Quantitative determination of K+, NH4+, Na+, Ca2+ and Mg2+ cations in secreted human sweat by capillary zone electrophoresis

Cations in human insensible perspiration were analyzed by capillary zone electrophoresis. A simple sampling method from the skin surface of the forefinger of a hand was devised. After washing the forefinger with tap water and then distilled water for 10 s, 40 μl of a 10% ethanol aqueous solution kept in a small vial (0.6 ml) was allowed to contact the treated forefinger for 3 minutes. The sweat sample was then analyzed by capillary zone electrophoresis. A mixture of 5.0 mmol l-1 copper (II) acetate, 10 mmol l-1 ethylendiamine and 1.0 mmol l-1 18-crown-6-ether at pH 6.5 was selected as the optimum medium for capillary zone electrophoresis. Six cations {Rb+(I.S.), K+, NH4+, Na+, Ca2+ and Mg2+} were completely separated in less than 3 min, and detected with indirect UV detection at 230 nm. Sweat samples were collected from seven volunteers. They were healthy males (n = 4) and females (n = 3), aged 21∼25 years. The mean values of the cation concentrations were K+ = 39.9 mM, Na+ = 54.0 mM, Ca2+ = 5.49 mM, Mg2+ = 1.67 mM, NH4+ = 5.13 mM. It shoud be noted that the concentration of K+ in secreted sweat is much higher than that in serum.