Computer-Aided Analytical Methods - a Review

COMPUTER-AIDED ANALYTICAL METHODS - A REVIEW

Läszlö Kekedy-Nagy

Chair of Analytical Chemistry Faculty of Chemistry and Chemical Engineering Babe§-Bolyai University 3400 Cluj-Napoca, Romania

INTRODUCTION

Digital computers have become integral components of modern methods of analysis, influencing both instrument design and analytical methods. To understand the role of a computer in a specific instrumental method, it is necessary to consider the interaction among instrument, computer and analyst. Computers are being increasingly used in analytical work, but a survey of the literature shows that their potential has not yet been fully utilized. They offer enormous flexibility and sophistication in the execution and control of experiments, and their influence will doubtless be more and more widely felt. The following should be mentioned as main concerns: 1) Determination of the optimum analytical conditions, selecting the values of different parameters (e.g., the input signal) such that the best response is possible. In this respect, in order to avoid excessive experimental work and calculations and simplify operations, the mathematical modeling of the relations investigated is necessary. 2) Control of the measurement of analytical signals, used, e.g., to control the timing of different phases of the experiment, to prevent or warn against operator errors. 3) Data acquisition and storage of the analytical information. 4) Processing of analytical data is perhaps the main benefit that computers offer for analytical chemists. The computer makes it possible to qualify and classify the hidden information, using various chemometric methods including application of analytical intelligence, such as pattern recognition or expert control of chemical analysis systems. These functions are widely utilized in instruments intended for routine analysis. In newer electroanalytical instruments, sophisticated routines for subtracting baselines,

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comparing responses with those from standards, calculating unknown concentrations, identifying peaks, and plotting rescaled results are incor- porated as standard features III. Computer-based instrumentation is a general term used to describe a group of the measuring and control instruments managed by any kind of computer, e.g., by a laboratory computer or microcomputer. The philosophy for the application of computers in analytical chemistry is still under formation and consideration /2/: "If we think only of all that is done in teleanalytical work, e.g., the results of the Voyager, Mariner, or Venera missions, or even the Space Shuttle experiments, then we get an idea of the importance of what is going on". Bond and Svetska /3/ conclude that developments to data in the use of computer-based technology have been conservative relative to those in spectroscopic forms of instrumentation. A new generation of "more intelligent" instruments would be available immediately if the full power of presently available digital hardware and software were to be implemented as has been the case with some other forms of instrumentation, e.g., spectroscopy /3/. The present review summarizes literature data concerning the analytical methods aided by computers published in the period 1980-1998. The material is limited only to the presentation of the role of computers in obtaining the analytical signal, data acquisition, instrument control, and computer- optimized operating conditions in different analytical determinations (e.g., voltammetry, polarography, potentiometry, etc.). Some aspects of the hardware are presented too, namely the interfaces used. No other fields concerning the analytical uses of computers will be presented, such as processing the analytical results, optimization, simulation techniques, software, etc. Because these aspects of computer-based analytical chemistry in main publications do not appear distinctly separated, some overlappings would occur. Further information can be obtained from textbooks recently published /4-12/, or in reports on the second conference on "Computer-Based Analytical Chemistiy (COBAC) held in Munich, 1982 /2,13/.

GENERAL ASPECTS OF COMPUTER APPLICATIONS IN ANALYTICAL CHEMISTRY

Several publications discuss general aspects of computer applications in the analytical laboratory. Bos states /14/ that in chemical analysis com-

