Hair Analysis for THC, THC-COOH, CBN and CBD with GC/MS-EI. Comparison with GC/MS-NCI for THC-COOH.

P.V. Monsanto(1), P.Marques(1,2), M.J.S. Baptista(1), S. Ávila(1), A.M. Castanheira(1), D.N. Vieira(1)

  1. National Institute of Legal Medicine; Largo da Sé Nova, 3000-213 Coimbra, Portugal
  2. Faculty of Medicine of the University of Coimbra; Largo da Sé Nova, 3000-213 Coimbra, Portugal

A sensitive method was developed for quantitative analysis of delta-9-tetrahydrocannabinol (THC), 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THC-COOH), Cannabinol (CBN) and Cannabidiol (CBD) in human hair. The identification of THC-COOH in hair would document Cannabis use more effectively than the detection of parent drug (THC), which might have come from environmental exposure.

Ketamine is added to hair samples as internal standard for CBN and CBD. Ketoprofen is added to hair samples as internal standard for the other compounds. Samples were hydrolysed with ?-glucoronidase/arylsulphatase. Samples were extracted with a liquid-liquid extraction procedure (with chloroform/isopropyl alcohol, after alkalinisation, and n-hexane/ethyl acetate, after acidification), which was developed in our laboratory. The extracts were analysed before and after derivatisation with pentafluoropropionic anhydride (APFP) and pentafluoro-1-propanol (PFPOH) by GC/MS (electronic ionisation, EI)

Derivatised THC-COOH was also analysed by GC/MS (negative chemical ionisation, NCI). Methane was used as the reagent gas. The assays were linear up to 10ng/mg hair (R2= 0,99) for all compounds and was capable of detecting 0,1ng/mg of CND, CBN and THC and 0,01ng/mg of THC-COOH. The intra-assay precisions ranged from 0 to 12,45% for all analytes. Extraction recoveries ranged from 80,9-104,0% for THC, 85,9-100,0% for THC-COOH, 76,7-95,8% for CBN and 71,0-80,0% for CBD.

The method was used for analysing 87 human hair samples obtained from individuals who testified in court to having committed drug related crimes.

Quantification of THC-COOH using GC/MS-NCI was found to be more convenient than GC/MS-EI. The latter may give rise to false negatives due the limit of detection.