Determination of an antisecretory trimethyl prostaglandin E2 analog in human plasma by combined capillary column gas chromatography-negative chemical ionization mass spectrometry.

A method is described for measuring a trimethyl prostaglandin E2 analog, TM-PGE2, in human plasma. Trideuterated and monofluorinated analogs of TM-PGE2 and added to plasma as internal standard and carrier, respectively. The plasma is adjusted to pH 3.0 and is extracted with a mixture of benzene-dichloromethane (9:1). The residue, following removal of the extracting solvent, is reacted consecutively with pentafluorobenzyl bromide and bistrimethylsilyltrifluoroacetamide. The excess derivatizing reagents are removed by evaporation, and an aliquot of the reconstituted residue is analyzed by capillary column gas chromatography using methane as the carrier gas. A quadrupole mass spectrometer is set to monitor in the gas chromatographic effluent the (M - C7H2F5)-fragment ion of TM-PGE2 (m/e 449) and trideuterated TM-PGE2 (m/e 452) generated by methane negative chemical ionization. Quantitation of unknowns is based on a comparison of the m/e 449 to m/e 452 ion ratio in each unknown to that obtained from the analysis of control plasma spiked with known amounts of TM-PGE2 and fixed amounts of internal standard and carrier. The sensitivity limit of the assay is approximately 100 pg ml-1, which is equivalent to 1 pg injected. The assay was used to measure the concentration of TM-PGE2 in the plasma of two subjects following a single 10 micrograms kg-1 oral dose of the drug.