Alternate sample/standard exchange method using a pair of identical ion-selective electrodes for the improvement of precision in an automated potentiometric analysis system

Abstract

The use of an automated potentiometric analysis system with a pair of identical ion-selective electrodes as the detector is described. The sample and standard solutions were introduced simultaneously into the flow cell, which was equipped with a pair of identical ion-selective electrodes. The sample and standard streams were then exchanged with each other by using a four-way valve controlled by a microcomputer. The potential difference between the two electrodes was measured before and after switching of the four-way valve. Hence the effect of the potential shift of the ion-selective electrodes could theoretically be cancelled. The characteristics of the system were investigated by using nitrate or chloride ion-selective electrode pairs. A precision of <1% was achieved for five successive measurements when the sample concentration was close to that of the base standard solution.