Hybrid multiple standard additions-analyte addition method for ion-selective electrodes with integral calibration

Abstract

A hybrid multiple standard additions-analyte addition method for ion-selective electrodes is described in which the calibration of the potentiometric cell and the determination of the unknown concentration of the sample are carried out in a single experiment. This ensures maximum constancy of the calibration characteristics, E°′ and S, of the cell. The proposed method allows the determination of trace amounts (100 µg) of a sample. The data treatment includes an iterative minimisation procedure using the least-squares sum method, which improves the accuracy and the statistical reproducibility of the results. The method can be automated by means of an automatic titrator, controlled by an HP-85B microcomputer. A BASIC program was constructed for this purpose. The method was tested by applying it to the determination of sodium, potassium, chloride and fluoride ions and the errors of the results were less than 1%. The limit of determination of the method was investigated by determining decreasing concentrations of fluoride ions. It was found that the method gives satisfactory results over the entire linear range of the ion-selective electrode.