Determination of acetate in wine : comparison between ion chromatography and ion-selective electrodes

Abstract

This thesis was carried out in the Laboratory of Analytical Chemistry at Åbo Akademi University in collaboration with the Analytical Chemistry Laboratory at Tartu University. This work was done under the supervision of Rose-Marie Latonen, Johan Bobacka, and Ivo Leito. In this thesis, potentiometric solid-contact ion-selective electrodes (SC-ISEs) selective to acetate were fabricated and used to determine acetate concentration in wine. The potentiometric determination of acetate concentration in wine was compared with measurements made by conventional ion chromatography (IC). The solid-contact (SC) acetate-selective electrodes were fabricated by galvanostatic electropolymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) on the surface of glassy carbon electrodes as the SC layer and drop-casting the acetate-selective ionophore 1,3-bis(carbazolyl)urea derivative containing membrane over the PEDOT layer. Both quantitative and qualitative determination of acetate in wine by SC-ISEs was evaluated by using the standard addition method. In parallel, the analysis conditions for acetate determination with ion chromatography were optimized to obtain better separation between lactate, acetate and formate by varying parameters such as the flow rate and the concentration of eluent components. The concentration of acetate in the same wine sample was measured by IC and potentiometric ISE techniques. A significant concentration difference was obtained between the two techniques. A higher concentration of acetate was obtained by the SC-ISEs compared to IC. It can be explained by the presence of lactate and formate ions in the wine sample that contribute to the ion activity measured by the acetate-SC-ISEs. Gradual leakage of the ionophore from the ISE membrane may also contribute to insufficient selectivity of the acetate-SC-ISEs used in this work.