which implicated hydroxystearic acid (HSA) as a contributing factor in altered biomembrane function, solvent-free planar BLMs and mono- layer films were prepared from a lipid mixture (by mass) containing 34% phosphatidylcholine, 19% dipalmitoylphos- phatidylserine , 47% cholesterol and variable amounts of 10- and 12-hydroxystearic acid (0-50%). The structures of mono- layer films at the air-water interface of a Langmuir-Blodgett trough were studied by pressure-area correlations and by further correlations with microscopic phase separation as revealed by fluorescence microscopy. In order to elucidate the role of the hydroxyl moieties in ion permeability the transmem- brane ion current was corrected for the effect of the negative surface charge of the carboxylic acid, and determined by replacement of the HSA component with stearic acid.The ion currents were found to increase approximately exponentially with the mole ratio of HSA. Two models of ion conduction through BLMs were considered: ‘hopping’ via hydrophilic sites within the hydrophobic zone of BLMs introduced by the hydroxyl moiety of 10- or 12-HSA; and transport through interfacial regions between phase domains which represent areas of low steric density and structural order within monolayers.While the two mechanisms are not distinct, the ion permeability and monolayer compression results did indicate that HSA had a large effect at low concentrations. The results suggested that the physical location of ion permeation through BLMs containing low concentrations of HSA was predominantly at interfacial zones at the edges between domains, and that artificial ‘ion channels’ had been generated by virtue of the edge activity of HSA. Electrochemistry of Surface-immobilized Membranes A portable admittance modulation measurement device was constructed, and was designed to measure both the in-phase and out-of-phase signal components for determination of ‘effective’ ion current and membrane capacitance. The sensiti- vity and detection limit for the a.c.system were tested by studying the interaction of the ionophore valinomycin with planar BLMs.’ The electrochemical effects were observed as conductance changes of the membrane, with the limit of detection for valinomycin being at the 1 nmol dm-3 concen- tration level. Metal electrodes were used as supports for covalent attach- ment of amphiphiles. Platinum electrodes with a surface area of 1 cm2 were oxidized to provide a high density of surface hydroxyl sites.3 Immobilization of amphiphiles was carried out by reaction of the hydroxyl sites with ~ i l a n e . ~ Gold electrodes were prepared by vacuum deposition of a 250 nm layer of the metal onto a 30 nm layer of chromium that covered borosilicate glass slides.Surface attachment of amphiphiles to this metal was achieved by sulphur-gold interaction^.^ A wide variety of amphiphiles differing in hydrocarbon chain length, number of chains (one or two), chain polarity, head group charge and head group size ( e . g . , acidic phosphate, carboxylic acid and ester, phosphatidylcholine) were attached to both the platinum and gold surfaces. Two-step attachment procedures, as exemplified by the initial deposition of amino- propyltriethoxysilane (APTES) onto platinum followed by linkage of a 10-carbon phosphatidylcholine through an amide bond to the amino group of APTES, often provided greater surface coverage than if an equivalent 16-carbon phosphatidyl- choline had been deposited directly by the reaction of hydroxyl moieties with silane at the metal surface.Surface coverage for most experiments was in the range 40-85% as determined by X-ray photoelectron spectroscopy, and was dependent on the deposition procedure, the chain length and the number of chains. The electrochemical results indicated that the best blockage of ion conductivity occurred when the amphiphiles contained long hydrocarbon chains. Species such as trichloro- octadecylsilane and octadecylthiol provided the best blockage, reducing the in-phase signal component by 95% for both types of metal electrode. Analogues of natural lipids such as dimyristoylphosphatidylcholine reduced the in-phase compo- nent by values of about 50%. Subsequent incubation of lipid- coated electrodes in solutions containing membrane-soluble species such as cholesterol greatly reduced the magnitude of the in-phase component of the signal to values approaching those found for BLMs.These latter electrodes were tested for response to the presence of valinomycin, and achieved detection limits in the range 10-100 nmol dm-3. A further series of analytical experiments were carried out to develop electrodes that were sensitive to pH variations to extend the concept of control of phase domain structure to immobilized membranes. Linear 10-carbon silane and thiol carboxylic acids were immobilized onto platinum and gold surfaces, and both systems showed good sensitivity to pH (e.g. , a pH change from 7 to 8 caused a conductivity change of 25% ). Modification of this system to evaluate a biosensing strategy was then carried out.Enzymically active urease has been adsorbed onto these acidic surfaces, and has also been covalently immobilized through the acidic functional group.372 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 The intent was to use the urease-urea reaction to generate a local transient pH gradient which would perturb the membrane structure. Tentative electrochemical results, and definitive spectroscopic results, indicate that this has been accomplished and that sub-micromolar detection levels can be achieved for the substrate with good reversibility and longevity. We are grateful to the Canadian Defense Research Establish- ment-Suffield and the Natural Sciences and Engineering Research Council of Canada for financial support of this work.References 1 Krull, U. J., and Thompson, M., ZEEE Electron Devices, 1985, 32, 1180. 2 Sugawara, M., Kojima, K., Sazawa, H., and Umezawa, Y . , Anal. Chem., 1987, 59, 2842. 3 Moody, G. J., Sanghera, G. S., and Thomas, J. D. R., Analyst, 1986, 111, 1235. 4 Ghaemmaghami, V., Kallury, K. M., Krull, U. J., Thompson, M., and Davies, M. C., Anal. Chim. Acta, 1989, 225, 369. Gas Sensors Using the Work Function of Organic Semiconductors Jiii Janata and Jan Langmaier Department of Materials Science and Engineering, University of Utah, Salt Lake City, UT 841 12, USA The key issue in the development of chemical sensors is the design of new chemically selective layers. Organic semiconduc- tors have attracted considerable attention as the materials for such diverse applications as power sources, non-linear optics, superconductors and molecular electronics.Not surprisingly, they are also being investigated as possible sensor materials in a wide range of applications. The parameters that are modulated by the chemical interactions include mass, optical absorptivity, conductance, Galvani potential and work function (WF). This paper will be restricted to a discussion of the interactions of organic semiconductors with the gaseous phase and will focus particularly on the chemical modulation of the WF. The electron WF is one of the fundamental material constants. It plays a key role in the distribution of electrons in solid-state structures, affects the catalytic properties of solid materials and determines the rate of corrosion and chemical resistance of materials.It is defined as the work that has to be used in order to extract an electron from the interior of a phase and place it outside the reach of image forces, in the so-called vacuum reference level. There are two components of the WF: the bulk contribution, which is related to the chemical potential of an electron in the phase and represents the affinity of the electron for the matrix; and the surface contribution, which is related to the electric field resulting from the surface dipole layer. Measurement of the WF provides information about the electronic properties of a material. For example, organic semiconductors prepared by electro-oxidation under different conditions have a different WF, which is further affected by the presence of other electron donors/acceptors.This phenom- enon is the basis for a new class of electrochemical sensors, particularly for the sensing of gases. To date, the WF has been used analytically only rarely. The best known device which measures the WF is the vibrating capacitor (Kelvin probe). Because of its size it is impractical as a sensor, although it was proposed as a gas chromatographic detector almost 40 years ago. The operating characteristics of solid-state devices based on metal-insulator-semiconductor junctions, such as insulated gate field-effect transistors or metal-insulator-semiconductor diodes, depend directly on the WF of the gate metal. This fact has been exploited in the design and development of well- known potentiometric sensors for hydrogen, which use palla- dium as the gate metal, and in transistors using organic semiconductors which have been shown to respond to a variety of organic vapours.In this paper the fundamental aspects of the WF will be reviewed, its potential for chemical analysis of gases assessed and examples of general solid-state chemical sensors based on its chemical modulation will be given. It is necessary to realize that organic semiconductors can be deposited in different ways, e.g., by sublimation, solvent casting or electrochemical deposition. The choice of the deposition technique used is determined by the constraints given by the sensor itself. In WF sensors it is a necessity that at least one interface of the selective layer is capacitively coupled to the remainder of the sensor structure.' This condition is satisfied in a suspended gate field-effect transistor ( SGFET)2 and in its macroscopic counterpart the vibrating capacitor.The latter has been used in this work to develop and characterize a selective layer for hydrogen cyanide based on electrochemi- cally prepared polyaniline (PANI) . Aniline can be easily polymerized from acidic media3 on the Pt plate of the vibrating capacitor and its WF can be measured against a suitable reference plate, e.g., stainless steel. A considerable advantage of this approach is that the film on the working plate can be examined by a variety of auxiliary spectroscopic and microscopic techniques. The WF of PANI itself is not affected by HCN. However, when the Ag-AgCN system is incorporated in PANI the layer becomes sensitive to HCN.The kinetics and the polarity of the change of the WF depend on several factors. When the PANI*Ag layer is prepared in the reduced state (PANI *Ag is a heterogeneous system; the asterisk signifies the heterogen- eity) its WF decreases on exposure to HCN. The response becomes reversible when the electropolymerization is carried out from a glycerine-1 mol dm-3 HZS04 mixture. Glycerine facilitates proton transfer from the silver clusters to the PANI backbone : e Slow 1 .c-- ~ ' [Pt-PANI-Ag] + HCN - [Pt-PANI-H+,AgCN] T - Glycerine On the other hand when the film is prepared in the oxidized state and/or when the AgCN complex is present the reaction proceeds according to the scheme: Fast [Pt-PANI-Ag-AgCN] + HCN - e- - 1 [ Pt-PANI-H+ , Ag( CN)2] ?-A tilycerine In this instance the HCN molecule dissociates forming a strong Ag(CN)* complex and the proton is again transferred toANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 373 the PANI backbone.The electroneutrality of PANI is main- tained by the inflow of electrons from the reference plate which is equivalent to the increase of the WF. This result confirms the mechanism of charge transfer between the guest molecule and the m a t r i ~ : ~ if the matrix is reduced (high value of WF) it acts as an electron donor and the WF decreases. When the matrix is oxidized (low WF) it can accept electrons and the WF increases. For polypyrrole and polythiophene this proton transfer reaction is absent and the response to HCN is irreversible. The response is logarithmic in the range 5-50 ppm and has square-root-time dependence, indicating predominantly bulk interaction. The selectivity of this material to a variety of environmentally important gases remains to be tested.This work was supported by a contract from BWB and by a grant from the EPA Office of Exploratory Research, Grant NO. R-816491-01-0. References 1 2 3 4 Janata, J., Principles of Chemical Sensors, Plenum Press, New York, 1989. Josowicz, M., and Janata, J., in Chemical Sensor Technology, ed. Seiyama, T., Elsevier, Amsterdam, 1988. Zotti, G., Cattarin, S., and Comisso, N., J. Electroanal. Chem., 1987, 235, 259. Blackwood, D., and Josowicz, M., J . Phys. Chem., 1991, 95, 493. Applications of Electropolymerized Films in Electrochemical Sensors Philip N.Bartlett Department of Chemistry, University of Warwick, Coventry CV4 7AL Electrochemical polymerization is a very convenient technique for the production of modified electrode surfaces. The method is simple to carry out and the deposition of the film is readily controlled by control of the electrode potential. The method is well suited to the deposition of films onto microelectrode electrode structures formed by photolithography.' We have investigated the application of electropolymerized films as a method for producing modified electrode surfaces for use in chemical sensors and biosensors. Much of this work has concentrated on the use of conducting polymer films formed from substituted pyrroles or other heterocyclic monomers but we have also made use of poly(pheno1ic) films.Ion-sensitive Polymers Films of poly(5-carboxyindole) can be grown from acetonitrile solutions. The resulting conducting polymer has a carboxylic acid substituent on every monomer unit of the chain. When the polymer is transferred into aqueous solution the degree of ionization of these groups varies with the solution pH and this, in turn, alters the electrochemistry of the film. The films are stable at pH values less than 5 but dissolve slowly in aqueous solution above pH 7. The pH dependency of the electro- chemistry of poly(5-carboxyindole) can be used to make small pH-sensitive electrodes. These were made by the electropoly- merization of the monomer from acetonitrile onto 125 pm diameter platinum wires sealed in heatshrink PTFE. The coated electrodes were then transferred into buffered aqueous solution at pH 2 and cycled until a stable response was attained, and then held at +800 mV versus SCE and the current allowed to decay to zero to convert the film into its oxidized form.pH measurements were made using the oxidized electrodes with a commercial pH meter and calomel reference electrode. At pH 7 some portion of the carboxylate groups in the poly(5-carboxyindole) are deprotonated and can be used to hydrogen bond to protonated lysine residues around the haem edge in cytochrome c. This leads to the adsorption of cytochrome c at the polymer surface in the correct orientation for electron transfer between the polymer and the haem group .2 This interaction between the carboxylate groups and the lysine residues mimics the hydrogen bonding interactions which are believed to play an important role in electron transfer between cytochrome c and cytochrome oxidase, its natural redox partner.In principle, it should be possible to confer ion selectivity on a conducting polymer film by attaching suitable substituents to the polymer. This might be advantageous because the mixed ionic and electronic conductivity of the resulting conducting polymer could then be utilized to make small ion-selective sensors. We have investigated this approach by synthesizing pyrrole substituted in the N-position with a benzo-15-crown-5 derivative. The resulting monomer can be electropolymerized, and the properties of the resulting conducting polymer films have been in~estigated.~ Immobilization of Glucose Oxidase The electropolymerization of pyrrole and N-methylpyrrole from buffered aqueous solutions can be used to immobilize glucose oxidase and other enzymes at electrode surfaces.In the resulting enzyme-loaded films the behaviour is determined by the balance of the diffusion of reactants and products within the film and the kinetics for the immobilized enzyme. In order to understand the behaviour of these films it is necessary to model these processes and to compare the predictions of these models with the experimental r e s ~ l t s . ~ Studies of glucose oxidase immobilized in poly( N-methyl- pyrrole) films show that when the natural redox partner, oxygen, is used as the mediator species the hydrogen peroxide produced is not oxidized on the polymer but rather must diffuse to the underlying electrode to be detected.' By using tritium-labelled glucose oxidase we have determined the concentration of enzyme entrapped within our electropolymer- ized films and, by using these data and data from the kinetic analysis of the response of these films to glucose, we have estimated the kinetics for the oxidation of glucose by the immobilized enzyme.It was found that these kinetics are not significantly different from the values obtained in homo- geneous solution. Studies in which oxygen is replaced by ferrocenecarboxylic acid or hexacyanoferrate(rI1) as an artificial mediator species show similar behaviour. In each instance the polymer appears to be electro-inactive towards re-oxidation of the mediator. Fourier transform infrared studies of the polymer films indicate that this loss of conductivity of the film is caused by reactions with hydrogen peroxide generated by the enzyme.Electrochemically polymerized films of phenols can also be used to immobilize glucose oxidase at an electrode surface.6 The immobilized enzyme remains active and glucose can be detected by using electrodes of this type either with oxygen as the mediator or when using an artificial redox mediator such as ferrocenecarboxylic acid. Analysis of the responses of such374 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 electrodes enables the rate constants for the enzyme-catalysed reactions to be estimated and the effect of the substituents on the phenol on the properties of the immobilized enzyme to be investigated. This work was supported by the SERC (Grant G R E 67108) and by MediSense. I thank the following colleagues and students who have contributed to this work: P.Moore, P. Tebbutt, A. Benniston, L-Y. Chung, R. Whitaker, Z . Ali, J. Farrington, D. Dawson, V. Eastwick-Field, D. Caruana, P. Birkin, V. Rhodes and C. Tyrrell. References 1 Bartlett, P. N., Gardner, J. W., and Whitaker, R. G., Sens. Actuators, 1990, A21-A23, 911. 2 Bartlett, P. N., and Farrington, J., J . Electroanal. Chem., 1989, 261, 51. 3 Bartlett, P. N., Benniston, A. C., Chung, L-Y., Dawson, D. H., and Moore, P., Electrochim. Acta, 1991, 36, 1377. 4 Bartlett, P. N., and Whitaker, R. G., J . Electroanal. Chem., 1987, 224, 27. 5 Bartlett, P. N., and Whitaker, R. G., J . Electroanal. Chem., 1987, 224, 37. 6 Bartlett, P.N., and Whitaker, R. G., Biosensors, 1987/88, 3, 359. Disposable Single-use Sensors Monika J. Green and Paul 1. Hilditch MediSense Inc., Units 3 & 4, 14/15 Eyston Way, Abingdon, Oxfordshire OX14 ITR For a medical diagnostic product, the advantages of a single- use disposable sensor are clear. Most importantly, problems with contamination or carryover are eliminated and steriliz- ation by the user is unnecessary. Further, with a re-usable sensor there might be concerns with drift and the need for recalibration, which are not an issue with a disposable device. In addition, the low cost of disposable sensors reduces the fear of expensive damage associated with a re-usable device. The principal criterion for successfully producing or adapt- ing a diagnostic test in disposable form is that a means must be found of constructing a device containing all the necessary components for the test, avoiding the need to add reagents at the time of use.The device should have a stable shelf-life of at least 12 months, and the whole should be capable of manufacture in large numbers relatively cheaply. Where the addition of reagents at the time of the test seems unavoidable, the usual solution has been to employ one of the large automated analysers to perform the test. This type of instrument, however, has little part to play in the rapidly expanding market of decentralized testing, which offers much for improved efficiency and quality of patient care. Glucose Monitoring The basic concept of a biosensor for personal glucose monitoring is simple: reagents and biochemicals necessary for detection are deposited on a disposable sensor device; this can be interfaced with an electronic meter system which monitors (and may control) the progress of the reaction, and interprets and displays the results.The detection chemistry which has been most successful in this area is that based on the interaction between glucose oxidase (GOD) and derivatives of ferrocene [bis(cyclopentadi- enyl)iron] .’ The oxidized forms of ferrocenes (ferricinium ions) are capable of accepting electrons from GOD which has been reduced by the reaction with glucose. It is therefore possible to set up a system whereby ferrocene, oxidized at an electrode to form ferricinium, is reduced by GOD in the presence of glucose, and re-oxidized at the electrode producing an electrical current dependent on the glucose concentration: Glucose + GOD,, - gluconolactone + GODred (1) G0Dp-d + Fe(cp)2+ + GOD,, + Fe(cp)2 F e ( ~ p ) ~ + Fe(cp)2f + e- (2) (3) This chemistry is produced commercially in the form of a disposable sensor .2 A poly(viny1 chloride) (PVC) substrate is printed with several layers (Fig.l), some of which provide the PVC substrate Conductive Working silver track elec!rode \ - ,Contacts I I I I I Dielectric layer Conductive carbon track I Ag-AgCI reference electrode Fig. 1 Schematic representation of a disposable glucose sensor strip two electrodes (working and reference) necessary for the electrochemical reaction, and transmit current and potential information to the meter during the measurement, and one of which contains enzyme and mediator in a labile matrix.A ‘second-generation’ sensor, which is also available in desk- top format, has several improved features including automatic detection of blood application (no button pressing), tempera- ture com ensation and almost complete freedom from inter- ferences.’ The last of these has been achieved by the incorporation on the sensor strip of a third electrode, which contains all the components of the normal working electrode except for the enzyme. Any redox-active interferents present in the sample will affect the response of this ‘dummy’ electrode in the same way as the working electrode, and a correction is performed by the meter to give the glucose value. The linearity and accuracy of this system are illustrated in Fig.2. Acetaminophen Known in the UK as ‘paracetamol’ and in the US as ‘tylenol’, acetaminophen is a widely used analgesic. Its ready availability and toxic effect in overdose make this a substance which is frequently suspected in emergency room admissions. In an acetaminophen ~ e n s o r , ~ the enzyme aryl acylamidase catalyses the deacylation of acetaminophen to yield p-aminophenol, which can be oxidized at an electrode to yield quinoneimine with consequent measurable current: NHCOCH3 NH2 I I 0 + H 2 0 - @ + CH3COOH (4) OH O HANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 375 Table 1 Design specifications for the bacterial assay system Alternative to 'standard plate count' Capable of producing results rapidly (< 1 h) Moderate sensitivity (10s cfu ml-' or better) Economical (<$1 per test) + &i ++ + 0 3 6 9 12 15 18 21 24 27 30 33 Mean YSI venous reading/mmol I-' Fig.2 Clinical response of the Satellite G glucose sensor compared with a laboratory reference analyser [Yellow Springs Instruments (YSI)]. The line on the graph is the line of identity OH Q A potential interferent is N-acetylcysteine, which is adminis- tered as the antidote for acetaminophen poisoning; this (and other thiol reagents) can react with the quinoneimine product of the first reactions, forming a substituted aminophenol which can be reduced at the electrode, augmenting the current already observed: NH NH, NH2 NH In order to eliminate this possible interference, the sensor strip described includes an absorbent overlay containing gluta- thione. This reagent ensures that the thiol augmentation of response is fully saturated irrespective of the thiol content of the blood.Salicy late N-Acetylsalicylate (aspirin) is another widely used analgesic, and is monitored in emergency situations for the same reasons as acetaminophen. Aspirin is also used as an anti-inflammatory agent in the management of conditions such as arthritis, and because of the toxicity of salicylate, monitoring of drug concentrations is desirable, N-Acetylsalicylate is rapidly con- verted by hepatic esterases into salicylic acid, which is the therapeutically active form of the drug, and it is this which is measured. The principle of the assag is similar to that for acetaminophen: salicylate is converted into catechol by the enzyme salicylate hydroxylase. Catechol is oxidized to o- benzoquinone by the electrode and the current measured.The cofactor NADH is required by the enzyme, and must be provided in the sensor. Linearity of response is obtained by the inclusion of sodium benzoate in the reaction chemistry. This acts as a pseudo-substrate for the enzyme, effectively modify- ing its kinetics to give a near-linear response in the clinical concentration range. Theophy lline There is a considerable market for sensors capable of monitoring therapeutic drugs present in blood at micromolar concentrations. These substances will usually not be directly detectable in the blood matrix, leaving as options an immuno- assay test or some other format such as enzyme inhibition.For theophylline, the latter approach has been pur~ued.~ Theophylline, a member of the xanthine family of com- pounds, is prescribed as a bronchodilator in cases of asthma, on a proph lactic basis. Above its therapeutic range of 55-110 monitoring of concentration is desirable. A disposable sensor for theophylline exploits the interaction of theophylline with the enzyme alkaline phosphatase: the drug behaves as an uncompetitive inhibitor, binding to the enzyme-substrate complex and preventing its further reaction. Alkaline phosphatase will hydrolyse a wide range of substrates, and that which is of most interest electrochemically is p-aminophenol phosphate. The parent compound is readily distinguishable electrochemically from the product, p-amino- phenol, and so the activity of a sample of alkaline phosphatase can be measured by providing p-aminophenol phosphate and measuring electrochemically the amount of p-aminophenol produced.Equally, providing a known amount of enzyme and substrate allows the concentration of inhibitor (theophylline) to be assessed. ymol 1- r , theophylline rapidly becomes toxic and so effective Bacterial Assay System A final example of a disposable sensor system is that developed for the detection and measurement of micro-organisms. The opportunities for this area of testing are almost endless, encompassing clinical, food and environmental applications. The objectives set out for the system described by Hilditch et ~ 1 . ~ are summarized in Table 1. The approach taken was the electrochemical interrogation of bacterial respiration using a mediator compound; the assay therefore measures viable biomass.The mediator used in the assay is p-benzoquinone, which resembles the quinones which occupy a pivotal position in the electron transport chain of bacteria and may compete with these for respiratory electrons, although the exact site of mediation is unclear. A wide range of quinones and related compounds have been screened and the simplest, p-benzo- quinone, has been found to be the most satisfactory. Bacteria respiring in the presence of p-benzoquinone cause it to become reduced to hydroquinone. This compound can then be re- oxidized at an electrode at the appropriate potential; the amount of hydroquinone formed in a given time is a measure of the rate of bacterial respiration in the sample and hence of the cell numbers.A simple assay of this type has certain limitations, in particular that its sensitivity is limited to about lo6 cfu ml-' (cfu = colony forming units) by the rate of bacterial respiration,376 2. 2 100 C 0 CL v) [r 10 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 - - and that redox-active substances in the sample will interfere. The system described overcomes these problems by concen- trating bacterial cells on a filter in close proximity to the measurement electrodes. This allows amplification of the response as cells from a relatively large volume of sample are concentrated into a small reaction volume; moreover, the cells can be washed when on the filter, removing soluble redox interferents. Filter and electrodes are contained in a disposable assembly (Fig.3) formed from PVC; the lower half has printed electrodes while the upper half has a recess to contain a disc of glass-fibre filter material. The disposable assembly fits into a housing built into the meter which automatically interfaces with the fluid handling and electrical contacts. The meter pumps sample, wash buffer and mediator solution as appropri- ate through the disposable assembly, which is maintained at constant temperature. After loading sample onto the dispos- able assembly, and washing with buffer, the assembly is flooded with mediator solution (which also contains carbon source for the bacteria) and is incubated for 10 min. During this time bacterial respiration is converting benzoquinone into hydroquinone, which is measured for 30 s at the end of the incubation. The total assay time is therefore of the order of 15 min.The performance of the assay has been validated with a considerable range of aerobic bacterial species; it has been Embossed and textured P V C A Filter disc c-> with electrodes Fig. 3 assay system Disposable sensor element for use in a biosensor bacterial typically found to give a linear response with a sensitivity of about lo4 cfu ml-' (Fig. 4). In addition to pure cultures, results loo0 i 0 r = 0.988 1 1 I I I 103 104 105 106 107 108 Se nsit ivi tykfu m I - 1 Fig. 4 Response of the bacterial assay system to bacteria (Pseudo- monas cepacia) have been obtained with mixed bacterial cultures, yeasts and food and environmental samples. Conclusion Single-use biosensor diagnostics are characterized by con- venience of use, rapidity, accuracy and freedom from sample pre-treatment.Application of the technology to other areas such as bacterial monitoring promises to extend further the boundaries of analytical chemistry. References Green, M. J., and Hill, H. A. O., J . Chem. SOC., Faruday Trans., 1986, 82, 1237. Matthews, D. R., Holman, R. R., Bown, E., Steemson, J., Watson, A., Hughes, S., and Scott, D., Lancet, 1987, 1, 778. Matthews, D. R., Burton, S. F., and Smith, E., in Proceedings, Artijicial Insulin Delivery Systems Pancreas and Islet Transplan- tation, European Association for the Study of Diabetes, Amsterdam, 1991. Jones, A. F., McAleer, J. F., Braithwaite, R.A., Scott, L. D., Brown, S. S., and Vale, J. A., Lancet, 1990, 335, 793. Frew, J. E., Bayliff, S. W., Gibbs, P. N. B., and Green, M. J., Anal. Chim. Actu, 1989, 224, 39. Foulds, N. C., Wilshere, J. M., and Green, M. J., Anal. Chim. Actu, 1990, 229, 57. Hilditch, P. I., Carter, N. F., Barrett, C. B., Sullivan, D. J., Charman, K. M., Green, M. J., and Williams, S. C . , in Advances in Bioreactor Monitoring, ed. Wang, N. S . , Academic Press, New York, 1991, in the press. Applications of Amperometric Biosensors Anthony P. F. Turner Biotechnolog y Centre, Cran field Institute of Technology, Cran field, Bedford MK43 OAL Numerous definitions of a biosensor pervade the recent scientific literature.' Taking a pragmatic view, a biosensor can be considered as one possible solution to a particular analytical problem. Whether this technical route should be pursued or not depends on the relevance of the features offered by biosensors to the problem.Biosensors generally provide continuous information about the concentration of a chemical or group of chemical^.^,^ They are capable of considerable specificity and sensitivity even when used directly in real samples, without necessarily incurring the need for complex and expensive instrumentation. Coupled with modern micro- electronics they form the basis for a new generation of 'sensitive' computers. This paper will review the requirements of several areas where amperometric biosensors are likely to make an impact. A few recent or new examples of biosensor technology that are likely to prove a commercial success4 will be illustrated. Clinical diagnostics have dominated biosensor development to date and are likely to continue to be the focus for commercial successes over the next five years .5 Clinical applications are driven by the need for cost effective patient care.Analytical instruments can be comprehensive and automated or decentralized and specialized. Some conditions, for example diabetes, benefit from self-tests usable in the home.6 Indeed,ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 377 the world's most successful biosensor is a pen-shaped blood glucose monitor which addresses this market. A key issue in tackling large markets is the requirement for inexpensive and reproducible mass production of the disposable biosensor element.Once investment has been made in such a production facility it is desirable to find further applications for the technology. Diagnostic tests that make sense to perform in the home are few and far between. Pregnancy testing is an obvious example, but the frequency with which these tests are performed makes an instrumented assay uncompetitive with the elegant visual assays now marketed. Other promising analytes that are attracting commercial development of pocket-sized devices include total cholesterol, ethanol and lactate. The printing technology that has been developed for the mass production of one-shot devices might find application in reusable or continuous use devices. Recent work in our laboratories has shown that screen-printed enzyme electrodes for glucose, using tetrathiafulvalene as mediator,' can be used over 2000 times.This has been achieved by using proprietary membrane technology acting as a reservoir of the mediator.' Such elements might be useful in larger machines where the throughput permitted by biosensors can out-perform conven- tional systems or where a competitive advantage can be achieved by broadening the spectrum of analyses offered to include, for example, glucose, urea, creatinine and lactate. Equally, simple amperometric devices can be constructed which are capable of highly sensitive immunoassay of analytes such as thyroid stimulating hormone, prostatic acid phospha- tase (a tumour marker) or estradiol.'**" Some speculative work is underway to perform electrochemical detection of DNA hybridization, furnishing the ossibility of detecting a wide range of pathogenic organisms.A further area of interest is in vivo m~nitoring.'~ Mediated amperometric enzyme electrodes offer advantages over oxy- gen-consuming systems in their relative independence from variations in oxygen tension. Concern has been expressed, however, about the toxicity of the mediators used. New evidence suggests that mediators can be less toxic than feared, for example, the LD50 in mice of tetracyan~quinodimethane'~ and tetrathiaf~lvalene~~' (two recently discovered mediators) is 1225 and 710 mg kg-', respectively.lS While many promising sensors have been described, lack of biocompatibility remains a major hurdle to the application of sensors inside the body for critical care or long-term therapeutic purposes.16.17 An inter- esting compromise has recently been announced by an Italian company; the proposed product consists of a wearable microdialysis system incorporating a non-mediated enzyme electrode for continuous monitoring in diabetics. Much of the technology developed for clinical applications will find other uses in industry, l8 environmental monitoring" and defence. Industry is seeking sensors to improve productiv- ity, quality and compliance with legislation. Amperometric biosensors have recently become commercially available for use in situ in fermentation monitoring with broad consequences for the food and biotechnology industries. Amperometric detection of microbial contamination2' of milk has reached the manufacturing prototype sta e in our hands with a detection limit of lo4 organisms ml-' obtained within 20 min in a completely 'hands off' format.Environmental applications of biosensors are characterized by a desire to protect workers and the public from toxic Y2 material, and compliance with legislation. One interesting new development with particular relevance to this area is the discovery of organic phase enzyme electrodes.21722 These instruments are capable of operating in oils or fats23 and can also offer improved performance in aqueous samples by, for example, automatically concentrating contaminants present in drinking water. As the academic literature on biosensors continues to diversify, a clear trend within industry critically to evaluate and invest in focused areas is emerging. Technical issues concern- ing the developers include fabrication technologies and a general drive towards miniaturization. Medicine and food provide the prime focus for new products, but many smaller companies are searching for niche markets and might furnish some fascinating new gadgets, allowing executives to transform themselves into skilled analytical chemists overnight. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 References Turner, A. P. F., Sens. Actuators, 1989, 17. 433. Turner, A. P. F., Karube, I., and Wilson, G. S., Biosensors: Fundamentals and Applications, Oxford University Press, Oxford, 1989. Turner, A. P. F., Advances in Biosensors, JAI Press, London, 1991, vol. 1. Turner, A. P. F., Int. Biotechnol. Lab., 1990, 8 (3A), 36. Anon, Biosensors: A New Realism, Cranfield Biotechnology, Cranfield, 1991. Cardosi, M. F., and Turner, A. P. F., in The Diabetes Annual, eds. Alberti, K. G. M. M., and Krall, L. P., Elsevier, Amsterdam, 1990, vol. 5 , pp. 254-272. Palleschi, G., and Turner, A. P. F., Anal. Chim. Acta, 1990, 234, 459. Turner, A. P. F., Hendry, S. P., and Cardosi, M. F., in Biosensors, Instrumentation and Processing: The World Biotech Report, Online, London, 1987, vol. 1(3), pp. 125-137. D'Costa, E. J., Br. Put. Appl., 9 019 126.3, 1990. Cardosi, M. F., Birch, S. W., Stanley, C. J., Johannsson, A., and Turner, A. P. F., Am. Biotechnol. Lab., 1989, 7, 50. Bannister, J . V., Higgins, I. J., and Turner, A. P. F., in Biosensors: Principles and Applications, eds. Blum, L. J., and Coulet, P. R., Marcel Dekker, New York, 1991, pp. 47-61. Downs, M. E. A., Warner, P. J., Fothergill, J. C., andTurner, A. P. F., Biomaterials, 1988, 9, 66. Cardosi, M. F., and Turner, A. P. F., in The Diabetes Annual, eds. Alberti, K. G. M. M., and Krall, L. P., Elsevier, Amsterdam, 1991, vol. 6, pp. 271-301. Hendry, S. P., andTurner, A. P. F., Horm. Metab. Res., 1988, 20, 37. Kulys, J., and Higgins, I. J., Biosens. Bioelectron., 1991, 6, in the press. Reach, G., Thevenot, D., and Coulet, P., Anal. Lett., 1989,22, 2393. Coughlan, M. P., and Alcock, S. J., Biosens. Bioelectron., 1991, 6, 87. Brooks, S. L., Higgins, I. J., Newman, J., andTurner, A. P. F., Enzyme Microb. Technol., 1991, in the press. Rawson, D. M., Willmer, A. J., and Turner, A. P. F., Biosensors, 1989, 4, 299. Turner, A. P. F., Allen, M., Schneider, B. H., Swain, A. S . , and Taylor, F., Int. Biodeterior. Bull., 1989, 25, 137. Saini, S . , and Turner, A. P. F., Biochem. SOC. Trans., 1991,19, 28. Saini, S . , Hall, G. F., Downs, M. E. A.. and Turner, A. P. F., Anal. Chim. Acta, 1991, 249, 1. Hall, G. F., and Turner, A. P. F., Anal. Lett., 1991, 24(8), in the press.

