在pH 10.0的氨水-氯化铵缓冲溶液中半胱氨酸与钴(Ⅱ)或镍(Ⅱ)能生成金属络合物,其吸收峰分别位于284,274 nm处;当钴(Ⅱ)的浓度为2×10-4mol·L-1时,与之反应的半胱氨酸浓度在2.5×10-5~2.0×10-4mol·L-1范围内与相应的吸光度之间呈线性关系,而当加入镍(Ⅱ)的浓度为1×10-4mol·L-1时,则与之反应的半胱氨酸浓度在1.0×10-5~2.0×10-4mol·L-1范围内与其吸光度之间呈线性关系。据此,提出可分别用钴(Ⅱ)或镍(Ⅱ)作为探针,以分光光度法测定半胱氨酸的含量。该方法可用于尿液中半胱氨酸的测定,加标回收率在95.7%~101%之间,测定值的相对标准偏差(n=5)在0.9%~3.3%之间。

It was found that a metal complex between cysteine (cys.) and Co(Ⅱ) ion or Ni(Ⅱ) ion was formed in an NH3(aq.)-NH4Cl buffer solution of pH 10.0 with the absorption maxima at 284 nm for cys-Co(Ⅱ) and at 274 nm for cys-Ni(Ⅱ). Linear relationships between values of absorbance and concentration of cysteine were kept in the ranges of 2.5×10-5-2.0×10-4mol·L-1 ［for cys-Co(Ⅱ)］ and 1.0×10-5-2.0×10-4mol·L-1 ［for cys-Ni(Ⅱ)］ when the concentration of Co(Ⅱ) ion and of Ni(Ⅱ) ion present in the reaction medium were kept at 2×10-4mol·L-1 and 1×10-4mol·L-1 respectively. Based on these facts, it was proposed to use Co(Ⅱ) ion or Ni(Ⅱ) ion as probe in the spectrophotmetric determination of cysteine. This method can be successfully applied to analysis of cysteine in urine, and values of recovery found by standard addition method were in the range of 95.7%-101%, with values of RSD (n=5) in the range of 0.9%-3.3%.