Ruengsitagoon, W., and C. Aromdee. “Determination of lead, copper, zinc and iron in centella asiatica by atomic absorption spectrophotometry (Thai)”. Asia-Pacific Journal of Science and Technology, vol. 14, no. 5, Apr. 2017, pp. 412-20, https://so01.tci-thaijo.org/index.php/APST/article/view/83452.