Abstract: A tetrathiafulvalene - tetracyanoquinodimethane polymer paste electrode was constructed by the procedure described by McKenna et al. (Ibid., 1988, 206, 75). The electrode was mounted in a flow cell and used as the detector in a flow injection system. The performance of the system was assessed by studying the electrochemical behavior of quinol, dopamine and ascorbic acid; the results were compared with those obtained with active and inactive vitreous-carbon electrodes. The sensitivity of the electrodes depended on the formation of an active electrode area and on the kinetics of the analytes. The dependence of the response on flow rate was also investigated.

Abstract: The principal feature of the cell is geometrical symmetry in the radial direction between the working electrode and the counter-electrode; this arrangement produces well-defined hydrodynamic voltammograms. The reticulated structure of the working electrode provides a large ratio of surface area to volume, so allowing rapid coulometric conversion without significant band broadening when the detector is used for flow injection analysis (FIA) or HPLC The sensitivity and detection limit (signal-to-noise ratio = 2) for quinol, dopamine, adrenaline and amoxycillin were determined, and the sensitivity was found to approach the theoretical value of 96,485 C per equiv at flow rates of 1 mL min-1, with detection limits close to 1 pequiv for the compounds studied by FIA. The residual current decays in <30 min to a steady-state value of ~1 µA, and detection at the pequiv level is possible after this equilibration period. It is concluded that the detector performs as well as existing amperometric detectors available for FIA and HPLC.

Abstract: The cited technique is a non-flow injection technique in which a small liquid sample is injected towards a nearby detector surface immersed in a large volume of stirred blank solution A transient peak-shaped response is recorded by the detector, which corresponds to passage of the sample zone over its surface. Determination was carried out in a cell that consisted of a retangular-shaped container (10 cm x 10 cm x 8 cm) made of Plexiglas and in which an inverted working disc electrode (e.g., a carbon-paste disc electrode) was introduced at the bottom corner. A micro-pipette, which was used for sample introduction, was positioned so that its tip was ~2 mm above the disc electrode surface. The counter and reference electrodes were mounted through two holes in the top cover of the cell, and the cell was placed over a magnetic stirrer. The system was used for the determination of K4Fe(CN)6, paracetamol, quinol, ascorbic acid and glucose with use of 0.1 M phosphate buffer (pH 7.4), 0.1 M KCl or 1 M NaOH as supporting electrolyte. In all instances, response increased rectilinearly with increasing analyte concentration. The technique is rapid and simple and performs well in terms of sensitivity and reproducibility.