ISSN:0144-557X    

DOI:10.1039/AP98926FX037

出版商:RSC    

年代:1989

数据来源: RSC

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October 1989 ANPRDI 26( 10) 329-360 (1 989) Analytical Proceedings Proceedings of the Analytical Division of The Royal Society of Chemistry CONTENTS 329 SUMMARIES OF PAPERS 329 331 329 International Symposium on Electroanalysis in Biomedical, Environmental and Indus- trial Sciences 'Arrays of Electrodes for Multi-component Analysis' by W. E. van der Linden, M. Bos and A. 60s 'Polyethers as Potentiometric Sensors' by J. D. R. Thomas 'Amperometric Biosensors' by Jane E. Frew and Monika J. Green 334 336 338 339 341 343 346 336 Research and Development Topics in Analytical Chemistry 'Complex Sample Analysis by Cybernetic Multi-dimensional Chromatography' by A. J. Packham and P. R. Fielden 'Design Parameter Studies of Ion-selective Field Effect Transistor (ISFET) Sensors' by S.Johnson, G. J. Moody and J. D. R. Thomas 'Chemotaxonomic Identification of Tanaceturn parthenium L. (Feverfew)' by Mark D. 'Some Recent Developments in Hig h-performance Liquid Chromatography in Biophar- 'Voltammetric Methods in the Analysis of Anaerobic Sealants' by M. C. Brennan and G. 'New Approaches to Chiral Resolution of Drug Enantiomers and Related Compounds 'Determination of Nicotine Metabolites by HPLC After Complexation with Diethylthio- Burford and Roger M. Smith maceutical Analysis' by Mary T. Kelly, Darioush Dadgar and Malcolm R. Smyth Svehla by HPLC' by A. M. Dyas, M. L. Robinson and A. F. Fell barbituric Acid' by C. L. Smith, S. O'Doherty, M. Cooke and D. J. Roberts 348 353 Equipment News 358 Publications Received 359 Analytical Division Diary Typeset and printed by Black Bear Press Limited, Cambridge, England ANALYTICAL PROCEEDINGS, OCTOBER 1989, VOL 26 SPECTROSCOPIC PROPERTIES OF INORGANIC AND ORGANOMETALLIC COMPOUNDS - VOLUME 21 Senior Reporters: G.Davidson, University ofhrottingham, and E.A.V. Ebsworth, University of Edinburgh This book reviews the recent literature published up to late 1987. Its Brief Contents are: Nuclear Magnetic Resonance Spectroscopy; Nuclear Quadruple Resonance Spectroscopy; Rotational Spectroscopy; Characteristic Vibrations of Compounds of Main-group Elements; Vibrational Spectra of Transition-element Compounds; Vibrational Spectra of Some Co-ordinated Ligands; Mossbauer Spectroscopy; Gas-phase Molecular Structures Determined by Electron Diffraction. ROYAL ISBN 0 85186 193 8 Hardcover 525 pp. Specialist Periodical Report (1989). Price $120.00 ($240.00) ~~~ For further information, please write to: Royal Society of Chemistry, Sales and Promotion department, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK. To Order, please write to Royal sodety of Chemistry, Distribution Centre, Blackhorse Road, Letchworth, Herk SG6 IHN, UK. or telephone: (0462) 6725% quoting your credit card details. We cannow accept Access, Visa, MasterCard k Eurocard. RSC Members are entitled to a discount on most Rsc publications and should write to: The Membership Manager, Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK. ... 111 SOCIETY OF CHEMISTRY Informat ion Services

