Study of Errors in Determination of Hydrogen Ion Concentrations in Rainwater Samples Using Glass Electrode Method

Abstract

The evaluation of the hydrogen ion concentration using the glass electrode method sometimes gives very serious errors when the method is applied to natural water samples of low ionic strength such as rainwater. The activity coefficient of the hydrogen ion and the liquid junction potential of the reference electrode are the sources of the error. In this report, the relations between the pH reading and the ionic strength of the sample solutions of 10^-4.5 N H₂SO₄ (N=equiv dm^-3) were examined for eleven commercially available electrodes. Results were grouped into three typical patterns. Quantitative estimates of the inaccuracies of the determination of hydrogen ion concentration were given, based on the calculation of Donnan potentials over the liquid junction and Debye-Hückel estimates of the activity coefficient. Recommendations for the choices of the reference electrode as well as the choices of the measurement protocols are also reported.