Determination of emodin and phenolic acids in the petioles of Rheum undulatum and Rheum rhaponticum

Emodin and twelve phenolic acids (ellagic, gallic, protocatechuic, homoprotocatechuic, caffeic, p -hydroxybenzoic, p -coumaric, syringic, vanillic, ferulic, α-resorcylic, and p -hydroxyphenylacetic) have been detected in the petioles of Rheum rhaponticum L. ( R. rhabarbarum L.) and Rheum undulatum L. by TLC. The amounts of emodin (4 μg g −1 for R. undulatum , 5.8 μg g −1 for R. rhaponticum ) were determined by TLC-densitometry. The amounts of the nine phenolic acids were determined by HPLC. The total amount of phenolic acids in the petioles was 327.4 μg g −1 for R. undulatum and 198.16 μg g −1 for R. rhaponticum .