The interior of a glass electrode is filled with a pH7 SOLUTION. If the glass electrode is immersed in a pH7 solution, the potential difference should be 0 MV because identical buffer solutions are present on both sides of the MEMBRANE of the glass electrode. In practice, a potential develops due to the strain caused during glass production, shape, glass compositions, or other factors. This is called the “asymmetry potential.” The asymmetry potential also occurs due to contamination of the internal solution of the REFERENCE electrode, dryness of or CLOGGING in the liquid junction, etc. in addition to the glass electrode. To eliminate this asymmetry potential, a pH sensor is zero calibrated using the pH7 standard solution (pH standard solution of neutral phosphate).

The interior of a glass electrode is filled with a pH7 solution. If the glass electrode is immersed in a pH7 solution, the potential difference should be 0 mV because identical buffer solutions are present on both sides of the membrane of the glass electrode. In practice, a potential develops due to the strain caused during glass production, shape, glass compositions, or other factors. This is called the “asymmetry potential.” The asymmetry potential also occurs due to contamination of the internal solution of the reference electrode, dryness of or clogging in the liquid junction, etc. in addition to the glass electrode. To eliminate this asymmetry potential, a pH sensor is zero calibrated using the pH7 standard solution (pH standard solution of neutral phosphate).