Coated graphite-epoxy ion-selective electrode for the determination of chromium(III) in oxalic medium

Abstract

A coated graphite-epoxy chromium(III) ion-selective electrode, based on the ion-pair between [Cr(oxalate)3]3- anion and tricaprylmethylammonium cation (Aliquat 336) in a poly(vinylchloride) (PVC) matrix is constructed. A thin membrane film of this ion-pair, dibutylphthalate (DBP) in PVC was deposited directly onto a Perspex® tube containing a graphite-epoxy conductor substrate attached to the end of a glass tube. The effect of membrane composition (ion-pair, DBP and PVC), oxalate concentration, pH and some cations and anions upon the electrode response is investigated. The electrode shows a linear anionic response to E vs. log [Cr3+] in the chromium(III) concentration range from 2.9×10-6 to 10-2 mol l-1, and a slope of -18.7±0.5 mV dec-1, at pH working range of 2-8 and 0.3 mol l-1 oxalate concentration. Variation in the potential of about ±2 mV was observed during a working day of 7-8 h. The response time was less than 5 s and the life time of this electrode was superior to 1 year (over 1500 determinations by each polymeric membrane), with a practical detection limit of 2.1×10-6 mol l-1. Application of this electrode for chromium(III) determination in some food materials and various types of plants is described. © 2003 Elsevier B.V. All rights reserved.