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Establishing the direct-potentiometric "normal" range for Na/K: residual liquid junction potential and activity
Clinical Chemistry
|September 1, 1982
Summary
Direct potentiometry for sodium and potassium measurements can yield higher reference intervals due to the volume displacement effect. This study proposes a convention to standardize these normal reference intervals, accounting for sample composition.
Area of Science:
- Clinical Chemistry
- Analytical Chemistry
- Biochemistry
Background:
- Reference ranges for sodium and potassium vary between instruments using direct potentiometry.
- This variation stems from differences in calibration standards and methodologies (direct vs. indirect).
- Confusion exists regarding the "normal" reference intervals for these electrolytes.
Purpose of the Study:
- To propose a standardized convention for electrolyte reference intervals.
- To account for the volume displacement effect in direct potentiometry.
- To resolve confusion surrounding "normal" sodium and potassium reference ranges.
Main Methods:
- Proposed a convention based on plasma-water concentration units.
- Accounted for the volume displacement effect of plasma components (proteins, lipids).
- Utilized aqueous-based calibrants and minimized errors from activity coefficients and liquid junction potentials.
Main Results:
- Proposed reference intervals for sodium and potassium are approximately 7% higher with direct potentiometry compared to dilution methods.
- Experimental data support the proposed convention.
- Identified activity coefficient and liquid junction potential effects as sources of error.
Conclusions:
- The proposed convention standardizes electrolyte reference intervals by accounting for sample matrix effects.
- Direct potentiometry yields higher normal reference intervals for sodium and potassium.
- Minimized errors in calibration and measurement are crucial for accurate results.