Application of electrodes modified with ion-exchange polymers for the amperometric detection of non-redox cations and anions in combination to ion chromatography

An amperometric sensor for non-electroactive ions was designed, evaluated i n flow injection analysis, and applied as a novel detector in suppressed io n chromatography. It consists of a carbon paste electrode modified with eit her a polycationic or a polyanionic polymer containing a suitable charge tr ansfer mediator (Fe(CN)(6)(3-) or Cu2+ operating in an indirect amperometri c mode. The detection mechanism involves ion exchange between the non-redox ionic analyte and the electroactive mediator, in the polymer particles loc ated at the electrode surface, followed by the electrochemical transformati on of the mediator species leached out of the polymer at the electrode I so lution interface. As detection was achieved in the absence of added support ing electrolyte, the amperometric signal contains both faradic and capaciti ve components. Optimisation was performed to get the highest faradic signal s, by varying various experimental parameters (i.e. applied potential, comp osition of the electrode). These systems were then successfully applied to the analysis of mixtures of cations (Li+, Na+, K+, NH4+ , Ca2+, Mg2+) and a nions (F-, Cl-, NO2- , NO3- , SO42- , PO43 -) subsequent to chromatographic separation. Good operational stability was observed, Wit typically less th an 5% signal loss for 50 successive measurements. (C) 2001 Elsevier Science Ltd. All rights reserved.