Detection of Cannabinoids by ELISA and GC-MS Methods in a Hair Sample Previously Used to Detect Other Drugs of Abuse.

A forensic standard procedure is described that combines enzyme-linked immunoassay for screening and gas chromatography-mass spectrometry (GC-MS) for confirmation to detect drugs of abuse in a sample before used to detect opioids and cocaine. We used two equal aliquots of the same previously selected cannabinoid positive hair samples, one of which was subjected to acid hydrolysis. Afterward, both the aliquots were subjected to basic extraction and then to immunoassay screening. After derivatization, the GC-MS parameters were the same for both the aliquots for the determination of the cannabinoids (Δ(9)-tetrahydrocannabinol, cannabidiol and cannabinol). The results show that there were no statistical differences between the nonpreviously treated and the pretreated hair samples for the quantification of the three cannabis products for immunochemical procedure. No differences between the two groups were shown as for GC-MS confirmation procedures. All substances showed a good linearity between 0.05 and 2 ng/mg. The limit of detection ranged from 0.02 to 0.03 ng/mg, and the limit of quantification was 0.05 ng/mg for all substances. To our knowledge, this is the first time that screening and confirmation procedures have been applied on the same sample of hair to detect more than one drug of abuse.