W. Po Cheng, Y. Tsang Lu, R. Fang Yu, X. Ru Lin, and H. Xin Li, “Finding the Reaction Constant Between Humic Acid and Metal Ions by Fluorescence Quenching Effect”, IJET, vol. 7, no. 3.32, pp. 4–6, Aug. 2018, doi: 10.14419/ijet.v7i3.32.18379.