Characterization of Hop Acids by Liquid Chromatography with Negative Electrospray Ionization Mass Spectrometry

Abstract

The analysis of hop acids, humulones and lupulones, with negative electrospray ionization mass spectrometry (MS) is described for two different chromatographic systems. One system focuses on the complete resolution of the ad- and normal homologues implying that no optimal mass spectrometric parameters can be used, whereas the other system makes no compromise to the MS and yields a high sensitivity. The latter system is especially suitable for the fast screening of bitter acids. With this system, the detection limit with selected ion monitoring (SIM)-MS could be estimated to be 10 ng/ml for the humulones and 5 ng/ml for the lupulones. The presence of hop acids in beer was investigated and was found to be positive for humulones, whereas lupulones could not be detected.