A vacuum ultraviolet lamp ionization source

Abstract

This invention relates to a vacuum ultraviolet lamp ionization source, comprising a vacuum ultraviolet lamp, a cylindrical pressure cap, a sealed pressure cap, a sealing O-ring, an ionization chamber, a repulsion electrode, an ionization region, a venting element, a venting hole, a focusing electrode, a lead-out electrode, a sample inlet, a heating aluminum block, a heating rod, and a temperature measuring element. The vacuum ultraviolet lamp is used to ionize sample molecules into target ions in the ionization region. After the heating rod and temperature measuring element heat the aluminum block, the repulsion electrode is maintained at a certain temperature. Applying a repulsion voltage propels the target ions in the ionization region into the venting element, while unionized sample molecules are discharged from the venting hole. The target ions travel along the venting element to the focusing electrode, where a focusing voltage is applied, and are then focused. Finally, they are pushed to the detector at the lead-out electrode for detection. This high-efficiency vacuum ultraviolet lamp ionization source ensures higher utilization efficiency of the ionized target ions after passing through the ionization region, venting element, focusing electrode, and lead-out electrode, thereby improving the detection sensitivity of the target sample.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of analytical chemistry instruments, and particularly relates to a high-efficiency vacuum ultraviolet lamp ionization source. BACKGROUND

[0002] Photoionization source is one of the most widely studied non-radioactive ionization sources. The commonly used light source is a light discharge lamp (such as a VUV lamp) or a laser generator that can emit ultraviolet light. Among them, the light discharge lamp emits photons by electrically exciting the gas filled in the lamp, and the commonly used commercial lamp can provide photons with energy of 6.7, 9.5, 10.2, 10.6 and 11.7 eV. Photoionization (PI) usually refers to the ionization mode in which a sample molecule absorbs the energy of a photon and loses an electron to form a molecular ion, also known as single-photon ionization. Its ionization principle is shown as follows:

[0003] M + hν → M + + e -

[0004] wherein hv represents the photon energy, M represents a neutral sample molecule, and M+ represents a molecular ion losing an electron. Hill et al. first proposed that photoionization as an ionization source has important advantages, that is, by selecting the photon energy of the lamp, the ionization selectivity can be improved to a certain extent.

[0005] The ionization efficiency of the vacuum ultraviolet lamp ionization source is not only related to the photon energy, but also related to the photoionization cross section of the substance itself

[0006] The distribution of photoionization cross-sections follows this pattern: aromatic hydrocarbons > alkenes > alkanes; unsaturated hydrocarbons > saturated hydrocarbons. Furthermore, the photoionization cross-section gradually increases with the degree of unsaturation of organic molecules. Although the vacuum ultraviolet lamp ionization cross-section for different organic molecules is approximately two orders of magnitude lower than the EI ionization cross-section, the sensitivity of vacuum ultraviolet lamp ionization can reach or even exceed that of EI. This is because, on one hand, ionizing organic matter with 70 eV EI generates a large number of fragment ions, even the strongest ions occupy only a small portion of the total ion current, while vacuum ultraviolet lamp ionization mainly generates molecular ions of the analyte, significantly increasing the signal intensity of single peaks in the mass spectrum. On the other hand, the ionization of a large amount of background gas in 70 eV EI, combined with the large number of organic fragment ions, generates high background noise in the mass spectrum, thus reducing the signal-to-noise ratio. Vacuum ultraviolet lamp ionization sources primarily generate molecular ions of the analyte, producing simple spectra and offering good versatility. They have broad application prospects in the rapid analysis of organic compounds and have been successfully used in petroleum component analysis, online monitoring of dioxins during waste incineration, and online detection of complex gas mixtures such as cigarette smoke. However, target ions ionized under a vacuum ultraviolet lamp experience varying degrees of loss during ionization and transport. To improve the sensitivity of the vacuum ultraviolet lamp ionization source in detecting target samples, this invention specifically designs an ionization and transport structure for the vacuum ultraviolet lamp ionization source. Summary of the Invention

[0007] A high-efficiency vacuum ultraviolet lamp ionization source includes a vacuum ultraviolet lamp, a cylindrical pressure cap, a sealed pressure cap, a sealing O-ring, a venting component, a lead electrode, a focusing electrode, a venting hole, an ionization zone, a sample inlet, a repulsion electrode, a temperature measuring element, a heating rod, an aluminum block, and an ionization chamber.

