Preparative separation of high-purity trans- and cis-ferulic acid from wheat bran by pH-zone-refining counter-current chromatography.

Ferulic acid stereoisomers are the most abundant phenolic acids in cereal bran. However, it is challenging to separate them because of the similar structures and properties. In this study, a preparative separation method of ferulic acid stereoisomers from the crude extract of wheat bran was successfully developed. The method contained a two-step separation, the traditional counter-current chromatography (CCC, hexane: ethyl acetate: methanol: water = 2:5:2:4) was followed with a pH-zone-refining CCC (hexane: ethyl acetate: acetonitrile: water = 2:5:2:2, 10 mmol L-1 trifluoroacetic acid in organic stationary phase and 10 mmol L-1 ammonia in aqueous mobile phase). Trans-ferulic acid and cis-ferulic acid with HPLC high purity over than 99% and 98% can be yielded in large-scale separation. Moreover, it is found that different proton affinity, deprotonation ability and interaction site of hydrogen bond result in distinct partition behavior of stereoisomers, which is illustrated by quantitative analysis of molecular surface. This contributes to our in-depth understanding of the separation mechanism toward pH-zone refining CCC. The developed method can be applied in the exploitation of ferulic acids and related phenolic acids from other resources.