Direct analysis of drugs in forensic applications using laser ablation electrospray ionization-tandem mass spectrometry (LAESI-MS/MS)

Abstract

Laser ablation electrospray ionization tandem mass spectrometry (LAESI-MS/MS) was applied to the analysis of scheduled drugs in a variety of forensically relevant media including solutions, hair and botanic matter. LAESI-MS/MS was generally able to identify unreacted drugs directly from solutions in which common presumptive color tests had been performed. A significant correlation of 0.7 was found between the pK_a of the drugs and the frequency of a positive identification in the solutions indicating that basic drugs are more favorably ionized. Basic drugs like amphetamine and methamphetamine were readily identified at 0.01 mg mL⁻¹, well below the normal limits of detection of the color test results. For hair analysis, LAESI-MS/MS could directly identify the presence of morphine, codeine and cocaine in human hair samples at biologically relevant levels of ∼10 ng mg⁻¹ of drug in hair. This detection was possible without any hydrolysis, extraction, derivatization, or separation of the drugs. LAESI-MS/MS could also identify the presence of tetrahydrocannabinol (THC) or cannabidiol (CBD) in cannabis leaves, in addition to mapping the spatial abundance of THC/CBD across the different leaves. The simplicity and lack of sample preparation for hair and plant analyses are noteworthy benefits, but the current detection limits are close to biologically relevant levels. These preliminary studies indicate that with some additional optimization and validation, LAESI-MS/MS could provide a direct confirmation of color spot test results at an average analysis time of 20 seconds per sample, which is considerably faster than any GC or LC run and could be a major benefit for large caseloads or backlog reduction.