A focused plasma ionization source-mass spectrometer detector and its preparation method

Abstract

A focused plasma ionization source-mass spectrometer detector and its preparation method, first preparing a hollow polymer cone, then inserting a metal conductive wire into the hollow polymer cylinder, and then introducing a gas pipeline at the rear end with a flow rate of 100-400 mL min ‑1 When a 3.0-4.0 kV DC voltage is applied to the metal conductive wire, a visible plasma flame is generated between the hollow polymer cone and the counter electrode. When a liquid sample solution is loaded on the counter electrode, a corresponding mass spectrum can be obtained through mass spectrometry detection. The present invention can not only effectively focus the reagent ions generated during the plasma ionization process, but also be used in conjunction with a commercial mass spectrometer. A low-current DC power supply is used to generate an observable plasma flame, which is also convenient for directly locating the position of the sample point. The cone structure can reduce the carrier flow rate of the plasma flame to 0.4 L min ‑1 The present invention has the advantages of simple operation, low price, good reproducibility, and high sensitivity of mass spectrometry analysis.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical, pharmaceutical and biochemical sample analysis, and particularly relates to a focused plasma ionization source-mass spectrometer detector and a preparation method thereof. Background Art

[0002] Mass spectrometry has been widely used in many fields due to its advantages such as high sensitivity, good selectivity and strong specificity. The development of mass spectrometry technology depends not only on the performance of mass analyzers and detectors, but also on the ionization efficiency of the ionization source for samples. Since Cooks of Purdue University first proposed the concept of atmospheric pressure ionization source ( Science 2004, 306 ,471-473), the development of mass spectrometry technology has entered a new era. According to the type of atmospheric pressure ionization source, it can be divided into spray type ionization source and plasma type ionization source. The most important difference between the two is that the former ionizes the target sample through charged droplets, while the latter ionizes the target sample through gas plasma beam or flame. Real-time direct analysis ionization source ( Anal. Chem. 2005, 77 , 2297-2302) as the first proposed plasma ionization source technology, has been commercialized and applied to the rapid analysis of various samples due to its simple operation, high analysis throughput, and no need for sample pretreatment. In order to further expand and improve the performance of plasma ionization sources, dielectric barrier discharge ionization sources ( J. Am. Soc. Mass Spectrom. 2007, 18 , 1859-1862), low-temperature plasma ionization source ( Anal. Chem. 2008, 80 , 9097-9104), atmospheric pressure solid analysis probe ion source ( Anal. Chem. 2005, 77 , 7826-7831), atmospheric pressure mobile afterglow ionization source ( Anal. Chem. 2011, 83, 5741-5748). The aforementioned ionization source uses helium, argon, or nitrogen as the carrier gas for plasma generation. When subjected to voltages ranging from several hundred volts to several thousand volts, the carrier gas is ionized into reagent ions such as free radicals and electrons. Under the purge of the carrier gas, the reagent ions not only ionize the target compounds in the sample but also desorb from the sample surface, where they are carried by the carrier gas to the mass spectrometer inlet for subsequent detection and analysis. Plasma ionization sources can be categorized as DC, AC, RF, and microwave plasma. Although AC, RF, and microwave plasma sources play an important role in ionizing different samples, commercial mass spectrometers are typically equipped with only DC ionization sources suitable for electrospray ionization and atmospheric pressure chemical ionization. Therefore, the aforementioned ionization source must be equipped with an additional power supply before it can be used with a commercial mass spectrometer for ionization analysis of target samples. From the above, it can be concluded that the developed DC ionization source is more suitable for direct connection with commercial mass spectrometers.

[0003] There are two types of plasma ionization sources based on DC voltage that have been developed. The main difference between the two is whether the plasma flame can be observed. When the plasma flame is not visible, the specific location of the plasma generated during the ionization process on the sample cannot be determined ( Analyst 2010, 135 , 688-695). On the contrary, when the plasma flame can extend from the carrier gas outlet, it will not only be beneficial to locate the position of the sample point, but also improve the desorption efficiency of the test compound on the sample surface ( Anal. Chem. 2008, 80 , 9097-9104). However, existing visible plasma flame ionization sources all use cylindrical structures to generate plasma flames, which has the disadvantage that they either require a high current power supply (mA level) to generate them ( Anal. Chem. 2016, 88 , 1667-1673), or require a complex and expensive pulse power supply ( Anal. Chem. 2015, 87 , 5707-5715), while commercial mass spectrometers can only provide μA-level DC power supply; at the same time, the existing visible plasma flame ionization source requires the use of a high flow rate of excited atoms / molecules (≥1 L min -1 ) to desorb / ionize the sample ( Anal. Chem. 2013, 85 , 9013-9020).

