Automated voltammetric analysis

The advent of inexpensive computing power has changed dramatically the way voltammetric determinations are performed. In particular, automated multielement determination schemes and high speed flow systems are now available for convenient and effective trace metal determination in biological samples. 

An automatic system, that couples the speed of square-wave polarography with a control of the sample handling is available commercially (Yarnitzky, 1985). Further reduction in assay time is achieved using a nebulizer to eliminate the time-consuming deaeration step. Microprocessor-based voltammetric analyzers are available from companies such as EG G PAR, Metrohm, Bioanalytical Systems, ECO Chemie or Tacussel. 

COMBINATIONS OF ELEMENTS MEASURABLE BY THE MULTIELEMENT VOLTAMMET-RIC SCHEME IN A SINGLE SAMPLE 

Elements determined sequentially No. of elements Range of techniques utilized Total analysis time , min 

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Figure 9 Manifold of an automated voltammetric system for field analysis of trace metals. Sample pickup could be from sample changer, or pumped seawater supply.

The versatility of the flow system enables the analyst to perform voltammetric analysis with the same detector or even using similar apparatus. Suteerapataranon etal. [116] have proposed the use of components of the SIA system similar to the FIA system with exception of the syringe pump and the 10-port selection valve for the simultaneous quantification of cadmium, copper, lead, and zinc. The proposed FIA and SIA systems associated with stripping voltammetry were easily operated and required little amount of sample (30 pi provided reproducible current signals) with high degree of automation. 

Figp 1X2 An automated instrument for routine voltammetric analysis. (Courtesy 0 G and PAR Electrocbeniical Instruments Divirioo.)... 

Voltammetry experiments are not often performed in flow cells for analytical purposes. One reason for this is the special problem of ohmic potential losses (iR drops) at an electrode in a confined stream. Another reason is the problem of precisely pumping solution at a carefully controlled velocity. In general, rotating electrodes are more easily controlled and do not involve serious plumbing problems. On the other hand, flow cells operated at a fixed potential (i.e., at one point along the steady-state voltammetric curve) are eminently useful for electrosynthesis, chromatographic detection, and automated analysis systems. These features will be described in later chapters. 

Maxwell, T.J. and Smyth, WF. (1996) A study of the stripping voltammetric behavior of selected metal chelates and its application to automated analysis of river waters. 

Finally, the possibilities of automation of amperometric and voltammetric electroanalysis should be stressed, as well as the use of solvents other than water43. Pulse techniques are semi-automated by nature the responses can be transmitted directly to a microcomputer for immediate analysis. Fast on-line analysis in flow systems with automated calibration is one of the great advantages, which will be much exploited in the future. 

For the determination of tin(ll) in kits an EG 8c G polarographic analyzer (model 384) with a static mercury drop electrode (model 303) and a cabinet reference electrode was used. Model 384 is a microprocessor-based polarographic analyzer with built-in floppy disk memory to store and recall analytical curves. By controlling each step of the analysis, the microprocessor automates polarographic and voltammetric measurements. All experimental parameters may be chosen by the operator. Concentrations are computed automatically aud recorded iu the rauge from 0.001 ppb to 9999 ppm. 

SIA has been proposed as an alternative to FIA especially in monitoring of industrial processes where robustness, low reagent consumption, stability, low maintenance, versatility, and automation are essential requirements. There are various review papers describing the fundamentals, potentialities, and limitations of SIA [16, 43, 44, II0-II2]. However the applications in agriculture and food analysis have still presented very few examples using electrochemical detectors, in particular voltammetric sensors. 

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