Spectrophotometric determination of loperamide hydrochloride by acid-dye and charge-transfer complexation methods in the presence of its degradation products

Two simple, sensitive and accurate spectrophotometric methods for the deter mination of loperamide hydrochloride (lop. HCl) are described. The first me thod is based on the formation of ion-pair association complex (1:1) with b romothymol blue (BTB), bromophenol blue (BPB) and naphthol blue black B (NB B). The coloured products are extracted into chloroform, and measured spect rophotometrically at 414 (BTB), 415 (BPB) and 627 nm (NBB). Beer's law was obeyed in the ranges of 5-35, 5-30 and 0.8-11.2 mu g ml(-1) for BTB, BPB an d NBB methods, respectively. The method was found to be specific for the an alysis of the drug in presence of its degradation products which can be det ected by HPLC procedure. The second method is based on the reaction of the basic loperamide with iodine in chloroform to give molecular charge-transfe r complex with intense bands at 295 and 363 nm. Beer's law was obeyed in: t he ranges 2.5-17.5 and 2.5-22.5 mu g ml(-1) for the method at 295 and 363 n m, respectively. Optimization of the different experimental conditions are described for both methods. The proposed methods have been applied successf ully for the analysis of the drug in pure form and in its dosage forms. The methods have the advantage of being highly sensitive and simple for the de termination of a small dose drug, which is also a weak UV-absorbing compoun d. (C) 2000 Elsevier Science B.V. All rights reserved.