Negative Paper Spray Ionization Mass Spectrometry for the Determination of Endocrine-Disrupting Chemicals with Application to Paraben Analysis in Cosmetics

Paper spray ionization mass spectrometry (PSI-MS) enables rapid analysis with minimal sample preparation, yet negative-ion mode performance has been limited by poor sensitivity and unstable signals, similar to conventional electrospray ionization. In this study, we optimized negative PSI tandem MS (MS/MS) for twelve endocrine-disrupting chemicals (EDCs) and related biomarkers—including bisphenols, phthalates, parabens, and substituted phenols—used as model analytes. A systematic solvent and additive screen identified 1 mM ammonium fluoride in methanol and 0.1% ammonium hydroxide in 9:1 MeOH/carbon tetrachloride as optimal conditions, providing enhanced deprotonated-ion intensities and improved stability. Calibration curves generated under these conditions showed excellent linearity, with limits of quantitation (LOQs) in the low-ppb range. Application to cosmetic formulations demonstrated reliable paraben quantitation. In fortified hand cream, LOQs below 1 mg/kg were achieved, with recoveries of 93–110% and intra- and inter-day precision below 10% RSD. Notably, PSI-MS/MS performance was comparable to LC–MS/MS, without a separation step. These results demonstrate the feasibility of optimized negative PSI-MS as a sensitive and robust tool for paraben determination in cosmetics and highlight its potential as a versatile platform for broader EDC quantification.