Electrospray ionization (ESI)-MS analyses of equimolar mixtures of cardiolipin molecular species at selected concentrations. Preparation of equimolar mixtures of 1,1′,2,2′-tetramyristoyl cardiolipin (T14:0 CL) and T18:1 CL at selected concentrations and negative ion ESI-MS analyses of these equimolar mixtures in the negative ion mode by direct infusion were performed on a triple-quadrupole (QqQ) mass spectrometer using a peak width setting of 0.7 Th, as described in detail in Materials and Methods. The abundant ions at m/z 619.5 and 727.5 are doubly charged T14:0 CL and T18:1 CL molecular species, respectively, as indicated. Inset A shows an expanded spectrum of the doubly charged T18:1 CL molecular ion. The dashed line peaks in inset A are the results of deconvolution analysis of the doubly charged T18:1 CL isotopomers.