Analytical Session
David H Thomas, Thermo Fisher Scientific, Chelmsford, MA, USA
Co-author(s): Paul Ullucci and Ian Acworth, Thermo Fisher Scientific, Chelmsford, MA, USA
ABSTRACT: Beer is the most widely consumed alcoholic
beverage in the world and the third most popular drink after water and
tea. Beer is brewed from four basic ingredients: water, a starch source
(e.g., malted barley), brewer’s yeast, and a flavoring agent such as
hops. Many varieties of beer result from differences in these
ingredients, the additives used, and the brewing process followed. While
there are many different types of beer, all have one characteristic in
common—bitterness. Hop or hop extracts are added during the boiling of
the wort. During this time the virtually insoluble alpha-acids
(humulones) are isomerized into the more soluble iso-alpha-acids, the
main bittering substances in beer. In addition, beta-acids (lupulones)
also add to the bitterness in beer. The analysis of hop acids in hops
and beer is important for quality control of the beverage. Many HPLC
methods have been applied to the determination of bitter acids in beer.
HPLC techniques using UV detection typically require a concentration
step in the analysis to be able to determine low levels of bitter acids.
Application of HPLC with electrochemical detection allows the
determination of bitter acids even in light beers without the need for
preconcentration. Chromatographic separation was performed on a Dionex
Acclaim C30 column (3 µm, 3.0 × 150 mm) at 35°C with gradient elution
and simultaneous UV (270 nm) and EC detection (500 and 800 mV). Sample
preparation involved extraction with acidified acetonitrile and
centrifugation. All calibration curves showed good linear regression (r2
> 0.996). RSDs over a 20-hr run are as follows: isoxanthohumol and
xantholhumol, 1.2%; alpha and beta bitter acids, 2.5%; and trans- and cis-iso-alpha-acids, 2.4%.
Dave
Thomas received a Ph.D. degree in analytical chemistry from the
University of Nebraska-Lincoln in 1994 for his work developing
high-performance immunoaffinity chromatography. In post-doctoral
appointments at Midwest Research Institute-California Operations and
Sandia National Laboratories, he worked to implement HPIAC and HPLC
approaches on miniaturized electrochromatographic separation and
analysis platforms. Later, he spent several years developing a variety
of IC, HPLC, and LC/MS applications at Dionex Corporation and Thermo
Fisher Scientific, where he also served as manager of the HPLC and LCMS
applications laboratory. After a few years in vaccine analytical
development at Wyeth and Pfizer, Dave returned to Thermo Fisher
Scientific, where he continues to develop applications for HPLC with
charged aerosol and electrochemical detection.
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