Applicable Measuring Range of Two-Electrode Type Commercial Electrolytic Conductivity Meter for Accurate Determination of Electrolytic Conductivity

Abstract

Applicable measuring range of electrolytic conductivity (EC) for commercially available two-electrode type EC meter was examined. The measurement error caused by a gap in ECs between the measurement sample and the standard solution was also evaluated. Seven potassium chloride (KCl) solutions including certified reference materials (CRMs) manufactured by the National Metrology Institute of Japan (NMIJ) were measured, and the cell constants observed for commercial EC meters as well as the effect of electrode polarization were compared in detail under strict temperature control. The effect of electrode polarization can be sufficiently small if the frequency is properly selected. In the case of KCl standard solution with concentrations of 0.1 mol kg-1 (1 S m-1) or less, the obtained cell constants were almost identical to those of declared ones. However, in the case of KCl standard solution with concentrations of 0.5 mol kg-1 (5 S m-1) or more, the obtained cell constants showed 2-10% higher than those of declared ones. From these results, the calibration by standard solution with closer EC to the measurement solution is especially important if about 1% accuracy of measurement by commercial EC meter is required in higher EC range such as 5 S m-1 or more.