Electrochemical Methods and Ion-Selective Electrodes

Ion-selective electrodes and an electrochemical blood gas analyzer

Electrochemical methods measure the electrical properties of a solution (potential, current or conductivity), which depend on the concentration of the ions being determined. In clinical chemistry, they underpin the measurement of electrolytes, blood gas analysis and acid-base balance testing. Ion-selective electrodes (ISEs), which respond selectively to a specific ion, play a key role.

Main Electrochemical Methods

Method	What is measured	Application
Potentiometry (ISE)	Electrode potential	Na+, K+, Cl-, Ca2+, pH
Amperometry	Current at a set potential	pO2, glucose, lactate
Conductometry	Electrical conductivity	Solution monitoring
Coulometry	Quantity of electricity	High-precision measurements

Ion-Selective Electrodes (ISE)

ISEs contain a selective membrane whose potential depends on the activity of a specific ion according to the Nernst equation. This is the most widely used method for measuring electrolytes in the clinical laboratory.

Direct and indirect potentiometry:

Direct ISE measures ion activity in an undiluted sample; it is closer to physiology and unaffected by pseudohyponatremia
Indirect ISE measures in a diluted sample and is integrated into clinical chemistry analyzers

Blood Gas and Acid-Base Analysis

Blood gas analyzers combine electrochemical sensors to simultaneously measure pH, pCO2 (potentiometry) and pO2 (amperometry), as well as electrolytes and metabolites. This is critical in intensive care, where the speed and accuracy of acid-base assessment shape treatment decisions.

Frequently Asked Questions

How does direct ISE differ from indirect ISE?

Direct ISE measures ion activity in an undiluted sample, indirect ISE in a diluted one. Direct ISE is unaffected by pseudohyponatremia at high lipid and protein concentrations.

Why are blood gases measured electrochemically?

Electrochemical sensors deliver fast, accurate pH, pCO2 and pO2 results in whole blood without complex sample preparation, which is essential in emergency medicine.

How often do ISEs need calibration?

Modern analyzers automatically calibrate against several standards at set intervals, which keeps results stable.

Selecting an Electrochemical Analyzer

KombiMED GmbH is an independent partner for procurement and market access for laboratory equipment from Europe. We will help you select an electrolyte or blood gas analyzer that fits your laboratory's needs and handle delivery, installation, commissioning and staff training.

See also:

Analytical methods in clinical chemistry: an overview
ICP-MS and trace element analysis
Laboratory diagnostics services
Contact KombiMED for equipment selection