Sensitive determination of THC and main metabolites in human plasma by means of microextraction in packed sorbent and gas chromatography-tandem mass spectrometry

•The method was fully validated and excellent limits of detection and quantitation using 0.25 mL of sample.•The developed method is suitable for regular analysis in the field of forensic and clinical toxicology.•This is the first reported method for THC and metabolites in plasma using MEPS and GC/MS-MS.

Cannabis is one of the most available and consumed illicit drug in the world and its identification and quantification in biological specimens can be a challenge given its low concentrations in body fluids. The present work describes a fast and fully validated procedure for the simultaneous detection and quantification of ▵9-tetrahydrocannabinol (▵9_THC) and its two main metabolites 11-hydroxy ▵9_tetrahydrocannabinol (11-OH-THC) and 11-nor-9-carboxy-▵9- tetrahydrocannbinol (THC-COOH) in plasma samples using microextraction by packed sorbent (MEPS) and gas chromatography-tandem mass spectrometry (GC-MS/MS). A small plasma volume (0.25 mL) pre-diluted (1:20), was extracted with MEPS M1 sorbent as follows: conditioning (4 cycles of 250 μL methanol and 4 cycles of 250 μL 0.1% formic acid in water); sample load (26 cycles of 250 μL); wash (100 μL of 3% acetic acid in water followed by 100 μL 5% methanol in water); and elution (6 cycles of 100 μL of 10% ammonium hydroxide in methanol). The procedure allowed the quantification of all analytes in the range of 0.1-30 ng/mL. Recoveries ranged from 53 to 78% (THC), 57 to 66% (11-OH-THC) and 62 to 65% (THC-COOH), allowing the limits of detection and quantification to be set at 0.1 ng/mL for all compounds. Intra-day precision and accuracy revealed coefficients of variation (CVs) lower than 10% at the studied concentrations, with a mean relative error within ±9%, while inter-day precision and accuracy showed CVs lower than 15% for all analytes at the tested concentrations, with an inaccuracy within ±8%.