Development and evaluation of the simultaneous determination of sweat sodium and chloride by ion-selective electrodes

A method for the simultaneous determination of sweat sodium and chloride was developed and evaluated using a Monarch 2000 centrifugal analyser with ion-selective electrodes. In order to measure sodium and chloride in diluted sweat samples and sweat paper eluates an analytical working range of below 10 mmol/L was required. This was achieved by modification of the Monarch ISE software parameters for urine electrolytes together with the use of calibrators within this range. Evaluation of the method has included linearity, recovery and precision studies and the correlation between ion-selective electrode and flame photometry for sweat sodium and between ion-selective electrode and a continuous flow method for sweat chloride. Of the patients studied so far, there has been good discrimination in sweat electrolytes between those with and without cystic fibrosis.