Determination of acetyltrimoprostil and its metabolite trimoprostil in human or dog plasma by gas chromatography—negative-ion chemical ionization mass spectrometry

Abstract

A sensitive and specific procedure is described for the determination of the antisecretory prostaglandin acetyltrimoprostil and its metabolite trimoprostil in human or dog plasma using gas chromatography—negative-ion chemical ionization mass spectrometry (GC—NICI- MS). Trideuterated analogues of both compounds are added to plasma as the internal standards. The plasma is extracted at pH 7.3 with benzene—dichloromethane (9:1), and the residue of the organic extract is reacted at room temperature with pentafluorobenzyl bromide in the presence of 18-crown-6-ether and potassium acetate. The derivatives are reconstituted in heptane, and appropriate aliquots are analyzed by GC—NICI-MS with selected-ion monitoring of the intense (M - C 6F 5CH 2) − fragment ions of acetyltrimoprostil ( m/ z 419), trimoprostil ( m/ z 377), and their respective trideuterated analogues ( m/ z 422 and m/ z 380, respectively). Quantitation of an experimental plasma sample is based on a comparison of the m/ z 419 versus m/ z 422 and m/ z 377 versus m/ z 380 ion ratios in each sample to that obtained from the analysis of drug-free plasma fortified with various amounts of both protio compounds, and a fixed amount of each trideuterated internal standard. The limit of quantitation of the assay for human plasma is 0.2 ng ml −1 with mean relative standard deviations at this concentration of 15.5% and 9.7% for acetyltrimoprostil and trimoprostil, respectively.