[0008] The specific content includes:

[0009] A vacuum ultraviolet lamp is used to ionize sample molecules into target ions in the ionization region. After the heating rod and temperature sensing element heat the aluminum block, the repulsion electrode is kept at a certain temperature. When a repulsion voltage is applied, the target ions in the ionization region are pushed into the venting device, and unionized sample molecules are discharged from the venting hole. The target ions travel along the venting device to the focusing electrode where a focusing voltage is applied and are focused. Then, they are pushed out to the detector at the lead-out electrode for detection.

[0010] The ionization chamber is a hollow cavity with openings at the top and right side, and the rest is sealed. The opening at the top of the ionization chamber is a recess that perfectly accommodates the size of the vacuum ultraviolet lamp head, and the opening on the right side of the ionization chamber is perfectly positioned to accommodate a cylindrical focusing electrode. The groove at the top of the ionization chamber has internal threads that perfectly mate with the internal threads below the cylindrical pressure cap. The vacuum ultraviolet lamp is sealed to the ionization chamber through the cylindrical pressure cap and a sealing O-ring. To ensure the reliability of the seal, a cylindrical sealing pressure cap is reinforced above the groove of the ionization chamber.

[0011] Repulsion voltage is between 1-180V; focusing voltage is between -1--180V; extraction voltage is between -1--180V.

[0012] The high-efficiency vacuum ultraviolet lamp ionization source makes the ionized target ions pass through the ionization zone, the evacuation part, the focusing electrode and the extraction electrode, so that the utilization efficiency of the target ions is higher, and the detection sensitivity of the target sample is improved. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The high-efficiency vacuum ultraviolet lamp ionization source comprises a vacuum ultraviolet lamp and an ionization chamber.

[0014] Figure 1 In the high-efficiency vacuum ultraviolet lamp ionization source, 1 is a vacuum ultraviolet lamp; 2 is a cylindrical compression cap; 3 is a sealed compression cap; 4 is a sealing O-ring; 5 is an evacuation part; 6 is an extraction electrode; 7 is a cylindrical focusing electrode; 8 is an evacuation hole; 9 is an ionization zone; 10 is a sample inlet; 11 is a repulsion electrode; 12 is a temperature measuring element; 13 is a heating rod; 14 is an aluminum block; and 15 is an ionization chamber. DETAILED DESCRIPTION

[0015] The high-efficiency vacuum ultraviolet lamp ionization source comprises a vacuum ultraviolet lamp and an ionization chamber; an annular protrusion is arranged on the side wall of the light outlet of the vacuum ultraviolet lamp and extends outward along a direction perpendicular to the outgoing light; the light outlet of the vacuum ultraviolet lamp is located in a middle through hole surrounded by the annular protrusion; the ionization chamber is a hollow sealed cavity; a cylindrical recess with an internal thread is arranged on the outer wall of the top of the ionization chamber; a through hole A is arranged at the bottom of the recess; the vacuum ultraviolet lamp is arranged in the recess; the light outlet of the vacuum ultraviolet lamp is arranged to face the through hole A; a sealing O-ring is arranged between the four sides of the through hole A and the light outlet of the vacuum ultraviolet lamp; the light emitted by the vacuum ultraviolet lamp is irradiated into the ionization chamber through the middle through hole of the sealing O-ring and the through hole A, forming an ionization zone; a hollow cylindrical compression cap with two open ends is arranged outside the vacuum ultraviolet lamp; the cylindrical compression cap is provided with an external thread; the cylindrical compression cap is screwed with the cylindrical recess; the vacuum ultraviolet lamp is sealed and connected with the ionization chamber through the cylindrical compression cap and the sealing O-ring.

