Determination of sodium with ion-selective electrodes

Area of Science:

• Clinical Chemistry
• Analytical Chemistry
• Biomedical Instrumentation

Background:

• Ion-selective electrodes (ISEs) enabled serum and plasma sodium potentiometry, initially using dilution methods similar to flame photometry.
• Direct potentiometry was developed for whole blood analysis to avoid dilution, but yields variable results.
• Direct methods may compensate for spurious hyponatremia caused by lipid or protein displacement, unlike indirect methods.

Purpose of the Study:

• To address the lack of a clear theoretical basis for choosing among direct ISE techniques for sodium analysis.
• To propose an alternative approach for accurate sodium measurement in the presence of interfering substances.

Main Methods:

• Evaluation of direct potentiometry techniques for whole blood sodium analysis.
• Development of a proposed method using indirect potentiometry with numerical corrections.
• Construction of a correction table for adjusting sodium values based on lipid and protein levels.

Main Results:

• Direct potentiometry results for whole blood sodium are variable.
• Direct potentiometry tends to correct for spurious hyponatremia seen in indirect methods.
• The proposed indirect method with corrections aims to standardize sodium measurements.

Conclusions:

• There is no definitive theoretical advantage of current direct ISE techniques over indirect methods.
• Indirect potentiometry with numerical corrections offers a viable alternative for accurate sodium determination.
• The proposed correction table facilitates accurate sodium measurements in samples with abnormal lipid and protein concentrations.