Chemical confirmation of diethylstillbestrol residues in beef livers

A simple chemical technique was developed to confirm the presence of diethylstillbestrol (DES) residues in beef tissues at 2 ppb. The DES-trifluoroacetate (TFA) from the previously published method is hydrolyzed in water-methanol at 55 degrees C for 20 min to free DES which is then extracted into benzene. Trimethylamine and a small amount of heptaafluorobutyric (HFB) anhydride are added to effect the smooth conversion of DES to its di-HFB at either room temperature or 60 degrees C. DES-HFB is determined by gas-liquid chromatography with electron capture detection on a 6' x 4 mm id column of 3% OV-210 at 190 degrees C. This procedure yields 2 peaks for DES-HFB (retention times 2.7 and 4.8 min for the cis and trans, respectively) which are resolved from the 2 DES-TFA peaks (retention times 2.3 and 3.3 min for cis and trans, respectively). The sensitivity of detection of DES-HFB is increased by a factor of 4-5 over that for DES-TFA. This chemical technique was successfully applied to purified extracts of beef liver fortified with DES at 2-10 ppb with recoveries from 60 to 110%.