制备好的冻干海产品样品0.2 g （精确至0.000 1 g）在pH 8.0的水溶液体系下，经30 mg木瓜蛋白酶（800 U·mg^-1）在50℃、180 r·min^-1的条件下酶解12 h，涡旋3 min，离心10 min。所得的上清液经0.22 μm滤膜过滤，以Agilent ZORBAX SB-AQ色谱柱（250 mm×4.6 mm，5 μm）为固定相，10 mmol·L^-1的柠檬酸溶液（pH 4.75）为流动相，于0.6 mL·min^-1下等度洗脱，可在11 min内实现对5种硒形态的分离，再采用电感耦合等离子体质谱法测定硒酸盐（Se⁶⁺）、亚硒酸盐（Se⁴⁺）、甲基硒代半胱氨酸（Me-Se-Cys）、硒代蛋氨酸（Se-Met）和硒代乙硫氨酸（Se-Et）的含量。结果表明，5种硒形态标准曲线的线性范围均在500 μg·L^-1内，检出限（3S/N）为1.231~2.423 μg·L^-1。按标准加入法对海产品样品进行3个浓度水平的回收试验，回收率为81.3%~118%，测定值的日内相对标准偏差（n=6）和日间相对标准偏差（n=6）均小于9.0%。方法用于市售海产品分析，结果表明小黄鱼和带鱼中硒代蛋氨酸的测定结果比文献报道的大西洋鲑鱼和大西洋鳕鱼的测定值都要高，说明在我国食用小黄鱼和带鱼能够为居民补充较高水平的硒代蛋氨酸。此外，口虾蛄也是补充硒代蛋氨酸的重要来源。

0.2 g (accurate to 0.000 1 g) of the prepared freeze-dried seafood product sample was hydrolyzed with 30 mg papain (800 U·mg^-1) in an aqueous solution system with pH 8.0 at 50℃ for 12 h with the speed of 180 r·min^-1. After vortex for 3 min and centrifugation for 10 min, the obtained supernatant was passed through 0.22 μm filter membrane, and 5 selenium species in the filtrate could be separated in 11 min, using Agilent ZORBAX SB-AQ column (250 mm×4.6 mm, 5 μm) as the stationary phase and 10 mmol·L^-1 citric acid solution (pH 4.75) as the mobile phase for isocratic elution at 0.6 mL·min^-1. Then selenate (Se⁶⁺), selenite (Se⁴⁺), L-Se-methylselenocysteine (Me-Se-Cys), selenomethionine (Se-Met) and selenoethionine (Se-Et) in seafood product sample solution were determined by inductively coupled plasma mass spectrometry. As shown by the results, the same linear ranges of the standard curves of 5 selenium species were found within 500 μg·L^-1, with detection limits (3S/N) in the range of 1.231-2.423 μg·L^-1. Tests for recovery were made on seafood product samples at three concentration levels by standard addition method, giving results in the range of 81.3%-118%, with intra-day RSDs (n=6) and inter-day RSDs (n=6) of the determined values less than 9.0%. This method was applied for the analysis of commercial seafood product sample, and it was shown that the determination results of selenomethionine in small yellow croaker and hairtail were higher than those of Atlantic salmon and Atlantic cod reported in the literature, indicating that eating small yellow croaker and hairtail in China could provide a higher level of selenomethionine for people. In addition, squilla was also an important source of selenomethionine supplement.