ISSN:0144-557X    

DOI:10.1039/AP98926BX039

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS. OCTOBER 1989, VOL 26 329 International Symposium on Electroanalysis in Biomedical, Environmental and Industrial Sciences ~~ The following are summaries of three of the papers presented at a Joint Meeting of the Electroanalytical Group and the Electrochemistry Group of the Faraday Division held on April 1 Ith-I4th, 1989, in Loughborough University of Technology. Arrays of Electrodes for Multi-component Analysis W. E. van der Linden, M. Bos and A. Bos laboratory for Chemical Analysis-CT, University of Twente, NL-7500 AE Enschede, The Netherlands In a discussion of arrays of electrodes it is useful to differentiate between voltammetric or amperometric sensing techniques on the one hand and potentiometric techniques on the other hand, because the objectives for applying arrays in these two instances are often quite different. Voltammetry and Arnperometry Most of the recent publications on arrays of electrodes deal with applications in voltammetry and amperometry.In these applications the arrays almost always consist of assemblies of (ultra) microelectrodes, with diameters generally much less than 50 pm, which have interesting specific properties. Such microelectrodes have, for instance, the following advantages: firstly, high mass transfer rates resulting from hemispherical rather than linear diffusion; secondly, less dependence of the signal on the conductivity of the solution because of the very small currents passing through the electrodes; and thirdly, reduced flow dependence when used in streaming media.l-3 Furthermore, it has been demonstrated by Cope and Tallmanj that the replacement of a traditional macroelectrode by an array of microelectrodes results in an enhancement of the signal.This can be attributed partly to the so-called edge effect, which is based on the fact that for flat inlaid electrodes the Cottrellian current, due to planar diffusion, is augmented by a constant term proportional to the perimeter of the flat electrode.5 The contribution of this effect becomes increasingly important as the perimeter to area ratio of microelectrodes increases. Another contribution to signal enhancement in flowing media is based on a depletion layer recharge which occurs when depletion zones generated by upstream electrodes during their passage over insulating regions are replenished by diffusion.6 This signal enhancement, together with the dimin- ished flow dependence, leads to a decrease in the limit of detection.I n the arrays of electrodes used in voltammetry, discussed so far, the separate electrodes are interconnected and only one current is measured for the whole ensemble. Similar to the approach in photodiode arrays, where each single diode generates a separate signal, it is also possible to apply different voltages to each single electrode of the array and to register the corresponding individual currents. This would allow the registration of a complete voltammogram in an extremely short period of time allowing on-line applications such as in chromatography or flow injection analysis. In the literature only one such application has been reported yet,7 and some have announced that work in this field is in progress.8 With regard to the construction of these voltammetic array electrodes three main approaches have been described: 1, embedding of (carbon) fibres in a polymeric matrix’.’ or in gIass1().11; 2, etching holes in a resist coating, an extreme example of this approach being presented by Hepel and Osteryoungl’ who prepared an electrode assembly consisting of over 1 million active electrodes per cm’; 3, direct vapour deposition or sputtering of electrode material.13 Procedures 2 and 3 can be combined as is common practice in the microlithographic fabrication of all types of integrated circuits.Moreover, the sputtered material, e . g . , aluminium, can be electroplated by more noble metals such as platinum.14 Potentiometry As discussed above the use of array electrodes in voltammetry and amperometry is mostly associated with the specific behaviour of microelectrodes; this is not necessarily so for potentiometry.Of course, miniaturisation of single (ion-selec- tive) electrodes will allow the construction of more manageable arrays which can be used for different types of in vivo measurements. 15 The development of ion-selective field effect transistors (ISFETs) is important in this respect, but, unfortu- nately, the high expectations for these types of electrodes have not yet been completely realised. The major problems encoun- tered in the construction of suitable and robust ISFETs are of a purely technological nature such as, for instance, encapsula- tion of the devices.Hopefully, some solutions will be found in the near future because the basic principle of the ISFET, and the available integrated circuit technology for the large scale production of complex arrays, make them very attractive. Chemometric Approach The particular interest in combining ion-selective electrodes in arrays is related to the availability of simultaneous output that can be achieved rather than in miniaturisation as such. This has been recognised recently by Otto and Thomas,l6 Beebe ez al. 17 and Beebe and Kowalski. 18 The last two authors claim that the use of sparingly selective electrodes in combination with a chemometric approach can result in multi-component analyses that are superior, in many cases, to those obtained when the electrodes are highly selective.I t was also correctly mentioned by them that for the mathematical procedures to have some real applicability, the stability and reproducibility of the sensor is more important than its selectivity. The chemometric approach chosen by Otto and Thomas16 was based on multiple linear regression and partial least330 ANALYTICAL PROCEEDINGS. OCTOBER 1989. VOL 26 squares for the construction of a calibration model based on variation of the two parameters in the extended Nikolsky equation, i.e., the Eo, and Kjk,, the selectivity factor of the jth electrode for the kth analyte with respect to the lth interfering ion. Beebe et ~ 1 . 1 7 have proposed a non-linear regression procedure in which not only the Eo and the selectivity factors are allowed to vary, but also the a priori unknown slope is considered as a variable which has to be estimated simul- taneously.In a very recent paper Beebe and Kowalski’g pursued this line and introduced a non-parametric multivariate technique called “projection pursuit regression.” It allows the calibration of a system without a priori information about the functional relations between the responses and the concentra- tions. The method can provide both this functional relationship (logarithmic, linear, parabolic, etc.) and the values of the descriptive model parameters. Once calibrated, precise esti- mates for the unknown concentrations of multi-component samples can be calculated. In the last section an alternative approach is presented based on pattern recognition by means of a so called neural network.19 Fig. 1. Schematic model of one neuron: Oj is output or neuron j ; w,, is the weight factor associated with the output from neuronj and used as input for neuron i; neti is the input function; ai is the state of activation; F is the activation hnction;fis the output function. a* and O* refer to the new state of activation and output, respectively Application of a Neural Network A neural network consists of an assembly of interrelated neurons that can be defined as processing units. Within each single neuronj the total operation can be sub-divided into three steps, each characterised by a mathematical expression. Firstly, an input function, which allows the calculation of an effective stimulus or input, net,, of the neuron.Often such an input function is simply a weighted summation of the outputs of the activating neurons (Fig. 1). Secondly, an activation function that allows the calculation a new state of activation, a,(t), from the previous state, u,(t - 1) and the input, net,. This function determines the time dependent response of the neuron on changes in the input. Finally, an output function, O,, that calculates the output signal of the neuron given a certain state of activation. These three functions completely charac- terise the behaviour of a single neuron. However, the n n n w w W Fig. 2. one neuron. Note the layered structure Schematic diagram of neural network. Each circle represents operation of the network as an ensemble is not simply determined by the single neurons and the inputs, but particu- larly by the mutual arrangement of the neurons.It is, in fact, just this topology and the values of the weight factors associated with each input of the neurons that determine the basic properties and “knowledge” of the network. A schematic picture of a neural network is presented in Fig. 2. The set of weight factors is found by presenting experimental data to the network and applying learning rule heuristics. In this aspect the network can be considered to be an adaptive system. The main focus of the work carried out in our laboratory was on the application of complex networks, using as learning heuristics the so-called “backward error propagation rule,” also called the “generalised delta rule.” In this case the network is separated in several layers; neurons from one layer have only inputs from preceding layers, mostly even from one and the same preceding layer.The procedure consists of a repeated sequence of two passes through the network. In the first step, or forward pass, a certain pattern of inputs is supplied to the first layer of a network with arbitrary weight factors and propagated through it until the final outputs of the last layer are calculated. Then the generated output is compared with the desired output (target) and an error is calculated. In the second step, or backward pass, the weight factors associated with the inputs of the last layer are adapted to minimise this error. This adaptation is propagated layer by layer backwards through the network.When coming at the input layer the procedure is repeated with the same input pattern. This forward and backward propagation is continued until an acceptable set of weight factors is obtained. The procedure is consecutively repeated for all patterns until the network can generate adequate outputs for all of these patterns. The number of iterations required can be quite large and so the efficiency of the calculation procedure, i.e., the activation function, is very important. Because in the adaptation of the t t + 2 Fig. 3. Recurrent network used for the simulation of Nikolsky type of behaviour: U, is potential; U,, is standard potential; a, is activity in the solution for ion i; K,, is the selectivity factor for ion i with respect to interferent j : n, is the charge of the ion.t, t + 1 and t + 2 refer to consecutive steps in the iteration procedureANALYTICAL PROCEEDINGS. OCTOBER 1989. VOL 26 weight factors the derivative of the activating function is used, it is important to choose a function, the derivative of which can be easily calculated. A sigmoid function of the form upi = 1/{ 1 + exp[-netpi]} fulfils the requirement because the derivative can be simply expressed as dup,/dnetpi = up, (1 - upi) where the value of the activation state, api, has been calculated alrcady in the forward pass. In a later stage the activation function was slightly adapted by introducing a bias factor, 0, and a “temperature factor,” T , that can be used to vary the learning rate api = 1/{ 1 + exp[( -netp, + @)/TI} Preliminary results were obtained with an array consisting of a potassium, a calcium, a nitrate, a chloride and a pH electrode.For mixtures with concentrations of about 10-4 M the correct concentrations were found within about 5-10%. This is very acceptable because for single ion measurements accuracies, when expressed in concentration units, are generally not better than 4%. A neural network can also be used for parameter estima- tions. So, a recurrent network was used for simulating the Nikolsky equation (Fig. 3). By measuring the potential values of the various electrodes for mixtures of known concentrations (activities) the relevant values of the standard potential, U,,, the slope, S, and the selectivity factors, K , can be found. The advantage of this approach over existing procedures is that the information can be obtained from solutions that can contain all the ions at the same time.Therefore, the results may be considered to be more realistic. Conclusions Arrays of electrodes form an interesting field of research with great potentials for practical applications. More specifically the further development of chemometric approaches deserve more attention when the electrodes show some selectivity but still a strong interaction occurs: it was shown that neural networks have very interesting features in this respect. 33 1 Linkage of this development to another area of growing interest, i.e., process analytical chemistry, means that one other useful application of arrays has to be mentioned, that is, the redundancy that can be built in.The operational lifetime of the array device can thus be extended until the last electrode of the set of equivalent electrodes breaks down. This is of particular interest if the device has to be installed in an inaccessible place or has to be implanted in a living body. 1 . 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 1s. 16. 17. 18. 19. References Caudill. W. L.. Howell. J. 0.. and Wightrnan, R. M.. Anal. Chem., 1982. 54. 2532. Thorrnann. W.. van den Bosch. P., and Bond. A. M.. Anal. Chem., 1985. 57. 2764. Khoo, S. B., Gunashingharn. H.. Ang. K. P., and Tay, B. T.. J. Electroanal. Chem.. 1987. 216, 115. Cope. D. K.. and Tallman. D. E.. J. Electroanal. Chem., 1985. 188.21. Oldharn. K. B.. J . Electroanal. Chem.. 1981. 122, 1. Cope. D. K.. and Tallman.D. E.. J. Electroanal. Chem.. 1986, 205. 101. Matson, W. R.. Garnache. P. G.. Beal. M. F.. and Bird. E. D.. Life Sci.. 1987. 41, 905. DeAbreu. M.. and Purdy. W. C.. Anal. Chem.. 1987.59.204. Belal. F.. and Anderson. J. L.. Analysr. 1985. 110. 1493. Aoki. K., Akimoto, K.. Matsuda. H.. and Osteryoung. J.. J. Elecrroanal. Chem.. 1984. 171, 219. Bond, A. M., Fleischrnann, M.. and Robinson, J., J. Electro- unal. Chem.. 1984. 180. 257. Hepel, T.. and Osteryoung, J., J. Electrochem. SOC.. 1986. 133. 752. Kittlesen. G. P.. White. H. S.. and Wrighton. M. S., J. Am. Chem. SOC.. 1984, 106. 7389. Glavina. P. G.. and Harrison. D. J.. Can. J . Chem.. 1987.65. 1072. Wise. K. D.. Angell, J . B.. and Sturr. A.. IEEE Trans. Rio-Med. Eng.. 1970, 17, 238. Otto. M., and Thomas, J . D.R.. Anal. Chem., 1985,57,2647. Beebe. K., Uerz. D.. Sandifer. J., and Kowalski. B.. Anal. Chem.. 1988. 60. 66. Bccbe. K.. and Kowalski. B.. Anal. Chem.. 1988. 60. 2273. Bos. A.. MSc Thesis. University of Twente. The Netherlands, 1988. Polyethers as Potentiometric Sensors J. D. R. Thomas School of Chemistrv and Amlied Chemistrv, University of Wales College of Cardiff, P.O. Box 912, Cardiff CF1 3TB Polyethers owe their function as potentiometric sensors to their ability to crown, grasp and coil around analates. Such complexation is facilitated by these neutral organic molecules carrying a sequence of localised charges of sufficient energy to form ion - dipole bonds with appropriate cations. The conformation of the molecule permits a solvation type shell around the cation which effectively replaces the ion hydration shell.The charged cationic complex so formed is electrically balanced by anions. The impetus for studies on polyethers as ion sensors is attributable to the observation of Moore and Pressman’ that valinomycin is capable of actively transporting potassium across rat mitochondria membranes. This led to the very successful valinomycin sensor for potassium.?.3 It is also relevant that Pedersen,j in 1967, described the function of crown ethers in promoting the dissolution of salts in which they are otherwise insoluble. However. cation adducts of polyethylene glycols had already been known for several years,S-’ and it was this category of polyethers that was first exploited8 in ion-selective electrodes (ISEs). The special properties of polyethylene glycols in this application is attributable to the alkoxylate units (AOUs) in the polyalkoxylate complex assuming a tight helical conformation, of appropriate ring radius for holding the ion in a cage of oxygen atoms of the AOUs, through ion - dipole interaction.8 For the particular case of barium ions complexing with an NP, a nonylphenoxypolyethoxylate (Antarox CO-880 with 30 ethoxylate units or EOUs), 12 EOUs are involved in holding the Baz+ ions in a tight helical arrangement with a ring radius of about 1.3 A, the cage for the barium ions being formed by the 12 oxygens in two loops of 6 EOUs each.8 For the crown ethers, some of the earliest ISE studies were by Rechnitz and Eyaly o n dicyclohexyl- and dibenzo-18-crown- 6 ligands synthesised by Pedersen .4 Shortly afterwards, Petranek and Rybal(j.11 assessed various types of crown-6 and larger crown compounds for potassium ion-sensing and favoured dimethyldibenzo-30-crown-10 with dipentyl phthalate in PVC as the best of the series.Although these and332 ANALYTICAL PROCEEDINGS, OCTOBER 1989. VOL 26 later studies on crown ether sensors have indicated that the selectivity for potassium does not exceed that of valinomycin, researches on pol yethers as potentiometric sensors have produced many interesting features as well as new directions in sensing. In the UWCC laboratories, such studies exploit the ability to coil by polyalkoxylate to crown by various crown ethers, and to grasp by certain “half-crown” acyclic pol yether types. Potentiometric Sensing Based on Polyalkoxylates The NP, Antarox CO-880, forms the basis of a very good barium ISE.8-12 This is in accordance with the bulk extraction constant, K M , data for the barium complex obtained for extractions into the organic phase by both picrate13 and dipicrylamine.Within each polyalkoxylate metal ion group, the barium complex systems provide the best PVC based ISEs,l2-14 and this is in compliance with the solvent extraction data. For the alkali metal cations, it is interesting that rubidium and potassium are the most strongly extracted alkali metal - polyalkoxylate complexes.13 Thus, these interfere more strongly with barium ISE behaviour than does sodium.12-14 Although not predictable from solvent extraction data, good lithium ISEs can be obtained from some of the polyalkoxylate systems, especially for an ISE membrane consisting of Ba.(PPG 1025)o,69.(TPB)2 plus dioctylphenyl phosphonate in PVC.15 The possibility of such a lithium ISE was indicated by the high lithium interference of a calcium ISE based on the calcium propoxylate anomer16 but, in the event, the best lithium ISE qualities were obtained with the tetraphenylborate (TPB) - barium propoxylate complex as sensor.In relation to the association of potentiometric response with complex stability, the facile conversion of an Antarox CO-880 based barium ISE to a thallium(1) electrode17 is interesting. This is effected by soaking the barium electrode in thallium(1) nitrate for 24 h, such conversion being consistent with dipicrylamine solvent extraction data.14 Of course, there must also be favourable kinetics for the exchange of ions for such conversion and to provide the charge transfer mechanism for ion sensing.Barium ISEs find little application in terms of actual barium determinations, but they can be used for the indirect determi- nation of sulphate,l?.1”-2” especially for the titration stage of the oxygen flask determination of sulphur in organic com- pounds.12 They can also be used for the determination of lithium.*5 Apart from being set up as conventional PVC membrane ISEs with inner filling solutions, the barium ISEs based on Antarox CO-880 can be of all solid state design, whereby the PVC membrane with the sensing material is applied to the outer surface of an epoxy resin and the filling solution eliminated.?