Determination of Δ9-tetrahydrocannabinol in indoor air as an indicator of marijuana cigarette smoking using adsorbent sampling and in-injector thermal desorption gas chromatography-mass spectrometry

The marijuana leaves are usually mixed with tobaccos and smoked at amusement places in Taiwan. Recently, for investigation-legal purposes, the police asked if we can identify the marijuana smoke in a KTV stateroom (a private room at the entertainment spot for singing, smoking, alcohol drinking, etc.) without marijuana residues. A personal air-sampler pump fitted with the GC liner-tube packed with Tenax-TA adsorbent was used for air sampling. The GC-adsorbent tube was placed in the GC injector port and desorbed directly, followed by GC-MS analysis for the determination of Δ9-tetrahydrocannabinol (Δ9-THC) in indoor air. The average desorption efficiency and limit of detection for Δ9-THC were 89% and 0.1 μg m−3, respectively, approximately needing 1.09 mg of marijuana leaves smoked in an unventilated closed room (3.0 m × 2.4 m × 2.7 m) to reach this level. The mean Δ9-THC contained in the 15 marijuana plants seized from diverse locations was measured to be 0.32%. The Δ9-THC in room air can be successfully identified from mock marijuana cigarettes, mixtures of marijuana and tobacco, and an actual case. The characteristic Δ9-THC peak in chromatogram can serve as the indicator of marijuana. Positive result suggests marijuana smoking at the specific scene in the recent past, facilitating the formulation of further investigation.