Ion-selective electrode

Ion-selective electrode (ISE) is a type of electrode used in analytical chemistry and biochemical/biophysical research to selectively measure the concentration of a particular ion in a complex mixture of ions. Ion-selective electrodes are used in a wide range of applications, from clinical diagnostics and environmental monitoring to food quality control and pharmaceuticals analysis.

Principle

The principle of operation of an ion-selective electrode involves the selective binding of the target ion from a mixture to a specific ionophore embedded in a membrane. This binding alters the electrical potential of the membrane in a way that is proportional to the concentration of the target ion in the mixture. The potential difference between the ion-selective electrode and a reference electrode is measured, which can be related to the concentration of the target ion through the Nernst equation.

Types

There are several types of ion-selective electrodes, classified based on the nature of the ion-selective membrane used:

• Glass electrodes, which are commonly used for measuring pH or specific ions such as sodium.
• Solid-state electrodes, which use a crystalline membrane to select for specific ions.
• Liquid-based electrodes, which use an organic liquid membrane containing the ionophore.
• Gas-sensing electrodes, which measure the concentration of gaseous ions by their dissolution into a liquid membrane.

Applications

Ion-selective electrodes are used in various fields for different purposes:

• In clinical diagnostics, they are used for the rapid measurement of electrolytes in blood, such as potassium, sodium, and calcium levels.
• In environmental monitoring, they help in the detection of pollutants like nitrates and heavy metals in water.
• In the food industry, they are used to ensure the quality and safety of products by measuring parameters like acidity and salt concentration.
• In pharmaceuticals, they assist in drug development and quality control by measuring active ingredients and excipients.

Advantages and Limitations

The main advantages of ion-selective electrodes include their specificity, rapid response time, and the ability to measure ions in turbid or colored solutions. However, they also have limitations such as interference from other ions, the need for regular calibration, and membrane degradation over time.

See Also

• Electrochemistry
• Analytical chemistry
• Potentiometric titration
• Reference electrode