Chromatographic analysis of simple phenols in some species from the genus Salix

Salicis Cortex, made from willow bark is a herbal remedy, which is standardised based on the content of salicin, a compound with analgesic and antiphlogistic properties. However, clinical trials suggest that other compounds also present in Salicis Cortex can contribute to the pharmacological effects.

To characterise the composition of phenolic acids in the barks of different species and clones from the genus Salix by use of chromatographic methods--HPTLC and HPLC.

The phenolic acid composition was analysed by MGD (multiple gradient development)-HPTLC technique. The separation was performed on HPTLC Diol plates with gradient elution using a mixture of chloroform:hexane:ethyl acetate with increasing concentration of ethyl acetate from 10 to 25%. Derivatisation with thymol reagent was employed for the first time for specific detection of phenolic acids containing methoxyl groups.

The presence of all phenolic acids previously reported in the genus Salix was confirmed, namely p-hydroxybenzoic, vanillic, cinnamic, p-coumaric, ferulic and caffeic acids. Furthermore, pyrocatechol as a constituent of willow bark was revealed. The highest concentration of this compound was observed in the S. purpurea bark (2.25 mg/g).

The presence of a relatively high content of pyrocatechol in Salix species may raise doubts about the safe application of this herbal medicine.