Water Quality
Parameters
ISE
Ion-selective measurement is a method for determining the concentration of dissolved ions. Potassium ions, sodium ions, fluoride or chloride are examples of such cations and anions which are directly measured in solutions. Indirect methods such as titration allow the determination of aluminum, nickel ions, or sulfate.

Measurement with ISE’s, like the measurement of pH, is a potentiometric method.
ISE’s are in two configurations:

1. separate ion-selective electrode and reference electrode
2. combined ion-selective electrode with built-in reference electrode

The ion-selective membrane of the electrode consists of a sparingly soluble salt of
the ion to be measured (solid state electrodes), a PVC-membrane, modified by an
ion exchanger or ion carrier (matrix electrodes), glass (glass electrode) or a gas-permeable plastic (gas-sensitive electrodes).

The activity of the ions to be measured determines the electrode current. With
increasing activity of the anions the voltage turns more negative, with increasing
activity of cations, more positive. A pH/ionmeter uses the electrode signal to
calculate the concentration of the sample.

The wide range of possible applications includes, for example, the measurement of fluoride concentration according to DIN 38 405. Chloride content determination in concrete samples or nitrate concentration determination in fruit juices are further examples of the ways in which ion-selective measurement technology can be applied.