Colorimetric determination of zidovudine in bulk and tablet dosage forms using potassium dichromate
A colorimetric method involving the oxidation of zidovudine (ZDV) using potassium dichromate in sulphuric acid has been developed for the determination of ZDV in bulk and tablet dosage forms. The wavelength of maximum absorption (λmax) of the oxidation product was determined and concentrations of sulphuric acid, potassium dichromate and amount/duration of heat were optimized. Beers plot was constructed at the λmax and used in the recovery studies for pure drug sample. Two methods (acid and methanol extraction) were used to extract ZDV from tablet samples. The developed method was then used to determine the percentage content of the drug in the tablets. The method was validated using the International Council for Harmonization of Technical Requirement for registration of Pharmaceuticals for Human Use (ICH) guideline. The λmax of the oxidation product was found to be 602 nm. The optimized conditions were as follows: 0.083M (potassium dichromate), 12 M (sulphuric acid) and heating at 90ºC for 30 mins. The regression equation for the Beer’s plots is: A = 0.4313C + 0.0018 (R2=0.9995) for ZDV. The recovery of ZDV from standard solutions was 100.36%±0.36. Thus the developed method was accurate and precise. The percentage contents determined for different brands of ZDV tablets were 99.07%±0.83, 98.70%±0.76, 93.46%±0.72 for the three brands of ZDV. These values compared well with results obtained with use of another method of assay. These values are within the specifications of the British Pharmacopoeia (90-110%). The limits of detection and limits of quantification were 0.004 and 0.014 mg/ml respectively. The developed method is simple, accurate, and utilizes readily available chemicals and equipment, and is inexpensive. It could therefore be used for the routine determination of ZDV.
Keywords: Zidovudine, Oxidation, Colorimetric, Absorbance