ISSN:0144-557X    

DOI:10.1039/AP9912800366

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

378 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 Non-faradaic Electrochemical Sensors: Principles and Practice Douglas B. Kell*.t and Andrew M. Woodward* *Department of Biological Sciences, University College of Wales, Aberystwyth, Dyfed SY23 3DA tAber Instruments, Unit 4, Science Park, Cefn Llan, Aberystwyth, Dyfed SY23 3AH In this paper the principles of non-faradaic electrochemistry are outlined, and non-faradaic electrochemical methods are described which provide: (i) a solution to the problem of devising a real-time biomass probe; and (ii) in certain instances a means of measuring enzymic behaviour in situ. The linear, non-faradaic or 'passive' electrical properties of a biological or other system are completely characterized by its conductance (siemens) and capacitance (farads), reflecting, respectively, the in- and out-of-phase portions of the alternat- ing potential difference caused in response to the application of an alternating current.These macroscopic properties depend in part on the size and geometry of the electrodes, and reflect the intrinsic properties of the system, permittivity and conduc- tivity (see, for example, references 1-3). For plane-parallel electrodes of area A separated by a distance d , the relationship between the conductivity 0' and conductance G is 0' = G(d/A), where d / A is known as the cell constant and has units of E' = C(d/A~od, where E~ is an experimental constant equal to 8.854 x lo-' F m-l, such that a cubic electrochemical cell of unit dimensions containing water (which has a permittivity of 78.4 at 298 K) has a capacitance of some 6.94 pF.By 'linear', we mean that the measured conductance and capacitance are independent of the magnitude of the exciting field, and that excitation by a current at a frequency f Hz leads only to an alternating potential difference at the same frequency. length- ( l ) . The capacitance C is related to the permittivity E' by Use of the Linear Dielectric Properties for Sensing Microbial Biomass The dielectric properties of cellular suspensions themselves (as opposed to those of the suspending medium or the electrodes) are generally characterized by three major areas of frequency- dependence, known (in order of increasing frequency) as the a-, @- and y-dispersions.2 The @-dispersion, centred in the radiofrequency region of the electromagnetic spectrum, is caused predominantly4 by the charging of the large membrane capacitance C, displa ed by all intact cells.This is typically of the order of 1 pF cm-', and is due to the possession by cells of non-micellar phospholipid membranes of molecular thickness. For spherical cells of radius Y , present at a volume fraction P, the permittivity at low radiofrequencies exceeds that of the background by a value given by 9PrCJ4~0. For non-spherical cells the factor 9/4 is different. Hence, by measuring the dielectric permittivity of cell suspensions at low radiofre- quencies, it is possible to design a biomass probe that is specific for viable cells (as necromass, particles, emulsions and gas bubbles do not have intact bilayer-type cell membranes; references 5-8).We have therefore developed a biomass probe (the pugmeter) suitable for the real-time estimation of biomass in fermentors in situ. The (steam-sterilizable) probe consists of four gold electrodes in an insulating matrix suitable for insertion in a standard 25 mm port. The outer two electrodes apply alternating current of a suitable frequency in the range 0.1-10 MHz while the inner two pick up the alternating potential difference. Biofouling can be obviated by the manual or automatic application of electrolytic cleaning pulses, while a similar system without cleaning pulses can be used to assess its extent.' The Pugmeter is suitable for use in all types of fermentations, and has been applied to various prokaryotic and eukaryotic pitching control in breweries," plant cells, l 1 animal cells,12 immobilized cells, l3 the solid-substrate tempe fermentati~n,'~,'~ and (as it measures biomass pos- sessed of an intact cell membrane, and not necromass lacking one) in assessing cytotoxicity.l6 The approach also represents a convenient means to control the biomass content of continuous microbial cultures. l7 Non-linear Dielectric Properties of Cell Suspensions: Applications in Sensing The above is based on 'classical' dielectric theory, which assumes that the system of interest contains structures, which, when excited by the field, relax only by frictional interactions with the (solvent) heat bath in which they are embedded, which obey the fluctuation-dissipation theorem, and which therefore give a linear response.None of these assumptions is likely to be true of enzymes in v i v ~ . ~ ~ ~ " We have constructed a dual-cell, non-linear dielectric spectrometer, and have ap lied it to the study of resting cell suspensions of S . cerevisiae !' Substantial, odd harmonics were generated by these cells when stimulated by modest sinusoidal electrical fields (about 2 V cm-', 20 Hz). The generation of these harmonics occurred only in living cells, and in a cell concentration-dependent manner. The ability to generate a third harmonic was observable only within narrow voltage and frequency windows, and was strongly inhibited by low concen- trations of sodium metavanadate, suggesting that it might be ascribed largely to the H+-ATPase present in the plasma membranes of these cells, the k,,, of which is close to that of the optimum exciting frequency.In glycolysing cells, the third harmonic disappeared and was replaced by strong second and fourth harmonics. The ability to distinguish populations of enzymes which are turning over from those which are not (by whether they generate even- or odd-numbered harmonics) opens u many possibilities for the study of metabolism in viv~.~' These non-linear dielectric properties can also be observed as the generation of 'beat' frequencies when cells are excited by more than one sinusoid at a time.22 Non-linear dielectric spectroscopy might provide a convincing mechanism by which to account for the many reports of the ability of very weak electromagnetic fields to affect biological activity,23 and should lead to a variety of novel biosensors. We thank the SERC, the DTI and the Wolfson Foundation for financial support.References Kell, D. B., in Biosensors: Fundamentals and Applications, eds. Turner, A. P. F., Karube, I., and Wilson, G. S., Oxford University Press, Oxford, 1987, p. 428. Pethig, R., and Kell, D. B . , Phys. Med. B i d , 1987, 32, 933. Kell, D. B., and Davey, C. L., in Biosensors: A Practical Approach, ed. Cass, A. E. G., Oxford University Press, Oxford, 1990, pp. 125-154. Ferris, L. E . , Davey, C. L., and Kell, D. B., Eur. Biophys. J., 1990, 18, 276. Harris, C. M., Todd, R. W., Bungard, S. J., Lovitt, R. W., Morris, J. G., and Kell, D. B., Enzyme Microb. Technol., 1987, 9, 181. Kell, D. B., and Todd, R. W., US Pat., 4 810 650, 1989. Kell, D.B., US Pat., 4 965 206, 1990. Kell, D. B., Markx, G. H., Davey, C. L., and Todd, R. W., TrAC, Trends Anal. Chem. (Pers. E d . ) , 1990, 9, 190. Markx, G. H., and Kell, D. B., Biofouling, 1990, 2 , 211.ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 379 10 Boulton, C. A., Maryan, P. S., and Loverage, D., Proceedings of the 22nd European Brewing Convention, Zurich, 1989, 11 Markz, G. H., ten Hoopen, H. J. G., Meijer, J. J., and Vinke, K. L., J. Biotechnol., 1991, in the press. 12 Davey, C. L., Kell, D. B., Kemp, R. B., and Meredith, R. W. J., Bioelectrochem. Bioenerg., 1988, 20, 83. 13 Salter, G. J., Kell, D. B., Ash, L. A., Adams, J. M., Brown, A.J., and James, R., Enzyme Microb. Technol., 1990,12,419. 14 Davey, C. L., Peiialoza, W., Kell, D. B., and Hedger, J.N., World J . Microbiol. Biotechnol., 1991, 7, 248. 15 Peiialoza, W., Davey, C. L., Hedger, J. N., and Kell, D. B., World J. Microbiol. Biotechnol., 1991, 7, 260. 16 Stoicheva, N. G., Davey, C. L., Markx, G. H., and Kell, D. B., Biocatalysis, 1989, 2, 245. pp. 653-661. 17 Markx, G. H., Davey, C. L., and Kell, D. B., J. Gen. Microbiol., 1991, 137, 735. 18 Kell, D. B., Astumian, R. D., and Westerhoff, H. V., Ferroelectrics, 1988, 86, 59. 19 Westerhoff, H. V., Astumian, R. D., and Kell, D. B., Ferroelectrics, 1988, 86, 79. 20 Woodward, A. M., and Kell, D. B., Bioelectrochem. Bioenerg., 1990, 24, 83. 21 Kell, D. B., and Woodward, A. M., in Proceedings of the 3rd BTK Meeting, Noordwijkerhout, ed. Westerhoff, H. V., Intercept Press, London, 1991, in the press. 22 Woodward, A.M., and Kell, D. B., Bioelectrochem. Bioenerg., 1991, 25, 395. 23 Davey, C. L., and Kell, D. B., in Emerging Electromagnetic Medicine, eds. O'Connor, M. E., Bentall, R. H. C., and Monahan, J. C., Springer-Verlag, New York, 1990, pp. 19-43. Recent Advances in Applied Electrochemical Gas Sensors Nigel J. Cade, T. Kim Gibbs, P. Julian lredale and Debra A. Williams Neotronics Limited, Parsonage Road, Takele y, Bishop's Stortford, Hertfordshire CMZZ 6PU Electrochemical gas sensors have been in commercial and research use since the work of Clarke.' Various groups have developed this technology for specific applications and some of the major advances have been seen in the work of Bergman,2 Niedrach and A l f ~ r d ; ~ latterly this technology has diversified, producing a body of literature and patents which now represents a significant academic as well as theoretical body of knowledge.Applications of the technology are widespread, a fact to which this symposium itself is a tribute. In being selective and presenting some of the work in which Neotronics has been involved one must not overlook the wide contributions which have been made by others, but the commercial position of much of the work renders it unavailable to the wider academic sphere. When dealing with the commercial exploitation of this technology strictly in the field of environmental gas detection (as opposed to medical or process control), one must acknowledge the contributions to the field from the following: development of permeable membranes for dissolved oxygen measurement; use of gas permeable membranes with sputtered electrode for atmospheric monitoring; and the development of porous PTFE electrodes using platinum black for fuel cells.These advances have enabled development of the electro- chemical gas sensor into a sophisticated, accurate and reliable device. Typically, these are three electrode devices with an internal reference or pseudoreference operated by an external potentiostatic circuit of the general form shown in Fig. 1. Here CE A I meas. - - Fig. 1 Potentiostatic circuit. CE = counter electrode; RE = reference electrode; WE = working electrode the secondary (counter) electrode potential is varied with respect to the working electrode such that the reference potential is at a constant potential to the working electrode.From this technological base, many companies are now developing these sensors into devices which have greater applicability. The commercial pressures forcing this develop- ment are providing many research groups with the opportunity to widen knowledge in other areas. The primary objectives which commercial companies are addressing at present are as follows: extending the range of gases to which this type of sensor is sensitive; reducing the size of this type of sensor to enable its use in smaller instrumentation without loss of performance; developing the electronic control and monitoring circuitry for this type of sensor to allow better performance and 'fail-safe' operation; improving the performance of existing sensors by the development of new catalyst formulations with particular properties; improving the understanding of the basic electrochemistry of these systems in order to deal with application-related problems.Recent Advances in Sensor Technology at Neotronics and Co-operating Institutions Whilst some of the work being undertaken at Neotronics is of a commercially sensitive nature, much can be described here in at least general terms. Extension of the Range of Gases Measured As a result of a collaboration with the group led by Pletcher4 at the University of Southampton, it has been possible to extend the range of this type of sensor to cover carbon dioxide. This has only been possible thus far in non-aqueous solvents, for example in the work of Albery and Barron.' In the work at Southampton an aqueous solution containing [Cu(DAP)2I2+ [bis(propane-l,3-diamine copper(II)] was used as a 'moder- ator'-like compound enabling the Cu"/Cu' couple to be accessed as an electrochemically active system.Upon dissolu- tion in the electrolyte, the C02 causes the [Cu(DAP)2I2+ to decompose, liberating Cu" ions; these are then reduced to Cu' which are themselves readily re-oxidised by atmospheric oxygen to Cu'I. The removal of the C02 atmosphere results in the reformation of the complex. This work is described in a patent .6,7 As an adjunct to the transfer of technology from the laboratory to the commercial sphere, much materials science and catalyst development work was undertaken to enable a reliable and reproducible product to be marketed. Collaboration with the University of Strathclyde has also resulted in interesting developments.Professor Hitchman's group has not only provided the chemistry of an NO sensor, but has also, in the course of a general study of the chemistry and electrochemistry of NO and NO2 on precious metal surfaces,380 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 established an understanding of this system which will lay the theoretical basis for much further work.* Miniaturization of Sensors The reduction in size of these devices is not so attractive technologically as some of the other recent developments in this field, but has lead, nevertheless, to a much greater understanding of the processes and chemistry of these systems. Several companies have now produced smaller versions of their sensors.As a result of several years' endeavour Neo- tronics have made certain advances in this area with a sensor that is approximately 10% of the volume of the standard sensor of this type. This has been achieved by the following: reduction in physical size of the electrodes; corresponding reduction in the output levels of the signal; better stability of the electro- nics; and better understanding of the linearity limitations of the sensors. This last point is the stumbling block which has hindered much development in this field. The basic problem is that in reducing the physical size of the sensors, the linearity and low temperature performance falls off. This is illustrated in Figs. 2 and 3. Fig. 2 shows the linearity of a standard sensor (CO is chosen as a typical example) compared with a miniature sensor made from the same materials.Fig. 3 is the same comparison for the low temperature performance. It can be seen that in both instances the miniature sensor is inferior. It is not clear at first sight why this should be so, as the catalyst surface area at the working electrode and output currents are in proportion and thus one might expect identical performance. This can easily be established by examination of the coefficient of variation curves for these sensors which show the working electrode to have the same surface characteristics in both instances. 5 E Y R 4 0 0 0 - - 3 -0 > z 2 .- -0 0 0 1 0 0 2 4 CO applied x 1000 (ppm) Fig. 2 Linearity of carbon monoxide sensor: 0, standard; +, mini - 20 0 20 40 Tern peraturePC Fig.3 Temperature behaviour of carbon monoxide sensors: 0, standard; +, mini An explanation of this effect was eventually discovered in the secondary electrode. The reaction occurring at the secondary is oxygen reduction: O2 + 4 e- + 4 H+ = 2H20 In the case of the standard sensor, activity of the catalyst on the secondary electrode is sufficient to balance the working electrode reaction over the temperature range. However, with the miniature sensor, the activity of the secondary is insuf- ficient, because of the fact that a wick carrying electrolyte into the electrode region reduces the available area disproportion- ately. A more active reduction catalyst at the secondary proved to be the required solution in this instance. This example serves to illustrate the difficulties encountered when simple size and geometry changes are made in this type of system.Improvement in Electronics The sensor will only be as good as the electronics used to drive it. Normally these sensors are supplied with a potentiostatic circuit of the type shown in Fig. 1. One variant of many systems can be seen, viz., the reference; in most instances pseudorefer- ence potential is maintained against a reference diode potential by variation of the secondary potential. The signal, corres- ponding to the current due to oxidation of the gaseous species on the electrode surface of the working electrode, is measured by recording the potential developed across a sensing resistor. This particular arrangement suffers a drawback when large currents pass through the cell, owing to change in the potential at the reference electrode caused by the sensing resistor.This method has the advantage of not being subject to existing patents. One problem with this arrangement is that it is capable of giving the appearance of functioning when there is no sensor fitted, or worse, when the sensor has malfunctioned. Some work at Neotronics has resulted in an electronic circuit to check the status of the sensor by monitoring its response to a potential pulse. With an on-board microprocessor it is possible to monitor the performance of the sensor at frequent intervals and give an alarm when the performance of the sensor is no longer acceptable. New Catalyst Formulations Although some manufacturers produce their own catalysts from readily available starting materials, others rely on the major catalyst producing companies such as JMC, Degussa, Platina, etc.These companies have experience in the produc- tion of catalysts for the automotive and chemical industries, many of which are applicable to gas sensors. One promising area of research currently being investigated by Neotronics and the University of Salford is that of ion implantation techniques to produce true alloys and mixed catalysts. This work is in its early stages, but it is hoped that following an academic study by Colligon and co-workers" there will be a development of useful technology in this field. One example of the effect that the catalyst can have is in the use of ruthenium catalysts for chlorine reduction. Chlorine can be reduced on platinum on carbon electrodes, but this results in a massive cross-sensitivity of these sensors to hydrogen sulphide and sulphur dioxide, both of which are found in the same applications as chlorine (see Table 1). By changing the Table 1 Percentage cross sensitivity Sensor type Gas c12 c12 100 HZS - 720 so2 - 170 H2 - 10 co - 20 NO2 180 NO 5 H2S - 10 100 13 5 20 0 -16 - SO? 0 98 100 0 0 -280 0 RuOZ- 9 - 22 0 0 0 100 -1 Ru 100 - 36 - 10 0 0 94 1ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 381 catalyst to ruthenium dioxide, the improvements in these mix of both the academic quest for basic understanding and the figures are impressive.However, pure ruthenium has a very commercial need for devices which will protect life and the different set of cross-sensitivities.This is curious, as those environment. This field will need the attention of both industry involved in the automotive catalyst industry experience little and academia in order to understand the function of these difference in the reactivity of ruthenium dioxide and sensors and design the next generation of instrumentation for ruthenium. safety and environmental protection. Improvements in Basic Electrochemistry As can be seen from the above discussion, the basic under- standing of these systems is patchy. Some electrochemical sensors are well understood: others, however, are in need of much basic research. As noted above, Hitchman's work at Strathclyde" has shown that a detailed understanding of these systems is possible. For example, it has been assumed that sensors of this type3 are limited in their output current by the rate of diffusion of the measurand species through the entrance hole or pore and over the working electrode. As can be seen in Section 2, this is not the case. Here the limiting factor was found, empirically, to be the activity of the secondary electrode. Conclusion In this brief review of the work currently being undertaken at Neotronics and its co-operating bodies, one can see that it is a field which poses more questions than answers. It is a fertile References 1 Clark, L. C., Jr, Trans. Am. SOC. Artv. Intern. Organs, 1956,2, 41. 2 Bergman, I., and Windle, D. A., Ann. Occup. Hyg., 1972, 15, 329. 3 4 5 6 7 8 9 10 11 Niedrach, L. W., and Alford, M. R., J. Electrochem. Soc., 1965, 112, 117. Evans, J . , Pletcher, D., Warburton, P. R. G., and Gibbs, T. K . , Anal. Chem., 1989, 61, 577. Albery, W. J., and Barron, P., J. Electroanal. Chem., 1982, 138, 79. Br. Pat., Application 8712582. Evans, J . , Pletcher, D., Warburton, P. R. G., and Gibbs, T. K . , Anal. Chem., 1989, 61, 577. McIntyre, A., Ph.D. Thesis, University of Strathclyde. Jones, G., and Iredale, P. J., Int. Pat., Application PCT/GB90/00507. Colligon, J. S., Vacuum, 1985. Hitchman, M. L., Personal Communication.