[0004] The patent application number CN202111530302.6 provides a glow discharge electron bombardment ionization source mass spectrometry system, wherein the glow discharge chamber includes: a glow discharge chamber, including a cathode plate, an anode plate, a cylinder and a first pressurizing assembly. The patent application is an electron bombardment ionization source generated by glow discharge formed under low pressure and high voltage electric field. The patent application number CN202111530302.6 discloses a chemical ionization source mass spectrometry device based on lossless ion migration, including a high-voltage discharge region, and the high-voltage discharge region is connected to the ion molecule reaction region. The above two patent applications analyze gas samples. At the same time, it is unknown whether they can produce visible plasma flames, and a high-voltage electric field is required to realize their functions. Summary of the Invention

[0005] In order to overcome the shortcomings of the above-mentioned existing plasma ionization source-mass spectrometer detector, the purpose of the present invention is to provide a focused plasma ionization source-mass spectrometer detector and a preparation method thereof. The core of the invention is to insert a conductive metal wire into a hollow polymer cone, and at the same time, a low-current DC power supply can be used to generate an observable plasma flame. The low-current ionization source can directly use the power supply of a commercial mass spectrometer, without the need for an additional power supply.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A focused plasma ionization source-mass spectrometer detector comprises a hollow polymer cone in which a metal conductive wire is inserted as an electrode; a counter electrode is placed at the front end of the hollow polymer cone and parallel to the coaxial line of the metal conductive wire, and a pipeline for loading gas is left at the rear end of the hollow polymer cone.

[0008] The distance between the front end of the hollow polymer cone and the counter electrode is 5 to 10 mm.

[0009] The hollow polymer cone is made of polymer resin, polyethylene or other polymer non-conductive materials, and has an inner diameter of 0.1 to 1.5 mm at the front end and 7.0 mm at the rear end.

[0010] The metal conductive wire includes stainless steel, copper wire, silver wire, gold wire or other conductive materials, and its diameter is 0.1-0.5 mm.

[0011] The counter electrode is a carbon nanotube coated paper matrix, a metal powder coated paper matrix, a metal grid or other conductive materials.

[0012] A method for preparing the above-mentioned focused plasma ionization source-mass spectrometer detector comprises the following steps:

[0013] Step 1: Preparation of a hollow polymer cone electrode containing metal conductive filaments:

[0014] First, a hollow polymer cone is prepared, with an inner diameter of 0.1 to 1.5 mm at the front outlet and 7.0 mm at the rear. A metal conductive filament with a diameter of 0.1 to 0.5 mm is then inserted into the hollow polymer cylinder to form a hollow polymer cone electrode containing the metal conductive filament. A gas-loading pipeline is also left at the rear end of the hollow polymer cone.

[0015] Step 2: Placement of electrodes:

[0016] Place the conductive counter electrode and the hollow polymer cone electrode containing the metal conductive wire coaxially and parallel to each other, with a distance of 5 to 10 mm between them;

[0017] Step 3: Generation of visible plasma flame:

[0018] Apply a DC voltage of 3.0 to 4.0 kV to the metal conductive wire and introduce a flow rate of 100 to 400 mL / min. -1 After the helium flow is applied, a visible plasma flame will be generated between the metal conductive wire electrode and the counter electrode;

[0019] Step 4: Focused plasma ionization source-mass spectrometry analysis process:

[0020] The liquid sample is directly dropped onto the counter electrode. Under the action of the visible plasma flame, the liquid sample loaded on the counter electrode will be desorbed and ionized by the carrier gas flow, and then enter the mass spectrometer for analysis and detection.

[0021] The hollow polymer cone is made of polymer resin, polyethylene or other polymer non-conductive materials.

[0022] The metal conductive wire includes stainless steel, copper wire, silver wire, gold wire or other conductive materials.

[0023] The counter electrode is a carbon nanotube coated paper matrix, a metal powder coated paper matrix, a metal grid or other conductive materials.

[0024] The DC voltage applied in step 3 can be replaced by an AC power supply.

