Rapid Analysis of Unsaturated Fatty Acids on Paper-Based Analytical Devices via Online Epoxidation and Ambient Mass Spectrometry

In this work, we demonstrate a novel design that allows rapid online identification and quantitation of unsaturated fatty acid C=C location isomers via epoxidation and ambient mass spectrometry (MS). Unsaturated fatty acid solution was loaded on a paper strip placed between a low-temperature plasma probe and the inlet of a mass spectrometer. Reactive oxygen species in the plasma promoted epoxidation at the C=C, and the product was simultaneously ionized. Upon collision-induced dissociation (CID), the epoxidation product was fragmented to release diagnostic ions specific to the C=C location. The whole analytical workflow can be completed within 5 s and is particularly promising for point-of-care (POC) clinical diagnosis, considering its fast, high-throughput nature, and coupling with paper-based analytical devices.