Document Detail

Identification and characterization of conjugated fatty acid methyl esters of mixed double bond geometry by acetonitrile chemical ionization tandem mass spectrometry.
MedLine Citation:
PMID:  14674473     Owner:  NLM     Status:  MEDLINE    
Fatty acids with conjugated double bonds have attracted great interest because of their reported potent bioactivities. However, there are currently no rapid methods for their structural characterization. We report here a convenient mass spectrometry-based strategy to establish double bond geometry by analysis of collisional dissociation products of cis/trans and trans/cis conjugated linoleic acids (CLAs), as methyl esters, and to distinguish CLAs from homoallylic (methylene-interrupted) fatty acids in a single-stage mass spectrum. A series of CLA standards with double bond positions 6,8; 7,9; 8,10; 9,11; 10,12; 11,13; 12,14; and 13,15, with all four possible geometries (cis/trans; trans/cis; cis/cis; trans/trans) were analyzed. The m/z 54 (1-methyleneimino)-1-ethenylium ion, generated by self-reaction of acetonitrile under chemical ionization conditions, reacts with unsaturated fatty acids to yield an [M + 54]+ ion, which decomposes in the single-stage mass spectrum by loss of neutral methanol to form [M + 54 - 32]+. The ratio of [M + 54]+/[M + 54 - 32]+ in the single-stage mass spectra of CLA isomers is 1 order of magnitude less than for homoallylic diene FAME. Collisional dissociation of the [M + 54]+ ion yields two diagnostic ions that contain the alpha- and omega-carbon atoms and is characteristic of double bond position in the analyte. The fragment vinylic to the trans double bond is significantly more abundant than that for the cis double bond, revealing double bond geometry. The ratio of alpha to we diagnostic ion abundances is >4.8 for cis/trans isomers, <0.5 for trans/cis isomers, and 0.7-3.2 for cis/cis and trans/trans isomers. This method provides a rapid alternative to conventional conjugated fatty acid analysis and, together with complementary elution time information provided by gas chromatography, enables rapid, positive identification of double bond position and geometry in most CLA FAME.
Anthony L Michaud; Martin P Yurawecz; Pierluigi Delmonte; Benjamin A Corl; Dale E Bauman; J Thomas Brenna
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Analytical chemistry     Volume:  75     ISSN:  0003-2700     ISO Abbreviation:  Anal. Chem.     Publication Date:  2003 Sep 
Date Detail:
Created Date:  2003-12-16     Completed Date:  2004-02-04     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  0370536     Medline TA:  Anal Chem     Country:  United States    
Other Details:
Languages:  eng     Pagination:  4925-30     Citation Subset:  IM    
Division of Nutritional Sciences, Cornell University, Savage Hall, Ithaca, New York 14853, USA.
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MeSH Terms
Fatty Acids / chemistry*
Mass Spectrometry / methods*
Grant Support
Reg. No./Substance:
0/Esters; 0/Fatty Acids

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