ISSN:0144-557X    

DOI:10.1039/AP9912800378

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

382 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 Geological and Nuclear Applications of Inductively Coupled Plasma Mass Spectrometry The following is a summary of one of the papers presented at a Meeting of the Atomic Spectroscopy Group held on January 30th, 1991, at the British Geological Survey, Keyworth. Detection of Actinides in Environmental Samples by Inductively Coupled Plasma Mass Spectrometry Roger D. Scott, Murdoch S. Baxter," Andrew S. Hursthouse,t Keith McKay, Kate Sampson and Joseph TooleS Scottish Universities Research and Reactor Centre, East Kilbride, Glasgo w G75 O W If the half-life of a radionuclide is sufficiently long it can be advantageous to detect the atoms themselves rather than their decay products. For instance, with the actinides, for which the mode of disintegration is usually a-decay, the necessity for extremely thin, chemically pure sources involves lengthy preparation procedures followed by days, or even weeks, of a- spectrometry.Generally speaking, environmental samples will contain concentrations of, for instance, 239Pu (ti = 24000 years), ranging from =Bq/kg-', resulting from fall-out from nuclear weapons testing, to thousands of Bq/kg-' in Irish Sea intertidal sediments in the vicinity of Sellafield, i.e. , 10'2-1015 atoms of 239Pu per kilogram of material but some three orders of magnitude fewer for the short-lived isotope 241Pu (t; = 14.4 years) at the same activity. Such numbers lie well within the range of conventional thermal ionization mass spectrometry even if only small (=1 g) samples are available.In fact, this technique is extremely sensitive with essentially blank-defined detection limits of a few times lo5 atoms' and is useful in biological assay where the samples can be both small and of low activity. Very high standards of chemical purification are required if this degree of sensitivity is to be achieved. In a- spectrometry, a reasonable detection limit is established by requiring 100 events to be registered in a clean surface barrier detector over a period of 1 month in 2n geometry. Assuming perfect chemical recovery, this translates to an activity in the region of lov4 Bq, equivalent to 10' atoms of 239Pu in the original sample. Inductively coupled plasma mass spectrometry (ICP-MS) is a technique which has been developed fairly recently2 and, as the sample to be analysed simply has to be in solution at 20.1% m/v, offers the advantages of simple source preparation together with high sensitivity and the ability to provide isotopic information which might not otherwise be readily available.The potential capabilities of ICP-MS for the detection of actinides were quickly recognized and there is a growing literature on the ~ u b j e c t . ~ - ~ Results and Discussion This work has concentrated on three main areas: ( a ) an investigation of the chemical processing which is necessary for * IAEA Laboratory of Marine Radioactivity, Monaco MC 98000. t Department of Chemistry, Paisley College of Technology, Paisley ?: AEA Environment and Energy, Hanvell Laboratory, Oxfordshire PA1 2BE. OX11 ORA. the detection of actinides in environmental samples; ( 6 ) the determination of 237Np and a comparison of the results with those obtained by a-spectrometry and neutron-activation analysis; and (c) establishment of detection limits both in conventional liquid nebulization and in electrothermal vapor- ization (ETV).Sample 1-20 g + yield monitors, 242Pu and 239Np 1 1 1 I 1 Dissolution with HCI and HN03 + 50 ml of 9 mot dm-3 HCI Remove iron Diisopropyl ether extraction Adjust oxidation states 1 g of NH3OHCI Add to anion-exchange column Dowex 1-X8,100-200 mesh Remove uranium 200 ml of 8 mot dm-3 HN03 Elute Pu and Np 200 ml of 1.2 mot dm-3 HCI 1 1 I 1 1 3-(2-Thenoyl)-lI 1,l -trifluoroacetone (TTA) extraction from 0.5 mot dm-3 HCI Back-extract with 8 mol dm-3 HN03 Take up in 2% HN03 1 ml E m , 5 ml liquid nebulization Count on Ge(Li) (237Np recovery) Add internal standard (236U) Aspirate into ICP Fig.1 Analytical procedure for the determination of neptunium and plutoniumANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 383 Table 1 Comparison of actinide results for environmental samples (k la mean) Sample type n Freshwater 1 3 Freshwater 2 3 Freshwater 3 3 Marine porewater 1 3 Marine porewater 2 3 Marine porewater 3 Seaweed 1 2 Seaweed 2 2 Soil 1 2 Soil 2 2 Soil 3 2 Mussel 2 Silt 2 Analyte 238u 238u 238u 238u 2 3 8 ~ 238u 2 3 8 ~ 23Xu 239Pu + 240pu 239Pu + 240Pu 237NP 239pu + 240pu 239pu + 240pu Units mBq 1-1 mBq I-' mBq 1-' mBq 1-l mBq 1-' mBq 1-l Bq kg-' Bq kg-' Bq kg-' Bq kg-' Bq kg-' Bq kg-' Bq kg-' NRPBI sediment 1 237Np Bq kg-' * a-Spectrometry of separate aliquot of material.t Fission track analysis. $ Weighted mean f standard error on mean. 9 Result from intercomparison exercises.s I National Radiological Protection Board. ICP-MS data 0.580 k 0.025 2.85 k 0.037 6.76 f 0.087 9.89 k 0.74 14.10 t 0.74 45.40 f 0.99 11.50 k 0.14 10.61 f 0.15 0.289 k 0.006 0.042 k 0.002 1.039 +_ 0.018 88 -t 17.00 3.70 f 0.28: (n = 18) 6.40 f 0.24 Reference values 0.620 f 0.032" 2.810 +_ 0.11* 6.430 k 0.25* 11.49 f 1.24t 13.22 f 1.111- 44.37 f 3.46t 10.21 k 0.32* 9.66 2 0.85" 0.311 -t 0.003* 0.038 k 0.003* 1.060 k 0.040" 78 f 10" 3.09 f 0.06$ (n = 4) 6.20 k 0.059 Considering the Pu isotopes, ICP-MS and a-spectrometry are complementary in that the 239Pu and 240Pu a-energies are too close to be separated by a-spectrometry with surface barrier detectors, whereas these isotopes are easily dis- tin uished by mass spectrometry. Conversely, the 238Pu and but, in mass spectrometry, 23 Pu will obviously suffer extreme isobaric interference from the naturally occurring 238U in the sample: if the activity of these nuclides were the same, then the number of 238U atoms would be some eight orders of magnitude greater.Meticulous removal of uranium would therefore be necessary before any attempt to measure 238Pu by mass spectrometry (a difficult task in any case, given the short half-life). There is a further problem arising from the formation of uranium h dride in liquid nebulization, at a level of some lop5 of the * 'U peak in the mass spectrum, and this implies that at least partial removal of 238U is necessary if acceptably low limits of detection are to be achieved for 239Pu.The development of the chemical processing has therefore been aimed towards a minimal procedure which would remove uranium but would at the same time allow simultaneous analysis of as many of the actinides as possible. Fig. 1 shows the separation method adopted and Fig. 2 the resulting mass spectrum (obtained by the electrothermal vaporization method discussed later) of the separated material leached from a mixed Ravenglass sediment. The Pu and Np isotopes are clearly seen and there is even an indication of a peak at mass 241, which probably arises from the very short-lived 241Pu. The longer- lived daughter, "'Am, is unlikely to contribute following l 239 5 4oPu a-particles can easil be resolved by a-spectrometry, Y separation in the HC1 column (Fig.1). Plutonium-242 is used both as a chemical yield tracer and as a spike in the mass spectrometry, but there is no suitable Np isotope which fulfils both of these functions, hence 239Np (short-lived and easily detectable by y-ray spectrometry) is the chemical yield tracer and 236U is added to the final solution to determine the efficiency of the mass spectrometry on the assumption that mass discrimination at these high mass numbers is small. The detection of 237Np has been treated exhaustively by Hursthouse,' who has shown that reasonable agreement can be obtained between results from ICP-MS and the two other methods suitable for this difficult analysis. Some measure- ments of more general interest are given in Table 1 which compares results obtained by ICP-MS (liquid nebulization) and by other means for a range of environmental materials.6 The agreement is generally very good.The attraction of the ICP-MS method is particularly obvious in the assay of 238U in marine porewaters; a 20-fold dilution provided sufficient sample at a reasonable solids content for liquid nebulization but the total volume of solution available was so small that fission track analysis was the only other feasible method. This is tedious and time consuming and requires access to a well thermalized neutron flux. The detection limit, taken as three times the uncertainty in the background, for liquid nebulization is about 2.4 x 10" atoms, equivalent to 10 pg at mass 240.This requires 3-5 ml of solution and the mass scan is limited in range (say 236-244). Electrothermal vaporization, on the other hand, typically employs a 50 pl injection followed by a heating cycle whereby 236 237 238 239 240 24 1 242 243 244 Mass number Fig. 2 Mass spectrum obtained from a sample of Ravenglass sediment after the chemical separation procedure384 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 the sample is dried, ashed and vaporized prior to injection into the flame. This method has the advantage of a lower background and the flame is not loaded with water so that interferences are reduced and, again over a limited mass scan, detection limits of 4 x lo7 atoms (15 fg) have been achieved. With single ion monitoring ( i . e ., with the mass spectrometer set on the single mass of interest), this can be reduced to about 2.5 x lo6 atoms (1 fg), but in this instance there can be, of course, no estimate of over-all yield. Such detection limits are particularly important in biological applications. To date, it has been very difficult to obtain good precision on the results from ETV and several factors contribute to this, including sample injection and possible time variations in the signal. Also, the short duration of the signal makes it very difficult to tune the ETV-ICP-MS combination and tuning by means of liquid nebulization is of limited assistance because different settings are required when the flame contains water. Table 2 Results for the determination of total uranium and total thorium (all values in ppm) Uranium Thorium a-Spec- a-Spec- Sample trometry ICP-MS ICP-MS trometry 1 20 21 18 22 2 17 16 53 51 3 90 96 33 38 4 17 18 84 82 5 48 46 111 117 6 2 665 3 213 29 54 7 31 000 16 700 97 387 8 9 000 4 920 22 62 9 164 91 53 86 10 26 21 44 75 11 46 31 66 131 12 47 37 50 69 13 61 52 29 34 14 123 108 24 33 15 198 164 15 22 16 44 46 20 17 Finally, it is interesting to examine the performance of ICP- MS when it is used in the ‘semi-quantitative’ mode of multi- element scanning.Here, the relative response across the entire mass range (2-250) is obtained from a set of standard solutions and the absolute response during a particular measurement by use of an internal standard (most usually In). Table 2 compares the results for a-spectrometric determinations of U and Th with those of semi-quantitative ICP-MS for a suite of samples from a uranium mine in Brazil.The agreement is evidently acceptable except for samples 6-9 which are from regions of uranium mineralization and show considerable suppression of the ICP signal both for uranium and thorium (with the exception of the uranium result for sample 6 ) . An internal standard was used, hence the suppression is not uniform over the mass range and there are several possible reasons for this type of effect including: non-linear behaviour of the electronics at high counting rates; inhomogeneity in the samples (100 mg aliquots were used) from the mineralized zone; and incomplete dissolution. This last possibility is difficult to detect and is not, of course, alleviated by the use of a spike.The uranium and thorium a-spectrometry results are average values derived from the independent results of several laboratories and were subject to a spread of less than 10% ; hence the essential point here is that information on uranium, thorium and some 70 other elements can be obtained in a matter of minutes easily to within k50% by semi-quantitative analysis even in instances of very high uranium content and to considerably better accuracy in more normal samples. References Perrin, R. E., Knobeloch, G. W., Armijo, V. M., and Efurd, D. W., High Precision Isotopic Analysis of Nanogram Quantities of Plutonium, Los Alamos Report, 1984, LA-10013-MS. Date, A. R., and Gray, A. L., Applications of Inductively Coupled Plasma Mass Spectrometry, Blackie, Glasgow, 1989. Hislop, J.S., Long, S. E., Brown, R. M., Morrison, R., and Pickford, C. J., The Use of Argon Plasma Sources for Measure- ment of Long Lived Radionuclides, ICRM-Low Level Tech- niques Meeting, Wiirenlingen, 1987. Kim, C. K., Takaku, A., Yamamoto, M., Kawamura, H., Shiraiski, K., Igarashi, Y., Igarashi, S., Takayama, H., and Ikeda, N., J. Radioanal. Nucl. Chem., 1989, 132, 131. Hursthouse, A. S., Ph.D. Thesis, University of Glasgow, 1990. Toole, J., Hursthouse, A. S . , McDonald, P., Sampson, K., Baxter, M. S., Scott, R. D., and McKay, K., in Plasma Source Mass Spectrometry, eds. Jarvis, K. E., Gray, A. L., Williams, J. G., and Jarvis, I., Royal Society of Chemistry Special Publication No. 85, Royal Society of Chemistry, Cambridge, Hursthouse, A. S., Baxter, M. S., Livens, F. R., and Duncan, H. J., J. Environ. Radioact., 1991, 14, in the press. 1990, pp. 155-162. ROYAL SOCIETY OF CHEMISTRY ELECTROANALYTICAL AND ELECTROCHEMISTRY GROUPS ANALYTICAL APPLICATIONS OF CHEMICALLY MODIFIED ELECTRODES January 7th-8th, 1992, University of Bristol The presentations at this meeting will range from the Design of Surface Modifications, through their Characterization, to the Performance of ‘Real’ Sensors. The speakers will be J. Wang (Plenary Lecture), L. Gorton (Plenary Lecture), P. N. Bartlett, S. Higgins, M. Lyons, M. Green, A. R. Hillman, J. M. Slater, M. R. Smyth and S. A. Wring and J. P. Hart. The registration fee will be fllO for RSC members and €130 for non-members. This will include accommodation for the night of January 7th and all meals and refreshments (from lunch on January 7th). Posters are still being sought. Cheques should be made out t o ’Bristol University CME ‘92’ and forwarded t o either Dr. A. R. Hillman, University of Bristol, School of Chemistry, Cantocks Close, Bristol BS8 I T S or Dr. J. P. Hart, Faculty of Applied Sciences, Bristol Polytechnic, Coldharbour Lane, Frenchay, Bristol BS16 1 QY.

