Alkylsilyl speciation and direct sample preparation of plant cannabinoids prior to their analysis by GC-MS

Abstract

A literature criticism is given on methods currently using gas chromatography mass spectrometry (GC-MS) to determine plant cannabinoids (p-CBDs). In this study, trialkylsilylation of seven p-CBDs (including their transformation products formed in the drug user's body) was compared applying various alkylsilyl reagents11such as hexamethyldisilazane (HMDS) and trifluoroacetic acid (TFA), N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA), N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) - along with their 1% trimethylchlorosilane (TMCS) containing alternatives, and MSTFA, activated by ammoniumiodide and ethanethiol, forming in situ the MSTFA/TMIS = 1000/2 (v/v) reagent (further on MSTFA+0.2% TMIS, as well as N-methyl-N-tert.-butyl dimethylsilyltrifluoroacetamide (MTBSTFA+1% tert. butyl dimethylchlorosilane, TBDMCS). and the mass fragmentation properties of the corresponding derivatives were characterized. Derivatization, mass fragmentation and quantitation related model investigations were optimized as a function of the reaction times and conditions. Special emphasis was put (i) on the maximum responses of species, (ii) on the proportions of formed stable products, suitable for selective quantitation of all seven p-CBDs simultaneously. Results, as novel to the field confirmed that HMDS + TFA, for p-CBDs never applied reagent before, serves as their derivatization reagent of choice. These species were characterized by their retention, mass fragmentation and analytical performance characteristics. In model solutions with injected amounts in the range of 20 pg–2000 pg, repeatability (average 4.98% RSD, varying between 2.98 and 6.2% RSD), linearity (R2, 0.9956–0.9995), LOQ (20–80 pg/μL injected species) and recovery (95.2–104%) values were defined. The practical utility of this proposal, along with method development validation, was shown in a particularly unique manner and supported by the novel, extraction free, direct sample preparation working strategy. For this purpose, two Cannabis-type ruderalis (C-trd) plant tissues (C-trd1, C-trd2) were directly derivatized in the presence of the matrix. This process, which approaches green chemistry, performed without the use of organic solvents, was associated with the quantitation of self p-CBD contents of C-trd plant tissues. Applying 0.5–2.0 mg dried tissues, adding standards, the following self p-CBDs contents were confirmed: in C-trd1 6.6 μg/mg CBD, 4.4 μg/mg CBN and 1.3 μg/mg CBC, while in C-trd2 0.46 μg/mg CBD, 0.27 μg/mg CBC and 0.19 μg/mg CBG were found. The latter results were characterized by repeatability (2.52–4.99% RSD), linearity (R2, 0.9640–0.9997) and recovery (87.9–109%) data.