Long-term stability of sufentanil quantified by UPLC–MS–MS in human plasma frozen for 11 years at −20°C

The long-term stability of drug concentrations in human plasma samples, when stored under normal laboratory conditions over several years, is important for research purposes and clinical re-evaluation, and forensic toxicology. Fifty human plasma samples from a former clinical trial were re-analyzed after storage at -20°C for 11 years. Plasma samples were extracted using solid-phase extraction. Isotope labeled sufentanil-d5 was used as internal standard. Sufentanil plasma concentrations were determined by ultra-performance liquid chromatography with gradient elution, followed by tandem mass spectrometry with electrospray ionization. The linear dynamic range was 25-2500 pg/mL, the limit of detection was 10 pg/mL, and the lower limit of quantification was 25 pg/mL. Intra- and inter-assay error did not exceed 6%. The deviation of the measured sufentanil plasma concentrations between the re-analysis and the first analysis was -63 ± 14% (mean ± SD). Therefore, sufentanil concentrations in human plasma were not stable in samples frozen at -20°C over 11 years.