Quantitative analyses of standard PC molecular species using MALDI-TOF MS. A) Mass spectrum of an equimolar mixture of D14:0-14:0 PtdCho, D16:0-16:0 PtdCho, D18:0-18:0 PtdCho, D20:0-20:0 PtdCho and D22:0-22:0 PtdCho; B) Mass spectrum of an equimolar mixture of D18:3-18:3 PtdCho, D18:2-18:2 PtdCho, D18:1-18:1 PtdCho and D18:0-18:0 PtdCho. Mass spectra were acquired on a 4800 MALDI-TOF/TOF Analyzer in the positive ion mode using 9-aminoacridine as matrix as described in the “Experimental Section”. Isopropanol/acetonitrile (60/40, v/v) was used as solvent for dissolving both matrix and PCs. The amount of each individual PC molecular species in each spot is 150 fmol. The prefix ‘‘D’’ stands for diacyl (i.e., phosphatidyl-) species.