Assessment of the stability of mephedrone in ante-mortem and post-mortem blood specimens

• −20 °C is the best storage temperature among the ones tested.
• Ante-mortem samples are more stable than post-mortem at all tested conditions.
• NaF/KOx maintains mephedrone's stability better than EDTA or no preservative.

AimsThe aim of this work is to test the stability of mephedrone added to whole blood collected from alive and dead mephedrone free-users and stored at three different temperatures (−20, +4 and +20 °C) with and without preservatives up to 6 months, trying to establish the best storage condition in order to reduce possible analyte loss/degradation during the storage period.Materials and methodsDifferent sources of blood were obtained as follow: 10 samples of blood came from 10 alive mephedrone free-users (mean age 34 ± 15.8 years old) (Group 1), whereas 10 post mortem blood samples were obtained from 10 cadavers, in which the post mortem interval was between 24 and 36 h (Group 2). The cause of death in post mortem cases (mean age 45 ± 14.2 years old) was not drug related. Pools of blood were spiked with mephedrone at the concentration of 1 mg/L and 1 mL aliquots were transferred in 2 mL Eppendorf capped tubes with and without preservatives as follow: with ethylenediaminetetraacetic acid (EDTA) 3%; with sodium fluoride/potassium oxalate (NaF/KOx) 1.67%/0.2%, respectively; without preservatives. All samples were stored at three different temperatures: −20 °C, 4 °C and 20 °C and extracted and analyzed in duplicate by GC–MS according to a previously published method by Dickson et al., every other day during the first month and then weekly up to 6 months.Results and conclusionsour study allow us to affirm that −20 °C is the best storage temperature for mephedrone stability in ante-mortem and post-mortem blood samples in comparison to the other two tested temperatures (+4 and +20 °C), showing higher values in both groups in samples stored with and without preservatives (p < 0.0001).The comparison of Group 1 (samples coming from alive subjects) and Group 2 (post-mortem samples) highlights a better stability of mephedrone in Group 1 (p < 0.001) at all tested storage conditions.Finally, the analysis of blood specimens stored with and without preservatives in both groups suggests that specimens stored with NaF/KOx maintain mephedrone stability better than those stored with EDTA (p < 0.001) and those stored without preservatives (p < 0.0001), therefore, we strongly recommend in order to maintain the highest mephedrone stability in blood, to store specimens at −20 °C adding NaF/KOx as preservative.