ISSN:0144-557X    

DOI:10.1039/AP98825FX029

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年代:1988

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ANPRDI 25(8) 261-288 (1988) Proceedings of the Analytical Division of The Royal Society of Chemistry 267 Analytical Applications of Lectins 267 268 269 261 Editorials 261 Correspondence 262. RSC Awards 1987 263 SUMMARIES OF PAPERS 263 Adsorptive Stripping Voltammetry-a Versatile Technique 263 265 'Adsorptive Cathodic Stripping Voltammetry and Chronopotentiometry of Trace Metals in Seawater' by Constant M. G. van den Berg 'Lectins Specific for Red Cell Antigens or Cryptantigens' by G. W. G. Bird 'Lectins in Microbiology' by A. R. Archibald 'Lectin - Gold Complexes as an Aid to Diagnosis in Histopathology' by David W. R. G riff it hs 27 1 Practical Chemical and Biological Sensors 27 1 272 274 276 278 'The Challenge of Modelling and Synthesising Novel Organic Sensing Materials' by J. D. Wright 'New Directions in lonophores' by Richard E. Moss and Ian 0. Sutherland 'What Does the Biomedical Area Require of Biosensors?' by P. Vadgama 'Biosensors for Clinical Analyses' by Jane E. Frew and Monika J. Green 'Water Quality Monitoring Using Chemical and Biological Sensors' by A. J. Dobbs and M. G. Briers 280 Equipment News 284 Ronald Belcher Memorial Lectureship 285 Analytical Division Distinguished Service Award 286 New British Standards 286 Publications Received 287 Conferences and Meetings 288 Courses iii Analytical Division Diary Typeset and printed by Black Bear Press Limited, Cambridge, England August 1988 Analytical Proceedings CONTENTS 'Trains, Loops and Tails: Adsorptive Voltammetry of Some Biological Macromolecules' by Eileen Buckley, Malcolm R. Smyth and Juana Rodriguez Flores

ISSN:0144-557X    

DOI:10.1039/AP98825BX031

出版商:RSC    

年代:1988

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ANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 26 1 Correspondence Correspondence is accepted on all matters of interest to analytical chemists. Letters should be addressed to the Editor, Analytical Proceedings, The Royal Society of Chemistry, Burlington House, London WIV OBN. Analytical Training of these thoughts then I believe life in the laboratory can be very enjoyable. Sir, Philosophy for the Analytical Chemist 2. If you give the end user the results he wants to hear. he will 3. You will always be judged by your worst result. Coming to an understanding of these ground rules makes the analyst aware of the importance of getting it right. at the right time, for the right person. With this in mind the analytical chemist can look forward to the beginning of each day with anticipation, excitement and a sense of challenge.He or she will also leave the laboratory at After reading a recent summary in Analytical Proceedings’ comments made. The training ofan analytical chemist is indeed a two-fold approach, i. e . , academic and industrial environ- ments. The comments made on the importance of the analytical chemist asking the questions “Why is the analysis required?” and “When are the results required for?” will most certainly overcome the black box syndrome. May I also add a further philosophy which may appear somewhat cynical but providing the analytical chemist is aware by J . Tillman on “Training the Analyst” I heartily endorse the 1. Whenever YOU walk into the laboratory YOU are On trial. never question them.262 ANALYTICAL PROCEEDINGS, AUGUST 1988. VOL 25 the end of each day feeling satisfied and fulfilled in their chosen career. ‘‘ Thurston, ” Alan Batho Harriseahead, Staff ords hire Reference Stoke-on- Trent, 1. Tillman, J., Anal. Proc., 1988, 25, 148.

ISSN:0144-557X    

DOI:10.1039/AP988250261b

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年代:1988

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262 ANALYTICAL PROCEEDINGS, AUGUST 1988. VOL 25 RSC Awards 1987 The Royal Society of Chemistry Awards for 1987 were presented at a ceremony held in Burlington House, Piccadilly, London W.l on June 8th, 1988. The awards of interest to analytical chemists were for Analytical Separation Methods (sponsored by Roche Products Ltd.), awarded to Professor D . E. Games of University College, Cardiff, for outstand- ing contributions to chromatographic separations and analysis, for Chemical Analysis and Instrumentation (sponsored by Perkin-Elmer Ltd.), awarded to Dr. R. P. W. Scott, formerly of Perkin-Elmer, USA, in recognition of his inventiveness in the field of chromatography, and for Health, Safety or Environmental Chem- istry (sponsored by Shell UK Ltd.), awarded to Dr. J. G. Firth of the Health and Safety Executive, for his develop- ment work on catalytic sensors and dif- fusive samples for measuring hazardous gases and vapours. The presentations were made by the President of the Royal Society of Chemistry, Professor Sir Jack Lewis.Our photograph shows (L-R) Professor Professor Sir Jack Lewis and Dr. J. G. of the Analytical Division, Mr. P. G. W. D. E. Games, Dr. R. P. W. Scott, Firth with the Immediate Past President Cobb. UK CHEMOMETRICS DISCUSSION GROUP PC SOFTWARE for CHEMOMETRICS Department of Chemistry, University of Warwick, September 27th, 1988 As personal computers, particularly the IBM PC, are becoming more powerful and more widely available, it is possible to do a lot of chemometric processing effectively at low cost. An increasing number of software packages are now available to do a variety of calculations. This one-day meeting is designed to introduce some software which members might like to see and hear about before considering purchase.All packages will be for the IBM PC of standard configuration. The morning will consist of two presentations by invited guests from Norway, where there is a strong community of chemometricians. Harald Martens will introduce UNSCRAMBLER, a package for the processing of spectra. Olaf Kvalheim will introduce SIRIUS, a general, multivariate data analysis package including SIMCA and PLS. The afternoon session will comprise shorter presentations of SPEAR and Ed Malinowski’s TFA package by UK CDG members. During the day it is hoped to have plenty of time for members to have some hands-on experience of the software. Information is available from Dr. R. L. Erskine, HP Research Centre, Sunbury-on-Thames, Middlesex TW16 7LN.

