Pulungan, Ainil Fithri, et al. “Simultaneous Spectrophotometric Determination of Paracetamol, Propyphenazone and Caffeine By Using Absorption Ratio Method”. Asian Journal of Pharmaceutical Research and Development, vol. 6, no. 5, Oct. 2018, pp. 5-8, doi:10.22270/ajprd.v6i5.412.