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Published:
Journal of Analytical Toxicology,
ISSN 0146-4760,
Volume 31, Number 6, July/August,
pp.304-312
Rapid and Unambiguous Identification of
Melamine in Contaminated Pet Food Based on Mass Spectrometry
with Four Degrees of Confirmation
Teresa M. Vail, Patrick R. Jones, and O. David Sparkman
University of the Pacific, Stockton, California
A method for analyzing pet food without sample
processing is described for rapid identification of melamine
based on mass spectrometry (MS) using soft ionization by direct
analysis in real time (DART) to provide accurate measurement
of mass and isotope-peak intensities, in-source collisionally
activated dissociation (CAD) fragmentation, and determination
of active hydrogens. Usually, MS analyses based on other than
electron ionization (EI) spectra can be suspect because of the
limited amount of information provided by a single mass spectral
peak (or very few peaks). In such cases, additional degrees of
confirmation are desirable to increase confidence in the experimental
results. Chromatographic retention time can provide a degree
of confidence; however, this requires time and, in some cases,
detailed sample processing. Currently, the United States Food
and Drug Administration uses a gas chromatography–EI-MS
technique for the determination of melamine in pet food that
involves sample extraction and derivatization prior to a lengthy
chromatographic separation. In the method described here, identification
is also confirmed through a determination of the number of active
hydrogen atoms in the analyte molecule achieved by hydrogen/deuterium
(H/D) exchange by treatment with deuterium oxide (D2O) at the
initial stage of analysis. Cross-correlation of these four experimental
data provides an unambiguous identification of melamine in contaminated
pet food without the need for any sample preparation or chromatography.
Limits of detection and the validity of the H/D exchange method
as a confirmatory technique are also presented.
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