MRM using mass transition m/z 353/193 detects 8-iso-PGF2α and PGF2α standards (A, top). Three major peaks are observed in most HFF samples (A, bottom). Based on nano-LC qTOF analysis, these peaks may contain co-eluting PGF2α isomers (see Discussion). MRM using mass transition m/z 351/189 detects PGE2 (B, top) and PGD2 standards (not shown at RT = 12.6 minutes). A single major peak is observed in most HFF samples corresponding to PGE2 (B, bottom). MRM using mass transition m/z 355/311 detects the PGF1α (C, top) standard. A peak at RT 12.1 is observed in most HFF samples corresponding to PGF1α (C, bottom). MRM using mass transition m/z 353/317 detects the PGE1 (D, top) standard. A peak at RT 12.5 is observed in most HFF samples corresponding to PGE1 (C, bottom). Cps, counts per second.