Behavior of the Cadmium Ion-Selective Electrode in Alcohol–Water Mixtures

Abstract

In an investigation on the behavior of a cadmium ion-selective electrode in methanol–water and ethanol–water mixtures, potential measurements were carried out with a digital pH/mV meter, a cadmium ion-selective indicator electrode and a silver–silver chloride reference electrode. The calibration curves, slopes of the response, response times, effects of temperature, relation between the potential and the pH-meter reading and selectivity of the electrode were discussed. The response of cadmium ions (electromotive force) was linear between 10−7–10−2 mol dm−3 in water. However, the linear range became narrower with an increase in the alcohol content. The slopes in alcohol–water mixtures (27–33 mV/decade in methanol–water mixtures, 21–29 mV/decade in ethanol–water mixtures) were nearly equal to the Nernstian slope (29.6 mV/decade). The response times of the cadmium ion-selective electrode in 99 v/v% methanol and in 99 v/v% ethanol were somewhat long, but were still within 5 min for all solutions consisting of 10−5–10−1 mol dm−3 of cadmium ions. The selectivity of the cadmium ion-selective electrode in various media was examined by the mixed-solution method using potassium, sodium, calcium and magnesium ions as the interfering ions. It was found that a cadmium ion-selective electrode could be used to determine cadmium ions in an alcohol–water solution, although the response time became longer and the linear range of the response became narrower with an increase in the alcohol content.