Quantitative analysis of tryptic protein mixtures using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

For the first time, quantitative analysis of tryptic protein mixtures, labeled with Quantification-Using-Enhanced-Signal-Tags (QUEST)-markers, were performed with electrospray ionization and a 9.4 T Fourier Transform Ion Cyclotron Resonance (FTICR) mass spectrometer. Coupling a High-Pressure Liquid Chromatography (HPLC) separation step prior to mass analysis resulted in an increased amount of identified labeled tryptic peptides. The range for the determined intensity ratios of two peptides in a labeled pair was large, but the obtained median intensity ratio correlated very well with the corresponding concentration ratio. This method can be used for observing protein dynamics in a specific cell type, tissue, or in body fluids.