Determination of electroinactive organic acids with LC and amperometric detection, using a PPy coated electrode.

This paper reports on the amperometric detection of electroinactive sulfonic acids, organic acids and phosphate esters subsequent to chromatographic separation. The working electrode consisted of a 3 mm diameter glassy 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 1x10(-6) to 1x10(-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.