Direct Measurement of Chloride in Sweat with an Ion-Selective Electrode

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Abstract
The use of a specific ion electrode for measuring sweat chloride has not been widely accepted because of poor precision and occasional falsely elevated chloride concentrations. We have studied this technique by using the Orion sweat-chloride instrument, and have eliminated these problems by modifying the methodology. An insufficient amount of sweat for determination with the electrode was responsible for both the imprecision and random inaccuracies. The following modifications eliminated these problems: (a) We freshly saturate felt pads with a solution of, per deciliter, 400 mg of pilocarpine nitrate and 1 g of NaHCO3 to replace the electrolyte pads supplied by the Orion Co. (b) The timed iontophoresis period commences after the meter indicates conduction of adequate current. (c) After iontophoresis, sweat is collected for 10 min under a plastic cap held over the induction area. Then chloride concentration is measured with the electrode. With these improvements in technique, the revised procedure should be as reliable as reference methodologies.

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