ISSN:0144-557X    

DOI:10.1039/AP9882500262

出版商:RSC    

年代:1988

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ANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 263 Adsorptive Stripping Voltammetry-a Versatile Tech n ique The following are summaries of two of the papers presented at a Joint Meeting of the Midlands Region and the Electroanalytical Group held on October 21st, 1987, in the University of Technology, Loughborough. Trains, Loops and Tails: Adsorptive Voltammetry of Some Biological Macromolecules Eileen Buckley and Malcolm R. Smyth School of Chemical Sciences, NlHE Dublin, Glasnevin, Dublin 9, Ireland Juana Rodriguez Flores Department of Analytical Chemistry and Electrochemistry, University of Extremadura, Badajoz, Spain Studies of the electrochemical behaviour of biological macro- molecules such as proteins and nucleic acids are important both from the viewpoint of a better understanding of biochemical processes and for the development of electroanalytical metho- dology.In recent years there has been much interest, for instance, in the development of biosensors based on enzyme electrodes and other potentiometric devices. In this paper, however, we shall discuss the analytical applications of the voltammetry of biological macromolecules, concentrating on the role that adsorption plays in determining the nature of the electrochemical processes exhibited by these molecules. Studies of the adsorption of biological macromolecules, however, are often difficult to interpret. Reynaud et al.1 have suggested that “the literature pertaining to the study of pro- tein adsorption at solid - liquid interfaces is often confused; contradictory and unclear laws seem to emerge.” The main reasons for this lie in the conformational changes that can occur when a protein or nucleic acid is adsorbed at an electrode surface.The different types of conformations in which bio- polymers can exist at a polarised electrode surface are many, but they can be represented diagrammatically2 in the form of “trains, loops and tails” (Fig. 1). Berg et al.3 have also suggested possible conformational changes (e.g. , potential- induced compaction of DNA) occurring in the structure of biological macromolecules during the adsorption step itself. For both proteins and nucleic acids, electron transfer usually follows the reactant adsorption step, and electrons generally have to travel distances of the order of 1 nm for electron transfer to occur.3 A = train B = loop C = tail B n Fig.1. ecule adsorbed at an electrode surface2 Trains, loops and tails-a model of a biological macromol- Nucleic Acids The electrochemical behaviour of nucleic acids has recently been surveyed by Palecek2 and Sequaris.4 The nucleic acids are made up of a specific sequence of purine - pyrimidine base pairs, held together by a deoxyribose sugar - phosphate backbone and linked through intramolecular hydrogen bonds. The bases (nucleotides) usually found in DNA, for instance, are adenine, guanine (purines), cytosine and thymine (pyrimi- dines). The adenine and cytosine bases are electroreducible at mercury electrodes, and the adenine and guanine bases can be oxidised at carbon electrodes. Nucleotides, in addition to their corresponding nucleosides, are first adsorbed at the electrode surface before electron transfer takes place.This adsorption process lowers the differential capacity of the electrode double layer, and the bases usually become reorientated at the electrode surface from the planar to the perpendicular posi- tion. Because of this requirement for adsorption to occur before electron transfer, it is possible to lower the limit of detection for the determination of these compounds using adsorptive stripping voltammetry (AdSV) down to the 10-8- 10-9 M level in pure solution.5-7 This compares with limits of detection for these bases using conventional differential pulse polarography of the order of 10-6-10-7 M. The adsorption of natural and synthetic polynucleotides at mercury electrodes is usually diffusion controlled for low surface coverages of the electrode.The orientation of poly- nucleotides adsorbed at electrode surfaces is still a matter of conjecture, but “trains, loops and tails” are often invoked to describe experimental findings. Much work in recent years has therefore been devoted to the study of adsorbed biological macromolecules using spectroscopic techniques such as surface enhanced Raman spectroscopy (SERS).4 In terms of the analysis of nucleic acids, work has recently been reported on the determination of nucleic acids by a.c. voltammetry following adsorption at a mercury electrode* and on the use of osmium labelling to determine nucleic acids by stripping voltammetry.9 In addition, Palecek and Postbiegloval” have recently reported a method based on the adsorptive pre- concentration of some biological macromolecules (including some nucleic acids and proteins) at an electrode surface, with subsequent transfer of the adsorbed layer into a new support- ing electrolyte and subsequent voltammetric analysis.This new technique is called adsorptive transfer stripping voltammetry (AdTSV), and offers the benefit of adsorption of some biological macromolecules at open circuit from small solution volumes. It may also be possible to use this technique to study the structural transitions of biological macromolecules caused by denaturation or intercalation.264 ANALYTICAL PROCEEDINGS, AUGUST 1988. VOL 25 Proteins The use of adsorptive voltammetry for the determination of proteins is currently a subject of increasing interest.Methods have been described for the determination of molecules such as cytochrome C, 1 1 based on adsorptive pre-concentration at mercury electrodes. Other workers have investigated the mechanism of reduction of cytochrome C at a variety of solid electrodes, e.g., gold modified with 4,4’-bipyridy1,12 graphite1 and Ru02. 13 Lecompte and co-workers14J5 have reported on studies of the adsorption of prothrombin and fragments derived from it. We have concentrated our efforts in recent years on studies of proteins involved in immunological reactions, with a view to developing direct voltammetric immunoassays. To date, those involved in this area of research have concentrated mainly on the development of either heterogeneous or homogeneous methods involving the determination of products of coupled enzymatic reactions.16 We have recently reported our results on the adsorptive stripping voltammetric behaviour of human serum albumin (HSA) and anti-HSAl7 and on mouse IgG and anti-mouse IgG.18 In both instances we were able to demon- strate the possibility of using voltammetry to monitor the reaction of a hapten and its antibody directly in solution. In order to understand better the electrochemical behaviour of such immunoglobulins, we have recently investigated the AdSV behaviour of Fab and F(ab’), fragments obtained following enzymatic digestion of anti-mouse IgG. The effect of varying the accumulation potential on the AdSV behaviour of F(ab’), fragments is shown in Fig. 2. From this it can be seen G H to., pLA I 0.125V Fig.2. Effect of accumulation potential on the adsorptive stripping voltammetric peak current of anti-mouse F(ab’), fragment. Condi- tions: E,,,, (A) -0.10 V, (B) -0.05 V, (C) 0.00 V, (D) +0.05 V, (E) +0.10 \’, (F) +0.15 V, (G) +0.20 V and (H) +0.25 V (all potentials vs. Ag - AgCl); scan rate, 5 mV s-1; E, 50 mV that the optimum accumulation potential is +0.15 V (vs. Ag - AgC1). Slight differences have been found in the voltam- metric behaviour of the Fab and F(ab’)z fragments when compared with the parent immunoglobulin, but it has not yet been possible to interpret the reasons for these. In addition, we have recently investigated the AdSV behaviour of some lectins, namely phytohemagglutininlg and concanavalin A,”) and investigated their interaction with a variety of sugars and proteins.Lipoproteins The adsorption of some lipoproteins and other proteins on polymer surfaces using a two-step electroimmunoassay tech- nique has recently been reported by Breemhaar et ~1.21 In addition, Nelson and Benton22 have investigated the adsorp- tion and orientation of phospholipids at the mercury - water interface, and reported that the lipids were orientated with their hydrocarbon moiety adsorbed at the surface of the electrode, that the lipid layers are fluid and that there is coiling and overlap of the hydrocarbon chains. Conclusion In conclusion, it can be seen that the area of adsorptive voltammetry of biological macromolecules is a very exciting area of research, not only from the mechanistic viewpoint, but also from the possibilities of developing both sensitive and selective methods of analysis.It is expected that many more applications involving the approaches mentioned in this paper will appear in the literature in the coming years. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. References Reynaud, J. A., Tavernier. I., Yu, L. T., and Cochet, J . M., Bioelectrochem. Bioenerg., 1986, 15, 103. Palecek, E., Bioelectrochem. Bioenerg., 1986. 15, 275. Berg, H., Fiedler, U., Flernrning, J., and Horn. G., Bioelectro- chem. Bioenerg., 1985, 14,417. Sequaris, J . M., in Smyth, M. R., and Vos, J. G.. Editors, “Electrochemistry, Sensors and Analysis,” Elsevier, Amster- dam. 1986, pp. 191-203. Palecek, E., and Jelen, F., Collect.Czech. Chem. Commun., 1980.45, 3472. Palecek, E . , Anal. Biochem., 1980, 108, 129. Glodowski, S . , Bilewicz, R., and Kublik, Z . , Anal. Chim. Acta. 1986, 186, 39. Krznaric, D.. and Cosovic. D., Anal. Biochem., 1986, 156, 454. Palecek. E., and Hung. M. A., Anal. Biochem.. 1983, 132, 236. Palecek, E., and Postbieglova, I., J . Efectroanaf. Chem.. 1986, 214, 359. Wang, J., and Meng, S . L., J . Electroanal. Chem., 1987, 221, 257. Albery, W. J . , Eddowes, M. J., Hill, H. A. O., and Hillman, A. R., J . Am. Chem. SOC., 1981, 103, 3904. Harmer, M. A . , and Hill, H. A. O., J . Electroanal. Chem., 1985, 189, 229. Lecompte, M. F., Clavilier, J . , Dode. C., Elion, J., and Miller, I. R., Bioelectrochem. Bioenerg., 1984, 13, 211. Lecompte. M. F., Clavilier.J., Dode, C., Elion, J., and Miller, I. R., J . Electroanal. Chem., 1984, 163, 345. Heineman, W. R., Deutsch, E., and Halsall, H. B.. in Smyth, M. R., and Vos, J. G., Editors, “Electrochemistry, Sensors and Analysis,” Elsevier, Amsterdam, 1986. pp. 345-353. Rodriguez, F. J.. and Smyth, M. R.. J . Electroanal. Chem., 1987, 235, 317. Smyth, M. R., Buckley, E., Rodriguez, F. J., and O’Kennedy, R., Analyst, 1988, 113, 31. Rodriguez, F. J., O’Kennedy, R., and Smyth, M. R., Anal. Lett., 1988, 21, 211. Rodriguez, F. J . , O’Kennedy, R., and Smyth. M. R., Analyst, 1988. 113, 525. Breemhaar, W., Brinkrnan, E., Ellens, D. J., Beugeling, T., and Bantjes, A., Biomaterials, 1984, 5, 267. Nelson, A., and Benton, A., J. Electroanal. Chem., 1986,202, 253.ANALYTICAL PROCEEDINGS, AUGUST 1988.VOL 25 265 Adsorptive Cathodic Stripping Voltammetry and Chronopotentiometry of Trace Metals in Seawater Constant M. G. van den Berg Department of Earth Sciences, Oceanography Laboratories, University of Liverpool, Liverpool L69 3BX The technique of adsorptive cathodic stripping voltammetry (CSV) of trace metals has progressed strongly since the development of procedures for the determination of nickel, I chromium2 and copper3 in water. The fundamental differences from the more conventional technique of anodic stripping voltammetry (ASV) lie in the deposition step, which is by adsorption of the chelate with an added chelator, and the potential scan, which is in a negative direction, hence the reduction (cathodic) current is measured. CSV is therefore not limited to amalgam-forming elements as in ASV, but in principle any adsorbable and chelate-forming element can be determined if it, or its ligand, can be reduced at potentials within the stability region of water and the electrode, usually between 0 and -1.6 V.Although the incidental use of adsorptive CSV is already over 10 years old,4 advances were made only when the reaction mechanism (chelate adsorption rather than precipitation of an insoluble compound) was understood. As a result it is now possible to determine 13 of a growing number of metals in seawater without pre-concentra- tion of the sample. A list of these metals with their experimen- tal conditions (chelating agent and solution pH) is given in Table 1. ~ ~ ~~ ~ ~ ~ ~~~~~ Table 1. Experimental conditions for the determination of trace metals using cathodic stripping voltammetry.The limits of detection are for 60 s deposition. Abbreviations: DASA = 1,2-dihydroxyanthraqui- none-3-sulphonic acid; HQ = 8-hydroxyquinoline; DMG = dimethyl glyoxime; DTPA = diethylenetriaminepentaacetic acid; APDC = ammonium tetramethylenedithiocarbamate (ammonium pyrrolidine- dithiocarbamate) A1 Cd co Cr c u Fe Mo Ni Pb Sb U V Zn Metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reagent DASA HQ DMG DTPA HQ Catechol HQ DMG HQ Catechol HQ Catechol APDC PH 7.1 7.8 9.2 6.2 7.9 6.9 2.5 9.2 7.8 6.0 6.8 6.8 7.3 Limit of detection/ nM 1 0.1 0.1 0.5 0.2 0.2 1 0.1 0.3 0.6 0.2 0.6 0.3 Reference 5 6 1 2 6 7 8 2 6 9 10 11 12 A useful aspect of CSV is the high sensitivity, inherent with the fact that the metal is present as a monomolecular film on the electrode surface; this causes the reduction to be 100% effective, so the entire amount of deposited metal is reduced at the reduction potential for the complex.As a result, the determination of Cu, Cd and Pb by CSV is at least ten times more sensitive than that by ASV using a hanging mercury drop electrode, and of similar sensitivity to a rotating disk elec- trode.6 The limits of detection given in Table 1 are given for a deposition period of 60 s; for most metals those limits are inversely and linearly related to the deposition time, so they can be lowered considerably. CSV is also a convenient method for studying metal speciation by means of ligand competition.The added chelator competes with natural organic material for metal ions; the peak height is directly related to the concentration of chelate formed, which is the so-called “labile metal” concentration. This is a function of the added ligand (CAL) concentration, the stability of the chelates (M-AL) formed (K’MAL), and the concentration of natural ligands (CL) and the stability constant (K’ML) for complexes ML. The total metal concentration is obtained by UV irradiation of the sample. Therefore, the following relationship exists between the ratio of the labile to the total dissolved metal concentration and the a-coefficient due to metal complexation by unknown ligands L13: [labile metal]/[total dissolved metal] = CYM-AL/(CYML + (YM-AL) where CYML.= 2 K’MLCL for all natural complexes ML. As all terms in this equation except CYML are known, a value for (xML can be calculated readily. This can then be used to calculate the free (not complexed by organic ligands L) metal concentration and the organic metal fraction. Hence a large amount of information about the metal speciation is obtained from just two measurements per sample: the labile and the total dissolved metal concentrations. Cathodic Stripping Chronopotentiometry (CSC)14 The deposition step of adsorptive CSC is the same as for CSV, in that chelate adsorption is carried out under potentiostatic control of the electrode. All the elements that can be determined using CSV can therefore also be determined using stripping chronopotentiometry.However, the potentiostat is disconnected during the scan, which is carried out by passing a constant cathodic current (0.1-50 pA) through the electrode; this causes the potential to drop rapidly until the reduction potential of the adsorbed chelate is reached; its reduction causes a “transition time” that is directly related to the amount of adsorbed matter and therefore to the dissolved metal concentration. The step-shaped waveform is converted to a peak as a result of the digitisation of the measurement: the potential is measured rapidly (every 4 ps) and continuously during the scan, and each time a particular potential (at a resolution of 1.5 mV) is measured the memory location corresponding to this potential is incremented. Thus, a transition time becomes a peak on a relatively flat base line, as shown for Ni in Fig.1. The transition time is very short (often less than 1 ms) for low metal concentrations, so a fast rate of data acquisition (250 kHz) is required to obtain a sufficient number of “counts” for a well defined peak. Dissolved oxygen causes a large transition time at around -0.8 V at low scan rates (low current setting). However, this 340 272 204 3 0 136 68 1 , I -0.9 -1.0 -1.1 -1.2 -1.3 PotentialiV Fig. 1. cathodic stripping chronopotentiometry Determination. of 8 n M dissolved nickel in seawater using266 ANALYTICAL PROCEEDINGS, AUGUST 1988, VOI, 25 reduction is irreversible and is shifted in a negative direction to around -1.2 V by increasing the current from 3 to 20 yA.14 Hence it is possible to determine metals in seawater without deaeration of the sample, which permits the use of continuous flow analysis.The determination of elements with relatively positive reduction potentials (<-0.8 V), such as copper, lead, cadmium, uranium, iron, vanadium and molybdenum, is not affected by the presence of dissolved oxygen using stripping chronopotentiometry, whereas increased current settings (which reduce the sensitivity) are used for metals with more negative reduction potentials, such as nickel and cobalt.14 Nevertheless, the limit of detection is easily low enough at -0.2 nM to detect nickel in undeaerated seawater. Generally, the sensitivity of stripping chronopotentiometry is comparable to linear sweep voltammetry when a very fast scan is employed. The sensitivity is therefore less than that for DPCSV for elements with a reversible reduction (e.g., copper, lead and cadmium) which benefit from application of the differential pulse modulation, whereas other elements can be determined with the same or better sensitivity at the very fast scan rates (10-20 V s-1) that occur with chronopotentiometry.Stripping chronopotentiometry has good potential as a field technique employing the continuous flow technique. It is the only technique by which trace metals can be determined automatically and in-line in seawater pumped on-board a ship, at concentration ranges between polluted estuarine and unpolluted seawater, as has been shown by the monitoring of dissolved nickel ,I4 copper and zinc15 throughout the Tamar estuary in the south of England.1. 2. 3. 4. 5 . 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. References Pihlar, B., Valenta, P., and Nurnberg, H. W., Fresenius Z. Anal. Chem., 1981, 307, 337. Golimowski, J . , Valenta, P., and Nurnberg, H. W., Fresenius Z. Anal. Chem., 1985, 322, 315. van den Berg, C. M. G . , Anal. Chim. Acta, 1984, 164, 195. Brainina, Kh. Z., “Stripping Voltammetry in Chemical Analy- sis,” Wiley, Chichester, 1974. van den Berg, C. M. G., Murphy, K., and Riley, J . P., Anal. Chim. Acta, 1986, 188, 177. van den Berg, C. M. G . , J. Electroanal. Chern., 1986,215,111. van den Berg, C. M. G . , and Huang, Z. Q., J . Electroanal. Chem., 1984, 177, 269. van den Berg, C. M. G., Anal. Chem., 1985, 57, 1532. Capodaglio, G., van den Berg, C. M. G . , and Scarponi, G., J . Electroanal. Chem., 1987, 235, 275.van den Berg, C. M. G., and Nimmo, M., Anal. Chern., 1987, 59, 924. van den Berg, C. M. G., and Huang, Z . Q., Anal. Chem., 1984, 56, 2383. van den Berg, C. M. G . , Talanta, 1984, 31, 1069. Nimmo, M., van den Berg, C. M. G., and Brown, J., Coastal Est. Shelf Sci., submitted for publication. Newton, M. P., and van den Berg, C. M. G . , Anal. Chim. Acta, in the press. van den Berg, C. M. G . , and Nimmo, M., unpublished data. ROYAL SOCIETY OF CHEMISTRY ANALYTICAL DIVISION : ELECTROANALYTICAL GROUP FARADAY DlVl SlO N : ELECTROCH EM ISTRY G ROU P ELECTROANALYSIS IN BIOCHEMICAL, ENVIRONMENTAL AND INDUSTRIAL SCIENCES April 1 Ith-I4th, 1989, Loughborough This international symposium will take place in the University of Technology. The emphasis of the programme will be laid on methodology and applications of the various electroanalytical techniques, especially regarding the use of amperometric and potentiometric membrane and membrane clad electrodes, gas sensors, modern polarography and voltammetry. Development, operation and mechanisms will be included where these relate to electroanalysis in the theme areas, including biosensors and other elect roc h em ica I sensors. ~ 1 A programme of plenary lectures has been arranged but contributed papers are now being sought. A special issue of The Analystwill be based on papers presented at this symposium. An exhibition is also being planned. For further information contact Dr. A. G. Fogg, Electroanalysis Conference, Chemistry Department, Loughborough University of Technology, Loughborough, Leicestershire LEI 1 3TU.

