Comparison of in-scene presumptive tests for the detection of Cannabis traces on the inner surfaces of clip seal plastic bags

Abstract

Queensland Police Service. Tetrahydrocannabinol (THC), the principal psychoactive constituent of Cannabis, and other cannabinoids can be transferred onto surfaces by direct or secondary contact. Identification of these traces generally involves time-consuming and expensive laboratory analysis away from the crime scene. A reliable, economical, in-scene presumptive test would thus be beneficial to target sampling in-scene, maximize evidence recovery, and reduce wastage. We addressed this by developing a sampling procedure for use with a commercial Duquenois–Levine (DL) test kit for detecting THC on sampled surfaces at scenes. We compared the augmented DL test with the DrugWipe® 5F (DW) surface sampling kit and confirmatory testing by gas chromatography-mass spectroscopy (GCMS) by sampling the inner surfaces of clip seal plastic bags that were exposed to pure Cannabis and Cannabis/tobacco mixtures. The novel sampling protocol developed here for the DL test was highly successful and will transfer easily to real-world crime scene use. Both DL and DW tests successfully detected traces of Cannabis on sampled surfaces, and whilst DW tests were more sensitive, DL tests more closely corresponded to confirmatory GCMS results. Such presumptive screening will allow more efficient targeting of items for sampling, minimize expensive testing, and provide valuable real-time intelligence at the scene to assist investigations.