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puterization can provide higher precision, higher speed and lower costs. Applications of on-line computers in the laboratory include data acquisition, treatment and automation. The performance of a general-purpose electrochemical instrument aided by a stand-alone microcomputer system is discussed by Fanelly et al. /15/. The system comprises a multibus IEEE-796 microcomputer with ASM-86, PLM-86 and Fortran language facilities. It was used to control and monitor the pulsed-flux Hg working electrode of a Polarographie cell. The most significant signal parameters were measured automatically. Smoothing, baseline drawing, subtraction and differentiation could be carried out as well. The application of computers to the solution of problems in the analytical laboratory and the underlying aims are discussed by Dessy /16/. The range of computers from personal to mainframe host-micro systems and their suitability are also considered. Belchamber et al. Ι\ΊI discuss the application of computers in analytical chemistry and chemometrics. A review on computer applications in analytical chemistry including instrumentation trends is discussed in /18/. Under the title "What is on the horizon?" the problem of computers and automation in analytical chemistry is presented by Borman /19/. A review on instrumentation and computers in analytical chemistry is published in /20/. Principles and problems of computer-based instruments and networks in analytical chemistry are reviewed by Smith /111. Some formalized concepts and quantitative estimation in computer-based chemical analysis are discussed by Gribov et al. 1221. The validation of analytical equipment using computers for instrument control, data acquisition and data evaluation, with definitions of some of the terminology used in computerized systems, is discussed by Huber 1221. The concept and implications of the use of microcomputers for multiple tasks (data acquisition, analysis, presentation) in the laboratory are also presented by Lam et al. /24/. A review with 58 references on the use of computers in analytical chemistry is published by Abramovic 1251. He states that computers are particularly useful in the simulation, optimization and automation of catalytic analysis. Li and Tong /26/ also summarize the applications of computers in analytical chemistry. Implementation of automated systems, e.g., computers and robotics, in laboratory automation is discussed by Liscouski Ι2ΊΙ. Hierarchically structured computer systems for analytical chemistry are described by Ziegler /28/. All real-time tasks like data acquisition and

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instrumental control are performed by local satellite computers. The satellites transfer data to a larger central (host) computer where the more complex tasks of data evaluation and archiving are performed. The dual VAX 11/80 system is described. Such systems are optimally suited for applications in analytical chemistry. The same principle of hierarchical control systems was described by Hoffmann and Eke /29/. A communication control was developed, whereby a microprocessor-controlled laboratory instrument could communicate with a central computer. The resulting hierarchical system greatly facilitated a distributed intelligence approach to instrumental control, data acquisition and data reduction. Several publications discuss the interface systems for connecting analytical instruments to personal computers. Instrument interfacing usually meant connecting an analog signal from the instrument to a computer system and digitizing it. Now that these processors are being sold as part of the package, much of what comes under the heading of instrument interfacing is really a problem of communications HII. Dehme /30/ introduces the non- expert in the field of personal computers to the various ways that PCs can be interfaced to laboratory equipment to control laboratory applications and data acquisition. A general overview is given of different interfacing methods as well as their advantages and drawbacks. Ewen and Adams /31/ interface an Apple II computer. The device permits serial transfer of data between computers or between a host computer and a laboratory instrument, e.g., an IR spectrophotometer. Kaplan et al. 132/ describe an interface between an analytical instrument and a PC. The system was used routinely in the ASV (anodic stripping voltammetry) analysis of waste-water and soils. Hä/.i et al. /33/ summarize the main trends expected in the application of computers in the field of analytical chemistry. An interface system built from two main parts has been developed. One of these consists of a fast and a slow 12 bit A/D converter, a 12 bit D/A converter, and a slow timer as well. The whole interface system has been developed as a plug-in card of the IBM PC. The application possibilities are demonstrated on examples taken from the fields of potentiometry and thermal analysis. An interface between the IBM PC and the PAR model 273 potentiostat-galvanostat was described by Carpenter et al. /35/. Buschman et al. developed a universal low-cost interface for coupling an Apple II computer to a number of analytical instruments: HPLC, AAS /36/, polarograph /37/, amperometric titration cell /38/, and computer-supported cyclic voltammetry with numerical IR-drop correction /3 9/. Interface selection problems are discussed by Haarmann et al. /40,41/. A

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method of coupling analogue measurement devices with a standard PC/XT computer is described and applied in the electrochemical analysis of semi- conductors and in electrochemical etching I AH.

