Hexamethyldisilazane as an Acylation Generator for Perfluorocarboxylic Acids in Quantitative Derivatization of Primary Phenylalkyl Amines Confirmed by GC/MS and Computations

Direct sample preparation and simultaneous perfluoroacylation - Trimethylsilylation of biogenic monoamines along with their acidic metabolites for a single step analysis by GC-MS

The GC-MS quantification of biogenic monoamines (BMAs), together with their acidic metabolites (ACMEs), in a single step, is presented here for the first time. This novel principle is based on the exceptional reactivity of the hexamethyldisilazane (HMDS) and perfluorocarboxylic acid (PFCA) couples [1,2], resulting in the simultaneous trimethylsilylation and acylation of BMAs and ACMEs. For this basic study, tyramine (TYR), 3-methoxytyramine (3-MeTYR), dopamine (DA), epinephrine (EP), normetanephrine (NORMNE), norepinephrine (NOREP), tryptamine (T), 3,4-dihydroxyphenylalanine (L-DOPA), 5-methoxytryptamine (5-MeT), serotonin (ST), and their ACMEs, such as homovanillic acid (HVA), vanillylmandelic acid (VMA), and 5-hydroxyindoleacetic acid (5-HIAA) were selected. These three ACMEs were derived from 3-MeTYR, NORMNE and ST, respectively. The mass fragmentation properties of the fully derivatized products proved to be of stoichiometric distribution. Informative high masses were obtained: such as the molecular ions [M]⁺⁼ and/or their [M-CH3]⁺ alternatives. The exceptions were EP and NOREP which decomposed to the same specific, abundant mass of m/z 355 representing the C₇H₃-tri-OTMS ions formed by the loss of their nitrogen-containing moieties. The general rule of this new principle was confirmed by using trifluoroacetic acid (TFA), pentafluoropropionic acid (PFPA), or heptafluorobutyric acid (HFBA) with HMDS in parallel tests. In all three cases, derivatives of close retention properties in a stoichiometric manner were obtained. On the basis of the optimum separation characteristics between the BMA-ACME pairs, the HMDS & PFPA couple was preferred as the reagent of choice. Method validation was carried out, both with model solutions and in the presence of the urine matrices (without any preliminary extraction). Analytical performance characteristics for the model solutions like repeatability (RSD% 3.88-6.4), linearity (R² 0.991-0.999) and limit of quantitation (LOQ 8.8-103 ng/mL) were determined. Analytical performance characteristics for urine matrices were calculated by using the standard addition method applying the urine of a healthy volunteer and also analyzing urines of patients diagnosed with neurological diseases.

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

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 reagents¹ 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.