ISSN:0144-557X    

DOI:10.1039/AP9882500263

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年代:1988

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ANALYTICAL PROCEEDINGS. AUGUST 1988. VOL 25 267 Analytical Applications of Lecti ns The following are summaries of three of the papers presented at a Joint Meeting of the Biological Methods Group and the Carbohydrate Group of the Perkin Division held on October 14th, 1987, in Guy’s Hospital, London. Lectins Specific for Red Cell Antigens or Cryptantigens G. W. G. Bird Blood Group Reference Laboratory, Oxford OX2 6HE Lectins combine specifically with monosaccharides, usually at the terminal position in the carbohydrate chains. The monosac- charide is sometimes termed the immunodominant sugar. Lectin specificity depends not only on the presence of the immunodominant sugar in the terminal position but also on its anomeric conformation, the nature of the subterminal struc- ture or structures.the site of its attachment to the subterminal structure and, in cellular glycoproteins or glycolipids, on the number and distribution of receptor sites and on the amount of steric hindrance caused by vicinal structures. The most important factor is the outward display of the carbohydrate chain, which may depend both on its native configuration and on the configuration imparted to it by the structure of the protein or lipid to which it is attached. Lectins are specifically inhibited by monosaccharides. They may be inhibited more strongly by appropriate oligosaccharides or polysaccharides. There are only seven sugar constituents of the human red cell membrane: galactose, mannose, fucose, glucose, N-acetyl-D- glucosamine, N-acetyl-D-galactosamine and N-acetylneur- aminic (sialic) acid.The carbohydrate portion of red cell glycolipids or glycoproteins consists of various combinations of these seven sugars. The various glycoconjugates differ in the serial order of the constituent sugars, the site of attachment of the sugars to each other and in the nature of the anomeric linkage between them. It is therefore not surprising that many lectins crossreact. What is surprising, however, is the high degree of specificity of some lectins. I n the last 40 years lectins have moved from being mere curiosities to a leading position in biological research in an extensive variety of scientific applications. The use of lectins in routine and research activities. first applied to red blood cell serology, has now extended to almost every body cell and body fluid.Chief Properties of Lectins The chief properties of lectins are that they bind sugars. agglutinate cells in suspension, precipitate antigens in solution. e.g., blood group specific macromolecules, and stimulate mitosis in lymphocytes. Applications of Lectins in Blood Banking and Haematology Lectins play a useful role in blood group serology. Two popular specific lectins deserve special mention: Dolichos biflorus and Aruchis hypogaea (peanut) lectin. 1.7 The Dolichos biflorus lectin is the most widely used in blood group serology. Its discovery revolutionised the means for distinguishing between the A, and A2 subgroups of the human blood group antigen A. This reagent simply and quickly makes a clear distinction between Al and the weaker forms of A.The Dolichos biflonis lectin is also a powerful precipitin in both conventional and gel diffusion techniques. The peanut lectin does not react with normal erythrocytes, but powerfully agglutinates red cells that have been exposed to the microbial enzyme neuraminidase. As exposure of red cells to neuraminidase splits off neuraminic (sialic) acid from the red cell surface and exposes the T-receptor of Friedenreich, the peanut lectin acts as anti-T. The discovery of the anti-T activity of the peanut lectin was of clinico-pathological importance because it marked the beginning of the fruitful application of lectins to the study of red cell cryptantigens and of red cell polyagglutinability. In addition to its application to red cell serology, the peanut lectin is widely used in scientific routine and research, particularly in studies of lymphocytes and cancer cells.This lectin specifically combines with the disaccharide galactose Pl-3 N-acetyl-D-galactosamine. Two other useful lectins for the classification of red cell polyagglutinability are Salvia sclarea, specific for the red cell cryptantigen Tn3, and Leonrirus cardiaca, specific for the surface antigen Cad .4 Examples of the Fine Specificity of Lectins N-Acetyl-D-galactosamine in either an a- or p-linked terminal position is the sugar for which the Dolichos biflorus lectin is specific. It is closely similar in chemical structure to N-acetyl-D- glucosamine. Nevertheless, the Dolichos lectin is quickly inhibited by N-acetyl-D-galactosamine but not at all by N-acet yl-D-glucosamine. The Tn-specific Salvia sclarea lectin is specific for &-linked N-acetyl-D-galactosamine and the Cad-specific lectin of Leo- nurus cardiaca is specific for (3-linked N-acetyl-D-galactos- amine, whereas the Dolichos biflorus lectin reacts with both Tn and Cad red cells.The monosaccharide specificities of these and other lectins which combine specifically with human red blood cell receptors zre shown in Table 1. Table 1. Monosaccharide specificities of some lectins for human red blood cell receptors Serological Monosaccharide Lectin specificity specificity Dolichos biflorus . . . . . . A. Tn, Cad Fomesfomentarius . . . . B Lotustetragonolobus . . . . FI Viciugraminea . . . . . . N A rachis hypogaea . . . . . . T Salvia sclarea .. . . . . Tn Leonuruscardiacu . . , . Cad Grifforzia simplicifolia I1 . . Tk Limuluspol~phemus . . . . Unspecific a- or fi-NAcGal ar-D-Gal CY-D-FUC (3-D-Gal P-D-Gal wNAcGal [3- N Ac Gal NAcGlc NeuAc The Limulus Polyphemus Lectin The Liinulus polyphemus lectin present in the blue haemo- lymph of the so-called horseshoe crab is specific for new-268 ANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 aminic (sialic) acid.5 It agglutinates all normal red cells but not T-transformed red cells, just the opposite of the peanut lectin. The colonisation factor antigen CFA/I possessed by some E. coli 078 is also a sialic acid-specific lectin.6 However, its reactions are not the same as those of Limulus polyphemus. This is one of many examples of how lectins with identical monosaccharide specificity do not all react in the same way.Lectins in Gel Diffusion Tests Lectins were first used in gel-diffusion tests by Bird.’ As they precipitate carbohydrate antigens they give more diffuse precipitation lines than protein antigens give against their antibodies. Conclusion From this very brief account it should be readily seen that lectins contribute usefully to red cell serology and biochemistry and to various aspects of clinical pathology. References 1. 2. 3. 4. 5 . 6. 7. Bird, G . W. G., Curr. Sci., 1951, 20, 298. Bird, G. W. G . , Vox Sang.. 1964, 9, 748. Bird, G . W. G., and Wingham. J . , Lancet, 1973, 1, 677. Bird, G . W. G., and Wingham, J . , Clin. Lab. Haematol.. 1979, 1, 57. Cohen. E . , Roberts, S. C . , Nordling, S.. and Uhlenbruck.G., Vox Sang., 1972, 23, 300. Lindahl, M., Faris, A , , and Waldstrom, T.. Lancet, 1982, 2, 280. Bird, G . W. G . , PhD Thesis, University of London, 1958. Lectins in Microbiology A. R. Archibald Microbial Technology Group, Department of Microbiology, The Medical School, Framlington Place, Newcastle upon Tyne NE2 4HH Following the early demonstration that bacteria could be agglutinated by lectins,’ the interaction between lectins and bacterial wall and surface polymers was observed by Hammar- strom and Kabat,2,3 who showed that Helix pomatia lectin precipitated streptococcal Group C polysaccharide and wall teichoic acid from Staphylococcus aureus, by Reeder and Eckstedt,4 who showed that concanavalin A precipitated staphylococcal wall teichoic acids that contained a-linked N-acetylglucosaminyl substituents, and by Archibald and Coapes,s who showed that concanavalin A precipitated isolated teichoic acid that contained a-glucosyl substituents and aggluti- nated various Gram-positive bacteria that contained such teichoic acids.Reaction between lectins and surface polymers was observed in Gram-negative bacteria by Hammarstrom et al. ,h who showed that Helix pomatia lectin precipitated polysaccharide from rough mutants of Salmonella typhi- rnurium. The interaction of bacterial dextrans, levans and mannans with concanavalin A was studied by Goldstein et al. in their classic series of papers7 published in the 1960s. Since these early studies, lectins have been applied in various areas of microbiology and selected examples are given in this paper.Microbial Lectins Microorganisms themselves contain a large number of differ- ent lectins that mediate the adhesion of the microorganism to surfaces. These microbial lectins are important as determinants of virulence in animal and plant pathogens, and in mediating the association between nitrogen-fixing bacteria and legumi- nous plants. The specificities of several of these lectins are well understood,x but the microbial lectins have not yet been exploited as analytical reagents, although this paper describes a study in which bacteriophages have been used as lectins specific for teichoic acid. Teichoic acid-specific bacteriophages include some having requirements for glucosyl, N-acetylglucosaminyl or N-ace tylgalactosaminyl substi tuen ts .‘I Use of Lectins in Diagnostic Microbiology Lectins have been used to differentiate“’ coagulase-negative and -positive staphylococci and for the laboratory identifica- tion” of Niesseria gonorrhoeae.Cole et al. 12 described the use of lectins to identify Bacillus anthracis, the causative agent of anthrax. Identification of the organism from clinical specimens is made difficult by its close relationships to B. cereus, B. mycoides and B. thuringiensis. However, rapid differentiation from other bacilli can be achieved by the use of appropriate lectins. Interaction of Lectins with Teichoic Acids Concanavalin A reacts with teichoic acids that contain a-glu- copyranosyl substituentss313 or a-N-acetylglucosaminyl substi- tuents4 and agglutinates bacteria that contain these teichoic acids.The specificity of the reaction has been used to show that different repeating glucosides in the wall teichoic acid of Lactobacillus plantarum C106 occur in different homogeneously substituted chains. l 4 Interaction with conca- navalin A has also been used to isolate and purify teichoic acid. 15 Wheat germ agglutinin precipitates both solubilised pepti- doglycan and teichoic acid that contains N-acetylglucosamine substituents and it agglutinates strains of Stuphylococcus aureus, Escherichia coli and Micrococcus luteus . I 6 Because of the polyelectrolyte nature of teichoic acid its interaction with Helix pomatia agglutinin,3 concanavalin A4.5.13 and possibly other lectins is more affected by salt and by extremes of pH than is the interaction of lectins with neutral polysaccharides.This appears to be due to pH- or salt-induced changes in conformation of the teichoic acid chains.” Localisation of Teichoic Acids in the Cell Wall Gold-labelled concanavalin A and wheat germ agglutinin and both ferritin- and peroxidase-labelled Helix pomatia agglutinin have been used to localise teichoic acid in walls of staphylo- cocci, streptococci and bacilli. 18-21 These studies have shown that teichoic acids are present at the outer surface of the cell wall and that some teichoic acid can also be detected at the inner wall surface. Birdsell et al.22 found that concanavalin A bound to B. subtilis in a discontinuous “fluffy“ layer of absorbed lectin extending about 40 nm outwards from the surface of the wall.The “fluffy” layer is thought to represent extended chains of teichoic acid sticking up from the surface of the wall and held together by the bound concanavalin A molecules. Attempts to determine the proportion of the total teichoic acid that is surface exposed have been reported by various workers. Doyle et al.23 showed that almost twice as much concanavalin A is bound by bacilli that have been treatedLectin - Gold Complexes as an Aid to Diagnosis in Histopathology David W. R. Griffiths City Hospital, Hucknall Road, Nottingham NG5 7 PB The use of lectin - gold complexes as probes for the ultrastruc- tural localisation of glycoconjugates is well established. 1- 3 Moreover, they are finding popularity at light level, where they can be used to replace conventional enzyme-labelled systems. especially when used in association with amplification pro- cedures incorporating a silver enhancement step.4.’ Selected areas of interest are included where specific lectin - gold complexes are used as an aid to diagnosis in the identification of vascular invasion in follicular carcinoma of the thyroid, renal transplant rejection and mesothelium in health and disease.Met hodolagy The application of directly conjugated lectin - gold probes for ultrastructural localisation of glycoproteins relies on the use of hydrophilic resins, such as Lowicryl K4M.l-3 The use of resins which are relatively stable in the electron beam, “cured” at low temperatures and hydrophilic in their polymerised form, removes the need to apply etching agents such as sodium ethoxide, sodium metaperiodate or hydrogen peroxide.which are usually required when hydrophobic epoxy resins are employed.270 ANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 The size of the gold particles used may be varied according to the initial reduction stages during the preparation of the monodispersed gold colloid. The use of appropriate reducing agents at different concentrations determines the range of particle size obtained.6 Different gold particle sizes are available commercially (Sigma, E.Y. Laboratories) conju- gated to specific lectins. Certain lectins, including those derived from Limax flavus and Triticum vulgaris, are difficult to conjugate to colloidal gold because of their relatively high isoelectric points,7 so indirect methods using highly selective glycoprotein bridges have been developed.Fetuin - gold complexes are used to localise the binding of L i m a fZavus,7 and similarly ovomu- coid - gold complexes localise binding to Triticum vulgaris.7~8 For light microscopical studies, it is either necessary to use gold particle diameters in excess of 20 nm in order that they may be resolved9 or alternatively to improve the over-all sensitivity of the method empl0yed.4~5.10 The increase in sensitivity may be achieved in a number of ways, e.g., immunolocalisation of the native lectin binding,lOJl silver enhancement of the gold probe4.5 or polarised epi-illumina- tion.12 These may also be used together in the same system. When using the preferred 5 nm diameter gold particles it is essential to incorporate the silver enhancement step and/or polarised epi-illumination, for visualisation purposes.Applications Current diagnostic applications of lectin - gold probes in histopathology include the demonstration of vascular invasion in tumours such as follicular carcinoma of the thyroid using the fuco-lectin Ulex europaeus agglutinin 1 (UEA 1), a marker of vascular endothelium. 10 With silver enhancement of the gold probe it has been shown that another fuco-lectin, Lotus tetragonolobus agglutinin, binds to vascular endothelium, albeit less strongly than UEA 1.10 The use of lectin - gold complexes in the assessment of renal transplant rejection is the subject of present research.13.14 Previous studies15 have demonstrated the ability of lectins to bind selectively to different sections of the human nephron and it is the potential of recognising different cell populations in sometimes morphologically indistinct samples such as those obtained using non-invasive and semi-invasive techniques (namely urine cytology and fine needle aspiration cytology) that may prove important.Identification of subtle changes in glycoprotein expression in proximal convoluted tubules may be found to be attributable to drug toxicity rather than changes found in the early stages of rejection. Similarly, demonstration of vascular endothelium in peri-glomerular vessels may iden- tify early damage and could be observed using UEA 1 - gold probes. In a pilot study assessing the lectin binding profiles in normal, benign and malignant mesothelium,16 early findings indicated that certain lectins, e.g., wheat germ agglutinin, bind selectively to the pleural surface of normal, reactive and malignant mesothelium.Where the differential diagnosis may depend on distinguishing the “epithelial”-type proliferations in mesothelioma from primary and secondary adenocarcinoma, such markers could prove invaluable. In the same study, Helix pomatia agglutinin was found to bind to the adenocarcinoma but not to the mesothelium. Although these are only prelimi- nary findings, it is apparent that lectin - gold complexes have exciting potential, especially in view of a recent study where monoclonal antibodies to antiepithelial antigens proved un- helpful in this area.17 Conclusion Lectin - gold complexes are relatively new histochemical tools, and their potential is enormous.Used with appropriate amplification procedures, light microscopical localisation of lectin binding in tissue sections and cytological preparations prove very sensitive. Already their uses in histological diag- nosis are well documented and in time we should see a greater use of lectin - gold probes in diagnostic histopathology. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. References Orci, L., Kunz, A., Amherdt, M., and Brown, D., Am. J. Pathol., 1984, 117, 286. Brown, D., Roth, J . , and Orci, L., Am. J. Physiol., 1985, 248, C348. Kunz, A., Brown, D., Vassalli, J. D., Kontturi, M., Kumpu- lainen, T., and Orci, L., Lab. Invesr., 1985, 53, 413. Holgate, C. S . , Jackson, P., Cowen, P. N., and Bird, C.C., J. Histochem. Cytochem., 1983, 31, 939. Hacker, G. W., Springall, D. R., Van Noorden, S., Bishop, A. T., Grimelius, L., and Polak, J. M., Virchows Arch. A , 1985, 406, 449. Horisberger, M., in Bullock, G. R., and Petrusz, P., Editors, “Techniques in Immunocytochemistry ,” Volume 3, Academic Press, London, 1985. Lucocq, J. M., and Roth, J., in Bullock, G. R., and Petrusz, P., Editors, “Techniques in Immunocytochemistry,” Volume 3, Academic Press, London, 1985. Geoghegan, W. D., and Ackerman, G. A., J. Hisrochem. Cytochem., 1977, 25, 1187. De May, J., Moeremans, M., Geuens, G., Nuydens, R., and De Brabander, M., Cell Biol. Int. Rep., 1981, 5, 889. Griffiths, D. W. R., and Stephenson, T. J., Med. Lab. Sci., 1988,45, 45. Leathem, A. J . C., and Atkins, N. J., in Bullock, G. R., and Petrusz, P., Editors, “Techniques in Immunocytochemistry,” Volume 2, Academic Press, London, 1983. De Mey, J., Hacker, G. W., De Waele, M., and Springall, D. R., in Polak, J. M., and van Noorden, S . , Editors, “Immunocy- tochemistry: Modern Methods and Applications,” Second Edition, Wright, Bristol, 1986. Griffiths, D. W. R., Cotton, R. E., and Hughes, D. A., in preparation. Hughes, D. A., Atkins, N. J., and Griffiths, D. W. R., Proc. R. Microsc. SOC., 1988, 2311, 4. Hennigar, R. A., Schulte, B. A., and Spicer, S. S . , Anat. Rec., 1985, 211, 370. Griffiths, D. W. R., Stephens, M., Dilks, B., and Jones, J. S . P., in preparation. Ghosh, A. K . , Gatter, K. C., Dunnill, M. S . , and Mason, D. Y., J. Clin. Pathol., 1987, 40, 19.

