| Popis: |
In the ion selective electrode standard addition technique the error of determination caused by a change in the response slope was evaluated. It was pointed out that the modified Gran's plot shows a straight line even if the response slope is different from the true one and that an erroneous concentration may be obtained by the use of such a straight line. A simple method for the determination of the response slope is proposed as follows : An indifferent electrolyte is added to a sample solution, standard solution and diluent in order to bring them to the same ionic strength. The volume, v', of the diluent is added to the initial volume, V, of the sample solution in which the ion-selective electrode and reference electrode are immersed. Prior to the addition of the diluent, the cell potential of the sample solution is measured and denoted by E1. The cell potential, E', after each addition of the diluent are measured and the response slope, k, is calculated by the following equation. E1-E' =k·log V/ ( V+ v' ).Then, the usual standard addition technique is applied to this diluted sample solution. |
