Hot cavity type ion source for hot surface ionization mass spectrometry

Abstract

The invention discloses a thermal cavity type ion source for thermal surface ionization mass spectrometry. The thermal cavity type ion source comprises a filament pin I, a filament pin II, a supporting plate, a cooling fin I, a cooling fin II and a thermal cavity, the supporting plate can be fixed on a sample turntable of the hot surface ionization mass spectrometer; the filament pin I and the filament pin II are fixed through a supporting plate. The radiating fin I is welded and fixed with the filament pin II, and the radiating fin II is welded and fixed with the filament pin I; one end of the hot cavity is in surface contact with the radiating fin I, and the other end is in point contact or line contact with the radiating fin II and is connected to the mass spectrometer; and the filament pin I, the radiating fin II, the hot cavity, the radiating fin I, the filament pin II and an external power supply form a current path. Through the design of different contact areas between the thermal cavity and the two cooling fins, evaporation and ionization of a sample can be realized based on single-layer and single thermal cavity bodies, the ionization efficiency of the sample is remarkably improved, meanwhile, the number of the cavity bodies is reduced, the mounting structure is simplified, and the assembly efficiency, the suitability of the thermal surface ionization mass spectrometer and the working safety are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of mass spectrometer equipment, and in particular relates to a hot cavity type ion source for hot surface ionization mass spectrometry. Background Art

[0002] Thermal surface ionization mass spectrometry is an important instrument for high-precision measurement of isotope ratios. Its principle is to generate ions from the sample and screen them through a mass analyzer to achieve the measurement of nuclides with different charge-to-mass ratios. The ion source is a key component in thermal surface ionization mass spectrometry. During the analysis and measurement process, sample atoms are ionized in the ion source to form ions. Therefore, improving the ionization efficiency of the ion source on sample atoms will help improve the instrument sensitivity of the thermal surface ionization mass spectrometry, thereby achieving the measurement of extremely low-content nuclides. The existing thermal surface ionization mass spectrometry ion sources on the market are all band structure ion sources, including single-band structures and double-band structures, such as the attached Figure 1 As shown, the material is mainly high-purity rhenium foil. Its working process is as follows: in a single-belt structure ion source, the sample solution is coated on the rhenium belt, and the rhenium belt is heated to a high temperature of about 2,000 degrees Celsius by loading an electric current on the belt to achieve sample evaporation (from solution state to atomic state) and ionization (from atomic state to ion state); in a double-belt structure ion source, the double belt is divided into an evaporation belt and an ionization belt. The sample is coated on the evaporation belt, and a small current is applied to the evaporation belt to control it to maintain a medium temperature of several hundred degrees Celsius, while a large current is applied to the ionization belt to control it to reach a high temperature of about 2,000 degrees Celsius, so that the sample slowly evaporates from the evaporation belt and reaches the ionization belt, and ionization occurs at the high temperature of the ionization belt to generate ions. Whether it is a single-band or dual-band ion source, since the band structure is an open structure, the sample atoms formed after sample evaporation are scattered, and only a small part remains near the high-temperature rhenium band for ionization, while most atoms are far away from the rhenium band and cannot undergo thermal surface ionization in the high-temperature thermal field of the rhenium band, which restricts the sample ionization efficiency. The semi-enclosed thermal surface ionization mass spectrometry ion source structure designed in the papers "Design of a thermal cavity ion source with high current heating" and "A new, ohmic-heating based thermal ionization cavity source for mass spectrometry" published by Zhai Lihua et al., as shown in the attached figure, is a semi-enclosed thermal surface ionization mass spectrometry ion source structure designed in the papers "Design of a thermal cavity ion source with high current heating" and "A new, ohmic-heating based thermal ionization cavity source for mass spectrometry" Figure 2As shown, the strip structure of the conventional ion source is changed to a tubular cavity structure to increase the collision between the evaporated sample atoms and the inner wall of the cavity, thereby improving the ionization efficiency. The structure is a two-stage three-electrode design, that is, the upper end (ionization chamber) and the lower end (evaporation chamber) are both independent cavities, connected to the support structure in the middle for heat dissipation; the cavity is made of multiple layers of rhenium foil or tantalum foil. During operation, the upper and lower cavities need to be energized to heat them respectively, so as to achieve sample evaporation and ionization respectively. The above-mentioned ion source has a higher ionization efficiency than the conventional strip ion source, but its manufacturing and assembly process is relatively complicated. And because the cavity is made of multiple layers of rhenium foil or tantalum foil, the resistance is smaller than that of the strip rhenium foil. Therefore, in order to achieve the high temperature required for work, two large currents of tens of amperes need to be applied to the evaporation chamber and the ionization chamber respectively, which reduces the safety of the instrument. In addition, in order to prevent the heat generated by large currents in working paths such as wires and brackets from accumulating and damaging instrument components, it is also necessary to set up cooling devices such as liquid nitrogen to cool the external chamber of the ion source, making the ion source not highly compatible with existing commercial thermal surface ionization mass spectrometers. Summary of the invention

