The PharmChek® Sweat Patch captures insensible perspiration, the uncontrolled loss of sweat from the skin, in an absorbent pad. Approximately 300–700 ml of insensible sweat is excreted each day, and about 2ml is absorbed in the patch each week.
The polyurethane film is a semi-permeable membrane that allows small molecules, such as oxygen, carbon dioxide, and water vapor to pass through the patch— leaving the skin underneath healthy and sterile.
Substances of large molecular weight are trapped in the absorbent pad and submitted to the laboratory for analysis by LC/MS/MS. The patch is used to test for drugs of abuse.