Amperometric Detection of Nonelectroactive Cations in Electrolyte-Free Flow Systems at Zeolite Modified Electrodes

Abstract

An electrochemical detector was designed and constructed, based upon a thin-layer cell with a working electrode prepared from carbon paste modi®ed with copper-(or silver-) exchanged zeolite particles. This electrode was then evaluated as a sensor for nonelectroactive cations in an electrolyte-free¯ow injection system and as an amperometric detector for suppressed ion chromatography. In the absence of supporting electrolyte, a higher signal-to-background ratio enhanced by about two order of magnitude the response obtained in electrolytic medium. Peak currents resulted from an important faradic component which was due to the electrochemical activity of the mediatorcontaining zeolites, while the capacitive counterpart was much lower. When applied to the analysis of alkali, alkaline earth metal and ammonium ions, in combination with a suppressed ion chromatography system, the zeolite-modi®ed detector gave rise to reproducible amperometric responses. This resulted in chromatograms comparable to those obtained simultaneously by using a conductivity detector in series, and any extra-column effects were never observed. The most sensitive responses were achieved when using zeolites displaying the largest pore size, the highest ion exchange capacity, and the most mobile mediator, to ensure the highest exchange rates for the analytes within the zeolite framework.

Electroanalytical Flow Measurements–Recent Advances

“…Electrooxidation at a nickel-based chemically modified glassy carbon electrode was used for amperometric detection in HPLC of aliphatic amines [143], while modification of a GC electrode with Pd/IrO 2 codeposition was employed for detection of glutathione and cysteine in a brain microdialyzate [144]. The non-electroactive cations can be detected amperometrically at zeolite modified carbon paste electrodes [145], whereas various neurotransmitters were detected using a sol-gel carbon composite working electrode [146]. For modification of working electrodes for amperometric detection in HPLC conducting electrodeposited polymers are used also.…”

Anodic stripping voltammetric determination of mercury by use of a sodium montmorillonite-modified carbon-paste electrode

“…Sodium-montmorillonitie (SWy-2) is a kind of clay and has properties similar to those of other clays which can adsorb electroactive species for their direct determination. Clays have been widely used in electroanalysis for all kinds of purposes [14,15,16]. Sodium montmorillonite is an excellent cation exchanger and can attract cations by ion-exchange interactions.…”