Spectrofluorimetric and derivative absorption spectrophotometric techniques for the determination of loperamide hydrochloride in pharmaceutical formulations.

Simple, sensitive and rapid spectrofluorimetric and derivative absorption spectrophotometric procedures are described for the accurate determination of loperamide hydrochloride. The spectrofluorimetric method involves the measurement of the fluorescence of the compound in an ethanol-sulphuric acid mixture (90:10, v/v) using either the direct or the synchronous modes of measurement. Optimum conditions for maximum fluorescence are described. The derivative spectrophotometric method involves the measurement of either the second derivative peak amplitude (crest to trough, i.e. maximum to minimum) between 258 and 263 nm or the second derivative peak height (i.e. maximum to zero line) at 224 nm of an ethanolic solution of the drug. The proposed methods have been used for the determination of loperamide in pharmaceutical formulations. Compared to the pharmacopoeial method, the proposed methods give equally accurate (t-test) and precise (f-test) results. The proposed methods have the advantages of being highly sensitive for the determination of small concentrations of loperamide, a weak UV-absorbing compound prescribed in low doses.