Gas chromatography–mass spectrometry/mass spectrometry analysis to determine natural and post-administration levels of oestrogens in bovine serum and urine

A novel analytical approach has been developed and shown to be capable of detecting the isomers of oestradiol in the low ppt (pg mL−1) range in bovine serum and urine. Following extractive derivatisation the analytes were detected as their 3-pentafluorobenzoyl 17-trimethylsilyl ether derivatives by gas chromatography–mass spectrometry/mass spectrometry (GC–MS/MS), using electron capture negative ion chemical ionisation. The isomers of oestradiol were quantified in both blank and post-administration urine and serum samples, with a view to setting action/threshold levels for these compounds, to allow discrimination between normal samples and samples from animals treated with growth promoting ear implants. A non-parametric statistical assessment of the data resulted in proposed action levels (with a false positive probability of 1 in 1000) of 1.6 and 2.7 ng mL−1 for 17α-oestradiol, in male and female urine, respectively, and 40 and 44 pg mL−1 for 17β-oestradiol, in male and female urine, respectively. An action level of 20 pg mL−1 was proposed for 17α- and 17β-oestradiol in male serum. In female serum the proposed action levels were 40 and 20 pg mL−1 for 17α- and 17β-oestradiol, respectively.