High-performance separation of unmodified and reduced hop and beer bitter compounds by a single high-performance liquid chromatographic method

An improved high-performance liquid chromatographic method for the separati on of the isoxanthohumol iso-alpha -acids, rho-iso-alpha -acids, tetrahydro -iso-alpha -acids, alpha -acids, and beta -acids in beer is presented. This is the first time a complete separation of all six isomers of iso-alpha -a cids has been described. It is done by using an isocratic elution system in beer. A gradient elution method is used for measuring all the main hop-bit tering substances such as alpha -acids, beta -acids, iso-alpha -acids, and all reduced compounds in light-stable beer, hop extracts, and wort. A chemi cally cross-linked "base deactivated" C18 column with a citrate-buffered (p H 7) acetonitrile-methanol gradient mobile phase enables the separation of the beer bitter components within 50 min. The analysis of wort samples was achieved with a tris-buffered (tris(hydroxymethyl)-aminomethane) (pH 7.5) a cetonitrile-methanol gradient mobile phase within 60 min. Sample preparatio n was by preconcentration on SPE C8 cartridges, which gave good reproducibi lity and separation of bitter components from the beer matrix. Due to the c omplex matrix of beer and wort, an optimized sample preparation procedure i s used to increase the life of the column.