Quantitative analysis of 11-nor-9-carboxy-tetrahydrocannbinol (THC–COOH) in urine by LC–MS/MS following a simple filtration

• Develop a rapid LC–MS/MS method for THC–COOH in urine for pain management.
• Fully validate the analytical method according to recommended guidelines.
• The first to describe an analytical clean-up procedure using a simple filtration column.
• Compare two types of filtration columns commercially available.

Quantification methods utilizing liquid chromatography tandem mass spectrometry (LC–MS/MS) are common in clinical and forensic toxicology laboratories and the efficiency and rapidity of such methods continues to evolve. In most cases, urine drug confirmation does not require a drug extraction and can quickly and easily be accomplished with a dilution followed by sample filtration. The report describes the validation of a simple confirmation method for 11-nor-9-carboxy-tetrahydrocannabinol (THC–COOH) and compared two types of filter extraction columns for sample clean-up. The method achieved a linear range of 10–3000 ng/mL, acceptable bias (−4.7–2.6%) and precision (0.9–6.9%) and autosampler stability up to 72 h. Universal filter columns offered less variable recovery over the linear range and fewer matrix interferences compared to THC–COOH specific filter columns. Authentic specimens testing positive for THC–COOH by LC–MS/MS were in good agreement with typically used GC–MS methods.