Utilization of matrix-assisted laser desorption/ionization imaging mass spectrometry to search for cannabis in herb mixtures

Herb mixtures including cannabis among the other herbs have recently appeared. When cannabinoids from herb extracts are detected by chemical examinations such as gas chromatography/mass spectrometry, forensic analysts have to determine whether cannabis is actually in the mixture or the cannabinoids are spiked. Morphological examinations are time-consuming, since it is difficult to find several pieces of cannabis among a large number of herb pieces using a microscope. Here, we propose a procedure for efficiently searching for cannabis in herb mixtures using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI/IMS). Pieces of herb mixtures were spread on double-sided adhesive tape attached to a stainless steel plate. The pieces were then covered with a conductive sheet and pressed. After a solution containing a matrix reagent was sprayed, the distribution of cannabinoids in the sample was visualized by MALDI/IMS. Then, just the pieces with cannabinoids could be picked up selectively with tweezers and decolorized. Cystolith hairs and trichomes, which are characteristic of cannabis, were observed in most of these pieces using a biological microscope. This MALDI/IMS procedure enables cannabis to be found in herb mixtures without inefficient random sampling and microscopic morphological examination.