() Corresponding lead(I1) ISEs have also been made from complexes of the metal with polyalkoxylates, and the most selective was found to be based on Pb.Antarox CO-880.TPB sensor with 2-nitrophenyl phenyl ether as plasticising solvent mediator.” However, this is not as suitable for use as an indicating system in sulphate titrations, as the lead(I1) titrant system is susceptible to interference by oxidants, such as hydrogen peroxide.21 A large number of metal polyalkoxylates have been characterised in association with the ion-sensing studies.21.22 Sensing of Non-ionic Surfactants An important application of barium ISEs is in the analysis of non-ionic surfactants,23-25 including the measurement of their critical micelle concentration23~~4 (CMC).The observed poten- tiometric response is an increase in the emf of the barium ISE of up to about 100 mV, according to the amount of added alkoxylate in the 2 x to range.23 The response is linear with log[alkoxylate], but is characterised by a break in the linearity, which it attributed to the CMC of this class of non-ionic surfactants. The barium ISE, based on the barium complex with Antarox CO-430 (an NP with 4 EOUs), is superior in its response to non-ionic surfactants.This gave good recoveries in the analysis of Dobanol25-7, Lutensol A07, and Synperonic 7 (polyethoxylates with 7 EOUs and alkyl hydrophobes of C12H25 to C1sH31) in detergent powders’s with relative standard deviations of between 0.8 and 4.0%. With regard to CMC, the inflections observed in the emf versus log[alkoxylate] graphs are quite definite and the breaks’j compare favourably with literature CMC values26.’7 and with a derived formula26 h(l@ X CMC) = A n + B .. . . (1) where A and B are constants for a particular hyrophobic group and n is the average number of EOUs in the molecule. There is a correlation between complexing tendencies of polyalkoxylates and barium, as evinced by solvent extraction data, and electrode qualities with respect to both cationl3.14 and non-ionic surfactant14 sensing. Also, factors such as those impressed by the substituent tail attached to the end of the alkoxylate chain can be involved.14 Scanning electron micro- scopy, ESCA spectra and XRF data, as well as radiotracer experiments, indicate that there are barium - polyalkoxylate interactions between the membrane and solutions, thus point- ing to a mechanism for potentiometric response to non-ionic surfactants in solution.28 However, with regard to ion permea- tion through membranes, there is only limited permeation29 of radioactive barium ions compared with the high levels previ- ously observed for permeation through ion-exchanger type organophosphate-type membranes.3” For the permeation of radiotracers through membranes under applied potential, the barium polyalkoxylate complex breaks down as shown by the rapid drop in current flowing through the membrane.31 Current flow ceases after just one reversal of potential.31 Potentiometric Ion Sensing with Crown Ethers Researches on crown ether derivatives for ion sensing are now quite widespread.Thus, Pungor’s group32 have studied the synthesis and application of various mono- and bis-crown ether derivatives with urethane and urea linkages. In studies33-35 of dibenzo-30-crown-10 (DB30C10) and its derivatives as ISE sensors for diquat (DQT) and paraquat (PQT), the best PVC ISEs are based on DB30C10 with DQT.2TPB and 2-nitrophenyl phenyl ether. This work integrates the molecular recognition researches of Stoddart at Sheffield and structural studies of Williams at Imperial College, London, with the sensor studies of UWCC.36 On the fundamental side, the researches have sh0wn36.3~ that DB30C10 changes its shape dramatically to accommodate the guest molecules, while bis-paraphenylene-34-crown- 10 (BP34C10) is hardly modified in shape when it engulfs PQT.However, this feature is not carried through to improving the POP+ electrodes which are best based on PQT.2TPB without crown ether, and activated by a charge transfer interaction38 between PQP+ and TPB-. There is no advantage to be gained in replacing TPB- by an alternative ani0n.3~ The importance of guanidine in the biological and medical fields has led to guanidinium ISEs. The most suitable were previously39,40 found to be based on crown ethers with di be nzo-27-crown-9 with di bu t yl ph t hala te plasticising solvent mediator, but recent studies41 have shown this to be super- seded by bis-metaphenylene-26-crown-8 (BMP26C8). The facility of such sensors is provided by the ability of the guanidinium cation, [(HzN)&]+ to complex with crown ethers of between 18 and 33 ring cations with 27 members being the most selective.42-44 X-ray and NMR spectrometry data support the [NH - - .01 arrangement of hydrogen bonds to yield stable complexes of 1 mol host to 1 mol guest in most instances, and 2 to 3 in some instances, depending on the solvent and the guanidinium salt. There has been prospecting in the area of bis-crownANALYTICAL PROCEEDINGS. OCTOBER 1989. VOL 26 ethers.32.4-7 For example, Shono and C O - W O T ~ ~ T S ~ ~ , ~ ~ have shown good potassium ion selectivity for some bis- (15-crown-5) derivatives, and one containing a dodecyl link exhibits good lipophilicity and longer lifetime for the resulting ISEs.46 Further studies47 on bis[ (benzo- 12-crown-4)-2- ylmethyl]-2-dodecyl-2-methylmalonate and bis(benzo-15- crown-5)-15-ylmethyl pimelate show the former to be selective to sodium and the latter to potassium, both being best used with 2-nitrophenyl phenyl ether plasticising solvent mediator and potassium tetra-4-chlorophenylborate anion excluder in PVC matrices.Although these electrodes offer promising alternatives to glass electrodes for sodium and to valinomycin electrodes for potassium, the data for measurements of ion in blood serum indicate a need for further research in order to improve the correlations with flame photometric measure- men ts.47 With regard to smaller crowns, a very useful dodecylmethyl- 14-crown-4 shows good selectivity towards lithium and sodium.48 However, lithium ISEs have to function over a small concentration range around 1 mM [Li] in complicated blood and blood serum matrices.Only relatively few sensors approach the required selectivity specifications,j” and many new materials continue to fail the stringent tests.”) Potentiometric Ion Sensing with Diphenyl Ethers of Tetraethylene Glycol Two derivatives of these have been studied,41-s‘)-51 namely 1,l l-bis(2-hydroxy-5-formylphenoxy)-3,6,9-t~oxaundecane and its benzyl ether. These can be looked upon as “graspers” of cations in ion sensing. The performance of ISE types with the diphenol compound depends on the solvent mediator.5 However, the system with dioctylphenyl phosphonate as plasticising solvent mediator did not fulfil its promise51 as a lithium 1SE.W Indeed, despite all of the effort to achieve optimisation, the sensors based on the diphenyl compound and the benzyl ether are so far inferior to existing ones.51 Continuing studies on the materials have yielded greater success with guanidinium ion sensing.41 Thus, both are better than the previously recommended dibenzo-27-crown-9, but marginally less good than the now recommended41 BMP26C8 (see above).Conclusion Polyethers offer many prospects as selective potentiometric sensors. The considerable researches in the field have led to some useful systems, but it is clear that the mechanisms involved and modifying influence of the plasticising solvent mediator needs to be much better understood in order to exploit fully this interesting range of materials. The co-workers of the various references are thanked for their dedication and co-operation.Also, thc various sponsors who have provided financial support are thanked for their generos- ity and interest. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. References Moore, C.. and Pressman. B. C.. Biochem. Biophys. Res. Commun., 1954. 15. 62. Stefanac. Z.. and Simon. W.. Chimia. 1966. 20, 436. Stefanac. Z., and Simon. W.. Microchem. J.. 1967, 12. 125. Pedersen. C. J.. J. Am. Chem. SOC., 1967. 89, 7017. Neu. R.. Arzneim. Forsch.. 1959, 9, 585. Uno, T.. and Miyajima, K., Chem. Pharm. Buff. (Tokyo). 1963. 11, 75. Levins. R. J., and Ikeda, R. M.. Anal. Chem., 1965, 37. 671. Levins, R. J., Anal. Chem.. 1971, 43, 1045. Rechnitz. G. A., and Eyal, E., And. Chem., 1972. 44. 370. PetrAnek. J., and Ryba, 0.. “IUPAC International Sympo- sium on Selective lon-Sensitive Electrodes. UWIST.Cardiff. 9-12 April 1973.” Paper 13. 11. 12. 13. 14. 1s. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 333 Ryba, 0.. and Petranck. J., J. Efecrroanaf. Chem., 1973. 44. 425. Jaber, A. M. Y.. Moody. Ci. J.. andThomas, J . D. R.. Anafysr. 1976. 101, 179. Jaber, A. M. Y.. Moody. G. J.. and Thomas, J. D. R., J. Inorg. Nucf. Chem.. 1977. 39. 1689. Alexander, P. H . V.. Moody, G . J.. and Thomas. J . D. R., Anufysr. 1987. 112, 113. Gadzekpo. V. P. Y.. Moody. G . J., and Thomas, J . D. R.. Anufysr. 1985. 110. 1381. Jaber. A. M. Y.. Moody, (i. J., andThomas. J . D. R.. Anafysr. 1977. 102, 943. Lima. J. L. F. C., and Machado, A. A. S. C . , personal communication. Jones. D. L.. Moody, G . J..Thomas. J . D. R.. and Hangos. M.. Anafysr, 1979, 104. 973. Moody, G . J., and Thomas. J. D. R.. Lab. Prucr., 1979, 28. 125. Moody. G . J.. Thomas, J . D. R.. Lima, J . L. F. C.. and Machado. A . A . S. C., Anafysr. 1988. 113. 1023. Jaber, A. M. Y.. Moody, G. J., andThomas. J . D. R., Anafysr. 1988. 113. 1409. Dclduca. P. G . . Jaber. A. M. Y.. Moody. G. J.. and Thomas. J . D . R.. J. Inorg. Nucf. C‘hem., 1978. 40. 187. Moody. G . J., and Thomas, J . D. R.. in Cross, J.. Editor. “Non-ionic Surfactants: Chemical Analysis,” Marcel Dekker, New York, 1986, p. 117. Jones. D. L.. Moody, G . J., and Thomas. J. D. R.. Anufysr. 1981, 106. 439. Jones, D. L., Moody. G . J.. Thomas, J. D . R., and Birch, B. J., Anafysr. 1981. 106. 439. Hsiao. L., Dunning, H . N.. and Lorenz.P. B., J. Phys. Chem., 1956. 60, 657. Schick, M. J., Atlas. S. M., and Elrich. F. R., J. Phys. Chem.. 1962. 66, 1326. Alexander. P. H. V.. Moody, G . J.. Thomas. J. D. R.. and Birch, B., Analyst. 1987, 112, 849. Doyle, B., Moody. G . J.. and Thomas, J . D. R.. Tufanta. 1982. 29. 257. Jaber. A . M. Y.. Moody, G . J.. Thomas, J. D . R.. and Willcox, A.. Tafanra. 1977. 24. 655. Doyle. B.. Moody. G . J.. and Thomas, J. D. R., Tafanra. 1982. 29, 614. Lindner, E., Toth, K.. Orvath. M.. Pungor, E.. Agai, B., Bitter, I., Toke, L.. and Hell. Z.. Fresenius Z. Anal. Chem.. 1985. 322. 157. Moody, G . J., Owusu. R. K.. andThomas J. D. R.. Analyst, 1987. 112. 121. Moody. G. J.. Owusu. R . K.. and Thomas. J. D. R.. Analysr. 1987. 112, 1347. Moody, G. J., Owusu. R. K.. and Thomas, J.D. R., Analyst, 1988. 113, 65. Stoddart, J. F.. and Thomas, J . D. R., Chem. Sensors Club News, 1987, 5 , 6. Colquhoun, H. M.. Stoddart. J. F.. and Williams, D. J . , New Scienrisr. May lst, 1986, 44. Moody, G. J.. Owusu. R . K., Slawin. A. M. Z.. and Spencer. N.. Angew. Chem. Int. Ed. Engf.. 1987. 26, 890. Bochenska. M., and Biernat, J . F., Anal. Chim. Acra. 1984, 162. 369. Assubaie. F. N.. Moody, G . J.. and Thomas. J . D. R., Analyst. 1988, 113, 61. Assubaie, F. N.. Moody. G. J., andThomas. J . D. R.. Analyst. in the press. Kyba. E. P., Helgeson. R . C.. Madan. K.. Gokel, G. W.. Tarnowski, T. L., Moore, S. S.. and Cram, D. J.. J. Am. Chem. SOC.. 1977, 99,2564. Lehn, J. M., Vierling, P., and Hayward, R. C.. J. Chem. SOC., Chern. Commun., 1979. 296. Stolwijk, T.B., Grootenhuis, P. D. J., van dcr Wal, P. D . , Sudholter, J. W. H. M., and Kruise. L.. J. Org. Chem., 1986, 51, 4891. Kimura. K.. Mazeda. T.. Tamura, H . , and Shono. T., J. Efecrroanaf. Chem.. 1979. 95. 91. Kimura, K.. Tamura, H.. and Shono, T.. J. Chem. Soc., Chem. Commun.. 1983.492. Moody, G. J.. Saad. B. B.. and Thomas. J . D. R.. Anafysr. 1989, 114, 15.334 ANALYTICAL PROCEEDINGS. OCTOBER 1989. VOL 26 48. 49. Kitazawa. S.. Kirnura. K., Yano, H.. and Shono. T.. Analysr. 1985, 110. 295. Gadzekpo. V. P. Y.. Moody, G. J.. Thomas, J. D. R.. and Christian. G. D.. Ion-Sel. Electrode Rev.. 1986, 8. 173. 50. 51. Beswick, C. W., Moody, G. J.. and Thoma;, J . D. R.. Anal. Proc., 1989, 26. 2. Moody, G. J.. Saad, B. B.. Thomas. J . D. R.. Kohnkc. F. H..and Stoddart. J . F.. Analyst. 1988. 113. 1295. Amperometric Biosensors Jane E. Frew and Monika J. Green MediSense (UK), Inc., 14 Blacklands Way, Abingdon, Oxfordshire OX14 IDY ‘The concept of performing clinical analyses outside the centralised hospital laboratory has stimulated great interest in the development of rapid and simple analytical procedures. The emphasis is on the design of tests that may be carried out nearer to the patient or even by the patient. This might be on a hospital ward, in a casualty department, in a doctor’s office or even in the patient’s home. At present the clinical chemistry laboratory is required to monitor a very wide range of analytes, including naturally occurring low relative molecular mass species, drugs and enzymes. Many of the existing assays for such species are spectrophotometric or colorimetric and often involve extensive sample pre-treatment.The application of electrochemical techniques to assay design offers the opportunity for simplify- ing experimental protocols; for example, it is possible to perform measurements on whole blood rather than having to obtain serum or plasma. Dry -strip Technology In order to reduce the number of manipulative steps involved in carrying out a given amperometric assay it is necessary to move away from the use of the standard electrochemical cells and electrode configurations that would be employed in a research laboratory. The exploitation of screen printing technology allows the design of electrode systems in the form of a strip.’ Each strip consists of two electrodes screen printed on to a solid support: a silver - silver chloride reference electrode and a carbon-based working electrode which con- tains the assay reagents.Electrochemical measurements are made by placing a small volume (approximately 25 pl) of test sample on the electrode area. The strips are intended to be used once only and then discarded. Strategies for the Design of Amperometric Biosensors Two basic approaches have been adopted in the development of amperometric biosensors for the detection of clinical analytes. These involve: (i) the direct electrochemical monitor- ing of the product of an enzymatic reaction; (ii) the use of electron transfer mediators in the construction of enzyme electrodes. The simplest approach is undoubtedly the direct electro- chemical monitoring of the product of an enzymatic reaction, the analyte being a substrate for a specific enzyme.The configuration of such assays can be illustrated by tests for paracetamol (acetaminophen) and aspirin (via measurement of salicylate). These drugs are commonly used in overdose situations’ and under these circumstances it is essential to be able to discriminate which drug or combination of drugs have been ingested by the patient. The concentration of free drug in the blood must be known before an appropriate course of treatment can be prescribed. Par ace tamol In the assay for paracetamol (acetaminophen) the enzyme aryl acylamidase (EC 3.5.1.13) converts the drug to p-amino- phenol: NH2 NHCOCH3 OH OH Paracetamol pAminophenol The p-aminophenol is detected electrochemically by oxidation at +250 mV versus Ag/AgCI.This approach is more satisfac- tory than attempting to design an assay based on monitoring the drug directly. The oxidation of paracetamol requires much higher potentials, at which there will be considerable interfer- ence from other species in blood. Conjugated forms of the drug will also be oxidised; clinicians are interested only in the unconjugated form of paracetamol. Under appropriate condi- tions paracetamol can be monitored over the clinical range (0-3 mM) in whole blood. Salicylate Many derivatives of salicylate are available commercially, but the most important is acetylsalicylic acid or aspirin. The drug is hydrolysed rapidly to salicylic acid, which circulates in the blood in the ionised form.3 The assay uses the monooxygenase salicylate hydroxylase (EC 1.14.13.1) to convert salicylate to catechol in the presence of reduced nicotinamide adenine dinucleotide (NADH) and molecular oxygen-‘: Catechol Salicylate The size of the oxidation current generated by electrochemical oxidation of catechol formed in the enzyme reaction provides an estimate of analyte. Measurements are performed at a fixed potential of +300 mV versus Ag/AgCl and results are obtained within 1 min.Although analyses are carried out on blood, calibrations have been constructed in terms of plasma salicylate to aid interpretation of the data; serum or plasma are the accepted media for salicylate tests. The limitation of this system is that it cannot distinguish between different concentrations of plasma salicylate above approximately 4 mM.However, the calibration can be ex- tended by including benzoate as an assay reagent. Benzoate is a pseudosubstrate for salicylate hydroxylases; unlike the reac- tion involving salicylate there is no hydroxylation of the aromatic compound and all oxygen utilisation is diverted towards the production of hydrogen peroxide. With this configuration analyses can be performed up to a concentration of 7.2 mM plasma salicylate, thereby covering the range for both acute and chronic cases of salicylate intoxication.ANALYTICAL PROCEEDINGS. OCTOBER 1989. VOL 26 335 a- Amy lase Assays based upon the direct electrochemical monitoring of the product of an enzymatic reaction are also appropriate for detection of an analyte that is itself an enzyme.In this case the analytical system relies upon the conversion of a labelled substrate into an electroactive product. This approach has been utilised in the design of a new amperometric assay for the hydrolytic enzyme a-amylase.6 The determination of a-amylase (1,4-a-~-glucan gluco- hydrolase, EC 3.2.1.1) is important in the diagnosis of acute and chronic pancreatitis and obstruction of the pancreatic duct. The key to the success of the assay is the use of a soluble, well defined oligosaccharide substrate, 4-aminophenyl-c~-malto- pentaoside. In the presence of a-amylase this compound is hydrolysed to smaller sub-units which are themselves sub- strates for another enzyme, agfucosidase (EC 3.2.1.20). The final product of the reaction sequence is p-aminophenol, which can be monitored electrochemically by oxidation at + 155 mV versus Ag/AgCI.Under appropriate conditions the extent of formation of p-aminophenol is related to the concentration of a-amylase present in the test sample. The assay yields a linear calibration for a-amylase in blood over the clinical range of 50-1000 U I-’. Electron Transfer Mediators in Enzyme Electrodes The direct transfer of electrons between redox enzymes and electrodes is difficult to achieve and is dependent upon the nature of the electrode surface and the solution conditions.’ As a consequence, redox active mediators are often used to enhance the rate of electron transfer between enzyme and electrode. Ferrocenes as Mediators in Enzyme Electrodes The use of ferrocene derivatives as mediators of electron transfer has proved particularly successful in the design of enzyme electrodes.An assay for hydrogen peroxide exploits the ability of a ferrocene derivative to function as an electron donor.8 The fundamental reaction is the enzymatic reduction of hydrogen peroxide by horseradish peroxidase; the native enzyme is regenerated by subsequent electron transfer from an electrode to the peroxidase via the ferrocene mediator. This system provides not only a direct assay for hydrogen peroxide, but can also be a component of other analytical systems in which hydrogen peroxide is a product of one or more further chemical reactions. An electrochemical method for detection of cholesterol has been devised which incorporates the peroxidase coupled assay.9 Cholesterol esters in serum are associated with lipoprotein complexes and the first step of the assay is the liberation of the ester by the action of surfactant.Conversion to free cholesterol can then be achieved in the presence of cholesterol oxidase. Hydrogen peroxide is a product of this reaction and it can be determined by the peroxidase based route. The assay is effective for the determination of cholesterol in the millimolar concentration range. There are two other possible approaches to determining cholesterol which also utilise ferrocene derivatives as media- tors. The cholesterol can be oxidised by a specific flavoprotein oxidase coupled to ferricinium ion or oxidised by a dehydro- genase and the NADH generated can then be detected by a coupled reaction based on diaphorase.4-Methyl-o-quinone as a Mediator to NADH Another example of the use of mediators in enzyme electrodes is in an assay for 3-hydroxybutyrate.10 This compound is the major component of the ketone bodies, the others being acetoacetate and acetone. They are produced by incomplete fatty-acid metabolism in the liver in conditions involving the impaired utilisation or inadequate supply of carbohydrates.2 The determination of ketone bodies in plasma or serum is an extremely reliable guide to monitoring the efficacy of insulin therapy in the treatment of diabetic ketoacidosis. I n the assay, 3-hydroxybutyrate is converted to acetoacetate by the enzyme 3-hydroxybutyrate dehydrogenase (EC 1.1.1.30); NAD+ is required as a co-factor.NADH is a product of the enzymatic reaction. Although NADH formation can be detected by direct oxidation at an electrode it is more convenient to use a redox mediator. The NADH is oxidised by the mediator, 4-methyl-o-quinone, which is itself converted to 4-methyl catechol. The latter is then re-oxidised to the quinone at the electrode. Measurements can be performed at +350 mV versus Ag/AgCl over the clinical range of serum 3-hydroxy- butyrate (approximately 0-20 mM). Conclusion The analytical configurations described in this paper illustrate the fundamental principles underlying the design of ampero- metric biosensors for use in rapid diagnostics. The application of screen printing technology to the development of dry-strip electrode systems transforms the assays from labour-intensive, laboratory-based tests to a format that enables analyses to be performed both easily and rapidly. The commercial viability of strip-based assays with electrochemical detection has been demonstrated by the successful development of a disposable biosensor for glucose, the Exactech system. l 1 Dry-strip elec- trodes incorporating essential reagents are used in conjunction with a pen-sized meter to measure whole blood glucose in only 30 s. The advantages of biosensors compared with other ana- lytical devices are often quoted; they are small, portable, easy to use, accurate, precise and yield results rapidly. Now these advantages have been exploited in the design of diagnostic systems that can find application in the “real world,” not simply in the research laboratory. The authors wish to thank their colleagues at MediSense for their contributions to the work described in this paper. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References Higgins. I. J., McCann, J . M., Davis, G.. Hill. H. A. O., Zwansiger, R., Treidl, B. L., Birket. N. N., and Plotkin, E. V.. Eur. Pat. Applic., Publication Number 127 958. Pesce. A. J., and Kaplan, L. A.. Editors, “Methods in Clinical Chemistry,” C. V. Mosby, St. Louis, MO, USA, 1987. Kwong, T. C., CRC Crit. Rev. Clin. Lab. Sci., 1987, 25. 137. Frew, J. E., Bayliff, S. W., Gibbs, P. N. B., and Green, M. J., Anal. Chim. Acta, in the press. White-Stevens, R. H., and Kamin. H.. J. Biol. Chem., 1972, 247, 2358. Batchelor. M. J.. Williams, S. C., and Green, M. J.. J. Electroanal. Chem., 1988, 246, 307. Frew, J. E., and Hill, H. A. O., Eur. J. Biochem., 1988, 172, 261. Frew. J. E.. Harmer, M. A., Hill, H. A. 0.. and Libor, S. I.. J. Electroanal. Chem., 1986, 201, 1. Ball. M. R., Frew, J . E., Green, M. J.. and Hill, H. A. O., Proc. Electrochem. Soc., 1986. 86-14, 16. Batchelor, M. J.. Green, M. J.. and Sketch, C. L., Anal. Chim. Acta. 1989, 221, 289. Matthews, D. R., Holman, R. R., Bown, E., Steemson, J., Watson, A., Hughes, S., and Scott, D.. Lancet, 1987, i, 778.

