An interface with a linear quadrupole ion guide for an electrospray-ion trap mass spectrometer system.

摘要

A new interface for an electrospray-3D ion trap mass spectrometer system has been developed and characterized. The interface allows ion accumulation, resonant ejection and ion isolation through dipole excitation. Linear quadrupoles have an intrinsic ion storage capability that can improve the duty cycle of the combined system. Also, dipole excitation with high resolution is possible in a quadrupole field in contrast to other linear multipole fields. Thus, selective resonant ejection allows the interface to achieve precise mass selection of ions trapped in the linear quadrupoles. The resolution of resonant ejection (m/Δm)_FWHM was found to be up to 308 with the molecular ion of reserpine. One useful way of utilizing the high resolution of resonant ejection is isolating ions by applying composite waveform excitation. A composite waveform is generated from a computer by superimposing a range of frequencies. Within a band of frequencies a notch is placed around the secular frequency of an analyte ion, so that the waveform can excite all the ions except the ion with the secular frequency matching the notch. Ion isolation is shown to improve the sensitivity and resolution of the ion trap dramatically compared to the electrospray-ion trap system without ion isolation. A demonstration with a PPG (polypropylene glycol) solution with a trace amount of reserpine proves that some trace analysis can benefit greatly by eliminating background ions and thus reducing space charge problems in the ion trap.; Quadrupole resonances are an alternative to dipole excitation for excitation of ions in the quadrupole trapping field. Although both dipole and quadrupole resonance excitation share similar characteristics, quadrupole excitation has a unique resonant frequency scheme. This complicated excitation frequency scheme for higher order resonances (n ≥ 1) was first investigated experimentally in this thesis work. The results show that the maximum mass resolution in quadrupole excitation was less than in dipole excitation. Many interesting aspects of quadrupole excitation remain to be further investigated.