A modified ion-selective electrode method for measurement of chloride in sweat.

A modified method of analysis of sweat chloride concentration with an ion-selective 
electrode is presented. The original method of sweat chloride analysis proposed 
by the Orion Research Corporation (Cambridge, Massachusetts 02139) is inadequate because 
it produces erratic and misleading results. The modified method was compared 
with the reference quantitative method of Gibson and Cooke. In the 
modified method, individual electrode pads are cut and placed in the 
electrodes rather than using the pads supplied by the company; pilocarpine 
nitrate (2,000 mg/l) is used in place of pilocarpine HCl (640 
mg/l); sodium bicarbonate as the weak electrolyte is used instead of 
K2SO4. A 10-minute period for sweat accumulation is employed rather than 
a zero-time collection as in the original Orion method. The modification 
has been studied for reproducibility in individuals, reproducibility between right and 
left arm in individuals; it has been compared extensively with the 
quantitative method of Gibson and Cooke, both in normal individuals and 
in patients with cystic fibrosis. There is excellent agreement between the 
modified method and the quantitative reference method. There appears to be 
a slight bias toward higher concentrations of chloride from the right 
arm compared with the left arm, but this difference is not 
medically significant. 