USE OF COMPUTERS IN ELECTROANALYTICAL CHEMISTRY

Several articles have appeared concerning some general aspects of the application of computers in electrochemical chemistry, mostly in voltammetry and polarography. Fang et al. /34/ published a review article with 48 references concerning the applications of computer techniques to pulse voltammetry, square-wave voltammetry and multiple-scanning stripping analysis, fast Fourtier transformation. In a paper published by Stefani et al. /43/ details are given concerning a POP-11/23 PLUS computer linked to the electrochemical cell. Control of voltammetric experiments by means of the Commodore 64 microcomputer was published by Wasberg and Sarkany /44/. It is of general use for fast data acquisition in the laboratory. Detailed literature concerning the use of 5 bite computers in voltammetry are given in /33/ (references 6-20). Under the title "Voltammetry with windows" Bogenschütz et al. /45/ discuss a new VA Trace Analyser 746, a microprocessor controlled instrument with 32 bits data bus system. The VA 747 is equipped for microelectrode operation, with dropping, static or hanging mercury drop electrode operation or disc electrodes of Pt, Ag, Au, vitreous C or Ultratrace graphite. Examples of different possible displays are illustrated, including the determination of trace of Hg in brine (3.87 μg/l). Computer-assisted rapid-scan cyclic staircase voltammetry in normal-pulse HPCL using a large wall-jet detector was reported by Gunnashingham et al. 1461. Presentation of a computer-controlled voltammetric instrument is made by Fülöp /47/. Examples of applications given are: semi-integration and digital smoothing of cyclic voltammograms. Computer-aided voltammetric method development employing a knowledge-base expert system is reported by Ruisanchez et al. /48/. The system makes recommendations to non- specialist analysts on the successive steps in the Polarographie or voltammetric determinations of metal ions in natural samples. It provides information about sample treatment and about determination of Cd, Co, Cu, Ni, Pb, T1 and Zn by polarography, adsorption stripping voltammetry (AdSV), anodic stripping voltammetry (ASV) or cathodic stripping

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voltammetry (CSV) and it calls external programs for peak resolution and calibration. Computer-assisted polarography and voltammetry was applied to kinetic studies of metal complexation /49/. The system consists of a commercially available polarograph, controller and scanner with an IBM AS compatible personal computer, which handle instrument control and data evaluation. A simple, programmable voltammetric system applicable to, e.g., differential- pulse polarography, cyclic or staircase voltammetry and chronocoulometry was presented by Srivastava and Upadhyay /50/. A microcomputer-controlled instrumentation for voltammetric techniques was proposed by Cukrowski et al. 151/. An Atari 800 XL microcomputer was connected to a laboratory-made A/D voltammetric analyser by a 2-directional serial transmission interface. The simple system provided the user with computer-aided execution of experiments including synthesis of potential waveforms and collection and development of responses. A versatile, microcomputer-controlled system for data acquisition and analysis in voltammetiy was reported by Nagaoka et al. /52/. Pulse and cyclic voltammographs were recorded and processed on an integrated computerized electrochemical system. A completely automated voltammetry-polarography system was described by Arts et al. /53/. The system is based on a PAR model 3 84A polarographic analyser controlled by an Apple II microcomputer. Special cells with automatic sampler, filling and draining facilities are described. The use of microcomputers to control a voltammetric instrument was discussed by Wasberg /54/. Voltammetric instrumentation controlled by two microcomputers was discussed by Baecklund and Danielsson/55/. An INTEL SYS 80/1 OA microcomputer, interfaced to the electrochemical cell, is used for control and measurement. A personal computer (Luxor/Scandia ABC 80) is used to control the microcomputer and to evaluate the results. The two low-cost computers can replace a multi-task system or a remote host-computer. Computer-controlled variable sweep-rate voltammetry was reported by Von-Vandrus2ka and Marashin /56/. Kirschenbuechler and Latscha /57/ report on computer-aided rapid polarography (CAR polarography) with E-t-i hypersurfaces as improvement and replacement of conventional polarographic techniques. The advantages are outlined of a computer-aided technique for recording three- dimensional (E-t-i) d.c. polarograms. Fielden and McCreedy /58/ report on voltammetric instrumentation for arrays of individually controlled electrodes and their potential for industrial process measurements. A computerized measurement and evaluation procedure for linear sweep and cyclic

