The determination of pH in hypersaline lakes with a conventional combination glass electrode

pH in natural waters is commonly measured with a pH glass combination electrode. This method, however, yields accurate results only in low ionic strength solutions whereas its application to high ionic strength solutions suffers from bias introduced mainly by liquid junction potential. The determination of pH in high ionic strength solutions was conducted with dual ion selective electrodes systems that are liquid-junction-free. In the present work, we provide a method for determining the pH over a very wide range of ionic strengths using a conventional glass pH electrode. The method is based on calibrating the signal of the conventional combination glass electrode against the signal of a liquid-junction-free H+|Cl- electrode pair. The calibration was conducted on the Dead Sea brine and its dilutions with deionized water. It yielded a pH correction function of ionic strength, Delta pH(I), that allows evaluating the pH of Dead Sea brines and other brines of similar compositions using a regular glass combination pH electrode, over an ionic strength range of similar to 1-10 m. A pH measurement of the Dead Sea brine with a conventional combination glass electrode yielded a value of 6.26 +/- 0.04 after applying the Delta pH(I) correction function, identical to the 6.27 +/- 0.03 value obtained by the liquid-junction-free H+|Cl- electrode pair.