Strano Rossi S., Marsili R., Chiarotti M.

Institute of Legal Medicine, Catholic University, L.go F. Vito, 1, Rome, Italy

Although hair analysis for drugs of abuse testing is a technique widely performed and many papers have been published, few are the papers about hair testing for cannabinoids. The detection of THC-COOH, the major metabolite of THC, is in fact a major problem due to the low affinity of this compound for hair matrix (1, 2). The presence of the major cannabis compounds (CBN, CBD, THC) in the hair of cannabis users was demonstrated (3). The objective of the present work was to develop a sensitive and rapid method for the detection of the principal cannabinoids in hair. Solid Phase Microextraction (SPME) is a technique that allows the sampling of small amounts of substances from aqueous mediums and their direct GC/MS analysis. This method has already been utilized to detect drugs in urine (4, 5). The technique avoids the use of organic solvents and can be applied for the screening of a large number of samples (for example for drug testing in workplace). SPME was applied for a rapid screening of cannabinoids in hair: 50 mg of sample were washed three times with methylene chloride, spiked with 50 ng of δD⁹-THC-D₃ (I.S.) and dissolved in 200 µl of NaOH; after neutralization, a fibre coated with polydimethylsiloxane was directly dipped in a small volume of the solution, let sampling 15 minutes, and then desorbed in the injection port of the gas chromatograph. The detection limit was of 0.1 ng/mg for THC and CBN and 02 ng/mg for CBD. In real samples obtained from subjects in methadone treatment that reported cannabis use, the levels of THC varied from 0.1 to 0.7 ng/mg, CBD from 0.7 to 14.1 ng/mg and CBN from 0.4 to 0.7 ng/mg. It was also possible with the same method to detect methadone in the subjects in treatment. External contamination was excluded in the samples tested by the analysis of the last washing solution. The positivity to these cannabinoids can hence be considered predictive of cannabis consumption. Anyway if further confirmation of positives is needed, the sample can be used for the detection of THC-COOH.

References

1. Nakahara Y., Takahashi K., Kikura R., Biol. Pharm. Bull., 1995, 18, 1223-7;
2. Wilkins D., Haughey, Cone E., Huestis M., Foltz R., Rollins D., J Anal. Toxicol., 1995, 19, 483-491;
3. Cirimele V., Sachs H., Kintz P., Mangin P., J Anal. Toxicol., 1996, 20, 13-16;
4. Chiarotti M., Marsili R., J. Microcol. Sep., 1994, 6, 577-580;
5. Chiarotti M., Strano Rossi S., Marsili R. J. Microcol. Sep., 1997, 9(3) (in press)