[0016] In the ionization chamber, a repulsion electrode is arranged on the left side of the ionization zone; an evacuation part, a cylindrical focusing electrode and an extraction electrode are sequentially arranged from left to right on the right side of the ionization zone; the evacuation part is a circular cylinder with two open ends; the cylindrical focusing electrode penetrates through the right side wall of the ionization chamber and extends to the outside of the ionization chamber; the extraction electrode is a flat plate electrode with a middle through hole; the axis of the cylindrical focusing electrode, the middle through hole of the extraction electrode and the axis of the evacuation part are coaxial, and the axes thereof are perpendicular to the surface of the repulsion electrode; a through hole as an evacuation hole is arranged on the side wall of the evacuation part; an aluminum block is arranged on the left side of the repulsion electrode; a temperature measuring element and an electric heating rod are arranged in the aluminum block; one end of a sample inlet pipe penetrates through the wall of the ionization chamber and extends to the ionization zone.

[0017] The upper opening end of the cylindrical compression cap is provided with a sealing compression cap, which can be a direct current ultraviolet lamp or a radio frequency ultraviolet lamp.

[0018] The temperature measuring element is a thermocouple or a temperature sensor, and the temperature measuring element is signal-connected to the temperature controller through a wire, and the electric heating rod is connected to an external power source through the temperature controller.

[0019] The vacuum ultraviolet lamp is used to ionize sample molecules into target ions in an ionization zone, the heating rod heats the aluminum block to maintain a certain temperature of the repelling electrode, the target ions in the ionization zone are pushed into the exhaust by applying a repelling voltage to the repelling electrode, and the un-ionized sample molecules are discharged from the exhaust hole; the target ions reach the cylindrical focusing electrode with a focusing voltage along the exhaust, and then are pushed out of the extraction electrode to the detector arranged on the right side for detection.

[0020] The ionization chamber is a hollow cavity with an opening on the top and the right side, and the rest is sealed; the opening on the top of the ionization chamber is a groove with a size that can accommodate the lamp holder of the vacuum ultraviolet lamp, and the opening on the right side of the ionization chamber can accommodate the cylindrical focusing electrode; the periphery of the groove on the top of the ionization chamber is provided with internal threads, which are matched with the internal threads on the bottom of the cylindrical compression cap; the vacuum ultraviolet lamp is sealed and connected with the ionization chamber through the cylindrical compression cap and the sealing O-ring, and at the same time, in order to ensure the reliability of the sealing, the cylindrical sealing compression cap is added on the top of the groove of the ionization chamber. The repelling voltage is between 1-180V. The focusing voltage is between -1--180V. The extraction voltage is between -1--180V.

[0021] Turn on the vacuum ultraviolet lamp to prevent sample molecules from remaining on the repelling electrode, heat the aluminum block to 220℃ by the heating rod, set the repelling voltage to 25V, set the focusing voltage to -140V, and set the extraction voltage to -45V. Taking 1ppm toluene sample as an example, toluene molecules are brought into the ionization zone from the sample inlet to ionize into target ions, the repelling electrode voltage pushes the target ions in the ionization zone into the exhaust, and the un-ionized toluene molecules are discharged from the exhaust hole. The target ions reach the focusing electrode along the exhaust, and then are pushed out of the extraction electrode to the ion trap mass spectrometer detector for detection, and the mass spectrum peak of M / Z 91 is detected.