ISSN:0144-557X    

DOI:10.1039/AP9892600329

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

336 ANALYTICAL PROCEEDINGS, OCTOBER 1989, VOL 26 Research and Development Topics in Analytical Chemistry The following are summaries of seven of the papers and posters presented at a Meeting of the Analytical Division held on March 21st-22ndr 1989, in the National Institute of Higher Education, Dublin. More summaries from this meeting will be published in the November issue. Complex Sample Analysis by Cybernetic Multi-dimensional Chromatography A. J. Packham and P. R. Fielden" 3epartment of Instrumentation and Analytical Science, UMIST, Manchester M60 1 OD Today, it is becoming necessary to analyse very complex mixtures such as environmental, biological, food and pet- roleum samples for low levels of potentially harmful sub- stances. However, owing to the large number of components in the sample they may be difficult to analyse by conventional HPLC techniques.This problem is further compounded as the composition is usually not fully understood and often the sample is not in a form that is directly analysable ( e . g . , plasma or crude oil). In order to overcome these problems a number of pre-analytical stages must be included in the analytical method. These may include solid-phase extraction, solvent - solvent extraction or even fractionation by a liquid chromatographic method. Unfortunatcly, by using these techniques the analysis time is lengthened and there is an increased risk of laboratory or personal contamination. Consideration of sample loss, cost and the difficulty of automation (making the method labour intensive) is important when determining the method of choice for a complex sample.Some of these disadvantages can be overcome by using multi-dimensional chromatography. This is a chromatographic technique aimed at the determination of the concentration of a specific analyte in a complex matrix. The technique provides the optimum efficiency for separations of the component of interest, whilst simultaneously minimising analysis time by decreasing the time spent in separating the components of a sample that are of no particular interest.'.? The separation occurs by both chromatographic and mechanical means and is achieved by using more than one column connected by switching valves so that different parts of the sample can follow different paths through the column configuration.The technique can be used for sample clean-up (using front, heart and end cuts), trace enrichment, method development and resolution improvement. The advantages of this technique are that it is rapid and easily automated. There is a greatly reduced risk of environmental contamination and sample degradation is also minimised. However, as with all analytical methods, there are some problems. The complexity and cost are often the limiting factors and there is also a possibility of sample dilution. The most important problem, however, is solvent incompatibility when different modes of liquid chro- matographic separation are used. It is necessary to couple chromatographic columns that have different modes of separa- tion, for example, normal and reversed phase or size exclusion and reversed phase, so that fractionation and analysis occur by * To whom correspondence should be addressed.different separation processes. If this multi-mode requirement is not met then the advantage given by this technique is negated. I n order to overcome the incompatibility problem off- or on-line solvent evaporation and solvent exchange proce- dures have been used, although these are slow and cumber- some. On-line Multi-dimensional Separation of Aviation Fuel A system has been developed that overcomes the solvent incompatibility problem whilst simultaneously fulfilling the multi-mode criterion. This is achieved by using a cyclo-dextrin bonded phase column as the fractionation column. The cyclo-dextrins are a series of phases primarily designed to allow chiral resolutions by virtue of their shape.The cyclo-dextrins form cup-shaped molecules into which molecules of the correct size and charge distribution can diffuse and so be retained. The effect occurs in reversed-phase solvents with around 5-30% of the organic modifier and so are ideal for interfacing with conventional CI8 columns. The order of elution from these two columns is very different, therefore fulfilling the criterion of mode difference. The configuration that has been developed consists of three columns, three switching valves, a sample injection valve, two pumps and two detectors, as seen in Fig. 1. This system allows a sample to be analysed on any of the three columns or to allow a sample to be fractionated on either the Pump and injection device 11 q I - Detector Fig. 1.Schcmatic of the multi-dimensional HPLC configuration used for the determination of bcnzo[a]pyrenc in aviation fuel. Columns 1 and 2 are (3- and y- cyclo-dextrin columns. whilc column 3 is a Vydac polymeric Clx. All switching valves are pnuematically actuated Rheodyne series 7o(Kl6-port valvesANALYTICAL PROCEEDINGS. OCTOBER 1989. VOL 26 337 first or second column with the fraction of interest analysed on the second or third column. The specific determination of benzo[a]pyrene, a highly active pro-carcinogen, in aviation fuel has been used to highlight the function of the system. Fig. 2 shows the chromatogram that is obtained when a P-acetylated cyclo- dextrin column is used to fractionate the sample and the fraction of interest is analysed on a Vydac CI8 column. The benzo(a1pyrene peak is clearly visible; the detection limit using this method is below the concentration of benzo[a]pyrene that is usually present in aviation fuel and similar to other conventional off-line techniques.As already stated this tech- nique may also be used to allow pre-concentration and so picogram levels of benzo[a]pyrene can be detected. Multi- column techniques thus represent a powerful means of obtaining the resolution necessary to enable the analysis of complex samples. Owing to the increased complexity of operation, and the need for precise instrument control and measurement, computer based operation is not just an advantage but a necessity. In the system used in this study the switching valves are Detector response J 0 I \ 5 10 Retention ti rne/mi n Detector response Retention ti rn e/m i n Fig.2. Chromatograms showing the heart cut (top) and the resulting analytical separation (bottom) for a direct injection of 20 pI of aviation fuel. The conditions for the heart cut were: mobile phase, 40% acetonitrile in water 1 ml min-1; column, y-cyclo-dextrin 25 cm x 4.2 mm i.d. (Technicol, Stockport); detector, fluorescence excitation 254 nm. emission 420 nm: cut window, 45 s starting at 3 min 30 s. For the analytical separation the conditions were: mobile phase, 30% aceto- nitrile in water to 100% acetonitrile over 40 min, 1 ml min-l; column, Vydac C18 polymeric (Technicol, Stockport); detector, fluorescence excitation 254 nm, emission 420 nm controlled by intermediary pneumatic valves and the gradient is controlled via an external gradient programme, both linked to the computer.The system is also capable of receiving data from two detectors. The software is arranged as a number of inter-communicating modules and can be divided into two major parts: the chromatographic data station, similar to those available commercially, and the cybernetic system, written in PROLOG, a widely used artificial intelligence language. The cybernetic system relies o n a database of previously used analytical methods to optimise the separation by a limited form of intelligent processing. I t is necessary to use a rule based optimisation scheme rather than a simplex based optimisation method because of the extent and dimension of the search area.Some of the more important parameters to be optimised are outlined below: Fractionation column: cyclo-dextrin size mobile phase composition timing and duration of cut. Analytical column: bonded phase carbon loaded mobile phase gradient and flow-rate. Detector system: type and (if appropriate) wave- length(s). Pre-concen t ra tion: sampling time bonded phase carbon loading cleaning solvent eluting solvent. The size of the cyclo-dextrin ring is particularly important when determining the extent to which the analyte of interest is retained by the fractionation column. By using two different columns a very high degree of fractionation is possible. The mobile phase used to fractionate the sample also has a profound effect on the nature of the fraction. I t is possible to change the type of organic modifier and the percentage of water specifically to alter the elution time of the analyte with respect to the interferences.The timing of the cut and the duration have an effect on the detection limit. Usually, the cut time is adjusted to include as much of the analyte as possible without allowing the fraction to move too far down the analytical column; however, if the degree of fractionation is low then it may be necessary to reduce the heart cut window to exclude the interfering substances. Analytical separation and pre-concentration parameters can also be optimised. Conclusion The use of multi-dimensional high-performance liquid chro- matography has been shown to be a powerful analytical technique that allows the analysis of complex mixtures.The use of a computer system based on cybernetic software combined with this analytical method significantly reduces the analyst’s work load by allowing the rapid automated analysis of such samples. Simultaneous development of both the software and the chromatographic apparatus will lead to a system capable of automatically developing analytical methods for a wide range of analytes in many different matrices. References 1. 2. Sonnefeld, W. J.. Zoller. W. H.. May. W. E., and Wise. S. A . . Anal. Chem., 1982. 54. 723. Frceman, D. H.. Anal. Chem.. 1981, 53, 2.338 ANALYTICAL PROCEEDINGS, OCTOBER 1989. VOL 26 1 1 I f \Source n J \ n Drain J 1 Design Parameter Studies of Ion-selective Field Effect Transistor (ISFET) Sensors S. Johnson, G. J. Moody and J.D. R. Thomas School of Chemistry and Applied Chemistry, University of Wales College of Cardiff, P.O. Box 912, Cardiff CFl 3TB An ISFET (Fig. 1) is essentially a metal oxide semiconductor field effect transistor (MOSFET) with the metal gate electrode replaced by a silicon nitride layer (acting as an ion barrier) covered with a chemically-sensitive structure, consisting of an ion-sensitive membrane, or layer, and is used in conjunction with a reference electrode.' It acts as a transducer with the ion-sensitive membrane converting the chemical activity of an analyte species into a potentiometric response, whilst the field effect transistor part converts this into a change in the drain current flowing through the device. - Reference electrode PVC matrix ion- sensitive membrane Al Si02 p substrate Fig.1. Cross section of an ISFET The output of both types of FET fall into two regions, namely, the unsaturated and saturated regions (Fig. 2). In the former, the drain current is controlled by both the gate and drain voltages, whereas, in the saturated region with increasing drain voltage, it is the gate voltage which takes control. The relationship between drain current, ID, and chemical activity, a, has been derived from the drain current equations for the MOSFET.1 ID Unsaturated Saturated region I VD Fig. 2. Output characteristics of a FET showing graph of drain current, I D , versus drain voltage, VD. and the effect of increasing gate voltage, VG Thus, for the unsaturated region: where p is electron mobility, Cox the capacitance of the oxide layer, VD the drain voltage, V , the threshold voltage, VG the gate voltage, ERef the reference electrode potential, W and L are the width and length of the gate area, respectively, a is the activity of the analyte species and R , T , n and F a r e the gas constant, absolute temperature, valence and Faraday constant, respectively.From equations 1 and 2, it can bc deduced that the drain current is proportional to the aspect ratio (WIL) of the gate dimensions in the unsaturated region and to the ratio W/2L for the saturated region. It is advantageous to have an ISFET with a threshold voltage of zero, as this renders the advice less susceptible to noise. Modifying the number of charge carriers in the semiconductor substrate by ion implantation provides a method of controlling this voltage.For the design parameter studies of this work, a series of ISFET chips have been made in the manner described previously? These have three levels of boron ion implantation, with four gate aspect ratios for each of these levels (Table 1). Each chip contains two ISFETs, a diode and two MOSFETs equivalent to the ISFETs on that chip. These features allow the chip to be used to sense two chemical species and temperature concurrently, and to be used in a differential measuring mode which compensates for temperature changes. Table 1. Design parameters of ISFETs studied Ion-implanr levels- Wafer number PD294 PD298 5 x 10'1 Ion-implan tl 1 x 10'' ion cm-2 Gate dimensions- Chip Width. W Length, L Aspect ratio number /Clm /CLm WIL 1 200 12 16.6 2 400 12 33.2 3 400 20 20.0 4 800 20 40.0 PD302 3 x 101' W 2L 8.3 16.7 10.0 20.0 - The ISFET chips were mounted on to printed circuit board (pcb) dip-type probes and encapsulated with epoxy resin.The ISFETs were then conveniently accessed by dipping into solution with a reference electrode and varying the concentra- tion by spiking. Results and Discussion Threshold voltages, equivalent to those of the ISFEI's, were measured for the MOSFETs of each design (Table 2). The highest ion-implant level (3 x 1012 ion cm-2, wafer PD302) gave the threshold voltage closest to zero. The functionality of each sensor chip was tested by dipping, alongside a saturated calomel electrode (EIL 1370-710), in a solution of fixed concentration and monitoring the drain currcnt whilst varying the drain voltage, VD, and reference electrode potential, ERef.It was found by using this method and for the saturated region:ANALYTICAL PROCEEDINGS. OCTOBER 1989. VOL 26 339 Table 2. Threshold voltages Chip PD294/4 PD 29412 PD 294/1 PD298/4 PD298/3 PD298/2 PD 302/3 PD 30212 PD302/1 v,/ v -1.19 - 1.71 - 1.66 -1.28 -1.18 - 1.04 -0.26 -0.28 -0.05 (s.d.. ( -* (0.03. (0.03. ( -3 (0.11. ( -- (0.19, ( -* (0.25, that as many as 104 out of 124 ISFETs tested were non- functional at this stage. This can be ascribed to manufacturing errors. such as alignment errors, and to failure of encapsulation to adhere to the silicon surface. These factors are under investigation. The functional devices were taken and their ISFET gates coated with a PVC matrix based potassium ion sensing membrane containing PVC, valinomycin and dioctyl adipate (DOA) or dioctylphenylphosphonate (DOPP) (Table 3).These were calibrated for their responses to potassium ions by spiking with standard potassium chloride solutions and com- pared to determine the optimum aspect ratio and operating conditions. ~ ~ ~~~~ Table 3. ISFET sensing membrane composition Sensor Plasticiser/mg (%) valinomycin Identity PVC /mg(%) DOA DOPP A 195 (30) 9.07 (1) 678 (69) B 308 ( 3 3 ) 10.20 (1) 613 (66) The effect of varying the drain and gate voltages for a single chip is illustrated in Fig. 3. Operating in the saturated region gives calibration slopes of 49-50 PA decade- 1 , as opposed to 27 PA decade-' for the unsaturated region with VD and V , = 1 V.A comparison of the gate aspect ratio is shown in Table 4. Except for chip 2, it can be. seen that as the aspect ratio increases (from 16.6 for chip 1 to 40 for chip 4), the sensitivity, Table 4. Comparison of gate aspect ratios. All chips from wafer PD298 (ion-implant = 5 x 1011 ion cm-2) v,= l V . v D = I V V G = l V . V D = 3 V (unsaturated region) (saturated region) SI opelm V Slope/mV Chip W/L decade-' Range/M decade- I Range/M I 16.6 17 2 x lo-'- lo-' - - 2 33.2 12 6~ 1 0 - 4 - 10-1 23 1 X 10-'X lo-' 3 20.0 27 6~ 10-4- 10-1 49 4~ 10-JX lo-' 4 40.0 28 3~ 10-5- 10-1 61 1 X 10-'X 10-l - 5 -4 -3 - 2 - 1 log ([KCI]/M) Fig. 3. Response of chip PD298/3(iv) to potassium ions. A , Response for VD = 1 V, VRef = 1 V (slope = 27 pA decade-'); 0, response for VD = 2 V, VHef = 1 V (slope = 49 pA decade-'); 0, response for VD = 2 V, VKef = 1 V (slope = 50 pA decade-'); A, response for VD = 3 V, VRef = 1 V (slope = 49 pA decade-') denoted by the slope, also increases in both the saturated and unsaturated regions.The low slope for chip 2 can be explained in terms of the encapsulating epoxy having partially flowed over the gate area during curing, thus effectively reducing the gate width and, hence, the apparent aspect ratio. It can be seen that the slope is greater when operating in the saturated region and that the linear range extends to lower concentrations. With regard to the effect of solvent mediator, studied on chips PD302/2, the greatest slope was found for dioctyl adipate (DOA), implying that it is more suitable for potassium sensing than dioctylphenylphosphonate (DOPP).Conclusion The most appropriate ion-implant level in the chips design was 3 x 1012 ion cm-2, as this yielded the threshold voltage closest to zero. Greater sensitivity in the design can be achieved by utilising a larger gate aspect ratio, and operating the ISFET in the saturated region. Dioctyl adipate is a better solvent mediator than dioctylphenylphosphonate for use with vali- nomycin potassium ion sensor as it gives a better response graph slope to potassium ions. The authors thank the Science and Engineering Research Council for a CASE studentship to S. J . in association with AERE, Harwell. They also thank Drs. T. B. Pierce and J. Totterdell (AERE, Harwell) for their practical interest and Dr. J. M.Slater (Birbeck College, University of London) for helpful discussions concerning his design of the ISFET chips. References 1. Janata. J.. and Huber. R. J . , Ion-Selective Electrode Rev., 2. 1979, 1. 31. Slater. J . M.. PhD Thesis. University of Wales. 1987. C h em otaxono m ic ldent if icat io n of Tanacetum parthenium L. (FeverFew) Mark D. Burford and Roger M. Smith Department of Chemistry, Loughborough University of Technology, Loughborough, Leicestershire L E I I 3TU Feverfew (Turzacerunz parrhvrzium L. Schultz bip.) has been used for many centuries as a folk medicine. It is a yellowish- green perennial, with a strong camphor aroma, which grows to a height of 2-3 feet. The flowering head has a daisy-like340 ANALYTICAL PROCEEDINGS, OCTOBER 1989, VOL 26 appearance, the commercial variety having a single row of white rays and a yellow centre.The herb grows wild in British gardens, hedgerows and areas of wasteland. It is also cultivated throughout most of Europe and has been introduced into America. Traditionally, an infusion of the herb has been used as a febrifuge to relieve migraine, rheumatism and menstrual pain.' As the science of medicine advanced, feverfew, together with many other traditional remedies, fell into relative obscurity. A revival has occurred over the last decade, with a spate of publicity,2 including an article in the Lancet.3 Sesquiterpene lactones have been identified as being respons- ible for the medicinal properties of feverfew, with the germacranolide, parthenolide, being the major component.4-5 As part of a review of herbal remedies, the Department of Health is requiring manufacturers to provide bibliographic evidence of efficacy, safety and quality. Suppliers in Britain have encountered problems with regard to quality, as both German chamomile (Matricaria chamomiffa L.) and tansy ( Tanacerum vufgare L.) have been reported as being incor- rectly supplied as feverfew.6 Feverfew can be distinguished from these species by the presence of particular types of glandular and covering trichomes on the underside of the leaves.6 The application of microscopic examination is limited, as some commercial feverfew products are tinctures or gel preparations.As an alternative, the presence of parthenolide has been used to identify the plant,' although objections to this have been raised.6.8 The parthenolide has also been reported as being present in the adulterant tansy.9 Therefore, an easier means of identifying feverfew specimens was sought and in the present study flavonoids were examined as possible finger- printing markers.Discussion Powdered samples of finely chopped, fresh plant material or dried commercial preparations were extracted with refluxing methanol. The methanol extract was evaporated to dryness, re-dissolved in a methanol and water solvent and filtered. The filtrate was analysed on a reversed-phase high-performance liquid chromatography (RP - HPLC) system by using an ODs-Hypersil 5-pm column. Detection was by means of an ultraviolet detector at 254 nm and a diode-array spectro- photometer. The plant extracts contained a range of components which, from their ultraviolet - visible spectra, were assigned as plant phenolics [Fig.l(a)]. The two most prominent components of feverfew have retention times of 7.9 and 9.5 min and ultraviolet - visible spectra characteristic of flavones. Geman chamomile possessed a simpler phenolic distribution, its main components having retention times of 4.0 and 9.8 minutes [Fig. l ( b ) ] . From the ultraviolet - visible spectra, these components have been tentatively identified as a phenolic acid and a flavone, respectively. The tansy extract has many similar components to feverfew and it is hard to distinguish the two species by the retention times alone. However, a distinction can be made by examining the ultraviolet - visible spectra of the components using a diode-array spectrophotometer.Although both tansy and feverfew contain a major component at 9.5 min, these have different ultraviolet - visible spectra. The majority of phenolic compounds appear to exist throughout the plant, though a minority were present in localised regions, such as the flowering heads. This has important implications, as the plant leaves are a waste product in the manufacture of German chamomile tea, and are therefore a potential adulterant. Chromatograms from a number of samples of feverfew, German chamomile and tansy were compared in a chemo- metrics study by principal component analysis using the GENSTAT V program. The data was entered as relative areas compared with the internal standard 3-bromophenol (retention time of 34 min).The components were distinguished by their I I I 0 4 8 12 16 20 Tirne/rnin 0 4 8 12 16 20 Ti m e h i n 0 4 8 12 16 20 Tirne/m i n Fig. 1. HPLC separation of methanolic extracts of plant material with a methanol - acetate buffer (30 + 70 V/V) eluent and an ODs-Hypersil 5 pm column (a, feverfew; b, German chamomile; c. feverfew tablet) retention times and ultraviolet - visible spectra. The two- dimensional plots obtained from this study appear to differen- tiate the three species into three distinct clusters. A plot of the first and second principal component scores distinguished feverfew and German chamomile [Fig. 2 ( a ) ] , and a plot of the first and third scores distinguished feverfew and tansy [Fig. 2(b)]. These three scores account for about 47% of the original variation in the data.The distribution of phenolic compounds in four brands of feverfew tablets were analysed by the same procedure as the plants. The technique required two to three tablets, represent- ing about 75 mg of plant material, in order to obtain adequate detection. The tablets possessed phenolic compounds similar to the feverfew plants [Fig. l(c)]. Some of the minor components in the tablets were not resolved, especially when using the diode-array spectrophotometer. An additional com- ponent in the tablets was noted with a retention time of 11.5 min. This is thought to be due to a packing or binder constituent in the tablets. The tablet data was incorporated into the chemometric study. All four brands of tablet appeared on the edge of the feverfew cluster (Fig.2).ANALYTICAL PROCEEDINGS, OCTOBER 1989. VOL 26 7.00 6.00 5.00 4.00 ; 3.00 0 2.00- C al g 1.00- f s O - - m u a-1.00- c k -2.00 F -3.00 -4.00 -5.00 -6.00 -7.00 6.0C 5.0C 4.0C 3.0C v) 2.oa ? 8 i.oa $ 0 n E -1.0 8 g -2.00 c. 0 - .- 0 .: -3.00 n 0 C -4.00 v, -5.00 s -6.00 -7.00 -8.00 -9.00 - - - - - A a - - - - - - A A An A a fiA A A A a a a n A a n A # 0 ouoO ou 00 0 A U - 0 0 0 0 U 0 00 0 0 0 0 0 34 1 I c a A 0 OC 0 0 0 0 0 0 0 0 00 I 1 I 1 I 1 I First principal component scores Plot of principal component scores. Feverfew = 0, feverfew tablet = a, German chamomile = A. tansy = 0 First principal component scores Fig. 2. Conclusion There appears to be sufficient variation in the distribution of phenolic compounds for principal component analysis to distinguish feverfew from the patented adulterants German chamomile and tansy.The limitations arise when trying to differentiate feverfew from the closely related tansy species. To enable such a classification, the ultraviolet - visible spectrum of the phenolic compounds is required and this lowers the limit of detection. We thank SERC for a studentship to M.D.B., to Chelsea Physic Gardens for donating the feverfew varieties and British Analytical Control for donating the dried commercial plant preparations of feverfew, tansy and German chamomile. References 1. Editorial. Lancet. 1985. 1. 1084. 2. 3. 4. 5. 6. 7. 8. 9. 10. Lees, P., "The Migraine Cure that Caused a Headache," Farmers Weekly, November 2 , 1979. Collier. H. 0. J.. Butt.N. M.. McDonald-Gibson, W. J.. and Saeed, S. A.. Lancet, 1980. 2.922. Groenewegen, W. A.. Knight. D. W.. and Hepinstall. S.. J. Pharm. Pharmacol.. 