Multiple Ion Isolation Applications in FT-ICR MS: Exact-Mass MSn Internal Calibration and Purification/Interrogation of Protein−Drug Complexes

Abstract
Two new applications using multiple ion isolations in the cell of a Fourier transform-ion cyclotron resonance mass spectrometer equipped with an electrospray ionization source are described. A procedure that uses multiple ion isolations of an analyte and calibrants for internal calibration at each stage in a MSn experiment, under high-resolution exact-mass conditions, for structural characterization/elucidation of angiotensin I and rapamycin is illustrated. Fragment ion mass accuracies n studies to elucidate the site of covalent drug bonding using IRMPD for a mixture of epidermal growth factor receptor (EGFr) protein and EGFr−drug complex. The procedure developed for multiple ion isolations is referred to as multi-CHEF, multiple correlated harmonic excitation fields, in which tailored waveforms are used to notch out multiple mass regions of a spectrum with minimal off-resonance excitation.

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