Freeze‐thaw stability and long‐term stability of 84 synthetic cannabinoids in serum

Information about stability of synthetic cannabinoids is important to give recommendations for storage conditions in cases in which use of synthetic cannabinoids is suspected. In this study, freeze-thaw stability (3 cycles at -20 °C at 1.5 ng/mL) and long-term stability at room temperature, 4°C and -20°C (for 150 days) were tested by a validated liquid chromatographic-mass spectrometric method for 80 synthetic cannabinoids. Results demonstrated good freeze-thaw stability for most of the substances. For 5 F-ABICA (72.6% of peak area of time point zero), 5 F- 2 ADB PINACA 2 Isomer (68.7 %), 5Cl-AB-PINACA (84.2 %), AB FUBINACA 2-Isomer (33.5 %), 5 F-PCN (89.7 %), ADB-FUBINACA (78.0 %), EG 018 (88.9 %), and PX-1 (89.4 %) three freeze-thaw cycles led to absolute peak areas < 90% compared to 6 control samples. For 51 of the 84 substances, stability in serum could be demonstrated after 315 days of storage at -20°C. For 82 of the 84 substances, stability in serum could be shown for at least 1 month at -20°C. Long- term stability at 4°C or 20°C showed worse results. Therefore, it is our recommendation to store real serum samples at -20°C until analysis.