[0003] In view of this, the present invention provides a hot cavity ion source which can be used for hot surface ionization mass spectrometry and has high sample ionization efficiency, simple structure, convenient installation and improved adaptability and safety.

[0004] To achieve this object, the present invention adopts the following technical solutions:

[0005] A hot cavity type ion source for hot surface ionization mass spectrometry comprises a filament pin I, a filament pin II, a support plate, a heat sink I, a heat sink II and a hot cavity; the support plate can be fixed on a sample turntable of a hot surface ionization mass spectrometer; the filament pin I and the filament pin II are fixed on the support plate at intervals and insulated from the support plate; the heat sink I is welded on the filament pin II, and the heat sink II is welded on the filament pin I; one end of the hot cavity is in surface contact with the heat sink I, and the other end is in point contact or line contact with the heat sink II and connected to the mass spectrometer; the filament pin I, the heat sink II, the hot cavity, the heat sink I, the filament pin II and an external power supply form a current path.

[0006] Preferably, one end of the heat chamber is flattened and welded to the heat sink I, and the other end passes through the middle opening of the heat sink II and is connected to the mass spectrometer.

[0007] Preferably, the heat cavity is a 0.025 mm high-purity rhenium foil rolled into a single-layer cylindrical cavity with an inner diameter of 0.5 mm.

[0008] Preferably, the heat sink I and heat sink II are cut from high-purity rhenium foil.

[0009] Preferably, the heat sink I is welded to the upper middle section of the filament pin II, and the heat sink II is welded to the upper middle section of the filament pin I.

[0010] Preferably, the support plate is made of stainless steel.

[0011] Preferably, an insulating ring is provided at the contact point between the filament pin I and the filament pin II and the support plate.

[0012] The hot cavity type ion source for thermal surface ionization mass spectrometry of the present invention has different heat dissipation speeds at both ends of the hot cavity structure by designing different contact areas between the hot cavity and two heat sinks, and can realize sample evaporation and ionization through a single-layer, single-cavity hot cavity structure. Compared with the existing ribbon ion source technology, a semi-enclosed hot cavity design is adopted, which can significantly improve the sample ionization efficiency; compared with the existing two-stage three-electrode design of the hot cavity type ion source structure, the number of cavities is reduced, the installation structure is simplified, and the assembly efficiency is improved. In addition, the hot cavity type ion source of the present invention can be directly adapted to the thermal surface ionization mass spectrometer and replace the conventional ribbon ion source, without the need to change the instrument power supply and power supply circuit, and has strong adaptability; and the single-layer cavity cross-section adopted by the present invention is smaller, and the resistance is larger than that of the multi-layer rolled cavity, so the current required to obtain the same ionization temperature is smaller, which improves work safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0014] Figure 1 It is a schematic diagram of an existing ribbon structure ion source;

[0015] Figure 2 It is a schematic diagram of the structure of an existing hot cavity type ion source;

[0016] Figure 3 The figure is a schematic diagram of the structure of the hot cavity type ion source for hot surface ionization mass spectrometry of the present invention.

