Determination of Cysteine by Discoloration Spectrophotometry using Copper(II)-Bis-Cyclohexanone Oxalydihydrazone

Abstract

In the alkaline medium of pH=9.18, Cu2+ can be reduced to Cu+ by the sulfhydryl (-SH) of cysteine, and it result in the decrease the amount of Cu2+ in the system. The decrement of Cu2+ is directly proportional to the addition of cysteine, then using bis-cyclohexanone oxalyldihydrazone (BCO) as chromogenic reagent for Cu2+ to determinate the content of cysteine indirectly by discoloration spectrophotometry. A new method for the determination of cysteine by discoloration spectrophotometry using Copper(II)-BCO has been established. The influencing factors of the determination of cysteine is investigated. The results show that the maximum absorption wavelength of chromogenic system was 602 nm, in the range of 0.008000~0.06800 mg/mL, the linear relationship between the decrease of absorbance and the mass concentration of methimazol is A=0.2162+2.4824C (mg/mL), and the linear correlation coefficient is r=0.9959. The method has been applied to the determination of cysteine in food, and the results are basically consistent with those determined by pharmacopoeial method.