Spectrophotometric study of bromide interference in a cholesterol reaction

A spectrophotometric study of the interference of bromide in the ferric chloride reaction for cholesterol has been described. The interference has been shown to be primarily an enhancement of the color reaction and secondarily an additive color owing to a change in the spectrum of the reagent blank. Tested methods of eliminating the interference included removal of bromide by ion exchange, metathetical exchange using AgIO₃, addition of bromide to a reaction plateau and a change in the solvent character of the reaction medium. It was determined that the use of an ion-exchange resin and the substitution of ethanol for acetic acid along with a modified iron reagent were the simplest choices for eliminating bromide interference in this determination. Iodate was shown to depress color formation and it appears to be a detrimental solution to the problem. Further work on the mechanism of the iodate interference is presently in progress.