ISSN:0144-557X    

DOI:10.1039/AP9882500267

出版商:RSC    

年代:1988

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, AUGUST 1988. VOL 25 27 1 Practical Chemical and Biological Sensors The following are summaries of five of the papers presented at a Joint Meeting of the Analytical Division, the Micro & Chemical Methods, Electroanalytical and Biological Methods Groups and the South East Region held on December gth-loth, 1987, in the Scientific Societies' Lecture Theatre, London, W.1. The Challenge of Modelling and Synthesising Novel Organic Sensing Materials J. D. Wright Chemical Laboratory, University of Kent at Canterbury, Canterbury, Kent CT2 7NH Advantages of Organic Sensing Materials Organic sensing materials have many advantages. They can be used as highly sensitive semiconductor sensors'; some of them (e.g., conducting polymers) show electrochemical activity for use in electrochemical sensors, and their range of optical properties (colour, fluorescence, non-linear optical phenom- ena, controllable refractive index variation, etc.) also suggest sensor applications.Furthermore, weak interactions at their surfaces favour a fast response and reversal at lower temperat- ures than for polar solids, fine tuning of these interactions is possible (for example, via substituent effects and by varying molecular size and shape) and they are inherently biocompat- ible. Definition of the Modelling Process The process of modelling organic sensing materials involves identifying a useful phenomenon, conducting experiments to determine the chemical and physical material characteristics that optimise this phenomenon and hence deducing a model to rationalise the observed sensor sensitivity, reversibility and kinetics. Finally, further experiments are designed to refine the model for optimum operating conditions, interference phenomena, calibration and failure characteristics. In this paper these processes are illustrated by the use of phthalocyan- ines and related materials as semiconductor gas sensors.Stages in Modelling Organic Semiconductor Gas Sensors Effects of the Strength of Surface Interactions Early experiments exploring the effects of sinall amounts of NOz and BF3 on the semi- and photoconductivity of single crystals of perylene and metal phthalocyanines in a vacuum chamber established the effect of the strength of surface charge-transfer interactions on the magnitude of conductivity changes.2-3 Subsequent studies of films of phthalocyanines in a flow of air with up to 3 p.p.m.of NOz revealed kinetic phenomena, the conductivity increasing approximately with the logarithm of time (Elovich equation). These results were modelled in terms of the rate-limiting step being the displace- ment of surface oxygen species, the strength of surface charge-transfer interactions again being crucial.4,' Thus, non- planar lead phthalocyanine, having a higher ionisation energy than planar phthalocyanines, interacts more weakly with oxygen and hence responds more rapidly to NO2. Finally, the stronger the surface interactions, the more difficult is the reversal of the effects of NO2. This model shows that the concept of an optimum operating temperature for a sensor is complex. Sensitivity, response rate and reversal rate may each require different temperatures for their optimisation.Hence, although the increase in semiconductivity for lead phthalo- cyanine films with 300 p.p.b. of NO2 in air is slower and smaller at 100 "C than at 150 "C, for the smaller macrocycle tetraaza- dibenzo[ 14lannulene the corresponding response is larger at 60°C than at 100°C, owing to weaker surface interactions leading to thermal desorption at the higher temperature. Measuring the Strength of Surface Interactions The challenge of modelling a sensing material involves not only forming hypotheses from experimental data, but also devising novel experiments to test these hypotheses. As few data are available on heats of adsorption to provide a quantitative basis for models involving correlatioris with the strengths of surface interactions, two approaches for obtaining such data have been adopted.The first, involving measurement of rates of reversal of conduction enhancement in clean air at various tempera- tures following standard exposure to low NO2 concentrations, effectively measures desorption activation energies. These are found to depend on the extent of reversal, due to surface heterogeneity, so that it is impossible to compare results for different materials. Values ranging from 40 to 90 kJ mol-1 are obtained for NO2 on various phthalocyanines, in the range expected for weak chemisorption. The second method involves a fibre-optic interferometric calorimeter in a novel system for direct measurement of heat released during adsorption.Temperature changes of less than 1 mK have been measured and the problems of background drift and stability have been overcome. The challenge of modelling thus includes the challenge of developing novel techniques.6 Modelling of Factors Controlling Reproducibility During the above kinetic studies, it was observed that the sensitivity and response rate of freshly sublimed films to NO2 increased for the first few alternate 3-h cycles of exposure to clean air with and without 300 p.p.b. of NO2 at 150°C. Comparison of films pre-heated in clean air overnight with films not so treated showed that thermal treatment alone will produce this initialisation effect. These observations can be interpreted in terms of a model in which the number of active adsorption sites is increased by thermally induced crystallisa- tion, which can be observed directly by electron microscopy and which also accounts for spectroscopic changes following heating.However, they could also arise as a result of existing adsorption sites being populated more rapidly due to lateral repulsions from strongly bound NO2- facilitating oxygen displacement. This model is favoured by the observation of initialisation phenomena even for single crystal samples, by the272 ANALYTICAL PROCEEDINGS, AUGUST 1988. VOL 25 observed need for re-initialisation following exposure of initialised films to ultra-high-vacuum conditions and by the observation of slower kinetics following very thorough reversal of the NO2 enhancement of conductivity in well initialised samples. Photoconductivity studies3 provide evidence for the existence of the proposed traces of strongly bound N02, while the surface heterogeneity implicit in the model is confirmed by XPS, kinetic and desorption studies.Implications for Sampling Strategies and Interference This extension of the sensor modelling has practical implica- tions for sampling and avoidance of interference effects. For reproducible kinetics, sampling techniques must avoid exces- sive desorption of NO2. Water vapour, which has also been shown by XPS to be strongly bound,6 reduces the sensor’s response to N025 but, by operating in conditions where only the weakest surface sites are used for sensing, this interference can be minimised. Following detailed modelling as described, appropriate phthalocyanine films can be operated as practical NO2 sensors in quantitative agreement with commercial chemiluminescent detectors yet substantially simpler, cheaper, lighter, smaller and with lower power requirements.The development of practical organic sensors with quantitative applications depends critically on detailed evaluation of all revelvant parameters, as in the above example. General Conclusions for Sensor Modelling These examples illustrate several important general features for modelling novel organic sensing materials. Firstly, a wide range of experimental techniques are required for detailed modelling (in this instance electrical, spectroscopic, XPS, electron microscopic, kinetic, fibre-optic and calorimetric measurements).Secondly, modelling should include response characteristics over wide concentration ranges, kinetics and conditions for reproducibility and freedom from interference. Thirdly, concepts such as optimum operating temperature for organic sensing materials are complex, and a compromise between the requirements of sensitivity, rate of response, rate of reversal and freedom from interference may often be required. Synthetic Aspects The critical step in devising new organic sensors is the identification of materials that optimise the parameters deduced from the modelling process. The challenge of syn- thesising candidate materials lies not only in devising reactions to produce the desired molecules, but also in obtaining the purity, physical and chemical stability and desired physical form (film, single crystal, etc.) of the materials.Alternative synthetic routes may produce material of differing purity (e.g., template or non-template synthesis of macrocyclic materials), while literature reports of syntheses of candidate molecules may omit vital data (e.g., volatility, stability, purity) simply because the original aims of the syntheses did not include such criteria. Given the skills and resources of a modern synthetic chemist, devising reactions to produce specific molecules identified from the modelling process is rarely the most difficult challenge in developing new sensing materials. 1. 2. 3. 4. 5. 6. References Bott, B., and Jones, T. A., Sensors Actuators, 1984, 5 , 43. van Ewyk, R. L., Chadwick, A. V., and Wright, J.D., J . Chem. SOC., Faraday Trans. I , 1980, 76, 2194.. van Ewyk, R. L., Chadwick, A. V., and Wright, J . D., .I. Chem. SOC., Faraday Trans. I, 1981, 77, 73. Wright, J. D., Chadwick, A. V., Meadows; B., and Miasik, J. J . , Mol. Cryst. Liq. Cryst., 1983, 93, 315. Chadwick, A. V., Dunning, P. B. M., and Wright, J. D., Mol. Cryst. Liq. Cryst., 1986, 134, 137. Wright, J. D., Muter. Sci., 1987, 13, 295. New Directions in lonophores Richard E. Moss and Ian 0. Sutherland Department of Organic Chemistry, Robert Robinson Laboratories, University of Liverpool, P.O. Box 147, Liverpool L 69 3BX The use of ionophores in analytical chemistry has to some extent been restricted to cation transport through the mem- branes of ion-selective electrodes and ion-selective devices such as ISFETs (for papers on electrochemical sensors, see reference 1).Ion transport does not require very high values for association constants, K,, for complexation [equation (l)]: Ion + Ionophore F Complex . . . . . . (1) and, although K, tends to increase with increased ligand pre-organisation, for example in the sequence podand (e.g., 1) + coronand (e.g., 2) + cryptand (e.g., 3),* the first two ligand types are generally more useful than the third. This paper is focused upon the use of ionophores in a different type of analytical device, an optical ion sensor, where high values of K!; are required. The selection of ions by macrocyclic carriers, such as the coronands and cryptands, would be expected to depend ori cavity size and cation diameter and to be predictable by the examination of space-filling molecular models (CPK) or Ks * It is a pleasure to note the recent award of a Nobel Prize to D.J . Cram, J.-M. Lehn and C. J. Pederson for the discovery and development of crown ethers (coronands) and cryptands. co 0 07 0 Podand (1) K, = 102-104 Cryptand K, = 106-108 (3) Coronand Ks = 104-105 (2)ANALYTICAL PROCEEDINGS, AUGUST 1988. VOL 25 273 2 : I complex Normal 1 : 1 complex Induced-fit complex 10.K' 15-Crown-5.K+ 18-Crown-6.K' Di benzo-30-crown- (4) (5) (6) Fig. 1. Different types of ionophore - cation complex through molecular mechanics calculations. Such predictions are still difficult to make with confidence, in spite of the availability of extensive software packages+ for graphical input and output of structural information and a variety of molecular mechanics procedures.Difficulties arise from (i) failure to model correctly the electrostatic interactions that provide the major binding force in cation - ionophore complexes,+ (ii) failure to model solvent and counter-ion effects and (iii) the large number of possible free and complexing conformations for all but the more rigid ionophores. Nevertheless, in spite of these current problems, there is little doubt that computer- based molecular models will play an increasingly important role in the development of new selective ionophores. \ "7 0 Cryptate (7) Hemispherand (8) Spherand (9) Bridged hemispherand (10) Further difficulties in predicting the complexing properties of ionophores arise from the formation of 2 : 1 complexes (4), in cases where the cavity is too small to accommodate the t Packages come from commercial, industrial and academic sources.Our own studies are based upon CHEMX (Molecular Design), COSMIC (Dr. J. G. Vinter of Smith Kline and French) and MACROMODEL (Dr. Clark Still, Columbia University). $ The charge scheme in our work has been developed by Professor R. J. Abraham (Liverpool University) and his co-workers. We thank Professor Abraham for making his program available. cation in the normal 1 : 1 complex ( 5 ) , and the formation of 1 : 1 complexes (6) by flexible ionophores with very large cavities in which the ionophore adopts a conformation, very different from the minimum energy conformation of the free ionophore, which enables it to encapsulate the cation (induced fit).Such phenomena account for the complexation of Na+ by 12-crown- 4, K+ by 15-crown-5 (2: 1 complexes) and the preferential complexation of K+ by the very large cavity of benzo-30- crown-10 (1 : 1 complex). These possibilities are illustrated diagramatically in Fig. 1. To some extent these problems can be avoided by approp- riate choice of ionophore type. Thus, the bi- and poly-macro- cyclic cryptands form cation complexes (cryptates, 7), which avoid the possibility of 2 : 1 complexes and rigid ionophores, such as hemispherands (8) and spherands (9), adopt well defined (pre-organised) conformations in which the possibility of induced fit is either reduced (hemispherands) or virtually eliminated (spherands). These two strategies may be combined in compounds such as bridged hemispherands (10).The cation selectivities of a wide range of synthetic ionophores have been listed in a number of reviews2; it should be noted that values of K,, and to a lesser extent selectivity, are solvent dependent. Applications for cation sensing tend to be related to K, values in organic solvents (such as chloroform), as the cation is usually extracted from an aqueous phase before sensing by electro- chemical or optical techniques. b- b- U (a) (b) ion isa ble (12) Fig. 2. Different types of chromoionophore Synthetic ionophores which include chromophoric groups in their structures (chromoionophores) may respond to cation complexation [equation (2)] with a change in the absorption, fluorescence or even phosphorescence of the chromophore.Chromoionophores for cation complexation are of two types, neutral and ionisable, as summarised in equations (2a) and (2b) and illustrated diagramatically in Fig. 2. Ion + Chromoionophore Complex . . (2) Neutral: CI + M+ e CI.M+ . . . . . . (2a) Ionisable: CIH + M+ s CI-.M+ . . . . (2b) Neutral chromoionophores (CI) contain a polarised chrom- phore linked to the ionophore in such a way that the electrostatic field of a complexed cation changes the absorption spectrum. The polarisation indicated in l l b gives better ion binding as the chromophore also functions as a binding site. Ionisable chromoionophores (CIH) ionise in the presence of a bound cation if the pH is appropriate; the resulting change in the absorption spectrum is usually greater than for a neutral chromoionophore and the absorption spectrum of the complex CT-.M+ (12a) shows a shift to longer wavelength compared with the spectrum of the anion CI-.Ionisable chromoiono- phores for M+ are ideally mono-protic (CIH) whereas those for M2f should be diprotic (CIH2) to give the complexes CP- .M2+ (12b). Chromoionophores of both types have been the subject of reviews.3 Our work on chromoionophore-based cation sensors4 has been carried out in collaboration with Dr. J. F. Alder and his274 ANALYTICAL PROCEEDINGS. AUGUST 1988. VOL 25 X a : X = NO2 (14) colleagues at UMIST (DIAS). The initial studies were based upon neutral chromoionophores of both types, l l a and l l b , but it soon became apparent that these were not sufficiently sensitive to detect metal cations in concentrations of interest (1-100 mM) and that, in any case, cation induced spectroscopic changes were small.The ionisable chromoionophores (CIH) 13 and 14 proved to be more promising and the possibility of incorporating these compounds into optical fibre probes was investigated by Dr. D. Ashworth (UMIST). All five compounds showed a substantial colour response (yellow --$ purple) on formation of the salts CI-M+ and one of them, 13b, proved to be suitable for the measurement of K+ concentration (KCI in H20) at concentra- tions found in human blood plasma (blood K+ = 4.5 mM) over the pH range 7-9. The K+ to Naf selectivity ratio (6.4) was too low to determine K+ levels in blood (Na+ : K+ ratio = 30) and current work is focused on improving this selectivity ratio by using a suitably modified hemispherand system,s such as 15, or a valinomycin mimic such as a suitably modified dibenzo-30- crown-10.6 We note that an optical fibre sensor for K+ in human blood plasma that is based on an ionisable chromoiono- phore CIH would require simultaneous pH measurement.In addition, the chromphore should have (i) K, for K+ in water between ca. 100 and ca. 1000 1 mol-1; (ii) a ratio of Kb for K+ to Naf of >300; (iii) a light-stable ionisable chromophore which gives optimum performance in the physiological pH range; and (iv) low water solubility to avoid leaching whem immobilised by absorption on polystyrene or a similar hydrophobic polymer support. Requirements such as these represent an exciting challenge for the rapidly developing area of host - guest chemistry.References 1. J . Chern. SOC., Faraday Trans I , 1986, 1033. 