ISSN:0144-557X    

DOI:10.1039/AP9912800382

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 385 Equipment News Glow Discharge Ion Source A low-cost glow discharge ion source option from Turner Scientific for the TS SOLA has been designed to be easily interchangeable with the IPC source. New features allow solid samples to be directly analysed either as pins or discs with virtually no constraint on sample size or geometry. In flat format time resolved data acquisition allows elemental analyses to be used to build a profile through such materials as plated steels. VSW UK Sales, Albert Drive, Burgess Hill, West Sussex RH15 9NX. X-ray Fluorescence Spectrometer The Spectro X-Lab is an energy dispersive XRF spectrometer manufactured by the German Spectro X-ray Instruments GmbH in Berlin. Sensitivity levels charac- teristic of trace analysis can be achieved, which had until now been attainable only by other analytical methods.A new instrument conception allows a consider- able reduction of scattering by exciting the fluorescent rays in the sample with polarized radiation. As a result the detec- tion limits reach the sub-ppm range, which is satisfactory €or trace analysis. At the same time, the advantages of energy- dispersive XRF spectroscopy are maintained. Spectro X-Ray Instruments GmbH, Ullsteinstrasse 73, D-1000 Berlin 42, Germany. On-Site Demonstration of Spectrolab F The Spectrolab F analytical system has been installed in a minibus and can be driven to the potential customer for a check of its capability using his own samples. With Spectrolab F it is possible to analyse within seconds up to 24 ele- ments simultaneously in pig iron, cast iron, steels, non-ferrous metals and their alloys.Spectro A. I., Marketing Department, Boschstrasse 10, D-4190 Kleve, Germany. Remote Diagnostics Facility for X-ray Systems A remote diagnostics facility for the makers' X-ray systems enables instru- ments in any locations to be tested using modems and the telephone network to provide direct connection with a computer in the relevant national service centre. Comprehensive system checks can be carried out automatically at regular intervals to monitor operation and signal the need for preventive action. Philips Analytical, P.O. Box 218, Building TQIII-1, 5600 MD Eindhoven, The Netherlands. Automatic Bead Preparation Machine The PERL'X 3* has been developed on the basis of experience with the PERL'X 2, of which 300 have been sold throughout the world.It brings increased speed and convenience to the production of samples for analysis by X-ray spectrometry. Con- structed as a free-standing console unit, the latest version features dual casting positions, permitting virtual doubling of output. In addition, enhanced control software, operating ergonomics and read- out display facilitate programming for all kinds of sample materials. Temperature control is also improved by the provision of an optical pyrometer, giving accuracy of f 1 0 "C over a range extending up to 1500 "C. The maximum heating gradient is 1000 "C min- l . Philips Test and Measurement, P. 0. BOX 218, Bldg TQIII-1, 5600 MD, Eindhoven, The Netherlands.Scandium Anode for Compact X-ray Tube Two unique technologies, target trans- mission design and the scandium anode, are incorporated into a new X-ray tube €or the compact PW1660 spectrometer. Ideal for use in conjunction with channels employing synthetic multilayer crystals, this innovation permits cost-effective de- termination of light elements down to F and Na. In addition, the measurement of Ca, Cr and Ni is much improved, making the PW1660 a more attractive option for the analysis of materials such as slags and low or high alloy steels. Philips, P.O. Box 218, 5600 MD Eindhoven, The Netherlands. Hydraulic High Pressure Nebulization (HHPN) With the Knauer HHPN system there is now a totally new and effective method for sample introduction in atomic spec- troscopy.The nebulization of liquids with pressures from 50 to 400 bar is already well known in the field of diesel engines. This principle is used in the Knauer HHPN system to produce an aerosol from the solution to be analysed, which is then passed into a spectroscopic source, for example a flame or an ICP, for elemental analysis. In principle, the HHPN system can be adapted to all spectrometers. Dr. H. Knauer Wissenschaftl. Gerate GmbH u. Co. KG, Heuchelheimer Strasse 9, D-6380 Bad Homburg, Germany. Ion Guns The AS15 series of ion guns for high rate ion beam etching is based on an efficient electron-impact source capable of provid- ing ion current densities in excess of 10 mA crn-'. The gun is differentially pumped to maintain low pressures in the working chamber.Scan plates are used to provide even etching over areas varying from 1 mm2 to 1 cm'. The gun is supplied with a power supply with an integral electronic scan unit with manual or exter- nal computer control. Versions of the guns are available for depth profiling, surface cleaning, small spot imaging and micro-analysis. VSW Technology Ltd., Albert Drive, Burgess Hill, West Sussex RH15 9NX. Software for Infrared Analysis of Oil- contaminated Water Designed for laboratories that handle a large number of samples, the new soft- ware package is compatible with the 1000 Series FTIR spectrometers. It can deter- mine the concentration of trace amounts of hydrocarbon oil in waters defined by 'Method for the determination of hydro- carbon oil in water by infrared absorp- tion', HMSO, 1983.This method is ideal for detecting oil in natural, saline and drinking waters as well as sewage and industrial effluents, and offers a detection limit down to 10 pg 1-l of sample water. Unicam Ltd., York Street, Cambridge CB1 2PX.386 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 Autosampler Interfaced to Spectrometer The flexibility of the PSA 20.099 auto- sampler fraction collector has been exploited by linking it directly to the Perkin-Elmer LS30 luminescence spec- trometer. The LS30 firmware control is designed to link to a specific sampler system, placing some constraints on the operation of the interface. The system developed by PSA performs reliably within these constraints. PS Analytical Ltd., Arthur House, B4 Chaucer Business Park, Watery Lane, Kemsing, Sevenoaks, Kent TN15 6QY.Fluorimeter The Model RFA 306 fluorimeter is designed for use on the RFA 300 micro- continuous flow analyser, Technicon's AAII" system, Tecator's flow injection analyser or other continuous flow ana- lysers, as well as for use with chroma- tography equipment. It is an easy to use, single-beam, narrow-band filter detector designed with dual 5 V recorder outputs, allowing compatibility with ALPKEM's data acquisition systems along with recorder interfacing. As on ALPKEM's RFA 30SA photometer, a liquid crystal display is used to indicate the recorder output signal. In addition, the RFA 306 offers continuously variable gain and baseline off-set controls. Perstorp Analytical Ltd., Cooper Road, Thornbury, Bristol, Avon BS12 2UW.Photometric Analyser and Field Kit The RPA-111 photometric analyser is a hand-held microprocessor-based pho- tometer with fully interchangeable filters for wavelength selection. It can be used for both enzyme immunoassays and general chemistry tests. Capable of high- precision absorbance readings, which are initiated as soon as reaction tubes are placed in the read station, the instrument achieves a precision of f1.S% or 0.0005 absorbance with a resolution of 0.001 absorbance. The lamp life is greater than 100 000 readings. The RPA-I11 field kit features a built-in rechargeable battery power source which allows 5-6 h of field operation, and a thermal printer provides for immediate hard copy of test results. This equipment is the latest addition to the makers' RaPID Assays System.town, PA 18940, USA. Ohmicron, 375 Pheasant Run, New- Chromatography Data System The Model 717 chromatography system and controller is a low-cost, entry level PC workstation for GC or HPLC. It acquires one analog detector signal using a com- pact, half-length converter card installed in any PC-XT, AT, 80386 or PS/2 computer. It offers the same high speed and performance as the 727, 737 and 747 multitasking systems, with real time signal display, file archiving to disk and standard walk-away batch analysis and reprocess- ing. An optional controller for up to three HPLC pumps is available. Axxiom Chromatography Inc., 11988 Challenger Court, Moorpark, CA 93021- 7122, USA. Data Handling System The 4880 is a data handling system that offers GC control and a Windows I11 environment.Ideal for both GC and LC data processing, the multitasking system features asynchronous two channel operation, enabling two analyses and re- analysis to be carried out simultaneously. The system complies with Good Lab- oratory Practice, with user programming for report customization, while full printer-plotter support allows users to select the unit that best suits their require- ments. There are comprehensive graphics facilities. Unicam Ltd., York Street, Cambridge CB12PX. Chiral Column Chiral columns from Shandon HPLC now include a bonded-protein column based on immobilized human serum albumin. Retention and stereo selectivity of the column directly relate to in vivo inter- actions, making the column particularly useful to pharmaceutical researchers for the rapid study of drug-binding mechanisms. Shandon Scientific Ltd., Chadwick Road, Astmoor, Runcorn, Cheshire WA7 1PR. Ion Chromatograph A modular ion chromatograph comprises a fast reciprocating pump which delivers pulse-free flow to ensure a stable baseline and high levels of detection.The high performance non-suppressed column technology provides resolution of a wide range of anions or cations in less than 10 min. The conductivity detector incor- porates a constant cell temperature con- troller enabling the detector rapidly to equilibrate ready for analysis. Applied Chromatography Systems Ltd., The Arsenal, Heapy Street, Macclesfield, Cheshire SK11 7JB. Liquid Chromatography Capillary Electrophoresis System The LCCE system includes the most recently introduced system in the P/ACE series, the System 2100CE, linked to the System Gold HPLC to provide control through a single computer with automatic data acquisition and handling and real time data display from both instruments simultaneously.Beckman, Progress Road, Sands Industrial Estate, High Wycombe, Buckinghamshire. Sterile Plastic Syringes The Primo range of individually packed, sterile syringes use a revolutionary silicon ring to provide an air-tight seal, whilst preventing particle contamination of sam- ples. Features include precise reference point, plunger stop, polypropylene plunger and barrel and 1-100 ml sizes. HPLC Technology Ltd., Wellington House, Waterloo Street West, Maccles- field, Cheshire SK11 6PJ. HPLC Solvent Degasser The DG-1300 offers biocompatibility (wetted parts are of PTFE, PEEK and PPS), the highest oxygen reduction rate ever produced, small dead volume (10 ml) allowing fast solvent change and operation, 3 separate channels, ultra- small bench footprint and a free of charge evaluation offer.HPLC Technology Ltd., Wellington House, Waterloo Street West, Maccles- field, Cheshire SKll 6PJ. Microspheres for Quantitative Immunoassa y s A wide variety of surface chemistries and magnetic grades, combined with remark- able size uniformity, make the Estapor range of latex microspheres ideal for use as reactive solid phase in quantitative immunoassays. Suitable for both radio- immunoassay and enzyme immunoassay techniques, the Estapore latex supports have a large surface area between 6 and 30 m2 g-I, which can support a large amount of totally accessible fixed protein and they eliminate completely the need for stirring during incubation.RhBne Poulenc Laboratory Products, Liverpool Road, Eccles, Manchester M30 7RT. Approval for Soxtec and Fibertec During the AOAC Official Methods Board meeting, May 30-June 1,1991, the final decision was taken to approve for the First Action the Soxtec for fat analysis in meat. At the same meeting approval was given for First Action on insoluble dietary fibre in food and food products, en- zymatic gravimetric method. The Fiber- tec E system was used in a number of the participating laboratories and showed good performance there. As an additionalANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 387 analysis to total dietary fibre, the analysis of insoluble dietary fibre will be a more important constituent in the controlling of raw materials, following the process in food manufacture as well as analysing finished food products.Perstorp Analytical Ltd., Cooper Road, Thornbury, Bristol BS12 2UW. Autosampling Titrator The automated Metrohm titration range has been extended with the development of a fully auto-sampling, robot-like titrat- ing system. Suitable for all types of liquid sample from water to used oils, it is capable of handling up to 300 samples per loading. The system is based on the Metrohm 670 titrator and can be fully interfaced with a computer. V. A. Howe and Co. Ltd., Beaumont Close, Banbury, Oxfordshire OX16 7RG. Hydrogen Sulphide Analyser The H2Salyser utilises a photoionization detector offering a good response to traces of hydrogen sulphide.It has a built- in automatic chromatographic system to separate the hydrogen sulphide response from other materials which may be present. The measuring range can be as low as 0-10 ppm, with a detection limit of 0.5 ppm. Other ranges such as 0-100 ppm or higher are readily set if required. The instrument is available as a fixed monitor with an eight point multi-stream sampling system or a battery operated portable single stream analyser. Cavendish Applied Technology Ltd., 24 Clifton Road, Cambridge CB14ZD. Oxygen Alarm The Model 335 oxygen monitor, which quickly and accurately measures oxygen concentration in control rooms, critical breathing circuits, etc., is provided with a power-fail back-up consisting of two NiCad battery packs maintained on a trickle charge.Primary power interrup- tion and subsequent battery operation is signalled by illumination of the LO AC panel light. Two oxygen alarm levels are available: Caution (19% 02) and Danger Teledyne Analytical Instruments, The Harlequin Centre, Southall Lane, Southall, Middlesex UB2 5NH. (174Yo 02). Temperature and Humidity Recorder The Thermo-Hygrograph Model 8147.R3 is an economy model specifically designed for permanent location in areas where the monitoring of temperature and relative humidity is critical. It can monitor con- ditions over a 7-d period or, via a simple operation, over 24 h. Standard recording ranges are -20 to +43 “C and 0-100% relative humidity; alternative ranges are available on request. The instrument has an all-Plexiglas housing and is supplied ready for use. A leaflet describes this and other recorders.Carrington Marketing, Keighley Business Centre, South Street, Keighley, BD21 1AG. Temperature Controllers Two temperature controllers with thermocouple and resistance temperature detector feedback improve the accuracy and reliability of reaction temperatures in laboratory experiments or processes. They are suitable for use with heating mantles, heating tapes, hot plates, ovens or other heat sources up to 1200 W. Aldrich Chemical Co. Ltd., The Old Brickyard, New Road, Gillingham, Dorset SP8 4JL. Portable Multi-gas Monitor for Hire Designed to provide users with precise indication of gas levels before entering confined areas, and throughout a main- tenance survey, the Exotox 40 monitors oxygen (&23%), methane (0-100% lel) and hydrogen sulphide (0-200 ppm) and is BASEEFA approved for intrinsic safety in explosive environments.It offers audible and visual alarms for all gases plus three separate alarm levels for toxic gases. These include the acceptable occu- pational exposure limit TWA (8 h time weighted average), the short term expo- sure limit (10 h STEL) and a higher instantaneous limit. Livingston Hire Ltd., The Rental Centre, Livingston House, 2-6 Queens Road, Teddington, Middlesex TWll OLB. Hand-held Intrinsically Safe Instrumentation Intrinsically safe approval by BASEEFA has been given to a range of Digitron’s hand-held instrumentation, including the P200 Series hand held digital manometers and Models 3208 and 3218 digital ther- mometers.Each instrument is supplied with a copy of the certificate and full operating instructions. The high standard EEx ia IIC T5 allows their use in inflam- mable or explosive atmospheres including Zone 0 high risk hazardous areas. Digitron Instrumentation Ltd. , Mead Lane, Hertford, Hertfordshire SG13 7AW. Auto Sampler System for Kjeldahl Analysis The Kjeltec