The comparison between the EIC of PE 34:1;Ep in heart and liver extract is shown in Figure and ), the highest intensity feature in the EIC is assigned to PE 16:0_18:1;9Ep. These spectra are highlighted by blue circles in Figure . With the additional information from the LC trace of the lipid without epoxide after reaction, the lipid PE 16:0_18:1(9Z) can be assigned. All investigated monounsaturated lipids for these two extracts contained only Z DB geometries as expected (see Figure for examples). The shoulder at 19.2 min in heart extract contains fragment ions at m/z 479.41 and m/z 495.40 revealing that PE 16:0_18:1;11Ep is responsible for the broadening of the chromatographic peak (MS 2 ; orange circles). For liver extracts the broadening of the EIC is not present and the majority of MS 2 spectra are assigned to PE 16:0/18:1;9Ep with the exception that two MS 2 spectra contain low intensity signals at m/z 465.39 and m/z 481.39 (Figure ). These signals are consistent with low levels of PE 16:0_18:1;10Ep. Therefore, these results in combination with LC traces from unreacted lipids after epoxidation reveal that heart extract and liver extract contains PE 16:0_18:1(9Z) as well as PE 16:0_18:1(11Z) and PE 16:0_18:1(9Z) as well as low levels of PE 16:0_18:1(10Z), respectively.