I had to look this up in my Principles of Surgery book. I hope this helps.
Eccrine sweat is the clear aqueous solution containing 99% water and 1% solids, half of which are ganic salts and half organic compounds. Under normal circumstances it is hypotonic, but at high rates of sweating it depends on material that is in the blood stream; it is not a simple ultrafiltrate of plasma but, but represents an active secretion. The concentration of sodium and chloride is lower than that in plasma, while the concentration of potassium is somewhat higher. The concentration of chloride depends on many factors and is usually in the range of 15 to 60 meq\L. The sodium concentration is almost entirely equivalent to that of chloride and varies in a parallel fashion. Chloride and sodium concentrations rise with prolongation of sweating and with the rate of sweating and temperature of the skin. The salt concentration of sweat also depends on the intake, and an adequate supply of drinking water depress the concentration. The loss of potassium through the skin ranges between 2.7 and 3.1 meq\L.
Nitrogen compounds are almost lost transdermally , and the concentration of urea in sweat is twice as high as that in the blood. Creatinine is present in sweat in only a minute amount, and amino acids have also been noted. Ammonia is a primary constituent of sweat, and it can be concentrated by the sweat glands with nearly the same efficiency as the renal excreting unit. Large amounts of lactic acid and lactate have been demonstrated in sweat, particularly during heavy musuclar exercise and in association with thermogenic sweat. The concentrations are 10 to 20 times higher then that in the blood, and it is felt that the lactic acid originates from breakdown of glycogen within the sweat glands.