Extraction of Ferulic Acid and Caffeic Acid with Ionic Liquids

The effects of pH value, temperature, phase ratio, type, and concentration of inorganic salts on the extraction efficiency of ferulic acid (FA) and caffeic acid (CA) were investigated using [C4mim][PF6] and [C6mim][PF6] as extracting agents by ultraviolet-visible spectrophotometry. Furthermore, the retrieval of the compounds extracted, the reuse of ionic liquids, and the possibility of the two ionic liquids as the substitutes of the traditional organic solvents for the extraction of the FA and/or CA were discussed. The results indicated that the changes in temperature, concentration, and type of inorganic salts had no obvious influence on the extraction efficiencies, but the pH value of aqueous phase significantly affected the extraction efficiencies. The appropriate pH value of FA was less than 3.67 and that of CA was less than 3.71. Extraction efficiencies of these two compounds were found to decrease with the increase of their concentrations and increase with the increase of the phase ratio. The extraction efficiencies of FA and CA using [C4mim][PF6] as extract agent were higher than those when using [C6mim][PF6] as extract agent. Interestingly, the extraction efficiency of FA was much higher than that of CA whether using [C4mim][PF6] or [C6mim][PF6] as extract agent, whereas the residue of [C6mim][PF6] in aqueous phase was less than that of [C4mim][PF6]. The FA and CA in the extraction phase could be retrieved quantitatively, and the ionic liquids could be reused.