The electric field that drives ion movement in the solution under test is generated by two electrodes in direct contact with the solution. These measuring electrodes must be made of chemically resistant materials; titanium is commonly used for this purpose. A pair of such electrodes is referred to as a Kohlrausch electrode.

The measurement of electrical conductivity requires clarification of two aspects: the conductivity of the solution and the geometric relationship of 1/A within the solution. Conductivity can be determined by measuring current and voltage, and this measurement principle is now implemented in direct-reading measuring instruments.

This value can be calculated based on the geometric dimensions. When two square electrodes, each with an area of 1 cm², are separated by a distance of 1 cm to form a capacitor, the cell constant under conditions of a uniform electric field is K = 1. If the conductance measured between these electrodes is G = 1000 μS, then the conductivity of the solution being measured is K = 1000 μS/cm.

In general, electrodes typically generate a partially non-uniform electric field. Under such conditions, the electrode constant must be determined using a standard solution. Potassium chloride (KCl) solutions are commonly used as standard solutions because the electrical conductivity of KCl remains highly stable and accurate across a wide range of temperatures and concentrations. For example, a 0.1 mol/L KCl solution has an electrical conductivity of 12.88 mS/cm at 25°C.

The so-called non-uniform electric field (also referred to as a stray or leakage field) is not constant; rather, it depends on the type and concentration of ions. Consequently, an electrode with a purely stray-field response is the worst possible choice, as a single calibration cannot accommodate a wide measurement range.

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Components of a Complete Conductivity Measurement System

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Components of a Complete Conductivity Measurement System