Quadrupolar Axialization for Improved Control of Electrosprayed Proteins in FTICR Mass Spectrometry

Quadrupolar axialization is implemented on a high-field electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer. The method is utilized to perform highly efficient remeasurement of small proteins which were not previously amenable to the remeasurement process. For example, 100 consecutive remeasurements of the same population of melittin ions (MW 2845) yield the theoretical 10-fold improvement in signal-to-noise ratio compared to the first measurement. The efficiency of the cooling process is evaluated as a function of excitation radius and ion mass, and the results are compared to instrumental performance prior to the implementation of quadrupolar axialization. The maximum achievable excitation radius for efficient remeasurement is increased from 18% to 52% of the trapped ion cell radius. The application of quadrupolar axialization during the electrospray ion accumulation event results in a factor of 3 improvement in sensitivity when acquiring bovine insulin (MW 5734) spectra under high-resolution conditions. The mass selectivity of the technique is used to isolate a single charge state of horse myoglobin (MW 16 951)