Multiple ion isolation applications in FT-ICR MS: Exact-mass MSn internal calibration and purification/interrogation of protein-drug complexes

摘要

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 < 1.0 ppm are demonstrated and routinely achieved. Purification of a mixture is illustrated by isolating multiple charge states of a.-protein-drug complex from residual protein for further MSn studies to elucidate the site of covalent drug bonding using IRMPD for a mixture of epidennal 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. [References: 66]