Abstract
In the previous paper it was shown that the decomposition of FAD was greatly accelerated in the presence of trace amounts of heavy metal ions which were brought into the solution from the glass ampule, and that this decomposition was prevented by adding a small amount of EDTA. In this paper, examinations were made on the stabilization of FAD in aqueous solution using EDTA and its analogues, such as polyphosphate, oxine derivative, dicarboxylic acid, hydroxycarboxylic acid and natural amino acids as the heavy metal sequestering agent. Among these compounds, EDTA, 1,2-cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacatic acid or hydroxyethylenediaminetriacetic acid, had a better stabilizing effect on FAD solution. This effect was also observed with sodium hexamethaphosphate, sodium pyrophosphate, 8-hydroxyquinoline-5-sulfonic acid, citric acid, malonic acid, malic acid, tartaric acid or nitrirotriacetic acid but not with amino acids. It is concluded that the larger the chelate formation constant of sequestering agents is, the superior its stabilizing effect on FAD solution is.
