ISSN:0144-557X    

DOI:10.1039/AP99128FX001

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

2 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 L. S. Theobald Lecture Meeting The following are summaries of two of the papers presented at a Meeting of the Analytical Division held on May 8th, 1990, in the Scientific Societies' Lecture Theatre, London W.1. Surface-active Chelating Agents in Analytical Chemistry Mehmet Uygur Garip and Michael Thompson Centre for Analytical Science, Birkbeck College, Gordon House, 29 Gordon Square, London WCI H OPP Foam fractionation,' which is a class of adsorptive bubble separation techniques, is a cheap and efficient method of removing and concentrating surface-active solutes from dilute solutions. The process relies on the tendency of the surfactant molecules to adsorb and concentrate at the gas-liquid inter- face. Foaming provides a large mass transfer area for the surface-active species while the volume of collapsed foam is small.Concentration factors of two orders of magnitude or more can be obtained by the design and selection of the operating conditions. Non-surface-active solutes can also be concentrated through association with suitable surfactants which interact strongly and preferentially with the solutes, rendering them surface-active. 1 The technique has been the subject of study by a number of workers in the field of separation science over the past 30 years.*-2 The main emphasis has been on its possible use for large scale industrial applications such as removal and/or recovery of pollutants, precious metals and radioactive metals from waste waters and effluents. An extensive review of the subject together with other adsorptive bubble separation techniques was presented by Grieves1 with 353 references covering the period up to 1979.A more recent review (1989) is provided by Carleson2 with 115 references. Although many workers have referred to the potential application of this technique as a pre-concentration method in analytical chemistry, as far as we can ascertain no such work has been reported in the literature. Considering the large concentrating ability and the possible selectivity obtainable by design of surfactants it is surprising that the method has not received attention from analytical chemists. We have concentrated on using chelating ionic and non-ionic surfactants to concentrate selectively transition metal cations from aqueous solutions at trace levels for the purpose of quantitative analysis.Below, we present some preliminary results. Theory A surface-active solute in aqueous solution adsorbs and concentrates at the air-solution interface with its hydrophobic tail sticking out of the solution and its chargedpolar head group remaining within the aqueous phase.3.4 The extent of adsorption depends on the bulk phase activity of the surfactant (also true for any solute in the solution), and is given by the Gibbs adsorption equation dy = -RT C Ti dlnai (1) where dy is the reduction in the surface tension of ihe solution, Ti is the surface excess concentration of the ith component and ai is the activity of the ith component in the solution. For dilute solutions activity can be equated with concentration without significant error.As the bulk concentration of the surfactant is increased, adsorption at the interface increases very rapidly initially and eventually reaches a maximum near the critical micelle concentration (CMC) when essentially the whole interface is covered with a monolayer of oriented surfactant molecules. n Silicone foam breaker \ Foam receiver (weighed) - -Foam drainage column Pyrex bottle for test solution (500 ml) - Fig. 1 Foam fractionation apparatus The maximum surface excess concentrations of most linear surfactants lie in the range 2-4 pmol m-2 while the CMCs vary from about 1 x 10-5 to 1 x 10-4 moll-' for non-ionics to 1 x 10-3-1 X 10-2 mol 1-1 for ionic surfactants,3 the latter being generally more soluble in water.I 8 0.1 0.06 0.08 0 0.02 0.04 Bulk [Cul (ppm) Fig. 2 Extract versus bulk concentration of Cu" with 0.001 M DDETA at pH 10 and gas flow-rate of 23 rnl min-1 (2 one standard deviation plotted about the means; solid line is least squares fit)ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 3 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Bulk [Cul (ppm) Fig. 3 ( a ) , Extract versus bulk concentration of CuI1 with DIBMP and DIBPA both at 23 ml min-1 gas flow-rate (k one standard deviation plotted about the means; lines are least squares fit): A, DIBMP 0.001 M, pH = 7; B, DIBPA 0.004 M, pH = 6. ( b ) , Mass of copper extracted per hour versus bulk concentration of Cu": A , DIBMP 0.001 M, pH = 7; B, DIBPA 0.004 M, pH = 6. ( c ) , Volume of extract per hour versus bulk concentration of Cu": *, DIBMP 0.001 M, pH = 7, 0; DIBPA 0.004 M, pH = 6 A typical single stage batch foam fractionation apparatus is illustrated in Fig.1. Gas bubbles (more properly cavities) are introduced into the body of the test solution, and surfactant molecules adsorb at the gas-solution interface of the rising cavities. On leaving the bulk phase the bubbles form a foam which continuously travels up the drainage column and flows into the collection tube. Some mechanism of foam collapse is used to collect the extract as a solution. For a given volume of the extract, the amount of surfactant extracted is given by equation (2) M(S)x = r s Af + [s]b vf (2) i.e., M ( S ) , is the mass of surfactant in the extract, Ts is the surface excess concentration of the surfactant, Af is the interfacial area collected, [S]b is the bulk concentration of the surfactant and Vf is the volume of the collapsed foam extract.If we define the pre-concentration factor as the ratio of the surfactant concentrations in the extract and the bulk, equation When the solution contains non-surface-active normal sol- utes that associate with the surfactant through such mechan- isms as complexation, ion pairing, chelation or simply replac- ing the counter ion, there will also be a surface excess concentration of the solutes at the interface as these solute- surfactant pairs. The surface excess concentration of these complexes will be a function of the surfactant and the normal solute concentrations in the bulk phase, and their stability const ants. A number of models have been proposed for the different mechanisms of possible interactions.These include ion pair- ing,S complexation and chelate formation in solution and subsequent adsorption at the interface ,6 ion exchange at the interface,S and counter-ion distribution at the electrical (dif- fuse) double layer as envisaged in the modified Debye-Huckel treatment.7.8 In each of these treatments it is possible to predict the selectivity and the extent of adsorption of different solutes, based on their differential interaction with the surfactants, (2) becomes both in type and in intensity. For the purpose of quantitative trace analysis we require a [ S I X TsAf + 1 (3) pre-concentration technique that is effective, selective, repro- LsIb - LsIb vf ducible for very dilute solutions and gives a useful calibration Therefore, to achieve high pre-concentration ratios both the surface excess concentration and the ratio of interfacial area removed to volume of the collapsed extract should be as large as possible while the bulk surfactant concentration should be low.The latter requires a well drained foam that carries Over as little of the bulk solution (as interstitial solution) as possible. As the surface excess concentration depends on the bulk range. The effectiveness depend On the tendency Of the sohte-surfactant to adsorb at the interface- The measure of this is the distribution ratio defined as the ratio of its Surface eXCeSS Concentration to its bulk phase COnCeIltratiOn' [equation (4)1 Ti concentration of the surfactant an optimum value of the latter D.=- needs to be found.' [il (4)4 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 As the surface excess concentration rapidly reaches a maxi- mum as the surfactant concentration approaches its CMC the distribution ratio will be smallest at high surfactant concentra- tions, diminishing the effectiveness of the process. Selectivity should be possible by using surfactants that show large affinity towards the targeted solute such as chelating surfactants for transition metal cations. Reproducibility will depend on the constancy of the interfa- cial area collected per unit time, i.e., constant foaming rate and bubble size and a stable foam. A useful calibration range should be possible as at low surfactant concentrations the surface excess concentration of a surfactant varies linearly with bulk concentration.4 Therefore, considering the solute-surfactant complex as distinct from the free surfactant in the solution we can expect the surface excess concentration of the complex to be proportional to its bulk concentration.This may not however be true if there are other interfering species also present. Preliminary Results Figs. 2 and 3 show the results obtained using Cu2+ as a model transition metal cation with three different chelating surfac- tants listed in Table 1. Table 1 Acronyms and formulae of surfactants tested Dodecyl Dodecyl iminobis Surfactant Acronym Formula diethylenetriamine DDETA C12H2sNHC2H4NHC2H4NH2 (methylene phos- phonic acid) disodium salt DIBMP C12H25N(CH2P03HNa)2 Dodecyl iminobis (propionic acid) monosodium salt DIBPA CI2H25N( C2H4CO2H)( C2H4C02Na) The plots show the concentration of Cu in the extract [Figs.2 and 3 ( a ) ] , the amount of Cu extracted per hour [Fig. 3(b)] and the volume of the collapsed extract [Fig. 3(c)] against bulk Cu concentration. Plus or minus one standard deviation is plotted about the means and the lines are least-squares fits. In all instances test solutions containing 0-1 mg 1-1 of Cu2+ (using 1000 mg 1-1 metal standards in 1 mol 1-1 HN03) were made up with purified water with the appropriate concentra- tion of the surfactants and the pH was adjusted using analytical-reagent grade NaOH or HN03. These solutions were then foam fractionated using the apparatus illustrated in Fig. 1 with a gas flow-rate of 23 ml min-1 for a period of 1 h.The extracts were diluted to a suitable volume and the copper content was determined by flame atomic absorption spec- trometry (AAS). Discussion Results show that a 5675-fold concentration of Cu is reprodu- cibly achieved for solutions containing Cu at pg 1-1-mg 1-1 levels. It also appears that a linear relationship holds between the extract and bulk concentration of Cu in the range 0-1 mg l - l , which is also true of the amount of Cu extracted per hour. Considering that for DIBMP and DIBPA, the solutions are at least 2 X 10-3 moll-' in Na+ while Cu2+ is 1.6 x 10-6-16 x 10-6 mol 1-1 the results support our initial guess that selectivity can be achieved by using chelating surfactants. The volumes of collapsed foam extracts plotted in Fig. 3(c) show that they are relatively constant at about 0.5 ml h-1.All three surfactants concentrated Cu to the same extent even though their concentrations in the test solutions and the pH were significantly different. These concentrations were chosen as the lowest concentration that gave a stable foam for each of the surfactants. Improvement in pre-concentration is possible with better drainage of the foam. This will, however, provide an even smaller volume of the extract which will need to be diluted by a larger factor for analysis by normal flame AAS. Therefore, increased foaming rate with longer foam drainage time may overcome this problem to some extent. The full potential of the system should be realized if a technique such as graphite furnace AAS or flow injection flame AAS is used, which requires only a few tens or hundreds of microlitres of analyte solutions.The extracts could then be analysed directly without further dilution. One of us (M. U. G.) is currently receiving an SERC postgraduate quota award. We are indebted to BDH for financial support. References Grieves, R. B . , in Treatise on Analytical Chemistry, eds. Elving, P. J., Grushka, E . , and Kolthoff, I . M., Wiley, New York, 2nd edn., 1982, Part 1, vol. 5 , ch. 9. Carleson, T. E., in Surfactant Based Separation Processes, eds. Scamehorn, J . F., and Harwell, J. H., Surfactant Science Series, Volume 33, Marcel Dekker, New York, 1989, ch. 10, pp. Rosen, M. J . , Surfactants and Interfacial Phenomena, Wiley , New York, 1978. Adamson, A. W., Physical Chemistry of Surfaces, Wiley, New York, 4th edn., 1982.Grieves, R. B., and Kyle, R. N., Sep. Sci. Technol., 1982, 17, 465. Chou, E. J . , and Okamaoto, Y . . Sep. Sci. Technol., 1978, 13, 439. Jorne, J . , and Rubin, E.. Sep. Sci.. 1969,4, 313. Kubota, K . , Hayashi, S . , and Morita, M., Can. 1. Chem. Eng.. 1978. 56, 130. 