Evaluation of the direct potentiometric method for serum chloride determination--comparison with the most commonly employed methodologies.

A new instrument (NOVA 4 + 4) designed to measure serum chloride by ion-selective electrode (ISE)-direct potentiometry (without sample dilution) was evaluated and compared with two widely used methodologies for chloride determination. Mean values obtained with the Nova were significantly higher than those obtained by a colorimetric method and by coulometric titration. Unlike these procedures, which are performed after sample dilution, direct potentiometry was unaffected by changes in plasma water caused by hyperlipemia and/or high protein concentrations. The only important interference was falsely high choride caused by administered bromide or iodide. Therefore, the direct potentiometric method should be more accurate than the colorimetric or coulometric procedures, especially when plasma lipids or proteins are very high.