醤油食塩の定量に関する研究 (第1報)

銀液に依る直接滴定法

抄録

A rapid accurate determination of NaCl in soy-sauce is very diff icult. Mohr's methood is unsuitable, because (1) organic substances hinder the color change of reagents, and (II) the color of soy-sauce resembles that of Ag₂CrO₄, and the end point of titration is obscure.
The author investigated on direct argentometric titration of soy-sauce and obtained the following results.
1) In the titration of Cl^- in soy-sauce with Ag⁺ satisfactory results are obtained in acidic solution (adjusted by acetic acid, optimum pH range, 2.7-3.4) with bromophenol blue as absorption indicator. The results are accurate in the presence of hundreds of organic compounds such as, various amino acids, peptones, peptides, proteins, amines, acetals, ketones, aldehydes, carbohydrates, alcohols, acids (lactic succinic, acetic, ketonic, etc), heterocyclic compounds (furfural etc), melanines, and their derivatives and polymers.
In this case, the color change becomes extremely sharp by addition of the peptone.
2) Metanil yellow, tropaeolin 0 0, fluoresceim, dichlorofluorescein, etc cannot be used chiefly nwing to the interference by proteins and their hydrolyzid or fermented products.
Tetrabromophenol-tetrabromosulfonphthalein is also applicable.(part II)