Dimethylisopropylsilyl ether derivatives in gas chromatography mass spectrometry of prostaglandins and thromboxane B2

Abstract

The dimethylisopropylsilyl ether derivatives of PGF1α and PGF2αmethyl esters and PGD2, PGE1, PGE2, 6-Keto PGF1α and thromboxane B2 methoxime-methyl esters were separated completely within 15 min by gas chromatography using open tubular glass capillary column coated with SE-30. The methylene unit values of these derivatives were slightly greater than those of the corresponding dimethyl-n-propylsilyl ether derivatives. The use of the dimethylisopropylsilyl ether derivatives made it possible to perform the baseline separation of PGs and thromboxane B2 which were not separated by the trimethylsilyl ether derivatives. The mass spectral fragmentation of these dimethylisopropylsilyl ether derivatives was similar to those of the corresponding trimethysilyl ether derivatives, reported in a previous paper. Their mass spectra were characterized by the molecular ion, [M]+., and the ions [M—15]+ and [M—43]+ like those in the hydroxysteroid dimethylisopropylsilyl ether derivatives reported previously. The ion [M—34]+, which is produced by the elimination of isopropyl group from [M]+., was observed as an intense peak. The appearance of this ion in the high mass region was very useful for quantitation of trace amounts of PGs and thromboxane B2 in biological fluids without disturbance of endogenous substances by selected ion monitoring. The detection limit of the dimethylisopropylsilyl ether derivative of PGF2α methyl ester was found to be 5 pg with a signal-to-noise ratio of 10:1 when monitoring the ion [M—43]+ (m/z 625).