Determination of cysteine content by Cu(І)-neocuproine spectrophotometry

Cu2+ can be reduced to Cu+ by -SH (sulfhydryl) in cysteine, then neocuproine as the chromogenic reagent reacts with Cu+ to form the yellow complex. At the maximum absorption wavelength, the amount of the yellow complex is directly proportional to the added amount of cysteine in a certain range. According to this principle, the content of cysteine can be determined by spectrophotometry. Thus, a method for determination of cysteine by copper(I)–neocuproine spectrophotometry is established. Under the optimal conditions, this method is used to determinate the cysteine content in food, and the determination results are basically close to the result by pharmacopoeia method. The recovery rates of standard addition are 102.4%~104.3%.