233-258. Carbon-based Electrodes and Their Application as Electrochemical Sensors for Selected Biomolecules John P. Hart and Stephen A. Wring Department of Science, Bristol Polpechnic, Coldharbour Lane, Frenchay, Bristol BS 16 1 QY Carbon, in the form of graphite, is an inexpensive and versatile Carbon Paste Electrodes for Adsorptive Stripping material and is particularly suitable for the fabrication of Voltammetry of Vitamin K1 electrodes.In recent reports,14 we have described the fabrication of several different types of carbon-based elec- The aim of this investigation was to determine the effect of trodes and discussed their applications as sensors for several different types of graphite, and other conditions, on the molecules of biomedical interest. This paper attempts to adsorptive stripping voltammetric (AdSV) behaviour of summarise our recent investigations with particular emphasis vitamin K1, then to use the optimised conditions for the being placed on the practical details for sensor construction. determination of low levels of the vitamin in plasma,ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 5 The technique known as AdSV has been discussed in detail elsewhere.7.8 Briefly, this is a two-stage technique: the first step involves the pre-concentration of the analyte at the electrode surface; this is followed by the measurement step, where the analyte is stripped back into solution by the application of a suitable voltammetric waveform.In some instances pre-concentration may be performed by applying an appropriate potential between the working and auxiliary electrodes; however, for certain organic molecules, using a carbon paste electrode, it is possible to carry out the pre-concentration step at open circuit. We investigated the latter technique in our studies. Fig. 1 shows the construction of the carbon paste electrode which was used in several of our studies. It consists of a Kel F barrel and an inner threaded brass rod arranged in a piston-like configuration which allows the thickness of the graphite paste to be adjusted; this also facilitates easy removal of the paste after each run.'A' Fig. 1 Schematic diagram of a carbon paste electrode: A, 3 mm diameter graphite paste working electrode; B, threaded brass rod; C, 15 x 1.3 cm 0.d. Kel F barrel; and D, position for electrical contact The carbon paste electrodes were prepared by adding the required amount of Nujol to the graphite powder and grinding this with a pestle and mortar for 30 min. The Nujol composition was varied between 20 and 40% m/m for one type of graphite; a total of four different types of graphite were investigated. Each type of carbon paste in turn was packed into the barrel of the electrode to a depth of 3 mm and the surface smoothed on a computer card.The electrode was then ready for use. We began our investigations with a type of graphite known as Ultra 'F' Purity (Ultra Carbon Corporation, Bay City, MI, USA). The effects of pre-concentration time and percentage of Nujol in the carbon paste electrode were investigated with a solution containing 1 x 10-5 M vitamin K1 dissolved in 50% ethanol - 0.05 M acetate buffer (pH 5.0). It was found that the magnitude of the AdSV peak currents increased with accumu- lation time for the four carbon paste electrodes containing 20, 25, 30 and 40% m/m Nujol; however, the largest signals were obtained with an electrode containing 25% m/m Nujol. This behaviour indicates that the magnitude of the voltammetric peaks is not determined solely by partitioning of high concen- trations of the vitamin into the Nujol phase as might be expected.However, at a critical Nujol concentration electrode resistance plays an important role. It was found that the electrode resistance increased from 22 52 at 20% m/m Nujol to 250 52 at 40% m/m Nujol; therefore, this might be expected to inhibit the electron-transfer process. From this study, 25% m/m Nujol appeared to be the optimum concentration and was, therefore, used in the remaining studies on vitamin K1. The effect on the AdSV behaviour of various types of graphite was also investigated: USP Graphite (Ultra Superior Purity, Ultra Carbon Corporation); Natural Graphite (Graphit- werk, Munich, FRG); and Synthetic Graphite (Lonza, Italy). The peak of greatest magnitude was obtained with USP-grade graphite.The effect appears to be related to the particle size of the graphite powders; USP-grade has a mean diameter of 36.4 pm and the sizes decrease to 5.8 pm for natural graphite. It appears that the larger the particle size the higher the rate of diffusion into the electrode body; this would, therefore, result in a greater degree of accumulation. From this study the USP-grade graphite appeared to give the best AdSV peaks for vitamin K1 and was, therefore, used in the remaining studies. We applied the optimised conditions to the determination of the vitamin in spiked plasma samples; the final concentration was selected to be in the range normally encountered when patients had been given oral or intravenous injections. Several different extraction procedures were investigated but the best recovery (91%), precision (3.6%, n = 5 at 2.9 pg ml-1) and limits of detection (450 ng ml-1 in plasma) were found when the extraction was performed with hexane and ethanol. Carbon Paste and Graphite - Epoxy Composite Electrodes Chemically Modified With Cobalt Phthaloc yanine The main purpose of these studies was to develop an electrochemical sensor for reduced glutathione (GSH) [N-(N- L-y-glutamyl-L-cysteinyl)glycine]. Although unmodified car- bon electrodes have been used to detect GSH, large working potentials are Eequired to initiate the oxidation reaction. Such high potentials are undesirable when determinations are to be made on biological fluids, due to the possibility of interference.In order to reduce the overpotential for the oxidation of GSH we decided to investigate the possibility of using a mediator; the electrocatalyst cobalt phthalocyanine (CoPC) was con- sidered worthy of investigation.Initial studies were carried out by incorporating CoPC in carbon paste electrodes; these were prepared by simply mulling the required amount of electrocatalyst with graphite powder and Nujol using a pestle and mortar. In one study, the electrode contained 2% m/m CoPC and this was used to study the cyclic voltammetric behaviour of GSH dissolved in Britton - Robinson buffer (pH 12.0). When this voltammo- gram was compared with those obtained with the same electrode in plain buffer it was found that the former contained three peaks (denoted as 1,2, and 3) whereas the latter showed only the two most positive peaks (peaks 2 and 3).A third voltammogram, obtained with an unmodified carbon paste electrode and a GSH solution of the same composition, did not show any peaks in the potential range studied. Therefore, peak 1 must have resulted from GSH chemically reacting with CoPC. The effect of concentration on the magnitude of peak current was studied and a linear relationship was found to exist; therefore, this peak appeared to be suitable for the measure- ment of GSH levels and was investigated in further studies. An investigation was carried out to ascertain the effect of pH and ionic strength of supporting electrolyte on the magnitude6 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 of peak 1. It was found that for optimum sensitivity buffers with a pH >7 should be used; however, GSH is very unstable in alkaline solutions and pH 5.0 was found to be the best compromise between improved stability and current response while maintaining a low applied potential.From our voltammetric data we have postulated a possible mechanism to explain the appearance of peak 1; this is shown below: (1) 2C02+ + 2GSH + 2Co+ + GSSG + 2H+ Co+ e Co2+ + e- Initially, cobalt is present in the +2 oxidation state and this is chemically reduced by GSH as shown in (1). Cobalt(1) is then oxidised electrochemically to cobalt( 11) in a one-electron diffusion-controlled process (2) to produce peak 1. (2) C- 'D + B t - Fig. 2 Schematic diagram of the carbon - epoxy resin composite electrode modified with CoPC: A, 13 cm long glass tube; B, 3 mm diameter composite electrode; C, threaded Quickfit sleeve; and D, position for electrical contact The chemically modified carbon paste electrode could be used in conjunction with differential-pulse voltammetry to determine 2.5 x 10-6-6.25 x 10-5 M of GSH.However, we had considered using the same electrode in two other modes of operation: as the working electrode with constant-potential amperometry in stirred solutions, and as the detector in a liquid chromatographic system. Unfortunately, it appeared that the CoPC and graphite were eroded from the electrode surface when using these techniques. It was, therefore, decided to investigate a different approach to immobilising the electrocat- alyst on to the electrode. For the construction of this electrode we replaced the Nujol with epoxy resin; in order to minimise electrode impedance for voltammetry a 50 + 50 mixture of graphite (containing 5% m/m CoPC) and epoxy resin was used.This was mixed thoroughly for 15 min and then packed into a glass tube of 3 mm i.d.; electrical contact was made by pushing a wire down the inside of the glass tube and into the back of the mixture (Fig. 2). The mixture was then allowed to cure. The resulting hardened electrode surface was polished with wet and dry emery paper (1200 grade) and finally with a slurry prepared from 0.03 pm aluminium oxide, placed on a suede pad. The electrode stability was tested using amperometry in a stirred solution containing GSH. The electrode was held at a constant potential of +0.50 V and the current response was continu- ously monitored; there was no loss of sensitivity over a period of 10 h. In order to test the suitability of this electrode as an amperometric sensor a 25-ml aliquot of plain phosphate buffer (pH 5.0) was introduced into the voltammetric cell and to this were added 25-pl aliquots of 0.01 M GSH; the current response was then measured after each addition.The calibration graph was found to be linear over the range 3-30 pg ml-1 and the limit of detection was 10 ng ml-1; in addition, the electrode showed rapid response times. The response of the chemically modified electrode to other compounds was also investigated. It was found that cysteine, uric acid and ascorbic acid all produced a response at the sensor but the largest signal was obtained with the last compound.For this reason we considered that it might be possible to use the sensor to determine ascorbic acid in pharmaceuticals. To test this possibility a sample solution was prepared from Boots vitamin C tablets; a 100-pl aliquot of this solution was added to the same buffer as previously described and the response was measured. Five separate standard additions of a pure solution containing vitamin C were made to the sample and the concentration was found from the resulting calibration graph. The recovery of the method was 97.6% and the precision was 5% for 50-mg tablets. Using this method a number of other multi-vitamin preparations were analysed and the results correlated well with those given by a high-performance liquid chroma tographic method.\ ' A Fig. 3 Diagram to show the preparation of screen-printed electrodes: A, PVC support; B, screen stencil showing six electrode shapes; C, graphite suspension; and D, squeegee As it appeared that common substances found in blood plasma would interfere in an amperometric determination of GSH in this matrix, we considered that the chemically modified electrode might be suitable as the working electrode in a flow-through cell system using liquid chromatography with electrochemical detection. It was shown that a reversed-phase column in conjunction with a modified TL3 cell (BAS) could be used to measure circulating plasma levels of GSH.3 Screen-printed Carbon Electrodes as Disposable Sensors for GSH, Vitamin C or Coenzyme A Screen-printing technology is potentially an ideal and simple technique for preparing thin-film carbon electrodes on inert supports.It does not require expensive or complicated equipment and different electrode shapes can be easilyANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 7 deposited. We set out to develop a simple screen-printing process for the production of disposable, chemically modified electrodes; we were particularly interested in a device that would act as a sensor for glutathione and which could possibly be adapted to other molecules. Initially, we prepared the screen stencil; the procedure for the construction of this has been described in detail elsewhere.5 The graphite suspension, for the preparation of the electrodes, was prepared by first mixing 1.5% cellulose acetate in cyclohexanone - acetone (1 + 1).To 1.25 g of this mixture was added 0.5 g of graphite containing 1.5% CoPC; this was carefully mixed for about 3 min to obtain a free-flowing suspension. The screen-printed chemically modified electrodes were made in the manner shown in Fig. 3. In this instance the inert support was poly(viny1 chloride) (PVC) and a suitable size was cut to accommodate four rows of six identical electrodes. The graphite suspension was placed on to the mesh (screen stencil) which had been previously treated to produce the desired electrode shapes. The squeegee was held at an angle of 60” to the screen stencil and moved forwards and backwards over the required region of the mesh. The PVC board containing the deposited electrodes was then removed from the apparatus and allowed to dry at room temperature.The resulting electrode is a 3 mm diameter circle with a 25 x 1 mm wide connecting strip. These electrodes were next investigated as possible sensors for GSH, vitamin C and coenzyme A. Hydrodynamic voltam- metry was carried out on separate solutions of these com- pounds dissolved in phosphate buffer (pH 5.0); all of the solutions produced a voltammetric wave which indicated that the electrode could be used to monitor these substances. In order to evaluate the sensors further we constructed calibration graphs for GSH and vitamin C over a wide concentration range. Glutathione showed a linear range from 2.0 X 10-3 M down to the detection limit, 1.48 x 10-7 M; vitamin C showed a linear range from 2.00 x 10-3 M down to the detection limit, 4.98 x 10-8 M. The excellent sensitivity and stability attainable using the modified electrode films, and the wide linear calibration ranges, are most encouraging for future work in this important area. It is possible to use these sensors as stand- alone devices or they could provide the basis for further development into biosensors incorporating enzymes to enhance selectivity. The authors are grateful to the National Advisory Board for financial support. They thank Louis Bracey, Ian Morgan and Brian Birch for their interest in the work and Mike Norman for technical assistance. References 1 Hart, J . P., Wring, S. A . , and Morgan, I . C., Analyst, 1989,114, 933. 2 Wring, S. A., Hart, J . P., and Birch, B. J., Analyst, 1989, 114, 1563. 3 Wring, S. A., Hart, J . P., and Birch, B. J . , Analyst, 1989, 114, 1571. 4 Wring, S. A., Hart, J . P., and Birch, B. J . , Anal. Chim. Acta, 1990, 229, 63. 5 Wring, S. A . , Hart, J. P., Bracey, L., and Birch, B. J . , Anal. Chim. Actu, 1990, 231, 203. 6 Wring, S. A . , Hart, J . P., Thompson, J. F. A., and Birch, B. J . , Anal. Proc., 1990, 27, 209. 7 Wang, J . , in Bard, A. J . , Editor, “Electroanalytical Chemistry,” Volume 13, Academic Press, New York, 1989, p. 2. 8 Hart, J . P., “Electroanalysis of Biologically Important Com- pounds,” Ellis Horwood, Chichester, 1990.