418 Läszlo Kekedy-Nagy Reviews in Analytical Chemistry voltammetric methods was developed by Simon and Kädär /59/. The new recording and evaluation procedure for computerized instrumentation is useful in carrying out two basic methods, namely LSV and CV at high rates of polarization. The LSV and CV curves can be displayed in the form of a table or a figure. The noise present in either type of curve can be filtered by applying a digital filter. In some cases computers are used as function generators to generate the perturbation signal in voltammetry. He and Faulkner /60/ present a flexible function-generator for computer-based electrochemical instruments. It contains a 16 bit D/A converter, a 4 bit synchronous up/down counter, a parallel input/ output interface and a programmable timer. Senaratne and Hanek /61/ describe a digital a.c. voltammetric technique in which the perturbation signal is obtained from a computer-controlled analogue function generator. The device overcomes the limitation of the upper frequency inherent in computer-generated sinusoidal signals. The frequency of the sine wave was computer-controlled. A program based on the Fast Fourier Transform (FFT) algorithm was used to extract the frequency information from the total cell current and to discriminate against charging current. Fung and Mo /62/ used a computer-generated square waveform for the SW voltammetric determination of the ascorbic acid in soft drinks and fruit juices using a FIA system. A computer-based programmable waveform generator was described by Mozota et al. 163/, and a versatile, easy-to-build digital function generator for voltammetry was proposed by Douche /64/. Developments, trends and commercial availability of instrumentation (hardware and software) in microcomputer-based voltammetry are thoroughly summarized by Bond and Svetska 1651. They state that, as voltammetry is based on the use of current-potential-time curves, voltammetric instrumentation is highly suited to computer-based forms and technology. The introduction of more powerful software into commercially available microcomputer-based instruments in the 1990s should mean (i) an improvement in the accuracy and speed of measurements, (ii) an increase in data throughput, (iii) automated preparation of the samples (e.g., by robotics), (iv) improved planning and control of experiments, data acquisition and data handling, (v) the introduction of new forms of calculation, involving for example application of statistical methods, digital smoothing and transformation of data, employment of methods of artificial intelligence and chemometrics, and (vi) the saving and printing of results in a more efficient format.

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COMPUTERS IN ANALYTICAL PRACTICE

In this section concrete applications of computers in analytical practice are presented for the period under review (1980-1998). Computer-aided differential thermal conductivity-data processing in the C, Η and Ν determinations in elemental analysis was reported by Tanimoto et al. 1661. Display of the real color of precipitates in inorganic qualitative analysis was performed by computer Ι6ΊΙ. Routine titrations per computer were discussed by Strohm et al. /68/. The Titrino automatic titration system is described. The system is compact and has a PC-user interface with titration- running software providing remote control of the titration from the PC. The data storage capability and the numbers of samples that can be analysed make the system compliant with ISO 900X and GPL. The PC can guide the operator through a procedure and provides modification when reagents need to be changed or when electrodes need to be calibrated. A compact least- squares computer program for acid-base titrations was proposed by Rigano et al. 1691. The program, written in BASIC and FORTRAN, is based on an algorithm incorporating the various titrimetric parameters. A computer program for interpretatioin of titration data was published by Kucharkowski and Kluge /70/ too. The program was written in FORTRAN IV for use on small computers for determination of the end-point of titrations. The experimental data can be entered manually, read from tape, or fed directly from the analysis apparatus. They can be checked and, if necessary, corrected before calculation of the end-point from the slope of the titration curve. The result can be displayed on a screen, printed, or stored. Examples given are Potentiometrie titrations of Fe2+ with Ce4+ and of CI" with Ag+ and photo- metric complexometric titrations of Al3+, La3+ and Ca2+. Computers have been used for optimization of end-point determination in catalytic titrimetry Π\Ι. For this purpose simulated titration curves were recorded in the integral or derivative mode. Various factors, which influence the accuracy of the determinations, were tested. The best procedure for end-point determinations involved graphical representation of straight portions of the titration curve before and after the e.p. A review with 58 references on the use of computers in analytical chemistry generally is also presented. Linear transformation of coulometric precipitation titration curves was used for off-line computer- aided evaluation of the quantity of electricity (Q) assumed in a given titration ΙΊ2Ι. The Q-value was computed as the slope of a straight line obtained by

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linear regression of the mathematically transformed titration curve. Arnold et al. ΙΊ7>Ι report on an equilibrium titrator based on a PC. The titrator uses an IBM computer with 64 kbyte RAM and allows unattended collection of high- precision Potentiometrie data from a motorized burette under control of a BASIC program. Titrations can be performed in mV and pH modes and titrant increments can be of constant volume or adjusted to provide constant changes in mV or pH. These methods are suited to obtain high-precision equilibrium data for metal-complexation studies. A microprocessor- controlled system for neutralization of the rest acidity of esters using a glass indicator electrode, was elaborated by Pap et al. ΠΜ. Computer-aided titration of an electroplating bath was made by Rehwald 1151. An algorithm to control and evaluate titrations whose indicator functions consist of, or can be transferred into, rectilinear sections was described by Buschmann et al. 1161. The system was used to perform amperometric titrations of Bi with EDTA. To simplify the amperometric measurement steps for quantitative and mechanicstic studies, a program in Turbo Pascal was elaborated by Wring et al. 1111 with the use of vitreous carbon electrodes. By application of Cottrell's equation and with the use of chronoamperometry of a solution containing [Fe(CN)6]4~, the effective working area of the above electrode was determined. The number of electrons transferred during the electrolytic oxidation of ascorbic acid was also evaluated. Rapid determination of dissolved oxygen by using sub-micro-electrodes and a computer-aided chronoamperometric method has been published by Palys et al. 118/. Best results were obtained with a C-disk microelectrode of 8 μηι. This method combined with computer control of online calculations provided a rapid, simple analysis of dissolved oxygen. A computer-aided in situ calibration method of oxygen sensors in sterile fermentation was

