On the Effect of Protein Precipitants for Sugar Determination by Bertrand's Method

Abstract

In Bertrand's method, sometimes yellowish brown precipitate is formed, without forming ordinary red cuprous oxide.
Our experiments have been carried out to clarify the above disturbance and to eliminate it.
Results obtained are as follows
1) Yellowish brown precipitate is produced sometimes as a result of the decomposition of alkali labile organic sulphur compounds such as cystine and thiamine.
2) Disturbance of this sort is also caused by the presence of protein.
3) In order to eliminate the disturbance caused by protein, we used 6 kinds of protein precipitants, i. e. Pb-acetate, basic Pb-acetate, Na-tungstate, zinc hydroxide, tannin together with basic Pb-acetate, , and perchloric acid. Among these precipitants, tannin and basic Pb-acetate are the best, though the technic is somewhat troublesome. Na-tungstate comes next.
4) These precipitants have been proved not to be applicable for the elimination of much cystine and peptone.