1986,38. 709. Johnson. E. S., Kadam, N . P., Anderson, D.. Jenkinson. P. C., Dewdney. R. S.. and Blowers, S. D.. Human Toxicol.. 1987.6. 533. Berry. N. I., Pharm. J.. 1984, 232. 611. Awang. D. V. C.. Pharm. J.. 1987. 239.487. "French Pharmacopoeia," Commission franqais de Pharmac- opee, Maisonneuve, 1987. Bloszyk, E., and Drozdz, B., Acra SOC. Bot. Pol., 1978, 47. 3. Nano. G. M., Appendino. G.. Bicchi, C.. and Frattini. C.. Fitoterapia. 1980. 51. 135. Some Recent Developments in High-performance Liquid Chromatography in Biopharmaceutical Analysis Mary T. Kelly, Darioush Dadgar and Malcolm R. Smyth School of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland High-performance liquid chromatography (HPLC) is a widely used technique in the field of biopharmaceutical analysis.It enjoys a number of advantages over other analytical methods which are used in this regard: it is selective, permitting the separation of closely related species, including metabolites and isomers; it exhibits a high degree of precision; it lends itself well to automation; and method development for new compounds is relatively uncomplicated. Since it was first developed as a routine separation technique in the 193Os,l liquid chromatography has evolved into a highly sophisticated method. In terms of separation there are now available a variety of mechanisms which can be employed for any particular analysis.These include hydrophobic, micellar and ion-pair separations on alkyl modified silica, ion-exchange separations on resin based materials, size exclusion chromato- graphy and chiral separations. Classical solid - liquid adsorp- tion (normal phase) chromatography, though still used, has been largely superseded by reversed-phase chromatography, where separations proceed via hydrophobic interactions between polar solutes and the alkyl-modified stationary phase.342 ANALYTICAL PROCEEDINGS, OCTOBER 1989, VOL 26 Hydrocarbon modified supports were first produced in the early 1950s by reacting silica with alkyl silanes2; nowadays, many types of modified surfaces are available, including the non-polar c18-, CS-, and C2-, and the polar CN- modified packing.The advantages of reversed-phase chromatography are that it is versatile and rugged, has wide applicability, and uses water-based mobile phases which are less hazardous and expensive than the typical organic eluents used in normal phase separations. A major problem with the use of reversed-phase materials, however, is poor chromato&aphic characteristics for basic compounds. This problem has been shown to originate from electrostatic interactions between the basic amino function and unreacted silanol moieties on the silica surface.3.4 Much attention has, therefore, been focused on the elimination of these remaining silanol groups through the use of secondary bonding reactions (end-capping) , paired-ion chromatography or ion suppression.5 By employing an unmodified silica column in conjunction with buffered, aqueous, methanol-rich eluents, as first proposed by Jane in 1975,6 the amine - silanol reaction is exploited and efficient separations are obtained for basic compounds via a mechanism that proceeds largely through ion-exchange interactions.7-9 As the silanol groups are weakly acidic, they are only ionised at neutral or basic pH values,8 and therefore at high pH values they are available to partake in ionic reactions with oppositely charged protonated bases.The mobile phases used in this chromatographic mode would typically contain 7&90% methanol, with the aqueous com- ponent buffered for reproducible separations. Ammonium salts are preferred to sodium salts as they tend less to dissolve the silica packing.If adequate care is taken in terms of analytical column maintenance, pH values of 10 or greater can be employed. The pH of the mobile phase will be determined by the pK, of the compounds to be separated; lowering the eluent pH, while rnaximising amine ionisation, will reduce the number of ionised silanol groups available to engage in electrostatic interactions. Assuming the ion exchange theory of retention, separations will be strongly influenced by factors such as pH, ionic strength and, to a lesser extent, the percentage methanol in the mobile phase. This chromatographic mode can be coupled to a column switching assembly in order to permit on-line extraction of plasma samples prior to ion-exchange separation. The instru- ment arrangement incorporating a six-port switching valve, which was used in this study, is shown in Fig.1. The plasma sample is introduced via the injector port and swept on to the concentration column by water from pump A. Drug com- pounds are selectively retained on the concentration column while the endogenous plasma components are eluted to waste. Concentration column Injector +)PumpA & I m Drain To detector I 0 Fig. 1. valve Column switching assembly incorporating a six-port switching Meanwhile, the mobile phase eluent is being passed by pump B through the analytical column, which is thus maintained in a state of constant equilibration. Upon switching the valve, the mobile phase flow is diverted in a backflush mode via the concentration column, from which the retained analytes are desorbed and swept on to the analytical column, where they are separated.In our recent studies10 it was found that the use of octyl-bonded silica in the concentration column gave better recoveries for most drugs than octadecyl-bonded silica. This may be explained in terms of the less hydrophobic material showing greater affinity for the more polar solutes. Sample chromatograms of some drugs extracted on-line by this method are shown in Fig. 2. A reproducibility study carried out on the analysis of 30 drugs of therapeutic interest, demonstrated that the coefficient of variation of quintuplicate spiked plasma standards never exceeded 8%, and was usually below 5 % . The low levels of variability, even in the absence of an internal standard, are possible because of the inherent reproducibility of the column-switching technique, especially when compared with liquid - liquid extractions which may require many steps, and can thus permit the introduction of artefacts. Recovery from plasma (measured by comparing peak heights of spiked plasma standards against aqueous solutions in the same concentrations) was found to be 90% or greater for most of the drugs studied.Some drugs do, however, exhibit particularly low percentage recoveries, which may result from protein binding, and these compounds would require more vigorous extraction methods, such as liquid - liquid extraction or protein precipitation. in order to liberate them from their binding sites. 0 a 6 12 0 Ti me/m i n A I I I 6 12 Fig. 2. Chromatograms of extracted plasma standards: ( a ) , propran- 0101, 1.25 pg ml-l (P) and atenolol, 5 pg ml-1 (A); ( b ) , propranolol, 0.25 pg ml-1 (P) and atenolol, 1 pg ml-1 (A).Mobile phase: ammonium nitrate - ammonia 0.05 M , pH 9.5 (20 + 80 in methanol) One of the disadvantages of using unmodified silica in this way is column deterioration, evinced by a loss in chromato- graphic efficiency, the development of voids and reduced column life. This may largely be overcome by the use of a guard column in order to trap contaminants, and a pre-column to saturate the mobile phase with silica.ANALYTICAL PROCEEDINGS. OCTOBER 1989. VOL 26 343 Recently, Laurent et al. re-appraised the application of alumina as a solid support in column liquid chromato- graphy.11.12 They demonstrated that alumina can be used in an ion-exchange mode in a manner similar to unmodified silica.However, the amphoteric nature of alumina confers on it the ability to behave as either a cation- or an anion-exchanger. The pH at which the alumina surface is neutral and bears no charge is the zero point charge (ZPC). The pH at which the ZPC occurs is related to the method of production of the alumina, and depends on the nature of the ions in the surrounding solution. For instance, in the presence of phosphate or acetate ions, the ZPC occurs at pH 6.5, whereas in the presence of citrate ions it is as low as 3.5.13 Therefore, alumina will behave as an anion exchanger if the pH is below these values, and as a cation exchanger if the pH is above these values, and hence the surface properties of the column, and retention characteristics of dissolved solutes.can be manipulated by judicious choice of pH and buffer ion. By use of a phosphate buffer system in methanol-rich eluents, the retention characteristics of a number of com- pounds of therapeutic interest have been studied.'.' Having selected a suitable mobile phase, the analytical system was coupled to the column switching assembly shown in Fig. 1. Alumina was found to be well suited to on-line solid - liquid extraction, and clear drug-free plasma chromatograms were obtained at both acidic and basic pH values. In contrast, when plasma spiked with 200 ng ml-1 of the drug fluphenazine was extracted and separated in this way, there was a pronounced shift in drug retention relative to that of the plasma constitu- ents with changing eluent pH.This would indicate that it is possible to manipulate the mobile phase to maximise separa- tion of the compounds of interest with little danger of introducing unacceptable interfering peaks from the plasma matrix. This type of chromatography would appear to offer an advantage over conventional bonded-phase methods, in that endogenous components are not sufficiently ionised to be retained via ion-exchange mechanisms, and hence are rapidly eluted with the solvent front. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. Dale, A. D.. Anal. Proc.. 1983, 20. 200. Howard. G . A., and Martin, A. J. P., Biochem. J., 1950. 46. 532. Papp, E.. and Vigh. Gy.. J. Chromatogr., 1983. 259, 49. Papp. E.. and Vigh. Gy., J. Chromatogr., 1983, 282.59. Wehrli, A.. Hildenbrand. J . C., Keller, H. P., and Stampfli, R., J. Chromatop.. 1978, 149, 199. Jane, I., J. Chromatogr., 1975, 111, 227. Schmid. R. W.. and Wolf, C.. Chromatographia, 1987.24. 713. Flanagan. R. J.. and Jane. I.. J. Chromatogr., 1985,323, 173. Cox, C. B., and Stout, R. W., J . Chromatogr.. 1987,384, 315. Kelly, M. T.. Smyth, M. R., and Dadgar. D., Analyst, in the press. Laurent. C. J . C. M., Billiet, H. A . H., and de Galan, L., Chromatograptiia, 1983, 17, 253. Laurent, C. J. C. M.. Billiet, H. A. H.. and de Galan, L., Chromatographia. 1983, 17, 394. Laurent, C. J . C . M.. Billiet, H. A. H., de Galan, L., Buytenhuys, F. A.. and Van der Maeden, F. P. B.. J. Chromatogr., 1984, 287, 45. Kelly, M. T., Smyth, M. R, and Dadgar, D., J.Chromatogr., 1989, 473, 55. Voltammetric Methods in the Analysis of Anaerobic Sealants M. C. Brennan Department of Chemistry, University College, Cork, and Loctite (Ireland), Tallaght, Dublin 24, Ireland G. Svehla Department of Chemistry, University College, Cork, Ireland Anaerobic sealants are made up of a complex mixture consisting of methacrylate monomers, free radical inhibitors, free metal inhibitors, initiators, accelerators, inert fillers, plasticisers, colouring agents, etc., formulated in rigidly controlled concentrations. They remain liquid while stabilised by the presence of oxygen. When squeezed into a screw thread, the monomer is starved of oxygen and this, together with the catalytic effect initiated by the metal parts, causes the acrylate resin to polymerise and set.Many analytical techniques are applied to monitor and characterise raw materials, intermediates and the final pro- ducts: among these voltammetry was found to be useful in solving certain problems. In this paper a few such cases are discussed briefly. The instrument employed in this study was an EGG(PAR) 384-4 polarographic analyser equipped with an X-Y recorder and a 384 microprocessor console, offering capabilities such as normal and sampled d.c. , normal and differential-pulse anodic and cathodic stripping, as well as linear sweep and cyclic voltammetry. The 384 console controls the experimental parameters, such as initial and final potential, along with drop time, scan increment and purge time. Both direct calibration and standard addition methods can be used, and the micro- processor provides peak location, peak height and peak area reading, blank subtraction, linear regression analysis for the calibration curve and final evaluation and printout.The Model 303 static mercury (dropping or hanging) electrode, combined with current sampling, provides currents which are almost completely faradaic. A silver - silver chloride reference electrode and a platinum wire counter electrode complete the cell, in which facilities for the removal of oxygen (by purging with nitrogen) are also provided. Results and Discussion Substrate Analysis1 A problem associated with the bonding of brass metal which contains mainly copper and zinc was traced to the fact that certain brasses can contain up to 5% of added lead.This metal inhibits the formation of free peroxide radicals. For the voltammetric determination of lead in brass, a known mass of the sample was dissolved in concentrated nitric acid and evaporated to dryness. The residue was taken up in 0.1 M ammonium citrate (pH = 3.0) and scanned by using differen- tial-pulse voltammetry (DPV) between -0.1 and - 1.2 V. The voltammograms in Fig. l(a) show the typical peaks associated with zinc and copper, but the presence of lead was evident in the slower curing brass composition [Fig. l(b)]. Trace Metal Analysis of a Typical Anaerobic Composition2~3 The presence of adventitious metal contamination, especially from raw materials or manufacturing processes, can be very pronounced and can have adverse effects on the final product quality.If oxygen was removed from the holding container, the334 ANALYTICAL PROCEEDINGS. OCTOBER 1989. VOL 26 4.0 3.0 .- 2.0 1 .o 0 4.0 3.0 2.0 1 .o 0 -0.9 -0.5 -0.1 I E I I I I I I -0.9 -0.5 -0.1 E Fig. 1. Typical DPV peaks obtained with brass in 0.1 M ammonium citrate. pH = 3.0: ( a ) . contains no lead; (b). contains4.5% lead, which was confirmed by rc-scanning with a known concentration of lead ~ Fe -1.2 -1.0 -0.0 -0.0 -0.4 -0.2 0 E -1.2 -1.0-0.8 -0.6 -0.4-0.2 0 E Fig. 2. DPASV of trace metal content of a typical anaerobic sealant in 0.1 ammonium citrate, pH = 3.0. ( a ) , Voltammogram in the presence of Zn, Fe. Cd, Pb and Cu; (b). voltammograms obtained with standards of 100 p.p.b. of Zn. Cd. Pb and Cu added to the same volume of supporting electrolyte Table 1.Comparison of AAS and DPV for the determination of iron species in commercial “oil soluble” iron salts Sample Sample Sample A,% B.% C,% Total Fe (as specified by manufacturer) 6.0 9.0 16.0 Total Fe (by atomic absorption) 6.0 8.8 16.0 Fe3+ (by DPC) 6.0 7.5 13.2 Fez+ (by DPV) 0.01 1.3 2.8 presence of these contaminated metals would lead to rapid polymerisation of the product and render it useless. Using differential-pulse anodic stripping voltammetry the determina- tion of such trace metals was canied out in the following way: 5.0 g of a sealant were ashed at 550 “C for 4 h along with 0.1 g of p-toluenesulphonic acid in order to avoid a loss of volatile metals. The resulting ash was dissolved in 20 cm3 of 0.1 M ammonium citrate - citric acid buffer (pH = 3.0) and 10 cm3 of this were added directly to the electrochemical cell.After deposition, metals were stripped by using DPV and scanning from -1.2 V to 0.3 V. Fig. 2(a) shows the voltammogram obtained with a commonly used sealant. Standards of 100 p.p.b. of Cu, Zn, Cd and Pb were added to the same volume of supporting electrolyte without sample and treated as before [Fig. 2(b)]. The large peak at 0.93 V, shown in Fig. 2(a), is due to iron which is generally present in higher concentrations than the other metals. Polarographic Study of Chelators in Anaerobic Sealants ( a ) Chelators are normally added to the anaerobic sealant to improve stability. For each formulation there exists an optimum concentration for the chelator. Quantifying the level of chelator in these products is therefore a frequent analytical task.It is possible to determine the concentration of EDTA in sealants using the DPV mode by taking advantage of the fact that certain metal - EDTA complexes are reduced at more E Fig. 3. Determination of EDTA-type chelators in anaerobic sealants in 0.1 M sodium acetate buffer. (a). Scan of Cu on its own; (b-d). scans of increasing concentration of sealant containing the chelator negative potentials than the metal itself.4 If an excess of a metal ion, such as copper, is added to a suitable electrolyte (e.g., 0.1 M acetate buffer of pH = 5.0) followed by a known amount of the sample dissolved in methanol, two separate peaks appear. Fig. 3 shows the voltammograms of copper alone (a) and of copper and copper - EDTA mixtures with increasing EDTA concentration (6-4. Knowing that the metal - ligand ratio in the complex is 1 : 1, it is possible to determine the concentra- tion of chelator using a standard addition method. (b) We used DPV for establishing the composition of the Cu - EDTPA complexS [EDTPA = l,l’,l”,l”’-ethylenedinitrilo- tetra(propan-2-01), a compound used in some formulations].Job’s method of continuous variation was used. The heights of the two peaks due to free copper and the Cu - EDTPA complex were measured [Fig. 4(a)] and a Job plot was prepared as in Fig. 4(b). From the intercept of the two lines the metal - ligand ratio was established as 1 : 1. Metal Speciation Study in Anaerobic Sealants6 It is well known in the sealant industry that certain oxidation states of metals behave differently, hence the determination of metals in different oxidation states are of great importance.The different oxidation states of iron can be determined in a pyrophosphate buffer at pH = 9.0. Under these circumstances iron(II1) forms a very stable complex with phospahte; the reduction of the complex occurs at a more negative potential than that of iron(I1) [Fig. 5 ( a ) ] . The results in Table 1 show an example of the advantage of voltammetry over atomic spectro- scopy, by which speciation would not be possible.ANALYTICAL PROCEEDINGS. OCTOBER 1989. VOL 26 345 1 ._ 0.5 0 E -0.1 -0.3 E -0.2 Fig. 6. Voltammograms for speciation of Sb3+ and Sbs+. ( a ) , Both Sb3+ and Sbs+ are determined in 6.0 M HCl; ( b ) , only Sb3+ is determined in 1.0 M HCl I I C Fig.4. Job’s method of continuous variation for the determination of the composition of the Cu - EDTPA complex I Cr Fe3- I E Fig. 5. Voltammograms showing speciation of Fez+ and Fe3+ in commercial “oil soluble” salts. ( a ) , Sample containing Fe3+ only; (b), sample containing both Fez+ and Fe3+ o L ‘ I 1 1 0- -0.6 -0.8 -1.0 -1.2 -0.8 -1.0 -1.2 E Fig. 7. Voltammograms of CP+ and Cr3+. ( a ) , The determination of Cr*+ was carried in 0.5 M NaOH; ( b ) . Cr3+ was determined in 0.2 M KSCN - CH3COOH (PH = 3.2) The relative amounts of antimony(I1) and antimony(V),7 present in various forms in sealants, have an effect on the adhesive qualities of the product. To measure the total concentration of antimony a very strong acidic electrolyte (6 M HCI) must be used.In 1 M hydrochloric acid only the Sb(II1) is reduced. Therefore, by simple subtraction, the concentration of both oxidation states can be estimated (Fig. 6). Chromium metal can exist in solution as chromium(II1) and chromium(VI)* (chromate). The quantity as well as oxidation state of the chromium is important where porous metal sealants are concerned. These special sealants are used to fill holes generated in the manufacturing of aluminium engine blocks for the automobile industry, and a high concentration of chro- mium(V1) can retard the curing rate to such an extent that production rate and quality of sealing may be adversely effected. Both oxidation states can be determined separately using 0.5 M sodium hydroxide for the determination of chromium(V1) and 0.2 M potassium thiocyanate - acetic acid (pH = 3.2) as supporting electrolyte for the determination of chromium(II1) (Fig.7). Examples of the Application of Voltammetry of Non-metallic and Organic Compounds The determination of sulphur dioxide,g which is added as a stabiliser to certain sealants, is important as its concentration is critical with regard to shelf life and the rate of curing on substrates. This gas, which is reduced at the mercury drop, can be determined by simply adding a known volume of the sealant to 10 cm3 of supporting electrolyte (DMSO containing 100 PI of sulphuric acid). Quantification by standard addition is the preferred method, using a standard solution of sodium sulphite in 75 + 25 ethanol - water solvent (Fig. 8). Trace amounts of fumaric acid in maleic acid10 can be readily determined in sealants, using 0.2 M phosphate buffer with 1 M ammonium chloride (pH = 8.2, see Fig.9). The determination of phosphate can be carried out after converting it to the phosphomolybdate complex, which can be determined” by DPV. The POj3- is first extracted intoANALYTICAL PROCEEDINGS, OCTOBER 1989. VOL 26 346 8 6 .-a 4 2 0 2 ! I 1.5 C 1 E Fig. 8. The determination of SO? in anaerobic sealant in 10 cm3 of DMSO containing 100 pl H2S02. ( a ) , The calibration curve; ( b ) , voltammograms 1u 1 I I 1 I I I -1.0 -1.2 -1.4 -1.6 -1.8 t Fig. 9. in 0.2 M phosphate - ammonium chloride buffer (pH = 8.2) Determination of traces of fumaric acid in maleic acid samples deionised water and the water layer is separated and treated with acidic ammonium molybdate followed by hydrazine sulphate.The mixture is then heated to 90 "C for 30 min to form molybdenum blue. After cooling to room temperature 5 cm3 of 2.5 M sulphuric acid is added, and this is followed by an extraction with isoamyl alcohol. After separation, the complex can be re-extracted into a tartrate buffer (pH = 3.0) and scanned (Fig. 10). Characteristic double peaks are obtained; the first peak is used for quantification. The analysis must be completed in less than 20 min as the complex begins to degrade after this. Conclusion This brief description of selected applications of voltammetry for the study of anaerobic sealants indicates the flexibility of 2.0 1.5 1 .o '_ 0.5 0 Fig. 10. 2 a) -0.3 -0.5 I I 2 1 u / -0.3 -0.5 E The determination of Pod3- in tartrate buffer (DH = 3.0).( a ) , Sample contaminated with P043L: ( b ) , as ( a ) , but with'i.O pgcm-3 of POJ3- added the method, allowing the determination of metals, gases and organic substances with only one instrument with little or no change in cell design. These are only a few examples of analyses that can be carried out on anaerobic sealants, without separation or pre-concentration. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References Kolthoff, I. M.. and Lingane, J. J.. "Polarography." Second Edition. Volumes 1 and 2. Interscience, New York, 1965. p. 582. Wang. J.. "Stripping Analysis. Principles. Instrumentation and Applications," VCH Publishers Inc., Weinheim. 1985. p. 109. "A Table of Selected Half-Wave Potentials for Inorganic Substances," EGG(PARC).Application Note H-1, 1980. Hoyle. W.. Sanderson, I. P.. and West. T. S.. J. Electroanal. Chem. ,1961, 2 . 166. Brennan, M. C.. MSc Thesis. Queens University Belfast. 1986, Kolthoff, I. M.. and Lingane, J. J.. "Polarography," Second Edition, Volumes 1 and 2, Interscience. New York. 1965. p. 475. Kolthoff, I. M.. and Lingane, J. J., "Polarography." Second Edition, Volumes 1 and 2. Interscience. New York, 1965. p. 545. "Application Brief C-2: Chromium by Differential Pulse Polaro- graphy," EGG(PAR), 1976. Sawyer, D. T.. George, R. S.. and Rhodes. R. C.. Anal. Chem., 1959, 31, 2. Elving, P. J.. and Rosenthal. I.. Anal. Chem.. 1954, 26. 1454. Grasshoff. K.. and Hahn. H., 2. Anal. Chem.. 1962. 187. 