ISSN:0144-557X    

DOI:10.1039/AP9912800002

出版商:RSC    

年代:1991

数据来源: RSC

ISSN:0144-557X    

DOI:10.1039/AP99128BX003

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

8 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 Research and Development Topics in Analytical Chemistry The following are summaries of seven of the papers presented at a Meeting of the Analytical Division held on July 16th-I7th, 1990, in ICI C and P Ltd., Runcorn, Cheshire. Thermospray Interface for High-performance Liquid Chromatography-Diffuse Reflectance Fourier Transform Infrared Analysis Alan M. Robertson, Lindsay Wylie and David Littlejohn Department of Pure and Applied Chemistry, Thomas Graham Building, University of Strathclyde, Cathedral Street, Glasgow GI IXL R. John Watling Philips Scientific, York Street, Cambridge CB I 2PX Christopher J. Dowle ICI Wilton Materials Research Centre, Wilton, Middlesbrough TS6 8JE Over the past decade, the use of combined techniques for solving complex analytical problems has become increasingly popular. This is particularly true in the interfacing of chromato- graphy with molecular spectroscopy.Techniques such as gas chromatography-mass spectrometry, gas chromatography- Fourier transform infrared spectrometry and high-perfor- mance liquid chromatography-mass spectrometry have become relatively commonplace. Unfortunately, owing to the presence of the condensed mobile phase in liquid chromato- graphy, no successful interface has been developed for high-performance liquid chromatography-Fourier transform infrared (HPLC-FTIR) spectrometry. The use of infrared detection in HPLC has many advantages. The high scan speed and sensitivity of FTIR spectrometers have made it possible to record the infrared spectra of individual components separated by HPLC.Further, most organic solutes exhibit an infrared absorption spectrum, and so the desirable characteristic of “universal” detection is more of a possibility than with ultraviolet (UV) absorption or refractive index measurements. The infrared detector can also provide chemically specific information by monitoring particular absorption bands, which may simplify the separation condi- tions required for some HPLC analyses. Various procedures have been proposed to interface HPLC with FTIR.14 Much of this work has involved the use of flow cells,1-3 but many problems have been encountered due to the absorption of infrared radiation in important wavelength regions by HPLC solvents. More favourable results can be obtained if solvent elimination is applied prior to FTIR detection.4-6 A thermospray can be used to evaporate the solvent and deposit a concentrated spot of solute on to a substrate, which may then be positioned into the diffuse reflectance (DRIFT) accessory of an FTIR spectrometer.A thermospray device has been constructed for operation in normal and reversed-phase HPLC. The column effluent is de-solvated and deposited on to a moving ribbon which continually transfers the solutes into the DRIFT detector. Various aspects of the interface design have been investigated and optimised. The interface has been applied to the analysis of plastic additives, saccharides, aliphatic carboxylic acids and amino acids. Computer programs have been developed to Glycine Methionine Phenylalaninc Tyros i ne 0 20 40 60 80 Filenumber 0 5 10 15 20 Umin Fig.1 HPLC-FTIR trace for the analysis of amino acids. Functional group: amine deformation. Wavenumber window = (1660-1550 cm-1). All four amino acids detected vv 0 20 Tyrosine I 40 60 80 Filenumber I I 1 I I 1 0 5 10 15 20 Umin Fig. 2 HPLC-FTIR trace for the analysis of amino acids. Functional group: aromatic C-C. Wavenumber window = (1460-1440 cm-l). Specific detection of aromatic amino acidsANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 9 provide FTIR chromatograms based on data from a number of infrared spectral windows corresponding to different func- tional groups. Experimental Instrumentation The instrument used for HPLC analysis was a PU 4100 liquid chromatograph in conjunction with a PU 41 10 UV-visible detector.The FTIR instrument was a PU 9800 series FTIR spectrometer. Both instruments were provided by Philips Scientific, Cambridge, UK. Method Effluent from the HPLC system was transferred into the thermospray system via HPLC stainless-steel tubing, coupled to a 30 cm length of capillary tubing (125 pm i.d., 1.5 mm 0.d.). The capillary tubing was inserted into a 10 cm length of copper tubing (1.5 mm i.d., 4 mm 0.d.). Thermocoax heating wire was brazed on to the outside of this copper tubing. The wire was connected to a 60 V, 3 A variable power supply. The capillary tubing protruded about 1.5 cm from the heating assembly. The temperature of the emerging HPLC effluent was monitored using a ‘K’ type thermocouple [Fluke (GB), Watford, Hert- fordshire] attached to the microbore tubing, midway between the heated region and capillary tip.Effluent from the thermospray (flow-rate normally 1 ml min-1) was sprayed on to a moving stainless-steel ribbon positioned 1 cm below the thermospray, and at right angles to it. The ribbon was 20 pm thick and 12 mm wide, and moved at 1 cm min-1. DRIFT spectra of deposited solutes were collected continuously as the moving ribbon passed through the infrared beam. The FTIR spectrometer was coupled to a Dell system 200 computer enabling acquired data to be stored and processed using commercial and specially developed software. Results and Discussion Fig. 1 shows the FTIR chromatogram obtained for the reversed-phase HPLC separation of four amino acids. The 0 20 40 60 80 Fi lenurn ber I I I I I I 0 5 10 15 20 Urnin Fig.3 HPLC-FTIR trace for the analysis of amino acids. Functional group: unknown. Wavenumber window = (940-870 cm-1). Specific detection of glycine wavenumber window chosen is characteristic for amino acids and all four amino acids have been “universally” detected. Of the amino acids analysed, only two are aromatic, and these may be specifically detected by monitoring the wavenumber window 1460-1440 cm-1 (Fig. 2). Similarly, Fig. 3 indicates that the wavenumber 940-870 cm-1 is specific for the detection of glycine among the amino acids chosen. The analysis of amino acids was carried out using a 100% aqueous mobile phase and a 250 x 4.6 mm i.d. ODS 2 column. As a result, the thermospray was operated at a temperature of 280 “C and the flow-rate reduced to 0.5 ml min- l .Fig. 4 shows the spectral overlay of the HPLC-DRIFT interface spectrum and the standard DRIFT spectrum for tyrosine. Comparison of the two spectra indicates that identification has been achieved for this particular analyte and that no sample degradation has taken place via passage through the thermospray, even at an operating temperature of 280 “C. 105.0 100 - - 90 80 f 70 60 0, .- 5 C 50 c 4000 3000 2000 1 500 1000 Wavenum berlcm - 1 Fig. 4 Spectral overlay of HPLC-DRIFT interface spectrum (upper), and standard DRIFT spectrum (lower) for tyrosine. Upper spectrum baseline corrected and multiplied by a factor of two Similar results were obtained for the analysis of phenolic antioxidants, and also for non-UV absorbing species such as saccharides and aliphatic carboxylic acids.No sample derivati- zation procedures were required for the analysis of aliphatic carboxylic acids and the results obtained indicated potential improvements over differential refractive index detection. Conclusion The development of a HPLC-FTIR interface has provided both ‘universal’ and chemically specific information on non- volatile complex samples which cannot be handled by gas chromatogrgphy-FTIR. The interface has been applied to a variety of sample types with little or no sample degradation being observed. Spectral identification of HPLC separated components may be achieved by comparison of interface spectra with standard spectra, and the interface can be used with most normal and reversed-phase HPLC solvent composi- tions.References 1 2 3 4 Yeung, E. S., in Chemical Analysis, ed. Winefordner, J. D., Wiley, New York, 1986, ch. 3. Fujimoto, C., Vematsu, G., and Jinno, K., Chromatographia, 1985, 20, 112. Hellgeth, J. W., and Taylor, L. T., Anal. Chern., 1987,59,295. Kalasinsky, V. F., Whitehead, K. G., Kenton, R. C., Smith, J. A. S., and Kalasinsky, K. S., J. Chromatogr. Sci., 1987, 25, 273. Griffiths, P. R., in Analytical Applications of Spectroscopy, eds. Creaser, C. S., and Davies, A. M. C., Royal Society of Chemistry, London, 1988. Gagel, J. J., and Biemann, K., Mikrochim. Acta, Part 11, 1988, 185. 5 610 ANALYTICAL PROCEEDINGS. JANUARY 1991, VOL 28 Determination of Nitrite and Nitrate Ions by Electron Paramagnetic Resonance Spectrometry Eric P.K. Tsang, D. Thorburn Burns and Brian D. Flockhart School of Chemistry, The Queen‘s University of Belfast, Belfast BT9 5AG Alkali nitrites and nitrates are used as essential additives in a variety of foods to prevent bacterial spoilage and food poisoning. Nevertheless, concern exists over the presence of nitrate in the diet, not because of any intrinsic behaviour of the ion itself, but rather because of its ability to form nitrite by microbiological or other biochemical processes. Consequently, whenever nitrate is ingested in food, there is always the possibility that some of it will be reduced to nitrite. Under the acidic conditions in the stomach the nitrite ion can react with dietary components to form products that are often associated with carcinogenesis. 1 It is therefore highly desirable that the amounts of nitrite and nitrate in foodstuffs should be moni- tored closely.Various methods are available for this purpose .2-4 This paper describes the application of electron paramagnetic resonance (EPR) spectrometry to the determination of these ions. Principle of the Method The early work of Michaelis et aZ.5 on one-electron oxidation- reduction processes revealed many classes of organic com- pound exhibiting this behaviour. The compounds studied included phenothiazine and its derivatives. Later, Sawicki et aZ.6 showed that nitrite can oxidize such compounds to form coloured products for spectrophotometric determinations and suggested that free radicals were present. The present method is based on this principle, viz., Nitrite + reagent + stable free radical The formation of the free radical is autocatalytic6 and hence nitrite can be determined at trace levels by EPR spectrometry.Results A variety of compounds that can be oxidized by the nitrite ion were studied but only the most effective reagents are reported herein. Nitrate was determined after prior reduction to nitrite by spongy cadmium metal. With mixtures of nitrite and nitrate, the nitrite was first removed by volatilization as nitrosyl chloride7 and the nitrate then determined. The nitrite plus nitrate content was obtained by reduction followed by determi- nation of the total nitrite present. Method A. Phenothiazine A 0.1 ml volume of the test solution, delivered from an Agla micrometer syringe, was diluted to 10 ml with a solution of 0.05% phenothiazine in glacial acetic acid.The measurements were taken 50 min after mixing. The calibration graph was linear in the range 0-1.5 pprn of nitrite. The precision at 0.3 ppm was 1.2% (ten measurements). The detection limit at three times the standard deviation was 0.012 ppm of nitrite. Nitrate and other strong oxidizing agents interfere but reducing agents such as sulphite can be tolerated. Method B. N,N,N’,N’-Tetramethyl-p-phenylenediamine A 0.1 ml volume of the test solution, delivered from an Agla micrometer syringe, was diluted to 10 ml with a 0.05% solution of the reagent in glacial acetic acid. One millilitre of sulphamic acid was added to stabilize the signal which then remained unchanged for at least 2 h. Measurements were taken 50 min after mixing.The calibration graph was linear from 0 to 1.3 ppm; the precision at 0.3 ppm was 1.5% (ten measurements). The detection limit at three times the standard deviation was 0.025 ppm of nitrite. Nitrate and strong oxidizing agents interfere but reducing agents can be tolerated. Applications The methods were applied to the determination of the nitrite and nitrate contents in pre-packed cooked ham and in soft spreading cheese. The results were compared with those obtained by International Standards Organization (IS0)g and Association of Official Analytical Chemists (AOAC)9 stan- dard methods for these samples. Cooked Ham The samples were prepared for analysis by the I S 0 procedure.8 The results are shown in Table 1. Table 1 Nitrite and nitrate content of cooked ham Method A B I S 0 Nitrite 50.2 49.8 50.5 (PPm) Nitrate 65.2 64.9 65.6 (PPm) Soft Cheese The samples were prepared for analysis by the AOAC procedure.9 The results are shown in Table 2.Table 2 Nitrite and nitrate content of soft cheese Nitrate Nitrite A 18.5 62.4 B 18.2 61.6 AOAC 18.8 62.6 Method (PPm) (PPm) Conclusions The EPR methods outlined are simple and sensitive and extraction is not required. Further, the methods can tolerate large amounts of reducing agents which should permit their application to pollution studies, such as the determination of nitrogen dioxide in the presence of sulphur dioxide. An additional advantage is that they are applicable to coloured solutions. It is envisaged that residual interferences can be dealt with by ion chromatography.References Glidewell, C., Chem. Br.. 1990, 26, 137. Williams, W. J . , Handbook of Anion Determination. Butter- worths, London, 1979. Snell, F. D.. Photometric und Fluorometric Methods of Anulysis -Nun Metals, Wiley. New York, 1981. Marczenko, Z., Separation and Spectrophotometric Determina- tion of Elements. Ellis Horwood, Chichester, 1986. Michaelis, L., Granick, S . . and Schubert, M. P., J. Am. Chem. Soc., 1941. 63. 351. Sawicki, E., Stanley, T. W., Pfaff, J., and Johnson, H . , Anal. Chem.. 1963, 35, 2183.ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 11 7 Velghc, N., and Claeys, A., Analyst, 1983, 108, 1018. 8 Meat and Meat Products, Determination of Nitrite Content (reference method), International Standards Organization, IS0 2918-1975(E), Sections 7.1-2, 8.3.1-5 and 8.4.1-4.9 Official Methods of Analysis of the Association of Official Analytical Chemists, ed. Williams, S . , Association of Official Analytical Chemists, Arlington, VA, 14th edn., 1984, Nitrate and Nitrite in Cheese, Section 16.278-16.283. Analysis of Fatty Acid Methyl Esters by Using Supercritical Fluid Chromatography with Mass Evaporative Light Scattering Detection Simon Cocks and Roger M. Smith Department of Chemistry, Loughborough University of Technology, Loughborough, Leicestershire LEI1 3TU The analysis of fatty acids and lipids is of great interest to the food, agricultural and pharmaceutical industries. 1 In the past, the need for the quantification of specific components as well as characterization in quality control has relied mainly on the established chromatographic techniques of gas chromato- graphy (GC) , high-performance liquid chromatography (HPLC)2 and thin-layer chromatography (TLC).For many samples HPLC has come to the forefront of these techniques as the conditions of separation lend themselves to thermally labile high relative molecular mass compounds.3 However, because of the relatively low separation efficiency isomeric components can be difficult to resolve and the absence of a chromophore means that detection of the lipids is a problem. The recent development of practical supercritical fluid chromatography (SFC) should provide a technique that is ideally suited to the separation of fatty acid methyl esters (FAMEs) and separations have been reported using both packed and capillary columns.4 The enhanced diffusivity and solubility of supercritical fluids with respect to liquids and gases potentially offer a fast, efficient separation.The low critical temperature and pressure of carbon dioxide, the most widely used mobile phase, are ideal for the analysis of non-volatile and thermally labile components, and the ability t o adjust the density of the mobile phase with temperature and pressure provides a wide range of possible conditions to effect a separation. Column eluent Light Nebulisation make-up gas- Nebuliser I Heated drift tube Scattered light detected source- md - I' t Exhaust Schematic diagram of a mass evaporative detector Fig. 1 Fatty acids possess a poor chromophore, hence ultraviolet detection, the most common non-destructive detection tech- nique, is of limited value.Although flame ionization detection is universal it is incompatible with modified mobile phases. Infrared spectroscopy is a possible method of detection; however, strong absorbances from carbon dioxide and modifi- ers limit the technique for on-line work. These difficulties led to the present study of the application of the evaporative light-scattering detector (LSD) to the SFC of fatty acids. It is a universal detector, the response of which should be indepen- dent of mobile phase composition. It has been successfully used for many years in liquid chromatography,5-7 and its advantages and disadvantages are well documented.8-10 Preliminary reports have appeared of its application in packed column SFC.11-13 The operation of the detector can be divided into three stages (Fig. 1).lo First, sample introduction: addition of make-up gas and nebulization. Second, evaporation: move- ment of the mist down the heated drift tube with evaporation of the volatile mobile phase components. Third, detection: scattering of the incident light by the remaining solute particles and detection by a photomultiplier tube. Discussion A range of fatty acids were examined in this preliminary study. They varied both in the degree of unsaturation and chain 1 0 8 6 4 2 Time/mi n Injection 20 pl 0 1 I I I 1 1 0 8 6 4 2 0 Ti me/mi n Injection 5 pI Fig. 2 Separation of CI8 fatty acid methyl esters on a Spherisorb column with supercritical fluid carbon dioxide 4 ml min-1 (density 0.871 g ml-1).Nitrogen make-up gas 60 lb in-2: (a), 20 p1 injection of analytes with small amount of glass wool in drift tube; (b), 5 pl injection with additional glass wool in drift tube showing reduced noise and increased sensitivity12 ANALYTICAL PROCEEDINGS. JANUARY 1991, VOL 28 length from CI2:o to CZ4: 1. All of the samples were made up in hexane to concentrations in the region of 1 x 10-6 g pl-1, and then analysed on a silica column (Spherisorb SSW), using an unmodified carbon dioxide mobile phase at selected densities in the region of 0.800 g ml-1. Pressure regulation within the SFC system was maintained using a heated Rheodyne 7037 pressure relief valve. The fluid conditions were extended into the nebulizer and detector of a Varex mass evaporative detector by means of a crimped tube.If the pressure was released between the regulator and detector the analytes condensed out in the connecting tubing, resulting in a small or negligible signal. It has been found to be essential to obtain good nebuliza- tion14 of the sample and the droplet size is controlled by the adjustment of the drift tube temperature and nebulizer gas flow-rate.15 The amount of light scattered is partially a function of the size of the nebulized particles as well as the wavelength of the incident light beam and the angle of collection. In contrast to the situation with HPLC, it was found that the addition of nitrogen as a make-up gas before nebulization was not necessary with SFC and could be omitted. Even at low flow-rates the large volumes of gas produced from the expansion of the carbon dioxide mobile phase gave good nebulization. Fig.3 24 20 15 12 6 0 Tirne/min Injection 10 KI Separation of C I ~ , Clh and CI8 fatty acid methyl esters on Spherisorb’column, eluent carbon dioxide (density 0.841 -g ml-I) 2.5 ml min-1 Initially, the detection of the FAMEs proved problematical owing to the presence of a large amount of base line noise. The noise was present only when carbon dioxide was passing into the detector,l6 and not when the system was being purged with nitrogen from the nebulizer head, thus suggesting that the noise was a function of the carbon dioxide. Removal of the column did not alleviate the problem. It appeared that as the carbon dioxide passed out of the interface into the detector small particles of solid carbon dioxide were formed during the adiabatic expansion, which then passed quickly down the drift tube and through the light source.Increasing the drift tube temperature up to 100°C did not eliminate the problem and worsened the detection limits as a result of partial evaporation of the more volatile analytes. However, it was found that the problem could be removed by plugging the base of the drift tube with a small amount of silanised glass wool. This appeared to act as a heat trap or heat exchanger, causing both turbulent flow and melting of the carbon dioxide particles. The base line noise was significantly reduced and the signal to noise ratio was further improved by additional plugging (Fig. 2). The addition of the glass wool had no apparent effect on the detection limits or peak efficiencies of the samples, which were easily detected at concentrations in the region of 1 x 10-7 g pl-1.The separation of the FAMEs followed a normal-phase type retention mechanism and was primarily dependent on the degree of unsaturation. The chain length played only a small part in the retention processes as C14:o was eluted slightly before Cl6:0 (Fig. 3). This was also true for the elution positions of Cl8:o and cz0:o esters. Separation of the isomeric oleic and elaidic acid methyl esters, c18:1, could readily be achieved with near base line resolution. In order to try to reduce the over-all retention time of the separation 1% methanol was used to modify the mobile phase, but the much shorter retention times brought about co-elution of the isomeric ClXz1 fatty acids.Conclusion The evaporative light scattering detector can be used with an SFC system if slight modifications are made to the drift tube. The results also show that SFC can be used successfully for the separation of both unsaturated and saturated FAMEs. A near baseline separation of the Clx:l isomers was achieved on a silica column. The authors thank the Trustees of the Analytical Trust Fund for the award of an SAC Studentship to S.C. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 References Hammond. E. W., J . Chromatogr.. 1981, 203, 397. Christie, W. W., Conner, K., and Nobel. R. C., J . Chromat- ogr., 1984, 298, 513. Shukla. V. K. S . , J . Disp. Sci. Tech., 1989, 10, 581. White, C. M.. J. High Resolut. Chromatogr.Chromatogr. Commun., 1985. 8,293. Stolyhwo, A., Colin, H., and Guiochon. G . , Anal. Chem., 1985,57, 1342. Robinson, J. L., Tsimidou, M., and Macrae, R., J . Chromat- ogr., 1985, 324, 35. Stolyhwo, A., Martin, M., and Guiochon, G., J . Liq. Chromat- ogr., 1987, 10, 1237. Stolyhwo, A., Colin. H., and Guiochon, G., J . Chromatogr.. 1983, 265, 1. Stolyhwo, A., Colin, H., Martin, M., and Guiochon, G., J . Chromatogr., 1984, 288,253. Macrae, R., Znt. Anal., 1987, 1, 14, 15, 21 and 24. Carraud, P., Thiebaut. D., Caude, M., Rosset. R., Laffosse. M., and Dreux, M., J. Chromatogr. Sci., 1987, 25, 395. Gorner, T., and Perrut, M., Liq. Chromatogr. Gas Chromat- ogr., 1989,7. 502. Nomura. A., Yamada. J . . Tsunoda, K . , Sakaki, K.. and Yokochi, T., Anal. Chem., 1989, 61, 2076.Mourey, T. H.. and Oppenheimer, L. E., Anal. Chem., 1984, 56, 2472. Charlesworth, J . M., Anal. Chem., 1978, 50, 1414. Nizery, D., Thiebaut, D., Caude, M., Rosset, R., Laffosse, M.. and Dreux, M.. J. Chromatogr., 1989. 467, 49.ANALYTICAL PROCEEDINGS. JANUARY 1991, VOL 28 13 Potassium-selective Electrode Based on a Dioxacalixarene: An Example of a New Series of lonophores Aodhamar Cadogan and Dermot Diamond* School of Chemical Sciences, Dublin City University, Dublin 9, Ireland Suzanne Cremin and Anthony M. McKervey Department of Chemistry, University College Cork, Cork, Ireland Stephen J. Harris Loctite (Ireland Ltd.), Whitestown Industrial Estate, Tallaght, County Dublin, Ireland The ability of calix[4]arenes to act as sodium sensors in ion-selective electrodes (1SEs) has been well established14 and successfully applied to the determination of sodium in human plasma samples.s.6 In contrast, poly(viny1 chloride) (PVC) membranes containing the larger hexameric calix[6]arenes have been used to produce caesium-selective electrodes .7 Hence, the ability of the calixarenes to act as host-guest receptors for alkali metal cations is clearly a size-related phenomenon.We now report on the properties of one of a new series of ionophores which possess polar cavities intermediate in dimensions between the tetramers and hexamers mentioned above. These ionophores differ from the normal tetrameric calixarenes in that they contain an additional ether-like oxygen in two of the four methylene bridges (Fig. 1). In the absence of any simple term to describe these substances, we propose the term “oxacalixarene” as a general trivial name, with the prefix “di-,” “tri-,” etc., depending on the number of modified methylene bridges.Bearing in mind the intermediate dimen- sions of this ligand, it was anticipated that it could be used to produce potassium-selective electrodes. Experimental Synthesis The ionophore [ 7,13,2 1,27-tetra-tert-butyl-29,30,3 1,32- tetrahydroxy-2,3,16,17-tetrahomo-3,17-dioxacalix[4]arene, Fig. 1, structure (lB)] was prepared by the procedure of Dhawan and Gutsche.8 A 1.17 g (0.006 mol) amount of tert-butyl bromoacetate, 0.65 g (0.0047 mol) of anhydrous potassium carbonate and 10 ml of AnalaR acetone were added to 0.5 g (0.0007 mol) of the parent dioxacalixarene [Fig.1, structure (lA)] and the mixture was refluxed under nitrogen with stirring for 120 h. After this time, all the volatiles were removed to give a sticky solid. This was taken up in 20 ml of dichloromethane and the extract washed twice with water. After drying with magnesium sulphate and removal of the solvent, 0.66 g (80%) of the product 1B was obtained as a pale yellow solid. Recrystallisation from tert-butanol gave 0.5 g of the colourless crystalline product 1B (m.p. 186.8- 187.8 “C). ISE Construction and Performance Materials The membrane components, PVC, 2-nitrophenyl octyl ether (2-NPOE) and AnalaR grade tetrahydrofuran (THF) were obtained from Fluka. AnalaR grade chlorides of sodium, potassium, lithium, caesium, magnesium and calcium were supplied by Riedel-de-Haen and dissolved in distilled, de- ionized water.Electrode fabrication and measurements The general procedure for the preparation of the polymeric membrane was as follows. The ligand (2.5 mg), plasticizer [2-NPOE (250 mg)] and PVC (125 mg) were mixed and * To whom correspondence should be addressed. dissolved in THF. The resulting solution was poured into a glass mould and left to set as described previously.9 Clear, flexible PVC membranes containing the ligand dissolved in the plasticizer were obtained on evaporation of the THF. Discs of suitable dimensions (diameter, 10 mm; thickness, about 0.1 mm) were cut from this master membrane and clipped into the tip of a blank Russell oxygen electrode body (reference number 98-7809). The internal reference electrolyte was 1 X 10-1 rnol dm-3 KCI.Fabricated electrodes were conditioned for at least 2 h prior to use. Potentiometric measurements were made relative to a saturated calomel electrode using a Philips PM9421 digital pWmillivoltmeter. The selectivity coefficients (kflq‘) were determined by the separate solution method using 1 x 10-1 mol dm-3 solutions of the salts of the cations involved (all chlorides). But But But But (lB) Fig. 1 the tetrabutyl ester [structure (lB)] Structure of tetrahomodioxacalix[4]arene [structure (lA)] and Results and Discussion Sensitivity and Limit of Detection Electrodes based on ligand (1) displayed near-Nernstian responses to potassium ions (Fig. 2) with detection limits in the range 1 x 10-3-1 x 10-4 rnol dm-3 KCl. In these preliminary investigations, however, a saturated calomel reference elec- trode was used, and it is very likely that leakage of KCI from the reference electrode salt-bridge affected the ISE signal in the less concentrated potassium standards (i.e., below 1 x 10-3 mol dm-3).Replacement of the KCI bridge with a different electrolyte should therefore extend the limit of detection reported above. Selectivity The selectivity data obtained with this ISE are summarised in Table 1. Reasonably good selectivity over sodium is evident, although not in the range of similar PVC electrodes incorporat-14 > y: E 80 c L' 60 40 20 ANALYTICAL PROCEEDINGS. JANUARY 1991, VOL 28 ' 140 120 100 I I 01 I I I I I -6 -5 -4 -3 - 2 - 1 Log aK Fig. 2 Calibration graph (e.m.f. versus log aK) for the ionophore incorporated in a plasticized PVC membrane.Average slope over the range 1 x 10-'-1 x mol dm-3 KCl is 53.7 mV per decade change in potassium activity ing the natural antibiotic valinomycin. However, these results demonstrate that the dioxa derivatives of the tetrameric calixarenes are potassium-selective, and can be used to produce functioning potassium-selective electrodes. Given the numerous options for structural modification of both calix- arenes and oxacalixarenes, and the attendant variable selectiv- ity, there is a clear possibility of producing a wide range of new Table 1 Selectivity coefficients (log k c ' ) for electrodes based on ligand 1. Values obtained by the separate solution method in 1 x 10-1 mol dm-3 solutions of each metal ion (all chlorides) Log k,qi"', i = K+ Na+ Li+ Cs+ Rb+ Ca2+ Mg2+ NH4+ -1.4 -2.4 -0.6 -0.1 -2.0 -2.1 -1.0 and more efficient ionophores for ISEs targeted at various cations.References Diamond, D., Anal. Chem. Symp. Ser.. 1986, 25, 155. Diamond, D.. Svehla. G.. Seward. E., and McKervey, M. A., Anal. Chim. Acta, 1988, 204, 223. Cadogan, A., Diamond, D.. Smyth. M. R.. Deasy. M., McKervey. M. A., and Harris, S. J., Analyst, 1989. 114. 1551. Kimura. K., Miura, T.. Matsuo. M.. and Shono, T., Anal. Chem., 1990, 62, 1510. Telting Diaz, M., Diamond, D.. Smyth. M. R.. Seward, E., McKervey. M. A., and Svehla, G., Anal. Proc., 1989.26,29. Telting Diaz, M.. Regan, F.. Diamond. D.. and Smyth, M. R., J . Pharm. Biomed. Anal., 1990, 115, 1207. Cadogan, A.. Diamond, D.. Smyth, M. R., Svehla.G., McKervey, M. A., Seward, E., and Harris. S. J., Analyst, 1990, 115, 1207. Dhawan, B.. and Gutsche. C. D., 1. Org. Chem., 1983,48.1536. Moody, G. J., and Thomas, J. D. R., in Chemical Sensors. ed. Edmonds. T. E.. Blackie. Chapman and Hall. New York, 1988. ch. 3, p. 76. Spectrophotometric End-point for the Phase-titration Determination of the Adulteration of Petrol With Kerosine M. Shahru Bahari, W. J. Criddle" and J. D. R. Thomas School of Chemistry and Applied Chemistry, University of Wales College of Cardiff, P.O. Box 912, Cardiff CFI 3TB The increasing number of instances of petrol adulteration with kerosine in countries where controls are difficult to exercise has led to various studies of procedures for detecting the adultera- tion. As adulteration occurs mostly during product delivery between refineries and petrol stations, researchers have endeavoured to find procedures for detecting the adulteration at this stage, in order to prevent the adulterated product reaching the public.. A mobile laboratory with a gas chromatograph set up in a van by deAndre Bruening and Branco in Brazil has been reported1 but no other work has been cited for an 'in-the-field' method of analysis. Although gas chromatography is arguably the best procedure for quantitatively detecting kerosine or other contaminants in petrol, the purchase cost could be a considerable problem in developing countries in the campaign against adulteration syndicates. Hence, an ideal instrument for detection should be simple to operate and affordable by petrol station owners, thus preventing the adulterated product from reaching customers.A phase-titration method, first investigated by Suri and co-workers,2 has recently been modified,3 the modified pro- cedure showing considerable improvements in linearity over the adulteration range of &20% v/v kerosine. The approach was based on the differences between the solubilities of petrol and kerosine in a water-based mixed solvent system arising from the variations in the hydrocarbon content. The introduc- tion of a surfactant, namely sodium dodecyl sulphate (SDS), * To whom correspondence should be addressed. Fig. 1 Schematic diagram of the flow-through phase-titration system: A. titrant; B, titration vessel; C. magnetic stirrer; D, peristaltic pump; E, spectrophotometer cell; F.spectrophotometer detector; and G. UV light source into the titrating solution has served to increase the titration volume difference for small percentages of adulteration, thus giving greater sensitivity and accuracy. However, the visual method of identifying the end-point of a phase titration has always been subject to uncertainties and hence criticism, and in order to reduce errors in the visual end-point it is necessary for the end-point to be determined instrumentally.ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 15 A spectrophotometric approach permits effective end-point detection in turbidimetric titrations4 and the same approach can also be applied to the clarification titrations depending on 1 .o 1 0.5 a C m 8 16 24 32 40 removal of turbidity.Hence, a spectrophotometer has been used in this study as a detector for a modified phase-titration procedure designed to reduce errors which can occur during the visual detection of the end-points. Experimental Reagents and sample preparations for the turbidimetric phase-titration procedure have been described previously.3 20.0 15.0 m E Y 10.0 n v) v) Lc 0 4 8 12 16 20 Volume of titranb'crns Fig. 2 Typical absorbance results for (a) the turbidimetric [propan-l- 01 (30.0 cm3), petrol (Premium grade, 20.0 cm3); titrant: 0.27 mol dm-3 SDS], and (b) the clarification [ethanol (20.0 cm3), petrol (Premium grade, 10.0 cm3) and water (5.0 cm3); titrant: ethanol] end-point titration v) 0 4 8 12 16 20 rc a - 5 0 > 20.0 15.0 10.0 0 4 8 12 16 20 Kerosine in petrol (% v/v) Fig.3 Titration results on mixtures of propan-1-01 (30.0 cm3) and petrol samples (20.0 cm3) at different concentrations of SDS. (a) Visual method; and ( b ) spectrophotometric method (h = 600 nm). [SDS]: 0, 0.13; W, 0.16; A, 0.19; 0, 0.23; 0, 0.27; and A , 0.30 mol dm-3 0 4 8 12 16 20 10.0 t 7 0 4 8 12 16 20 Kerosine in petrol (% v/v) Fig. 4 Effect of batch variations on titration results of mixtures of propan-1-01 (30.0 cm3) and petrol samples (20.0 cm3) at 24.0 k 0.5 "C. (a) Visual method; and ( b ) spectrophotometric method (A = 600 nm). 0, Batch 1; 0, batch 2; and A , batch 3 15.0 m 1: C E 2 10.0 c v- E $ 20.0 > 15.0 10.0 0 4 8 12 16 20 0 4 8 12 16 20 Kerosine in petrol (% v/v) Fig. 5 (a) Visual and ( b ) spectrophotometric clarification titration results on mixtures of petrol (Premium grade, 10.0 cm3), ethanol (20.0 cm3) and water (5.0 cm3) at 24.0 k 0.5 "C16 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 For the clarification titrations, mixtures of absolute ethanol (BDH, 20.0 cm3) petrol (Premium grade, 10.0 cm3) containing kerosine (0-20% v/v) and water (5.0 cm3) were titrated with the same absolute ethanol.Both these phase-titration pro- cedures were based on a flow-through system operated at 24.0 k 0.5"C. The flow-through system, shown schematically in Fig. 1, consisted of a peristaltic pump (Cole Palmer) circulating the titration mixture continuously from the titration vessel to the spectrophotometer (Shimadzu UV-120-02), fitted with a flow- through cell, and back to the titration vessel.The wavelength of the spectrophotometer was set at 600 nm. Table 1 Statistical data for the titration results. Titration results at 24.0 -t- 0.5 "C for typical petrol samples with added kerosine Volume of titrant/cm' Kerosine in petrol (% v/v) Visual Spectrophotometric 0 2 4 6 8 10 12 14 16 18 20 19.74 f 0.10 18.46 f 0.05 17.44 f 0.03 16.44 k 0.19 15.28 f 0.05 14.19 k 0.06 13.23 f 0.14 12.18 k 0.13 1 1.39 f 0.06 10.60 k 0.08 9.95 k 0.10 20.70 f 0.08 19.60 -I- 0.22 18.60 f 0.08 17.50 k 0.18 16.50 f 0.08 15.50 k 0.34 14.56 k 0.10 13.50 f 0.14 12.40 f 0.14 11.50+0.18 10.80 k 0.08 Regression analysis: Regressionequation y = 19.41 - 0 . 5 0 ~ y = 20.58 - 0 . 5 0 ~ coefficient ( r ) 0.997 0.999 Aliquots of the titrating solution were introduced into the titration mixture through a burette and vigorously stirred with a magnetic stirrer.The flow of the mixture was controlled at a maximum of 2.0 cm3 s-1 in order to prevent the formation of bubbles which could interfere with the absorbance reading. The turbidimetric end-point was chosen as the point causing an increase in the absorbance of the mixture from a constant value, while the clarification end-point was that corresponding to a levelling off of absorbance to constant values (Fig. 2). Results and Discussion Repetition of turbidimetric end-point titrations at various SDS concentrations gave similar titration behaviour (Fig. 3) to the results obtained from the visual detection of the end-points. However, the procedure gives significantly better linearity over a wider range of 0-20% v/v kerosine in petrol compared with only a O-l6% v/v range in the visual end-point study.3 Such improvements in the linearity range are clearly seen in Fig.4. The plot shown in Fig. 4(b) essentially eliminates the deviation from linearity for the 0.27 mol dm-3 added SDS system that is clearly apparent in Fig. 4(a). Another noticeable advantage of the modified procedure is the reduction of the titration volume difference in batch variations. The 2% v/v adulteration error arising from this batch variation of the visual method has been reduced to 1% v/v adulteration with the introduction of the spectrophoto- metric approach. Table 2 Statistical data for the titration results. Data for the titration results of Fig. 5 Volume of titrant/cm3 Kerosine in petrol (Yo v/v) Visual Spectrophotometric 0 10.50 k 0.57 10.78 f 0.38 2 11.10 t- 0.62 11.91 f 0.86 4 12.31 k 0.19 11.99 k 0.35 6 12.63 k 0.15 14.09 f 0.37 8 13.72 k 0.56 15.15 f 0.40 10 15.14 k 0.71 16.29 k 0.57 12 15.47 k 0.74 17.18 k 0.36 14 16.49 k 1.65 18.11 k 0.48 16 17.04 k 0.90 19.67 k 0.47 18 (Not recorded) 20.02 f 0.25 20 18.23 k 0.72 21.65 k 0.68 Regression analysis: Regression equation Correlation coefficient ( r ) 0.994 0.999 y = 10.53 + 0.41 x y = 10.78 + 0 .5 4 ~ A linear correlation is also observed for the clarification end-point titration (Fig. 5 ) . However, the relatively large standard deviation limits the sensitivity of this approach, and although the procedure can still be an effective monitor for field-type analysis, we would not recommend this procedure in preference to the turbidimetric end-point.A statistical analysis of the data quoted in this paper is shown in Tables 1 and 2. Conclusion The modified phase-titration method for determining the adulteration of petrol with kerosine has been made more sensitive, repeatable and precise by using a spectrophotometric end-point detector and the flow-through system described is a stage in the development of a miniaturized portable instrument designed to combat adulteration syndicates. The authors thank the Public Services Department of Malaysia, Kuala Lumpur, and the University of Technology of Malaysia for financial support to M.S.B. References 1 2 3 4 deAndre Bruening, I . M. R.. and Branco, V. A. C., Bof. Tech. Petrobras, 1980, 23, 117. Suri, S. K ., Ahluwalia. J . C., and Rogers, D. W., Tafanra, 1981, 28, 281. Bahari, M. S . , Criddle. W. J . , and Thomas, J. D. R.. Analyst, 1990, 115,417. Rogers, D. W . , and Ozsogomonyan, A., Talanta, 1964,ll. 652. Determination of Trace Amounts of Bacitracin by Differential-pulse Adsorptive Stripping Voltammetry at a Hanging Mercury Drop Electrode Josino C. Moreira, Royston D. Miller and Arnold G. Fogg Department of Chemistry, Lo ug h boro ug h University of Tech nolog y, Lo ug h boro ug h, L eicesters h ire LEI1 3TU Bacitracin consists of a group of polypeptide antibiotics Bacitracin has been added to animal feed for growth promo- containing several amino acid residues such as L-cysteine, tion, feed efficiency and disease control as bacitracin base or as D-ornithine , L-lysine, L-histidine, D-aspartic acid, D-glutamic a zinc or methylene disalicylate salt .* acid, L-isoleucine, L-leucine and D-phenylalanine.Bacitracin Bacitracin is usually assayed by microbiological methods A is the most potent and main bacitracin component. such as the plate agar diffusion technique or a turbidimetricANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 17 method.