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

Direct characterization of bitter acids in a crude hop extract by liquid chromatography-atmospheric pressurechemical ionization mass spectrometry

“…Under (nagative) APCI conditions, the fragmentation of precursor ions occurred mainly on the prenyl groups as observed in negative ESI-MS/MS experiment [10] and no abundant product ion corresponding to the loss of acyl group was formed (see Figure 3). Under (positive) APCI conditions, fragmentation of protonated ions could present more characteristic product ions than fragmentation of deprotonated molecular ions (see Figure 4).…”

“…If scanning of each of protonated ion-product ion transition for any bitter acid produced a positive response in the MS/MS chromatogram at the same retention time, the existence of such a targeted compound in the herb was confirmed. Discrimination between the isomers was also performed in considering their retention characteristics and relative amounts as reported [4,10]. Using MS/MS analysis in combination with chromatographic rule, the five minor hop acids, posthumulone, prehumulone, adprehumulone, prelupulone, and "adprelupulone", were determined with retention times at 8.54 min, 14.20 min, 14.98 min, 25.47 min, and 26.67 min, respectively ( Figure 5).…”

“…Van der Hoeven et al [10] reported on (negative) LC/ESI/ MS/MS application to the analysis of the six major bitter acids in the extract of hop. In the ESI experiment, MS/MS spectra of ␤-acids exhibit abundant product ions corresponding to loss of a series of alkyl radicals.…”

Liquid Chromatography-Diode Array and Electrospray High-Accuracy Mass Spectrometry of Iso-α-Acids in DCHA-Iso Standard and Beer

“…In the past, the application of an acidic mobile phase, gradient elution and UV detection was a common approach for the separation of iso-␣-acids 23 . However, it has been recently shown 10,21 that neutral and alkaline mobile phases, in combination with advanced reversed-phase sorbents, can provide much better selectivity for iso-␣-acids. Baseline separation is attainable especially when isocratic elution is utilized 9 .…”

“…Baseline separation is attainable especially when isocratic elution is utilized 9 . The se-lectivity and sensitivity of the measurements has been improved by mass spectrometric (MS) detection employing negative electrospray and atmospheric pressure chemical ionisation 7,10,21 . Finally, the selectivity has been further enhanced by the application of the liquid chromatographynuclear magnetic resonance tandem for the characterization of beer bitter acids 17 .…”