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Sweat testing, an alternative matrix for establishing drug abuse, offers additional benefits to the more common biological samples. The authors developed a procedure using gas chromatography-mass spectrometry to test for Δ9-tetrahydrocannabinol, 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid, cannabinol and cannabidiol in a sweat patch. The results were compared with urine and hair sample results.


Urine, hair, and sweat samples were simultaneously collected from 12 patients who were involved, respectively, in forensic case and monitoring abuse. Selectivity, linearity, limit of detection, limit of quantification, recovery, intra- and inter-day imprecision, and inaccuracy of the quantification procedure were validated. Limits of detection in hair were 0.05 ng/mg for Δ9-tetrahydrocannabinol, cannabinol, cannabidiol and 0.005 ng/mg for 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid. The limit of detection for sweat was 0.30 ng/patch for all substances. The limit of quantification in hair was 0.1 ng/mg for Δ9-tetrahydrocannabinol, cannabinol, cannabidiol and 0.01 ng/mg for 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid. The limit of quantification was 0.4 ng/patch in sweat for each analyte. Cannabinoid in urine was determined by means of immunochemical screening (cutoff 11-nor-Δ-tetrahydrocannabinol-9-carboxylic acid 50 ng/ml).


All subjects tested positive for 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid and Δ9-tetrahydrocannabinol in urine and hair. In sweat samples, Δ9-tetrahydrocannabinol was found in all patches (0.4-2.0 ng/patch); six cases were positive for cannabinol (0.4-0.5 ng/patch) and three for cannabidiol (0.4-0.6 ng/patch); 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid was never detected in patches.


Present sweat analysis results integrated the information from hair and urine and showed that sweat analysis is a suitable, non-invasive method for monitoring compliance with rehabilitation therapy and for detecting recent cumulative use of cannabinoids.