Determination of oxyphenisatine and its total ester derivatives content in fermented green plum by ultra performance liquid chromatography-tandem mass spectrometry.

Illegal additives such as oxyphenisatine and its esters are prevalent in the slimming food industry, necessitating a robust analytical method for their detection. This study presents a novel UPLC-MS/MS method for the rapid and accurate quantification of total oxyphenisatine levels in fermented green plum, following hydrolysis of its esters. An efficient ultrasonic extraction with a methanol and 0.1 mol/L NaOH mixture (5:5, v/v) was optimised to hydrolyse esters to oxyphenisatine within 18 min. Chromatographic separation was conducted on a C18 column (Waters Acquity UPLC BEH, 2.1 × 100 mm, 1.7 μm) with a mobile phase of 5 mmol/L ammonium acetate and acetonitrile under gradient elution at a flow rate of 0.3 mL/min. The method demonstrated linearity (r2 > 0.999) over 0.1-500 µg/L, with a LOD of 10 µg/kg and LOQ of 30 µg/kg. Quantitative analysis employed positive ion multi-response monitoring and external standardisation, achieving recoveries of 92.4-97.0% and RSDs of 2.9-4.1%. Application to ten real samples gave a 90% detection rate, with measured values closely aligning with theoretical predictions (-11.3 to 13.2% relative difference) and oxyphenisatine content ranging from 159 µg/kg to 452 mg/kg. This UPLC-MS/MS method provides a reliable and efficient tool for monitoring the presence of oxyphenisatine and its derivatives in the context of food safety.