Determination of Methyltestosterone Residues in Aquatic Products by Ultra-High Performance Liquid Chromatography

The sample (5.000 g) was added into 15 mL of acetonitrile-formic acid (199+1) solution, and the mixture was homogenized for 30 s, then extracted by shaking for 10 min and centrifuged. The lower solid was then extracted with 8 mL of acetonitrile-formic acid (199+1) aolution. The supernatant was merged in a parallel evaporation tube and evaporated to dryness at 55℃. The residue was dissolved with 3 mL of methanol, and 7 mL of water was added. The solution was freezed in the freezer for 30 min and then centrifuged. The methanol solution layer was purified with poly-sery HLB solid phase extraction column, using 6 mL of 20% (φ) methanol solution for rinse and 4 mL of 90% (φ) methanol solution for elution. After the eluate was dried at 50℃ by nitrogen blowing, the residue was dissolved in 1 mL of acetonitrile (1+1) solution and the solution was filtered with a 0.22 μm microporous membrane filter. The filtrate was separated on a BEH C₁₈ column (50 mm×2.1 mm, 1.7 μm) with acetonitrile (1+1) solution as the mobile phase. Methyltestosterone was detected by a UV detector at the wavelength of 254 nm. Linear relationship was found between peak area and mass concentration of methyltestosterone in the range of 0.05-1.00 mg·L^-1, with detection limit (3S/N) of 5.0 μg·kg^-1. Test for recovery by standard addition method was carred out at the spike level of 10.0, 50.0, 100 μg·kg^-1, giving results in the range of 73.6%-91.4%, and RSDs (n=5) were less than 9.0%.