Results for other lipid compositions are shown in Figure . Because E/Z assignment was not possible for PUFAs, only DB position and FA composition are reported. Photo-epoxidation of unsaturated lipids and RPLC-MS 2 enables the assignment of the FA composition as well as DB positions for DG, TG, PC, PE, PS, LPC, and LPE enabling to differentiate the isomer composition between the two extracts. For example, DG 36:1 in liver only contains DG 18:0_18:1(9), whereas the same lipid is composed of DG 18:0_18:1(9) and DG 18:0_18:1 (11) in heart (Figure ). Beside revealing DB positional isomers, FA compositional isomers can be resolved. This is the case for TG 52:2 for which TG 16:0_18:1_18:1(9), TG 16:0_18:1_18:1 (11), and TG 16:0_18:0_18:2 (9,12) are observed in both extracts but their relative abundance differs (Figure ). Beside the well-known DB positions for FA 18:1 at Δ9 and Δ11, our method identifies DBs at Δ10 and Δ12 in low relative abundance. These results are consistent with PB assignments of these DB isomers from bovine extracts and were recently also observed in low abundance for FAs. All other DB positions are in line with canonical DB positions and have the highest abundance (above 85 %). That the determination of DB positions is not limited to lipids with only a few DBs is showcased for PEs and PCs. For example, PE 38:4 consists only of PE 16:0_22:4 (5,8,11,14) in heart extract but liver is composed of PE 16:0_22:4 (5,8,11,14), PE 18:0_20:4 (7,10,13,16), and low abundant PE 18:1(12)_20:3 (Figure ). These results demonstrate that the coupling of photo-chemical epoxidation with chromatographic separation enables assignment of DB positions, FA composition, and for lipids with monounsaturated FA moieties the DB geometry in complex mixtures supporting RPLC-MS workflows for global lipidomics.