* The presence of bivalent metal ions such as zinc, cobalt, manganese, calcium or copper in the solution can interfere with the biological activity of bacitracin. Copper causes a negative bias in the microbiological assay and must be removed before the assay.3 Alternative methods are important in instances where the microbiological assay results are uncertain or when the interest is in biological transformation or degradation products.These methods include thin-layer chro- matography with ultraviolet detection, electrophoresis, high- performance liquid chromatography and pulse polarography . Bacitracin A exhibits a double wave at the dropping mercury electrode over the pH range 1-8. Its polarographic activity is probably due to reduction of the >C=N- group in the thiazoline ring.4 By using differential-pulse polarography, a concentration of 5 pg ml-1 (approximately 4 x 10-6 mol dm-3) can be detected. In this paper a voltammetric method capable of determining bacitracin A at levels as low as 30 ng ml-1 is described. Experimental Differential-pulse adsorptive stripping voltammetry was car- ried out by using a Metrohm 626 Polarecord with a 663 VA stand in conjunction with a multi-mode electrode in the hanging mercury drop electrode (HMDE) mode.The three- electrode system was completed by means of a glassy carbon auxiliary electrode and a silver-silver chloride reference electrode. -40 - 35 - 30 -25 5 -20 L 3 0 -15 -10 - 5 A D 1 0 I I I 1 I -0.10 -0.30 -0.50 -0.70 -0.90 -1.10 -1.30 PotentialN Fig. 1 Differential-pulse adsorptive stripping voltammograms of a 1 .O x lo-' M solution of bacitracin in acetate buffer, pH 4.5, at different accumulation times: A, no accumulation; B , 1 min; C, 2 min; and D, 3 min. Accumulation at -0.1 V All potentials given are relative to this silver-silver chloride electrode. A pulse amplitude of 50 mV was used with a scan rate of 10 mV s-' and a pulse interval of 1 s.pH measurements were made with a Corning combined pH-reference electrode using a Radiometer PHM 64 pH meter. Bacitracin was obtained from the Sigma Chemical Company and was used without further purification. A 0.001 mol dm-3 solution of bacitracin was prepared by dissolving 0.014 g of bacitracin in water containing a few drops of an acetate buffer solution (pH 5.0) in a 10 ml calibrated flask. This solution had to be freshly prepared. Bacitracin F solution was prepared by leaving the bacitracin A standard solution at 37°C and pH 7.5 for 2 weeks. 30 20 P ? 2 3 Y m a 10 0 0 2 4 6 8 10 Accumulation time/mi n Fig. 2 Influence of the accumulation time on the peak current of a 1 .0 x 10-7 M solution of bacitracin in acetate buffer, pH 4.5. Accumulation at -0.1 V Procedure The general procedure used to obtain differential-pulse adsorptive stripping voltammograms was as follows.A 20 ml aliquot of 0.1 mol dm-3 acetate buffer solution was placed in a voltammetric cell and the required amounts of standard bacitracin solution were added. The stirrer was switched on and the solution was purged with nitrogen gas for 6 min. Subsequently, a 15 s deoxygenation was made between adsorptive stripping cycles. After forming a new HMDE a 3 min accumulation was effected at -0.1 V whilst stirring the solution. At the end of the accumulation period the stirrer was switched off, and, after 20 s had elapsed to allow the solution to become quiescent, a negative potential scan was initiated between the accumulation potential and -1.2 V. Results and Discussion The differential-pulse adsorptive stripping voltammograms of bacitracin A at four different accumulation times are shown in Fig.1. The peaks at -1.05 and -1.15 V are due to bacitracin A. Bacitracin F, an inactive form of bacitracin formed from bacitracin A, gave a peak at -0.67 V and can be differentiated from the active form. A shift of 59.5 mV pH-l to more negative potentials was observed for the bacitracin A peak potentials with increasing pH from 1 to 7, showing consumption of hydrogen ions in the electrode reaction. The peak shape and the peak separation were not affected greatly by varying the pH from 1 to 7. The influence of the pH on the peak current is shown in Table 1. Acetate buffer, pH 4.5, was selected as the optimum because of the higher response obtained and the stability of bacitracin in this medium.1 The effect of accumulation time on the peak height for bacitracin in 0.1 mol dm-3 acetate buffer, pH 4.5, is shown in Fig. 2. The peak current increased rectilinearly with accumula-18 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 Table 1 Influence of pH on the height of the peak for bacitracin at -1.05 V. Bacitracin concentration = 1.0 x mol dm-'. Accumula- tion step: 2 min at -0.1 V PH i,lnA 1.0 4.5 3.0 3.5 4.5 5.9 7.0 5.2 tion time up to 5 min. After this time a deviation of the linearity was observed suggesting saturation of the electrode surface. A small peak was observed even with a 'no accumulation' scan showing that accumulation of the antibiotic occurs at the electrode surface during the scan. An accumulation time of 3 min was used generally in this work.The effect of the accumulation potential on the peak height of bacitracin is shown in Table 2. The highest peak was obtained by accumulating at -0.1 V and this accumulation potential was selected as ideal. The calibration graph obtained under the optimized condi- tions was linear. A rectilinear relationship between the peak current and the bacitracin concentration was observed from 2.5 x 10-8 to 3.5 x 10-7 mol dm-3. The slope obtained was 10.7 x lo7 nA mol-1 and the correlation coefficient was 0.996. At concentrations higher than 3.5 x 10-7 mol dm-3 the deviation of the linearity observed in the calibration graph suggests saturation of the electrode surface. No interference of surfactants at the sub-microgram per litre level was observed on the peak height of bacitracin.The peak, however, was suppressed by the presence of5 x 10-8 mol dm-3 albumin in the solution. Small decreases in the peak height of bacitracin were observed in the presence of zinc, copper(II), manganese, nickel and chromium(II1) ions. This is probably Table 2 Influence of the accumulation potential on the peak height for 1.0 x mol dm-3 of bacitracin in acetate buffer, pH = 4.5. Accumulation time: 3 min idnA at E x , JV -1.05 V -0.1 9.5 -0.3 7.0 -0.5 6.5 -0.7 6.0 associated with complex formation between the antibiotic and the metal ions."6 This kind of interference can be avoided by the addition of EDTA. References 1 Froyshov, 0.. Drugs Pharm. Sci., 1984,22, 694. 2 Ragheb, H. S., J .Assoc. Off. Anal. Chem., 1981, 64, 980. 3 Grynne, B . , Hoff, E., Silsand, T.. and Vaaje, K., Analyst. 1973, 98, 906. 4 Jacobsen, E., and Pederstad, J. H.. Anal. Chim. Acta, 1977,91, 121. 5 Garbutt, J. T., Morehouse, A. L., and Hanson, A. M., Agric. Food Chem., 1961, 9, 284. 6 Cornell, N. W., and Guiney, D. G., Jr., Biochem. Biophys. Res. Commun., 1970, 40, 530. Determination of Selenium in Copper Metal Using Flow Injection Hydride Generation Atomic Absorption Spectrometry With Continuous Flow Matrix Isolation Stephen G. Offley and Nichola J. Seare Department of Chemistry, University of Technology, Loughborough, Leicestershire L E 1 I 3TU Julian F. Tyson Department of Chemistry, University of Massachusetts, Amherst, MA 0 1003, USA Helen A. B. Kibble Development Department, Philips Scientific, Analytical Division, Cambridge CB 1 2PX Hydride generation atomic absorption spectrometry (HGAAS), although a highly sensitive technique for the determination of hydride-forming elements, has the disadvan- tage of being susceptible to interference from a large number of transition metals.' One of the most severe interferences is that of copper on the determination of selenium.l-4 Many attempts A R H ~ r 5 ,Abw Ar Fig.1 Schematic diagram of the FI manifold with continuous flow matrix isolation unit: P, peristaltic pump; S, sample; H, water; A, HCI; R, sodium tetrahydroborate(II1); W, waste; V1, switching valve; V2, sample injection valve; C , micro-column; and G, gas-liquid separator have been made to reduce this interference but with varying degrees of success.3-7 Recent developments involve the introduction of both continuous flow8 and flow injection (FI)9.10 methodology.Flow injection hydride generation was first reported by Astromg for the determination of bismuth. A significant reduction in interference effects was reported. Although on-line matrix isolation has been applied to flame AAS (FAAS) using FI, to date only one or two attempts have been made to apply such methodology to interference removal in HGAAS.11-12 This paper reports the determination of selenium by FI-HGAAS. Elimination of the interference from copper is achieved in a continuous flow matrix isolation manifold containing a micro-column of cation-exchange resin. This is coupled to the FI manifold via the injection valve.Experimental Reagents Analytical-reagent grade water, produced by a LiquiPurc RG System (reverse osmosis followed by ion exchange), was used for all solutions and as a carrier stream. A sodium tetrahydro-ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 19 borate(m) solution (1% m/v in a 0.1% m/v NaOH solution) was prepared using sodium tetrahydroborate(rI1) pellets (Spec- trosol, BDH) and filtered through a Whatman 541 filter- paper. With refrigeration this solution was usable for up to 3 days. The hydrochloric acid (6 mol dm-3) reagent solution was of SpectrosoL grade (BDH). All selenium(1v) standard solutions were prepared by dilution of a standard solution of selenous acid (SpectrosoL, BDH) containing loo0 pg ml-1 of Se'V. For the interference investigation work copper(11) sulphate pentahydrate (AnalaR, BDH) was used to prepare interferent standards.Conditioning of the T-shaped silica atomization cell was carried out using a 5% v/v solution of hydrofluoric acid (AnalaR, BDH). High-purity argon was used as the purge gas (99.998% Ar, BOC). The digestion of certified copper metal standard reference materials was carried out using nitric acid (Aristar, BDH) and hydrochloric acid (Aristar, BDH). The cation-exchange resin used was Dowex 50W-X8 (Drymesh 100-200, hydrogen form, 8% cross linkage, Sigma). Two certified copper metal standard reference materials, National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 454 and Bundes- anstalt fur Materialforschung und -priifung (BAM) SRM 361 , were obtained from the Bureau of Analysed Samples (Middles- brough, Cleveland).Table 1 Optimized variables for HGAAS with continuous flow matrix isolation HGAAS- Reagent Concentration Flow-rate/ml min-1 H20 carrier - 6.0 HCI 6 mol dm-3 4.2 NaBH4 1 .O% m/v 3.2 Argon - 600 (Injection volume, 409 PI) Reagent Concentration Flow-rate/ml min-1 Continuous flow matrix isolation- Sample 61000pgml-1Cu 2.0 HCI (column regenerant) 1.2 rnol dm-3 2.0 Apparatus A Philips Scientific SP9 atomic absorption spectrometer equipped with a Philips data coded selenium hollow-cathode lamp, operated at 7.5 mA, was used for all determinations. A spectral bandpass of 1.0 nm was used with the 196.0 nm selenium spectral line. The signals were recorded on a Tekman TE 200 chart recorder (2-10 mV range), all measurements being expressed as peak-height absorbance.A 50 mm Philips Scientific universal burner was used to support the air-acety- lene flame heated T-shaped silica cell (air flow setting 28, acetylene flow setting 15). The FI hydride generation manifold shown in Fig. 1 was developed around the gas-liquid separator and hydride atomization systems of a Philips Scientific PU9360 continuous flow vapour system. Two peristaltic pumps were employed: a Gilson Minipuls 3 peristaltic pump used for the hydride generation manifold and a Gilson Minipuls 2 peristaltic pump for the matrix isolation unit. Control of flow-rates was achieved by application of different bore standard manifold tubing (Altec). All manifold tubing consisted of 0.8 mm i.d. PTFE tubing (Anachem).Manifold channels were connected by three-way connector T-pieces (Anachem) which aided reagent mixing. A microbore glass column (50 X 3.0 mm i.d., Anachem) fitted with porous 25 pm PTFE frits was incorpor- ated in the external sample loop of a rotary sample injection valve (Anachem). Sample injection was achieved using a Rheodyne Model 5020 fixed volume loop injector valve operated by an electrically activated universal valve switching unit (Anachem). Sample loops of various volumes were prepared by using PTFE tubing (0.5-1.5 mm i.d.) cut to appropriate lengths. Preliminary Experiments The manifold design allows the two manifolds to be optimized independently. The parameters optimized are shown in Table 1. The efficiency of the micro-column to retain copper was assessed by pumping a lo00 pg ml-1 copper standard solution through the column and continuously monitoring the copper concentration of the column eluent by FAAS.Breakthrough of the column was adjudged to have occurred when the copper concentration of the column eluent exceeded 1.0 yg ml-1. Sample Preparation Weigh accurately approximately 0.5 g of copper metal sample into a 100 ml Pyrex beaker. Add 10 ml of 8 rnol dm-3 nitric acid and cover with a watch-glass. Heat to near dryness on a hotplate and after cooling add 10 ml of 6 rnol dm-3 hydrochloric acid. Cover again with a watch-glass and heat on a steam-bath for approximately 15 min to dissolve the sample residue then allow to cool. Transfer the cool digest solution into a calibrated flask (100 ml) and dilute to volume with analytical-reagent grade water.Prior to analysis dilute the digest solutions further to produce working samples containing <lo00 yg ml-1 of Cu. The NIST SRM 454 and BAM SRM 361 working sample solutions contained 75 and lo00 pg ml-1 of Cu, respectively. Column Packing and Conditioning Pack the micro-column with an aqueous slurry of Dowex 5OW-X8-200 resin under suction (250 mg of dry resin). Prior to use, pump a solution of hydrochloric acid (1.2 rnol dm-3) through the column for approximately 5 min (2 ml min-1) to condition the cation-exchange resin and achieve optimum efficiency for copper retention. l 2 1 I I I 0 1 .o 2.0 3.0 Flow-rate/m I m in - Fig. 2 the micro-column Retention of copper as a function of sample flow-rate through Conditioning of Silica Atomization T-cell To achieve optimum system sensitivity and precision new T-cells should be pre-treated as follows.Soak the T-cell in a solution of 5.0% v/v hydrofluoric acid for a period of 4 h in order to etch the surface of the silica cell and therefore aid hydride atomization.*3 At the start of each analysis inject a standard solution of 1000 ng ml-1 of Se*V two or three times prior to the analysis of standards and samples, respectively. Operation of FI Manifolds Operate the hydride generation and matrix isolation manifolds (Fig. 1) according to the optimized variables shown in Table 1. To obtain an SelV calibration, pump standard solutions requiring no matrix isolation through the injection valve, by-passing the micro-column. Activate the injection valve intermittently (load time 20 s, injection 10 s).Following the introduction of standards switch the micro- column into the sample line and pump analytical-reagent grade20 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 water continuously through it to remove the hydrochloric acid. After washing, pump sample through the column in the same way. Pump continuously for 60 s to fill the void volume of the column and pump tubing and sample the column eluent as described earlier. After carrying out triplicate injections switch the micro-column back into the HCI regenerant line to regenerate the column and, by pumping analytical-reagent grade water, wash out the sample line. Following a short period of regeneration (30 s) switch the column back in-line and repeat the procedure for subsequent samples.In order to prevent any introduction of air on to the column, during transfer of the sample uptake tube from sample to analytical- reagent grade water the sample pump should be stopped. 0 1 .o 2.0 3.0 4.0 5.0 Fig. 3 Retention of copper on the micro-column as a function of sample solution pH Sample solution pH Results and Discussion Investigation into parameters affecting the performance of the hydride generation manifold resulted in the optimum variables shown in Table 1. The relationship between copper retention and sample flow-rate (lo00 pg ml-1 of Cu, pH 4.0) is shown in Fig. 2. The efficiency of the resin improved with reduced sample flow-rate because of the increased contact time between copper ions and the active sites of the resin. With the matrix isolation unit being independent of the hydride generation manifold, the sample flow-rate through the column could be kept low to keep column efficiency high without having to compromise the sensitivity of the hydride generation manifold as reported for the system of Riby et al.12 By pumping sample at low flow-rates, problems with resin compaction in the column and build up of high back-pressures were eliminated. Column compaction was further prevented by introducing the HC1 regenerant solution in the opposite direction to the sample flow. A sample flow-rate through the column of 2.0 ml min-1 was chosen after consideration of both column efficiency and sampling rate. At a flow-rate of 2.0 ml min-1 the 409 PI sample loop of the injection valve could be filled in 20 s.As shown in Fig. 3 the efficiency of the resin at 2.0 ml min-1 reached a maximum at about pH 2.0. Even at a pH of 1.0 (typical of a working sample solution containing 1000 pg ml-1 of Cu with no pH adjustment), the column capacity exceeded 5.0 mg of Cu permitting triplicate analyses of each sample before column regeneration was needed. Table 2 Analysis of copper metal standard reference materials SetV certified/ SeIV found*/ Yg g-' Yg g- NIST SRM 454 479 k 8 476.0 k 7.2 BAM SRM 361 36 k 0.6 37.1 k 0.7 * t95% Confidence interval. As shown in Table 2, the results for the analyses of the two standard reference materials, NIST SRM 454 and BAM SRM 361, agree with the certified values. Performance characteris- tics of the system for the determination of copper metal are summarized in Table 3. These figures give evidence for the benefits of the proposed manifold design in comparison with previous systems. 11712 The performance characteristics of the resin were retained after continued use for 3 months without any need for column repacking. Table 3 Performance characteristics of the system for copper metal determination Characterization concentration 1 .O ng ml- 1 SeIV Limit of detection* 2.1 ng ml-1 SeIV Relative standard deviation 1.5% (10ngml-l SeIV, n = 12) Sample throughput 17 h- * (triplicate analyses) * Reference 14. As the manifold components are similar to those of a totally automated system reported previously,ls automation of this system is possible. The same system could be used, with minor modifications, for the determination of other hydride-forming elements in the presence of a variety of interfering species such as Ni, Fe, Co and Ag. Financial support for S. G. 0. by the SERC and both provision of equipment and financial support from Philips Scientific (Cambridge) is gratefully acknowledged. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 References Smith, A. E., Analyst. 1975, 100, 300. Meyer, A., Hofer. C., Tolg, G., Raptis, S . . and Knapp. G., Fresenius Z. Anal. Chem., 1979, 296. 337. Welz. B., and Melcher, M., Analyst, 1984, 109, 569. Welz, B., and Schubert-Jacobs, M.. J . Anal. At. Spectrom., 1986, 1, 23. Peacock. C. J., and Singh. S. C., Analyst, 1981, 106. 931. Bedard, M., and Kerbyson, J. D., Can. J . Spectrosc.. 1976,21, 64. Hershey, J . W., and Keliher, P. N., Spectrochim. Acta, Part B, 1989. 44. 145. Narasaki, H . . and Ikeda, M.. Anal. Chem., 1984, 56, 2059. Astrom. 0.. Anal. Chem., 1982, 54, 190. Fang, Z . , Xu, S., Wang. X., and Zhang, S.. Anal. Chim. Acta, 1986,179,325. Ikeda. M.. Anal. Chim. Acra, 1985, 170. 217. Riby, P. G.. Haswell. S. J., and Grzeskowiak, R., J. Anal. At. Spectrom., 1989, 4, 181. Welz, B., and Melcher, M.. Analyst. 1983, 108. 213. Miller, J. C., and Miller. J. N., Statistics for Analytical Chemistry, Ellis Horwood, Chichester, 1984, p. 96. Bysouth, S. R., Tyson, J . F . , and Stockwell. P. B., J . Autom. Chem., 1989, 11. 36.

