Analytical Chemistry
Article
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Figure 5. Product ion scans of oleamide (bottom trace) and 13C2-9,10-
oleamide (top trace). All samples were approximately 10 μM and were
directly infused into an ESI-QToF at a rate of 500 μL/min. Both
spectra were collected at 20 V collision energy. The top trace is offset
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Increasing chain length increased the appearance of higher mass
product ions when exposed to constant collision energy. The
product ions are expected to be terminal alkenes, however
observed masses do not support a pericyclic fragmentation
mechanism. A change in the position or stereochemistry of the
double bond did not change the product ions observed,
consistent with the previous report of unsaturated fatty acids.37
For this reason, the identity of isobaric compounds could not
be differentiated. Therefore, if isomer identification by MS
alone is necessary, the double bond should first be derivatized
to prevent labiality37 or a front end LC method capable of
separating isobars must be developed.
The important role of lipids in biology and health, as well as
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spectrometry, have driven the field of lipidomics (recently
reviewed in a special Chemical Review issue on “Lipid
Biochemistry, Metabolism, and Signaling”).38 Despite the
physiological significance of PFAMs,2−18 this class of lipids
have not been extensively characterized and is not well
represented in the LIPID Metabolites and Pathways Strategy
work we have reported CID patterns for various saturated and
monounsaturated PFAMs and successfully employed isotope
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AUTHOR INFORMATION
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Corresponding Author
(31) Castro-Perez, J.; Roddy, T. P.; Nibbering, N. M.; Shah, V.;
McLaren, D. G.; Previs, S.; Attygalle, A. B.; Herath, K.; Chen, Z.;
Wang, S. P.; Mitnaul, L.; Hubbard, B. K.; Vreeken, R. J.; Johns, D. G.;
Hankemeier, T. J. Am. Soc. Mass Spectrom. 2011, 22, 1552.
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This manuscript is dedicated to the late Dr. Mitchell E.
Johnson. The authors thank the National Institute of Health
(2R15 NS038443) for support of this work and the National
Science Foundation (MRIDBI-0821401) for support towards
purchase of mass spectrometers.
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(36) Kerwin, J. L.; Wiens, A. M.; Ericsson, L. H. J. Mass Spectrom.
1996, 31, 184.
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dx.doi.org/10.1021/ac203158u | Anal. Chem. 2012, 84, 2388−2394