Abstract
ABSTRACT J. Inst. Brew. 113(1), 48–54, 2007 Excellent liquid chromatographic (LC) separation of cis / trans stereoisomers of iso- -acids has been achieved with reversed-phase 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 -isoposthumu-lone was identified combining photo diode array (PDA) spectra and electrospray high-accuracy mass spectrometric (MS) data. Moreover, the molecular mass of two degradation products re-sulting from the in-solution storage of the DCHA-Iso standard was determined. The presence of trans and cis isomers of iso-posthumulone, isocohumulone, isoadhumulone and iso-n-humu-lone in beer samples was confirmed. The trans isomers of iso- -acids showed characteristic and reproducibly slightly different ultraviolet absorbance spectra with respect to cis isomers. Key words: Beer, DCHA-Iso standard, electrospray, food analy-sis, high-accuracy mass spectrometry, isoadhumulone, isocohu-mulone, iso-n-humulone, isoposthumulone, UV spectra.
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