Abstract
A method was developed for the simultaneous quantitation of isobars from unresolved chromatographic peaks. The method is based on differences in branching ratios of ion abundances in their tandem mass spectra and an assumption that the product ion mass spectra of a mixture can be considered as a linear combination of the spectra of individual constituents. We present analytical equations and a matrixβbased approach for deconvoluting the concentration of individual components from the total peak intensity for two and three isobars and also a matrixβbased generalization to any number of compounds. The feasibility of the simultaneous analysis of mixtures containing two compounds was assessed. The approach was evaluated for the analysis of structural isomers of methylmalonic and succinic acids in human plasma and urine samples for a group of 270 samples. The linear regression equation, standard error and correlation coefficient for the agreement with a traditional method utilizing chromatographic separation of the isomers were y = 0.999__x__ β 0.005, 0.024 Β΅mol l^β1^, and 0.985, respectively. The utility of a spectral contrast angle as a predictor of analysis feasibility was evaluated. Copyright Β© 2004 John Wiley & Sons, Ltd.