2. Inoue, Y., and Hakushi, T., J . Chem. SOC., Perkin Trans. I , 1985, 935. 3. Takagi, M., and Ueno, K . , Top. Curr. Chem., 1984, 121, 39. 4. Alder, J. F., Ashworth, D. C., Narayanaswamy, R., Moss, R. E., and Sutherland, I. O., Analyst, 1987, 112, 1191. 5. Cram, D. J., and Ho, S. P.. J . Am. Chern. SOC., 1986,108,2998. 6. Grootenhuis, P. D. J . Van der Wal, P. D.. and Reinhoudt, D. N., Tetrahedron, 1987, 43, 397. What Does the Biomedical Area Require of Biosensors? P. Vadgama Department of Clinical Biochemistry, The Medical School, Framlington Place, Newcastle upon Tyne NE2 4HH The sheer size of the medical diagnostic market makes the biomedical area remain ill defined and somewhat controver- biomedical area one of the most important targets for sial.The reality is that the medical environment is a complex biosensor research. In addition to practical benefits for patient and rapidly evolving one, often making contrasting demands and clinical end user alike, biosensors offer a powerful on support technologies. additional investigative tool for biomedical research. It may It has become relatively easy to cite the range of ideal appear surprising, therefore, that despite a growing academic requirements for biosensors (Table 1) which remain the same and commercial interest in biosensors, the precise needs for the as for any chemical sensor. Few biosensors, however, can nowANALYTICAL PROCEEDINGS.AUGUST 1988. VOL 25 275 match up to these requirements in their entirety, and in practice there has been a stepwise progression towards improved tolerances and performances. varying with a chosen medical application. A biosensor incorporates immobilised biochemical or chemical reagents, and so, for example, re-usability has proved the most easily attainable; good precision is also readily possible as few steps are involved in a biosensor analysis. The most difficult requirement to achieve has been predictable behaviour in blood, and to date most biosensors lack the biocompatability necessary for reliable operation for even short periods in blood. There also remains some uncertainty over the medical acceptability of even the most practical of devices. Choice of a system in the medical area can be governed more by prior practice and convention than the usefulness of a novel technology; slow acceptance is the norm here.This article will briefly outline some of the issues surrounding laboratory and bedside biochemical testing that may have a bearing on the future biomedical use of sensors. Table 1. Important requirements for chemical sensors” Selective Small Cheap Robust Manufacturable Non- toxic Reliable Precise Reusable Predictable Stable Accepted (in blood) * Adapted from reference I Laboratory Use Large , expensive analysers are currently the dominant feature of central hospital biochemistry laboratories, where the bulk of medical analyses are carried out. Such analysers are able to process upwards of 60 specimens per hour with 15 tests per specimen.The resulting high over-all throughput has been made possible by a careful adaptation of standard chemistries over the years to the special needs of automation. It would seem highly unlikely that biosensors in their present form, with their relatively slow response, would be able to make any significant inroad into this sphere of high-speed analysis. The test request input of the laboratory, however, is highly variable’ with additional. unpredictable demands for emergency analysis; large analysers lack the flexibility to respond to these unscheduled demands, and there remains a need for smaller. more flexible systems for small batch analysis. It is here that cheap, and operationally simple, biosensors could make a major contribution.In order to achieve success it may not always be necessary to invent new biosensors. The need, at present, is more for existing biosen- sors to be developed to a stage at which they can be used for the assay of biological fluids. It is also important that they furnish the degree of analytical simplification that can be competitive with current technologies. The best example of success without “new science” is the slide-format ion-selective electrode of the Kodak Ektachem Analyser.3 No new chemistry has been invented here, but the fabrication of electrodes in a reprodu- cible slide format has permitted electrode use without a pre-calibration step, and furthermore has been a good example of technological inventiveness. Automated, self-calibrating blood gas analysers (for blood pH, pCOz and PO, measure- ment) provide the more obvious example of classical sensors adapted for clinical use; the current generation of analysers incorporate trouble-shooting and computational facilities which now permit their use by clinical personnel. The greater internal complexity of such analysers, however, precludes simple maintenance, and difficulties can arise in acute care laboratories that are away from main laboratory supervision; a useful pointer as regards needs from these laboratories is that other than blood gas and electrolyte (Na+, K+, Ca2+) analysis, work has centred on the measurement of haemoglobin, haemotocrit and osmolality,4 parameters not readily amenable to sensors.while of the metabolites, only an established need, as yet, exists for glucose.Whatever the perceived advantages of biosensors there is no guarantee that novel metabolite- and immuno-sensors would see immediate use in the acute-care laboratory. For clinical diagnostic purposes the requirement for preci- sion is rather greater than that for accuracy; the objective here is essentially to relate a given parameter measured in the patient to the corresponding reference range in a normal population using a similar method. Based on clinical opinion, precision requirements would permit coefficients of variation of -3%. With regard to the highly competitive diagnostic market, however, a more appropriate target would be CVs of under 170, as attained by many large analysers. The precision requirement may vary with the level of the measured parameter, and will be greatest for levels at or near the limit of the reference range; correct designation of a result here as either “normal” or “abnormal” becomes important for diag- nostic purposes.5 Bedside Use In-vitro Assay There is a current vogue for decentralised biochemical testing; the wholesale transfer of biochemistry to the bedside, or even to a supervised side-room, however, must await appropriate, highly robust analysers capable of resisting a spectrum of operator errors.Avoidance of the need to calibrate with an ability to assay whole blood would be the minimum functional requirements. However, it is vital that whatever the analyser capability. the results generated should match those of the main laboratory, and that assays should form part of a laboratory-run quality assurance programme. Demands on accuracy and precision could be made less stringent than those for a laboratory analyser if there remained a clearly identifiable benefit to the patient, such as earlier, more effective therapy.Part of the need for extra-laboratory assay is already being satisfied by desk-top analysers, which employ dry reagent chemistries and measure reflectance. Indeed, in one such system (Reflotron, Boehringer, Mannheim) a filtration step for red-cell removal allows the assay of whole blood. The commercial viability of competing biosensors may thus eventu- ally depend on marginal differences in cost, ease of use or reliability. For the present, it would appear that instrumenta- tion for biosensors can be made cheaper, at least for devices based on electrochemical detection, that plasma separation from whole blood can be avoided, and that the equilibrium signal of a biosensor would eliminate the need to time a reaction. It is.furthermore, possible that biosensors may provide more precise data. Thus, a recent evaluation of commercial glucose home monitors employing dry reagent chemistries demonstrated a generally unacceptable precision and accuracy% there are also reports that performance during routine use falls below that reported under controlled labora- tory conditions. For any analytical system, precision in any case is poorer for low concentration analytes (drugs or hormones) , and the problem may be compounded with measurements made at the bed-side. Screening It is useful to consider what consequences might follow from the blanket availability of reliable biosensors usable by the clinician.It is attractive to believe that screening would become commonplace with major health benefits to society and a resounding commercial success for the manufacturers. Past experience of screening indicates that such a situation is unlikely to be realised. For any measured parameter, key criteria would first need to be satisfied, notably whether a test276 ANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 detected the disease early, whether there was any benefit of earlier therapy and what risks there were to a misclassification and inappropriate therapy. One problem of interpretation arises simply from the definition of a normal result.If “normal” is regarded as being within k 2 s.d. of the mean of population, then 5% without the disease will have an abnormal result; with 6 screening tests, 26% of the population will have an abnormal test result and for 12 tests 46% will have an abnormal test result. Indeed a recent report7 has emphasised that there is no indication for the general biochemical profiling of either the ambulatory or the preadmission patient, that the value of grouped tests was uncertain and that only screening for specific, individual parameters was indicated ( v i z . , glucose, cholesterol, creatinine). Continuous Monitoring The one undisputed feature of biosensors to have captured the imagination of analyst and clinical end-user alike is the ability to provide continuous measurement of biochemical paramet- ers.This makes for an important departure from intermittent sampling and estimating of blood biochemistry, the predomi- nant feature of contemporary clinical practice. Continuous monitoring may be of particular benefit, however, as regards metabolically unstable, or critically ill patients, and may not only give early warning of an unexpected deterioration in the condition of a patient, but would provide a rapid indication of any response to therapy, permitting more accurate titration of appropriate therapy. Additional scientific benefits would be: improved understanding of short-term fluctuations of para-. meters; insight into dynamic interactions between inter- mediary metabolites; and the eventual designing of improved artificial biofeedback systems.An early example of the benefits that might accrue is illustrated by transcutaneous pOz monitoring of critically ill neonates using heated skin sensors. The high instability of blood p 0 2 in such patients, unmasked by this monitoring, has done much to modify neonatal intensive care practice and reduce the cumulative dangers of hyper- and hypoxia. Certainly here, accuracy has not been a primary consideration, and even with adult patients, where transcu- taneous O2 measurements do not fully correspond to arterial p02, there have been important advantages to using the sensors for trend monitoring. Equivalent opportunities exist for metabolite and ion sensors, provided they are capable of clinical, rather than experimental use; some indication of this is provided by the information obtained from implantable glucose sensors used so far for short-term monitoring.It needs to be recognised, though, that continuous monitoring offers much smaller market opportunities than those relating to in vitro testing. Conclusion Biosensors could satisfy analytical needs in the biomedical area at several different levels. However, even if all the hoped-for goals are achieved (Table l), it is unlikely that biosensors will ever entirely replace existing methods; it seems more likely that they will have a complementary role to play. In order to target biosensors more reliably to clinical needs, it is now important to have research efforts which involve the clinical end-user more fully than has been the case in the past.1. 2. 3. 4. 5. 6. 