Abstract：Cystine was indirectly determined by flame atomic absorption spectrometry with ZnS. Base on the determination mechanism,the composition of complex, the complex balance reaction of soluble zinc ion,which formed in the determination of cystine by FAAS,and the stability constant of complex balance were discussed in the present paper. Under the alkalescent conditions,cystine (Cys-Cys) can react with zinc sulfide suspension solution to form a soluble complex or chelate of zinc cystine. The maximum concentration was reached at pH 9.4 and the quantity of the chelate was determined by flame atomic absorption spectrometry with zinc sulfide. The stability constants of the complex compound of zinc cystine were studied successfully,after the numeric measurements and theoretical investigations under the best-optimized acidity for determination. In conclusion,at the best optimized acidity pH 9.4,the stability constant of alkalescent zinc cystine is between 9.542×1032 and 10.353×1032,the average value is βW=9.916×1032,and log βW＝32.996. The standard deviation is 0.301×1032. It is shown that the atomic absorption spectrometry can be used not only for the determination of trace elements and the indirect determination of organic compound,but also for the study of physical configuration and the determination of physical constant of complex ion.
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