Spectrophotometric Determination of Niclosamide by Prior Reduction and Subsequent Diazotization-Coupling with 2,6-Dihydroxybenzoic acid – Application to Tablets

A simple, rapid and sensitive spectrophotometric method is proposed for the determination of niclosamide (NIC) in pure form and in its pharmaceutical preparations. The method is based on the reduction of niclosamide by zinc powder in acidic medium followed by the diazotization of reduced niclosamide, then coupling with 2,6dihydroxybenzoic acid to give a yellow colored product which is water – soluble and has a maximum absorption at 456 nm with a molar absorptivity of 2.36×10 l.mol. cm. The color reaction is highly stable and does not show a significant change in absorbance up to 24 hours. Beersُ law is obeyed in the concentration range of 5–300 μg of niclosamide in a final volume of 10 ml. The method has been successfully applied to the determination of niclosamide in tablets.