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%.