Khaodee, W., R. Wongkiti, and S. Madang. “The Application of Using Natural Reagent Extracted from Purple Sweet Potato for Naked-Eye Detection of Copper in Water Samples”. Asian Health, Science and Technology Reports, vol. 26, no. 3, Sept. 2018, pp. 181-8, doi:10.14456/nujst.2018.9.