Determination of the synthetic steroid norgestomet in bovine plasma by capillary column gas chromatography/negative chemical ionization mass spectrometry

A sensitive and specific method is described for the determination of norgestomet in bovine plasma as low as 10 ppt with better than 83% average recovery and a relative standard deviation (RSD) of range 1–3%. Norgestomet is separated from the bulk of the endogenous substances in plasma by adsorption on a PrepSep C18 extraction column and elution with acetonitrile. The residue after evaporation of acetonitrile is reacted with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride to form syn and anti geometric isomers of the mono-oxime derivative. The derivative, after further clean-up and evaporation of solvent, is reconstituted with cyclohexane, and an aliquot is analyzed by capillary column gas chromatography/negative chemical ionization mass spectrometry using methane as the carrier gas. Selected ion monitoring was employed to detect the [M – HF]− fragment ion of the norgestomet mono-oxime derivative (m/z 547) and its dideuterated mono-oxime analog (m/z 549) which serves as the internal standard. Quantification is achieved by using the Quantitative Selectd Ion Monitoring Processing System (QSIMPS) softwere to generate a standard curve of fragment ion area ratios v. concentration of norgestomet, and then calculate sample concentrations.