Kinjal R Patel, Laxman M Prajapati, Amit K Joshi, Mahammadali L Kharodiya, and Jimish R Patel, “Application of Chemometrics in Simultaneous Spectrophotometric Quantification of Etophylline and Theophylline: The Drugs with Same Chromophore: Chemometrics in Simultaneous Spectrophotometric Determination”, Iran J Pharm Sci, vol. 9, no. 3, pp. 17–28, Jul. 2013.