Application of DMS combined with RP-UPLC to enhance selectivity. A: RP-UPLC separation of lipids extracted from human serum in positive ion mode (left panels) or negative ion mode (right panels) without DMS (A) or with DMS (B). Top panel of A shows total ion current of RP chromatogram by EMS scan. Bottom panel shows mass spectral data of EMS scan. Top panel of B shows total ion current of RP chromatograms by EMS scan with application of COV values specific for each phospholipid class (sum of 14 scans). Bottom panel shows three selected EMS scans with COV voltages of 0.3, 2.5, and −5.0 specific for PC, SM, and Cer in positive ion mode or −3.0, −2.9, and 3.0 for PC, PA, and PI in negative ion mode. Also shown are mass spectral data.