SELECTED-ION ACCUMULATION FROM AN EXTERNAL ELECTROSPRAY-IONIZATION SOURCE WITH A FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE MASS-SPECTROMETER

The coupling of an electrospray ionization (ESI) source to a Fourier-t ransform ion cyclotron resonance (FTICR) mass spectrometer provides a facility for the high resolution, accurate mass analysis of large biop olymers. Typically the m/z range of the electrosprayed ions injected a nd trapped in the FTICR cell is between m/z 500 and 2500 (but can vary considerably with solution conditions). Recent reports on quadrupole excitation have demonstrated the ability to cool the magnetron motion of ions trapped in the FTICR mass spectrometer cell by converting this motion to cyclotron motion which, under appropriate pressure conditio ns, damps readily to the center of the cell. The use of a broadband wa veform (swept frequency or stored waveform inverse Fourier-transform) for the quadrupole cooling pulse was shown to provide cooling of a wid e range of m/z ions, while implementation of a single frequency demons trated a much narrower m/z response. This report demonstrates the succ essful combination of single-frequency quadrupole cooling with externa l injection of electrosprayed ions into an FTICR mass spectrometer for m/z selected-ion accumulation. This capability is particularly signif icant with electrospray ionization since it allows ions of only one ch arge state to be accumulated in the cell, and greatly increases the po tential dynamic range of ESI-FTICR.