Quantification of diethylstilbestrol residues in meat samples by gas chromatography-isotope-dilution mass spectrometry

A method is described for the quantitative determination of residues of the synthetic estrogen diethylstilbestrol (DES) in meat at levels as low as 0.1 ppb. Samples were enzymatically digested with subtilisin and and extracted with diethyl ether. The organic phase was then subjected to a cleanup, consisting of two liquid-liquid partitioning. Residues of DES in the extract were derivatized to bis(heptafluorobutyryl)-DES and assayed by electron-impact mass spectrometry. Quantification was achieved by measuring the intensity ratio of the m/z 660 ion (molecular ion of DES) and the m/z 666 ion (molecular ion of the hexadeuteriated DES analogue). The latter not only served as the internal standard but also monitored the derivatization efficiency and stabilized the cis/trans DES isomers ratio. Analytical recovery from meat, as assayed with a /sup 3/H-labeled DES, was about 90%. The method was used to confirm positive radioimmunoassay results.