Improved analysis by liquid chromatography of iso‐alpha acids

Abstract

SummaryThis 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.

Development of preparative and analytical methods of the hop bitter acid oxide fraction and chemical properties of its components

“…Because the UV absorption characteristics of the MHBA components were attributed to the common chromophore (β-tricarbonyl moiety), the difference in the molar absorbance coefficient among the components at 270 nm was assumed to be small. 41) Therefore, we quantified the total MHBA components using the calibration curve prepared from tricyclooxyiso-n-humu-lone A (9b), which is an abundant (Fig. 6) and stable constituent of MHBA.…”

Stir bar sorptive extraction‐liquid desorption applied to the analysis of hop‐derived bitter acids in beer by micellar electrokinetic chromatography

“…Reduced iso-a-acids such as rho-iso-a-acids and tetrahydro-iso-a-acids are nowadays often added in the brewing process to enhance the light and foam stability. HPLC is intensively used for the analysis of a-and b-acids in hops [5][6][7] and iso-a-acids in beer [2,8]. Problems related with interaction of the solutes with trace metals in the chromatographic system resulting in poor resolution and quantitation have been reported [2,8].…”

“…HPLC is intensively used for the analysis of a-and b-acids in hops [5][6][7] and iso-a-acids in beer [2,8]. Problems related with interaction of the solutes with trace metals in the chromatographic system resulting in poor resolution and quantitation have been reported [2,8]. Electrodriven separation techniques such as micellar electrokinetic chro-matography (MEKC) [9,10], microemulsion electrokinetic chromatography (MEEKC) [11], and capillary electrochromatography (CEC) [12] have been evaluated for the analysis of the hop acids while the iso-a-acids were successfully separated by MEKC [13,14].…”

Analysis of iso-α-acids and reduced iso-α-acids in beer by direct injection and liquid chromatography with ultraviolet absorbance detection or with mass spectrometry

“…Liquid chromatography (LC) is intensively used for the analysis of ␣-and ␤-acids in hops [5,6] and iso-␣-acids in beer [2,7]. Problems related with interaction of the solutes with trace metals in the chromatographic system resulting in poor resolution and quantitation, have been reported [2,7].…”

“…Problems related with interaction of the solutes with trace metals in the chromatographic system resulting in poor resolution and quantitation, have been reported [2,7]. Many LC methods use involatile buffer additives such as phosphate and citrate for the separation of iso-␣-acids and reduced iso-␣-acids [8,9].…”