Radio-frequency discharge VUV composite ionization source used for mass spectrometry

Abstract

The invention relates to an ionization source, in particular to a composite ionization source which comprises a VUV single-photon ionization source based on radio-frequency voltage discharge and a chemical ionization source obtained by utilizing photoelectron ionization reagent gas in the photoelectric effect. The composite ionization source comprises a radio-frequency VUV source, an ion transmission optical system and an ion source cavity. An ion repulsing electrode, an ion focusing electrode and a difference interface electrode plate are sequentially arranged in the VUV source emergent direction of radio-frequency discharge, the three electrodes are all round sheet electrodes with round holes in the centers, and the three electrodes are spaced through insulation pads and are coaxially arranged in parallel. The VUV light beam of the radio-frequency voltage discharge and coaxial light beams of all the round sheet electrodes penetrate through the center holes of all the electrodes in the axis direction, and finally the beams are irradiated on the surface of the difference interface electrode plate. Chemical ionization is acted on the photoelectrons after reagent gas is added. Soft ionization of sample molecules with ionization energy higher than the photon energy is achieved, the range of analyzable samples is enlarged, and the detection sensitivity of instruments is improved.

Description

technical field [0001] The invention relates to an ionization source, in particular to a radio frequency discharge vacuum ultraviolet light composite ionization source for mass spectrometry analysis. Background technique [0002] Volatile organic compounds and semi-volatile organic pollutants are very low in the atmosphere, but most of them have pathogenic and carcinogenic effects. Therefore, the monitoring of organic pollutants has been widely concerned by people. Mass spectrometry has good universality and high sensitivity, so online mass spectrometry has become a key development direction for rapid and highly sensitive detection of organic pollutants in recent years. 70eV electron beam bombardment ionization is currently the most widely used mass spectrometry ionization source in the detection of volatile organic compounds. Electron beam bombardment ionization uses thermal electron emission. The electron beam bombardment ionization filament area needs to be heated to 300 ...

AI Technical Summary

Problems solved by technology

70eV electron beam bombardment ionization is currently the most widely used mass spectrometry ionization source in the detection of volatile organic compounds. Electron beam bombardment ionization uses thermal electron emission. The electron beam bombardment ionization filament area needs to be heated to 300 degrees Celsius or even higher, and accelerated by an electric field. Electrons carry out electron bombardment ionization. In order to prevent the filament from blowing out, the vacuum degree of ionization is required to be high, at least 10 -3 The filament can only operate normally under Pa, which makes the vacuum system complicated; moreover, because the filament operates at high temperature, the oxidizing compound or gas will react with the high-temperature filament and reduce the electron emission ability, so the electron beam bombardment ionization cannot be used for the analysis of oxidizing compounds. The most important thing is to increase the ionization cross section of the sample and improve the efficiency of electron beam bombardment ionization. The electron energy is generally 70eV, but the ionization energy of general volatile organic compounds generally does not exceed 11eV, so electron beam bombardment ionization often produces a lot of Fragment ions, the molecular ion peaks obtained are very weak, and some compounds even have no molecular ion peaks, which affects the identification of parent ions; a large number of fragment ions reduces the sensitivity of the analysis, and the overlapping of fragment peaks also brings difficulties to qualitative analysis

However, commercial VUV lamps generate fewer photons per unit time10 10 photon / s, instrument sensitivity is low

At present, there is no glass material that can pass through photon energy higher than 12eV, so it is impossible to ionize compounds with ionization energy higher than 12eV by single photon

In addition, the high-intensity vacuum ultraviolet light source has high manufacturing cost and is difficult to apply and promote

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