Continuous potentiometric determination of sulphate in a differential flow system

Continuous monitoring of sulphate in a differential flow system equipped with two lead ion-selective electrodes is described. All solutions contained 75% methanol and were adjusted to pH 4. In the flow cell, a standard solution of lead(II) is pumped past the first sensing electrode and is mixed with the sample stream containing sulphate in a small mixing chamber; the mixture containing excess of lead(II) and lead sulphate precipitate then flows through the second sensing electrode chamber. The potential difference depends on the sulphate content in the sample. The effects of lead electrode passivation and the interferences of calcium and chloride are discussed. The system is useful for routine sulphate determination in the range 30–400 mg l^-1 with an accuracy of ±5%