Titrimetric and spectrophotometric determination of zidovudine in pharmaceuticals using chloramine-T and two dyes

200-203Three new methods using titrimetry and spectrophotometry are described for the assay of zidovudine (ZDV) in bulk drug and in dosage forms using chloramine-T (CAT) and two dyes, methyl orange and indigocarmine, as reagents. Titrimetry involves treating of ZDV with a measured excess of CAT in hydrochloric acid medium, and after the oxidation of ZDV is seemed to be complete, the unreacted oxidant is determined iodometrically. Spectrophotometric methods entail the addition of a known excess of CAT to ZDV in hydrochloric acid medium followed by determination of residual oxidant by reacting with a fixed amount of either methyl orange and measuring the absorbance at 520 nm (Method A) or indigo carmine and measuring the absorbance at 610 nm (Method B). In all the methods, the amount of CAT reacted corresponds to the amount of ZDV. In titrimetric method, the reaction follows a reaction stoichiometry of 1:1 (ZDV: CAT), and is applicable over a range 3-10 mg of ZDV. In spectrophotometric methods, the absorbance is found to increase linearly with concentration of ZDV. The systems obey Beer’s law for 0.5-5.0 and 2.5-20.0 μg mL⁻¹ for method A and method B, respectively. The apparent molar absorptivities are calculated to be 3.4x10⁴ and 7.4x10³ L mol⁻¹ cm⁻¹for method A and method B, respectively. The methods were successfully applied to the assay of ZDV in tablet and capsule formulations