[0025] The advantages of the present invention are:

[0026] (1) The conductive metal wire is inserted into a hollow polymer cone. The advantage is that it can effectively focus the reagent ions generated during the plasma ionization process and use a low-current DC power supply to generate an observable plasma flame, which is convenient for directly locating the position of the sample point. The cone structure can reduce the carrier flow rate of the plasma flame to 0.4 L min -1 the following.

[0027] (2) A DC voltage of 3.0 to 4.0 kV is applied to the metal conductive wire. The ionization source can be directly connected to a commercial mass spectrometer without the need for an additional power supply.

[0028] (3) The present invention is based on a low current, DC voltage plasma ionization source, which will not only lay a solid foundation for the direct combination of this type of ionization source with a commercial mass spectrometer, but also use a low flow rate to excite atomic / molecular gas flow to desorb / ionize samples, which can save carrier gas consumption. At the same time, compared with existing similar instruments, the focused plasma ionization source-mass spectrometer has the characteristics of simple operation, low price, good reproducibility, and high sensitivity of mass spectrometry analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the focused plasma ionization source-mass spectrometer detector of the present invention; wherein 1 is a hollow polymer cone, 2 is a conductive metal wire, 3 is a counter electrode, 4 is a pipeline, 5 is a DC power supply, 6 is a mass spectrometer, 7 is a liquid sample, and 8 is a mass spectrometer.

[0030] FIG2 (A) is a photograph of the actual process of the focused plasma ionization source-mass spectrometer detector of the present invention; FIG2 (B) is a mass spectrum of commercial gasoline analyzed using the focused plasma ionization source-mass spectrometer detector of the present invention, wherein m / z 94, 108, 122 and 136 are characteristic molecular ion peaks of C1-C4 alkyl-substituted pyridine compounds in the gasoline sample, and m / z 134, 148, 162, 176, 190, 204, 218, 232 and 246 are characteristic molecular ion peaks of C0-C7 alkyl-substituted tetrahydroquinoline compounds.

[0031] Figure 3 (A) is a photograph of a plasma flame generated by a hollow polymer tube with an inner diameter of 0.4 mm; Figure 3 (B) is a photograph of a plasma flame generated by a hollow polymer tube with an inner diameter of 7.0 mm; Figure 3 (C) is a photograph of a plasma flame generated by a hollow polymer cone tube with an inner diameter of 0.4 mm at the front outlet and an inner diameter of 7.0 mm at the rear end; Figure 3 (D) is a comparison of the mass spectrometry signal intensities after ionizing acetone using hollow polymer tubes with inner diameters of 0.4 mm and 7.0 mm, and a hollow polymer cone tube with an inner diameter of 0.4 mm at the front outlet and an inner diameter of 7.0 mm at the rear end (the mass spectrometry signal intensities are compared by comparing the characteristic molecular ion peak of acetone at m / z 59); Figure 3 (E) is a comparison of the acetone ionization performance of focused plasma ionization sources made of different materials (including stainless steel, quartz, resin, and polypropylene) with a hollow cone with an inner diameter of 0.4 mm at the front outlet and an inner diameter of 7.0 mm at the rear end.

[0032] FIG4 (A) is a comparison of the ionization-mass spectrometry performance of acetone when ink-marked paper substrate, carbon nanotube-coated paper substrate, and metal grids of different pore sizes are used as FPDI and LTP sample drop loading electrodes; FIG4 (B) is a comparison of the actual current values ​​measured at the sample loading point when FPDI and LTP generate plasma when different sample drop loading electrodes are used; FIG4 (C) is a mass spectrum of acetone ionization-mass spectrometry analysis using the FPDI of the present invention; FIG4 (D) is a mass spectrum of acetone ionization-mass spectrometry analysis using LTP.

[0033] Figure 5 (A) is a schematic diagram of the structure of the atmospheric pressure mobile afterglow ionization source used; Figure 5 (B) shows the effect of applied voltage on the ionization performance of acetone analyzed by the atmospheric pressure mobile afterglow ionization source (evaluated using the signal intensity of the acetone characteristic molecular ion peak m / z 59); Figure 5 (C) is the spectrum obtained by mass spectrometry detection after ionizing acetone using the atmospheric pressure mobile afterglow ionization source at an applied voltage of -1.2 kV. DETAILED DESCRIPTION

[0034] The specific application process of the present invention regarding the focused plasma ionization source-mass spectrometer detector is described below through specific examples, but the present invention is not limited to the following examples.

