Determination of diphenhydramine hydrochloride in some single tertiary alkylamine pharmaceutical preparations by flow injection spectrophotometry

A simple and rapid spectrophotometric method with flow injection is proposed for determination of diphenhydramine hydrochloride in some single tertiary alkylamine pharmaceutical preparations (capsule and syrup). It is based on ion pair formation with bromocresol green in a pH 3 buffer which a yellow ion pair compound is extracted into chloroform layer. An aqueous layer containing excess bromocresol green is injected into a carrier stream of 0.01 M borax solution and absorbance of the stream is continuously monitored at 610 nm. Diminution of the bromocresol green is related to an amount of diphenhydramine hydrochloride that can be evaluated from a calibration graph established by a plot of diphenhydramine hydrochloride concentration (micro gm l(-1)) and peak height (mV). Optimization will be discussed. The calibration graph is linear over the concentration ranges of 5-21 and 75-188 micro gm l(-1). A throughput of 100 injections h(-1) can be obtained. Application to assay for capsule and syrup samples has been demonstrated. The method is validated by comparing the results with HPLC analyses.