Mass Spectrometry-Based Shotgun Lipidomics Using Charge-Switch Derivatization for Analysis of Complex Long-Chain Fatty Acids

Charge-switch derivatization to convert long-chain fatty acids (LCFAs) to their N-(4-aminomethylphenyl) pyridinium (AMPP) derivatives (FA-AMPP derivative) drastically increases their sensitivity (>10²) detected by electrospray ionization (ESI) or matrix assisted laser desorption ionization (MALDI). Lipidomic analyses of the FA-AMPP derivatives by ESI combined with CID tandem mass spectrometry (MS²), or by MALDI-TOF/TOF affords unambiguous structural characterization of LCFAs, including many unusual microbial LCFAs that contain various functional groups such as methyl, hydroxyl, cyclopropyl, and double bond(s). The ease of preparation of the FA-AMPP derivatives, the tremendous gain in sensitivity after derivatization, and more importantly, the readily recognizable product ion spectra that contain rich structurally informative fragment ions for locating functional groups make this method one of the most powerful techniques for LCFA identification and quantification.