[0017] In the figure, 1. Filament pin I; 2. Filament pin II; 3. Support plate; 4. Insulation ring; 5. Heat sink I; 6. Heat sink II; 7. Heat cavity. DETAILED DESCRIPTION

[0018] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0019] A hot cavity type ion source for hot surface ionization mass spectrometry, such as Figure 3As shown, it includes a filament pin I, a filament pin II, a support plate, a heat sink I, a heat sink II and a thermal cavity; the support plate can be fixed on a sample turntable of a thermal surface ionization mass spectrometer; the filament pin I and the filament pin II are fixed on the support plate at intervals and are insulated from the support plate; the heat sink I is welded on the filament pin II, and the heat sink II is welded on the filament pin I; one end of the thermal cavity is in surface contact with the heat sink I, and the other end is in point contact or line contact with the heat sink II and is connected to the mass spectrometer; the filament pin I, the heat sink II, the thermal cavity, the heat sink I, the filament pin II and the external power supply form a current path.

[0020] During operation, after the sample to be tested is loaded to the bottom of the hot chamber, the ion source is installed in the hot surface ionization mass spectrometer, and current is loaded to the filament pins I and II to form a current path: power supply-filament pin I-heat sink II-hot chamber-heat sink I-filament pin II-power supply, and the temperature of the hot chamber rises through ohmic heating. Since the bottom of the hot chamber is flattened and welded to the heat sink I, the contact area is large and the heat dissipation is faster; the top of the hot chamber has a small contact area with the heat sink II and the heat dissipation is slow; therefore, the temperature at the bottom of the hot chamber is lower and the temperature at the top is higher. In this case, the sample can evaporate at the bottom of the hot chamber and collide with the inner wall multiple times, and ionize under the action of the high temperature field of the inner wall and be led out from the top under the action of the electric field at the rear end of the mass spectrometer, so that it can be separated and detected by the subsequent mass spectrometry components.

[0021] This design achieves sample evaporation and ionization by adopting a single-layer, single-cavity hot cavity structure design. It has a simple structure, simple manufacturing and installation operations, and avoids the complex preparation and installation process of multi-layer, segmented cavities in existing literature. In addition, the single-layer cavity has a smaller cross-section and a larger resistance than the multi-layer rolled cavity. Therefore, the current required to obtain the same ionization temperature is smaller, that is, the hot cavity ion source proposed in this design requires less current to work, and has higher safety and adaptability. At the same time, because the cavity structure is a semi-enclosed structure, it has a higher sample ionization efficiency than the existing ribbon structure ion source, which is conducive to sample measurement.

[0022] In a preferred embodiment, one end of the heat chamber is flattened and welded to the heat sink I, and the other end passes through the middle opening of the heat sink II and is connected to the mass spectrometer. The contact area is further reduced through the overlapping connection between the top of the heat chamber and the heat sink II, thereby reducing the heat dissipation rate of the top of the heat chamber.

[0023] In order to improve the sample ionization effect, the hot cavity is made of 0.025mm high-purity rhenium foil rolled into a single-layer cylindrical cavity with an inner diameter of 0.5mm. A larger resistance is achieved through thinner rhenium sheets to achieve a higher heating temperature under the same working current.

[0024] In another preferred embodiment, heat sink I and heat sink II are cut from high-purity rhenium foil, which has the characteristics of high melting point and good ductility, and is the same as the heat chamber material, which is convenient for welding.

[0025] Further preferably, the heat sink I is welded to the upper middle section of the filament pin II, and the heat sink II is welded to the upper middle section of the filament pin I.

[0026] In another preferred embodiment, the support plate is made of stainless steel having a relatively high melting point and high mechanical strength.

[0027] Further preferably, an insulating ring is provided at the contact point between the filament pin I and the filament pin II and the support plate.