ISSN:0144-557X    

DOI:10.1039/AP9912800008

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 21 Equipment News Connections for Mass Spectrometry Workstation The MACH 3 data processing work- station for mass spectrometry can be connected to computer systems from Kratos, VG, Finnigan and JEOL. The user can compare data from different systems or simply upgrade the perfor- mance of an existing mass spectrometry computer system. By bringing data from several systems on to a MACH 3, they can be viewed simultaneously in any one of the many MACH 3 processing windows, and if required data can be transferred via the in-built Ethernet facilities to a LIMS or corporate computing facility. Special software is available to convert data from other systems into formats optimised for MACH 3 processing. 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Particle Beam Interface for Mass Spectrometry A new particle beam interface for the makers’ Profile and Concept high perfor- mance mass spectrometers has a wide range of applications, including hydrocar- bon analysis, fossil fuel analysis, environ- mental studies and analysis of labile materials such as herbicides and pesti- cides.The interface can be used in appli- cations for which separation by liquid chromatography is the preferred tech- nique. It consists of a nebuliser, desolva- tion chamber and separator assembly and it is supplied complete with the required pumping system, temperature controller and heater supplies. Kratos Analytical Ltd., Barton Dock Road, Urmston, Manchester M31 2LD. Dissolution Testing Software for Diode-array Spectrophotometer New high-volume dissolution testing soft- ware for the HP 8452A diode-array spectrophotometer provides multiple- bath capabilities, controlling sampling and evaluation from up to four dissolution baths.Offering the same measurement, evaluation and reporting features as the makers’ existing single-bath software, this is believed to be the only four-bath solution for automated dissolution test- ing. Hewlett-Packard SA, 150 route du Nant-d’Avril, CH-1217 Meyrin 2, Switzerland. wetry PRISM spectrometer Spectrophotometer The Shimadzu UV3101 is a double beam scanning ultraviolet-visible-NIR spectro- photometer combining the proved optical bench of the UV3100 with an industry standard personal computer, running cus- tomised Shimadzu software in a Microsoft Windows environment.Users can select from several software options, including spectrum scanning, time course measure- ments and quantification measurements. V. A. Howe and Co. Ltd., Beaumont Close, Banbury, Oxfordshire OX16 7RG. Spectrophotometer The HP 8452A option 003, another mem- ber of the HP 8452A diode array spectro- photometer family, operates in the visible to short-wave near-infrared range (470- 1100 nm), allowing measurement of many compounds that do not absorb in the normal ultraviolet-visible range. The rugged, non-moving optical system is well suited for process control applications. Hewlett-Packard SA, 150 route du Nant-d’Avril, CH-1217 Meyrin 2, Geneva, Switzerland. Spectrometer The 16 PC FT-IR spectrometer combines spectrometer, data system and expand- able software.It is controlled by a per- sonal computer and uses the Infrared Data Manager software package for fast, efficient collection, processing and stor- age of infrared data. IRDM software supports PC-SEARCH, PC-QUANT and OBEY macro language advanced software packages to extend the range of analytical applications further. Perkin-Elmer Ltd., Maxwell Road, Beaconsfield, Buckinghamshire HP9 1QA. Enzyme Kinetics Software for Spectrophotometry A software module for the HP 8452A diode-array ultraviolet-visible spectro- photometer provides capability for multi- cell enzyme assays and multi-cell enzyme kinetics. With this software the diode- array instrument performs these measure- ments with far greater speed and precision than are possible with conventional spectrophotometers.Various calculation parameters are included, and data can be evaluated by this software and transferred to spreadsheets. Methods and parameters can be stored and recalled from memory. Hewlett-Packard SA, 150 route du Nant-d’Avril, CH-1217 Meyrin 2, Switzerland. Meat Analyser The Infratec 1255 food and feed analyser is a near infrared transmittance analyser to analyse raw meat and processed meat products. It determines fat, moisture and protein simultaneously within 45-60 s with very high accuracy. A traditional meat grinder is used for sample prepara- tion. The instrument is dust, water and vibration proof, and its rugged design makes it suited to be operated on-line, in plant. Tecator AB, Box 70, S-263 21 Hoganas, Sweden.22 Temperature Controlled Spray Chamber for ICP Spectroscopy A complete, easy to fit system for temper- ature controlled operation of the spray chamber in ICP spectroscopy consists of a double walled spray chamber and a cool- ing liquid circulating bath.Not only does Charge Coupled Device Detectors for Spectroscopy and Imaging Three basic types of high performance, low noise charge coupled device (CCD) detectors are announced: thermoelectric- ally cooled (TE), liquid nitrogen cooled (LN) and microchannel-plate (MCP) ARL spray chamber for ICP spectroscopy the cooling liquid flow between the two walls but it also passes through the im- portant impact bead, on which most of the gases and droplets impinge. The effect is to lower the vapour pressure and hence to produce a more stable plasma. ARL Applied Research Laboratories SA, en Vallaire, 1024 Ecublens, Switzerland.D.c. Arc Stand for Trace Element Analysis The d.c. arc stand is a modern alternative for classical d.c. arc spectrometry. It is a fully regulated and computer controlled d.c. arc source unit (1-30 A with polarity inversion). Its features include electrode viewing and adjustment during arc, polarisation filters, and a special optic to select the best analytical region of the analytical gap. ARL Applied Research Laboratories SA, en Vallaire, 1024 Ecublens, Switzerland. Spectrophotometer The Color-Eye 7000 dual-beam spectro- photometer provides extremely high col- our measurement performance. Designed for quality control and colour formulation in the paint and coatings, plastics, textiles, printing ink and pulp and paper indus- tries, its exceptional repeatability (AE <0.01 RMS CIELAB) and inter-instru- ment agreement (AE <0.08 average) ensure accuracy to a known degree with- out reference to colour standards.Measurement data are provided at 10 nm intervals over the 360-750 nm range to three decimal places, providing enhanced sensitivity when analysing a colour’s spec- tral characteristics. Macbeth, Macbeth House, Pacific Road, Altrincham, Cheshire WA14 5BJ. ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 image intensified (also TE cooled). All are suitable for imaging applications and all can be controlled by using the new ST-130 detector controller. New data acquisition and manipulation software (PC-AT compatible) allows exploitation of the 2-D and gating characteristics of the new detectors.For high speed imaging applications a range of specialised TV- type CCDs (8-bit, 20-40 Hz) are also offered. Spectroscopy Instruments Ltd., P.O. Box 1032, Marlow, Buckinghamshire SL7 1GG. Gas Chromatography Column Cyclodex-B, a new gas chromatography column, separates hard to detect mirror image chiral compounds in highly com- plex samples, such as pharmaceuticals, flavourings and essential oils, along with positional isomers and non-chiral com- ponents. It uses beta-cyclodextrin suspen- ded in a moderately polar phase and a fused silica column, minimising the need for derivatisation. J and W Scientific, 91 Blue Ravine Road, Folsom, CA 95630, USA. Thick Film Capillary Columns The 3 and 5 pm thick film, 0.53 mm i.d.SPB-1 and SPB-5 capillary columns pro- vide excellent separations for a variety of analyses of petrochemical products con- taining low boiling components. Supelchem UK Ltd., Shire Hill, Saffron Walden, Essex CBll 3AZ. Environmental Chemical Standards Supelco VOC reference standards are specifically designed for capillary gas chromatography analysis of volatile organic compounds. High component concentrations in these standards allow determination of response factors for each analyte over a wide range of dilu- tions. The standards are supplied in sealed glass amber ampoules. Supelchem UK Ltd., Shire Hill, Saffron Walden, Essex CBll 3AZ. Flame Ionisation Detector for HPLC A novel transport system removes volatile solvents from a chromatographic eluent, enabling sample residues to be detected using a flame ionisation detector (FID).The eluent is collected by drawn quartz rods which protrude from a rotating disc. Solvent is evaporated by a series of heaters before the rod passes directly into the FID flame. The rod is then cooled prior to the collection of another drop of eluent. The detector shows linearity from the low nanogram level up to around 15 Applied Chromatography Systems Ltd., The Arsenal, Heapy Street, Mac- clesfield, Cheshire SKll 7JB. HPLC Autosampler The PU4247 HPLC autosampler features reproducible injection volumes with mini- mum carry-over, together with ease of use and reliability. Only flushed loop injec- tions are used. Philips Scientific, Analytical Division, York Street, Cambridge CB1 2PX. HPLC Column The HISEP HPLC microbore column is designed to allow the analysis of small molecules, such as drugs, in biological samples by direct injection of the sample on to the column.The shielded hydro- phobic phase (silica based) is a unique polymeric bonded stationary phase, which consists of hydrophobic pockets protected by a hydrophilic network, a configuration which prevents proteins from entering the hydrophobic region. Supelchem UK Ltd., Shire Hill, Saffron Walden, Essex CBll 3AZ. Automated HPLC Method Development System The makers’ HPLC method development system now features pump control via a personal computer. The upgraded system includes software operating in a Windows environment for full control of instrument parameters. Consisting of a pump, diode- array detector, autosampler and solvent optimisation software, the system makes HPLC method development a matter of routine.Philips Analytical Chromatography, York Street, Cambridge CB1 2PX. HPLC Detector Replacement Lamps Replacement source lamps for all Waters HPLC detctors are available at prices considerably lower than from the original manufacturer. HPLC Technology Ltd., WellingtonANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 23 House, Waterloo Street West, Maccles- field. Cheshire S K l l 6PJ. Integrator The Model 1020 personal integrator from PE Nelson occupies only 12 in of bench space and has a built-in screen for real- time viewing and manipulation of chro- matograms and a hard disk for long-term storage. It is fully compatible with PCs and larger systems, and it can be used with all commercial liquid and gas chromato- graphs.The chromatographer can view one or two real-time plots, and stored or sample chromatograms can be examined in detail and compared with reference standards. Perkin Elmer Ltd., Maxwell Road, Beaconsfield, Buckinghamshire HP9 1QA. Electrophoresis System The Desaphor HF electrophoresis system for horizontal isoelectric focusing is announced. Two different sets of elec- trodes, both freely movable, can be used. There is also the option of adding extra electrodes for double focusing. Two types of cooling plates are available, glass or ceramic, which are each available in three sizes (125, 200 and 254 mm). A range of accessories are also available. Uniscience Ltd., Wildmere Road, Banbury, Oxfordshire OX16 7JU.Extraction Vacuum Manifold The Visiprep solid phase extraction vac- uum manifold allows simultaneous clean- up of up to 12 samples for HPLC or other analyses. Precise flow control is provided through each SPE tube by simply rotating the 12 independent, screw-type valves built into the cover. A built-in vacuum bleed valve and gauge enable accurate adjustment of the vacuum. The rugged but crystal clear glass basin permits obser- vation of the extraction process. Supelchem UK Ltd., Shire Hill, Saffron Walden, Essex C B l l 3AZ. Ion Chromatograph A new version of the IC 690 offers simple trace analysis using automatic sample enrichment. This new version, from Met- rohm, makes it possible to perform analy- sis of either anions or cations to low ppb levels on, for example, cooling waters or other ultra-pure waters.A typical pack- age would comprise two pumps, an TC 690 and integrator. The new IC 690 contains two electrically operated injection valves where the timing and sequence can be controlled from the injector. V. A. Howe and Co. Ltd., Beaumont Close, Banbury, Oxfordshire OX16 7RG. Oxygen Transducer Claimed to be the smallest of its type, the 11 11 miniature oxygen transducer uses the paramagnetic principle to give a light- weight, rugged unit. Designed with a very minimum of internal gas volume, it offers an exceptionally fast response: a 50 ml min-1 sample flow-rate, for example, gives a response time of less than 1 s. Servomex (UK) Ltd., Crowborough, Sussex TN6 3DU. Software for Densitometry Quantascan 2-D image analysis software for the Shimadzu CS9000 scanning densi- tometer is run by using an IBM PC with Micro-soft Windows, methods being created and stored on hard disk.Func- tions include data processing (smoothing, display of chromatogram in X and Y axis, etc.), spot detection (automatic or man- ual) and quantification. The package will be important for users in biotechnology and university research laboratories. V. A. Howe and Co. Ltd., Beaumont Close, Banbury, Oxfordshire OX16 7RG. Stirrers for Viscosity Measurement A range of IKAVISC measuring stirrers enable accurate viscosity and rheology measurements to be recorded. The cur- rent range of 8 models and associated impellers makes the stirrers suitable for a wide variety of applications: paints and varnish, petrochemical, textile, paper, cellulose, pharmaceutical and gypsum type industries.The stirrers have been grouped into the MR highly precise range, which offers readouts from as low as 1 N m N-1 cm-1 to 200 N m N-l cm-l, and the MR Universal range, which has torque ratings from 100 to 1200 N cm. Sartorius Ltd., Scientific Division, Longmead Business Centre, Blenheim Road, Epsom, Surrey KT19 9QN. Software for Polarograph Instruments Software for use with IBM PCs and PS/2s (or clones) allows the user to store and manipulate data collected by the Model 646 Polarograph range of instruFents. It is compatible with the range of sample changer systems currently available for the Model 646 VA processor, giving full automation capability for 100 or more samples.V. A. Howe and Co. Ltd., Beaumont Close, Banbury, Oxfordshire OX16 7RG. Chamber Furnaces A new family of high-temperature pro- grammable chamber furnaces has the advantage of being mounted on castors to simplify movement and location in the laboratory. Designed for general heat treatment and low-volume production applications, the UCF 17/2 and 17/3 offer a maximum operational temperature of 1700 "C and a choice of 12 or 27 1 chamber sizes. Both models have an electrically operated door interlocked with a key switch to prevent inadvertent or un- aut horised opening. Lenton Thermal Designs Ltd., Unit C2, Valley Way, Market Harborough, Leicestershire LE16 7QE. Centrifugal Concentrator and Freeze Dryer The SF50 combined centrifugal concen- trator and freeze dryer, when used with the CVPlOO Cole vacuum pump, offers an effective evaporation and freeze drying system which operates without the need for chemical or cold traps.There are three versions of the SF50: the basic version has a heating and spin facility; the gauge version provides an at-a-glance bar graph display, giving readings of vacuum pressure at the rotor chamber; and the Vac-Stop version includes a vacuum gauge and a controller allowing the SF50 to be operated in the Vac-Stop mode in which the system shuts down automatic- ally when the required level of dryness is reached. Genevac Ltd., 9 Farthing Road, Sproughton, Ipswich IP1 5AP. Centrifuge Ware Nalgene UltraPlus centrifuge ware, a safe, easy, leakproof ultracentrifugation system, has expanded with the introduc- tion of smaller UltraLok tubes, UltraLok spacers and UltraTubes for vertical and swinging bucket ultracentrifuges.The UltraLok tube system now includes smaller 3.5 ml and 5.1 ml tube sizes. Re-usable aluminium spacers permit the tubes to fit five popular Beckman vertical rotors, and a polymethylpentene spacer allows the original 29 ml UltraLok tube to fit three swinging bucket Beckman rotors. Nalge Co., 75 Panorama Creek Drive, Box 20365, Rochester, NY 14602-0365, USA. Diaphragm Pumps A range of air operated double diaphragm pumps incorporates twin diaphragms to avoid contamination of the pumped liquid in the event of a diaphragm failure, making them suitable for handling expen- sive, corrosive and ultra-pure liquids. In the unlikely event of a diaphragm failure inbuilt sensors can be used to activate an alarm or shut down the pump. Chem-Resist Plastic Fabrications Ltd., Britannia House, Lockway, Ravens- thorpe Industrial Estate, Dewsbury, West Yorkshire WF13 3SX.Filter Cartridges The Osmonics Corporation have pro- duced two new grades of their Hytrex pure polypropylene fibre spun filter cart- ridge. A new grade called Select has been designed with excellent particle cut-off properties, high dirt loading and absolute retention from 1 pm upward with a number of grades. Where absolute filtra- tion is not required a new grade called Purtrex has been introduced with econ- omy in mind. Fileder Filter Systems Ltd., Orchard24 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 Business Centre, 20/20 Maidstone, Kent ME16 OJZ. Electron Microscope The CM20 FEG, a 200 kV TEM/STEM system equipped with a thermal field emission gun, provides the ultimate per- formance in high resolution TEM imag- ing, diffraction and analysis.The thermal field emission gun is the ideal electron source for the transmission electron microscope, providing high brightness, high maximum beam current, low energy spread, high coherence and exceedingly high stability. Philips Industrial and Electro-Acoustic Systems Division, Building HKF, 5600 MD Eindhoven, The Netherlands. Cry0 Electron Microscope Based on the CM12 120 kV transmission electron microscope, the CM12 CRY0 has the added benefit of a complete cry0 hardware and software package, provid- ing the ultimate in specimen protection during investigation of frozen beam-sensi- tive specimens.The Cryo-microscopy package is also available for other Philips CM-series TEMs. Philips Industrial and Electro-Acous- tical Systems Division, Building HKF, 5600 MD Eindhoven, The Netherlands. Desk Top Microscopy By using their experience with the micro- controller concept and the CM family of transmission microscopes, Philips have replaced the usual high-tech array of SEM controls, indicators and function keys by a clean-look office desk with monitor, key- board, mouse and column in the new XL Series. This consists of three basic con- figurations: the XL20 featuring a eucen- tric 20 X 20 mm stage and a resolution down to 3 nm, the XL30 equipped with a large chamber and eucentric 50 x 50 mm stage, and the XL40 with a 150 mm travel motorised eucentric stage.Philips Industrial and Electro-Acoustic Systems Division, Building HKF, 5600 MD Eindhoven. The Netherlands. Consumables In a 96-Well Format A wide range of disposable plastic con- sumables is available, including deep 96- well plates and Cube 2ubes. Both are available in a choice of polystyrene or polypropylene, sterile or non-sterile. The 96-well plates have a sample capacity of 1 ml per well. The Cube 2ubes are square in cross-section and are individuals of 2 ml capacity arranged in a rack of 8 X 12 tubes. Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. Fume Cupboards A range of metal or timber fume cup- boards provides a high degree of contain- ment and complies with the COSHH Regulations with regard to operator safety and environmental protection.Designed to meet the requirements of BS 7258, with timber or epoxy-coated metal outer shells and with a choice of interior linings and worktops, the cupboards range in size up to a length of 3.0 m. Styles available are free standing, bench mounted or walk-in, and units can also be designed for building into new or existing premises. Envair (UK) Ltd., York Avenue, Haslingden, Rossendale, Lancashire BB4 4HX. Vibration -free Tables The Microvibe AVM-704 vibration isola- tion system employs an air piston and diaphragm method of vibration and shock absorption. It has a natural fre- quency of 2.5 Hz and provides a usable surface area of 350 x 500 mm, which is capable of supporting loads up to 100 kg. Wentworth Laboratories Ltd., 1 Gos- forth Close, Sunderland Road, Sandy, Bedfordshire SG19 1RB.Laser A semiconductor laser that operates as a transmitter with small signal modulation bandwidths up to 14 GHz is designed for low dissipation and high reliability. Small- signal modulation bandwidths of up to 14 GHz have been measured with these lasers. The modulation bandwidth achieved so far is limited by parasitic effects (contact capacitance, lead induct- ance). Similar high limiting values have so far been attained for more complex struc- tures, which are less suitable for high reliability. Siemens plc, Siemens House, Windmill Road, Sunbury on Thames, TW16 7HS. Standards Database on CD-ROM Standards Infodisk offers on CD-ROM details of over 150000 standards and specifications from more than sixty issu- ing authorities from the UK, US industry, US military, West Germany, the interna- tional bodies IEC, I S 0 and CEN, France, Japan, Canada and Australia.ILI, Index House, Ascot, Berkshire SL5 7EU. Sliced Dry Ice Dry ice (solid carbon dioxide) slices are now available. Cardice Slices have a nominal weight of 1 kg and measure approximately 210 x 125 X 25 mm. Supplied in packs of ten, each slice is individually wrapped and sealed in strong paper. Distillers MG Ltd., Cedar House, 39 London Road, Reigate, Surrey RH2 9QE. Literature The GCMS Companion Series is a con- cept in mass spectral data collections. Designed both as a training tool and as a reference handbook, it provides com- prehensive single-source references for workers using gas chromatography-mass spectrometry.Volumes 1 and 2 cover amino acid derivatives and pollutants, respectively. Future volumes will feature organic acid derivatives, steroid deriva- tives, drugs and drugs of abuse. HD Science Ltd., 4A Bessell Lane, Stapleford, Nottingham NG9 7BX. Supelco’s 1990 Environmental Catalogue contains more than 90 pages on products for drinking water, industrial wastewater, hazardous waste and air monitoring analyses. Supelchem UK Ltd., Shire Hill, Saffron Walden, Essex CBll 3AZ. Hewlett-Packard’s Unified Laboratory brochure (Publication 5952-1059) de- scribes how the Company’s comprehen- sive offering in laboratory data handling, computer and networking systems helps different instrument techniques, researchers, scientists and laboratories to work together more effectively. Hewlett-Packard SA, 150 route du Nant-d’Avril, CH-1217 Meyrin 2, Switzerland. A 24-page illustrated applications guide covers the DU Series 60 spectropho- tometers and deals with quantitative and qualitative analyses, protein and nucleic acid studies, enzyme activity applications and gel scanning. Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. Supelco’s 16-page Reporter (Vol. IX, No. 4) features new 105 m x 0.53 mm i.d. VOCOL capillary columns designed to ensure maximum separation of volati!e compounds in water, according to EPA Method 502.2. Other subjects include the Omegawax 320 capillary column for fish oil fatty acid methyl ester analyses. Supelco Inc., Supelco Park, Bellefonte, PA 16823-0048, USA. The Health and Safety Executive have published a leaflet aimed at employees who work with hydrofluoric acid. It is called ‘Hydrofluoric Acid and You’. HSE, Baynards House, 1 Chepstow Place, London W2 4TF. A leaflet gives information on the Klin- gersil range of asbestos-free sealing materials. Richard Klinger Ltd., Sidcup, Kent DA14 5AG.

