将硒半胱氨酸（ＳｅＣｙｓＨ）甲基化，对硒胱氨酸（ＳｅＣｙｓ）需还原后再甲基化。它们生成的甲基硒半胱氨酸（ＣＨ＿３ＳｅＣｙｓＨ）能与溴化氰（ＣＮＢｒ）发生专一性反应，定量生成的硒氰酸甲酯（ＣＨ＿３ＳｅＮ）可用气相色谱法（ＧＣ）测定。此法简称ＣＮＢｒ－ＧＣ法，检测限４×１０￣（－８）克ＳｅＣｙｓ，准确度８９．５％，相对标准差１２．１％，非含硒氨基酸不干扰。此法适于样品中微量硒氨基酸（硒蛋氨酸ＳｅＭｅｔ，ＳｅＣｙｓＨ和Ｓｅｃｙｓ）的测定。 Methyl selenocysteine ​​(SeCysH) is methylated and SeCys is reduced and then methylated. The methylselenocysteine ​​(CH_3SeCysH) generated by them can specifically react with cyanogen bromide (CNBr). The quantitative determination of methyl selenocyanate (CH_3SeN) can be determined by gas chromatography (GC). The method referred to CNBr-GC method, the detection limit of 4 × 10 ~ (-8) g SeCys, the accuracy of 89.5%, the relative standard deviation of 12.1%, non-selenium-free amino acids do not interfere. This method is suitable for the determination of trace selenoamino acids (SeMet, SeCysH and Secys) in samples.