[0035] Reference Figure 1 A focused plasma ionization source-mass spectrometer detector includes a hollow polymer cone 1, in which a metal conductive wire 2 is inserted as an electrode; a counter electrode 3 is placed parallel to the coaxial line of the metal conductive wire 2 at the front end of the hollow polymer cone 1, and a pipeline 4 for loading gas is left at the rear end of the hollow polymer cone 1.

[0036] A method for preparing the above-mentioned focused plasma ionization source-mass spectrometer detector comprises the following steps:

[0037] Step 1: Preparation of a hollow polymer cone electrode containing metal conductive filaments:

[0038] First, a hollow polymer cone 1 is prepared, with an inner diameter of 0.1 to 1.5 mm at the front outlet and 7.0 mm at the rear end. A metal conductive wire 2 with a diameter of 0.1 to 0.5 mm is then inserted into the hollow polymer cone 1, and a pipeline 4 for loading gas is left at its rear end.

[0039] Step 2: Placement of electrodes:

[0040] To generate a visible plasma flame, in addition to inserting a wire electrode 2 into the hollow polymer cone 1, a grounded counter electrode 3 is also required. In this invention, carbon nanotubes are coated on the surface of commercial filter paper using a vacuum filtration coating method. This paper is then cut into a 1 cm x 2 cm rectangle. Alternatively, a metal powder-coated paper substrate or metal mesh is used as the counter electrode, which is placed coaxially and parallel to the hollow polymer cone electrode containing the wire, with a distance of 5 to 10 mm between the two. It should be noted that the counter electrode must be grounded.

[0041] Step 3: Generation of visible plasma flame:

[0042] In order to generate a visible plasma flame, a DC voltage of 3.0 to 4.0 kV is applied to the hollow polymer cone electrode containing the metal conductive wire 2. The current is in the microampere level, and the DC power supply of a commercial mass spectrometer can be directly used. When the flow rate is 100 to 400 mL min -1 After the helium flow is applied, a visible plasma flame is generated between the electrode and the paper substrate counter electrode.

[0043] Step 4: Focused plasma ionization source-mass spectrometer analysis process:

[0044] In order to use the above-mentioned focused plasma ionization source to directly ionize the target compound and perform mass spectrometry analysis, 2 μL of liquid sample 7 is directly dropped onto the counter electrode. Under the action of the visible plasma flame, the sample loaded on the counter electrode will be desorbed and ionized by the carrier gas flow, and then enter the mass spectrometer 8 together with the carrier gas flow for analysis and detection.

[0045] The hollow polymer cone 1 is made of polymer resin, polyethylene or other polymer non-conductive materials.

[0046] The metal conductive wire 2 includes stainless steel, copper wire, silver wire, gold wire or other conductive materials.

[0047] The counter electrode 3 is a carbon nanotube-coated paper substrate, a metal powder-coated paper substrate, a metal grid, or other conductive materials.

[0048] The DC voltage applied in step three can be replaced by an AC power supply.

[0049] Example 1

[0050] The preparation method of this embodiment is as follows: first, a hollow polymer cone is prepared, the inner diameter of the front outlet of which is 0.4 mm and the inner diameter of the rear end is 7.0 mm. Then, a copper wire with a diameter of 0.2 mm is inserted into the hollow polymer cone, and then a gas pipeline at a flow rate of 200 mL min is introduced into the rear end of the cone. -1 A helium flow is generated; when a 3.0 kV DC voltage is applied to the copper wire, a visible plasma flame is generated between the hollow polymer cone and the carbon nanotube-coated paper substrate counter electrode (as shown in Figure 2(A)). The distance between the two electrodes is 8 mm. When a 2 μL gasoline sample is loaded onto the carbon nanotube-coated paper substrate, the resulting mass spectrum is shown in Figure 2(B). This figure demonstrates that the focused plasma ionization source-mass spectrometer of the present invention effectively ionizes the gasoline sample, generating corresponding characteristic ion peaks, facilitating rapid gasoline analysis.

[0051] Example 2

[0052] The preparation method of this embodiment is as follows: first, a hollow polymer cone is prepared, the inner diameter of the front outlet of which is 0.8 mm and the inner diameter of the rear end is 7.0 mm. Then, a copper wire with a diameter of 0.2 mm is inserted into the hollow polymer cone, and then a gas pipeline at a flow rate of 200 mL min is introduced into the rear end of the cone. -1 A helium flow was generated; when a 3.0 kV DC voltage was applied to the copper wire, a visible plasma flame was generated between the hollow polymer cone and the carbon nanotube-coated paper substrate counter electrode, with the distance between the two electrodes being 8 mm. When a 2 μL gasoline sample was loaded onto the carbon nanotube-coated paper substrate, characteristic ion mass spectrometric peaks corresponding to gasoline were obtained.

