Photoionization and discharge ionization combined ionization source

Abstract

The application discloses a photoionization and discharge ionization combined ion source. After sample molecules are photoionized, the sample molecules are focused through an ion transmission hexapole, and the peak-to-peak value of a radio frequency voltage applied to the ion transmission hexapole is increased, so that discharge ionization is introduced between the ion transmission hexapole and an open electrode. Sample molecules which are not photoionized can be continuously subjected to discharge ionization, so that the signal strength and sensitivity are improved. Meanwhile, the discharge ionization has high energy, can ionize substances which cannot be ionized by photoionization, and widens the application range of the ion source.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of mass spectrometry instrument, in particular to a photoionization and discharge ionization combined ion source. The peak-to-peak value of the radio frequency voltage applied to the ion transmission hexapole can cause a discharge between the ion transmission hexapole and the open-hole electrode to introduce discharge ionization. After the sample molecules are photoionized, they are focused by the ion transmission hexapole, and the sample molecules that are not photoionized can be further subjected to discharge ionization to improve signal strength and sensitivity. At the same time, the discharge ionization has high energy and can ionize substances that cannot be ionized by photoionization, thereby widening the application range of the ion source. BACKGROUND

[0002] Photoionization is a threshold ionization technology, and its ionization process can be achieved only by making the photon energy equal to or higher than the ionization energy threshold of the sample molecules. Since the SPI ionization cross section of organic matter is about 2 orders of magnitude lower than the 70 eV EI ionization cross section, the ionization efficiency of SPI is relatively low, thereby affecting the detection sensitivity of the instrument. At the same time, photoionization cannot ionize substances with ionization energy higher than 10.6 eV, and therefore a photoionization source and a photochemical ionization source need to be developed to form a combined ion source.

[0003] In order to improve the ionization efficiency of photoionization and widen the application range of the photoionization source, Li Haiyang et al. developed a combined ion source for photoionization and chemical ionization for mass spectrometry analysis. For substances exceeding the photoionization threshold, chemical ionization is introduced to achieve efficient ionization of the substances. Shen Chengyin et al. also developed a volatile organic matter detection device and method for mass spectrometry of a combined source of chemical ionization and photoionization, which realizes the simultaneous double ionization of various volatile organic matters through a discharge ion source and a photoionization lamp.

[0004] Discharge ionization is a commonly used ionization technology, which has high ionization efficiency and can ionize substances that cannot be ionized by photoionization, thereby being a good supplement to photoionization. If discharge ionization is placed behind the photoionization zone to supplement the ionization of neutral sample molecules that are not photoionized or cannot be photoionized, the combined ion source of photoionization and discharge ionization can greatly improve the ionization efficiency and widen the application range of the ion source. Ion transmission multipole is commonly used behind the photoionization zone to improve the transmission efficiency of ions, and the introduction of discharge ionization through the ion transmission multipole is a good supplement to photoionization. SUMMARY

[0005] The application discloses a photoionization and discharge ionization combined ion source.

[0006] In order to achieve the above object, the application adopts the following technical scheme:

[0007] The application aims to provide a photoionization and discharge ionization combined ion source.

[0008] In order to achieve the above object, the application adopts the following technical scheme:

[0009] A photoionization and discharge ionization combined ion source, characterized in that it comprises a sample inlet capillary 1, a direct current lamp 2, a first-stage vacuum cavity 3, an ion transmission hexapole 4, an aperture electrode 5, a mass analyzer 6 and a mechanical pump 8.

[0010] The first-stage vacuum cavity 3 is connected with the gas inlet of the mechanical pump 8 through a pipeline.

[0011] A light-transmitting window is arranged on the upper wall of the first-stage vacuum cavity 3, and the direct current lamp 2 is arranged at the light-transmitting window outside the first-stage vacuum cavity 3, with the light outlet of the direct current lamp 2 facing the light-transmitting window.

[0012] The ion transmission hexapole 4 is arranged in the first-stage vacuum cavity 3, and the ion transmission hexapole 4 is composed of six cylindrical electrodes 7. pp The peak-to-peak value of the radio frequency voltage applied to the adjacent electrodes is opposite in phase and the same in amplitude, and the peak-to-peak value of the radio frequency voltage is 0-500 V.

