Relative quantification of carboxylic acid metabolites by liquid chromatography-mass spectrometry using isotopic variants of cholamine.
Labeling reagents that differ only in their isotopic composition offer a powerful approach to achieve relative quantification between samples by ESI-MS. Heavy and light isotopic forms of cholamine, which contain a positively charged quaternary ammonium group, were synthesized and tested as new labeling reagents for the relative quantification of carboxylic acid-containing metabolites, specifically fatty acids. The positive charge on cholamine ensures that the labeled product is also positively charged under all LC-MS conditions, regardless of mobile-phase pH. This leads to high ionization efficiency and correspondingly high detection sensitivity, demonstrated here for the analysis of fatty acids in positive ion mode ESI-MS after reversed-phase separation under acidic conditions. Good accuracy and precision were obtained by mixing heavy- and light-labeled hydrolyzed egg lipid extracts in different known ratios. The relative quantification results for 10 observed fatty acids had an average absolute error of 4.6% and an average coefficient of variation (CV) of 2.6%. The labeling strategy yielded a median CV of 6% when employed for fatty acid analysis of eggs from chickens fed various dietary supplements.
Lamos
Shane M
SM
Department of Chemistry, Saint Michael's College, One Winooski Park, Colchester, Vermont 05439, USA.
Shortreed
Michael R
MR
Frey
Brian L
BL
Belshaw
Peter J
PJ
Smith
Lloyd M
LM
D000818:Animals; D002264:Carboxylic Acids / Q000737:chemistry / Q000378:metabolism*; D002645:Chickens; D002853:Chromatography, Liquid / Q000379:methods*; D004530:Egg Yolk / Q000737:chemistry; D005227:Fatty Acids / Q000032:analysis*; D006868:Hydrolysis; D007553:Isotope Labeling; D008055:Lipids / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D050337:Trimethyl Ammonium Compounds / Q000737:chemistry*
D002264:Carboxylic Acids; D005227:Fatty Acids; D008055:Lipids; D050337:Trimethyl Ammonium Compounds; C522723:cholamine