On-line self-cleaning method for vacuum ultraviolet lamp

Abstract

The invention provides an on-line self-cleaning method for a vacuum ultraviolet lamp, and belongs to the technical field of performance optimizing and maintaining of single-photon ionization time-of-flight mass spectrometers. The obtained method is designed for the problem that the light intensity is damped after the vacuum ultraviolet lamp is used for a long term. The method comprises the steps that when the light intensity is damped caused by the fact that a vacuum ultraviolet lamp window is polluted or oxidized by organic matter, oxyhydrogen with a certain concentration is pumped into the surface of the lamp window under on-line medium vacuum, and normal proceeding of a test is not affected; due to the strong reducing property of hydrogen, the surface of the oxidized lamp window can be recovered in a certain degree; in addition, the oxyhydrogen can generate hydroxyl radical, the hydroxyl radical reacts with hydrocarbon adhered to the surface of the lamp window to obtain the volatile organic matter to be off from the lamp window. Based on the above steps, on-line self-cleaning of the vacuum ultraviolet lamp is achieved, a device does not need to be disassembled, normal proceeding of the test is not affected, no interference on a collected spectrogram exists, and the advantages of being convenient to operate, simple in method, stable and reliable in performance and long in service life are achieved.

Description

technical field [0001] The invention relates to an online self-cleaning method for a vacuum ultraviolet lamp, belonging to the technical field of instrument performance optimization. Specifically, under the premise of not affecting the normal analysis and detection of the sample, the clean gas is introduced, and the sample is analyzed while cleaning the vacuum ultraviolet lamp. The whole process does not need to disassemble the ionization area to wipe the light window of the vacuum ultraviolet lamp, the operation is simple and the cleaning effect is obvious. Background technique [0002] In recent years, vacuum ultraviolet lamps have been more and more widely used in the field of mass spectrometry due to their small size, simple structure and low cost. Among them, the stability of the light intensity emitted by the vacuum ultraviolet lamp in the ionization region is one of the keys to the overall signal stability of the instrument. During the experiment, it was found that ...

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Problems solved by technology

[0003] 1. The organic matter (sample or pump oil) in the ionization chamber is ionized under the action of the VUV lamp. The ionized ions or unionized sample molecules are adsorbed to the magnesium fluoride window of the lamp head, resulting in window pollution and lower light transmittance. reduce

[0004] 2. The light emission efficiency of the VUV lamp itself is reduced due to internal discharge heating and electrode sputtering, etc.

[0005] 3. When using a vacuum ultraviolet lamp for photoelectron ionization or chemical ionization, it is necessary to emit photons on the surface of the metal electrode to generate photoelectrons. When the surface of the electrode where the photoelectric effect occurs is oxidized or polluted by organic matter, the photoelectron emission efficiency will decrease. Therefore, the measured photocurrent Reduced in size, resulting in attenuation of the measured light intensity signal

[0006] 4. It is reported in the literature that the long-term use of the light window of the vacuum ultraviolet lamp will cause MgF 2 Oxidation of the light window, producing MgF 2 o x , so that the transparency of the light window decreases, and it also leads to a decrease in the intensity of the emitted vacuum ultraviolet light

[0007] In general, the main reasons for the strong attenuation of vacuum ultraviolet light are the pollution of the detected organic matter and the oxidation of the light window.

The traditional method of cleaning the lamp head is to turn off the mass spectrometer, disassemble the ionization source, remove the vacuum UV lamp, and wipe the lamp head with alcohol, but this method is time-consuming and laborious

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