Collision-Induced Gas-Phase Reactions of PFB-TMS Derivatives of F₂-Prostaglandins in Quadrupole GC-NICI-MS/MS: A...

Arachidonic acid (eicosatetraenoic acid) is the precursor of the eicosanoids, which include prostaglandins (PG). Methods based on GC-MS/MS are the Gold Standard for the quantitative analysis of eicosanoids in biological samples. After extraction and derivatization, biological F₂-prostaglandins are analyzed on quadrupole GC-MS/MS apparatus as pentafluorobenzyl (PFB) ester trimethylsilyl (TMS) ether derivatives, i.e., PFB-TMS. Negative-ion chemical ionization (NICI) in the ion source generates abundant anions due to [M-PFB]^-, which are detected in the selected ion monitoring (SIM) mode. Collision-induced dissociation (CID) of [M-PFB]^- in the collision cell generates numerous product ions, which are suitable candidates for quantitative analyses in the selected reaction monitoring (SRM) mode. In this article, we report on investigations of gas-phase reactions of PFB-TMS derivatives of F₂-prostaglandins, which consist of PGF_2α, 8-iso-PGF_2α, and up to 62 further isomers, known as the F₂-isoprostanes. We performed a meta-analysis of previously reported CID mass spectra (32 eV) of PFB-(TMS)₃ of seven chemically closely related isomeric F₂-prostaglandins of the 15-F_2t-IsoP type. This unique dataset contains 19 product ions generated by CID of the common precursor at m/z 569 [M-PFB]^- in the m/z range of 150-600. All isomers produced the same product ions, which, however, greatly differed in their intensity. Principal Component Analysis (PCA) and Receiver Operating Characteristic (ROC) Analysis (ROCA) were performed. Two compounds, i.e., 8-iso-9β,11α-PGF_2α and 9α,11β-PGF_2α, and two product ions, i.e., m/z 299 [M-PFB-3×TMSOH]^- and m/z 215 [M-PFB-3×TMSOH-C₄H₈-C₂H₄]^-, were noticeable. ROCA revealed the highest disagreement between PGF_2α and 8-iso-9β,11α-PGF_2α (AUC = 0.7075 ± 0.0834, p = 0.0248). PCA and ROCA are of limited value in the GC-MS/MS of closely chemically related F₂-prostaglandins. Fragmentation mechanisms were proposed for the formation of all 19 product ions generated by CID of common precursor anions due to [M-PFB]^-.