A. Phani Kumar, V. Ganesh, K. Hari Prasad, V. Hariharakrishnan, P. Dubey, and B. Venugopala Rao, “Liquid-Chromatography Determination of Impurities in Sildenafil Citrate”, ajc, vol. 23, no. 3, pp. 1219–1222, Nov. 2010.