MFQL identification of phosphatidylcholines (PC). The chemical structure of PC is shown in Figure 5. Upon their collisional fragmentation, molecular cations of PC species produce the specific head group fragment with m/z 184.07 and sum composition 'C5 H15 O4 P1 N1'. (a) MS spectrum acquired by direct infusion of a total lipid extract into a QSTAR mass spectrometer (inset). All detectable peaks were subjected to MS/MS. The spectrum acquired from the precursor m/z 788.55 (designated by arrow) is presented at the lower panel. The precursor ion was isolated within 1 Da mass range and therefore several isobaric lipid precursors were co-isolated for MS/MS and produced abundant fragment ions unrelated to PC. These ions were disregarded by this MFQL query and did not affect PC identification. (b) MFQL query identifying PC species, details are provided in the text. (c) Screenshot of the output spreadsheet file; column annotation and content is determined by the REPORT section of the above MFQL (see also text for details).