Tavallali, Hossein, and Maryam Salami. “Simultaneous Determination of Caffeine and Paracetamol by Zero-Crossing Second Derivative Spectrophotometry in Pharmaceutical Preparations”. Asian Journal of Chemistry, vol. 21, no. 3, Mar. 2010, pp. 1949-56, https://asianpubs.org/index.php/ajchem/article/view/18682.