Preparative separation of bitter acids from hop extracts by centrifugal partition chromatography

Centrifugal partition chromatography was used for preparative separation of alpha- and beta- bitter acids from a crude supercritical carbon dioxide extract of hop cones. A one-step gradient was applied; after elution of the alpha-acids in the system toluene-0.1 M triethanolamine-HCl pH 8.4 in water the aqueous mobile phase was changed to 0.2 M diethanolamine-PO4 pH 9.75 in water-methanol (4:1, v/v) for elution of the beta-acids. For the alpha-acids the yield/cost ratio was optimized through sample size and injection volume. The role of pK(2) values and hydrophobicity in the separation mechanism for the alpha-acids is discussed. The elution order differs from the order predicted after measurement of the partition coefficients.