Abstract
It has been occasionally observed that, in some kinds of riboflavin injections, solutions became turbid during storage and considerable amounts of precipitates were formed ultimately. This research has been undertaken for the purpose of characterizing these precipitates and ascertaining the causes of the phenomenon. In most cases of preparations containing riboflavin, main constituent of the precipitates was found to be riboflavin, its reduced form or lumichrome. In some cases, the precipitates were composed of the mixture of the latter two or the decomposition product of folic acid. The finding indicates that the competent causes seem to be breakdown of supersaturated state, contamination of reducing microorganisms or action of light. In the precipitates which occurred in FMN preparations, riboflavin, FMN or lumichrome was detected, but not any reduced forms of them, except one case. The existence of riboflavin in the precipitates may be due to the use of impure FMN. The reason for that FMN itself precipitated might be adequately explained by either the limited solubility of FMN in the low pH solution as observed or formation of difficult soluble salts with heavy metal ions. The presence of riboflavin was observed as the sole component in the precipitates of almost all samples of FAD injections with the exception of one case, in which lumichrome was found.