autosampler system designed and produced by Tecator allows up to 3 x 20 tubes to be loaded in the sampler for walk-away operation, whilst multi- tasking processors allow simultaneous analysis and further sample registration or result reporting. User definable programs allow the operator to select the degree of automation.For instance, sample weights can be entered directly from a balance, manually via the keyboard or run at constant weight. Perstorp Analytical Ltd., Cooper Road, Thornbury, Bristol, Avon BS12 2UW. pH Meters The PHM92 is the first of a new family of pH meters, forming an integral part of the makers’ MeterLab concept, which guar- antees the best possible results in pH, ion and conductivity measurement by supply- ing meters, electrodes, buffers and all other accessories such as beaker dis- pensers, electrode maintenance kits and holders, etc. With its Autocal and Auto- read functions, the PHM92 is easy to operate and ideal for general laboratory applications. Both pH and temperature are shown on the clear two-line display along with stability indication and error warnings.Radiometer Ltd., The Manor Royal, Crawley, West Sussex RHlO 2PY. Filtration Medium The Anotec range of micro-filtration devices offer excellent filtration efficiency with good chemical resistance flow rates. The innovative inorganic membrane at the heart of these products has a non- deformable honeycomb structure and extremely narrow pore size distribution. The absence of plasticizers and binders prevents the extraction of additives into the filtrate. The product range includes Anotop syringe filters and Anodisc mem- brane filter discs. Whatman Scientific Ltd. , Whatman House, St. Leonard’s Road, 20/20 Maidstone, Kent ME16 OLS. Filter Units Nalgene 115-ml pre-sterilized, disposable filter units are available with a choice of three membrane materials: cellulose nitrate, nylon and the makers’ exclusive surfactant-free cellulose acetate. Nalge Co., 75 Panorama Creek Drive, Box 20365, Rochester, NY 146024365 , USA.Syringe Filters The new range of 13 mm syringe filters are recommended for maximum filtrate recovery from volumes of 10 ml or less. They are manufactured in various pore sizes, from 0.1 to 1.0 pm and in 11 different filter media: PVDF (a low pro- tein binding membrane) , hydrophilic Nylon 66, hydrophobic PTFE, low pro- tein binding polysulfone, polypropylene, five popular glass micro fibre membranes and 934-AH. Whatman Scientific Ltd. , Whatman House, St. Leonard’s Road, 20/20 Maidstone, Kent ME16 OLS. Microwave Digestor The Microdigest 301 is the first microwave sample preparation system capable of evaporating digestion mixtures to dry- ness, allowing mineralization of the sample and removal of excess concen-388 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 trated acid.It is capable of reducing sample digestion times by factors as high as 20 times compared with traditional heating methods. It can be programmed with automatic reagent additions to give precisely reproducible results. Up to 40 routines, each of up to eight digestion steps, can be programmed into the Micro- digest 301. Sample sizes can be between 100 mg and 2 g, using a 100 ml reaction vessel. Rh8ne Poulenc Laboratory Products, Liverpool Road, Eccles, Manchester M30 7RT. Ultracentrifuge Rotor The TLA-100.4 titanium fixed angle rotor for the makers' benchtop ultracentrifuges has a sample capacity of 8 x 5.1 ml and can achieve speeds up to 100 000 rev min-' and forces of up to 543 000 g for a wide range of subcellular separations.It was designed for the Optima TL and TLX series micro-ultra-centrifuges. However, an upgrading kit is available to allow its use in the earlier TL-100 benchtop unit. Beckman, Progress Road, Sands Industrial Estate, High Wycombe, Buckinghamshire. Rheometer The CV20N has been developed for comprehensive rheological measure- ments. Besides the simple measurement of viscosity, oscillation and normal stress measurements are possible. Haake Mess-Technik GmbH u. Co., Dieselstrasse 4, D-7500 Karlsruhe 41, Germany. Thermal Analysis Software Shimadzu is offering its current TA cus- tomers the TA-501 personal thermal analysis software, version 2.02 upgrade, free of charge.This software allows the user to automate many of the basic analysis tasks previously performed manually, e. g., identification of tempera- tures and heat capacities. It is valid for DSC, TGA, DTA and TMA. The multi- tasking operation allows simultaneous control of up to 4 modules, including accessories. V. A. Howe and Co. Ltd., Beaumont Close, Banbury, Oxfordshire OX16 7RG. Thermogravimetry GC-MS Coupling System Besides the quantitative analysis of the weight loss, Shimadzu's TG-GC-MS coupling system is able to identify and quantify the resulting decomposition pro- ducts. The system consists of the TGA-50 (ambient to 1500 "C) and the GCMS QP- 1000EX (1-100 amu). The temperature of the interface is microprocessor controlled.The control of the instruments and the interpretation of the data are carried out by one IBM PC. V. A. Howe and Co. Ltd., Beaumont Close, Banbury, Oxfordshire OX16 7RG. Cone and Plate Viscometer The VT500/PK100 is a new viscometer system designed for the quality control of varnishes, paints, printing pastes or cos- metics. Based on two tried and tested components, the microprocessor controlled Viscotester VT500 and the robust cone and plate measuring sensor PK100, it is an easy-to-use viscometer with integrated evaluation electronics. The measuring results are shown via the display. The VT500/PK100 can be oper- ated automatically and the VT500 can be connected to a computer. If a cone and plate system is not required the VT500 can be used with other sensors, i.e., I S 0 rotors or coaxial cylinder sensors.A brochure is available. Haake Mess-Technik GmbH u. Co., Dieselstrasse 4, D-7500 Karlsruhe 41, Germany. Combustion Calorimeter The HClO isothermal combustion calori- meter is designed on the basis of the requirements according to DIN 51900 as well as the corresponding international regulations like ASTM, I S 0 and BS. It is a microprocessor controlled unit which minimizes testing time and offers a good reproducibility of results (<O.l%). Haake Mess-Technik GmbH u. Co., Dieselstrasse 4, D7500 Karlsruhe 41, Germany. Transmission Electron Microscopes Ultra-high resolution at 200 kV, unprece- dented freedom of tilting and full nano- probed capabilities are important charac- teristics of the latest addition to the makers' CM Series of instruments, the CM20-UltraTWIN, which combines an entirely new objective lens with a high resolution TEM operational mode to provide a number of exceptional high- resolution imaging features, including high resolution image shift with coupled beam shift, direct access to the coma-free alignment, stigmater and objective lens current read-out on the operational page of the microcontroller display, Philips, P.O. Box 218, 5600 MD, Eindhoven, The Netherlands.Electron Microscopy Data Manage- ment System The eXL is an integrated electron micro- scope data management system with three prime functions: it is a fast and accurate energy dispersive X-ray microanalysis system, it offers extremely high speed data processing including real-time quantitative analysis and imaging process- ing and fast X-ray mapping, and it offers control of every standard electron micro- scope currently available.The eXL is an interactive system with a simple menu- driven approach and it can be linked to a second graphics console where its multi- program, multi-tasking abilities allow two users to access the full data processing and acquisition facilities simultaneously. A brochure is available. Link Analytical Ltd., Halifax Road, High Wycombe, Buckinghamshire HP12 3SE. Electron Backscatter Detector System Tetra is an interactive software controlled backscatter detector that is fully in- tegrated into the ED system. It incor- porates colour coded quantitative atomic number analysis and offers a number of benefits such as automatic brightness and contrast, TV operation for use with inte- grated frame stores and automatic calib- ration of 2-range with recalibration for beam current changes.Link Analytical Ltd., Halifax Road, High Wycombe, Buckinghamshire HP12 3SE. Laboratory Microscope The new Standard 25 features a large, 5 objective nosepiece, large stage and a selection of interchangeable condensers, equipping the instrument for all routine tasks: brightfield, darkfield, phase con- trast, fluorescence and polarizing micro- scopy. A new range of A-Plan objectives provide a perfectly flat field over the entire field of view, making them ideal for edge-to-edge screening of blood smears, etc. Carl Zeiss (Oberkochen) Ltd., P.O. Box 78, Woodfield Road, Welwyn Garden City, Hertfordshire AL7 1LU.Polarized Visible Light Accessory for FT-IR Microscope A polarized visible light accessory isANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 389 available for the makers’ FT-IR micro- scope. Typical applications include polymer fibres, gel imperfections in a polymer film or different layers in a laminated structure. After visual differen- tiation under polarized light, infrared spectra can be recorded to provide identification. Perkin-Elmer Ltd., Maxwell Road, Beaconsfield, Buckinghamshire HP9 1QA. Laboratory Information Management System A new data-driven result exporting pack- age has been added to the latest release of the VAX-based ACCOMPLIS system. The package, which requires no program- ming to set up, makes it easy to transfer analytical results directly to external computers of almost any type.ICI Chemicals and Polymers Ltd., P.O. Box No. 1, Billingham, Cleveland TS23 1LB. Specification Management for Quality Control Laboratories The SQL*QC module from PE Nelson provides international product specifica- tion management for QC laboratories working with Good Manufacturing Prac- tice and International Organization for Standardization 9000 guidelines. Used with PE Nelson’s SQL*LIMS, SQL*QC tests existing products with established specifications, provides on-line validation of results, develops and checks new speci- fications before they are introduced to the manufacturing environment and keeps historical records of traceability. Perkin-Elmer Ltd., Maxwell Road, B eaconsfield , Buckinghamshire HP9 1QA. Fibre Optic Connector A new fibre optic cable connector can be assembled in only 5 minutes and obviates the need for the contact face to be polished; it is therefore ideally suited to field operation.Insertion and return losses are stated as 0.4 dB (SMF) or 0.2 dB (MMF), and 44.0 or 35.0 dB, respec- tively. A durability of in excess of 1000 cycles is claimed and the connector is capable of withstanding shock greater than 100 g and vibration of 1.5 mm ampli- tude over a frequency from 10 to 55 Hz without detriment to performance. It has an operational temperature range of from Hakuto International (UK) Ltd., Eleanor House, 33-35 Eleanor Cross Road, Waltham Cross, Hertfordshire EN8 7LF. -40 to +80 “C. Portable Safe Containment Station The Fumebubble FX1 provides a personal space where the operator can work with hazardous materials in safe uncontami- nated conditions.Compact and econ- omic, it can be used to replace existing, more expensive and less flexible station- ary facilities such as fume cupboards. It weighs only 15 kg and has a 0.3 m2 footprint. Radleys, Shire Hill, Saffron Walden, Essex CBll 3AZ. Clear Plastic Tubing Nalgene 180 poly(viny1 chloride) auto- clavable tubing is made from the highest grade resins and special plasticizers with- out fillers or extenders. It resists a wide range of chemicals, is dimensionally stable and highly resistant to hardening and discoloration. It is made of materials which comply with the Food Additives Amendment of the US Federal Food, Drug and Cosmetic Act and US Pharma- copoeia Class VI requirements for plastic materials.Nalge Company, Sevenoaks, Kent TN14 5BQ. Marker The Securiline Lab Marker is a special purpose marker designed to write through moisture as easily as it writes on dry surfaces. It provides permanent marking on plastic throw-aways, glass or metal re- usables, or on porcelain surfaces. The ink will not smear when subjected to water or alcohol during normal use. It can, how- ever, be washed off these surfaces. Radleys, Shire Hill, Saffron Walden, Essex CBll 3AZ. Clean-up Materials A new range of Hazardous Spill Response Kits are available in a variety of sizes from a 5 1 laboratory spills kit to a large pallet- sized response kit sealed in a 550 1 con- tainer on wheels. The kits comprise the user’s selection of Powersorb universal sorbent booms, sheets, rolls and pillows in a high density, polypropylene or polyeth- ylene container. Environmental Safety Group, 3M United Kingdom plc, 3M House, P.O.Box 1, Market Place, Bracknell, Berk- shire RG12 1JU. Literature A brochure describes the DU-7000 Series ultraviolet-visible spectrophotometer for routine assays and method development. Beckman, Progress Road, Sands Industrial Estate, High Wycombe, Buckinghamshire HP12 3BR. A brochure entitled ‘Focused Ion and Electron Beam Columns’ gives infor- mation on the capabilities and appli- cations of FEI’s line of sources and focusing columns for nanometer scale technology, electron focusing columns using ZrO/W Schottky field emitters and ion focusing columns using gallium liquid metal ion sources. FEI Company, 19500 N.W. Gibbs Drive, Suite 100, Beaverton, OR 97006- 6907, USA. LC Views, a new international news- letter, keeps liquid chromatography users up to date on technology and industry trends, advances in LC-MS, data hand- ling and management and new appli- cations for specialized laboratory requirements. Perkin-Elmer Ltd., Maxwell Road, Beaconsfield, Buckinghamshire HP9 1QA. Focus on Chromatography gives infor- mation on solvent delivery, detectors, autosamplers, software and systems, opti- mal chromatography and UltraSpherogel columns, and Focus on Centrifugation gives details of centrifugation equipment. Beckman, Progress Road, Sands Industrial Estate, High Wycombe, Buckinghamshire HP12 4JL. A brochure gives details of the 502 and 507 autosamplers, which are new addi- tions to the System Gold family of intelli- gent HPLC modules with true single- point control. Beckman, Progress Road, Sands Industrial Estate, High Wycombe, Buckinghamshire HP12 3BR.The first issue of the twice-yearly news- letter, ACS News, has as its theme food analysis, with the leading article describ- ing the ACS food analysis system. A review of food analysis is also available on request; it expands the theme of the newsletter. Applied Chromatography Systems Ltd., The Arsenal, Heapy Street, Macclesfield, Cheshire SK11 7JB. A brochure describes the Model 717 chromatography data system and con- troller, a low-cost entry level PC work- station for GC or HPLC. Axxiom Chromatography Inc., 11988 Challenger Court, Moorpark, CA 93021- 7122, USA. GS-Alumina, a four-page brochure, de- scribes the recently developed porous layer open tube (PLOT) gas chroma- tography columns designed for extended hydrocarbon analysis. J and W Scientific, 91 Blue Ravine Road, Folsom, CA 95630-4714, USA. A brochure describes the automation of routine ELISA procedures and most com- mercially available microplate-based ELISA kits, using the Beckman Biomek automated laboratory workstation. Beckman, Progress Road, Sands Industrial Estate, High Wycombe, Buckinghamshire . Application Bulletins describe analytical procedures for the water and environ-390 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 mental industry, including colorimetric determination of boron, silicic acid and free cyanide, polarographic deter- minations of nitrate in water, plant and soil extracts, vegetable juices, fertilizers, compost, manure, etc. V. A. Howe and Co. Ltd., Beaumont Close, Banbury, Oxfordshire OX16 7RG. A brochure presents an extensive range of programmable tube and chamber furnaces. Lenton Thermal Designs Ltd., Unit C2, Valley Way, Welland Industrial Estate, Market Harborough, Leicester- shire LE6 7PS. A brochure gives details of the TMX 2000 scanning probe microscope system, which offers unique capabilites due to its in- tegrated, modular design and advanced technology. TopoMetrix, 1505 Wyatt Drive, Santa Clara, CA 95054, USA. A shortform catalogue describes several new Rustrak recorders, including a chilled food monitor for those wishing to comply with the latest Food Hygiene Regulations. Mark IV Instruments Ltd., The Hyde, Brighton BN2 4JU. A brochure gives details of the N4-R, N3-R, F4-K and F3-K compact cryostats. Haake Mess-Technik GmbH u. Co., Dieselstrasse 4, D7500 Karlsruhe 41, Germany.

