Qualitative and quantitative analysis of phenolic acids in Asclepias syriaca L.

TLC and HPLC was applied to qualitative and quantitative determination of phenolic acids free and liberated by acid and alkaline hydrolysis in common milkweed. The presence of phenolic acids, namely p-hydroxybenzoic, p-coumaric, protocatechuic and caffeic acids, was confirmed in the leaves and flowers. Moreover, the flowers contained gallic acid, and the leaves contained alpha-resorcylic, vanilic and chlorogenic acids. Conjugated forms of phenolic acids predominate in the plant. They hydrolyse mainly to coffeic, p-coumaric, ferulic and p-hydroxybenzoic acids.