EPI spectra of (A) precursor mass of 704.40 of synthetic PA (16:0D31/18:1). (A’) The resulting sn−1 fatty acid carboxylate ion and sn−2 counterpart are shown in the inset. (B) XIC of 671.34–253.2 MRM transition and (C) of 671.4–255.2 MRM transition from Drosophila head lipid extract. The ion count of the corresponding transitions are represented (y-axis) with reference to the elution time of the molecules from the LC column (x-axis). (D) EPI spectra of precursor mass of 671.34 from Drosophila head lipid extract. (D’) Fatty acid carboxylate ions observed are as follows: m/z 253.42, 255.28, 279.25, 281.27, and relative levels of these masses are shown in the inset.