Ion Selective Electrodes (ISE) are commonly employed as online sensors due to their speed and simplicity as well as low maintenance and purchase cost.
With careful use, frequent calibration ideal measurement conditions being maintained, they can achieve higher accuracy and precision.
Hence, in theory the configuration and embodiment of an ISE, makes it an ideal sensing probe for on-site, real time monitoring applications.
Data obtained from online ISE measurements, although continuous, is usually semiquantitative in nature. This is because the analytical signal of the ISE is known to be affected by matrix interferences, drift, contamination (e.g. by organic molecules), non-linear responses at the lower end of the detection, temperature in the non-ideal measurement conditions.
These factors in turn cause measurements errors. To improve its reliability, especially in the field, an ISE must be regularly calibrated with standards and samples should be analysed according to prescribed measurement conditions.
However, the economic costs associated with calibration especially for instruments that require ex-situ calibration with skilled personnel, have greatly limited its adoption.