Senthamil Selvan, P., et al. “Simultaneous Estimation of Levocetirizine, Ambroxol, Phenylpropanolamine and Paracetamol in Combined Dosage Forms by RP-HPLC Method”. Asian Journal of Chemistry, vol. 18, no. 4, Mar. 2010, pp. 2591-6, https://asianpubs.org/index.php/ajchem/article/view/20624.