In situ detection of fatty acid C=C positional isomers by coupling on-tissue mCPBA epoxidation with infrared matrix-assisted laser desorption electrospray ionization mass spectrometry.

The on-tissue mCPBA epoxidation was implemented into an ambient MS imaging workflow to offer a rapid and simple way for in situ identification and relative quantification of double-bond positional isomers without the requirement for instrument modification. The method can be readily implemented on many other MS platforms to reveal the role of double-bond positional isomers in lipid biology and to discover potential biomarkers.