DETERMINATION OF PROSTAGLANDIN E(1) AND ITS MAIN PLASMA METABOLITES 15-KETO-PROSTAGLANDIN E(0) AND PROSTAGLANDIN E(0) BY GAS-CHROMATOGRAPHY NEGATIVE-ION CHEMICAL-IONIZATION TRIPLE-STAGE QUADRUPOLE MASS-SPECTROMETRY

Prostaglandin E(1) (PGE(1)), 15-keto-PGE(0) and PGE(0) in plasma were determined in an isotope dilution assay by gas chromatography/triple-stage quadrupole mass spectrometry. After addition of deuterated internal standards, the prostaglandins were extracted by a solid-phase cartridge and derivatized to the pentafluorobenzyl ester methoxime. The samples were purified by thin-layer chromatography, converted to the trimethylsilyl ethers and quantified by gas chromatography/triple-stage quadrupole mass spectrometry. The parent ions in the negative ion chemical ionization mode were [M-pentafluorobenzyl](-) ([P](-)), the daughter ions used for quantification were [P-(CH3)(3)SiOH](-) (PGE(0) and 15-keto-PGE(0)) and [P-2(CH3)(3)SiOH](-) (PGE(1)), respectively. Plasma concentrations in healthy subjects were at about 1-3 pg ml(-1) for PGE(1) and PGE(0) and 2-15 pg ml(-1) for 15-keto-PGE(0). After infusion of 60 mu g PGE(1) in 2 h, the concentrations in plasma were 3-10 pg ml(-1) for PGE(1), 8-17 pg ml(-1) for PGE(0) and 115-205 pg ml(-1) for 15-keto-PGE(0).