Sruthi R., Biju C. R., Jyotisree G., Amita S. Menon, Ayswarya K., and Babu G., “Formulation, Evaluation and HPTLC Analysis of Topical Ointment Containing Calendula officinalis and Echinacae purpurae Mother Tinctures”, Int. j. res. appl. sci. biotechnol., vol. 7, no. 6, pp. 78–84, Nov. 2020.