Bromination methods for determination of phenylephrine hydrochloride in nose drops, salicylamide in tablets, and tetracycline hydrochloride in capsules.

Two methods, kinetic and titrimetric, based on an electrophilic substitution reaction with bromine, are described for the assay of phenylephrine hydrochloride in nose drops, salicylamide in tablets, and tetracycline hydrochloride in capsules. The kinetic method depends on the linear relationship between concentration of the drug (microgram/mL) and time (s) for nuclear monobromination, indicated by bleaching of the methyl orange acid color. The titrimetric method is based on addition of excess of bromate-bromide with subsequent determination of excess bromine by an iodide-thiosulfate procedure. This method is also used to count the number of bromine atoms necessary for the electrophilic substitution reaction. Preservatives or tablet-capsule bases do not interfere in either method. Recoveries of drugs added to laboratory-prepared samples were good. As indicated by the F-test, the methods are equally reproducible.