Determination of β-Estradiol Residues in Fish/Shellfish Muscle by Gas Chromatography-Mass Spectrometry

A gas chromatography-mass spectrometry (GC-MS) method was developed for the identification and quantitative determination of β-estradiol residues in the muscle tissues of various fishes/shellfishes, using deuterated internal standard. Homogenized tissue samples added with β-estradiol-D2 and acetate buffer (pH5.2) were extracted by acetonitrile under ultrasonication. Clean-up was carried out with hexane, followed by C18-solid phase extraction (SPE). To enhance detection sensitivity, derivatization was achieved prior to GC-MS analysis with N-methyl-N-(trimethylsilyl)-trifluoroacetamide/iodotrimethylsilane/dithioerythritol (MSTFA-TMIS-DTE). Quantitation using isotope-labelled internal standard was based on the ratio of peak area of β-estradiol derivative to peak area of internal standard derivative in the selected ion monitoring (SIM) mode with electron impact (EI) source. Good linearity ranged from 0.005 to 0.25 μg ml−1. The limit of quantitation (LOQ) was 0.2 μg kg−1. At 0.2, 1.0, 5.0 μg kg−1 spiked levels, the mean recoveries were in the range of 68.5%–100.1%, and the relative standard deviations were in the range of 4.8%–10.1%. The application of this method was further demonstrated by analyzing various real samples from local markets.