elaborated by Voss et al. 1191, in which the function p02 vs. time is measured continuously and modulated with the use of periodic rectangular or triangular test signals. A microcomputer evaluates the sensor response, and the corrected slope, zero-current response time and hysteresis of the sensor are calculated. The development of sensors, which can operate in conjunction with computers, is summarized by Wright /80/. Chan reports on a pH-measuring system in which an IBM PC was interfaced to an Orion SA 700 meter via the RS-232C protocol carrying out acid-base titrations /81/. Menzl et al. /82/ have reported on a self-adaptive computer-based pH measurement and fuzzy control system. Applications could include pH-control of fermentation

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processes and neutralization of waste-water streams. Several publications deal with the use of computers in potentiometry. Generally the software contains the different evaluation procedures, like smoothing, the Gran method and nonlinear regression analysis. A versatile, inexpensive single- board computer-controlled potentiostat has been constructed by Von- Vandruszka and Gottschalk /83/. The instrument is controlled by an Apple microcomputer and provides a wide range of data handling and storage options. Linear cyclic voltage scans may be carried out with a choice of five scan rates. The design and construction of a microprocessor-controlled potentiostat is described by Eccles and Purdy /84/. Particular emphasis is placed on the IBM-PC computer interface and control and modifier boards. Lingerak et al. /85/ describe a computerized flow-injection analysis (FIA)- differential pulse anodic stripping voltammetric system controlled by an Apple II computer /85/. Application of the method of seawater, surface water and acid digests of biological samples is discussed. Wasberg and Ivaska /86/ also published a computer-controlled FIA system, while Dohmen and Thijssen /87/ reported on a FORTH package for computer-controlled FIA analysis. The system comprises a computer-controlled sample changer, injection device and digital photometer for use with an Apple II microcomputer. Prop et al. /88/ describe a similar instrument - a computer- controlled sample changer, injection device and digital photometer - the program being written in BASIC. Mynt et al. /89/ have reported on a computer program for radiometric flow-injection analysis. A PC/XT computer enables instrument control and data processing, via an interface card, which permits direct reading of the γ-ray counter. Extended application of computers in chromatography continues. Simon et al. 1901 report on the application of computers to qualitative analysis by gas chromatography. A computerized method is described for identification of compounds by comparison of retention indices. An automatic gas- chromatographic retention time matching method applied to synthetic petroleum products (Fischer-Tropsch) was published by Snavely and Subramanian /91/ using HP Chemostation software. Computer-based graphical display tools of chromatograms are described by Ouchi 1921. Improvement of GC-MS analysis of organochlorine pesticides in sediments by use of a computer-optimized temperature program is reported by Pichler et al. 1931. A simulation technique of the chromatographic process with an analogue computer was proposed by Lehnart and Zinn /94/. De-Galan 1951 published a computer-aided optimization method of high-performance liquid

