Simultaneous quantitation of delta-9-tetrahydrocannabinol (THC) and 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THC-COOH) in serum by GC/MS using deuterated internal standards and its application to a smoking study and forensic cases. 
A new procedure for the simultaneous detection of delta-9-tetrahydrocannabinol (THC) and its major metabolite, 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THC-COOH) in serum has been evaluated.  The method combines rapid, efficient, solid-phase extraction and simple derivatization by methylation.  Analysis and quantitation is performed by gas chromatography/mass spectrometry (GC/MS) using deuterated cannabinoids as internal standards (IS).  Reproducibility and sensitivity of the method are good.  The procedure is applied to serum specimens collected from a smoking study with 24 volunteers and 212 forensic cases.  Results are interpreted based upon the current knowledge about THC metabolism and pharmacokinetics.