Quantification of Δ9-tetrahydrocannabinol in urine as a marker of cannabis abuse

Abstract

Background objectives: Cannabis use has long been associated with celebration and hospitality, although abuse must be confirmed through testing. It has always been difficult to develop an accurate and reliable confirmatory method for the quantification of tetrahydrocannabinol carboxylic acid (THC-COOH) that meets local requirements. The goal was to develop a rapid, cost-effective analytical technique that can handle large batches.

Methods: Because of the wide metabolite detection window and ease of collection, urine was preferable sample. The extraction of a pre-screened urine sample (adulteration and multidrug screening) was done on Bond Elut cartridges using a positive pressure vacuum manifold, followed by quantification using a gas chromatograph and mass spectrometer.

Results: The assay was linear between 15 and 300 ng/ml ( r2 of 0.99). The intra-day precision was 8.69 per cent and the inter-day precision was 10.78 per cent, respectively with a 97.5 per cent recovery rate for the lowest concentration. A total of 939 urine samples were examined, with 213 detecting cannabis. Sixty per cent of the total individuals tested positive for simply cannabinoids, 33 per cent for cannabinoids and sedatives, five per cent for cannabinoids and morphine and one for cannabis, morphine and cocaine.

Interpretation conclusions: Assay characteristics included modest sample preparation, rapid chromatography, high specificity and small sample volume with a processing time of 12 h. The assay described here can be applied for diagnostic laboratories and in forensic settings as well.

Fig. 1

Mass spectrum showing m/z of THC-COOH. THC-COOH, 11-nor-Δ9-tetrahydrocannabinol-carboxylic-acid

Fig. 2

Graph showing a sequential decline in THC-COOH levels among patients.

Fig. 3

Chromatogram showing all three masses of THC-COOH.