ISSN:0144-557X    

DOI:10.1039/AP9912800021

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 25 I Partnership Award 1 NIST SRM 1548 The Analytical Science degree course run The Partnership Awards have attracted by Thames Polytechnic’s School of widespread interest and support among Chemistry has won this year’s Glaxo Prize those involved in or concerned with de- for Analytical and Bioanalytical Chem- veloping more effective undergraduate istry. The 24000 prize is one of the 1990 education. In 1989 20 prizes were offered; Partnership Awards, launched in 1989 by in 1991 there will be 27, extending over a the Council for Industry and Higher broad range of subjects. Education. The award assessors praised the course team for their ‘considerable imagination. ’ They commented that the Thames Poly- technic degree had ‘the ingredients of a novel, stimulating and effective course’.A Certificate of Analysis for Standard Reference Material 1548, Total Diet, has been received from the National Institute of Standards and Technology in the USA. This SRM is intended primarily for use in evaluating the reliability of analytical methods used for the determination of major, minor and trace constituent ele- ments: cholesterol; proximate content of fat, ash, protein (Kjeldahl nitrogen); and caloric content (bomb calorimetry) in mixed diets and similar foods and bio- logical materials.26 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 VDI Guidelines The Commission on Air Pollution of which are translated into English. The Prevention of the Association of German following guideline has recently been Engineers (VDI) and the German Insti- received. VDI 3453: Emission Control. tute for Standardization (DIN) produce Nitric Fertilizers. technical and scientific guidelines, many Deaths We regret to announce the deaths of Dr. H. J. Cluley, formerly of the GEC Hirst Research Centre, Wembley, and Professor H. A. Willis, formerly of ICI Plastics Division, Welwyn Garden City.

ISSN:0144-557X    

DOI:10.1039/AP991280025c

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

26 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 New British Standards BS 611: Petri Dishes. Part 2. Specification for Plastics Petri Dishes for Single Use. BS 658: Apparatus for the Determination of Distillation Range (Including Flasks and Receivers). BS 684: Fats and Fatty Oils. Part 0. General Introduction. Part 1. Physical Methods. Section 1.15. Determination of Ultraviolet Absorbance. Part 2. Other Methods. Section 2.13. Determination of Iodine Value. BS 791: Specification for Solid-stem Calorimeter Thermometers. BS 903: Method for Physical Testing of Rubber. B4 1741: Chemical Analysis of Liquid Milk and Cream. Part 2. Determination of Total Solids Content of Liquid Milk, Cream and Unsweetened Condensed Milk. Part 5. Determination of the Ni- trogen Content of Liquid Milk.Section 5.2. Routine Method. Part 6. Determina- tion of Casein Nitrogen Content of Liquid Milk. Section 6.1. Reference Method. BS 1742: Chemical Analysis of Con- densed Milks. Part 1. General Introduc- tion, Including Preparation of Test Samples. Part 2. Determination of Total Solids Content of Sweetened Condensed Milks. Part 3. Determination of Fat Con- tent. Part 6. Determination of Sucrose Content of Sweetened Condensed Milk. BS 2000: Petroleum and Its Products. Part 71. Kinematic Viscosity of Transparent and Opaque Liquids and Calculation of Dynamic Viscosity. BS 3424: Testing Coated Fabrics. Part 9. Methods 11A, 11B, 11C and 11D. Methods for Determination of Resistance to Damage by Flexing. BS 3762: Analysis of Formulated Detergents. Part 3. Quantitative Test Methods.Section 3.1. Method for Deter- mination of Anionic-active Matter Con- tent. Section 3.23. Method for Deter- mination of Chelating Agents Content. BS 4258: Methods of Test for Phosphoric Acid (Orthophosphoric Acid) for Indus- trial Use. Part 13. Determination of Soluble Sulphate Content (Potentio- metric Method). BS 4285: Microbiological Examination for Dairy Purposes. Part 0. General Intro- duction. BS 5248: Specification for Aspirated Hygrometer. BS 5430: Periodic Inspection, Testing and Maintenance of Transportable Gas Con- tainers (Excluding Dissolved Acetylene Containers). Part 1. Specification for Seamless Steel Containers of Water Capacity 0.5 Litres and Above. BS 5659: Methods of Test for Acid-grade Fluorspar. Part 6. Determination of Total Phosphorus Content.BS 6068: Water Quality. Part 1. Glossary. Section 1.2. Additional Terms Relating to Types of Water, and Treatment and Storage of Water and Waste Water, and Terms Used in Sampling and Analysis of Water. Part 2. Physical, Chemical and Biochemical Methods. Section 2.37. Method for the Determination of Chloride Via a Silver Nitrate Titration With Chromate Indicator (Mohr’s Method). Part 5. Biological Methods. Section 5.9. Method for Assessing the Inhibition of Nitrification of Activated Sludge Micro-organisms by Chemicals and Waste Waters. BS 6069: Characterization of Air Quality. Part 4. Stationary Source Emissions. Sec- tion 4.1. Method for the Determination of the Mass Concentration of Sulphur Dioxide: Hydrogen Peroxide-Barium Perchlorate-Thorin Method.BS 6376: Reagents for Chemical Analy- sis. Part 3. Specifications (Second Series). BS 6424: QAC Based Aromatic Disinfec- tant Fluids. BS 6829: Analysis of Surface Active Agents (Raw Materials). Part 1. General Methods. Section 1.5. Methods for Deter- mination of Water Content. BS 6920: Suitability of Non-metallic Pro- ducts for Use in Contact With Water Intended for Human Consumption With Regard to Their Effect on the Quality of the Water. Part 1. Specification. Part 2. Methods of Test. Section 2.1. Samples for Testing. Section 2.2. Taste of Water. Subsection 2.2.3. Method of Testing Tastes Imparted to Water by Hoses for Conveying Water for Food and Drink Preparation. Section 2.3. Appearance of Water. Section 2.5. The Extraction of Substances That May Be of Concern to Public Health. BS 6939: Recommendations for Inter- mediate Bulk Containers (IBCs) for Dangerous Goods.Part 2. Specific Re- quirements for Metallic IBCs. BS 7164: Chemical Tests for Raw and Vulcanized Rubber. Part 7. Methods for Determination of Polymer Content. Sec- tion 7.1. Polyisoprene Content. Part 14. Methods for Determination of Carbon Black Content. Part 21. Determination of Nitrogen Content. Part 24. Determina- tion of Extractable Sulphur. Part 25. Method for Determination of Sulphide Sulphur Content. Part 26. Methods for Determination of Manganese Content. Section 26.1. Atomic Absorption Spec- trometry. Section 26.2. Sodium Periodate Photometric Methods. Part 27. Methods for Determination of Iron Content. Sec- tion 27.2. Photometric Method. Part 28. Methods for Determination of Copper Content. Section 28.1. Atomic Absorp- tion Spectrometry. Section 28.2. Photo- metric Method. BS 7207: Crude Vegetable Fats. BS 7258: Laboratory Fume Cupboards. Part 1. Specification for Safety and Per- formance. Part 2. Recommendations for the Exchange of Information and Recom- mendations for Installation. Part 3. Recommendations for Selection, Use and Maintenance. BS 7310: Specification for Ion-selective Electrodes, Reference Electrodes, Com- bination Electrodes and Ion-selective Electrode Meters for Determination of Ions in Solution.

ISSN:0144-557X    

DOI:10.1039/AP9912800026

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 27 Conferences and Meetings Protecting the North Sea-The Analytical Challenge February 20-21,1991, Willerby This meeting, which will be organised by the North East Region of the Analytical Division of the RSC, will discuss the role and tech- niques of chemical analysis used in the as- sessment and protection of the aquatic environment with particular reference to the North Sea. Details are available from Dr. John D. Green, BP Chemicals Ltd., Saltend, Hull HU 12 8DS. The Chemical Safety of Food March 28,1991, Chorleywood Food Safety is currently attracting a lot of interest from consumers, the Government and the media alike. The conference aims to pro- vide an overview of the present situation by reviewing the areas giving rise to most con- cern and considering what can be done to improve the position. Topics for discussion will include toxins, agrochemical residues and contamination from environmental sour- ces.The relative importance of these will be considered, with reference to any existing legislative controls and monitoring pro- grammes. The conference will be held at the Flour Milling and Baking Research Associ- ation. Further details can be obtained from Angela Lonergan, FMBRA, Chorleywood, Hertfordshire WD3 5SH. Light Microscopy for the Analytical Chemist April 16,1991, London This meeting will be jointly organised with the Royal Society of Chemistry and held in the Institute of Child Health. Further details are available from The Administrator, Royal Microscopical Society, 37/38 St Clements, Oxford OX4 1AJ.Laboratory Manchester April 1 7-1 8,1991, Manchester There are only 12 stands left for Laboratory Manchester, which is to be held at the G- MEX exhibition centre. The venue proved popular with exhibitors and visitors alike when it was used in 1990 for the first time and 85% of space was re-booked immedi- ately after the 1990 exhibition. Bookings for the Laboratory Scotland exhibition, which is to be held at the Glasgow Scottish Exhibition and Conference Centre on May 15-16, are also coming in rapidly. For further information contact Bob Kyte, Evan Steadman Communications Group, The Hub, Emson Close, Saffron Walden, Essex associated with analyte lability, stereoselec- CBlO IHL. tivity or interferents. For registration and the post-forum book the fee is El24 (rebates claimable); 230 per day can suffice for other Information can be obtained from Dr.E. AOAC 105th Annual International Meet- costs including on-site residence. ing and Exposition August 12-1 5,1991, Phoenix, AZ, USA The 1991 Annual Meeting will be held at The Reid, Guildford Academic Associates, 72 The Chase, Guildford, Surrey GU2 5UL. Pointe at South Mountain, Phoenix. For information contact Margaret Ridgell, Total Quality in the Chemical Industry AOAC, 2200 Wilson Boulevard, Suite 400, September 4-5, I 991, SaIford Arlington, VA 22201 -3301, USA. - A joint symposium of the North West Re- gions of the Analytical and Industrial Divi- IuPAC International COngreSS On Analyti- sions of Royal Society of Chemistry and the cal Sciences 1991 (ICAS '91) Manchester Sections of The Royal Society of August 25-31,1991, Chiba, Japan Chemistry and Society of Chemical Industry, will be held in the University of Salford. The The next ICAS will be held in Makuhari- main topics include registration for BS5750 Messe, Chiba, Japan.The scientific pro- in the context of total quality management gramme will consider: Separation Sciences; (TQM); business management for TQM at Chemica 1 Speciation and Characterization; Board level and in differing sizes of corn- New Principles, Reactions and Techniques; pany; coping with variations in natural pro- Chemometrics and Robotics; Biochemi- ducts; toll manufacture; integration with cal/Biomedical Analysis; Environmental service suppliers - transport, packaging and Analysis; and High-Tech Materials. There distribution; European Scene - assessment Will also be symposia (AsianalYsis and New bodies and experiences of transnational com- Frontiers of Electroanalytical Chemistry, panies.The meeting will allow ample time Tokyo Conference on AnalY tical Instrumen- for discussion and exchange of experiences. tation, etc.) It 1s hoped that the Plenary and The symposium will interest managers in the keynote lecturers will be: L.A. Currie, R. fields of QA, Sales, R and D, Production, Ernst, K. Fuwa, H. Rohrer, G.A. Somorjai; S . Distribution and Engineering. Beman, G.R. Eaton and s. Eaton, M. Gas- Requests for further details to: Mrs. C.L. serbauer, D. Griepink, N. Ishibashi, S. Mina- Sharp, Conference Secretary, 41 Exeter mi, N. Omenetto, N.Otto, E. Pungor, J. Road, Davyhulme, Manchester M31 1RF. Ruzicka, W. Simon, A. Townshend, D. West- erlund, B. Wittmann-Liebolt. Contributed papers will consist of oral and poster presen- tations. When submitting an abstract, the ab- October 14-18, 1991, Pittsburgh, PA, stract form attached to the second circular must be used. The conference language will The Center for Energy Research in the be English. The deadline for contributed University of Pittsburgh's School Of Engin- paper submission is March 3 l , 199 l . eering will host the Eighth Annual Interna- TO request the second circular or further tiOnal Pittsburgh Coal Conference at the infomation contact: 'Secretariat ICAS '91 7, Pittsburgh Hilton Tower. Over 30 organiza- The Japan Society for Analytical Chemistry, tions who are acknowledged leaders in coal 1-26-2, Nishigotanda, Shinagawa, Tokyo technology research and Utilization Will par- 14 1, Japan.ticipate in this conference. Papers are currently being solicited in all subject areas dealing with coal technology, Bioanalysis of Drugs, Including Anti-dler- coal utilization and related policy issues. A gics and Anti-asthmatics 250 word abstract should be submitted for review no later than February 15, 1991. The September 34,1991, Guildford abstract should be sent to: Mrs. Ann McDo- -Energy and the Environment The focus of the 9th International Bioanalyti- cal Forum, which will be held in the Univer- sity of Surrey, is on the assay of blood and other biological samples, especially for drugs which are given in low dosage or which yield metabolites that need shrewd investigation. There will be surveys of strategies for method development and for exploiting and interfacing techniques such as HPLC, SFC, CZE, MS and other detectors, NMR, and automated sample handling. Diverse drugs will be considered, some presenting problems nald, Program Secretary, The Pittsburgh Coal Conference, University of Pittsburgh, 1140 Benedum Hall, Pittsburgh, PA 15261, USA. As the leading Conference on emerging coal technologies in the United States, approxi- mately 600 attendees are expected to partici- pate in the programme, exchange technical information and exhibit the latest innovations in coal technology and coal utilization. Additional information is available from the University of Pittsburgh, 1140 Benedum Hall, Pittsburgh, PA 15261, USA.

