Rapid simultaneous assay of serum estrone, estradiol, and estriol in pregnant women using methyl ether acetate derivatives by capillary gas chromatography and electron-impact mass spectrometry

A simple gas chromatographic--mass spectrometric method capable of measuring estrone, estradiol, and estriol simultaneously with a sensitivity close to that of radioimmunoassay has been developed. The estrogens in serum were extracted with diethyl ether, and internal standards (3-O-C2H3-estrone, 3-O-C2H3-estradiol, and 3-O-C2H3-estriol) were added, followed by converting to methyl ether compounds with an extractive alkylation procedure. The methyl ethers were then acetylated. Analyses were performed using a SP-2250 capillary column gas chromatograph coupled with an electron-impact mass spectrometer. The estrogen methyl ether acetate derivatives were more stable chemically and gave less fragmentation upon electron impact than the conventional trimethylsilyl derivatives. The use of selected ion monitoring of molecular ions and that of the corresponding internal standards (M + 3) provides a sensitivity down to 10 pg for estrone and estradiol and to 200 pg for estriol. The time required for the preparation of multiple samples is within 4 hours.