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chromatography (HPLC). Berridge summarizes computer-aided methods in liquid chromatography 1961. Pollak discusses the use of computers in quantitative thin-layer chromatography (TLC) 1911. There are many publications dealing with computer-aided spectroscopy. Duclos summarized UV/VIS absorption spectroscopy /98/. Choulis et al. 1991 report on computers in drug analysis via IR spectroscopy. Leporati /100/ presents a rapid and precise computer-aided method for spectrophotometric determination of substances in solution. Vershinin et al. /101/ have reported on computer-aided qualitative analysis of complex mixtures of polycyclic aromatic hydrocarbons by quasi-linear luminescence spectra. Feng et al. /102/ present a computer-aided UV/VIS spectrophotometric analysis system. Second-derivative spectra of the ultra-violet and visible absorption spectra were obtained by a personal computer-aided Savitzky-Golay method /103/. The use of expert system shells in the design of automated absorption spectrometry is discussed by Bowelt and Stillman /104/ in an article entitled "Computer-aided chemistry VI". The use of expert system shells to solve chemical problems is discussed in general. The elaborated system can be used to control all aspects of metal-ion determination by atomic absorption spectrometry (AAS). Woodruff summarizes the use of computers to interpret IR spectra of complex molecules /105/. The same topic is also discussed by Ford /106/. Computer-aided analysis of infrared circular dichroism and absorption spectra is presented by Galat /107/. Shabanov et al. /108/ summarize the use of computers in atomic spectroscopic research and AAS analysis of metals and alloys. Lopez-Garcia et al. /109/ describe a computer-controlled manifold for online dilution of solutions that are too concentrate to be analysed by direct aspiration into the flame. Improvement of atomic emission spectral analysis (AES) of metals and alloys using computers is presented by Morozov /110/. A system for automatic selection of operating conditions (parameters and methodology) for analysis by ICP AES is proposed by Branagh et al. /111/. Computer-aided quantifi- cation of AES (in this case Auger emission spectroscopy) and XPX (X-ray photoelectron spectroscopy) is proposed by Moir et al. /112/. Price discusses the influence of computers, microprocessors and micro- electronics in the evaluation of XRF (X-ray fluorescence) instrumentation /II3/. Driscoll and Jakobus /114/ describe a PC-based energy-dispersive XRF analyser for analysis of environmental samples. A microcomputer linked to the XRF equipment has been used by Pascual-Fernandez et al. /II5/ for correction for the Ni-Fe-Cr inter-element effect in analysis of alloy steels by

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X-ray fluorescence spectrometry. Leyden et al. /II6/ discuss the impact of personal computers and new instrumentation on environmental applications of the X-ray fluorescence. Gilbert et al. I\\ΊI summarize the use of computers in multi-element analysis of high-purity compounds and metal- organic materials by neutron-activation and X-ray spectrometric methods. Coates discusses the problems of computers in spectroscopy /II8,119/. Matherny reviews the use of computers in emission spectrometry /120/, while Matherny and Ondas summarize the use of computers in emission spectroscopy for the estabalishment. evaluation and linearization of analytical calibration curves /121,122/. A microcomputer-aided microdensitometer system for quantitative evaluation of spectrograms was published by Kardos and Zimmer /123/. Martinsen presents and survey of computer-aided methods for mass-spectral (MS) interpretation /124/. Drinkwater et al. /125/ describe a personal computer-based data control interface for neutralization/re- ionization tandem mass spectrometry. Developments in computer-aided mass spectrometry together with a networked workstation environment for data analysis systems are presented by Chapman and Ryan /126/. Control of sample evaporation and selected-ion monitoring by PC in MS is discussed by Varmuza et al. /127. Computer utilization in the Food and Drug Administration's Bureau of Foods MS laboratory is presented by Dreiffiiss and Dusold /128/. A single-board VME Mössbauer-spectroscopy module was presented by de Blois et al. /129/. A detailed description is given of a VME module for interfacing a Mössbauer spectrometer with a computer system. The impact of computers in thermal analysis was reviewed by Wunderlich /130/. An investigation of computer-aided differential thermal analysis of drugs was presented by Braun and Wollmann /131/. The system was calibrated thermometrically or calorimetrically. Several pharmaceutical prepara- tions were estimated with the use of a modified vant'Hoff equation. The results are compatible with those by DSC. Amano et al. /132/ report on computer-aided analysis of pyrolysis gas-chromatographic and thermogravi- metric data of polymers. A personal-computer-based system for the automation of kinetic thermometric methods of analysis is reported by Oms et al. /133/. The system is of modular design and permits acquisition of experimental data and application of the four classical kinetic methods of analysis. Fang et al. /34/ report on the earlier application of 8 byte computers in thermoanalysis /134-139/. A microcomputer-controlled titration calori- meter was described by Caceci and Choppin /140/.

