Over the last few years stimulant substances, such as amphetamine-type stimulants (ATS) and synthetic cathinones (SC), have dramatically increased the frequency of lethal intoxications. The spread of these stimulant drugs has caused a complex challenge to the forensic toxicology community. Most analytical methods focus on detection and quantification of a specific class of drugs instead of an extensive variety of compounds. A method for the detection and quantification of 29 ATS and SC drugs in a single procedure was carried out using solid-phase extraction (SPE), pentafluoropropionic anhydride (PFPA) agent and gas chromatography—mass spectrometry (GC−MS). The method was validated in accordance with SWGTOX guidelines using human urine samples. The limits of detection (LOD) and lower limits of quantification (LLOQ) were between (0.5 and 10) ng mL−1, and (5 and 50) ng mL−1, respectively. The linearity range was between 50 and 2000 ng mL−1 with a R2 >0.990 for 20 compounds. The bias and RSD were ≤20%, and no interferences or carryover were observed. The recovery was 80 to 120% for the majority of analytes.
Prior to testing the substances, the GC−MS was initially optimised in terms of the oven and injector port temperatures. The sensitivity and selectivity of the GC−MS were then improved using acidified methanol and derivatisation agents. Six acylation reagents were compared and investigated using PFPA, trifluoroacetic anhydride (TFA), chlorodifluoroacetic anhydride (CLF2AA), heptafluorobutyric anhydride (HFBA), acetic anhydride (AA) and propionic anhydride (PA). The derivatisation method was optimised by modifying incubation time and temperature during the reaction and evaporation stages. Several parameters were used to evaluate the performance of the reagents, including the number of ions, relative ion ratio, peak area values, number of unique ions with some validation parameters. The reagents were further inspected using recovery through SPE in whole blood. The results of the comparison study showed that PFPA was the favoured reagent. All the derivatisation reagents were suitable for use on cathinones.
Long term stability was investigated for the 29 stimulant compounds in human urine specimens over a period of 381 days at room temperature (RT), refrigerator (4°C) and freezer (−20°C) conditions. ATS were stable under all conditions, and all tested substances were stable at freezer conditions. Most SC at RT had lost more than 20% of the compound after two days, and had completely disappeared after a month. Most SC’s at refrigerator temperatures were unstable after day 21, and gradually decreased until undetected between days 77 and 349. The substances were stable on the autosampler for three days. No concentration-dependent variations were observed. Half-lives of selected drugs were briefly discussed.
A sample preparation method that meets green analytic chemistry (GAC) requirements is desirable. Therefore, a method using solid phase microextraction (SPME) tips were initially developed via 13 processing steps and then validated using GC−MS in urine for eight ATS and SC substances. LOD and LLOQ were (5−25) ng mL-1, and (25−100) ng mL-1, respectively. The bias and RSD were <15% error with R2 ≥0.992 for all analytes. Applying green analytical chemistry (GAC) parameters, the procedure had minor effects on health, waste and safety proportionate to LLE and SPE by adding the only microscale amounts of methanol and salt.
Attention to the prevalence of new psychoactive substances (NPS) such as SC, is significant to the justice system and the forensic toxicology community. The prevalence of SC was studied using 273 urine specimens collected from Riyadh City in Saudi Arabia. The cathinone compound estimation prevalence rate was 1.01%. No other cathinones were identified. Further prevalence studies should be conducted in the future using a larger sample size and incorporating more drug substances and metabolites
