J. Inst. Brew. vol.113:1 (2007)Liquid Chromatography–Diode Array and Electrospray High-Accuracy Mass Spectrometry of Iso-a-Acids in DCHA-Iso Standard and Beer

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

Pavel Hofta¹, Pavel Dostálek^1,3 and David Sýkora²
¹ Department of Fermentation Chemistry and Bioengineering, Institute of Chemical Technology, Prague, Technická 5, Prague 6, CZ-166 28, Czech Republic.
² Department of Analytical Chemistry, Institute of Chemical Technology, Prague, Technická 5, Prague 6, CZ-166 28, Czech Republic.
³ Corresponding author. E-mail: Pavel.Dostalek@vscht.cz

J. Inst. Brew. 113(1), 48–54, 2007 | VIEW ARTICLE

ABSTRACT
Excellent liquid chromatographic (LC) separation of cis/trans stereoisomers of iso- a -acids has been achieved with reversedphase sorbent XTerra MS C18. An isocratic alkaline mobile phase, consisting of a mixture of 5 mmol l–1 ammonium acetate (pH 8)-acetonitrile-methanol, 62:21:17 (v/v/v), was used. In the DCHA-Iso international calibration standard trans-isoposthumulone was identified combining photo diode array (PDA) spectra and electrospray high-accuracy mass spectrometric (MS) data. Moreover, the molecular mass of two degradation products resulting from the in-solution storage of the DCHA-Iso standard was determined. The presence of trans and cis isomers of isoposthumulone, isocohumulone, isoadhumulone and iso-n-humulone in beer samples was confirmed. The trans isomers of iso-a-acids showed characteristic and reproducibly slightly different ultraviolet absorbance spectra with respect to cis isomers.

Key words:
DCHA-Iso standard, electrospray, food analysis, high-accuracy mass spectrometry, isoadhumulone, isocohumulone, iso-n-humulone, isoposthumulone, UV spectra.