A Comprehensive Strategy for a Novel PDE-5 Inhibitor Adulterant in Foods: from Identification in Blending Liquor to Multi-Matrix Quantitative Analysis

This study developed a comprehensive strategy to identify and quantify a novel vardenafil analogue, SLX-2101, which was detected as an undeclared adulterant in functional foods. The compound was initially screened and characterized using ultra-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (UHPLC-UV-Q-TOF/MS), and its structure was confirmed via nuclear magnetic resonance (NMR) spectroscopy and comparison with a custom-synthesized reference standard. A quantitative ultra-performance liquid chromatography–tandem mass spectrometry (UHPLC-QqQ/MS) method was established and validated, demonstrating good linearity (1.0–100.0 μg/L, r  > 0.997), with a limit of detection of 0.3 μg/kg and a limit of quantification of 1.0 μg/kg. Mean recoveries ranged from 74.2% to 115.8% across various food matrices, with relative standard deviations between 0.4% and 12.5%. Application to 61 commercial samples revealed SLX-2101 in two functional wines marketed for their purported aphrodisiac effects at concentrations of 19.3 mg/kg and 1.3 × 10 3  mg/kg. The validated method enables reliable surveillance of this emerging adulterant, thereby providing a practical solution to address the critical gap left by conventional targeted screening protocols.