[0013] A through hole is formed in the side wall of the first-stage vacuum cavity 3, and the aperture electrode 5 is arranged at the through hole.

[0014] The distance between the end surface of the six cylindrical electrodes 7 (the end surface close to the opening electrode) and the opening electrode 5 is 0.2-1mm, and the area formed between the end surface of the six cylindrical electrodes 7 (the end surface close to the opening electrode) and the left end surface of the opening electrode 5 (the end surface far from the mass analyzer) is the discharge ionization area, which is filled with the discharge gas, and according to the Paschen's law, when the radio frequency voltage is higher than the breakdown voltage of the discharge gas, the discharge ionization occurs, and the peak-peak value of the radio frequency voltage is higher than 350V when the discharge ionization occurs. pp .

[0015] The one end of the sample injection capillary 1 extends into the first-stage vacuum cavity 3, and the sample enters the first-stage vacuum cavity 3 through the sample injection capillary 1, and the ions are generated by photoionization of the sample by the direct current lamp 2, and the generated ions are focused and transmitted by the radio frequency electric field of the ion transmission hexapole 4, and the sample not photoionized by the direct current lamp diffuses freely into the discharge ionization area and is ionized again.

[0016] The outlet end axis of the sample injection capillary 1 is on the same axis as the center of the inscribed circle of the ion transmission hexapole 4 and the axis of the central through hole of the opening electrode 5.

[0017] The right end surface (the outlet end) of the sample injection capillary 1 is located at the center of the light path of the direct current lamp 2.

[0018] The sample carrier gas is nitrogen or humidified air, and the humidity of the humidified air ranges from 50% to 99%, and due to the pressure difference between the two ends of the sample injection capillary 1, the sample and the carrier gas are passively sucked into the first-stage vacuum cavity 3 through the sample injection capillary, and a sealed light-transmitting glass sheet is arranged on the light-transmitting window, and the sample injection capillary 1 and the opening electrode 5 are arranged at the left and right two ends of the first-stage vacuum cavity 3, respectively.

[0019] The direct current voltages V1 and V2 are respectively applied to the six cylindrical electrodes 7 and the opening electrode 5, and V1 is greater than V2 to ensure the smooth transmission of the ions.

[0020] The mass analyzer 6 is a time-of-flight mass analyzer or an ion trap mass analyzer.

[0021] After the sample molecules are photoionized, the ions are focused by the ion transmission hexapole, the peak-peak value of the radio frequency voltage applied to the ion transmission hexapole is increased, and the discharge ionization occurs between the ion transmission hexapole and the opening electrode. The sample molecules not photoionized can be continuously discharge ionized, and the signal strength and sensitivity are improved. At the same time, the discharge ionization energy is high, and the substances that cannot be ionized by photoionization can be ionized, which widens the application range of the ionization source.

[0022] The advantages of the present application are:

[0023] 1. The advantage of the present application is that the ion transmission hexapole voltage is raised to introduce discharge ionization between the ion transmission hexapole and the aperture electrode, which ionizes samples that are not or cannot be photoionized, effectively improves ionization efficiency and widens the application range of the ionization source.

[0024] 2. The ion transmission hexapole can not only introduce discharge ionization by raising the radio frequency voltage, but also efficiently focus the ions generated by photoionization to improve transmission efficiency and thus sensitivity.

[0025] 3. The composite ionization source has a simple structure and can be connected with a miniaturized mass analyzer such as an ion trap mass analyzer, which has potential applications in field analysis. BRIEF DESCRIPTION OF DRAWINGS

[0026] The present application will be further described in detail below with reference to the accompanying drawings and examples:

[0027] Figure 1 is a structural schematic diagram of the present application;

[0028] Wherein 1 is a sample introduction capillary, 2 is a direct current lamp, 3 is a first stage vacuum chamber, 4 is an ion transmission hexapole, 5 is an aperture electrode, 6 is a mass analyzer, and 7 is six cylindrical electrodes.

[0029] Figure 2 is a mass spectrum of aniline in discharge ionization mode;

[0030] Figure 3 is a mass spectrum of carbon tetrachloride in discharge ionization mode, which cannot be photoionized. DETAILED DESCRIPTION

[0031] A photoionization and discharge ionization composite ionization source, characterized by comprising a sample introduction capillary 1, a direct current lamp 2, a first stage vacuum chamber 3, an ion transmission hexapole 4, an aperture electrode 5, a mass analyzer 6, and a mechanical pump 8.

