Dried blood spot (DBS) analysis of synthetic cathinones by different liquid chromatography-mass spectrometry techniques and interlaboratory validation for application in forensic toxicology

[Display omitted] •DBS.•Synthetic cathinones analysis.•Interlaboratory validation.•Stability evaluation.•Application to postmortem forensic casework with metabolites study. Dried Blood Spot (DBS) technique was employed as sample pretreatment for the detection of synthetic cathinones in blood samples, including from postmortem caseworks, by Liquid Chromatography-tandem Mass spectrometry (LC-MS/MS) techniques. The study involved the interlaboratory validation to evaluate the applicability of the method with different instruments, to assess the applicability and the ruggedness of the method for its wide application. The stability of cathinones in DBS was also evaluated. Authentic casework from drug-related deaths (DRD) involving synthetic cathinones were analysed and results compared in the two laboratories, using the developed methods. Metabolites were studied by two different LC-HRMS methods, orbitrap and Q-TOF. Validation results obtained in both laboratories demonstrated the suitability of DBS as sample storage and pre-treatment technique, allowing good sensitivities, repeatability, matrix effect and %bias. Limits of detection LOD and of quantification LOQ ranged between 0.3 and 1 ng/ml and between 0.5 and 10 ng/mL, respectively, for the studied cathinones in both laboratories. Stability studies demonstrated the high percent of degradation of cathinones, depending on their molecular structure, not attributable to DBS. The analysis of forensic caseworks containing α-PHP and MDPHP by DBS allowed their identification and quantification and the detection of various metabolites in postmortem blood samples. α-PHP degraded over time, while MDPHP concentration did not show significant differences in a three-months period, probably due to the presence of the metylendioxy moiety. These results demonstrate DBS to be a rapid and efficient technique for the analysis of cathinones, and that quantitative results for these analytes should be carefully interpreted due to their possible degradation.