“Formulation evaluation development and validation of simultaneous equation method for estimation of vitamin C and vitamin D in multivitamin lipstick”, AJPHS, vol. 10, no. 2, pp. 2239–2247, Jun. 2020, Accessed: Feb. 27, 2026. [Online]. Available: https://www.ajphs.com/index.php/ajphs/article/view/204