Analysis of hop acids by thin-layer chromatography and the Molecular Ionization Desorption Analysis Source (MIDAS) for mass spectrometry

Abstract

A thin-layer chromatography ambient mass spectrometry method was developed for the quantitative analysis of hop acids. Hop acids were extracted from three varieties of hop pellets, Apollo, Cluster and Czech Saaz. Reversed-phase thin-layer chromatography provided the optimum stationary phase for separation and ionization. Using standards, a method was developed to separate α-, iso-α- and β-acids by thin-layer chromatography. Each thin-layer chromatography plate was analyzed directly by the Molecular Ionization Desorption Analysis Source (MIDAS). MIDAS is an atmospheric pressure ambient ionization source for mass spectrometry. Quantitative analysis of the hop extracts was made by successive analysis of known amounts of standards and the determination of a response factor. The expected trend of total α-acid content with Apollo>Cluster>Czech Saaz was observed. Variation in the results was attributed to manual TLC plate spotting and not to the ionization source.