The method was validated and shown linearity range from 0.18 ppm to 0.72 ppm with high correlation coefficient, detection limit and quantitation limit of 0.04 ppm and 0.18 ppm, respectively for impurity D, and of 0.01 ppm and 0.04 ppm, respectively for impurity E, accuracy with recovery ratio in 98% - 102%, and precision with RSD < 3%.