A validated method for the analysis of cannabinoids in post-mortem blood using liquid–liquid extraction and two-dimensional gas chromatography–mass spectrometry

A validated method for the identification and quantification of ▵9-tetrahydrocannabinol (THC), cannabidiol (CBD), cannabinol (CBN), 11-hydroxy-▵9-tetrahydrocannabinol (11-OH-THC) and 11-nor-▵9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) in post-mortem blood specimens is described. Liquid–liquid extraction was used to extract the cannabinoids from 1 mL of post-mortem blood. The extracts were derivatized with N-methyl-N-(trimethylsilyl)trifluoroacetamide. The final derivatized extracts were analyzed using two-dimensional gas chromatography–mass spectrometry. The limit of detection was 0.25 ng/mL for all analytes and the limit of quantification of the assay was 0.25 ng/mL for THC, CBN, 11-OH-THC and 0.5 ng/mL for CBD and THC-COOH. The assay was linear across the concentration range 0.25–50 ng/mL (determined with a low and a high calibration range) with correlation coefficients ≥0.992 for all analytes. Inter-day and intra-day accuracy was within ±15% of the target concentration for all analytes. The co-efficients of variation (%CV) for inter-day and intra-day precision were ≤12% for all analytes. The extraction efficiency was >73% for all analytes. The method has successfully been applied to 54 post-mortem blood specimens to date. To the authors knowledge this is the first validated 2D GC–MS method for the analysis of THC, CBD, CBN, 11-OH-THC and THC-COOH following LLE and its application to post-mortem specimens.