M. A. El Hamd, S. M. Derayeab, O. H. Abdelmageedc, and H. F. Askald, “Colorimetric Method for Determination of some 1,4-Dihydropyridine Drugs in their Tablets and Capsules”, JAC, vol. 4, no. 1, pp. 278–287, Apr. 2008.