[0053] Example 3

[0054] The preparation method of this embodiment is as follows: first, a hollow polymer cone is prepared, the inner diameter of the front outlet of which is 0.4 mm and the inner diameter of the rear end is 7.0 mm. Then, a copper wire with a diameter of 0.4 mm is inserted into the hollow polymer cone, and then a gas pipeline at a flow rate of 200 mL min is introduced into the rear end of the cone. -1A helium flow was generated; when a 3.0 kV DC voltage was applied to the copper wire, a visible plasma flame was generated between the hollow polymer cone and the carbon nanotube-coated paper substrate counter electrode, with the distance between the two electrodes being 8 mm. When a 2 μL gasoline sample was loaded onto the carbon nanotube-coated paper substrate, characteristic ion mass spectrometric peaks corresponding to gasoline were obtained.

[0055] Example 4

[0056] The preparation method of this embodiment is as follows: first, a hollow polymer cone is prepared, the inner diameter of the front outlet of which is 0.4 mm and the inner diameter of the rear end is 7.0 mm. Then, a copper wire with a diameter of 0.2 mm is inserted into the hollow polymer cone, and then a gas pipeline at a flow rate of 400 mL min is introduced into the rear end of the cone. -1 A helium flow was generated; when a 3.5 kV DC voltage was applied to the copper wire, a visible plasma flame was generated between the hollow polymer cone and the carbon nanotube-coated paper substrate counter electrode, with the distance between the two electrodes being 8 mm. When a 2 μL gasoline sample was loaded onto the carbon nanotube-coated paper substrate, the corresponding characteristic ion mass spectrum peaks were obtained.

[0057] Example 5

[0058] The preparation method of this embodiment is as follows: first, a hollow polymer cone is prepared, the inner diameter of the front outlet of which is 0.4 mm and the inner diameter of the rear end is 7.0 mm. Then, a copper wire with a diameter of 0.2 mm is inserted into the hollow polymer cone, and then a gas pipeline at a flow rate of 200 mL min is introduced into the rear end of the cone. -1 A helium flow was generated; when a 4.0 kV DC voltage was applied to the silver wire, a visible plasma flame was generated between the hollow polymer cone and the carbon nanotube-coated paper substrate counter electrode, with the distance between the two electrodes being 8 mm. When a 2 μL gasoline sample was loaded onto the carbon nanotube-coated paper substrate, the corresponding characteristic ion mass spectrum peaks were obtained.

[0059] Example 6

[0060] The preparation method of this embodiment is as follows: first, a hollow polymer cone is prepared, the inner diameter of the front outlet of which is 0.4 mm and the inner diameter of the rear end is 7.0 mm. Then, a copper wire with a diameter of 0.2 mm is inserted into the hollow polymer cone, and then a gas pipeline at a flow rate of 200 mL min is introduced into the rear end of the cone. -1A helium flow was generated; when a 3.0 kV DC voltage was applied to the silver wire, a visible plasma flame was generated between the hollow polymer cone and the metal mesh counter electrode, with the distance between the two electrodes being 8 mm. When a 2 μL gasoline sample was loaded onto the carbon nanotube-coated paper substrate, characteristic ion mass spectrometry peaks corresponding to gasoline were obtained.

[0061] Example 7

[0062] The preparation method of this embodiment is as follows: first, a hollow polymer cone is prepared, the inner diameter of the front outlet of which is 0.4 mm and the inner diameter of the rear end is 7.0 mm. Then, a copper wire with a diameter of 0.2 mm is inserted into the hollow polymer cone, and then a gas pipeline at a flow rate of 200 mL min is introduced into the rear end of the cone. -1 When the power is 5 W, the frequency is 3.0 kHz and the voltage is 2.5 kV, the helium flow is p-p When an AC voltage of 100 nm is applied, a visible plasma flame is generated between the hollow polymer cone and the carbon nanotube-coated paper substrate. The distance between the two electrodes is 8 mm. When a 2 μL gasoline sample is loaded onto the carbon nanotube-coated paper substrate, characteristic ion mass spectrometry peaks corresponding to gasoline are obtained.

