Improved analysis by liquid chromatography of iso‐alpha acids

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Abstract
This paper shows that the liquid chromatography (LC) methods so far described in the literature for iso‐alpha acids analysis are unsatisfactory. The main reasons for this are the failure of the advocated eluent systems to completely suppress trace metal activity of commercial LC columns and the lack of a stable reference iso‐alpha acid.The trace metal problem can be solved by using a column packing material specifically designed for “Hop Acid” analysis and by adding ethylenediaminetetraacetate (EDTA) to the eluent. The reference problem is more difficult, but possibly a formulation of the iso‐alpha acids in their acid form may be the answer.Chromatographic conditions changing the elution pattern of the individual iso‐alpha acids are studied. This leads to better control of their co‐elution in the analytical procedure.