Carbon nanotube electron ionization sources

Abstract

An ion source for use in a mass spectrometer includes an electron emitter assembly configured to emit electron beams, wherein the electron emitter assembly comprises carbon nanotube bundles fixed to a substrate for emitting the electron beams, a first control grid configured to control emission of the electron beams, and a second control grid configured to control energies of the electron beams; an ionization chamber having an electron-beam inlet to allow the electron beams to enter the ionization chamber, a sample inlet for sample introduction, and an ion-beam outlet to provide an exit for ionized sample molecules; an electron lens disposed between the electron emitter assembly and the ionization chamber to focus the electron beams; and at least one electrode disposed proximate the ion-beam outlet to focus the ionized sample molecules exiting the ionization chamber.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] Not Applicable.BACKGROUND OF INVENTION [0002] 1. Field of the Invention [0003] The invention relates generally to ion sources for mass spectrometers, and, more particularly, to carbon nanotube-based ion sources for mass spectrometers. [0004] 2. Background Art [0005] Mass spectrometers are powerful instruments for the analysis of a wide variety of samples. In order to perform mass analysis, the samples need to be vaporized. The gas molecules are then ionized by an ion source. An efficient ion source will convert as many sample molecules into ions as possible and produce an optimal beam for the specific type of analyzer. The most common ion source is the electron ionization (EI) source. In an EI source, electrons are produced by thermal emission from a hot filament, which is heated by a current flowing through it, located outside the ionization chamber. The electrons are accelerated by an electric field to a desired level of energy. This ...

AI Technical Summary

Benefits of technology

[0041] The advantages of the invention may include one or more of the following. In designing an ion source in accordance with embodiments of the invention, a computer program may be used to simulate the ion trajectory and reduce the number of variables associated with the performance characteristics of the ion source. The same program can also be used to model and monitor changes in the performance of the CNT-based ion source, once it is in service. The ability to monitor and account for changes in the performance of the ion source in turn allows for easy calibration of the instruments, for example, using application gas library with software correction provided by measuring a single certified calibration gas blend. This would provide a significant reduction in the complexity of operation, as compared to a traditional EI equipped mass spectrometer. Because the CNT-based ion source design removes the need for regular filament replacement, it is possible to design an extremely capable and reliable general-purpose industrial gas analyzer with no moving parts. This is made possible because the traditional turbo molecular vacuum pump can be replaced with an ion pump because there is no longer a requirement for a fast pump-down time—the vacuum does not need to be interrupted for routine maintenance. The CNT-based ion sources in accordance with the invention can be operated with minimal thermal perturbation and can respond to fast voltage regulation. This makes it possible to run the mass analysis in a pulsed mode.

[0042] While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Problems solved by technology

Interactions between the sample gas and the hot filament may result in changes in the electron work function of the filament.

There are several problems associated with the filament assemblies used in electron impact or chemical ionization source.

The primary problem is that the origin and trajectory of the electrons are ill defined.

Additionally, the electron emission relies on the vaporization of material, which results in a limited filament lifetime.

Interactions between the sample gas and the hot filament may result in changes in the electron work function of the filament.

However, regulation of the trap current will alter filament temperature.

This can lead to fluctuation in the temperature distribution in the ion source and cause the assembly to become misaligned.

As a result, it is often difficult, if not impossible, to de-convolute a mass spectrum of a complex mixture sample, due to inevitable uncertainties in the contributions from the components in the mixture.

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