[0032] The first stage vacuum chamber 3 is connected to the gas inlet of the mechanical pump 8 through a pipeline;

[0033] A light transmission window is provided on the upper wall of the first stage vacuum chamber 3, and a direct current lamp 2 is provided outside the light transmission window of the first stage vacuum chamber 3, with the light outlet of the direct current lamp 2 facing the light transmission window;

[0034] An ion transmission hexapole 4 is provided in the first stage vacuum chamber 3, which is composed of six cylindrical electrodes 7; adjacent electrodes of the six cylindrical electrodes 7 apply radio frequency voltages with opposite phases and the same amplitude; the peak-to-peak value of the radio frequency voltage is adjustable and is 320V in photoionization mode only. pp pp ​;

[0035] A through hole is formed on the side wall surface of the first-stage vacuum cavity 3, and an aperture electrode 5 is arranged at the through hole. The four peripheral edges of the aperture electrode 5 are in close connection with the inner wall surface or the opening end surface of the through hole. The aperture electrode 5 is a plate with a through hole in the middle. The first-stage vacuum cavity 3 is connected with the mass analyzer 6 through the middle through hole of the aperture electrode 5.

[0036] The distance between the end surface (the end surface close to the aperture electrode) of the six cylindrical electrodes 7 in the ion transmission hexapole 4 and the aperture electrode 5 is 0.5 mm. The region formed between the end surface (the end surface close to the aperture electrode) of the six cylindrical electrodes 7 and the left end surface (the end surface far from the mass analyzer) of the aperture electrode 5 is the discharge ionization occurrence region. The gas filled in the discharge ionization occurrence region is the discharge gas (sample carrier gas). According to the Paschen law, when the radio frequency voltage is higher than the breakdown voltage of the discharge gas, the gas will be broken down to produce discharge ionization. The peak-to-peak value of the radio frequency voltage when the discharge ionization occurs is 420 V. pp .

[0037] One end of the sample injection capillary 1 extends into the first-stage vacuum cavity 3. After the sample enters the first-stage vacuum cavity 3 through the sample injection capillary 1, the sample is photoionized by the direct current lamp 2 to generate ions. The generated ions are focused and transmitted by the radio frequency electric field of the ion transmission hexapole 4. The sample not photoionized by the direct current lamp diffuses freely into the discharge ionization occurrence region to be ionized again.

[0038] The outlet end axis of the sample injection capillary 1 is on the same axis as the center of the inscribed circle of the ion transmission hexapole 4 and the axis of the middle through hole of the aperture electrode 5.

[0039] The right end surface (the outlet end) of the sample injection capillary 1 is located at the center of the light path of the direct current lamp 2.

[0040] The sample carrier gas is nitrogen. Due to the pressure difference between the two ends of the sample injection capillary 1, the sample and the carrier gas are passively sucked into the first-stage vacuum cavity 3 through the sample injection capillary. A sealed light-transmitting glass sheet is arranged on the light-transmitting window. The sample injection capillary 1 and the aperture electrode 5 are arranged at the left and right two ends of the first-stage vacuum cavity 3, respectively.

[0041] Direct current voltages V1 and V2 of 5 V and 2 V are respectively applied to the six cylindrical electrodes 7 and the aperture electrode 5.

[0042] The mass analyzer 6 is an ion trap mass analyzer.

[0043] Example 1

[0044] Detection of aniline in the discharge ionization mode.

[0045] Nitrogen was used as carrier gas to configure 100 ppbv aniline, nitrogen flow rate was 180 ml / min, cylinder gas 1 ppmv aniline (background gas was nitrogen) flow rate was 20 ml / min, through the three-way valve one way through the sampling capillary into the first stage vacuum chamber, one way through the exhaust pipe into the fume hood, without opening the direct current lamp, the peak value of radio frequency voltage was 420 V pp The mass spectrum of aniline in the discharge ionization mode was detected.

[0046] Example 2

[0047] Carbon tetrachloride in the discharge ionization mode.