ISSN:0144-557X    

DOI:10.1039/AP9912800385

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

390 ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 Analytical Chemistry Trust Fund SAC Studentships The Trustees invite proposals from super- visors for research projects likely to make important contributions to the advance- ment of analytical chemistry in the UK and which are suitable for well qualified postgraduate students. Projects will be assessed particularly on the originality of the research proposed and its application to industrial needs. Applications may be submitted by research supervisors, who must be members of the Analytical Div- ision of The Royal Society of Chemistry of at least 2 years’ standing. If any form of equipment grant is likely to be required this should be included in the submission. The allocation of the limited amount of money available for proposals for projects to start in the Autumn term of 1992 will be considered early in that year when a tentative award may be made, subject to the Trustees being satisfied by the Sum- mer of 1992 that a student acceptable to them is available.The flat rate value of the studentship is &8000 per year (to include maintenance grant to the student, fees at UK rates, support grant to the academic institution and travelling). Industrial SAC Studentships The Trustees wish to encourage collabor- ation between industrial and academic organizations on significant topics of ana- lytical research orientated towards indus- trial programmes. Suitable projects would be those appropriate for the well qualified postgraduate student and proposals will be assessed on originality and on their relevance to industrial needs.Trustees will be particularly interested in receiving proposals which give the student the opportunity to carry out part of the programme on the premises of the indus- trial partner, perhaps making use of special facilities available there to assist the research. Programmes will have to be agreed by industrial and academic partners, one of whom should be a member of the Analytical Division of The Royal Society of Chemistry of at least 2 years’ standing. The Trust will provide funds to cover one half of the cost of the studentship up to a maximum of f4000 per annum, with the industrial partner expected to provide the balance. The allocation of the limited amount of money available for programmes to start in the Autumn Term of 1992 will be considered early in that year, when a tentative award may be made, subject to the Trustees being satisfied by the Summer of 1992 that a student acceptable to them is available. Regulations for all Studentships can be obtained from The Secretary, Analytical Division, The Royal Society of Chemistry, Burlington House, London W1VOBN. The closing date for appli- cations is January 16th, 1992.

