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 (CH 3 ) 3 SiOH] − (PGE 0 and 15‐keto‐PGE 0 ) and [P 2 (CH 3 ) 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 μg 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 .