Development of an On-Site Forensically Defensible Determination of THC in Human Breath Samples

Cannabis smokers have THC (tetrahydrocannabinol) present in the aerosol particles of exhaled breath samples after smoking. Breath samples were collected using the BreathExplor™ collection device. Each collected breath sample was extracted on a shaker with 150 uL ethanol solution containing 600 pg of internal standard, d3-THC, followed by centrifugation (5 min). The centrifugate solution was pipetted to micro autosampler vials for SIM LC/MS analysis using an Advion compact mass spectrometer (CMS). Positive ion SIM LC/MS analyses under atmospheric pressure chemical ionization (APCI) conditions were used for analyses of the breath sample extracts. Calibrators prepared at six concentrations from 50 pg to 50,000 pg THC/sample using blank fortified breath samples showed a linear relationship for THC using the THC-d0/THC-d3 peak area ratio, with a coefficient of determination equal to R 2 > 0.99. The LLOQ was 50 pg/sample for SIM LC/MS and 10 pg for LC/MS/MS analyses. Authentic (positive) samples following cannabis smoking were obtained from volunteer male and female smokers. Twelve Exhaled breath samples were collected for each time point at zero-hour (prior to smoking), 30 min and at one-hour time points from one through six hours post marijuana smoking. All post-smoking breath samples showed detectable THC concentrations ranging from 0.1 to 20 ng/sample. The 0-6-hour pharmacokinetic (PK) curves for each subject showed maximum THC levels at up to 20 ng/collector with a subsequent reduction of THC levels in breath through the six-hour time period. Confirmatory analyses were subsequently performed on the 'B-samples' by LC-MS/MS which mirrored the SIM LC/MS qualitative and quantitative THC results in the positive specimens. In development is the integration of a sophisticated robot coupled with SIM LC/MS analysis where the breath samples can be robotically prepared in a fully automated manner with analysis by APCI SIM LC/MS in less than 10 minutes.