Carotenoid Isotopolog Profiling in C-Labeled Leaf Extracts by LC-MS and LC-FTICR-MS.

Mass spectrometry (MS)-based metabolite analysis combined with stable isotope labeling offers a powerful tool to study dynamic regulation of metabolic pathways and metabolite fluxes in biological systems. Here we describe a method to analyze the composition of carotenoid isotopologs in C-labeled leaf extracts by using liquid chromatography (LC)-MS and LC-Fourier transform ion cyclotron resonance (FTICR)-MS. High mass resolution of the latter enables unambiguous assignment of observed mass to a unique chemical formula. Based on peak intensity the relative abundance and the degree of C labeling are calculated for individual carotenoid isotopologs.