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The use of computers in different domains of stripping analysis - anodic stripping voltammetry (ASV), cathodic stripping voltammetry (CSV), Potentiometrie stripping voltammetry (PSV) and adsorptive stripping voltammetry (AdSV) - is also discussed in the literature. Malyaev and Grigor'ev /141/ present an electrochemical setup with the use of computers in stripping voltammetry to select a low-amplitude analytical signal. The setup, consisting of a stationary Hg-electrode, a PU-I polarograph, an A/D converter, a microcomputer, interfaces, a XY chart recorder and an appropriate software, enables digitalized separation of the analytical signal, e.g., a differential pulse voltammetric peak from the background electrolyte signal. Hernandez-Brito et al. /142/ have developed a computerized electrochemical system for the determination of heavy metals and cysteine by ASV and CSV with different types of waveform. Computer automation of ASV with a mercury-film wall-jet electrode was presented by Gunashingham et al. /143/. Computer control of the system is used to adjust the plating of ions to be analysed. The criteria for the wall-jet cell geometry are discussed. Subtractive hydrodynamic ASV is evaluated for d.c., differential pulse and staircase waveforms for both "pre-plated" and "/'« situ plated" mercury films. Bond et al. /144/ report on the development of a microprocessor-based electrochemical system interfaced to a microcomputer system for differential pulse anodic stripping voltammetry in different time domains. The instrument described has been developed for use in chemically hazardous, radiation or clean laboratories. The microcomputer system is external to the laboratory and has all the required peripherals associated with larger laboratory computers. Yang and Huang /145/ present a review with 20 references on the development and application of computer-based Potentiometrie stripping voltammetiy including multi-channel, multi-step, continuous multi-sweep, differential multi-sweep and computer-based flow potential stripping voltammetry. Cladera et al. /146/ describe a semi-automated system for Potentiometrie stripping analysis with RS 232 C interface and personal computer. The software developed allowed automated control of the pre- electrolysis time. Economu et al. I\MI report on batch and flow determinations of U (VI) by adsorptive stripping voltammetry on Hg-film electrodes. For the flow-through configuration the combination of a novel wall-jet cell with an automated flow system and a commercial computer- controlled potentiostat allowed complete keyboard control of the sequence of operations. Schreiber and Last /148/ developed a computer-controlled coulostatic stripping analysis system used for analysis of solutions containing

425 Vol. 19, No. 6, 2000 Computer-Aided Analytical Methods trace quantities of heavy metals (Cd2f, Pb2+, Cu+). The chronopotentiometric and linear sweep anodic stripping modes have been demonstrated. By summation of data from multiple stripping scans an increased sensitivity can be achieved The LSI-microcomputer controls the instrument and performs data acquisition and reduction. Timing control of the motors (rotating electrode) and gas flow is performed by the computer to yield greater precision and easy operation. The literature contains several publications on the use of computers in very different domains of analytical practice. Reviews with many references on the use of computers in biochemical analysis were published by Crabbe /149/ and by Carrick on analysis of surfaces and surface coatings /150/. The general principles and merits of the following techniques are discussed: X-ray photoelectron spectroscopy, secondary ion MS and ion scattering spectroscopy. Tarasov et al. /151/ and later Tarasov /152/ have reviewed the use of computers in micro-probe studies. Schneider et al. /153/ report on the development and application of a computer-controlled system for an analytical microscope. The computer controls the high-voltage supply lenses and alignment system. The system was used in conjunction with a digital image-acquisition system. A computer- based instrument for AC electrochemical measurements is presented by He and Chen/154/. Advantages of automation and computerization to a soil-testing laboratory are presented by Brown /155/, and in the water industry by Thomson /156/. The computer-aided interpretation of analytical data in water analysis, e.g., conductivity, pH and hardness for evaluation of the water quality for domestic or irrigation usage, was proposed by Gabriels et al.

/157/. Computer-aided processing of BOD5 (biological oxygen demand in 5 days) was published by Gottschalk and Lohmaier /158/. Continuous Polarographie control of the concentration of industrial solution components by computer-aided solid renewable electrode was investigated by Kletenik et al. /159/. Heidenreich and Kloeden reported on the interpretation of particle size analysis results by using a computer /160/. Possibilities and trends in the introduction of computers into metallurgical laboratories are discussed by Luft and Richling /161/, and in the iron and steel industries by Baumgart and Busch /162/ and Taguchi and Hamada /163/. Further applications of computers are discussed: in chemometrics and analytical chemistry /164/, in large scale activation analysis /165/, in instrumental chemical analysis /166,167/, in classical chemical analysis /14/, to

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characterize chemical systems /168/, to analyse gamma spectra /169,170/, applications in a detergents laboratory /171/, in a lipid laboratory 172/, in analysis of pesticides /173/, landfill gas /174/ and for automation of coal petrographic analysis /175/. A computer-based trigger system for laser- induced plasma spectrometers is described by Chan et al. HI61. PC-based LIMS (Laboratory Information Management System) for the 1990s is presented by Verost and Levey /177/.

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