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

Abstract

Two simple, sensitive and accurate spectrophotometric methods for the determination of loperamide hydrochloride (lop. HCl) are described. The first method is based on the formation of ion-pair association complex (1:1) with bromothymol blue (BTB), bromophenol blue (BPB) and naphthol blue black B (NBB). The coloured products are extracted into chloroform, and measured spectrophotometrically 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 μg ml −1 for BTB, BPB and NBB methods, respectively. The method was found to be specific for the analysis of the drug in presence of its degradation products which can be detected by HPLC procedure. The second method is based on the reaction of the basic loperamide with iodine in chloroform to give molecular charge-transfer complex with intense bands at 295 and 363 nm. Beer’s law was obeyed in the ranges 2.5–17.5 and 2.5–22.5 μg ml −1 for the method at 295 and 363 nm, respectively. Optimization of the different experimental conditions are described for both methods. The proposed methods have been applied successfully 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 determination of a small dose drug, which is also a weak UV-absorbing compound.