7. References Savory, J . , Bertholf, R. L., Boyd, J. C., Burns, D. E., Felder, R. A., Lovell, M., Shipe. J . R., Wills, M. R., Czabas, J . D., and Coffey, K. F., Anal. Chim. Acta, 1986, 180, 99. Johnstone, J . H., in Alberti, K. G. M. M., and Price, C. P., Editors, “Recent Advances in Clinical Biochemistry,” Churchill Livingstone, Edinburgh, 1978, pp. 201-227. Walter, B., Anal. Chem., 1983, 55, 498A. Hall, J . R., and Shapiro, B. A., Crit. Cure Med., 1984, 12,530. Fraser, C. G., Pathology, 1980, 12, 214. North, S . , Steiner, J . F., Woodhouse, K. M., and Maddy, J . A . , 1987, 10, 360. Cebul, R. D., and Beck, J . R., Ann. inntern. Med., 1987, 106, 403. Biosensors for Clinical Analyses Jane E. Frew and Monika J. Green MediSense Inc., 14 Blacklands Way, Abingdon, Oxfordshire OX 14 1 DY The clinical chemistry laboratory monitors a multitude of analytes ranging from naturally occurring low relative molecular mass species such as glucose, cholesterol and triglycerides to drugs including aspirin, paracetamol, tricyclic antidepressants and antibiotics.There is also a requirement to measure elevated enzyme levels as indicators of diseased states. Mosl: of the existing assays for such analytes are spectrophotometric: or colorimetric, very often involving extensive sample pre-treat- ment . The application of electrochemical techniques to clinical diagnostics offers a number of advantages over these pro- cedures. For instance, the ability to perform measurements on turbid solutions removes the need to centrifuge whole bllood samples prior to assay.This paper describes three different approaches to the design of amperometric biosensors. Direct Electrochemical Monitoring of the Product of an Enzymatic Reaction The analyte is a substrate for a specific enzyme This is the simplest of the three approaches, the analyte of interest being converted to an electroactive product by the action of a specific enzyme. Assays for paracetamol (acefami- nophen) and aspirin (acetyl salicylate) can be configured i n this way. These are two of the most commonly used drugs in overdose situations1 and it is particularly important to be able to discriminate which drug or combination of drugs has been taken by the patient. Treatment is not only dependent on the type of drug taken, but also the levels of free drug present in the blood. Par acetamol Although paracetamol is itself electrochemically active, there are a number of reasons for not monitoring it directly.It is important that the assay is specific for paracetamol and not subject to interference from either conjugated forms of the drug (clinicians are interested only in monitoring the unconju- gated levels) or any other compounds. At the potentials required to oxidise paracetamol there will be considerable interference from oxidation of other species in blood and possibly some conjugated forms of the drug. An assay specific for paracetamol can be designed based on the following enzymatic reaction: NHCOCH3 OH Paracetamol OH p-Am i no p h e n o IANALYTICAL PROCEEDINGS, AUGUST 1988.VOL 25 277 Aryl acylamidase (E.C. 3.5.1.13) catalyses the hydrolysis of the unconjugated drug to yield p-aminophenol, which under- goes electrochemical oxidation at much lower potentials. Under appropriate conditions paracetamol may be monitored over the clinical range (0-3 mM) not only in buffer, but also in serum and whole blood. Aspirin The rapid deacetylation of aspirin in blood yields salicylate, which can be detected in an assay incorporating salicylate hydroxylase (E. C. 1.14.13.1): Salicylate hydroxylase + 0 2 + NADH + 2H' coo- Sa l i cy l ate Catechol Catechol is a product of the enzymatic reaction and can be readily oxidised electrochemically. Preliminary data suggest that this could form the basis of a quantitative assay for salicylate over the clinical range (0-10 mM).The analyte is an enzyme The assay is based on the conversion of a labelled substrate into an electroactive product. This approach lends itself to assays for hydrolytic enzymes and is demonstrated for the detection of a-amylase. The determination of a-amylase (1,4-a-~-glucan glucanohy- drolase, E.C. 3.2.1.1) activity is widely accepted as a test for the diagnosis of acute pancreatitis and obstruction of the pancreatic duct. A variety of methods have been described,'-' but many of these use ill-defined insoluble substrates, leading to heterogeneous kinetics and hence slow, insensitive assays. A more satisfactory approach is to use a soluble, well defined substrate. Thus, an assay for a-amylase has been devised using 4-aminophenyl-a-maltopentaoside as substrate.In the presence of analyte this compound is hydrolysed to smaller subunits which are themselves substrates for a-glucosidase (E.C. 3.2.1.20). p-Aminophenol is the final product and the assay is dependent on monitoring p-aminophenol formation. The sensitivity can be increased by the use of longer incubation times and elevated temperatures. A linear calibration over the clinical range (50-1000 U 1-1) has been obtained in whole blood. Mediated Enzyme Electrodes This final type of assay relies on electrochemically interroga- ting the redox state of an enzyme using small-molecule, redox-active species or mediators. The principle is illustrated by assays for cholesterol. The analysis of total cholesterol is routinely performed in the clinical laboratory. Excessive cholesterol in plasma can lead to atherosclerosis, which is the progressive deposition of choles- terol into arterial plaques, ultimately resulting in arterial occlusion.The normal range of serum total cholesterol in adults varies from 3 to 12 mM and is dependent on the age, sex and diet of the individual.4 Traditional assays are non-enzymatic, involving chemical treatment of cholesterol to yield coloured products that can be measured spectrophotometrically.5 More recently, the specificity afforded by enzyme reagents has been introduced into cholesterol determinations.6 Cholesterol esters in serum must first be dissociated from lipoprotein complexes by the action of a surfactant before the enzymes can act on the substrate esters. Free cholesterol may then be liberated by the action of cholesterol esterase (E.C.3.1.1.13): Cholesterol esters + Cholesterol esterase cholesterol + fatty acids Three amperometric assays for cholesterol have been designed,' all of which use ferrocene derivatives to mediate electron transfer between enzyme and electrode. The choles- terol can be: (a) oxidised by a specific flavoprotein oxidase coupled to the ferricinium ion; (b) oxidised by a dehydrogenase and the NADH generated can then be detected by a coupled reaction based on diaphorase - ferricinium ion; or (c) oxidised by an oxidase and the hydrogen peroxide formed detected using horseradish peroxidase; ferrocene is acting as an electron donor in this instance and the ferricinium ion is reduced at the electrode. All three assays measure cholesterol satisfactorily.Conclusions A number of approaches to assay design have been described, but what are the commercial possibilities for such systems'? It is now approximately 5 years since ferrocene (Fc) derivatives were found to act as mediators to a range of flavoprotein enzymes.s.9 including glucose oxidase. In this period a dispos- able biosensor for glucose has been developed9.") based on the following sequence of reactions: GOD,, + glucose --+ GODred + gluconolactone 2Fc z 2Fc-t + 2e- GOD,,d + 2Fc+ -+ GOD,, + 2Fc + 2H+ Single-use disposable strips incorporating enzyme and mediator are used in conjunction with a pen-sized glucose meter to measure glucose in whole blood samples. The test takes 30 s after application of the blood to the strip.The results compare favourably with those given by existing systems. This example illustrates those features of biosensors that should ensure future success in the commercial marketplace, namely small size, portability, ease-of-use, rapid results, accuracy and precision. 1. 2. 3. 4. 5 . 6. 7. 8. 9. 10. References Pesce. A. J . , and Kaplan, L. A., Editors. -'Methods in Clinical Chemistry," C. V. Mosby, St. Louis, MO. USA. 1987. Renneberg. R., Scheller, F., Riedel. K., Litschko, E.. and Richter, M., Anal. Lett., 1983, 16(B12). 877. Ying Foo, A.. and Brosalki, S.. Ann. Clin. Riochem., 1986.23. 624. Tietz, N. M., Editor, "Fundamentals of Clinical Chemistry." Saunders, Philadelphia, 1976. Tonks, D. B . , Clin. Biochem, 1967, 1, 12. Zak. B., Clin. Chem., 1977, 23.1201. Ball, M. R . , Frew, J . E., Green. M. J . , and Hill, H. A. 0.. Proc. Electrochem. Soc., 1986, 8614. 7. Cass, A. E. G., Davis. G . . Francis, G . D.. Hill, H. A. O., Aston. W. J . , Higgins, I. J . , Plotkin. E. V.. Scott, L. D. L.. and Turner, A. P. F.. Anal. Chem.. 1984, 56, 667. Cass. A. E. G., Davis, G . . Green, M. J . . and Hill. H. A. 0.. J . Electroanal. Chem., 1985, 190. 117. Matthews. D . R . , Holman. R. R., Bown. E., Steemson. J., Watson, A., Hughes. S.. and Scott, D.. Lancet. 1987, 1, 778.278 ANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 Water Quality Monitoring Using Chemical and Biological Sensors A. J. Dobbs and M. G. Briers Water Research Centre, Medmenham Laboratory, P. 0. Box 16, Marlow, Buckinghamshire SL7 2HD A great deal of water quality monitoring is undertaken in the UK by water utilities, usually for one of four reasons: compliance with regulations; monitoring of process operation; early warning of possible problems; or surveys.In the main, such monitoring is carried out using conven- tional laboratory equipment. But in the area of intake protection, the main subject of this paper, sensors are used for water quality monitoring. The Water Research Centre (WRc) is involved with the development of such sensors and this paper presents aspects of the work. The term intake protection is used to cover the monitoring of surface water that is being abstracted for treatment to produce drinking water, the aim being to detect abnormally high concentrations of chemicals which could affect consumers or damage the treatment plant.In the UK about 30% of the water we drink comes from lowland rivers, other major sources being upland reservoirs and groundwater. Lowland rivers are a cheap source of water, but are more prone to pollution, accidental or otherwise, than the other sources. The pollutants involved in the closure of lowland intakes are shown in Table 1. Table 1. Pollutants affecting lowland intakes Percentage Pollutant occurrence. 94 Fuel oils 40 Farm waste 10 Sewage 10 Plating effluent 5 Phenols 5 Other chemicals from industry or road accident 30 About half of the major intakes in the country have bankside storage of raw water with residence times of between 1 and 60 d, but the remainder have none and water typically passes through the treatment works and into distribution within 4.h. With or without storage the raw water needs to be continuously monitored and if there is no bankside storage the monitors need to have a fairly rapid response. At most intakes temperature, dissolved oxygen, conductiv- ity, pH and turbidity are routinely measured. These are mainly used for feed-forward control of the treatment process. Of these five criteria only dissolved oxygen and turbidity are likely to provide an indication of river condition and possible pollution. An on-line ammonia monitor can provide a better indication of pollution because ammonia is one of the most common pollutants discharged into rivers in the UK, usually from sewage overflows and farm slurries. High ammonia levels will result in higher chlorine demands during treatment in order to maintain a fixed chlorine residual after the treatment process, and may also indicate higher levels of organics than usual.Oil pollution is disruptive to treatment processes but the warning surface film can often be seen and can be boomed off if necessary as most intakes are submerged. The dissolved oil fraction cannot be so readily removed. WRc has developed a monitor which can measure this dissolved fraction. It works by bubbling air through the water to strip off the volatiles. The air is then passed over semiconductor gas sensors which detect the presence of hydrocarbons. Although the monitor was designed for measurement of oils it also has potential for monitoring other volatile organics and this potential is currently being assessed.Previous incidents can provoke the installation of instru- ments to monitor specific pollutants, a particular example being the HPLC configured for phenol installed by North West Water after an incident in the River Dee in January, 1984, which lead to about 1 million people in Liverpool receiving water contaminated with chlorophenols. Such a system could be extended to other specific pollutants, although both the capital and operating costs are high and there remains the problem of unidentified or unexpected pollutants. What is required is a sensor that shows a fast response and is relatively non-specific or broad band, so that it responds to a wide range of potential pollutants. This is an unusual requirement compared with those of most users of chemical and biological sensors, who require specificity.For several years now WRc have been considering fish as potential sensor systems. This research has resulted in the development of a monitor based on fish respiration: this could be considered to be a biosensor with whole, live fish as the sensor element.' The WRc fish monitor has now been combined with a computer and communications package to provide an intake protection system. In the fish monitor eight fish (rainbow trout) swim freely in individual tanks. Each fish produces small voltages in the surrounding water of about 100 pV in amplitude. When the fish is stationary most of the signal comes from the muscles associated with ventilation and is approximately sinusoidal. The small voltages are amplified and digitised.A computer is used to calculate the frequency and power of the signals from each fish. A sensitive test of fish condition is made by comparing current breathing frequencies with those of the recent past. If the frequencies stray outside pre-determined limits the computer raises an alarm and can initiate other actions, such as flashing warning lights, etc. Micro-organisms are also being studied for possible use as broad-band pollution monitors. One way is to measure the rate of substrate consumption or product formation. Another method is to look at the inhibition of the electron transport systems of the cells. WRc has let a contract to Luton College of Higher Education to develop this approach with assistance from Cranfield Institute of Technology. At present the photosynthesis in selected species of cyanobacteria is being studied .2 Chemical mediators, such as potassium hexacyanofer- rate(III), are used to take electrons from the electron transport system of the cells and deliver them to an electrode which is poised with respect to an Ag - AgCl reference electrode.The resultant current is related to the metabolic rate of the Dark Light Dark 4 I 3 f . g 2 - L 3 u 1 0 12 24 36 48 60 Time/m in Fig. 1. Effect of diuron on cyanobacteriaANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 Edited by A. Berlin, Health and Safety Directorate, Commission of the European Communities. R. H. Brown, Occupational Medicine and Hygiene Laboratories, Health and Safety Executive. K. J. Saunders, B.P. Research. ’ The main purpose of this important new book is to: I 0 review the state of the art of diffusive sampling techniques.0 stimulate the exchange of technical information. 0 assess the suitability and range of applications for workplace air monitoring. 0 promote the further development of this technique and its wider use. 279 organisms. The cells are held on to the working electrode by nylon mesh. This electrode, together with a reference elec- trode, is then housed in a flow cell. The mediator and water sample are pumped over the electrodes. A red LED mounted in the flow cell above the working electrode provides the energy to stimulate photosynthesis. The stimulation is applied inter- mittently with the change of current which results from light off to light on being measured. An early result is shown in Fig. 1. This shows the effect of a herbicide, diuron, at 1 VM on cyanobacteria. After 8 min or SO the light is turned on: both control and test currents show an increase in current. Diuron is added to the test at about minute 15 and a sudden drop in current occurs at about minute 20. The control current remains constant until the light is switched off. Tests that have been conducted so far have shown that the sensors are particularly sensitive to herbicides. References 1. Evans, G. P., Johnson, D., and Withell, C., “Development of the WRc MkIII Fish Monitor: Description of the System and its Response to Some Commonly Encountered Pollutants,” WRc Environment Technical Report 233, Water Research Centre, Medmenham, 1986. Rawson, D. M., Willmer, A. J . , and Cardosi, M. F., Toxicity Assess, 1987, 2, 325. 2. DIFFUSIVE SAMPLING An Alternative Approach to Workplace Air Monitoring ROYAL SOCIETY OF CHEMISTRY lnformat ion Services Diffusive Sampling is based on a symposium held in Luxembourg in September 1986 and organised jointly by the Commission of the European Communities and the United Kingdom Health and Safety Executive, in cooperation with the World Health Organisation and the Royal Society of Chemistry. The meeting was attended by an international audience including delegates from the USA as well as all major European countries. The book will therefore be of interest to health and safety officers and environmentalists, in industry, hospitals, governmental and academic institutions worldwide. Hardcover 500pp ISBN 0 85186 343 4 Price €45.00 ($87.00) To order or for further information, please write to: Royal Society of Chemistry, Distribution Centre, Blackhorse Road, Letchworth, Herts SG6 IHN, UK, or telephone (0462) 672555 quoting your credit card details. We now accept Access/Visa/MasterCard/EuroCard. RSC Members are entitled to a discount on most RSC publications and should write to: Membership Manager, Royal Society of Chemistry, 30 Russell Square, London WClB 5DT, UK.

