Solid-phase extraction of THC metabolite from urine using the Empore disk cartridge prior to analysis by GC-MS.

The Empore disk cartridges (C18) were evaluated for sample preparation in the gas chromatography-mass spectrometry confirmational assay for the 11-nor-9-carboxy-delta 9-tetrahydro-cannabinol (THCCOOH) metabolite. The performance of the Empore disk cartridges, determined by the recovery, precision, limit of detection (LOD), and limit of quantitation (LOQ) of the assay was comparable with the performance of a widely used solid-phase extraction cartridge (Spec C18 cartridges) and the traditional liquid-liquid extraction technique. The Empore disk cartridges showed an average recovery of 89% at low concentrations of 6 ng/mL of the THC metabolite spiked into urine. The recovery was consistent across three different lots of Empore disk cartridges. The within-run precision of the assay at a concentration of 18 ng/mL had a coefficient of variation of 2%, and the LOD and LOQ were determined to be 1 ng/mL.