Singtongratana, N. .; Vadhanasin, S. .; Singkhonrat, J. . Hydroxychavicol and Eugenol Profiling of Betel Leaves from Piper Betle L. Obtained by Liquid-Liquid Extraction and Supercritical Fluid Extraction. Agr. Nat. Resour. 2013, 47, 614-623.