Pulsed amperometric detection of carbohydrates, amines and sulfur species in ion chromatography -the current state of research

Abstract

A review is given of so-called pulsed amperometric detection at Au and Pt electrodes. Of greatest interest is the application of pulsed amperometric detection for polar aliphatic compounds not easily detected by conventional photometric or fluorometric techniques. The anodic detection mechanisms are electrocatalytic in nature under the control of potential-dependent surface states. Oxidations of carbohydrates at Au electrodes in alkaline media occur in a potential region where a submonolayer of adsorbed hydroxyl radicals (·OHads) is formed and speculation is offered on the role of this species in the anodic mechanisms. Very little anodic signal is obtained at Au electrodes for low-molecular-mass n-alcohols; however, a large response is obtained from oxidation of the alcohol moiety of n-alkanolamines. This is attributed to the beneficial effect of adsorption via the amine moiety with the result that the residence time of the molecules at the electrode surface is increased to give a high probability for ultimate oxidation. Amines and sulfur compounds with non-bonded electrons on the N and S atom, respectively, are adsorbed at Au electrodes and are oxidatively desorbed concomitantly with formation of inert surface oxide (AuO). The simultaneous formation of surface oxide produces a large background signal in pulsed amperometric detection. Hence, a modification of the pulsed waveform is described whose application is called integrated pulsed amperometric detection. Applications are shown for pulsed amperometric detection and integrated pulsed amperometric detection in ion chromatography to illustrate strengths of these combined technologies. © 1993.