N. . Singtongratana, S. . Vadhanasin, and J. . Singkhonrat, “Hydroxychavicol and Eugenol Profiling of Betel Leaves from Piper betle L. Obtained by Liquid-Liquid Extraction and Supercritical Fluid Extraction”, Agr. Nat. Resour., vol. 47, no. 4, pp. 614–623, Aug. 2013.