Investigation of adulterated seized heroin samples and direct stereochemical analysis of methorphan by chiral HPLC–MS/MS

This research was focused on an in-depth investigation of 45 heroin samples seized in Northeast Italy, using complementary hyphenated analytical techniques. Gas chromatography coupled with mass spectrometry (GC–MS) and solid deposition Fourier transform infrared (FTIR) spectroscopy were employed to identify the seizure components. Common adulterants like caffeine and paracetamol were detected almost ubiquitously, along with other cutting agents from various chemical classes. Noticeably, some of them are known for their synergistic effects with heroin. Additionally, two unknown minor components were tentatively identified using combined GC–MS and GC–FTIR data. Notably, all samples contained methorphan, a chiral molecule with enantiomers having distinct effects and toxicological profiles. Thus, enantioselective liquid chromatography-tandem mass spectrometry (HPLC–MS/MS) was implemented using a vancomycin-based column, obtaining an enantioselectivity (α) of approximately 1.2. Analyses were performed on a triple quadrupole mass spectrometer with atmospheric pressure chemical ionization in multiple reaction monitoring mode. The method was validated with calibration curves (0.0005–5 mg/L), limit of detection (0.0026 mg/L), limit of quantification (0.0088 mg/L), intra-day and inter-day precision (1.6–5.3%), and trueness (88.7–105.3%). Results showed that dextromethorphan was present in all samples (2.86–1,190 mg/L), while levomethorphan was detected at trace levels (0.21 and 0.038 mg/L) in two samples only, besides dextromethorphan.