[0048] Nitrogen was used as carrier gas to configure 100 ppbv aniline, nitrogen flow rate was 180 ml / min, cylinder gas 1 ppmv aniline (background gas was nitrogen) flow rate was 20 ml / min, through the three-way valve one way through the sampling capillary into the first stage vacuum chamber, one way through the exhaust pipe into the fume hood, without opening the direct current lamp, the peak value of radio frequency voltage was 420 V pp No signal, because carbon tetrachloride cannot be photoionized. When the direct current lamp is closed, the peak value of radio frequency voltage is 420 V pp The mass spectrum of carbon tetrachloride in the discharge ionization mode was detected.

Claims

1. A combined photoionization and discharge ionization source, characterized by: It comprises a sample injection capillary (1), a direct current lamp (2), a first stage vacuum chamber (3), an ion transmission hexapole (4), an aperture electrode (5), a mass analyzer (6) and a mechanical pump (8); The first stage vacuum chamber (3) is connected with the gas inlet of the mechanical pump (8) through a pipeline; A light transmission window is arranged on the upper wall of the first stage vacuum chamber (3), and the direct current lamp (2) is arranged outside the light transmission window of the first stage vacuum chamber (3), and the light outlet of the direct current lamp (2) faces the light transmission window; In the first-stage vacuum cavity (3), an ion transmission hexapole (4) is arranged, and the ion transmission hexapole (4) is composed of six cylindrical electrodes (7); among the six cylindrical electrodes (7), adjacent electrodes apply radio frequency voltages with opposite phases and the same amplitude; the peak-to-peak value of the radio frequency voltage is 0-500V pp Adjustable; A through hole is arranged on the side wall of the first stage vacuum chamber (3), and the aperture electrode (5) is arranged at the through hole, the four peripheral edges of the aperture electrode (5) are in sealed connection with the inner wall or the opening end face of the through hole, the aperture electrode (5) is a plate with a through hole in the middle, and the first stage vacuum chamber (3) is connected with the mass analyzer (6) through the middle through hole of the aperture electrode (5); The distance between the end surface of the six cylindrical electrodes (7) close to the orifice electrode and the orifice electrode (5) is 0.2-1mm, the region formed by the end surface of the six cylindrical electrodes (7) close to the orifice electrode and the middle of the left end surface of the orifice electrode (5) away from the mass analyzer is a discharge ionization occurrence region, the discharge ionization occurrence region is filled with a discharge gas, the discharge gas is a sample carrier gas, according to the Paschen law, when the radio frequency voltage is higher than the breakdown voltage of the discharge gas, the gas will be broken down to produce discharge ionization, and the peak-to-peak value of the radio frequency voltage is higher than 350V when the discharge ionization occurs pp ; The sample injection capillary (1) extends into the first stage vacuum chamber (3), the sample enters the first stage vacuum chamber (3) through the sample injection capillary (1), is photoionized by the direct current lamp (2) to generate ions, the generated ions are focused and transmitted by the radio frequency electric field of the ion transmission hexapole (4), and the sample not photoionized by the direct current lamp is diffused into the discharge ionization area to be ionized again.

2. The photoionization and discharge ionization combined ion source according to claim 1, wherein: The outlet end axis of the sample injection capillary (1), the center of the inscribed circle of the ion transmission hexapole (4) and the axis of the middle through hole of the aperture electrode (5) are on the same axis.

3. The photoionization and discharge ionization combined ion source according to claim 1, wherein: The outlet end of the sample injection capillary (1) is located at the center of the light path of the direct current lamp (2).

4. The photoionization and discharge ionization combined ion source according to claim 1, wherein: The sample carrier gas is nitrogen or humidified air, the humidity of the humidified air ranges from 50% to 99%, the sample and the carrier gas are passively sucked into the first stage vacuum chamber (3) through the sample injection capillary due to the pressure difference between the two ends of the sample injection capillary, a sealed light transmission glass sheet is arranged on the light transmission window, and the sample injection capillary (1) and the aperture electrode (5) are arranged at the left and right ends of the first stage vacuum chamber (3) respectively.

5. The photoionization and discharge ionization combined ion source according to claim 1, wherein: Direct current voltages V1 and V2 are respectively applied to the six cylindrical electrodes (7) and the aperture electrode (5), and V1 is greater than V2 to ensure the smooth transmission of ions.

6. The photoionization and discharge ionization combined ion source according to claim 1, wherein: The mass analyzer (6) is a time-of-flight mass analyzer or an ion trap mass analyzer.

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