[0028] In the verification experiment, a single-layer cylindrical heat chamber with an inner diameter of 0.5 mm was rolled using 0.025 mm high-purity rhenium foil; 0.025 mm high-purity rhenium foil was cut into heat sinks I and II, and the support plate was made of stainless steel. The bottom of the rolled heat chamber was flattened with tweezers and spot welded to heat sink I. After welding, heat sink I was spot welded to the upper middle section of filament pin II; heat sink II was spot welded to the upper middle section of filament pin I, with the same height as the welding height of heat sink I, and its extended length after welding was controlled so that it did not exceed the distance between filament pin I and filament pin II (avoiding direct connection between filament pin I and filament pin II). After welding, a hole was opened on heat sink II with a hole diameter of about 0.55 mm so that the heat chamber could just pass through. Finally, the heat chamber was inserted into the middle hole of heat sink II, and the length of the outlet at the top of the heat chamber extending out of the hole of heat sink II was adjusted to make it flush with the plane of the hole. After completing the above installation, the plutonium standard solution (containing 1pg 242Pu) is loaded into the bottom of the hot cavity, and the hot cavity type ion source is fixed on the sample turntable of the hot surface ionization mass spectrometer through a support plate, and the ion source is passed through the filament pin I and the filament pin II by the standard power supply of the hot surface ionization mass spectrometer to realize the evaporation and ionization of the sample. Comparison of the hot surface ionization mass spectrometry measurement results of loading the plutonium standard solution (containing 1pg 242Pu) onto the single-band ion source, in the case where the working current is set to be no more than 10 amperes in both cases, the sample is measured by a conventional full evaporation method, all signals of the sample are collected and the overall ionization efficiency of the sample is calculated by integration. According to calculations, the ionization efficiency of plutonium in the case of using a single-band ion source is about 0.1%, while the ionization efficiency of plutonium in the case of using the hot cavity type ion source of the present invention is about 1%, which means that the semi-enclosed hot cavity type ion source of the present design can significantly improve the ionization efficiency of the sample compared to the conventional ribbon ion source.

[0029] The present invention is described in detail above in combination with specific implementation methods and exemplary examples. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments; the above description cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, the technical solution of the present invention and its implementation methods may be subjected to a variety of equivalent substitutions, modifications or improvements, all of which fall within the scope of the present invention; the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A hot cavity ion source for hot surface ionization mass spectrometry, characterized in that: It comprises a filament pin I, a filament pin II, a support plate, a heat sink I, a heat sink II and a heat cavity; the support plate can be fixed on a sample turntable of a thermal surface ionization mass spectrometer; the filament pin I and the filament pin II are fixed to the support plate at intervals and are insulated from the support plate; The heat sink I is welded on the filament pin II, and the heat sink II is welded on the filament pin I; one end of the heat chamber is in surface contact with the heat sink I, and the other end is in point contact or line contact with the heat sink II and connected to the mass spectrometer; the filament pin I, the heat sink II, the heat chamber, the heat sink I, the filament pin II and the external power supply form a current path.

2. The hot cavity type ion source for thermal surface ionization mass spectrometry according to claim 1, characterized in that: One end of the heat chamber is flattened and welded to the heat sink I, and the other end passes through the middle opening of the heat sink II and is connected to the mass spectrometer.

3. The hot cavity ion source for thermal surface ionization mass spectrometry according to claim 1, characterized in that: The heat cavity is a 0.025 mm high-purity rhenium foil rolled into a single-layer cylindrical cavity with an inner diameter of 0.5 mm.

4. The hot cavity ion source for thermal surface ionization mass spectrometry according to claim 1, characterized in that: The heat sink I and heat sink II are cut from high-purity rhenium foil.

5. The hot cavity ion source for thermal surface ionization mass spectrometry according to any one of claims 1 to 4, characterized in that: The heat sink I is welded to the upper middle section of the filament pin II, and the heat sink II is welded to the upper middle section of the filament pin I.

6. The hot cavity ion source for thermal surface ionization mass spectrometry according to claim 1, characterized in that: The support plate is made of stainless steel.

7. The hot cavity ion source for thermal surface ionization mass spectrometry according to claim 6, characterized in that: An insulating ring is provided at the contact point between the filament pin I and the filament pin II and the support plate.

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