ISSN:0144-557X    

DOI:10.1039/AP991280390b

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 39 1 Education and Training Committee- Aims and Activities Although the present Education and Training Committee made its first appear- ance in 1986, activities by the Analytical Division in this area started at an earlier date. An Education and Training Com- mittee was originally set up in 1968. This was subsequently given group status in 1970, at an inaugural meeting at Lough- borough University of Technology. Its activities included a series of surveys on the nature and content of analytical chemistry courses at universities, poly- technics and colleges. In addition, it organized meetings with Groups and Regions of the Analytical Division on the teaching of analytical chemistry. By the 1980s it was felt necessary to reassess its activities, and in 1986 the present Educa- tion and Training Committee emerged as a committee of AD Council.Its terms of reference are wide, and include: conducting surveys and, where necessary, making recommendations; projecting analytical chemistry to young people; producing suitable syllabuses in analytical chemistry for use in schools, higher education, public services and industry; reviewing education and train- ing in analytical chemistry in relation to new research, new government policies and legislation, and newer industrial pro- cesses, as well as requirements in other areas, such as health care and the environ- ment; and recommending, where appro- priate, teaching approaches to individual topics in analytical chemistry. The present report covers the main activities of ETC from 1986 to the present.Video ‘Chemical Detectives’ Much of the earlier period was concerned with completing this video, with a small sub-committee being responsible for details. The finished product has received high praise and will have shown modern analytical chemistry in action to many pupils since its introduction. National Schools’ Analyst Compe- tition This project was first suggested by Dr. T. B. Pierce in August, 1988, and was based on the existing regional compe- titions held at London and Manchester. The decision to hold the first national competition in July, 1990, involved a considerable effort, particularly in regions not having organized such events previously. Experience acquired in Lon- don and Manchester was heavily drawn on and the first National Analyst Compe- tition made its modest beginnings at the Polytechnic of North London in 1990.This was an appropriate location in view of the pioneering work by PNL on Schools’ Analyst Competititions (Anal. Proc., 1986, 23, 333). Generous financial support was provided by the Analytical Chemistry Trust, Industry and Govern- ment establishments. This enabled prizes to be awarded to the winning schools as well as meeting other expenses that a competition of this kind incurs. The second National Competition has taken place this year with its final in London on June 26th. A report of this will appear in a future issue of Analytical Proceedings. These competitions have clearly been successful, and will have illustrated to many pupils some modern methods of analytical chemistry, and in particular the need for skilful experimental work. School Publicity Material A decision was made to look afresh at school publicity material on analytical chemistry.Our previous efforts in this direction were informative and sensible, but perhaps not in the style particularly to interest a younger age group. In order to remedy this we sought the assistance of the RSC Education Officer’s department and drew on their extensive experience of dealing with schoolchildren. A working party of the ETC is now producing new publicity material targeted at pupils from 13 to 15, and possibly up to 17, years of age. We are grateful to the Analytical Chemistry Trust for financial support. Other Educational Matters The past four years has seen the imple- mentation of the National Curriculum, but as yet it is too early to see its effect on the number of pupils wishing to follow chemistry, including analytical chemistry, into the tertiary stage.At the tertiary stage itself, involvement with other Euro- pean countries in the teaching of analyti- cal chemistry has become important. Cur- rent ETC work includes collecting and assessing information on the following matters. Credit Accumulation and Transfer Schemes as a means of making Education and Training in analytical science more widely available. This is in accordance with recommendation 1.2.7 of the Ana- lytical Division Report ‘Analytical Chemistry-A Strategy For The Future’. ERASMUS (EuRopean Community Action Scheme for the Mobility of Univer- sity Students) Schemes. The ETC has convened a small working party to investi- gate the current position of ERASMUS and related schemes.This is clearly an area of interest to other parts of the Society; members of ETC have already held a meeting with members of the Qualifications and Education Board to discuss its wider implications within the Society. Harmonization of Analytical Chemistry Curricula in Europe. The Working Party on Analytical Chemistry of The Fede- ration of European Chemical Societies (WPAC/FECS) recommended in August, 1990, that steps should be taken in this direction. ETC will compare the Recom- mended Curricula in Analytical Chemistry of WPAC/FECS with the Syllabus of the Education and Training Group published in Analytical Proceed- ings in 1982.Other ETC activities include preparing an up-to-date bibliography on analytical chemistry, which has been of assistance to the Association of Clinical Biochemistry in updating their Study Guide and has provided assistance to ACOL in the new edition of their mono- graph on gas chromatography, and arranging a meeting with the Tertiary Education Group on the teaching of analytical chemistry. The Future It is important to subject the work of any committee to scrutiny in order to justify its continuation. In the context of ETC there can be no better indication of its future role than the document referred to earlier: ‘Analytical Chemistry-A Stra- tegy For The Future’ (Anal. Proc., 1990, 27, 166). Here, education and training aspects of analytical chemistry appear as a recurring theme. In relation to schools, higher education, industry and public relations, the need for an effective educa- tional approach is recognized and empha- sized. Its activities will extend into such areas as undergraduate and postgraduate curricula in analytical chemistry/science, accreditation and registration, and stan- dardization of analytical methodology. If the Analytical Division is to play its full part in United Kingdom and European analytical affairs, the Education and Training Committee will have a vital role to play. In conclusion, the now retired Chair- man of ETC would like to thank the many committee members, past and present, for their valuable contributions to its activities. Finally, he thanks Analytical Division Council and the Analytical Chemistry Trust for their support, finan- cial and otherwise. W. J . WILLIAMS

ISSN:0144-557X    

DOI:10.1039/AP9912800391

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

392 ANALYTICAL PROCEEDINGS, NOVEMBER 1991 , VOL 28 Conferences and Meetings The Major Hazard Aspects of the ’kans- portation of Dangerous Substances January 21-22,1991, London Autumn, 1991, saw the publication of a re- port by the UK Health and Safety Com- mission on the risks associated with the UK Transportation of hazardous substances in ‘major hazard’ quantities. This committee has, for the past five years, conducted the most searching and in-depth review ever into the transport of dangerous goods in Great Britain and has produced conclusions which challenge many of the existing conceptions about the transport of hazardous materials. This is one of the most fundamental research programmes ever undertaken into transport risks, which has brought to bear expertise from the chemical industry, the emergency services, transport operators, independent consultants and government scientists.The conference, which will be held at the Cafe Royal, will look at the sub-committee’s re- port and provide a review of the current state of play in Great Britain, the techniques used in risk analysis studies, the results of those studies and the conclusions of the committee in terms of future controls. For further information please contact Liz Hide, IBC Technical Services Ltd., Bath House (3rd Floor), 56 Holborn Viaduct, Lon- don EC 1 A 2EX. Third Annual Conference on Contami- nated Land: Policy, Regulation and Tech- nology February 6-7,1992, London There have been significant advances in pol- icy and regulation within the UK during the past year.The Department of the Environ- ment has published proposals for registers of sites subject to potentially contaminating uses under the Environmental Protection Act 1990. The National Rivers Authority is ex- pected to announce further policy initiatives shortly. The conference, which is to be held in the Inn on the Park Hotel, will provide an update on these developments and give back- ground information on the legal and regula- tory situation in Northern Ireland and Scotland. It will provide an opportunity to learn of new developments and services of- fered by UK companies in the field of soil clean-up. The event will also examine efforts to improve the guidance available in the UK and will investigate technologies which are developing through international collabora- tion. For further information on the 1992 Con- taminated Land event please contact Amanda Wright, IBC Technical Services Ltd., Gil- mmra House, 57-61 Mortimer Street, Lon- don W1N 7TD.Groundwater Pollution February 25-26,1992, London Traditionally, groundwater has had two ad- vantages over surface water. The first of these is that the aquifer acts as a natural reser- voir, which can be trapped as and when re- quired, thus obviating the need to construct expensive structures with their attendant en- vironmental problems. Secondly, ground- water is much less vulnerable to pollution and has long been looked upon as a source of high quality water requiring minimal treat- ment. Unfortunately, there is increasing evi- dence that this latter advantage is being eroded and that groundwater resources are being polluted from both point and diffuse sources associated with urban and industrial environments and modem agricultural prac- tices. This event will provide participants with up-to-date coverage of the groundwater pollution problems currently causing concern and will place these within a legislative and administrative framework.The conference, which will be held in the Cafe Royal, will interest those in industry and agriculture and researchers, regulators, consultants and administrators dealing with groundwater pollution. For further details please contact Amanda Wright, IBC Technical Services Ltd., Gil- mmra House, 57-61 Mortimer Street, Lon- don W 1 N 7TD. Biological Processing of Coal May 4-7,1992, Clearwater Beach, FL, USA The US Department of Energy’s (DOE) Pitts- burgh Energy Technology Center is seeking papers for the Third International Symposium on the Biological Processing of Coal to be held in the Sheraton Sand Key Resort in Clearwater Beach.The symposium, jointly sponsored by DOE and the Electric Power Research Institute, will promote interest and identify new technologies in this emerging area of coal research. Papers should be classified in one of the following categories: coal structure and bioreactivity; coal analysis; coal biosolubilization, biogasification and biobeneficiation (including de-ashing, desul- furization, denitrification, and bio-assisted flotation); bioconversion of coal-derived sub- stances (including bioconversion of syn- thesis gas and coal combustion gases, and bioprocessing of tars and sludges); and mole- cular biology of coal processing bacteria. Those interested in preparing a paper for consideration should submit a 200-400 word abstract, including the author’s name, title, business address and telephone number by December 13, 199 1.Abstracts should be sent to Dr. Gregory J. Olson, US Department of Energy, Pittsburgh Energy Technology Center, P.O. Box 10940, M.S. 141-L, Pittsburgh, PA 15236, USA. Fifth International Symposium on Biologi- cal and Environmental Reference Materi- als May 11-14,1991, Aachen, Germany The Fifth International Symposium in Biol- ogical and Environmental Reference Materi- als will be held in the Novotel, Aachen, Germany. The excellent exchange of ideas and information described in the Proceedings of the Fourth Symposium held in February, 1990, at Orlando, Florida, USA, covered a wide variety and scope of information in this topical area.Activities at the Fifth Sympo- sium are expected both to broaden these dis- cussions and to focus on more specific aspects of further research on problems and progress of projects discussed at the previous symposium. The major aim of this sympo- sium series is to bring together efforts in the production, study and use of Reference Ma- terials in the analytical, biological, biomedi- cal, clinical, environmental and nutritional communities. For information contact Dr. Wayne R. Wolf, BERM-5, Nutrient Composition La- boratory, United States Department of Agri- culture, Beltsville, Maryland 20705, USA, or Dr.Markus Stoeppler, KFA, Postfach 1913, D-5 170, Julich, Germany. Trace Elements in Health and Disease May 25-29,1992, Stockholm, Sweden This conference is the Third ISTERH (Inter- national Society for Trace Elements Research in Humans) Conference, and the Fourth NTES (Nordic Trace Elements) Conference. It will consist of plenary lectures as well as contributed papers and posters in areas of clinical, toxicological and nutritional signific- ance for trace elements. The main topics dis- cussed will be: analytical methods for quality control; trace element speciation; bioavaila- bility of trace elements in various foods and drinking water; hepatobiliary metabolism of trace elements; nutrition and trace elements; clinical effects of trace elements on health; trace elements and physical activity; nutri- tional toxicology of trace elements; environ- mental acidification-changes in trace elements and effects on human health; mech- anisms of trace element toxicology; and biol- ogical monitoring of trace elements.Further information is available from IS- TERH/NTES 1992, Scientific Secretariat, Dr, Lars-Olaf Plantin, Clinical Research Centre, Huddinge Hospital, S 141 86 Huddinge, Sweden . ESEAC ’92: Fourth European Conference on ElectroanalysisANALYTICAL PROCEEDINGS, NOVEMBER 1991, VOL 28 393 May 31-June 3, 1992, Noordwijkerhout, The Netherlands Under the auspices of the European Society for Electroanalytical Chemistry, this Con- ference will be organized in the conference centre ‘De Leeuwenhorst’ in Noordwijker- hout.As before, it is entirely devoted to modem electroanalytical subjects. The cur- rent status of electroanalytical techniques, in- cluding theoretical developments 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. International Symposium on Capillary Electrophoresis August 26-28,1992, York This symposium, which will be organized jointly by the Chromatographic Society, the British Electrophoresis Society and the University of York, and held in the Depart- Chemistry, University of York, Heslington, ment of Chemistry of the University of York, York, YO1 5DD. will follow the format of the first highly suc- cessful international symposium on Capillary Electrophoresis (CE) held in the UK in 1990. The enormous topical interest in this rapidly 12th International Symposium on Micro- expanding technique promises that it will be chemical Techniques a lively event. Plenary speakers will include leading international investigators. The sym- September 7-1 2,1992, Cdrdoba, Spain

ISSN:0144-557X    

DOI:10.1039/AP9912800392

出版商:RSC    

年代:1991

数据来源: RSC