BACKGROUND:
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.
METHODS:
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).
RESULTS:
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.
CONCLUSIONS:
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.