THOMAS, ASHA, et al. “Simultaneous Spectrophotometric Estimation of Pioglitazone, Metformin HCl and Glimepiride in Bulk and Formulation”. Asian Journal of Chemistry, vol. 19, no. 5, Mar. 2010, pp. 3821-30, https://asianpubs.org/index.php/ajchem/article/view/13285.