ISSN:0144-557X    

DOI:10.1039/AP9882500271

出版商:RSC    

年代:1988

数据来源: RSC

摘要:

2x0 ANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 Equipment News Computerised Gas Analysis An inclusion piercing system, developed from known computer-controlled mass spectrometry techniques, offers accurate quality control for integrated circuit pro- duction. Based on the makers' QMG 511 quadrupole mass spectrometer, the GIA707 system is designed for the failure analysis of hermetically sealed integrated circuit packages and the identification of minute gas inclusions, or bubbles, often found in integrated circuit packaging materials, such as minerals, plastics and glass. Balzers High Vacuum Ltd., North- bridge Road, Berkhamsted, Hertford- shire HP4 IEN. Ultraviolet - Visible Spectrophotometer The Spectrascan 2800 is a double-beam instrument offering maximum flexibility by means of plug-in modules, which allow research and routine analyses to be per- formed on the same optical bench.In its standard format the 2800 is a fully opera- tional low-cost scanning spectropho- tometer, with an interactive 32-character LCD, enabling routine parameters to be set and data to be displayed in real time. With the addition of a chart recorder full spectral recording in the range 200-1100 nm can be completed at a maximum speed of 2400 nm min-1. For quality control applications a full quantitative analysis program with four methods of standard plotting is provided. Module options include a monochrome or 6-colour CRT, a chart recorder and a multi-colour X - Y plotter. Ciba Corning Diagnostics Ltd., Hal- stead, Essex C 0 9 2DX. Data Management Systems for Spectrometry The Polyvac control and data manage- ment software offered for the makers' range of optical emission spectrometers is now available for use with a wide variety of IBM and IBM-compatible computers.The new IBM-compatible software is faster than earlier Polyvac software, and a 20 Mbyte Winchester disk allows more results storage capacity than previously offered. The new software can be used together with commercially available standard software, so that, for example, analytical results can be transferred into standard database or word processor files. A choice of hardware is offered with the Polyvac systems. Hilger Analytical Ltd., Westwood, Margate, Kent CT9 4JL. Data System for Infrared Analysis The PU9500BDS IR data system com- bines the PU9500 ratio-recording spectro- tions.As the makers have overcome the photometer with the Amstrad PC1640 problem of peak tailing, the LGEM running Philips colour graphics BIRD soft- detectors are suited to analysing softer ware. This software offers interactive X-rays, allowing excellent linearity and Philips Analytical PU9500BDS IR data system spectral subtraction, disk storage, quanti- tative spectroscopy and both a split- screen and superimpose facility for quali- tative comparison. Philips Analytical, York Street, Cam- bridge CB1 2PX. Fourier Transform Infrared Spectrometer The FTS-7 instrument introduces the first Digilab spectrometer with a newly devel- oped mechanical bearing. A 60" Michel- son interferometer and 12 mm beam size ensure high throughput and good signal to noise ratios.An external beam option is available. The spectral range is 4800-400 cm-1 with standard resolution of 2 cm-l. The FTS-7 is supported by an advanced data station and software package. A 26 MB Winchester and floppy disk back-up is standard with up to 280 MB Winches- ters available. SEARCH and QUANT pack- ages are available as options. Polaron Equipment Ltd., 53-63 Green- hill Business Park, Watford, Hertford- shire WD1 8QS. Materials Analysis Detector A range of intrinsic hyper-pure german- ium detectors for materials analysis is announced. Known as LGEM, these new devices offer a viable alternative to con- ventional lithium drifted silicon [Si(Li)] detectors. Germanium has a significantly higher stopping power than silicon, there- by extending the efficiency range. This is exhibited in the detection of higher- energy X-rays, such as those from K-shell transitions for heavy elements, and resol- ution does not suffer from overlaps asso- ciated with lower-energy L and M transi- line shape right down to carbon.LGEM detectors also offer high resolution, resol- utions better than 130 eV having been regularly obtained, while peak widths less than 120 eV have been observed. Link Analytical Ltd., High Wycombe, Buckinghamshire. Raman Spectrograph The Jobin Yvon S-3000 Raman triple spectrograph is suited to both research and routine industrial applications. Unlike the current generation of Raman spectrometers, in which data acquisition and spectrometer control are often independent functions, the S-3000 is a completely integrated system combining all the hardware and software functions into a simple and easy to use package.A large number of security and validity tests are incorporated and the S-3000 software also performs automatic background sub- traction and linearisation of spectra from diode position to wavelength for multi- channel detectors. Automatic wavelength calibration ensures precise and reprodu- cible positioning of the spectrometer. Instruments SA-EDT Ltd., 14 Trading Estate Road, Park Royal, London NWlO 7LU. Columns for Sample Preparation The Bond Elut LRC range of columns feature a re-designed extraction column capable of accepting liquid volumes of up to 10 ml. This large reservoir capacity means that sample loading, column wash- ing and elution steps can be performed easily without fear of spillage.Extractions may often be carried out without having to resort to additional reservoirs, thusANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 28 1 reducing manipulations to a minimum. The columns are therefore especially suit- able for applications involving potentially hazardous samples, such as biological fluids. Available with 100, 200 or 500 mg sorbent beds, LRC columns can be used with the makers’ Vac Elut and the recently announced Vac Elut SPS 24. Analytichem International, P.O. Box 234, Cambridge CB2 1PE. Interface for Chromatography Data Handling Systems A new interface allows the makers’ Model 727 single-channel integrator and Model 747 multi-channel, multi-tasking data system to be run on the IBM PS/2 series of computers.The interface consists of a module with a special high-speed com- munications link to permit the real-time acquisition and display of data from 1 to 6 detectors. Simultaneous chromatogram editing and reprocessing are offered in the same way as on the XT and AT compat- ible computers. The PS/2 can be linked into the makers’ high-speed laboratory computer network. Quadrant Scientific Ltd., 36 Brunswick Road, Gloucester GL1 1JJ. Chromatography Systems The Econo-Column chromatography col- umns have been re-designed and now include two new features: moulded Luer- lock end fittings and precision sealed polypropylene fittings. Added flexibility is conferred by a complementary line of stopcocks, connectors and tubing,which can be firmly secured to the columns.Increased throughput in affinity, ion exchange and other applications is also possible with the introduction of new 5 cm i.d. columns in 10, 20 and 30 cm lengths. A brochure is available. Bio-Rad Laboratories Ltd., Caxton Way, Watford Business Park, Watford, Hertfordshire WD1 8RP. Liquid Chromatography Controller - Fluid Delivery System The Model 7000 is a totally integrated, stand-alone SFC controller - fluid delivery system, which can transform almost any gas chromatograph into a fully functional supercritical fluid chromatograph. It can be simply connected to the GC by means of hardware and software interface com- ponents available from the makers, and once it has been installed on the GC the instrument can be operated in either SFC or GC mode through the keyboard of the Model 7000.Severn Analytical Ltd., 36 Brunswick Road, Gloucester GL1 1JJ. Analysis of Hydrocarbons in Coals The Chrompack thermal desorption cold trap (TCT) injector, combined with capil- lary GC, is being used for the analysis of hydrocarbons present in coal samples. The finely ground coal sample (1-5 mg sample mass, 0.06-0.2 mm grain size) is placed in the desorption tube. After desorption (usually at 300°C) the com- pounds are trapped at - 120 “C. By heat- ing the cold trap to 250°C the hydro- carbons are injected into the capillary column. Chrompack UK Ltd., Unit 4, Indescon Court, Millharbour, London E l 4 9TN. Capillary Columns Rescom capillary columns for gas and supercritical fluid chromatography have highly deactivated mobile phases and offer a wide range of selectivities.Five series of columns are available: silicone, polyethylene glycol, tuned phases, high temperature phases and aluminium oxide PLOTS. Internal diameters range from 50 to 530 ym. Rescom also make tailor-made columns for mono-, di- and triglyceride analysis by capillary and SCF chromato- Dyson Instruments Ltd., Hetton Lyons Industrial Estate, Hetton, Houghton le Spring DH5 ORH. graphy * Capillary Columns A new range of fused silica capillary columns are coated using a static coating procedure, with the stationary phase being bonded to the column. A mere handful of stationary phases will allow separation and identification of: 1, phe- nols, hydrocarbons, amines, sulphur com- pounds, pesticides, PCBs; 2, amino acid derivatives and essential oils; 3, fatty acids, methyl esters, alkaloids, drugs, halogenated compounds; 4, drugs, ster- oids, pesticides and glycols; 5, fatty acid methyl esters, alditol acetates; 6, acids, alcohols, aldehydes, acrylates, nitriles, ketones; 7, free acids, alcohols, ethers, essential oils, glycols, solvents.Field Analytical, Weybridge, Surrey KT13 9UZ. Data Handling System Omega-2 is a PC based analytical work- station developed expressly to meet the needs of chromatographers. It is designed to handle all GC and LC requirements from data collection to report generation. It incorporates a co-processor, the C-En- gine, which supports parallel processing and multi-tasking, and gives the user the power to alter methods, collect data and generate reports, all at the same time.Perkin-Elmer Ltd., Post Office Lane, Beaconsfield, Buckinghamshire HP9 1QA. HPLC Material for Preparative Chromatography Apex PrepSil is a spherical HPLC material for preparative chromatography. It is available in 8, 15 and 20 ym sizes, in Cg, CI8 and plain silica and is analogous to the 3, 5 and 10 ym Apex materials, allowing easy scale-up from analytical to preparative chromatography. Develop- ment of the JCL6000 data acquisition system continues; new developments include the expansion to 2-channel capa- bility and the inclusion of mouse control as a standard option. Also announced are the EG+ G Model 400 electrochemical detector and the SPS sample processing station from Analytichem International. Jones Chromatography, New Road, Hengoed, Mid Glamorgan CF8 8AU.Fatty Acid Methyl Ester Analyser Two dedicated capillary based FAME analysers have been introduced. The first, the standard version, analyses positional and geometric fatty acid methyl ester isomers on a single Chrompack CP-Si1 88 column. Optimal separation of the CIS cisltrans isomer group is achieved. The second, advanced system, the FAME Analyser PLUS, uses the makers’ multi-282 ANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 switching intelligent controller (MUSIC) and a dual-capillary column combination consisting of a non-polar CP-Sil 5 CB column and a CP-SiI 88 analytical column to resolve completely the fraction of interest, the C18 isomers, and those esters with different carbon numbers. Chrompack UK Ltd., Unit 4, Indescon Court, Millharbour, London E l 4 9TN.Integrator The memory capacity of the IC card available for use with the Shimadzu C-RSA integrator has been expanded from 8 to 16 kbyte. This doubling will permit the storage of more user-defined analysis files or of more chromatograms for later analysis. Within the IC card concept there is scope for the develop- ment of 32 and 64 kbyte memories and work on these is in progress. Dyson Instruments Ltd., Hetton Lyons Industrial Estate, Hetton, Houghton le Spring DH5 ORH. Dissolution Tester The seventh reaction vessel provided with the Dissolutest dissolution tester is specif- ically intended as a reservoir for HPLC applications or as a convenient reference. Also announced is a disintegrator for those Dissolutest users who employ the tablet disintegration technique.Like the Dissolutest, this unit conforms to USP XXI standards. May and Baker Ltd., Liverpool Road, Eccles, Manchester M30 7RT. Computing Densitometer The 300A computing densitometer quan- tifies an entire electrophoresis gel in approximately 3 min. It uses a line scan- ner and an integrating cylinder to analyse the gel area. The sample moves in one Microprocessor Controlled Power Supplies The Model 1000/500 can monitor current down to the milliamp level, provide cur- rent to 500 MA and voltage to 1000 V, and control power output for specific V-h periods. It is therefore suitable for both large- and small-scale 2D or SDS-PAGE electrophoresis and, being programm- able, it is good for focusing in the Model 111 Mini IEF cell or for any electro- phoresis application requiring step changes in the power conditions.Its performance sits in the middle of the makers’ power-supply range, between the Model 3000xi and the Model 200/2.0. Bio-Rad Laboratories Inc., 19 Drkve De Sknechal, B-1180 Brussels, Belgium. Carbon Monoxide Gas Analyser Teledyne’s Model 826 instrument pro- vides accurate on-line monitoring of gases in combustion exhausts, heat treating furnace atmospheres, FCC catalyst regeneration, basic oxygen furnaces, enclosed environments and numerous other industrial and commercial applica- tions. It features two measuring ranges: 0-500 and 0-1000 p.p.m. of carbon monoxide. Optional ranges as low as 0-100 p.p.m. and as high as 0-2.5% are available. Acal Auriema Ltd., 442 Bath Road, Slough SL16BB.Moisture Determination The Tempeau Moisture Profiler is an electronic probe that reads moisture and temperature. Most granular and pow- dered materials can be measured as well as liquids. A moisture content range of 0.5-35740 is covered. The Tempeau gives instant readings, pinpointing moisture content in seconds. Molecular Dynamics 300A computing densitometer direction, while the light beam moves in a Scanflow Systems Ltd., 312-313 Solent perpendicular direction, providing a com- Business Centre, Millbrook Road West, plete analysis of samples as large as 36 X Southampton SO5 OHW. 43 cm. Molecular Dynamics, 240 Santa Ana Court, Sunnyvale, California 94086, Turbidity Meter USA. The Turbidimeter has a range of 0.1-100 nephelometric turbidity units across three ranges.It is particularly suitable for water authorities requiring daily turbidity measurements to verify water cleanliness. The unit is compact and is supplied with three standard solution cells for calibra- tion, four sample tubes, light shield, filament centraliser and spare light, as well as an instruction manual. C.P. Instrument Co. Ltd., P.O. Box 22, Bishops Stortford, Hertfordshire CM23 3DH. Balances The FWFY range of balances are compact and are available in capacities from 310 x 0.001 g to 6100 X 0.1 g, including two models with dual weighing ranges. Each balance can incorporate ten different weight units, such as gram, pound/ounce, decimal pound/ounce, troy ounce, carat and grain. All balances feature integral counting and percentage functions and an underhook for density measurement applications.For counting operations an automatic counting accuracy improve- ment system ensures accurate results by revising the unit weights automatically as more pieces are added. The percentage function enables an item to be weighed as a percentage of a pre-set weight, speeding up check weighing operations and enabl- ing weight loss or gain measurements to be calculated easily. An RS 232C current loop can be fitted and the balances can be used with the makers’ AD-8117 thermal dot matrix printer. Salter Industrial Measurement Ltd., George Street, West Bromwich, West Midlands B70 6AP. Software for Thermoanalysis TA72 Graphware supports the process- ing of thermoanalytical measured values and curves determined by the makers’ TA3000 system and prepared and trans- ferred by the TClOA TA processor.The broad application area of this evaluation software covers not only the checking of materials and their development but also the investigation of thermal effects of new compounds. In all these investigations TA72 Graphware offers the possibility to compare and process simultaneously several thermoanalytical curves. Mettler Instrumente AG, CH-8606 Greifensee, Switzerland. Backscattered Electron Detector A new BSE detector, designed for use in all scanning electron microscope applica- tions, consists of four N-type silicon dif- fused junction diodes, each of approxi- mately 1 cm2, arranged in annular form. Designed to eliminate “sag” effects, it operates in a biased TV mode as well as zero-biased mode for quantitative analy- sis.In the TV mode resolution is good, the band width being up to 5 MHz, and detection is possible where energies fall below 2 keV. In addition, the detectorANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 283 features very low noise at high gains. Resolution is less than 0.1 atomic number at atomic number 29. Link Analytical Ltd., High Wycombe, Buckinghamshire. Surface Area Analyser The 4200 surface area analyser is fully automatic and can provide BET surface area measurements in less than 5 min. It accepts samples with surface areas rang- ing from 0.5 m2 g -1 to over 4000 m2 g-1. By using nitrogen absorption and dynamic flow principles to analyse cor- rectly, it displays a direct digital read-out of total surface area in m2 when the absorption is complete, at which point an audible alarm alerts the operator.The Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. Blood Gas Analysis Neonatal blood gadoxygenation profiles have been made more accurate by the direct measurement of foetal haemoglo- bin (HbF) by the DSM3 Hemoximeter. This instrument now reports accurately Hb02 or Hb02SAT, HbCO, MetHb, tHb, 02ct, RHb and O2 capacity for samples of any HbF content. Calcium status (actual ionised calcium, pH and standard ionised calcium, i. e., ionised calcium at pH 7.40) is provided in a 45 s stat analysis by the fully automatic ICA2 ionised calcium analyser . Leeds and Northrup 4200 surface area analyser direct read-out of parameters such as temperature, voltage and current, with built-in linearisation for seven different types of thermocouple as well as RTD sensors.It is programmable via RS232C or IEEE-488 interfaces and offers alpha- numeric print-out and digital display in addition to continuous recording via a seven-colour ink-jet writing system. The DASA 9000 data acquisition and signal analysis system can acquire, display and analyse data on up to 112 analogue channels at frequencies of up to 50 kHz and with transients down to 10 p. The TA550 thermal recorder provides up to three channels of information and on- chart annotation of parameters such as channel identification, scale, elapsed time and event markers. Included in the mak- ers’ range of digital storage oscilloscopes is the 1604, which features a wide range of automatic measurement functions assessed by means of a cursor-menu system with on-screen alphanumerics.Gould Electronics Ltd., Roebuck Road, Hainault, Ilford, Essex IG6 3UE. Chart Recorder The P70M is smaller than the P105M circular chart recorder and provides ver- satile control of input ranging and lineari- sation with control of the pen drive and referencing, visual alarms and control outputs. Recording on a circular chart with a writing width of 70 mm, it is available in one or two channel versions with up to two set points and two relays per channel for alarm or control. Kent Industrial Measurements Ltd., Howard Road, Eaton Socon, St. Neots, Huntingdon, cambridgeshire p ~ 1 9 3EU. Model 4200 is capable of multi-point analysis with manual selection of different Radiometer Ltd., The Manor, Manor Royal, Crawley, West Sussex RHlO 2PY.gas mixtures. Also available is the 4210 sample preparation facility for use in continuous analysis of a large number of samples. Leeds and Northrup Ltd., Wharfdale Road, Tyseley, Birmingham B11 2DJ. Sampler for Particle Size Analysis A new sampler has been developed for the makers’ Nicomp dynamic light scat- tering particle size analyser. The Nicomp 370 autosampler allows the analysis of 1-76 samples continuously. Coupled with the Nicomp 370 autodiluter, it will pro- vide a fully automated multiple run capability for all powder and colloid sub-micron particle sizing requirements. Pacific Scientific, 4 First Avenue, Globe Park, Marlow, Buckinghamshire SL7 1YA. Data Acquisition System Introduced as an expansion of the makers’ CALS laboratory automation system, the new IDAS instrument data acquisition system provides 2-way communication between virtually any analytical instru- ment and a DEC VAX, HPlOOO or IBM S/370 host minicomputer. Furnaces A range of chamber furnaces consists of nine models: six general-purpOse fur- naces, three operating up to 1 1 0 0 0 ~ and Metanephrine Detection The Model 1340 electrochemical detector is suitable for the quantification of metanephrines.Optimum detection con- ditions such as potential can be selected: eleven ranges of sensitivitiy, from 200 to 0.1 nA V-1 are available and levels as little as 20 pg per injection can be detec- ted. Bio-Rad Laboratories Inc., 19 Dreve De Senechal, B-1180, Brussels, Belgium.Isotype Specific Conjugates The Bio-Rad range of isotype specific conjugates now includes goat antimouse IgG and IgM, together with goat anti- human IgG, IgE and IgA. All the new conjugates are available labelled with horseradish peroxidase. The goat anti- mouse IgM can also be supplied labelled with alkaline phosphatase. Bio-Rad Laboratories Inc., 19 Dreve De Senkchal, B-1180, Brussels, Belgium. Recording Systems The SC2130 logging recorder, for multi- point long-term testing, offers 30 logging channels on a 250 mm-wide chart and254 ANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 three to 12OO0C, the largest having a capacity of 13 1; and three rapid heating furnaces operating up to 1200°C and incorporating low thermal mass insulation and high performance heating elements, the smallest furnace reaching 1000°C in only 10 min.Carbolite Furnaces Ltd., Bamford Mill, Bamford, Sheffield S30 2AU. Petri Dishes A range of sterile petri dishes made from clear polystyrene are distortion free with a completely flat surface. All are indepen- dently evaluated for sterility and can be conveniently packaged in sleeves of 20 per case. Elkay Laboratory Products (UK) Ltd., Unit 2, Crockford Lane, Basingstoke, Hampshire RG24 ONA. Literature Brochures give details of the Jobin Yvon JY24 compact, low-cost inductively coupled plasma spectrometer and the JY70 Plus combined sequential/simultaneous inductively coupled plasma spectrometer. Instruments S.A. - EDTA Ltd., 14 Trading Estate Road, London NWlO 7LU. Brochures describe the Chrompack Pack- ard Models 437A and 438A gas chromato- graphs, which have been specifically designed for routine analysis.Also included are details of the range of injectors and detectors. A brochure is also available on the Models 910 and 911 automatic liquid samplers, which give continuous high speed sampling with accurate reproducible injection of up to 110 samples. The brochure gives informa- tion, too, on control software and clean- ing modes. Chrompack UK Ltd., Unit 4, Indescon Court, Millharbour, London El4 9TN. An up-to-date comprehensive Applica- tions Bibliography for sample preparation lists over 500 articles and procedures which cite the use of Analytichem’s solid- phase extraction products in the extrac- tion and purification of a wide variety of chemical compounds found in biomed- ical, clinical, environmental, food and general industrial applications.Jones Chromatography Ltd., New Road, Hengoed, Mid Glamorgan CF8 8AU. A brochure describes the Model 2600 chromatography workstation, which is based on the IBM-PC and run under MS-DOS. Suitable for routine applica- tions in both testing and quality control laboratories, the Model 2600 enables the laboratory PC to use third-party software programs for applications such as word processing and data base management. It can be linked to the makers’ RLABII laboratory information management package or networked with either Ether- net or IBM networking systems. Nelson Analytical Ltd., 860 Birchwood Boulevard, Birchwood, Warrington, Cheshire WA3 7QZ. New product literature is available on the Model SA700 sulphur dioxide analyser, which is a continuous fluorescence instru- ment using an ultraviolet source of inter- mediate intensity and high stability.Columbia Scientific Industries. Leaflets describe the Mopet cordless motorised pipette controller, the Stedi- pette pipette controller designed for use in a safety hood, the Portapet, which combines the fine control of the Mopet with the simplicity and lightness of a rubber bulb, and a range of precision bottle-top dispensers. Camlab Ltd., Nuffield Road, Cam- bridge CB4 1TH. “Unique in Materials Testing” provides a comprehensive introduction to the Rosand precision range of instrumenta- tion for materials testing. Rosand claim advances in softening-point apparatus, melt flow-rate instruments, temperature monitors, heat-seal testers and falling dart testers.Their range of falling weight and pendulum systems are suitable for research applications and routine quality control. Microprocessor control allows fully automatic operation. The Rosand range of capillary extrusion rheometers features autocalibration and auto-zero. Rosand Precision Ltd., 11 Little Ridge, Welwyn Garden City, Hertfordshire AL7 2BH. “A Guide to Colorimetry” traces the history of colorimetry and explains the principles behind the method. There are chapters on theory and practical consider- ations with regard to the choice of cuvettes or test-tubes, and measurement routines. Several application methods, their equipment, reagents, procedures and calculations, are listed. Ciba Corning Diagnostics Ltd., Hal- stead, Essex C 0 9 2DX. A catalogue containing well over 300 pages gives information on hundreds of products for GC, HPLC, SPE, capillary, sample preparation, chemical standards and industrial hygiene. Supelchem, London Road, Sawbridge- worth, Hertfordshire CM21 9JH. A catalogue, “High Resolution Chromat- ography Products,’’ contains 141 pages of data on equipment and accessories for the analytical laboratory. J & W Scientific, 91 Blue Ravine Road, Folsom, CA 95630, USA. A catalogue gives information on a range of consurnables for trace metal analysis. These plastic disposables are metal free, being precision moulded from poly- propylene. A range of centrifuge tubes, pipette tips and microcentrifuge tubes are all provided with a written guarantee of performance as detailed in the US Phar- macopeia, XXI Revision. Elkay Laboratory Products (UK) Ltd., Unit 2, Crockford Lane, Basingstoke, Hampshire RG24 ONA. A range of fact sheets highlights the latest application and research work using elec- trical conductance methods. The first of these relates to the dairy industry, where the Malthus-AT microbiological analyser can be used to set up final production specifications and to determine shelf-life. Malthus Instruments Ltd., William Clowes Street, Burslem, Stoke-on-Trent ST6 3AT.

