Countercurrent supercritical fluid extraction of phenolic compounds from aqueous matrices

Low-molecular weight aromatic compounds were extracted from aqueous samples in a packed high-pressure stainless steel column with supercritical carbon dioxide. A countercurrent flow approach was utilised to remove several phenolic and two non-phenolic compounds with similar aromatic structures directly from aqueous standard solutions as well as a real sample (a lignocellulose dilute-acid hydrolysate of spruce) with supercritical carbon dioxide without sample pre-treatment. Phenolics are a diverse group of compounds that vary with regard to number, position and nature of their functional groups. The main purpose of this work was to investigate the influence of substituents on the extraction efficiency during countercurrent supercritical fluid extraction (SFE). The extraction column was 1100 mm long with an inner diameter of 25 mm. It was filled with Sulzer packings to increase the contact area between the solvent and the sample. The results showed that extraction efficiencies ranging from 2 to 100% in the standard solutions and 11 to 98% in the hydrolysate could be achieved depending on the various substituents. No correlation was observed between polarity indexes and extraction efficiencies for the investigated compounds; however, a relationship between retention in RP-HPLC and extractability could be established. (C) 2002 Elsevier Science B.V. All rights reserved.