Automated analytical systems

Trojanowicz, M., Electrochemical Detectors in Automated Analytical Systems , in Modem Techniques in Electroanalysis, Vanysek P. (Ed.), Wiley-Interscience, New York, 1996, pp. 187-239. This chapter contains a fairly thorough discussion of the possible arrangements of electrodes within flow systems, and for a variety of applications. 

Compatibility between sensors and automatic and automated analytical systems is crucial as it allows two Analytical Chemistry trends to be combined (see Fig. 1.1). Probe-type and planar sensors can be used in automated batch systems including robot stations, as well as in continuous (mixed in-line/on-line) systems. On the other hand, flow-through sensors are only compatible with continuous configurations. 

The technical development is still very rapid and addresses the growing need within process monitoring. The current trend includes further improvement of instrument design for smaller and more rugged equipment, integration into automated analytical systems and miniaturisation for multiple installations and portability. 

The state-of-the-art laboratories are equipped with the latest models of analytical instruments and computer systems, while others may have older, less sophisticated equipment or a mix of modern and outdated instruments. The goal of production laboratories is to analyze samples in the fastest possible manner. To be competitive, laboratories must have fully automated analytical systems allowing unattended sequential analysis of samples and computerized output of analytical results. Data acquisition computers, programmed with specialty software, control analytical instruments, collect the raw data, and convert them into analytical results. These computers are typically interfaced with the LIMS, which networks different laboratory sections into a single computer system and transforms analytical results into laboratory reports. 

One of the most successful applications of microsystem technology is the use of pTAS in diagnostics [332-335]. Microreactors have been integrated into automated analytical systems, which eliminate errors associated with manual protocols. Furthermore microreactors can be coupled with numerous detection techniques and pretreatment of samples can be carried out on the chip. In addition, analytical systems that comprise microreactors are expected to display outstanding reproducibility by replacing batch iterative steps and discrete sample treatment by flow injection systems. The possibility of performing similar analyses in parallel is an attractive feature for screening and routine use. 

In many ways, this example is typical of modem analytical problems, where increasingly people are looking to automated analytical systems to provide the answer. It also demonstrates that with the increasing complexity of such systems, it is no longer sufficient for the analyst to rely on his knowledge of chemistry alone. In... 

Y. L. Hsieh, H. Wang, C. Ehcone, J. Mark, S. A. Martin, and E. Regnier, Automated analytical system for the examination of protein primary structure, Anal. Chem. 68(3) 455 (1996). 

Nephelometric and turbidimetric methods (see Chapter 3) are performed on most current automated analytical systems, although most nephelometric assays are performed on dedicated instruments. RID requires no instrumentation other than pipettes, although some type of illuminated plate reader is advantageous. RIA requires radiation scintillation counters and an automated pipetting station. 

Shah, K.P. Chang, M. Riley, C.M. Automated analytical systems for drug development studies. 3. Multivessel dissolution testing system based on microdialysis sampling. J.Pharm.Biomed.Anal., 1995, 13, 1235-1241... 

Sioufi, A. Richard, J. Mangoni, R Godbillon, J. Determination of diclofenac in plasma using a fully automated analytical system combining liquid-solid extraction with liquid chromatography. J.Chromatogr., 1991, 565, 401-407 [plasma SPE pharmacokinetics LOQ 31 nM]... 

Filter fluorometers can be used in automated analytical systems, for example the Technicon AutoAnalyzer . 

As an example, I will use the determinations of DOC and DON, partly because the discussions are very recent and partly because they are very familiar to me. The question of the accuracy of measurements of DOC in seawater has been disputed at least since the publications of Putter [62] and Krogh [63] the early work has been reviewed at length in an earher pubhcation [64]. While a variety of wet oxidation methods [65] were proposed for marine samples, the use of persulfate [35] provided the first real approach to a standard method. Persulfate oxidation, however, hke all purely chemical oxidations, was a batch process, and not easily automated. A number of workers proposed photo oxidation using ultraviolet (UV) hght [66-70], and automated analytical systems which produced data almost in real time were soon constructed [71-73]. Commercial units soon appeared, but many of the units in the field were jerry-built, constructed out of parts scavenged from discarded autoanalyzers formerly used for nutrient analysis. 

McLafferty, F. W. An automated analytical system for complex mixtures. In Analytic pyrolysis. Jones, C. E. R., Cramers, C. A. (eds.), p. 39. Amsterdam. London, New York Elsevier, Publ. Co. 1977... 

Chemical reactions for cleanup are especially interesting in the analysis of organic compoimds at very low concentrations in samples contaminated with many interfering compounds. One of the remarkable features of reaction detectors is their abifity to fit into automated analytical systems. Their selectivity and sensitivity in the reaction itself will often permit a drastic reduction in the amount of sample preparation or the requirements for a powerful separation. Band broadening and interference of the detection signal with the reagent can be a problem. 

The large amount of data produced by an automated analytical system has to be processed by an on-line computer. Owing to the miniaturization of analytical and electronic components multi-channel nutrient analysers may be designed as rather compact and handy units, even fit to be used on small vessels. However, they are very complex and by no means switch on-measure-switch off machines. Well trained personnel, skilled in analytical chemistry, mechanics and data processing, and a great deal of experience is required to reliably operate nutrient analysers. Automated analysis is most profitable in every day routine measurements of large sample numbers. A few occasional nutrient samples, however, are better analysed by manual methods. 

All modern automated analytical systems are wet chemical analysers based on the Continuous Flow Analysis (CFA, Technicon) introduced by Weichart (1%3) and Grasshoff (1964). For seawater analysis a continuous stream of sample water is taken either from sample bottles or from a direct seawater intake. All operations such as the addition of reagents, heating, dialysing or phase transfer are performed in a closed tubing system between the inlet and flow-through cell of the detector system (usually a spectrophotometric cell). 

However, increasing environmental concerns have fostered the development of automated analytical systems for environmental monitoring with added features for in situ, real time and remote operation. The use of electrochemical sensors as detectors integrated in automated flow systems has proved to achieve simple, robust, and automatic analyzers for enviromnental monitoring. 

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