ISSN:0144-557X    

DOI:10.1039/AP9882500280

出版商:RSC    

年代:1988

数据来源: RSC

摘要:

254 ANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 Ronald Belcher Memorial Lectureship In recognition of the late Professor Ronald Belcher’s interest in education, the Council of the Analytical Division has instituted a Belcher Memorial Lecture to be given annually on an analytical topic by a graduate student. The award will be considered by the Honours Committee, acting on behalf of the Council of the AD. Students will be considered to be eligible if they are registered for an academic session in the year of the award. The decision concerning the award will be made in December. The aim of the award is to commemorate Professor Belcher as a teacher, by encouraging students to make a positive contribution to, and take an active part in, the profession of analytical chemistry. The paper, to be written by the student (see rule 2 below), should be in the form required for submission to “The Analyst.” Rules 1. Candidates must currently be regis- tered postgraduate students of a British University or Polytechnic. 2. The merits of a particular candidateANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 285 may be brought to the notice of the Honours Committee by any super- visor of postgraduate students regis- tered with a British University or Polytechnic who desires to recom- mend the candidate, by letter addressed to the President of the Division. The letter shall be accom- panied by a paper written by the Student. 3. The award shall be made annually in December and shall be based on an over-all assessment of the originality of the work described in the paper and the significance of its contribu- tion to analytical chemistry. The winner of the award will be expected to present his or her work at the Research and Development Topics Meeting following the award.4. The award will take the form of a presentation scroll plus a sum of f150. The sum is to assist the candi- date to attend a national or inter- national conference. It will be given to the candidate, up to two years after the granting of the award, on presentation of satisfactory evidence of the candidate’s intention to attend such a conference. 5. An award shall not be made if it is considered by the Honours Com- mitee that none of the papers sub- mitted reaches the required stan- dard. 6. The decision of the Council of the Analytical Division shall be final. 7. Any alteration to these Rules shall be subject to the approval of the Council of the Analytical Division. Submissions should be sent to the President, Analytical Division, Royal Society of Chemistry, Burlington House, London, W1V OBN. The closing date is Friday, September 30th, 1988.

ISSN:0144-557X    

DOI:10.1039/AP9882500284

出版商:RSC    

年代:1988

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, AUGUST 1988, VOL 25 285 ~~~ ~ Analytical Division Distinguished Service Award Nominations are invited for the Division's the Division shall agree. Analytical Division, which shall Distinguished Service Award, the Rules recommend to Council of the Divi- for which are as follows: sion (a) to whom an award should be 3. Nominations for the Award will be invited annually from members of 1. The aim of the Award is to recognise exceptional voluntary service over a period of years to the Analytical Division of The Royal Society of Chemistry (including that to the Society for Analytical Chemistry). 2. The Award shall normally be in the form of an illuminated address which may be accompanied by such Council of the Division, and may be received from any member of the Division.They shall be made in writing, with supporting evidence, to the President of the Analytical Division, Royal Society of Chem- istry, Burlington House, London, W1V OBN. 4. Nominations shall be considered by made, ( b ) the nature of the award or (c) that no award should be made. 5. The Award shall be made by the Council of the Analytical Division, which must approve any alteration of these Rules. Nominations for the Award should be sent to the President of the Analytical additionai recognition as Council of the Honours Committee of the Division before September 30th, 1988. ROYAL SOCIETY OF CHEMISTRY: ANALYTICAL DIVISION MEETINGS OF THE CHEMOMETRICS GROUP Winter 1988-1989 The Chemometrics Group will be holding the following meetings in the coming months. "Signal Processing in Molecular Spectroscopy," December 1 st, 1988, Scientific Societies Lecture Theatre, New Burlington Place, London W.l (organised jointly with the Analytical Division and the Molecular Spectroscopy Group); "Chemometrics in Clinical and Pharmaceutical Analysis," December 15th, 1988, Queen Elizabeth Medical Centre, University of Birmingham (the Annual General Meeting of the Group); "An Introduction to Chemometric Methods," February 14th, 1989, Warren Spring Laboratory, Gunnels Wood Road, Stevenage; "Chemometric Techniques for the Clinical and Pharmaceutical Industry," April 19th, 1989, University of Salford. For details of these meetings please contact Dr. S. J. Haswell, School of Chemistry, Thames Polytechnic, Wellington Street, Woolwich, London SE18 6PF.

ISSN:0144-557X    

DOI:10.1039/AP9882500285

出版商:RSC    

年代:1988

数据来源: RSC