328. p. 38. New Approaches to Chiral Resolution of Drug Enantiomers and Related Compounds by HPLC A.M. Dyas and M. L. Robinson International Development Laboratory, E. R. Squibb & Sons, Moreton, Merseyside 146 10 W A. F. Fell Pharmaceutical Analysis Research Unit, School of Pharmacy, University of Bradford, Bradford, West Yorkshire BD7 1DP It has long been appreciated that drug - receptor interactions are highly orientation-specific, with subtle changes in structure eliciting profound pharmacological results. Recent investiga- tions have shown that this specificity involves the stereochem- ical nature of a molecule with chiral drugs exhibiting stereospe- cific pharmacology. This specificity can result, for example, inANALYTICAL PROCEEDINGS. OCTOBER 1089. VOL 26 347 one enantiomer being the more active, as in the case of the antihypertensive agent propranolol, where the (S)-form is 100 times more potent than the (R)-form.l In some instances the other enantiomer may exhibit undesirable properties such as toxicity (e.g., thalidomide, where the S-form is primarily responsible for birth defects’), differential metabolism andor excretion, or even a completely different therapeutic action.In 1082 it was observed that many of the most frequently prescribed drugs in the US were chiral in nature,3 and in 1986 it was shown that approximately one quarter of the 700 most frequently prescribed drugs worldwide were marketed as racemic mixtures.4 These statistics, coupled with the potential pharmacological implications of drug chirality, have led to growing legislative concern which has, in turn, added to the impetus to develop suitable separation mechanisms for the analysis of enantiomers in drug development and quality assurance.Separation Strategies Three HPLC separation strategies are currently in common use for the separation of enantiomers, namely diastereomer formation, chiral mobile phase additives and chiral stationary phases. Diastereomer formation is an indirect technique in which the sample mixture of enantiomers is derivatised with a pure chiral reagent to introduce another chiral centre into the molecule and thus give rise to a pair of diastereomers. Whereas enantiomeric pairs have identical physical properties (except for optical activity), diastereomers differ in their internal energy and can thus be separated on conventional columns, which is a major advantage of this approach.However, the derivatisation stage can be laborious, display differential reaction rates and requires a pure reagent to avoid formation of interfering diastereomeric pairs. Side-reactions can also pro- duce peaks, which may cause confusion. The use of chiral mobile phase additives is also popular as they offer direct separation of enantiomers whilst allowing the use of existing column technology. The additives form short-lived dias- tereomeric complexes with the enantiomeric analyte, with the complex having a different retention time from the enan- tiomer. Thus, one enantiomer will form a more stable complex than the other so that the two can be resolved. A drawback of this procedure is that the additive might interfere with detection, might be difficult to remove in the case of preparative LC, and can be expensive. The third approach is based on a different column technology using chiral stationary phases, where the chiral selector is bound to a support material such as silica.Transient diastereomeric complexes are formed between the enantiomeric analyte and the bound chiral selector. Chiral column technology is a rapidly expanding field in which over 50 phases are commercially available. In 1987 Wainers classified the available phases into the following five categories according to the putative separation mechanism. Table 1. Chiral stationary phase classification (after reference 5) TY Pe Mechanism Example I Attractive-interaction DNBPG* I1 Interaction - inclusion Cellulose triacetate I11 Cavity-inclusion 0-Cyclodextrin IV Ligand-exchange Proline.valine V Protein affinity Bovine serum albumin. ru,-acid glycoprotein * (R)-N-(3,5-Dinitrobenzoyl)phenylglycine. The fact that the separation mechanisms occurring have not been adequately elucidated presents a major drawback to the use of chiral stationary phases. Thus, no satisfactory guidelines for the selection and optimisation of a given separation are currently available so that method development has to be approached empirically. This paper describes the preliminary work undertaken as part of a wide ranging investigation of the principal factors affecting the separation of a variety of compounds on a number of stationary phases, the objective being to evaluate the relationship between molecular structure and chromatographic separation.In the present work, the separation of a number of @-blocker drugs on a Type I phase has been examined. Type I “Pirkle” Phases Type I phases are often called “Pirkle Phases” after their inventor, who developed the first commercially available version in 1981.6 This first phase consisted of DNBPG ionically bound to aminopropyl silica (Fig. 1). A number of more stable, C-N -CH - C- II I d A 0 OZN Fig. 1. Pirkle stationary phase I covalently-bonded Pirkle phases have since been developed. Wainer categorised these as “attractive-interaction phases,” where the enantiomeric analyte is attracted to the chiral selector at three points in its structure, in accordance with the Dalgliesh theory.’ The enantiomer with the more favourable spatial arrangement is able to form the more stable complex, while the less stable complex elutes first. Enantiomers are thought to interact with the phase by means of n-n bonding with the benzene rings, dipole stacking with carboxyl groups and hydrogen bonding to ester and amide groups.This phase is elegantly simple and can be prepared by mixing the silica support with a solution of DNBPG in a suitable solvent, such as tetrahydrofuran, a procedure which can be carried out in situ on a ready packed amino column. However, the column must be handled with care as the chiral selector is only held on the column by ionic attraction; thus, the presence of water in the solvents and the use of high concentrations of polar solvents, such as methanol, leads to gradual stripping of the selector from the column. This can be partially remedied by passing a solution of the chiral selector through the column again, a procedure which improves performance slightly, but does not necessarily remove any contaminants bound to the exposed support. Type I phases were chosen as the first phase to be investigated, as they are relatively inexpensive and can be prepared simply in-house.The P-blocker drugs were selected as model compounds because of their wide availability, clinical importance and the fact that they represent a broad range of structures. Separation of P-Blockers on a Pirkle Phase Despite the vulnerability of the ionic DNBPG phase it is popular because it is very easy to prepare.The chromatogram shown in Fig. 2 was obtained less than 2 days after starting to prepare the packing. The column is a 100 x 4.6 mm (i.d.) steel column containing 5 pm aminopropyl silica coated with 6.5% m/m DNBPG. The eluent was propan-2-01 - hexane (1 + 4 V/V) flowing at 2 ml min-1 with detection at 254 nm. The enantiomers of propranolol are partially resolved ( R , = 0.75) with some peak tailing, the column exhibiting over 15000 theoretical plates per metre. The racemic mixture of pro- pranolol could not be injected directly as the secondary amino group had first to be derivatised. This was achieved by use of a348 ANALYTICAL PROCEEDINGS, OCTOBER 1989, VOL 26 I I 1 10 20 30 Elution ti me/mi n Fig. 2. ary phase (see text for details) Separation of P-blocker enantiomers on a Pirkle-type station- facile procedure developed by Yang et aZ.,s where the P-blocker was mixed with a solution of phenylisocyanate (three-fold excess) in hexane. The amino group rearranges with the isocyanate group to give the phenylureide shown in Fig.3. However, when the same procedure was applied to the P-blocker nadolol (Fig. 3) the same separation was not achieved. The nadolol enantiomers, differing in their configu- ration at the a-carbon (C2), were unresolved and strongly retained on the column (Fig. 2). Nadolol is the tetrahydronaph- thalenediol analogue of propranolol, in which the naphthalene ring is saturated. If the x electron interaction is involved in the separation procedure, the loss of planar configuration and delocalised JC electrons would be expected to lead to loss of resolution and reduced retention.The lack of resolution observed in Fig. 2 is coupled with increased retention; this may be due to the strong polar attraction between the diol group and the stationary phase masking the delicate polar forces which characterise chiral separation on the Pirkle phase. Work R1-OCH2CHCH2NHC(CH3)2-R2 + N=C=O -+ NH-C-i I OH I Id ‘C H ~ C H CH +R, OH Nadolol R, = R2 = CH3 Fig. 3. Derivatisation procedure for P-blockers is currently proceeding to evaluate the effect of the structure of other P-blockers on separation by DNBPG as well as the effect of the naphthalene C6 or C7 substituents of nadolol on its chromatography. 1. 2. 3 . 4. 5 . 6. 7. 8. References Barrett, A . M., and Cullum, V.A, Brit. J. Pharmacol., 1968, 34,43. von Blaschke, G., Kraft, H. P., Fickentscher, K . , and Kohler, F., Arzneim.-Forsch., 1979, 29, 1640. Dennis, R., Pharmacy International, October, 1986, p. 246. Noctor, T. A. G., Clark, B. J., and Fell, A . F., Anal. Proc., 1986, 23, 441. Wainer, I. W., Trends Anal. Chem., 1987, 6, 125. Pirkle, W. H., Finn, J. M., Schriner, J. L . , and Hamper, B. C., J. Am. Chem. SOC., 1981, 103,3964. Dalgliesh, C. E., J. Chem. SOC., 1952, 3940. Quin Yang, Zeng-Pei Sun and Da-Kui Ling, J. Chromatogr., 1988, 447, 208. Determination of Nicotine Metabolites by HPLC After Complexation with Diethylthiobarbituric Acid C. L. Smith, S. O‘Doherty, M. Cooke and D. J. Roberts* Department of Inorganic Chemistry Cantock’s Close, Bristol BS8 1 TS There is a need to find a suitable biochemical marker to determine whether or not a patient in a clinical situation has been subjected to tobacco smoke.Tobacco smoke is a mixture of gaseous and particulate phases in which at least 2000 compounds have been identified. 1 The gaseous phase contains carbon monoxide, carbon dioxide, ammonia and hydrogen cyanide, amongst other compounds, and the particulate phase consists of “tar”, water and tobacco alkaloids, mainly nicotine. As the nicotine found in the human body is present mainly as a consequence of either active smoking, i. e . , direct inhalation from the cigarette, or passive smoking, i . e . , the inhalation of other people’s tobacco smoke in the atmosphere, the measure- ment of nicotine and its metabolites has proved to be a useful marker for indicating smoking activity. Of the nicotine that enters the body 8&90% is metabolised.The metabolism of nicotine is complex and is not yet fully * 1’0 whom ail correspondence should be addressed. understood. There are, however, believed to be two main pathways by which nicotine can be metabolised. About 70% of the nicotine is metabolised by the oxidation of the 5’ carbon to give cotinine. This then undergoes further metabolism, and recent research shows that a major metabolite of cotinine may be 3’-hydroxycotinine with only trans-3-hydroxycotinine present in biological samples. A further 4% of the nicotine is N-oxidised to form nicotine-N-oxide. None of these metabol- ites is retained by the body and are all excreted in the urine.This is fortunate because urine is an easier biological sample to handle as its collection is non-intrusive compared with the collection of blood samples. There have been many methods reported in the literature for the determination of nicotine and its metabolites in biological fluids, including ultraviolet spectroscopy, radioimmunoassays, thin-layer chromatography, gas chromatography, high-perfor- mance liquid chromatography and high-performance liquid chromatography - mass spectrometry. Ultraviolet (UV) spec-ANALYTICAL PROCEEDINGS. OCTOBER 1989. VOL 26 349 troscopy, however, is not very sensitive or specific for determining nicotine metabolites. Radioimmunoassays, on the other hand, are very sensitive but require frequent checking of standards and can be very expensive.Thin-layer chromato- graphy (TLC) is another technique that is a useful qualitative method but is of very little quantitative use. A technique which is in regular use is gas chromatography (GC). However, before GC can be used, nicotine and its metabolites must be extracted from the biological fluids and this often involves lengthy procedures which usually result in the loss of some of the metabolites. The GC method is often specific for only one or two metabolites, and is, of course, limited to thermally stable, volatile species: a classification which excludes the majority of nicotine metabolites. Experimental The HPLC system consisted of Shimadzu pumps and gradient system with a Pye Unicam UV detector fitted with the visible kit and the complexes monitored at 530 nm.The mobile phase was a mixture of distilled methanol and distilled water, containing sodium heptanesulphonate as an ion pairing agent. The gradient was linear from 35% methanol to 70% methanol. A 10 cm Lichroma c18 ROSil column with 3 pm particles was used as this was found to give the best peak separation. However, several other types of reversed phase material are capable of separating cis- and truns-3'-hydroxycotinine. The outline of the extraction procedure is as follows: 1 ml of urine was taken and 0.4 ml of a pH 4.7 acetate buffer added. At 15-s intervals, KCN, chloramine T and diethylthiobarbituric acid were added. The timing of the addition of the reagents was important and had to be strictly adhered to, otherwise the intensity of the red coloration changed.The reaction mixture was left for 20 min in order to standardise colour development and then passed through a CI8 Sep Pak. Extraction with methanol yielded an extract suitable for injection into the HPLC system. Colour stability is lower in the absence of excess reagents and so analysis should follow extraction as quickly as possible. 4 nl, 5 & I I I I 1 I I I 0 10 20 30 40 Retention tirne/min Fig. 1. Gas chromatogram of smoker's urine. Column, 10 m Carbowax 20 M capillary; temperature gradient, hold at 60 "C for 2 min then 5 "C min-1 from 60 to 180 "C, 7 "C min-* from 180 to 235 "C; detector, nitrogen selective. Peak: 1, nicotine; 2, CllHZ3CN internal standard; 3, C&133CN internal standard; 4, cotinine; 5 , caffeine; 6, 3'-hydroxycotinine Results and Discussion A preliminary GC study was undertaken using a simple clean-up method with c18 Sep Pak, a small solid phase extraction cartridge filled with a reversed-phase adsorption material.This has proved to be a successful simple technique, 3HC 4N N NIC - 5 10 15 20 25 30 Retention timehnin Fig. 2. HPLC of diethylthiobarbituric acid complex of a 10 p.p.m. mixture of nicotine metabolites. Column, 10 cm x 4.6 mm LiChroma ROSil CIS (3 pm particles); hold for 5 min at 35% then gradient. 3545% methanol at 1% min-'. 45-70% methanol at 2% min . I ; detection at 530 nm which can be used to extract nicotine and some of its metabolites simultaneously. The chromatogram in Fig. 1 shows the GC of a sample of a smoker's urine which was passed through a Sep Pak prior to its injection on to a capillary GC with a nitrogen selective detector, Nicotine and cotinine can be easily determined by this method, but the more polar metabolites, such as 3'-hydroxycotinine, give a very poor peak shape (peak number 6 on the trace) and need to be derivatised for more successful detection.Undecyl cyanide and hexadecyl cyanide were both used as internal standards. As caffeine is present in quite high levels in tea and coffee it was anticipated that because it contained nitrogen it would also be detected by the nitrogen detector. This was shown to be the case and it can be seen as peak 5. The GC technique needs to be very sensitive as the amount of metabolites present in humans is low. Full scale deflection is 0.08 absorbance, and the concentrations of the compounds were 0.4, 0.8 and 1.4 p.p.m.for nicotine, cotinine and caffeine, respectively, in this particular sample. However, wide variation of concentration is observed between samples from a single subject as well as between subjects. The mechanism of the formation of the coloured complex to be used in the HPLC determination is complicated and a possible reaction mechanism has been proposed. The potas- sium cyanide and chloramine-T produce cyanogen chloride, which cleaves the pyridine ring in nicotine and its metabolites to give glutacondialdehyde. This then condenses with the diethylthiobarbituric acid to give a polymethine dye and the red colour produced may be measured on a ultraviolet - visible spectrometer at 525-535 nm. Concentrations of the different metabolites in urine vary from person to person, so the method was found to be unreliable as a means of assessing the degree of smoking activity, but it does allow considerable scope as the basis for the assay of 3'-hydroxycotinine and other polar metabolites by HPLC in the visible region at 530 nm.2 The following compounds have been shown to react and respond satisfactorily to this approach: nicotine, cotinine, demethylco- tinine, cis- and trun~-3'-hydroxycotinine, 3-pyridyl acetic acid and 3-pyridylcarbinol .Conventional HPLC with UV detection is satisfactory for the detection of nicotine and cotinine, but is not much more successful than GC for determining the more polar com- pounds, because of the difficulty of extracting the metabolites350 ANALYTICAL PROCEEDINGS. OCTOBER 1989.VOL 26 5 10 15 20 -d Retent ion ti m e/mi n Fig. 3. HPLC of diethylthiobarbituric acid complex of a 10 p.p.m. mixture of cis- and rruns-3‘-hydroxycotinine and 3-pyridylcarbinol. Column, 10 cm x 4.6 mm LiChroma ROSil Cle (3 pm particles); hold for 5 min at 35% then gradient, 3545% methanol at 1% min-’, 45-70% methanol at 2% min-1: detection at 530 nm from an aqueous medium into a suitable solvent for the HPLC determination .3 Derivatisation of the urine samples with diethylthiobarbi- turic acid produces a red-coloured complex and is a more sensitive method for determining the metabolites than calcula- tion from their molar absorptivity. For example, in the case of 3’-hydroxycotinine, the molar absorptivity for the base com- pound in the ultraviolet range is 3260 1 mol-1 cm-1, while for the coloured complex it is 48000 1 mol-1 cm-1.This method is more sensitive by at least a factor of 14. The diethylthiobarbi- turic acid extraction method is modified from a test used for determining 3-pyridine derivatives incorporating the Konig reaction. It was first used spectrophotometrically as a simple, inexpensive test of smoking activity by Peach and co-workers.4 A red colouration is formed on reaction with smokers urine which does not occur with non-smokers urine. The extraction procedure using Sep Paks works well for the following nicotine metabolites: nicotine(NIC), cotinine (COT), demethylcotinine (DMC), cis- and trans-3-hydroxyco- tinine (3HC), 3-pyridyl acetic acid (3PAA) and 3-pyridylcarbi- no1 (3PC).A standard 10 p.p.m. aqueous mixture of nicotine metabolites which have undergone derivatisation is shown in Fig. 2. Peaks due to 3-pyridylacetic acid, 3-pyridylcarbinol, 3’-hydroxycotinine, demethylcotinine, cotinine and nicotine can be seen clearly separated. n-Acetylnornicotine (ANN) was used as an external standard. Full-scale deflection is 0.08 absorbance and the peak shapes of 3’-hydroxycotinine and the other polar metabolites are far better than those obtained in GC. A recent publication by Barlow and co-workers’ using this method suggested that 3-pyridylcarbinol was a major com- ponent of smoker’s urine instead of 3’-hydroxycotinine. However, under our present conditions we have shown that it is possible to separate cis- (3HCI) and trans- (3HCII) 3’-hydroxycotinine and 3-pyridylcarbinol as shown in Fig.3. The peaks all elute within the space of about 7 min, so that the choice of column is important in enabling this to occur. Separation was not obtained, for example, when using a 15 cm 9 1 1 , 5 10 15 20 25 Retention timelmin Fig. 4. HPLC of diethylthiobarbituric acid complex of urine samples. Column. 10 cm x 4.6 mm LiChroma ROSil CI8 (3 pm particles); hold for 5 min at 35% then gradient, 3545% methanol at 1% min-l. 45-70% methanol at 2% min-l; detection at 530 nm. ( a ) . Smoker’s urine sample; (6) non-smoker’s urine sample I I 1 I - , I 0 5 10 15 20 25 3 Retention time/m in Fig. 5. HPLC of diethylthiobarbituric acid complex of smoker’s urine spiked with 10 p.p.m. of 3-pyridylcarbinol. Column, 10 cm x 4.6 mm LiChroma ROSil CI8 (3 pm particles); hold for 5 min at 35% then gradient, 3545% methanol at 1% min-1, 45-70% methanol at 2% min-l; detection at 530 nm 5 pm ultrasphere ODS column or a 25 cm 5 pm RSlL C18 column.A recording integrator was used to establish the retention times of the different peaks. The chromatograms of smoker’s and non-smoker’s urine show the specificity of the test, i.e. , no peaks are obtained for non-smoker’s urine, whereas in smoker’s urine, 3’-hydroxyco- tinine, cotinine and nicotine can be identified (Fig. 4). Typical levels are 1-5 p.p.m. for 3-hydroxycotinine, 0.5-2.0 p.p.m. for cotinine and 0.5-1.5 p.p.m. for nicotine. A sample of smoker’s urine was spiked with 10 p.p.m. of 3-pyridylcarbinol and a small peak on the side of the main peak observed in the smoker’s urine can be clearly seen, Fig.5. The retention times of the peaks suggest that the large peak is due to trun~-3’-hydroxycotinine and the small peak on the side to 3-pyridylcarbinol. Other recent reports have confirmed the major importance of the trans-3’-hydroxy compound.ANALYTICAL PROCEEDINGS. OCTOBER 1989, VOL 26 35 1 0 5 10 15 20 25 30 Retention ti m elmi n Fig. 6. HPLC of diethylthiobarbituric acid complex of smoker’s urine spiked with 10 p.p.m. of demethylcotinine. Column, 10 crn x 4.6 mm LiChroma ROSil CIS (3 pm particles); hold for 5 rnin at 35% then gradient, 3545% methanol at 1% min-I, 45-70% methanol at 2% min-I; detection at 530 nm A 10-p.p.m. sample of demethylcotinine, another polar lnformat on Services nicotine metabolite, was added to a smoker’s urine sample.The peak obtained suggests that the small peak sometimes observed between trans-3-hydroxycotinine and cotinine is due to demethylcotinine, Fig. 6. Conclusions The diethylthiobarbituric acid extraction method followed by HPLC has proved to be a useful method for the detection of the various nicotine metabolites in the urine of cigarette smokers. Trans-3-hydroxycotinine now appears to be the major metab- olite of nicotine, replacing cotinine in importance and with this method up to 50% of the input nicotine can be traced as nicotine, cotinine and 3-hydroxycotinine. More complicated procedures, such as radiometric HPLC - MS, are able to trace up to 85% of the metabolites and it is hoped that this colorimetric method will enable further studies on the complex metabolism of nicotine to take place, and other metabolites to be identified and quantitated.References 1. 2. 3. Stedman, R. L., Chem. Rev.. 1968, 68. 153. Smith, C. L., and Cooke. M.. Analyst, 1987, 112, 1515. O‘Doherty, S . , Revans, A., Smith, C. L.. McBride, M., and Cooke, M., “Determination of cis- and trans-3-hydroxycotinine by High Performance Liquid Chromatography,” J . High Resolut. Chromatogr. Chromatogr. Commun., 1988, 11, 723. 4. Peach, H., Ellard, G . A., Jenner, P. J., and Morris, R. W.. Thorax, 1985, 40. 351. 5 . Parviainen. M. T., and Barlow. R. D., J . Chromatogr., 1988, 431. 216. COSHH IN LABORATORIES The Control of Substances Hazardous to Health Regulations 1988 (COSHH) are the most significant legislation on occupational health in the UK since the Health and Safety at Work etc.Act was passed in 1974. This booklet gives practical guidance on the application of the regulations in laboratories. The booklet was prepared by an expert Working Party of the Health, Safety and Environment Committee (HSEC) of the Royal Society of Chemistry. It takes account of both the wide variety of laboratories that exist and the special problems that the implementation of COSHH may cause in some of them. Broader questions of health and safety in chemical laboratories are dealt with in the Society’s related publication ‘Safe Practices in Chemical Laboratories’. Users are strongly recommended to read the two publications in conjunction. ISBN 0 85186 319 1 Softcover, 16 pages JULY 1989 Price €7.50 For turther information, please write to Royal Society of Chemistry, Sales and Promotion Department, Thomas Graham House. Science Park, Milton Road, Cambridge CB4 4WF U.K To Order, please write to: Royal Society of Chemistry, Distribution Centre, Blackhorse Road, Letchworth, Herts SG6 1HN. U.K. or telephone (0462) 672555 quoting your credit card details. We can now accept AccessNisal MasterCard/Eurocard. ASC Membewr are entifled to a discount on most RSC publications and should write to: The Membership Manager, Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge C84 4WF. U.K.ROYAL SOCIETY OF CHEMISTRY lnfotmation Services Aluminium in Food and the Environment Edited by Robert C. Massey, Ministry of Agriculture, Fisheries and Food, Norwich David Taylor, Imperial Chemical Industries PIC, Brixham Special Publication No. 73 Description and Contents: The first half of this important new book looks at the adverse health effects associated with aluminium. The evidence for aluminium’s involvement in both dialysis dementia and Alzheimer’s disease are reviewed and biochemical mechanisms by which aluminium may exert its detrimental effects on brain tissue are discussed. In the second half of the book dietary sources of exposure to aluminium are described. These include water, toothpaste, antacid tablets, infant formulae, food and leaching of aluminium cookware. For the majority of the population tea is likely to be a major source although much higher amounts may be ingested in the form of antacid preparations. It is concluded however that further information is needed on the extent to which aluminium is absorbed from the gastrointestinal tract before the possible health risks can be assessed. Contents: Aluminium in Food and the Environment Aluminium Toxicity in Individuals with Chronic Renal Failure Aluminium and the Pathogenesis of Neurodegenerative Disorders An Epidemiological Approach to Aluminium and Alzheimer’s Disease The Chemistry of Aluminium and Silicon within the Biological Environment The Determination of Aluminium in Foods and Biological Materials Aluminium in Foods and the Diet Aluminium in Infant Formulae and Tea and Leaching during Cooking The Use of Aluminium - Especially as Packaging Material - in the Food Industry Subject Index ISBN 0 85186 846 0 Softcover, 11 6 pages July 1989 Price f22.50 For further information, please write to: Royal Society of Chemistry, Sales and Promotion Department, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF. U.K. To Order, please write to: Royal Society of Chemistry, Distribution Centre, Blackhorse Road, Letchworth, Herts SG6 1HN. U.K. or telephone (0462) 672555 quoting your credit card details. We can no% accept AccessNisal MasterCardlEurocard. RSC Members are entitled to a discount on most RSC publications and should write to: The Membership Manager, Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF. U.K.

