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Spectrophotometry is a widely used determination method because of its fast, simple and simple instrument. In this paper, spectrophotometric determination of cysteine using 2,2'-bipyridine color system is explored. Under certain experimental conditions, the sulfhydryl (-SH) contained in cysteine can quantitatively reduce Fe (Ⅲ) to Fe (Ⅱ), Fe(Ⅱ) and 2,2'-bipyridine to produce orange-red complexes. A directly proportional relationship between the amount of orange-red complex and the dosage of cysteine added. So, the determination of cysteine content can be obtained by indirectly determining the absorbance of orange-red complexes. Under the optimal experimental conditions, standard curve equation is A=75.232C+0.0129 (mg/mL) when the cysteine concentration is in 0.0008000 ~ 0.009600 mg/mL. The determination results of cysteine content in food grade cysteine is satisfactory.
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