[0063] Comparative Example 1

[0064] To demonstrate the unique performance of the hollow polymer cone structure, the present invention compared the plasma flame generation performance of a hollow polymer tube with an inner diameter of 0.4 mm, a hollow polymer tube with an inner diameter of 7.0 mm, and a hollow polymer cone with an inner diameter of 0.4 mm at the front outlet and an inner diameter of 7.0 mm at the rear. Other conditions were the same as in Case 1. It can be seen that when the hollow polymer tube with an inner diameter of 0.4 mm was used, only a weak plasma flame was observed (as shown in Figure 3(A)); while when the hollow polymer tube with an inner diameter of 7.0 mm was used, no plasma flame was observed (as shown in Figure 3(B)), indicating that the pore size of the hollow polymer plays a key role in plasma flame generation. When the hollow polymer cone with an inner diameter of 0.4 mm at the front outlet and an inner diameter of 7.0 mm at the rear was used, a clear focused plasma flame was observed (as shown in Figure 3(C)), demonstrating that the hollow polymer cone structure proposed in the present invention plays a key role in plasma flame generation. To further demonstrate the performance of the proposed cone structure, the present invention used acetone as a probe molecule and compared the intensity changes of the molecular ion peak m / z 59 generated by ionization through the three polymer tubes described above. The results are shown in Figure 3(D). It can be seen that compared with hollow polymer tubes with inner diameters of 0.4 mm and 7.0 mm, the hollow polymer cone with a front outlet inner diameter of 0.4 mm and a rear outlet inner diameter of 7.0 mm is more likely to produce higher mass spectrometry sensitivity.

[0065] Comparative Example 2

[0066] To demonstrate the influence of the hollow cone material on focused plasma ionization performance, the present invention compared the analytical performance of acetone ionization-mass spectrometry using stainless steel, quartz, resin, and polypropylene. Other conditions were the same as in Case 1. The results are shown in Figure 3(E). It can be seen that when stainless steel was used, no acetone analytical signal was observed. However, when quartz, resin, and polypropylene were used, the acetone signal intensity showed a gradually increasing trend, indicating that as the insulation properties of the material gradually improved, its acetone ionization performance gradually improved.

[0067] Comparative Example 3

[0068] In order to demonstrate the performance difference between the focused plasma ionization source (FPDI) of the present invention using a DC power supply and the low temperature plasma ionization source (LTP) using an AC power supply reported in the literature, the present invention systematically compares the mass spectrometry performance of different loaded sample materials. Figure 4A As shown, when using the focused plasma ionization source of the present invention to ionize acetone, both ink-dotted paper and carbon nanotube-coated paper produce very high mass spectrometry signals. However, when using grids of varying apertures, the acetone mass spectrometry signal shows a decreasing trend as the grid aperture increases. When using a low-temperature plasma ionization source, the performance of the coated paper matrix is ​​poor, while when using a metal grid, the acetone mass spectrometry signal shows an initial increase followed by a decrease as the grid aperture increases, reaching its highest level when the grid aperture is 1.1 mm. Comparing the analytical performance of the focused plasma ionization source of the present invention with that of the low-temperature plasma ionization source for acetone reveals that the focused plasma ionization source of the present invention exhibits higher sensitivity for acetone mass spectrometry analysis, with a difference of 8.7 times under their respective optimal conditions.

[0069] It was also found that when different sample matrices were loaded, the current value measured for the focused plasma ionization source of the present invention was less than 100 μA (e.g. Figure 4B ), and mass spectrometry sensitivity increases with decreasing current. However, for the low-temperature plasma ionization source, the current values ​​were consistently greater than 1500 μA for different sample loading matrices. These results demonstrate that the focused plasma of the present invention can generate smaller current values, making operation safer.

[0070] Figures 4(C) and 4(D) show the mass spectra obtained by mass spectrometry analysis after ionizing acetone using the focused plasma ionization source and the low-temperature plasma ionization source of the present invention. It can be seen that the focused plasma ionization source of the present invention has higher mass spectrometry sensitivity when ionizing acetone, indicating that the ionization source proposed by the present invention has higher sample ionization efficiency.