ISSN:0144-557X    

DOI:10.1039/AP9892600336

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, OCTOBER 1989, VOL 26 353 Equipment News Test-tube Racks Test-tube racks made of polypropylene are available which are repeatedly auto- clavable and will not float in water-baths. They have no slots, slot tabs, edge tabs or holes to harbour contamination, and no side posts to restrict visibility of tubes. They securely hold a full load of filled 33-, 16- or 20-mm test-tubes, and, when empty, stack to save space. Nalge Company, Box 20365, Roches- ter, New York 14602-8431, USA. Lasers Switchless excimer lasers are available in which thyristors are used to charge a capacitor across two electrodes, and sat- urable inductances are used to shorten the electric pulses. A fast, low energy corona pre-ionisation pulse sows excited mol- ecules between the electrodes. Gas impedence is decreased and the main discharge takes place with the laser effect, and the laser is thus its own switch.Spectrolab Ltd., P.O. Box 25, New- bury, Berkshire RG16 8BQ. Urine Robot A robotic system applies classical micro- biology for screening and total bacterial count in urine with screening, semi-quan- titative analysis and colony separation performed in the same Petri dish. It is capable of handling 120 samples per hour. International PBI SPA, Via Novara 89, 20153 Milano, Italy. Disposable Tubes "Cube 2ubes" are disposable tubes of 2-ml capacity and are used in microassay work, including ELISA, hybridoma, MICs, DNA sequencing and receptor binding studies. They are packaged in 20 racks, each of 96 tubes. Sterile and non-sterile caps are available. Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire.Titre Plates Deep-Well titre plates of 1-ml capacity capped (1.2-ml uncapped) are manufac- tured in polystyrene and supplied in boxes of 25 x 96 well. They are compatible with single-, eight- and twelve-tip pipettors. Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. Micro pH Electrode The microelectrode is small enough to measure pH in microwell plates, serum cups and capillary tubes, and is also useful for veterinary work with small animals. Tip diameter is less than 1000 pm and measurement can be as small as 10 p1. CP Instrument Co. Ltd., P.O. Box 22, Bishop's Stortford, Hertfordshire CM23 3DH. pH Meter The Hi-8417 bench pH meter includes automatic retention of 6 different pH buffer values and has dual LCD display, pH and ion selective electrode input, automatic calibration and a built in recorder output.It also has an internal back up battery. UK Instruments Ltd., Happy Valley Industrial Park, Primrose Hill, King's Langley, Hertfordshire WD4 8HZ. pH Meter The pH1 72 is set up to operate from simple menus with full help screens, and automatically recognises nine widely used pH buffers and compensates for temper- ature variations. Manual inputs can also be accepted. Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. Electrodes The makers' Futura Plus range of elec- trodes are available in pairs matched to sample requirements. The standard pH electrode covers the full pH range at temperatures from -5 to 100"C, whilst the rugged bulb electrode indicates pH in more robust environments at tempera- tures from 10 to 100°C.The quartz fibre junction reference electrode is available in calomel style for all applications below 60 "C or in silver - silver chloride style for applications up to 100°C. A ceramic junction reference electrode is recom- mended for applications where contami- nation of the sample by filling solution is to be minimised. Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. Viscometer A microprocessor controlled rotational viscometer, the VT500, is capable of measuring viscosities from 1 to 107 mPa. Viscosity, shear rate, temperature, tor- que and speed are digitally monitored and displayed.Addition of an analog recorder allows measurement of time-dependent rheological behaviour, such as curing and thixotropy, and an RS232C interface and use of the maker's software package allows further mathematical models to be used. Haake Mess-Technik GmbH u Co., Dieselstrasse 4, 7500 Karlsruhe 41. Karl Fischer Systems The Metrohm Model 684 automates coulometric moisture measurements from 10 pg to 10 mg and provides results within 30 s at the maximum titration rate of 2 mg s-1. An alphanumeric readout dis- plays results in per cent. or p.p.m. The Model 658 streamlines ampero- metric measurement over the range 1-100 mg. All procedures require just one key- stroke, and a built-in printer documents all results. An electronic balance can be coupled up, and automation can be com- pleted by interfacing to a central or host computer.V. A. Howe and Co. Ltd., 12-14 St. Ann's Crescent, London SW18 2LS. Sulphur Dioxide A dedicated instrument measures free and total sulphur dioxide contents of foodstuffs within a few minutes. It uses amperometric detection to measure SO2 from 1 to 100 mg I-' and is microproces- sor controlled. Calibration, measurement and calculation are all automatic. Roth Scientific Co. Ltd., Alpha House, Alexandra Road, Farnborough, Hamp- shire GU14 6BU. Computerised Temperature Control System packages are based on an IBM or IBM compatible computer with RS232C interface. For connection of the computer to the circulator or cryostat, the maker's IF24-1 interface and suitable software are used, which allow the user to set the desired temperature, to run time - linear temperature programmes, to switch on or off additional heaters or valves, or to monitor the safety functions of the circu- lator.The system is designed for circula- tors with an accuracy of 0.01 "C. Haake Mess-Technik GmbH u. Co., Dieselstrasse 4, 7500 Karlsruhe 41. Fibre Optic Temperature Transmitter The P940 temperature transmitter oper- ates via a single optical fibre which can be up to 2 km in length and covers a temperature range of -70 to 515 "C. The transmitter comprises three parts: the fibre optic resistance thermometer; the high speed optical receiver which converts optical signals to electrical pulses; and the optical pulse time interval converter which computes the RT resistance, linearises the information and provides a proportional 4-20 mA output signal.The system is designed to meet BASEEFA Intrinsically Safe and Flameproof certifi- cation to CENELEC requirements. Kent Industrial Measurements Ltd., Howard Road, Eaton Socon, Hunting- don, Cambridgeshire PE19 3EU. Mass Flow Measurement The Kay Ray Model 3860 is a field-354 ANALYTICAL PROCEEDINGS, OCTOBER 1989, VOL 26 mountable, two-compartment , gamma density/mass flow transmitter. It condi- tions and combines input signals from the Kay Ray family of density sensors and almost any available volumetric flow meter to calculate slurry conveyed solids or total mass flow. Acal Auriema Ltd., 442 Bath Road, Slough SL16BB. Dissolved Oxygen Analyser The Royce Model 9010 is a microproces- sor based instrument capable of measur- ing dissolved oxygen at levels up to 100 p.p.m.With options such as automatic self-cleaning of the probe sensing mem- brane and a microprocessor based step controller it can continually control and maintain the dissolved oxygen in the aqueous system being monitored. There are two standard high - low setpoint control relays for controlling external aeration devices, pumps, valves, or other electronic equipment. Acal Auriema Ltd., 442 Bath Road, Slough SL16BB. Oxygen Gas Analyser The Model 315 trace oxygen analyser uses a micro-scale fuel cell and is designed specifically for applications that have very little panel space available for on-line gas monitoring instrumentation. It measures 11 X 4.5 x 7.5 in. No zero gases are required and atmospheric air is used for calibration.Teledyne Analytical Instruments, The Harlequin Centre, Southall Lane, Southall, Middlesex UB2 5NH. Elemental Oxygen Analysis An oxygen analysis accessory is available for the Model 2400 elemental analyser which allows oxygen analysis to be per- formed as one mode or CHN analysis as another. Perkin-Elmer Ltd., Maxwell Road, Beaconsfield, Buckinghamshire HP9 1QA. Cryogenic Systems The RGH range of cryogenic systems includes liquid transfer cryosta ts, pourfill Dewars and closed refrigeration systems. These are augmented by a variety of sample mounts and ultra-high vacuum fittings. Spectrolab Ltd., P.O. Box 25, New- bury, Berkshire RG16 8BQ. Autosampler for Atomic Spectrometry The Model AS-90 is a computer con- trolled, multi-purpose sampling system for flame and flow injection atomic absorption, ICP-AES, ICP-MS and other spectrometric analysis techniques. It automates instrument calibration, sample introduction and element programme change in the spectrometer via software commands.Random access programming increases flexibility in locating different samples and references. Perkin-Elmer Ltd., Post Office Lane, Beaconsfield, Buckinghamshire HP9 1QA. Flow Injection Atomic Spectrometry The FIAS-200 system has two indepen- dently controlled peristaltic pumps for carrier stream, sample and reagents, and with computer-based electronics and a computer-controlled AS-90 Autosampler it can be used with automatic sequential multi-element AA systems with both FIA - mercury hydride and FIA - flame tech- niques.It can also be readily adapted for other applications, such as automatic dilution or addition of matrix modifiers. Perkin-Elmer Ltd., Post Office Lane, Beaconsfield, Buckinghamshire HP9 1QA. Automatic SEM - EDS System The PHAX-SCAN can typically complete an analysis on over 2000 particles in less than 20 min. A complete range of micro- analytical software is available including full quantitative analysis, digital X-ray mapping, digital linescan, unattended analysis, 3-D metrology, particle analysis, library sorting and random analysis. Philips Electronics Instruments Co., 85 McKee Drive, Mahwah, NJ 07430, USA. GC Autosampler Designed for use with the Shimadzu GC14A GC, the AOC14 personal injec- tor eliminates sample carry-over by isolat- ing each sample between air bubbles taken up on sampling.It copes with both high and low viscosity liquids and can be used with thermally sensitive samples by flushing the sample rack with chiller. Dyson Instruments Ltd., Hetton Lyons Industrial Estate, Houghton le Spring, Tyne & Wear DH5 ORH. Kinetic Analysis with Ultraviolet - Visible Spectrometry A supplementary program (slice) is avail- able which permits kinetic analysis using an array of stored spectra generated by the makers’ computerised spectroscopy software. PC based storage of this soft- ware combined with the 2880 nm min-* fast scanning speed of a Lambda 2 spec- trometer enables wavelength optimisa- tion for kinetic analysis after the data have been collected. Perkin-Elmer Ltd., Maxwell Road, Beaconsfield, Buckinghamshire HP9 1QA.Portable Gas Calibrator A portable instrument uses two gas sup- plies with fourteen nominally spaced ratios over the 0-100% range. Delivery flow-rate is variable up to 1.2 1 min-1 and the unit incorporates a self-check function for routine equipment checks and for establishing appropriate inlet pressures. It operates with a PP9 battery, measures 230 x 340 x 270 mm and weighs 9.5 kg. The Analytical Development Co. Ltd., Pindar Road, Hoddesdon, Hert- fordshire EN11 OAQ. HPLC Autosampler The GINA 160 can handle up to 160 samples, each of 2 ml in volume, and this can be further increased by the possibility of replenishing one of the two sampling trays without interrupting the run. Injec- tion volumes from 1-250 vl or 0.1-25 1-11 can be selected for each vial, which must contain a minimum of 5 1-11 of sample.Parameters such as start position, run time, multiple injections and column tem- perature can also be programmed for each sample, as can addition of one or two reagents for pre-column derivatisation. An RS232 interface is provided for con- trol by an external computer or for control of an integrator. Roth Scientific Co. Ltd., Alpha House, Farnborough, Hampshire GU14 6BU. Packings for Preparative HPLC Hyperprep 120 has a mean pore diameter of 120 A and particle size of 12 ym and is normally used for scaling up preparation of small peptides and other biologically active molecules in the 12-15 kDalton range. Hyperpre 300, with a mean pore pm, is designed for preparative separation of larger molecules up to 300 kDaltons.Shandon Scientific Ltd., Chadwick Road, Astmoor, Runcorn, Cheshire WA7 1PR. diameter of 300 8: and a particle size of 15 HPLC Columns Ultracarb CI8 columns are available with carbon loads of 20 and 30% and in 5 and 10 ym particle size. The ODS 30 is designed for use with polar compounds such as basic drugs and other amines which show extensive tailing and poor efficiencies on standard ODS columns. The ODS 20 is used for free fatty acids, triglycerides, fat soluble vitamins and other lipophilic compounds. HPLC Technology Ltd., Wellington House, Waterloo Street West, Maccles- field, Cheshire SKl1 6PJ. Radiochromatography The system incorporates two fully pro- grammable detectors, the Beckman Model 166 ultraviolet - visible and Model 171 for detection of radioisotopes. All components are linked on a bi-directional digital communications network.Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. Supercritical Fluid Technology A range of accessories is available. The PrepMaster provides sample preparation capability by using supercritical fluid extraction prior to injection into a gasANALYTICAL PROCEEDINGS, OCTOBER 1989, VOL 26 355 chromatograph. An in-line micro-extrac- tion system can be used in conjunction with a supercritical fluid chromatograph. An interface allows coupling of SFC to MS, and a photoionisation detector is available. Dyson Instruments Ltd., Hetton Lyons Industrial Estate, Hetton, Tyne and Wear DH5 ORH. Magnetic Sector Mass Spectrometer The MAT 900 system, integrated for full digital control, is a forward geometry (electric - magnetic sector) double focus- ing, high mass, high resolution mass spectrometer.It uses a combined array - SEM detector and a differentially pumped ion source for optimum sensitiv- ity with high pressure inlet techniques. Finnigan Corporation, 355 River Oaks Parkway, San Jose, CA 95134, USA. Quadrupole Mass Spectrometers The SP 4000 is a compact research quad- rupole mass spectrometer with an upper mass limit of 4250 Daltons (amu). A PC-based data system with a choice of 2000 u, 1200 u or 800 u mass ranges is also available. The EXT 1000 glow discharge quad- rupole mass spectrometer is used for elemental analysis of metals and alloys and features a sample holder for solid samples, high sensitivity for low p.p.b. detection limits, and a d.c.discharge source that minimises redeposition effects. It has a mass range from 1 to 300 u and operates under PC control. Extrel Corporation, 240 Alpha Drive, Box 1152, Pittsburgh, PA 15238, USA. Liquid Chromatography - Mass Spectrometry Interface ThermaBeam LC - MS interface is a high-enrichment particle-beam introduc- tion device that operates in either EI or CI modes and permits practical LC flow- rates of 0.1-1.0 ml min-1. Typical FAB matrices such as glycerol, thioglycerol, DTT : DTE (“magic bullet”) or nitro- benzyl alcohol are added as dilute solu- tions post-column, which causes the analytes to be mixed with the FAB matrix as particles are formed in the interface. As the solvent is pumped away in the momentum separator, the analyte - gly- cerol particles are accelerated toward a conventional FAB target in the ioniser.Extrel Corporation, 240 Alpha Drive, Box 1152, Pittsburgh, PA 15238, USA. Interfaces A universal interface can couple HPLC to any gas phase detection system. The Model 902 is a thermospray SFC - MS interface, and a digital control system is available for it. Replaceable vaporiser nozzle tips are available for the maker’s interfaces in kit form containing an assort- ment of sapphire, laser drilled tips ranging in size from 62.5 to 100 ym, vaporiser tip assemblies, spare nozzle tip holders and wrenches. Vestec Corporation, 9229 Kirby Drive, Houston, TX 770054, USA. Pyroprobe The CDS Pyroprobe 1000 is a digital, microprocessor controlled filament pyroliser which allows solid materials to be analysed by GC, MS or FTIR.Dyson Instruments Ltd., Hetton Lyons Industrial Estate, Houghton le Spring, Tyne & Wear DH5 ORH. Capillary Columns Nordion capillary GC columns are made in lengths of 15,25 and 50 m, with i.d. of 0.2 and 0.32 mm and all commonly used phases are available. HPLC Technology Ltd., Wellington House, Waterloo St. West, Macclesfield, Cheshire SKl1 6PJ. Chromatography Systems Chromatography application tailored systems (CATS) are available which con- tain all that is needed, in both instrumen- tation and documentation categories, to perform a particular analysis in an optimal way. The instrumentation is assembled and tested to ensure accurate results, and the documentation covers not only methods but also statutory limits and literature references. Philips Scientific, Analytical Division, York Street, Cambridge CB1 2PX.Capillary Columns Restek capillary columns are available ranging from 15 to 105 m in length and from 0.25 to 0.53 mm in internal diameter. The Stabilwax column incor- porates free radical scavengers to protect the polymer from oxidative degradation whilst retaining upper stability at 280 “C and true carbowax polarity. Thames Chromatography, 16 Raymead Court, Maidenhead, Berkshire SL6 8TN. Deionisation Columns Pre-filled deionisation columns are packed with 10 ml of AG 501-X8 resin, and have a minimum capacity of 7 mequiv for both anions and cations. They are capable of producing water of a quality equal to 10 MQ, and can be used with a wide range of samples including formamide, glyoxal, acrylamide and PEG.Bio-Rad Laboratories Ltd., Caxton Way, Watford Business Park, Watford, Hertfordshire WD1 8RP. Multi-dimensional Columns OmniPac columns are polymeric and combine the power of ion exchange, ion pairing and reversed phase into a single column. They are compatible with the full pH range of G14 and mobile phases of up to 100% organic solvent can be used. Dionex(UK) Ltd., 4 Albany Court, Camberley, Surrey GU15 2PL. TLC Plate Cutter The cutter consists of a carbide scriber mounted into a movable plastic head; it is designed to cut glass-backed TLC plates 20 X 20 cm, 10 x 20 cm and 10 x 10 cm. Camlab Ltd., Nuffield Road, Cam- bridge CB4 1TH. Gel Electrophoresis A range of pre-mixed acrylamide - bis reagents is available to which the operator need only add water. Bio-Rad Laboratories Ltd., Caxton Way, Watford Business Park, Watford, Hertfordshire WDl 8RP.Electrophoresis Standards Pulsed field electrophoresis certified DNA standards, including DNA con- catemers, Schizosaccharomyces pombe and Saccharomyces cerevisiae whole chromosomes are available. Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. Platinum Electrodes for Trans-Blot Transfer Cell Platinum plate electrode cards are avail- able for the Trans-Blot electrophoretic transfer cell. They provide a uniform electrical field that exposes all molecules to an equal field strength, thus ensuring even transfer in all areas of the gel. Bio-Rad Laboratories Ltd., Caxton Way, Watford Business Park, Watford, Hertfordshire WD1 8RP.Extraction Disks Disks are available which provide effi- cient extraction of organic compounds from water. They can extract pollutants such as PCBs, phthalates and pesticides from a 1-1 sample in less than 45 min and are in standard filter sizes of 25 or 47 mm. Analytichem International, P.O. Box 234, Cambridge CB2 1PE. Recorders The PM 8277 single-pen and PM 8278 dual-pen X - Y recorders accept a variety of paper sizes, including A3 and Z-fold, and can, at the press of a key, label a recording with time, date and instrument settings, as well as with characters and drawings from a remote computer. Both have an optional IEEE-488 or RS-232 interface for remote control and data transfer, and the PM8278 features pen synchronisation.Philips Test and Measurement, York Street, Cambridge CB1 2PX. Laser Sampler The Model 320 Laser Sampler is designed for use with ICP - MS instruments and permits elemental analysis of solid Sam-356 ANALYTICAL PROCEEDINGS, OCTOBER 1989, VOL 26 ples without prior dissolution. A single laser pulse can be used to analyse a small area on the sample surface, or repetitive pulses can be used to analyse linear or rectangular regions of the sample. Perkin-Elmer Ltd., Maxwell Road, Beaconsfield, Buckinghamshire HP9 1QA. Capillary Electrophoresis A CE component package includes a choice of either a variable wavelength absorbance detector or a fluorescence out with return flow under vacuum or normal pressure. Sartorius Ltd., Longmead Business Centre, Blenheim Road, Epsom, Surrey KT19 9QN.Titrator The Model 670 titrator programs in BASIC, accepts plain English controls and commands, and has 30 titration routines with 4 individual titrations per routine. It controls sample changers, up to four Dosimat automatic burettes and twelve Spectrovision capillary electrophoresis package detector, a high voltage power supply, a safety-interlocked instrument housing and a CE starter kit. Spectrovision, Scientia Park, 25 Indus- trial Avenue, Chelmsford, MA 01824, USA. Portable Continuous Flow Centrifuge The Contifuge 300 MD is based on a continuous flow rotor which operates in a refrigerated or non-refrigerated benchtop high speed centrifuge. A built-in micro- processor enables users to pre-select and store 32 centrifugation procedures in the memory.Heraeus Equipment Ltd., 9 Wates Way, Brentwood, Essex CM15 9TB. Industrial Wipes Kon-Ton non-woven industrial wipes are used for fine cleaning and polishing tasks and are available in two sizes, 34 x 34 cm and 43 x 50 cm. Johnson & Johnson Ltd., Chicopee, Grafton Way, Basingstoke RG22 6PM. Rotary Evaporators Four models are available in the range which includes vertical and horizontal condensers with a total surface area of 1200 cm2, and vertical with flux and reflux, these last embodying a PTFE valve which allows reflux distillation and switch-over to distilling off. Equally, reac- tions in the rotating flask can be carried auxiliary burettes. Real-time monitoring permits parameter or program changes. V. A.Howe & Co. Ltd., 12-14 St. Ann’s Crescent, London SW18 2LS. Particle Sizer Capable of working within the range 0.5-1200 pm, the QA-1 uses scanning laser optics to produce direct measure- ments of particle size. All measurements are independent of factors such as refrac- tive index, Brownian motion and thermal convection. Roth Scientific Co. Ltd., Alpha House, Alexandra Road, Farnborough, Hamp- shire GU14 6BU. Auger Microprobe The JAMP 7100 Auger microprobe has a minimum electron probe size of 25 nm and is capable of Auger electron spectro- scopy on micro areas of 50 nm diameter. Scanning Auger images can be collected with a corresponding ultra-high spatial resolution. Jeol (UK) Ltd., Jeol House, Grove Park, Colindale, London NW9 OJN. Transmission Electron Microscope A 200 kV transmission electron micro- scope incorporates special facilities for scanning (STEWSEM) operation as well as optimised interfacing of sub-systems including TV cameras, X-ray microanaly- tical systems and electron spectrometers.A microprocessor-based control system enables efficient customised software configuration matched to the require- ments of the user, and also allows subse- quent upgrades and expansion to occur as a work programme develops. Philips Scientific, Analytical Division, York Street, Cambridge CB1 2PX. Water Still A still is available which produces 4 1 h-1 of distilled water of a quality complying with the European Pharmacopoeia and US standard ASTM Type 4. J. Bibby Science Products Ltd., Tilling Drive, Stone, Staffordshire ST15 OSA.Reverse Osmosis Membrane OSMO 60 series membranes are 60 in long with diameters of 4 or 8 in. They are spiral wound and require fewer O-rings, concentrate (brine) seals and sealing sur- faces. Osmonics, Inc., 5951 Clearwater Drive, Minnetonka, Minnesota 55343, USA. Software for Ultraviolet - Visible Spectroscopy The software package contains options for general scanning (including spectral display and mathematical manipulation), quantification and kinetics applications. Other programs can be started inter- actively. Hewle tt-Packard, 3000 Hanover Street, Palo Alto, CA 94304, USA. GC - MS Data System and Environmental Software Package The EL 2000 data system has a DEC host CPU residing in a 9-slot backplane with 1 MB memory standard and up to 4 MB available as an option.Disk- and tape- drive options provide more storage capac- ity (170 MB or 380 MB on-line and 60 or 125 MB off-line). The software package, designed for environmental work, features an acquisition-method editor to simplify batch analysis of multiple sam- ples. Data review and reporting software is automated to require minimal interven- tion.ANALYTICAL PROCEEDINGS, OCTOBER 1989, VOL 26 357 Extrel Corporation, 240 Alpha Drive, Box 11512, Pittsburgh, PA 15238, USA. Thermal Analysis Software A range of specialised software programs is offered for the makers’ DSC 7 Differen- tial Scanning Calorimeter, run by an Epson PC or IBM PS-2. Perkin-Elmer Ltd., Maxwell Road, Beaconsfield, Buckinghamshire HP9 1QA. Electrochemical Analysis Software The Model 270 software package allows every major electroanalytical technique to be performed automatically using the makers’ Model 273 potentiostat/galvano- stat and a personal computer.An eight- page brochure gives more details. EG & G Instruments, Sorbus House, Mulberry Business Park, Wokingham, Berkshire RG112GY. Mass Spectrometry Data System The data system, designed for use with the makers’ 400 Series mass spectromet- ers, includes a 20 MHz Compaq 386 computer with 1 MB of RAM, a 40 MB hard disk, a 1.2 MB floppy and a 15 in colour monitor with 1024 x 768 resolu- tion. The mouse driven software package operates in a windows environment and has a library search routine with fully plottable chemical structures. Extrel Corporation, 240 Alpha Drive, Box 11512, Pittsburgh, PA 15238, USA.Computational Chemistry and Molecular Modelling The pUMa CHEMMOD is built round the Motorola 68020 and Inmos Trans- puter processors. The former runs an industry standard multi-user, multi-task- ing operating system and controls such peripherals as disks and printers. The latter runs the main application code and interfaces to the graphics system. The CHEMMOD software package provides comprehensive modelling facilities. U-Microcomputers Ltd., 12 Chetham Court, Calver Road, Winwick Quay, Warrington, Cheshire WA2 8RF. Laboratory Partitions Clipsolab are relocatable airtight parti- tions designed for laboratories and clean assembly areas. The 70-mm partition uses double adhesive foam strips for head and base abutments, while every joint is fitted with a neoprene seal.Floor and ceiling connections are covered with a radiused PVC profile, and the panels are finished with an acid resistant laminate. Clips Partitions Ltd., Unit B5, Haslemere Industrial Estate, Pig Lane, Bishop’s Stortford, Hertfordshire CM22 7PA. Literature The latest “Philips Analytical Bulletin” contains information on new transmission electron microscopes, a chromatography data station, a gasohols analyser, analysis of fats by GC and HPLC, and laboratory management software. Philips Scientific, Analytical Division, York Street, Cambridge CB1 2PX. “Reflections,” a technical newsletter, is published three times a year and covers materials characterisation. It typically includes applications briefs, new tech- niques and services, literature abstracts, and one or two in-depth articles on a specific type of problem solving or surface characterisation.Surface Science Laboratories, 1206 Charleston Road, Mountain View, CA 94043, USA. A book is available in English, German, French, Italian and Japanese entitled “The New Mettler AT Analytical B a1 ance . ” Mettler Instrumente AG, CH-8606 Griefensee, Switzerland. A brochure gives details of Coulometrics instruments for measurement of total organic carbon, total inorganic carbon, total sulphur and sulphite. Roth Scientific Co. Ltd., Alpha House, Alexandra Road, Farnborough, Hamp- shire GU14 6BU. A brochure is available on automated sample preparation. Millipore (UK) Ltd., Waters Chromat- ography Division, The Boulevard, Ascot Road, Croxley Green, Watford, Hert- fordshire WD1 8WD.A booklet on PSA402 Infrared Analysers gives detailed specifications and outlines features, options, and general and typical applications. Servomex (UK) Ltd., Crowborough, Sussex TN6 3DU. An eighteen page catalogue is dedicated to replacement parts for Waters HPLC equipment. HPLC Technology Ltd., Wellington House, Waterloo Street West, Maccles- field, Cheshire SKll 6PJ. A brochure gives detailed information on the 19C Series low pressure reverse osmo- sis equipment for water purification. Osmonics, Inc., 5951 Clearwater Drive, Minnetonka, Minnesota 55343, USA. The “Supelco Biotext” is a House Journal which provides information on equipment and applications. Supelco, Inc., Supelco Park, Belle- fonte, PA 16823, USA. A 29-page bibliography lists over 750 references for amino acid analysis of food and feeds. Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. “In Focus” is a house journal of instrumental and analytical techniques for nutritional analysis, agricultural research, and related areas. Tecator AB, Box 70, S-263 21, Hoga- nas, Sweden. “Aldrichimica Acta” is a house journal containing information on chemicals, equipment and applications. Aldrich Chemical Co. Ltd., The Old Brickyard, New Road, Gillingham, Dor- set SP8 4JL. “Sigma ImmuNotes,” No. 2, 1989, con- tains articles on gold - antibody conju- gates, and R-Phycoerythrin antibody con- jugates. Sigma Chemical Co. Ltd., Fancy Road, Poole, Dorset BH17 7NH. “EDT Digest” contains information on the makers’ equipment and applications. EDT Analytical Ltd., 14 Trading Estate Road. London NWlO 7LU. A brochure gives details and specifica- tions of the makers’ equipment for measurements in electrochemistry, including pH - ion, conductivity and dissolved oxygen. EDT Instruments Ltd., Lorne Road, Dover, Kent CT16 2AA. A brochure contains details in tabular form on ion selective electrodes covering type, concentration range, lower limit, temperature range, interference and selectivity ratios. EDT Instruments Ltd., Lorne Road, Dover, Kent CT16 2AA. A brochure gives an update on equipment for HPLC and TLC. Camlab Ltd., Nuffield Road, Cam- bridge CB4 1TH. The 1989 Hamilton Chromatographers Catalogue gives information on syringes, columns, septa, needles, capillary tubing and miniature valves. V. A. Howe & Co. Ltd., 12-14 St. Ann’s Crescent, London SW18 2LS.

