Negative-ion ESI-MS of E. coli lipids that elute from DEAE cellulose column with 30 mM NH4Ac. The prominent ions at m/z 691.487, 693.489, 705.513, 717.508, 719.462, 733.498, 745.496, 747.497, 759.554, 761.558, and 773.544 correspond to the [M-H]- ions of phosphatidylglycerol with 30:1, 30:0, 31:1cyclopropane (cp), 32:2, 32:1, 33:1cp, 34:2, 34:1, 35:2cp, 35:1cp, 36:2 acyl chains, respectively. The inset shows an expansion of the region from m/z 630 – 700 revealing the unknown ions.