Claims

1. A vacuum ultraviolet lamp ionization source, comprising a vacuum ultraviolet lamp (1) and an ionization chamber (15); A ring-shaped protrusion is provided on the side wall of the light outlet of the vacuum ultraviolet lamp (1) in a direction perpendicular to the emitted light. The light outlet of the vacuum ultraviolet lamp (1) is located in the area of ​​the central through hole surrounded by the ring-shaped protrusion. The ionization chamber (15) is a hollow and sealed cavity. A cylindrical groove with internal threads is provided on the outer wall surface of the top of the ionization chamber (15). A through hole A is provided at the bottom of the groove. The vacuum ultraviolet lamp (1) is placed in the groove. The light outlet of the vacuum ultraviolet lamp (1) faces the through hole A. A sealing O-ring (4) is provided around the through hole A and between the light outlet of the vacuum ultraviolet lamp (1). The light emitted by the vacuum ultraviolet lamp (1) enters the ionization chamber (15) after passing through the through hole in the middle of the sealing O-ring and the through hole A, forming an ionization zone (9). A hollow cylindrical pressure cap (2) with open top and bottom is fitted on the outside of the vacuum ultraviolet lamp (1). The cylindrical pressure cap (2) has external threads. The cylindrical pressure cap (2) is screwed into the cylindrical groove. The vacuum ultraviolet lamp (1) is sealed to the ionization chamber (15) through the cylindrical pressure cap (2) and the sealing O-ring (4). Inside the ionization chamber (15), a repulsion electrode (11) is provided on the left side of the ionization region (9), and from left to right on the right side of the ionization region (9), a venting device (5), a cylindrical focusing electrode (7), and an extraction electrode (6) are provided. The venting device (5) is a cylindrical body with openings at both ends. The cylindrical focusing electrode (7) extends through the right wall of the ionization chamber (15) to the outside of the ionization chamber (15). The extraction electrodes (6) are all flat plates with through holes in the middle. The axis of the cylindrical focusing electrode (7), the through hole in the middle of the extraction electrode (6), and the axis of the venting device (5) are coaxial, and their axes are perpendicular to the surface of the repulsion electrode (11). A through hole (8) is provided on the side wall of the venting component (5); an aluminum block (14) is provided on the left side of the repulsion electrode (11), and a temperature measuring element (12) and an electric heating rod (13) are provided inside the aluminum block (14). One end of the sample inlet tube (10) extends through the wall of the ionization chamber (15) to the ionization region (9).

2. The vacuum ultraviolet lamp ionization source according to claim 1, characterized in that: A sealed cap (3) is provided at the upper opening end of the cylindrical cap (2), which can be a DC ultraviolet lamp or an RF ultraviolet lamp.

3. The vacuum ultraviolet lamp ionization source according to claim 1, characterized in that: The temperature sensing element (12) is a thermocouple or a temperature sensor. The temperature sensing element (12) is connected to the temperature controller via a wire. The electric heating rod (13) is connected to an external power source via a wire through the temperature controller.

4. The vacuum ultraviolet lamp ionization source according to claim 1, characterized in that: The vacuum ultraviolet lamp (1) is used to ionize sample molecules into target ions in the ionization region (9). After the heating rod (13) heats the aluminum block (14), the repulsion electrode is kept at a certain temperature. After the repulsion electrode is subjected to a repulsion voltage, the target ions in the ionization region (9) are pushed into the venting device (5). The unionized sample molecules are discharged from the venting hole (8). The target ion is focused along the venting element (5) to the cylindrical focusing electrode (7) with the focusing voltage applied, and then pushed out to the detector located on its right side by the lead-out electrode (6) for detection.

5. The vacuum ultraviolet lamp ionization source according to claim 1, characterized in that: The ionization chamber (15) is a hollow cavity with openings on the top and right sides, and the rest is sealed. The opening on the top of the ionization chamber (15) is a groove that can accommodate the size of the vacuum ultraviolet lamp (1) head. The opening on the right side of the ionization chamber (15) can accommodate the cylindrical focusing electrode (7). The groove on the top of the ionization chamber (15) has internal threads around it, which fit perfectly with the internal threads below the cylindrical pressure cap (2). The vacuum ultraviolet lamp (1) is sealed to the ionization chamber (15) through the cylindrical pressure cap (2) and the sealing O-ring (4). At the same time, to ensure the reliability of the seal, a cylindrical sealing pressure cap (3) is reinforced above the groove of the ionization chamber (15).

6. The vacuum ultraviolet lamp ionization source according to claim 1, characterized in that: The repulsion voltage is between 1 and 180V.

7. The vacuum ultraviolet lamp ionization source according to claim 1, characterized in that: The focusing voltage is between -1 and -180V.

8. The vacuum ultraviolet lamp ionization source according to claim 1, characterized in that: The output voltage is between -1 and -180V.

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