Confirmation of THC in Oral Fluids Using High-Resolution 2-D GC/MS

Oral fluids are being used as an alternative matrix to urine for drug testing. Oral fluid is considered to be less invasive and much more difficult to adulterate than urine samples. Samples of oral fluid are typically screened by an ELISA immunoassay method. Those found to be positive must be further analyzed with a mass spectrometry confirmation technique. The confirmation technique must be able to detect the drugs of abuse (DOA) in oral fluids down to concentrations lower then those used in urine testing. For example, tetrahydrocannabinol (THC) must be measured down to 0.5 ng/mL of diluted oral fluid when collected with the Intercept oral fluid collector. The analysis is complicated by interferences from the complex sample matrix. For these samples, techniques like gas chromatography/mass spectrometry/mass spectrometry (GC/MS/MS) and liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS) have been used. The higher Confirmation of THC in Oral Fluids Using High-Resolution 2-D GC/MS Application Note level of selectivity afforded by a secondary mass spectral step is used to overcome interference problems. GC/MS has the required sensitivity to confirm THC but lacks the selectivity over matrix interferences. This application describes a two-dimensional (heart cutting) GC/MS system where THC is heartcut from a nonpolar DB-1ms column to a polar DB-17ms column. An aircooled focusing trap is used to improve resolution and sensitivity. Coupling high-resolution two-dimensional (2-D) GC with a standard benchtop quadrupole gas chromatography/mass selective detector (GC/MSD) provides the required selectivity and sensitivity for THC confirmations.