Conducting polymer and oligomer micro-electrodes for the potentiometric detection of anions in capillary electrophoresis

Abstract

A conducting polymer (polypyrrole (PPy)) electrode and a conducting oligomer (CO) (phenylene vinylene trimer) electrode were used in a potentiometric detector for capillary electrophoresis (CE). The coated-wire electrodes had diameters of 250 μm. A home-made capillary + electrode holder was described which allowed an easy electrode alignment. Mixtures of low molecular weight carboxylic acids and inorganic anions were separated in a co-electroosmotic mode. They could be detected in injected concentrations down to 5 × 10 −6 M. The interelectrode variation was 7.2%, and the electrode materials were used for 2 months without loss of sensitivity. The addition of a quaternary ammonium ion to the buffer electrolyte as an electroosmotic flow (EOF) modifier was compatible with the electrode materials used. A theoretical model is presented to describe the behaviour of the coated-wire potentiometric detectors. The PPy electrode is very suitable for use in miniaturised separation systems as PPy can be deposited electrochemically.