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Computer-Aided Analytical Methods - a Review

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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 investi- gated 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, 413 Vol. 19. No. 6, 2000 Computer-Aided Analytical Methods 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- 414 Läszlo Kekedy-Nagy Reviews in Analytical Chemistry 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 electro- chemical 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 appli- cations 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 415 Vol. 19. No. 6. 2000 Computer-Aided Analytical Methods 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 inter-
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