The synthetic cathinones are powerful psychostimulants that have been associated with impairment, intoxication and fatal overdose. Forensic laboratories must be able to identify these new drugs as part of antemortem and postmortem toxicology investigations. Preliminary reports have indicated that some of the synthetic cathinones are unstable in biological matrices. It is important to understand drug stability in biological evidence so that analytical findings can be interpreted appropriately. The objective of this study was to systematically evaluate the concentration, temperature and analyte-dependent stability of synthetic cathinones in preserved blood using liquid-chromatography/quadrupole-time of flight-mass spectrometry (LC/Q-TOF-MS). Cathinone stability was investigated at frozen, refrigerated, ambient and elevated temperature (-20°C, 4°C, 20°C and 32°C). Although no concentration dependent differences in stability were observed, cathinone stability was highly temperature and analyte-dependent. Substituents on the aromatic ring and nitrogen profoundly influenced stability. Tertiary amines (pyrrolidinyl analogs) were significantly more stable than their N-alkylated (secondary amine) counterparts. Furthermore, the methylenedioxy (MD) group also exerted a significant stabilizing effect, for both secondary and tertiary amines. The unsubstituted and ring-substituted secondary amines were the least stable, most notably 3-fluoromethcathinone (3-FMC). Under some conditions, significant losses were observed within hours of storage. Half-lives ranged from a little as 8 h (3-FMC) to 21 days (3,4-methylenedioxy-α-pyrrolidinobutiophenone, MDPBP) at elevated temperature (32°C). In contrast, half-lives ranged from 0.4 to >10 months when refrigerated and demonstrated even greater stability when frozen. Biological evidence may be subjected to a variety of environmental conditions prior to, and during transport to the laboratory. These findings highlight the need to consider the potential for both temperature and analyte-dependent differences. Due to the inherent instability of certain drugs within the class, quantitative drug findings in toxicological investigations must be interpreted with caution, and within the context of specimen storage and integrity.
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