Alshabrawy, Ali, et al. “Utilization of Oxidation-Reduction Reaction of Folin-Ciocalteu’s Phenol Reagent in Colorimetric Determination of Amlodipine in Pharmaceutical Dosage Form”. European Journal of Chemistry, vol. 7, no. 4, Dec. 2016, pp. 387-90, doi:10.5155/eurjchem.7.4.387-390.1451.