VIEW ARTICLE    DOI: 10.1094/ASBCJ-46-0051

Automated and Manual In-Line Solid-Phase Sample Preparation for High-Performance Liquid Chromatography Analysis of Bittering Substances in Worts and Beers. I. McMurrough, J. Byrne, E. Collins, Research Centre, Guinness Brewing Worldwide, Dublin, Ireland, and M. R. Smyth, J. Cooney, and P. James, School of Chemical Sciences, National Institute of Higher Education, Dublin, Ireland. J. Am. Soc. Brew. Chem. 46:0051, 1988.

The feasibility of in-line solid-phase treatment of samples (5-50 µl) of stout, ale, and lager beers prior to their injection for high-performance liquid chromatographic measurement of their contents of iso-α-acids was established using manual column-switching. Samples were injected directly onto a short (1 cm) precolumn packed with octadecyl-silica and were purged free from interfering substances by sequential step elution with solvents of decreasing polarity. The analytes were then recovered from the precolumn by elution with the chromatographic mobile phase and transferred to an analytical column. Different sample pretreatments using sequential step elution were then developed using fully automated column switching equipment. The protocols used were shown to give accurate and precise measurements of iso-α-acids and accomplished satisfactory "cleanup" of the beer samples. Automated column-switching methodology was then developed to analyze simultaneously the iso-α-acids, α-acids, and β-acids in wort samples, using a precolumn and two analytical columns. Column switching allowed satisfactory analyses of wort samples to be performed in one-third of the time taken by conventional isocratic elution. An electrochemical detector was shown to be more than 50 times more sensitive for the measurement of α-acids and β-acids than an ultraviolet detector. The methods were applied to the measurement of iso-α-acids in beers bittered either with hops or pre-isomerized hop extracts. In addition, the course of α-acid isomerization was monitored in kettles boiled at atmospheric pressure.

Keywords: α-Acids, β-Acids, Bitterness, Electrochemical measurement, Iso-α-acids, High-performance liquid chromatography