ISSN:0144-557X    

DOI:10.1039/AP9912800027

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

28 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 Publications Received An Introduction to Laboratory Automat- ion. Victor Cerda and Guillermo Ramis. Volume 110 in Chemical Analysis: A Series of Mono- graphs on Analytical Chemistry and Its Ap- plications. Pp. xiv + 321. Wiley-Interscience. 1990. Price E55.15. ISBN 0-471-61818-7. PCs for Chemists. Edited by J. Zupan. Data Handling in Science and Technology, 5. Pp. xvi + 212. Elsevier. 1990. Price $100.00; Df1195.00. ISBN 0-444- 88623-0. Advanced Methodologies in Coal Charac- terization. Edited by Henri Charcosset. Coal Science and Technology, 15. Pp. xxiv + 442. Elsevier. 1990. Price $182.00; Df1355.00. ISBN 0-444-88695-8. Biological Mass Spectrometry. Edited by A.L. Burlingame and J.A. McClos- key. Proceedings of the Second International Symposium on Mass Spectrometry in the Health and Life Scien- ces, San Francisco, CA, USA, August 27-31, 1989.P. ix + 700. Else- vier. 1990. Price DORA ’90-91: Directory of Rare Analyses. Jocelyn M. Hicks and Donald S. Young. Pp. 240. American Association for Clinical Chemistry (AACC) Press. 1990. Price $35.00 (AACC Members); $60.00 (Others); (Outside US include $3.00 per book postage). ISBN 0-9 15274-54-X. Subcellular Biochemistry. Volume 16. In- tracellular Transfer of Lipid Molecules. Edited by H.J. Hilderson. Pp. xix + 412. Ple- ISBN 0-444-88837-3. Thermal Analysis. Part E: Pulse Method of Measuring. Basic Thermophysical Parameters. L‘udovit Kubicar. Wilson and Wilson’s Com- prehensive Analytical Chemistry. Volume XII. Pp. xx + 341. Elsevier.1990. Price $148.75; Df1265.00. ISBN 0-444-9885 1-3. Edited by D.R. Randell and W. Neagle. Pp. vi + 173. The Royal Society of Chemistry. 1990. Price E37.50. ISBN 085 186-597-6. Photon Migration in Tissues. Edited by Britton Chance. Pp. x + 195. Ple- num Press. 1990. Price $62.50. ISBN 0-306- 43522-5. Plasma Source Mass Spectrometry. Edited by K.E. Jarvis, A.L. Gray, I. Jarvis and matography and Mass Spectrometry. Surrey Conference on Plasma Source Mass Edited by Alvin Fox, Stephen L. Morgan, Spectrometry, University of Surrey, 16th- Lennart Larsson and Goran Odham. pp. viii 19th July, 1989. Pp. viii + 172. The Royal + 280. Plenum Press. 1990. ISBN 0-306- Society of Chemistry. Price E35.00. ISBN 0- Analytical Microbiology Methods. Chro- J. Williams. The Proceedings of the Third 43536-5.85 186-567-4. Chemometrics I’utorials. Pesticide Residues in Food. Technologies for Edited by D.L. Massart, R.G. Brereton, R.E. Detection. Dessy, P.K. Hopke, C.H. Spiegelman and W. US Congress, Office of Technology Assess- Wegscheider. Collected from Chemometrics ment. OTA Workshop Participants, March and Intelligent Laboratory Systems - An In- 14-16, 1989. Pp. 230. Technomic Publishing. ternational Journal, Volumes 1-5. Pp. vii + 1989. Price SwFrl08.00. ISBN 0-87762-667- $230.75; Df1450.00. ISBN 0-444-88341-X. 427. Elsevier. 1990. Price $66.75. Df1130.00. 7.28 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 Publications Received An Introduction to Laboratory Automat- ion. Victor Cerda and Guillermo Ramis. Volume 110 in Chemical Analysis: A Series of Mono- graphs on Analytical Chemistry and Its Ap- plications.Pp. xiv + 321. Wiley-Interscience. 1990. Price E55.15. ISBN 0-471-61818-7. PCs for Chemists. Edited by J. Zupan. Data Handling in Science and Technology, 5. Pp. xvi + 212. Elsevier. 1990. Price $100.00; Df1195.00. ISBN 0-444- 88623-0. Advanced Methodologies in Coal Charac- terization. Edited by Henri Charcosset. Coal Science and Technology, 15. Pp. xxiv + 442. Elsevier. 1990. Price $182.00; Df1355.00. ISBN 0-444-88695-8. Biological Mass Spectrometry. Edited by A.L. Burlingame and J.A. McClos- key. Proceedings of the Second International Symposium on Mass Spectrometry in the Health and Life Scien- ces, San Francisco, CA, USA, August 27-31, 1989. P. ix + 700. Else- vier. 1990. Price DORA ’90-91: Directory of Rare Analyses. Jocelyn M.Hicks and Donald S. Young. Pp. 240. American Association for Clinical Chemistry (AACC) Press. 1990. Price $35.00 (AACC Members); $60.00 (Others); (Outside US include $3.00 per book postage). ISBN 0-9 15274-54-X. Subcellular Biochemistry. Volume 16. In- tracellular Transfer of Lipid Molecules. Edited by H.J. Hilderson. Pp. xix + 412. Ple- ISBN 0-444-88837-3. Thermal Analysis. Part E: Pulse Method of Measuring. Basic Thermophysical Parameters. L‘udovit Kubicar. Wilson and Wilson’s Com- prehensive Analytical Chemistry. Volume XII. Pp. xx + 341. Elsevier. 1990. Price $148.75; Df1265.00. ISBN 0-444-9885 1-3. Edited by D.R. Randell and W. Neagle. Pp. vi + 173. The Royal Society of Chemistry. 1990. Price E37.50. ISBN 085 186-597-6.Photon Migration in Tissues. Edited by Britton Chance. Pp. x + 195. Ple- num Press. 1990. Price $62.50. ISBN 0-306- 43522-5. Plasma Source Mass Spectrometry. Edited by K.E. Jarvis, A.L. Gray, I. Jarvis and matography and Mass Spectrometry. Surrey Conference on Plasma Source Mass Edited by Alvin Fox, Stephen L. Morgan, Spectrometry, University of Surrey, 16th- Lennart Larsson and Goran Odham. pp. viii 19th July, 1989. Pp. viii + 172. The Royal + 280. Plenum Press. 1990. ISBN 0-306- Society of Chemistry. Price E35.00. ISBN 0- Analytical Microbiology Methods. Chro- J. Williams. The Proceedings of the Third 43536-5. 85 186-567-4. Chemometrics I’utorials. Pesticide Residues in Food. Technologies for Edited by D.L. Massart, R.G. Brereton, R.E. Detection. Dessy, P.K.Hopke, C.H. Spiegelman and W. US Congress, Office of Technology Assess- Wegscheider. Collected from Chemometrics ment. OTA Workshop Participants, March and Intelligent Laboratory Systems - An In- 14-16, 1989. Pp. 230. Technomic Publishing. ternational Journal, Volumes 1-5. Pp. vii + 1989. Price SwFrl08.00. ISBN 0-87762-667- $230.75; Df1450.00. ISBN 0-444-88341-X. 427. Elsevier. 1990. Price $66.75. Df1130.00. 7.28 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 Publications Received An Introduction to Laboratory Automat- ion. Victor Cerda and Guillermo Ramis. Volume 110 in Chemical Analysis: A Series of Mono- graphs on Analytical Chemistry and Its Ap- plications. Pp. xiv + 321. Wiley-Interscience. 1990. Price E55.15. ISBN 0-471-61818-7. PCs for Chemists.Edited by J. Zupan. Data Handling in Science and Technology, 5. Pp. xvi + 212. Elsevier. 1990. Price $100.00; Df1195.00. ISBN 0-444- 88623-0. Advanced Methodologies in Coal Charac- terization. Edited by Henri Charcosset. Coal Science and Technology, 15. Pp. xxiv + 442. Elsevier. 1990. Price $182.00; Df1355.00. ISBN 0-444-88695-8. Biological Mass Spectrometry. Edited by A.L. Burlingame and J.A. McClos- key. Proceedings of the Second International Symposium on Mass Spectrometry in the Health and Life Scien- ces, San Francisco, CA, USA, August 27-31, 1989. P. ix + 700. Else- vier. 1990. Price DORA ’90-91: Directory of Rare Analyses. Jocelyn M. Hicks and Donald S. Young. Pp. 240. American Association for Clinical Chemistry (AACC) Press. 1990. Price $35.00 (AACC Members); $60.00 (Others); (Outside US include $3.00 per book postage).ISBN 0-9 15274-54-X. Subcellular Biochemistry. Volume 16. In- tracellular Transfer of Lipid Molecules. Edited by H.J. Hilderson. Pp. xix + 412. Ple- ISBN 0-444-88837-3. Thermal Analysis. Part E: Pulse Method of Measuring. Basic Thermophysical Parameters. L‘udovit Kubicar. Wilson and Wilson’s Com- prehensive Analytical Chemistry. Volume XII. Pp. xx + 341. Elsevier. 1990. Price $148.75; Df1265.00. ISBN 0-444-9885 1-3. Edited by D.R. Randell and W. Neagle. Pp. vi + 173. The Royal Society of Chemistry. 1990. Price E37.50. ISBN 085 186-597-6. Photon Migration in Tissues. Edited by Britton Chance. Pp. x + 195. Ple- num Press. 1990. Price $62.50. ISBN 0-306- 43522-5. Plasma Source Mass Spectrometry. Edited by K.E. Jarvis, A.L. Gray, I. Jarvis and matography and Mass Spectrometry. Surrey Conference on Plasma Source Mass Edited by Alvin Fox, Stephen L. Morgan, Spectrometry, University of Surrey, 16th- Lennart Larsson and Goran Odham. pp. viii 19th July, 1989. Pp. viii + 172. The Royal + 280. Plenum Press. 1990. ISBN 0-306- Society of Chemistry. Price E35.00. ISBN 0- Analytical Microbiology Methods. Chro- J. Williams. The Proceedings of the Third 43536-5. 85 186-567-4. Chemometrics I’utorials. Pesticide Residues in Food. Technologies for Edited by D.L. Massart, R.G. Brereton, R.E. Detection. Dessy, P.K. Hopke, C.H. Spiegelman and W. US Congress, Office of Technology Assess- Wegscheider. Collected from Chemometrics ment. OTA Workshop Participants, March and Intelligent Laboratory Systems - An In- 14-16, 1989. Pp. 230. Technomic Publishing. ternational Journal, Volumes 1-5. Pp. vii + 1989. Price SwFrl08.00. ISBN 0-87762-667- $230.75; Df1450.00. ISBN 0-444-88341-X. 427. Elsevier. 1990. Price $66.75. Df1130.00. 7.

ISSN:0144-557X    

DOI:10.1039/AP991280028b

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

31 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 Analytical Division Diary FEBRUARY Thursday, 7th, 10 a.m.: London Chromatography and Electrophoresis Group, jointly with Chromatography in Analytical Toxicology. Session 1 : Samplc Preparation and Analysis. ‘Solid-phase Extraction in Toxicology’, by R. Whelpton. ‘Capillary Gas Chromatography of Solvents and Other Volatiles’, by ‘Supercritical Fluid Extraction and Chromatography of Drugs’, by Session 2: HPLC and Related Techniques. ‘Porous Graphitized Carbon as a Column Packing’, by C. K. Lim. ‘Capillary Zone Electrophoresis of Drugs’, by D. Perrett. ‘Towards a Universal HPLC System’, by R. Gill. Scientific Societies’ Lecture Theatre, New Burlington Place, London W1. Registration is necessary. Cost f40 to members, f60 to non-members and f20 to student, non-employed and retired members.Contact: Dr. D. Simpson, Analysis For Industry, Factories 2/3, Bosworth House, High Street, Thorpe-le-Soken, Essex C016 OEA. (Tel. 0255-861714). the Chromatographic Society. R. J . Flanagan. D. E. Games. Tuesday, 12th, 4.15 p.m.: Loughborough Midlands Region, jointly with the Loughborough Students Lunar Society and Midlands Chemists. Speaker: D. Thorburn Burns. Lecture Room JOOl , Edward Herbert Building, University There are no registration formalities. Contact: Dr. R. M. Smith, Department of Chemistry, University of Technology, Loughborough, Leicestershire LE 1 1 3TU. (Tel . 0509-222563). Union Chemical Society. of Technology, Loughborough, Leicestershire. Tuesday, 12th, 4.10 p.m.: Swansea Western Region, jointly with the South Wales West Section FAB-10 Years On.Speaker: M. Barber. University College of Swansea. There are no registration formalities. Contact: Dr. S. J. Hill, Department of Environmental Sciences, Polytechnic South West, Drake Circus, Plymouth, Devon PL4 8AA. (Tel. 0752-233012). of the RSC. Wednesday, 13th, 10 a.m.: London Radiochemical Methods Group. Applications and Uses of Radioisotopes in Medicine. ‘An Overview of the Uses of Radioisotopes in Medicine’, by P. J . ‘Technetium-99m: The Generator System and Labelling Methods’, ‘Radionuclide Generators in Medicine: 81Rb/81mKr, 82Sr/82Rb, ‘Some Research Applications of Single Photon Emission Computed ‘The Radiochemistry of the Short-lived Cyclotron-produced Iso- ‘Principles and Applications of Positron Emission Tomography’, by Ell.by J. R. Thornback. 1910s/191mIr’, by C. Brihaye. Tomography’, by V. R. McCready. topes “C and lXF for PET’. by D. Roeda. ‘r. Jones. ‘Labelled Monoclonal Antibodies’, by M. Stalteri. ‘Radiopharmaceutical Dosimetry’, by M. J. Myers. ‘Radiopharmaceuticals for Radiotherapy’, by I . Brown. Registration is necessary. Cost to members of Group f25, non-members 235 and students 210. Contact: Dr. J. A. Troke, Department of Drug Metabolism, HPRL Hoechst UK Ltd., Walton Manor, Walton, Milton Keynes MK7 7AJ. (Tel. 0908-680244). Thursday, 14th, 12 noon: Birmingham Midlands Region, jointly with the Birmingham Students Lunar Society and Midlands Chemists. Speaker: D. Thorburn Burns. Lecture Theatre, Haworth Building, The University, There are no registration formalities.Contact: Dr. R. M. Smith, Department of Chemistry, University of Technology, Loughborough, Leicestershire LE 11 3TU. (Tel. 0509-222563). Union Chemical Society. Birmingham. Wednesday and Thursday, 20th and 21st: Willerby Analytical Division, organised by the North East Region: Annual General Meeting of North East Region; 10 a.m. on 20th. Protecting the North Sea: The Analytical Challenge. Wednesday, February 20th- Introductory Session ‘Coordination of North Sea Research and the North Sea Database’, by P. C. Reid. ‘Analytical Requirements in View of Environmental North Sea Policy’, by W. P. Cofino. ‘Environmental Monitoring and Analysis in the North Sea Under the North Sea Task Force’, by R. J . Law. Sampling Considerations ‘Sampling Considerations in the North Sea’, by A.Bale. ‘Analytical Difficulties in the Full Characterisation of Industrial Thursday, February 21st- Trace Metal Analysis ‘Analysis of Dissolved Trace Metals in the North Sea’, by P. Statham. ‘The Determination and Speciation of Heavy Metals in Seawater- An Overview of Methods Available and Results Achievable’, by P. del Castilho. ‘Monitoring of Trace Metal Speciation in Sea Water’, by C . M. G. van den Berg. lnorganic Analysis ‘Interpretation of Inorganic Nutrient Distributions in the North ‘Ion Chromatography for Seawater and Brines’, by I . Marr. ‘The Contribution of Radionuclides to the Study of the Environ- Organic Analysis ‘Purge and Trap of Volatile Organics in the Marine Environment ‘Problems Associated with the Analysis of Hydrocarbons in Marine ‘Environmental Surveying of Industrial Effluents Using Biological Grange Park Hotel, Willerby, nr.Hull. Effluents’, by P. Johnston. Sea’, by D. Hydes. mental Processes in the North Sea’, by s. Malcolm. Using GUMS’, by M. Varney. Sediments’, by R. Large. Monitoring’, by D. Maughan. [continued on p . 32132 ANALYTICAL PROCEEDINGS, JANUARY 1991, VOL 28 Analytical Division Diary, continued February, continued The Chemistry of Wood Preservation. Thursday, 28th- Treatment Processes Introduction and Overview: ‘Biological Aspects, Nature of Pests and Threats’, by David J. Dickinson. ‘History, Development Uses, Advantage and Future Trends’, by Mike Connell. ‘Diffusion Treatment of Wood-An American Perspective’, by Lonnie H. Williams.‘Diffusion Treatment (Solids)’, by William N. Beauford. Treatment Mechanisms ‘Organic Solvent Preservatives: Application and Composition’, by E. Austin Hilditch. ‘Wood/Chemical Interactions and Effect on Performance’, by Alan F. Preston and Lehong Jin. ‘Water-based Fixed Preservatives’, by David G. Anderson. ‘Strategies for the Future’, by John Butcher. Friday 1st- Reaction and Analysis ‘Creosote Treatment’, by W. D. Betts. ‘PCP and the Environment: Analysis and Residues’ (speaker from ‘Developing QC Procedures and Standards for Diffusible Preserva- ‘Tributyltin Compounds’ (speaker from Germany to be confirmed). ‘Analysis of Wood Preservatives: BS Specifications’, by Reg J. Ecology and Control ‘Biocides and Their Assessment in Wood Preservation’, by Anthony F.Bravery. ‘Progress Towards European Standards in Wood Preservation’, by Frank W. Brookes. ‘The Market for Chemical Products in the Building and Civil Engineering Industries’, by Chris R. Coggins. ‘Preservation of Ancient Timber’, by Mark Jones. Government Science Park, Queens Road, Teddington, Middlesex. Registration is necessary. Cost to RSC members f90, non-members f135 and students and retired members 245. Contact: Mr. S. S. Langer, The Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN. (Tel. France to be confirmed). tives’, by Edward L. Docks. Orsler. 071-437-8656). Registration is necessary. Cost (including accommodation) is El70 to RSC members and f200 to non-members; student and retired members (without accommodation) f30. Contact: Dr.John D. Green, BP Chemicals Ltd., R & D Department, Hull Laboratory, Saltend, Hull HU12 8DS. (Tel: 0482-896251, Ex. 2730). Thursday, 21st, 2 p.m.: Montrose Scottish Region, jointly with the Aberdeen and North of Scotland Section of the RSC and the Aberdeen Students Chemical Society. Analysis in the Development of New Drugs. Speaker: Miss C. E. Meir. Glaxochem, Montrose. Registration is necessary; no charge. Contact: Mr. E. C. Smith, ICI FCMO, Earls Road, Grangemouth, Stirlingshire FK3 8XG. (Tel. 0324- 494891). Wednesday, 27th, 12 noon: Lancaster North West Region: Annual General Meeting; 7 p.m. Accreditation-Necessity or Nuisance. Although analytical laboratories clearly need good quality assurance procedures, do they need to go through the formality of accreditation by an outside body or is this just a bureaucratic paper chase adding little in reality to a laboratory’s performance? Even if accreditation is thought helpful, or even just expedient, what accreditation? How should we decide between BS 7570 and NAMAS? This meeting hopes to present people’s experiences of accreditation and allow ample time for discussion.What BS 5750 accreditation has to offer. What NAMAS accreditation has to offer. Experiences of those who have attempted accreditation. Round table discussion. The University, Lancaster. Registration is necessary. Cost f25 to RSC members, f45 to non-members and f l O to retired members and students. Contact: Dr. C. J. Peacock, Chemical Analysis Service, School of Physics and Materials, The University, Lancas- ter LA1 4YA.(Tel. 0524-65201, Ex. 3366). Wednesday, 27th, 6.30 pm.: London Micro & Chemical Methods Group and South East Region. COSHH-One Year On. It is expected that the discussion will centre round the impact of COSHH regulations on working practices in the analytical laboratory. Discussion introduced by P. Wusteman. Room A506, London School of Economics, Houghton There are no registration formalities. Contact: Miss L. Dixon, Metal Box Group Technology, Denchworth Road, Wantage, Oxfordshire OX12 9BH. (Tel. 081-840-0999, Ex. 2019). Street, London WC2. Thursday and Friday, 28th and March 1st: Teddington South East Region, jointly with the South East Region of the Industrial Division and in conjunction with the Laboratory of the Government Chemist. MARCH Friday, lst, 10 a.m.: Cardiff Analytical Division: Annual General Meeting; 4.45 p.m.Gas and Headspace Vapour Analysers. The Symposium will be concerned with recent developments in the design of devices for monitoring gases and vapours in workplaces, of headspace vapour analysis-as in the control of fermenta- tion processes, and for determining gas components in the clinical and biomedical field-including food products. ‘Competitive Adsorption on to Coated Surface Acoustic Wave Sensors’, by J. F. Alder. ‘Piezoelectric Devices Based on Quartz Crystals Coated with Cyclic Organic Materials Facilitate the Detection of Organic Vapours’, by G. J . Moody. ‘Use of Ion Mobility Spectrometry for the Detection and Analysis of Vapours’, by P. Watts. ‘Solid State Gas Sensors: Prospects for Selectivity’, by D. E. Williams. ‘Gas Monitoring Based on Phthalocyanines and Related Materials’, by C. L. Honeybourne. ‘Fuel Cell Sensor Design for Carbon Monoxide and Methanol Using Platinum Single Crystals’, by G. A. Attard. ‘Developments in Membrane-covered Gas Sensors for Oxygen and Other Gases in Relation to the Clinical and Biomedical Field’, by C. E. W. Hahn. [continued inside back cover]... ANALYTICAL PROCEEDINGS. JANUARY 1991. VOL 28 111 Analytical Division Diary, continued March, continued Criddle. Registration is necessary. Cost 245 to RSC members, &80 to non-members and f 1 5 to student and retired members; accommodation and the Symposium Dinner are extra. Contact: Miss P. E. Hutchinson, Analytical Division, The Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN. (Tel. 071-437-8656). ‘Use of Platinum-based Fuel Cells for Ethanol Analysis’. by W. J . ‘Odour Detection Using Sensor Arrays‘, by K. C. Persaud. School of Chemistry and Applied Chemistry, University of Wales College of Cardiff, Cardiff.

ISSN:0144-557X    

DOI:10.1039/AP9912800031

出版商:RSC    

年代:1991

数据来源: RSC