An assessment of the stability of MDMA, methamphetamine and THC in oral fluid

The stability of drugs proscribed under the Victorian Road Safety Act 1986 (MDMA, MA and THC) was determined in authentic drug-positive oral fluid following short-term storage at room temperature, 4°C, fluctuating temperatures and long-term storage at -20 °C. Following pH adjustment with ammonium carbonate solution, drugs were extracted using chloroform:isopropanol (9:1) and analysed by LC-MS/MS operating in multiple reaction monitoring mode. The results were analysed using Wilcoxon matched-pairs signed ranks and interpreted in the context of AS4760:2006 cut-offs. For MA and MDMA only minor changes occurred following all storage conditions, but THC concentrations were reduced by 70-87% (n=10) following storage at fluctuating temperatures (room temperature to 60°C) for 2 weeks. Of the 10 samples that were positive for THC prior to storage, only one remained positive after 2 weeks. This has significant implications for the interpretation of THC concentrations in cases where the possibility exists that samples were stored at higher temperatures.