[0071] Comparative Example 4

[0072] To further demonstrate the performance of the focused plasma ionization source (FPDI) using a DC power supply, the present invention compared its performance with that of a reported atmospheric pressure flow afterglow ionization source using a DC power supply. The specific structure of the FPDI source is shown in Figure 5(A). To compare their performance under optimal conditions, the FPDI voltage was optimized. It was found that the analytical performance for acetone was optimal when the applied voltage was greater than -1.2 kV, as shown in Figure 5(B). Figure 5(C) shows the mass spectrum of acetone ionized using the FPDI source. Compared to the performance of the focused plasma ionization source using the present invention (shown in Figure 4(C)), the mass spectrometry sensitivity was reduced by a factor of 10. This result further demonstrates that the proposed focused plasma ionization source has higher ionization performance and can produce more sensitive mass spectrometry results.

Claims

1. A focused plasma ionization source-mass spectrometer detector, characterized in that: The invention comprises a hollow polymer cone (1), wherein a metal conductive wire (2) is inserted into the hollow polymer cone (1) as an electrode; a counter electrode (3) is placed at the front end of the hollow polymer cone (1) and parallel to the coaxial line of the metal conductive wire (2); and a pipeline (4) for loading gas is left at the rear end of the hollow polymer cone (1); The distance between the front end of the hollow polymer cone (1) and the counter electrode (3) is 5 to 10 mm; The hollow polymer cone (1) is made of polymer resin, polyethylene or other polymer non-conductive materials, and has an inner diameter of 0.1 to 1.5 mm at its front end and 7.0 mm at its rear end. Apply a DC voltage of 3.0 to 4.0 kV or an AC voltage to the metal conductive wire (2), with a current of microampere level and a flow rate of 100 to 400 mL min -1 After the helium flow, a visible plasma flame is generated between the metal conductive wire electrode (2) and the counter electrode (3); The liquid sample (7) is directly dripped onto the counter electrode (3). Under the action of the visible plasma flame, the liquid sample (7) loaded on the counter electrode (3) is desorbed and ionized by the carrier gas flow, and then enters the mass spectrometer (8) for analysis and detection. The mass spectrometer inlet of the mass spectrometer (8) is located in front of the counter electrode (3); The diameter of the metal conductive wire (2) is 0.1 to 0.5 mm; The counter electrode (3) is a carbon nanotube-coated paper matrix, or the counter electrode (3) is a metal mesh with a pore size of 0.3 to 2.1 mm.

2. A focused plasma ionization source-mass spectrometer according to claim 1, characterized in that: The metal conductive wire (2) includes stainless steel, copper wire, silver wire, gold wire or other conductive materials.

3. A method for preparing a focused plasma ionization source-mass spectrometer detector, characterized in that: The following steps are involved: Step 1: Preparation of a hollow polymer cone electrode containing metal conductive filaments: First, a hollow polymer cone (1) is prepared, wherein the inner diameter of the front outlet is 0.1 to 1.5 mm and the inner diameter of the rear end is 7.0 mm; then, a metal conductive wire with a diameter of 0.1 to 0.5 mm is inserted into the hollow polymer cone to form a hollow polymer cone electrode containing the metal conductive wire, and a pipeline (4) for loading gas is left at the rear end of the hollow polymer cone (1); the hollow polymer cone (1) is made of polymer resin, polyethylene or other polymer non-conductive materials; Step 2: Placement of electrodes: The conductive counter electrode (3) is placed coaxially and parallel to the hollow polymer cone electrode containing the metal conductive wire (2), with a distance between the two being 5 to 10 mm; The counter electrode (3) is a carbon nanotube-coated paper substrate, or the counter electrode (3) is a metal mesh with a pore size of 0.3 to 2.1 mm; Step 3: Generation of visible plasma flame: Apply a DC voltage of 3.0 to 4.0 kV or an AC voltage to the metal conductive wire (2), with a current of microampere level and a flow rate of 100 to 400 mL min -1 After the helium flow is applied, a visible plasma flame will be generated between the metal conductive wire electrode and the counter electrode; Step 4: Focused plasma ionization source-mass spectrometry analysis process: The liquid sample (7) is directly dropped onto the counter electrode (3). Under the action of the visible plasma flame, the liquid sample (7) loaded on the counter electrode (3) will be desorbed and ionized by the carrier gas flow, and then enter the mass spectrometer (8) for analysis and detection; the mass spectrometer injection port of the mass spectrometer (8) is located in front of the counter electrode (3).

4. The method for preparing a focused plasma ionization source-mass spectrometer according to claim 3, characterized in that: The metal conductive wire (2) includes stainless steel, copper wire, silver wire, gold wire or other conductive materials.

Images