ISSN:0144-557X    

DOI:10.1039/AP9892600353

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

358 ANALYTICAL PROCEEDINGS. OCTOBER 1989. VOL 26 Publications Received Analytical Artifacts. GC, MS, HPLC, TLC and PC. B. S. Middleditch. Journal of Chromato- graphy Library. Volume 44. Pp. xxiii + 1033. Elsevier. 1989. Price $241.50; Dfl 495. ISBN 0 444 87158 6. Modern Methods of Plant Analysis. New Series. Volume 6. Wine Analysis. Edited by H. F. Linskens and J. F. Jackson. Pp. xiv + 381. Springer-Verlag. 1988. Price DM298. ISBN 3 540 18819 3. Quantitative Trace Analysis of Biological Materials. Edited by H. A. McKenzie and L. E. Smythe. Pp. xiv + 791. Elsevier. 1988. Price $289; Dfl550. ISBN 0 444 80958 9. Biological Monitoring for Pesticide Expo- sure; Measurement, Estimation and Risk Reduction. Edited by Rhoda G. M. Wang, Claire A. Franklin, Richard C. Honeycutt and Joseph C.Reinert. ACS Symposium Series No. 382. Pp. x + 387. American Chemical Society. 1989. Price $69.95 (USA and Canada); $83.95 (Export). ISBN 0 8412 1559 6. The Scientific Examination of Documents. Methods and Techniques. David Ellen. Ellis Horwood Series in Forensic Science. Pp, 182. Ellis Honvood. 1989. Price f33.95. ISBN 0 7458 0551 5 (Ellis Honvood); 0 470 21347 7 (Halsted Press). Hair Analysis. Applications in the Biomedical and Environmental Sciences. Amares Chatt and Sidney A. Katz. Pp. x + 134. VCH. 1988. Price DM74; f25. ISBN 0 89573 310 2 (VCH Publishers); 3 527 26787 5 (VCH Verlagsgesellschaft). Protein - Dye Interactions: Developments and Applications. Edited by M. A. Vijayalakshmi and 0. Bertrand. Pp. xiii + 342. Elsevier. 1989. Price &42.ISBN 1 85166 316 9. Luminescence Applications in Biological, Chemical, Environmental and Hydrolog- ical Sciences. Edited by Marvin C . Goldberg. ACS Symposium Series 383. Pp. xii + 251. American Chemical Society. 1989. Price $59.95 (USA and Canada); $71.95 (Export). ISBN 0 8412 1560 X. Chiral Liquid Chromatography. Edited by W. J. Lough. Pp. 276. Blackie. 1989. Price f45. ISBN 0 216 92499 5. Troubleshooting LC Systems. A Com- prehensive Approach to Troubleshooting LC Equipment and Separations. John W. Dolan and Lloyd R. Snyder. Pp. vii + 515. Humana Press. 1989. Price $65; $75 (Export). ISBN 0 89603 151 9. The Cambridge Guide to the Material World. Rodney Cotterill. Pp. vii + 352. Cam- bridge University Press. 1989. Price f14.95; $27.95. ISBN 0 521 37932 6. Measurement of Radionuclides in Food and the Environment.A Guidebook. Technical Report Series No. 295. Pp. 169. International Atomic Energy Agency, Vienna, 1989. Price Sch480. ISBN 92 0 125189 0. Computational Methods in the Chemical Sciences. A. F. Cavley and P. H. Morgan. Ellis Horwood Series in Chemical Information Science. Pp. 337. Ellis Honvood. 1989. Price f65. ISBN 0 85312 746 8 (Ellis Honvood); 0 470 21490 2 (Halsted Press). Analytical Aspects of Drug Testing. Edited by Dale G. Deutsch. Volume 100 in Chemical Analysis. A Series of Mono- graphs on Analytical Chemistry and its Applications. Pp. xiii + 304. Wiley-Inter- science. 1989. Price f54.30. ISBN 0 471 85309 7. Chemical Inst rumen ta t ion: A Systematic Approach. Third Edition. Howard A. Strobel and William R.Heineman. Pp. xii + 1210. Wiley-Inter- science. 1989. Price f34.85. ISBN 0 471 61223 5. Process Chromatography. A Practical Guide. G. K. Sofer and L. E. Nystrom. Pp. ix i- 145. Academic Press. 1989. Price X19.95. ISBN 0 12 654268 6. Nuclear Magnetic Resonance, Volume 18. Senior Reporter G. A. Webb. Specialist Periodical Report. Pp. lvi + 511. Royal Society of Chemistry. 1989. Price 2110; $232. ISBN 0 85186 412 0. Algorithms for Chemists. Jure Zupan. Pp. xv + 290. Wiley. 1989. Price X39.50. ISBN 0 471 92173 4. Chiral Separation by HPLC: Applications to Pharmaceutical Compounds. Edited by A. M. Krstulovi6. Ellis Hor- wood Series in Medicinal Chemistry. Pp. 548. Ellis Honvood. 1989. Price f69.50. ISBN 0 7458 0331 8 (Ellis Horwood); 0 470 212993 (Halsted Press).Principles and Practice of Chromato- B. Ravindranath. Ellis Horwood Series in Analytical chemistry. Pp. 502. Ellis Hor- wood. 1989. Price f58.50. ISBN 0 7458 0296 6. (Ellis Honvood); 0 470 21328 0 (Halsted Press). graphy - Handbook of Static Secondary Ion Mass Spectrometry (SIMS). David Briggs, Alan Brown and John C. Vickerman. Pp. vii + 156. Wiley. 1989. Price f125. ISBN 0 471 91627 7. Computers in the Laboratory. A Student Guide to Microprocessor Interfacing. John Littler and John Maher. Pp. xiii + 385. Longman. 1989. Price f14.95. ISBN 0 582 00472 1. Principles and Practice of Chromato- B. Ravindranath. Ellis Horwood Series in Analytical Chemistry. Pp. 502. Ellis Hor- wood. 1989. Price X58.50. ISBN 0 7458 0296 6 (Ellis Horwood); 0 470 213280 (Halsted Press). graphy - Handbook Series in Inorganic Electroche- mistry. Volume VIII: U-Zr. Louis Meites, Petr Zuman, Elinore B. Rupp, Theodore L. Fenner and Anan- thrakrishnan Narayanan. Pp. 538. CRC Press. 1989. Price X76.50. ISBN 0 8493 0369 9. Analysis of Trace Organics in the Aquatic Environment. Edited by B. K. Afghan and Alfred S. Y. Chau. Pp. 346. CRC Press. 1989. Price f130.50. ISBN 0 8493 4626 6. 5 Day Biochemical Oxygen Demand (BODS). Second Edition, 1988 (with Dis- solved Oxygen in Water, Amendments 1988). Methods for the Examination of Water and Associated Materials. Pp. 35. Her Majesty’s Stationery Office. 1989. Price f4.80 ISBN 0 11 752212 0. Chiral Separation by HPLC Applications to Pharmaceutical Compounds. Edited by A. M. Krstulovik. Ellis Hor- wood Series in Medical Chemistry. Pp. 548. Ellis Honvood. 1989. Price f69.50. ISBN 0 7458 0331 8 (Ellis Horwood); 0 470 212993 (Halsted Press).

ISSN:0144-557X    

DOI:10.1039/AP9892600358

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, OCTOBER 1989, VOL 26 359 Analytical Division Diary NOVEMBER Wednesday, lst, 12 noon: London Atomic Spectroscopy and Chemometrics Groups and South Calibration and Optimisation on Atomic Spectroscopy. “Advances in Monte Carlo Modelling of Processes in Graphite Furnace Atomic Absorption Spectrometry,’’ by W. Wegscheider. “Possibilities for Automated Method Development in Analytical Atomic Spectrometry Using Expert Systems,” by J . Carroll. “Solutions to Spectrum Processing and Quantitative Calibration Problems in Energy Dispersive XRF Spectrometry,’’ by A. T. Ellis. “Computerised Tomography-Its Use in Atomic Spectrometry.” by S. J. Hill and L. Ebdon. “Atomic spectrometry and Chemometrics-The Dynamic Duo.” by M. Thompson. Thames Polytechnic, Wellington Street, London SE18 6PF.Registration is necessary. Cost to RSC members 235, non-members f60, and students, unemployed and retired members of the RSC f 5 . Contact: Dr. J . R. Dean, Department of Chemical and Life Sciences, Newcastle upon Tyne Polytechnic, Ellison Building, Newcastle upon Tyne NE1 8ST. (Tel. 091-232- 6002, ex. 3517). East Region. Thursday, 2nd, 9 a.m.: Warrington North West Region, jointly with the Chromatographic Large Scale Chromatography. “A Framework for Optimising Preparative HPLC,” by 3 . H. Knox. “Large Scale Preparative LC-Personal Experiences,” by P. Car- “Frontal Analysis in Large Scale Preparative LC,” by D. Hill. “Valve Switching and Recycling Techniques in Preparative Chro- “The Application of High-performance Preparative Liquid Chro- “The Design of Stationary Phases for Large-scale Chromato- Lord Daresbury Hotel, Nr.Warrington. Registration is necessary. Cost f46 to RSC and Chromato- graphic Society members, f69 to non-members and Z11.50 to students and retired members. Contact: The Executive Secretary, The Chromatographic Society, Trent Polytechnic, Nottingham NG1 4BU. (Tel. Society. penter. matography Using Cartridge Columns,” by N. Herbert. matography,” by K. Evans. graphy,” by I. Chappel. 0602-418418). Friday, 3rd, 7 p.m.: Edinburgh Scottish Region: Annual General Meeting. The Chemistry of Fibre-forming Polymers. Speaker: R. Wardman. University of Edinburgh Staff Club, Chambers Street, Edinburgh. Contact: Mr. R. I. Aylott, United Distillers PLC, Group Central Laboratory, Menstrie, Clackmannanshire F K l l 7ES.(Tel. 0259-61481). Wednesday, 8th, 4 p.m.: Belfast Northern Ireland Region: Annual General Meeting and joint meeting with the Andrews Club. Thermal Analysis. Queen’s University, Belfast. Contact: Mr. W. J. Swindall, Department of Chemistry, David Keir Building, Queen’s University, Belfast BT9 SAG. (Tel. 0232-661111, Ex. 4428). Wednesday to Friday, 8th to 10th: Ferndown Automatic Methods Group. Analysis and its Commercial Significance in the 90s. In both public and private sectors there is an ever increasing emphasis on incisive measurement to set and monitor performance levels. As a generator of information this will, obviously, impact on the role of the analytical chemist. Success will be judged against his ability to keep pace with change undertaken in his organisation to remain competi- tive.Throughout the 1980’s the analyst has been waiting patiently and optimistically for novel developments in technology to achieve these objectives. In the event, they have not materialised and it is now important that the situation is re-appraised in terms of existing technologies and realistic developments. What will this mean for the analytical chemist in reality? It will require a re-assessment of the value of any given measurement to a customer, or even more fundamentally, why is the measurement needed at all, how robust is the measurement and how can it impact more effectively on performance? The analyst will also have to be mindful that quality, by design, can only be achieved by working smarter rather than harder.In short, the analytical chemist will have to become more pro-active, commercially aware and capable of effectively interfacing with all relevant disciplines within his organisation. The subject matter will be reviewed in the following four theme sessions. 1. The Role of Analytical Measurement in Production Performance Assessment. Where are we now? Are we meeting customer needs? How can we improve? 2. Developing Analytical Strategies to Support Statistical Process Control. Deriving further benefits from information technology, e.g. , cost benefit analysis Experimental design Chemometric assessment of databases Quality assurance 3. Automated Analysis-its Role in Total Quality Assurance. A review of developments in automation for both laboratory and production applications: e.g., Improving experimental control Creating more effective sample and user interfaces Improving information flow 4.Resourcing to Meet the Needs. e.g. , Analytical requirements stemming from COSHH Future requirements for training analytical scientists Facilities The over-all objective of the conference is to review automated analysis and its total impact on business efficiency irrespective of application area and will be of interest to all those seeking to improve cost effectiveness of analysis in their organisation. The Dormy Hotel, Ferndown, Dorset. Registration is necessary. The cost, including full-board accommodation, conference dinner, etc., is anticipated to be &350 for RSC members and &430 for non-members (VAT to be added).Full details of the programme and registration will be available shortly. Contact: Mr. R. Lidgett, Fron Cottage, Llandynan, Llan- gollen, Clywd LL20 7AJ. (Tel. 0978-860571). [continued on p . 3601360 ANALYTICAL PROCEEDINGS, OCTOBER 1989, VOL 26 Scientific Societies’ Lecture Theatre, Savile Row, London. Registration is necessary. Cost f45 for members, f60 for non-members and 220 for bona fide students and retired members. Contact: Dr. C. J. Keattch, Industrial and Laboratory Services, P.O. Box 9, Lyme Regis, Dorset DT7 3BT. (Tel. 02974-2472). Analytical Division Diary, continued November, continued Thursday, 9th, 10.30 a.m.: Ware East Anglia Region: Annual General Meeting. GLP and Computing. “Training and GLP,” by A. Harrison. “The Application of GLP Principles to Computer Systems,” by D.22nd Annual General Meeting of the East Anglia Region: 1.45 p.m. “The User’s Point of View,” by speaker to be announced. “Quality Assurance of Computer Applications,” by a Member of the Quality Assurance Group, UK. “GLP Aspects of LIMs,” by J. Boother. Glaxo Group Research Ltd., Park Road, Ware, Hertford- shire. Registration is necessary. Cost f25 to RSC members, f40 to non-members and &10 to studentshetired members. Contact: Mr. R. P. Munden, (RSC Meeting), Pharmaceut- ical Analysis Department, Glaxo Group Research Ltd., Park Road, Ware, Hertfordshire SG12 ODP. (Tel. 0920- 469469). Moore. Tuesday, 14th, 7 p.m.: Birmingham Midlands Region. Analysis and Crime. Speaker: R. L. Williams. Department of Chemistry, The University, Birmingham.Contact: Dr. R. M. Smith, Department of Chemistry, University of Technology, Loughborough, Leicestershire LE11 3TU. (Tel. 0509-222563). Tuesday, 14th: Carlisle North West Region. Analysis and Crime. Speaker: R. L. Williams. Carlisle. Contact: Dr. G. Davison, 34 Beechfields, Doctors Lane, Eccleston, Chorley, Lancashire PR7 5RE. (Tel. 0257- 452537). Wednesday, 15th, 10 a.m.: London Thermal Methods Group: Annual General Meeting. Applications of Evolved Gas Analysis. Introduction by Mr. P. J . Haines (Chairman, Thermal Methods “Evolved Gas Analysis Techniques,” by P. Barnes. “A Simple Evolved Gas Detector Facility for the Characterisation of “EGA of Diesel Exhaust Particles,” by D. R. Glasson, C. Seebold “Measurement of HCl Evolution in Temperature-programmed Group).Textile Fibres,” by J . S. Crighton. and G. E. Millward. Reduction of Supported Metal Chlorides,” by G. C. Bond. “Simultaneous TG - Quantitative Evolved H20 and C02 Analysis “Use of EGA to Investigate the Effect of Flame Retardants on Toxic “Applications of TG Coupled to FTIR Spectroscopy,” by J . Sellors “Industrial Applications of Simultaneous TA - MS,” by E. L. “Application of Combined TG-DSC-MS in the Field of Polymers by NDIR,” by D. Thornley and N. Pallat. Gas Evolution from Pyrolysed Cotton Fabric,” by D. Price. and R. A. Spragg. Charlsey and S. B. Warrington. and Ceramics,” by E. Kaiserburger and M. P. Doherty. Wednesday, 15th, 10 a.m.: Risley Radiochemical Methods Group: Annual General Meeting. Radionuclide Measurement and Characterisation. “Industrial Applications of Radionuclides and Relevant Measure- “Medical Applications of Radionuclides and Relevant Measure- “Radionuclide Standards and Their Calibration,” by A.Ainsworth. “The Availability and Application of Nuclear Data,” by P. “Nuclear Decay Data Libraries-Evaluations and Compilations,” “Nuclear Data Measurement Techniques,” by S. Woods. Daresbury Room, Risley Restaurant and Conference Cen- tre, AEA Technology, Risley, Warrington, Cheshire. Registration is necessary. Costs to non-members f30, members f20 and OAP’s and students (in full-time education) f15. Contact: Dr. P. Robb, Radiochemical Analysis Unit, Petroleum and Analytical Chemistry Group, Chemistry Division, Winfrith Technology Centre, Dorchester, Dorset DT2 8DH. (Tel. 0305-251888, Ex.3291). ment Techniques,” by J . A. Heslop. ment Techniques,” by G. Lawrence. Christmas. by A. L. Nichols. Thursday, 16th, 6 p.m.: London Biological Methods Group: Annual General Meeting and Usage and Abusage of Drugs in Sport. Speaker: D. A. Cowan. Royal Society of Chemistry, Burlington House, Piccadilly, Registration for the Buffet with Wine is necessary. Cost 28. Contact: Mr. A. J. Crooks, Molecular Virology Group, Biologics Division, PHLS Centre for Applied Microbiol- ogy and Research, Porton Down, Salisbury SP4 OJG. (Tel. Buffet with Wine. London W1. 0980-61039 1, EX. 382). Friday, 17th: Liverpool North West Region. Young Scientists Meeting. The Polytechnic, Liverpool. Contact: Dr. G. Davison, 34 Beechfields, Doctors Lane, Eccleston, Chorley, Lancashire PR7 5RE.(Tel. 0257- 452537). Tuesday, 21st, 10 a.m.: London Chromatography and Electrophoresis Group: Annual General Meeting and joint meeting with the Chromato- graphic Society. Modern Thin-layer Chromatography. “Experiences with Overpressure Layer Chromatography “Industrial Environmental Monitoring via TLC-Prospects and “Direct Spectroscopic Analysis of Components on TLC Plates ,” by (‘OPLC’),” by I. D. Wilson. Future Trends,” by J . Futter. C. Dewy. [continued inside back cover]ANALYTICAL PROCEEDINGS, OCTOBER 1989, VOL 26 ... 111 Analytical Division Diary, continued November, continued DNA Profiling in Forensic Science. Speaker: B. Parkin. Small Lecture Theatre, Main Building, UWCC, Museum There are no registration formalities. Contact: Mr. F. W. Sweeting, Wessex Water, Scientific Centre, Mead Lane, Saltford, Bristol BS18 3ER.(Tel. Avenue, Cardiff. 022543355861834898). Short Talks by manufacturers and suppliers of TLC equipment, “Advances in Bonded Phases for Quantitative HPTLC,” by P. E. “Separation of Drugs and Metabolites Using Automated Multiple “Future Trends,” by H. Read. Meeting Room, Zoological Society of London, Regents Park, London NW14RY. Registration is necessary. Costs to members of the RSC and/or the Chromatographic Society Z30.00; non-mem- bers Z40.00; bona fide full-time student members, non- employed or retired members, f15.00. Contact: Dr. D. Simpson, Analysis For Industry, Factories 2/3, Bosworth House, High Street, Thorpe-le-Soken, Essex C016 OEA. (Tel. 0255-861714). media etc. Wall. Development (AMD),” by P.V. Colthup. Wednesday, 22nd, 10.30 a.m.: Hereford Atomic Spectroscopy Group and Midlands Region. Industrial and Environmental Applications of XRF Spec- trometry. “TXRF-A New Analytical Tool,” by S. J. Haswell. “Applications of EDXRF in Plastics and Petrochemical Industry,” Annual General Meeting of Atomic Spectroscopy Group: 2 p.m. ”Ceramics-Specimen Preparation, Removal of Particle Effect, Inter-Element Corrections,” by G. Oliver. “Exploiting EDXRF in the Determination of Trace Elements in Geological Samples,” by P. J . Potts. “Monitoring Workplace Exposure to Hazardous Substances-The Role of X-ray Spectrometry,” by N. G. West. Inco Alloys Ltd., Holmer Road, Hereford. Registration is necessary. Cost to RSC members f15, non-members &30, and students, unemployed and retired members of the RSC gratis.Contact: Dr. A. T. Ellis, Link Analytical Ltd., Halifax Road, High Wycombe, Buckinghamshire HP12 3SE. (Tel . 0494-442255). by P. Warren. Thursday, 23rd, 5 p.m.: Cardiff Western Region, jointly with the South East Wales Section of the RSC and the University of Wales College of Cardiff Student Chemical Society. Thursday, 23rd, 7 p.m.: Glasgow Scottish Region, jointly with the Glasgow and West of Scotland Section of the RSC and the Andersonian Society. Where is Analytical Chemistry Heading in the 1990s? Speaker: D. Littlejohn. The Music Room, Strathclyde University Staff Club, Cathedral Street, Glasgow. Contact: Mr. R. I. Aylott, United Distillers PLC, Group Central Laboratory, Menstrie, Clackmannanshire FK11 7ES. (Tel. 0259-61481). Wednesday, 29th: Teesside North East Region: Annual General Meeting. Effect Material-The Analytical Challenge. ICI Wilton Materials Research Centre, Teesside. Contact: Dr. J. Marshall, TCI PLC, Wilton Materials Research Centre, Materials Analysis and Testing Group, P.O. Box 90, Middlesbrough, Cleveland TS6 8JE. (Tel. 0642-432029). Wednesday, 29th, 6.30 p.m.: London Micro & Chemical Methods and Chromatography & Electro- Annual General Meeting of the Micro & Chemical Methods Ion Chromatography, with Particular Reference to Oxy- anions. Discussion to be introduced by Miss L. Dixon. London School of Economics, Houghton Street, London Contact: Mr. P. R. W. Baker, 55 Braemar Gardens, West phoresis Groups and South East Region. Group. w c 2 . Wickham, Kent BR4 OJN. (Tel. 01-777-1225).

ISSN:0144-557X    

DOI:10.1039/AP9892600359

出版商:RSC    

年代:1989

数据来源: RSC