Abstract: This paper reports on the amperometric detection of electroinactive sulfonic acids, organic acids and phosphate eaters subsequent to chromatographic separation: The working electrode consisted of a 3 mm diameter grassy carbon electrode, coated with electrochemically deposited polypyrrole. The electrode was placed in a large Volume wall jet cell, and a potential of + 750 mV versus SCE was applied. The electroinactive analytes were detected as they induce a current, which originates from their effect on the doping of the polypyrrole coating. This allows sensitive detection of electrochemically inactive organic acids. Detection limits for sulfonic acids in LC with 4.6-mm ID columns (1 mL min-1 flow rate) were 3 ng. The electrode had a linear response in the 1 x 10^-6 to 1 x 10^-3 M concentration range. The response time of the electrode was 3.6 s in a FIA set up. Peak heights are quasi independent on the flow rate, indicating that the phenomenon is not controlled by mass transfer in the diffusion layer. The electrode activity decreases to 50% after 24 h of continuous use. The electrode can be partly reactivated after application of a potential of - 300 mV (versus SCE) for 1 h.

Abstract: A novel amperometric electrode based on a conducting polymer is presented and its properties are compared with those of a glassy carbon electrode. The electrode material was made by mixing 2,5-dimethoxy-1,4-bis(2-(3,4,5-trimethoxy-phenyl)ethenyl)benzene with iodine and polycarbonate. The blend was coated on a glassy carbon electrode by evaporation from a chloroform solution. Catecholamines were used as test substances in LC and FIA measurements. They were oxidized at a potential of +0.7 V (vs. SCE). The electrode exhibited a linear response for injected concentrations from 2.5 X 10^-6 M to 2.5 X 10^-3 M. It had a response time of 1.2 s and a coulometric efficiency of 0.74% at a linear flow rate of 1 mL/min. The electrode material is stable for several months under normal operating conditions. Hydrodynamic voltammograms showed E1/2 values shifted by approximately 100 mV as compared to glassy carbon. The novel redox-conducting coating is proposed as an alternative material for the development of enzyme electrodes and chemically modified electrodes.