Relative Response Factor for Lamivudine and Zidovudine Related substances by RP-HPLC with DAD detection

A study was conducted to establish the Relative Response Factors for Zidovudine related impurity C, Lamivudine salicylic acid and Zidovudine related impurity B.  A simple and fast isocratic Reverse Phase High Performance Liquid Chromatography (RP-HPLC) method was used for the simultaneous determination of the related impurities. The method consists of a mobile phase combination of Acetonitrile (HPLC grade) and Buffer (0.0680 g of Potassium Dihydrogen Orthophosphate, 0.3 ml of Triethylamine, pH adjusted to 8.0 with Orthophosphoric acid to a final volume preparation of 100 ml) in the ratio 10:90 using Phenomenex Luna 5-µm C18 (2)-250 x 4.6-mm, 5-µm) as a stationary phase, flow rate of 1.0 mL/min with detection at 270 nm. The RRF for Zidovudine related impurity C, Lamivudine salicylic acid and Zidovudine related impurity B were 2.07, 0.13 and 1.28 respectively.   Results obtained for quantification of the related substance in lamivudine and zidovudine single dose oral solid dosage form using the RRF and know standards shows no significant difference at 95 % confidence interval. The RRF can therefore be used for the quantification of know related impurities in lamivudine zidovudine oral dosage form using the stated chromatographic conditions