Determination of Five Kinds of Mercury Species in Shrimp Feed by LC-AFS with Accelerated Solvent Extraction

The sample (1.000 0 g) was added into the accelerated solvent extraction tank, then 10 mL of 5 mol·L^-1 hydrochloric acid solution, 1 mL of 5 mol·L^-1 potassium chloride solution and 2 mL of 10 mol·L^-1 cysteine solution were added. The mixture was preheated at 8.0 MPa and 70℃ for 2 min, heated for 5 min, extracted statically for 5 min, and seperated. After repeating extraction twice, the extract was combined. Then 0.2 mL of 0.5 mol·L^-1 cysteine solution and 1.5 mL of 6 mol·L^-1 sodium hydroxide solution were added into the extract, and the mixture was centrifuged at 10 000 r·min^-1 for 5 min. The supernatant was concentrated by nitrogen-blowing and the residue was diluted to 1 mL with nitric acid (5+95) solution. After filtration with 0.45 μm nylon membrane, methylmercury, ethylmercury, inorganic mercury, thiomersal and phenylmercury in the solution were separated on an Eclipse XDB-C₁₈ reversed-phase column (150 mm×4.6 mm, 5.0 μm), with a mixture of 50 g·L^-1 acetonitrile solution, 5 g·L^-1 ammonium acetate solution and 1 g·L^-1 cysteine solution (1:1:1, volume ratio) as the mobile phase, and determined by atomic fluorescence spectrometry. Linear relationships were found between the fluorescence intensity and mass concentraion of the five kinds of mercury species in definite ranges, with lower limits of determination (10S/N) in the range of 1.0-2.5 μg·kg^-1. Values of recovery obtained by standard addition method ranged from 91.0% to 98.3%, and RSDs (n=6) ranged from 0.94% to 2.7%.