Quantification and distribution of 4-fluoroisobutyryl fentanyl (4-FiBF) in postmortem biological samples using UHPLC–QqQ-MS/MS

Abstract Purpose Development of ultra-high-performance liquid chromatography-triple quadrupole tandem mass spectrometry method for quantification 4-fluoroisobutyryl fentanyl (4-FiBF) and its distribution in postmortem biological samples four fatal intoxication cases, which occurred September 2018, Poland. Methods Biological fluids (blood, urine, vitreous humor, bile, gastric content) tissues (brain, kidney, liver, stomach wall) were extracted with ethyl acetate from alkaline medium (pH 9). Fentanyl- d 5 was used as internal standard. Results The validation parameters follows: lower limit quantification: 0.1 ng/mL (biological fluids) ng/g (solid tissues), intra- inter-day accuracies precisions: not greater than 20%; recovery values: 86.9–110%; matrix effect: − 13.1–10.4%. Among all tested fluid, the highest concentration 4-FiBF found bile (average 3390 ng/mL) while among tissues, liver 1650 ng/g). Furthermore, collected specimens, there also other drugs new psychoactive substances (NPS) e.g. N- ethylpentylon, 4-chloromethcathinone (4-CMC) α-pyrrolidinoisohexanophenone (α-PiHP). Concentrations distributions these have been detailed. Examinations seized drug (in case 4) revealed that it included mix α-PiHP. Conclusions developed fully validated enabled determination tissues. To our knowledge, this is first report study NPS ( N -ethylpentylon, 4-CMC α-PiHP) authentic cases.