Spectrophotometric Determination of Cysteine with Metal Ion as Probe

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%.