Fourier Transform Ion Cyclotron Resonance mass spectrometry instrumentation design and development: Reduction of ion cloud de-phasing and time-of-flight discrimination.

摘要

Fourier Transform Ion Cyclotron Resonance (FTICR) mass spectrometers are the instruments of choice for analysis of biological ions produced through electrospray ionization. FTICR mass spectrometers offer highest possible resolution and greatest mass measurement accuracy of any current mass spectrometer. Though FTICR mass spectrometers are the highest performance mass spectrometers available, it is a relatively new technique and still not fully understood in terms of ion dynamics during image current detection. Thus, there are still many improvements to be made to FTICR instrumentation. In this research, we explore a novel way to improve ion current detection and develop instrumentation to overcome the shortcomings of the current ion injection methods.;We have developed a new technique called Electron Promoted Ion Coherence or EPIC to improve duration of the detected time-domain signals. The EPIC technique consists of injecting a high density beam of electrons through the center of the ICR cell during detection. De-phasing of ion packets during image current detection leads to loss of signal. In principle, the longer the signal is detected the greater the instrument performance. With EPIC, we have been able to detect image current for up to 70 seconds as well as obtain isotopic fine structure. Both experimental and theoretical studies were carried out to establish a theory on how EPIC improves image current detection. The basis of the enhancement is from the alteration of the radial electric fields with the application of the electron beam.;A novel FTICR mass spectrometer which utilizes a 3 Tesla magnet has been developed in our laboratory. There are number of novel features implemented in this instrument, such as a flared capillary inlet tube, electrodynamic ion funnel, Restrained Ion Population Transfer (RIPT) ion guide and a Trapping Ring Electrode Cell (TREC). The RIPT ion guide was developed to eliminate time-of-flight mass discrimination, as well as transfer ions of low kinetic energy to the ICR cell. TREC was designed to allow tuning of radial electric fields during the ICR experiment to improve overall performance.