Technical Session 02: Analytical I Session
Andre R Venter, Western Michigan University
Co-author(s): Kari Blain, Western Michigan University, MI, USA
ABSTRACT: Paper spray ionization is a novel method of mass
spectrometric analysis that allows for rapid, easy, and accurate direct
chemical analysis of plant materials and extracts. Paper spray is an
ambient ionization method related to desorption electrospray ionization
(DESI) and direct analysis in real time (DART). With papers pray a small
isosceles triangle made from paper is used directly as the ion source.
An extension of this technique (known as leaf spray) uses plant material
directly. A small drop of aqueous solvent, typically 5–20 µL, is
spotted onto a leaf to which 3–5 kV is applied by alligator clip. Ions
are then produced from compounds in the leaf or on the surface of the
leaf when these are soluble in the spray solvent. These ions are sampled
into a mass spectrometer for analysis. In this presentation we
demonstrate direct analysis of hops by leaf spray. A single bract is
separated from a hop cone and analyzed directly. The entire analysis
takes less than 30 sec per run, so a representative analysis can be
obtained by analyzing multiple bracts from a sample. Rich spectra are
obtained and the alpha- and beta-acids can be quantified relatively, so,
for example, cohumulone ratios can be calculated. In addition various
classes of lipids and polyphenolic compounds are also observed, allowing
for accurate typification of hops varieties by fingerprint matching or
principle components analysis. Hop is a relatively new agricultural, but
rapidly expanding, crop in Michigan, with around 150 acres currently
under hop yards. This presentation also highlights some differences
between Michigan and other U.S. hop-growing regions in the ratios of
alpha- and beta-acids and other flavor compounds.
Andre Venter
completed both his bachelor’s and master’s (cum laude) degrees at the
University of Pretoria, South Africa. He received his Ph.D. degree in
2003 from the University of Pretoria, where he developed a comprehensive
multidimensional supercritical fluid and gas chromatography (SFC×GC)
method for petrochemical and natural product analyses. He worked with R.
Graham Cooks as a post-doctoral researcher at Purdue University, West
Lafayette, IN. There he investigated the fundamentals of desorption
electrospray ionization mass spectrometry and other ionization methods.
Since 2008 he has been an assistant professor in the Department of
Chemistry at Western Michigan University, where his research in ambient
desorption ionization continues. His research focuses on ambient surface
analysis and ionization mechanisms involving the solvent-air interface
and further development of ambient ionization and mass spectrometry
technology. Applications and method development in agricultural product,
food chemistry, industrial, environmental, and occupational health
monitoring are being pursued.
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