An in-situ ionization mass spectrometry system and analysis method

Abstract

The present invention belongs to the field of analytical chemistry, and particularly relates to an in-situ ionization mass spectrometry system and an analysis method. The in-situ ionization mass spectrometry system includes an ionization device, a mass spectrometry device, and a sample platform disposed between the two. The sample platform includes a sample plate and a fixing device. The sample plate is used to support the sample to be measured, and the fixing device is used to fix the sample plate and enable the sample plate to move in the horizontal direction. The in-situ ionization mass spectrometry system of the present invention can not only measure samples continuously and multiple times, but also be applicable to samples of different shapes and sizes, and has the advantages of high detection efficiency and good universality. And by setting a flow limiting member at the gas flow outlet of the ionization device, the metastable particle flow generated by the ionization device can be concentrated and led to the surface of the sample to be measured, improving the resolution of surface analysis of the sample; by setting the inlet transfer tube of the mass spectrometry device as a bent tube with different angles, the ionized compound to be measured can be efficiently transmitted into the mass spectrometry device for real-time analysis.

Description

Technical Field

[0001] The invention belongs to the technical field of analytical chemistry, and in particular relates to an in-situ ionization mass spectrometry system and an analysis method for direct analysis of a sample surface. Background Art

[0002] The surface of samples contains a lot of chemical information, such as whether fruits, vegetables, Chinese herbal medicines contain nutrients and pesticide residues, whether packaging materials, plastic products, fiber products contain toxic components, etc. Exploring the material composition information on the surface of samples is very important for human production and life.

[0003] Traditional mass spectrometry-based methods, such as gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry, cannot directly analyze the original sample surface. These analyses require sample pretreatment processes such as extraction, centrifugation, and purification. The steps are cumbersome, complicated, and time-consuming. In addition, they provide average signals inside and on the surface of the sample, which cannot well reflect the effective component information on the sample surface.

[0004] The matrix-assisted laser desorption ionization (MALDI) technology, which has been developing in recent years, can analyze substances on the sample surface and visualize the location of molecules in biological tissues, with the characteristics of precise imaging and high sensitivity. However, this method requires specific matrices and lasers when analyzing samples, and there are many sample processing steps, high requirements for sample morphology, and it is not possible to perform direct analysis under atmospheric pressure.

[0005] Therefore, in-situ ionization mass spectrometry (AIMS) technology came into being. This technology can ionize and analyze the target sample under atmospheric pressure conditions, and can directly perform rapid surface analysis on the sample without the need for sample preparation. The main feature of in-situ ionization mass spectrometry technology is that it connects the atmospheric pressure ion source with the mass spectrometer, directly injects samples and ionizes them in an open atmospheric pressure environment, which facilitates the simplification of mass spectrometry analysis.

[0006] Direct analysis in real time (DART) ionization source is an atmospheric pressure ionization method developed in recent years. Its working principle is as follows: under atmospheric pressure conditions, neutral or inert gases (such as nitrogen or helium) are discharged to generate excited atoms, which desorb and instantaneously ionize the compounds to be measured on the surface of the sample to be measured, thereby realizing the real-time direct analysis of the sample. The DART ion source can be compatible with different types of mass spectrometers, called direct analysis in real time mass spectrometry (DART-MS). DART-MS can analyze compounds present in gases, liquids, solids or on the surface of materials within a few seconds, without or only requiring simple sample pretreatment, with a short analysis time, simple operation, and high ionization efficiency for both polar and non-polar substances. Nowadays, DART-MS has demonstrated unique advantages in the analysis of multiple fields, and its application scope is increasing day by day.

[0007] However, the existing DART-MS devices cannot continuously analyze the surface of the sample, have low detection efficiency, have high requirements for the shape and size of the sample, and poor universality, resulting in certain deficiencies in the direct analysis of the solid surface. Therefore, it is of great significance to develop an in-situ ionization mass spectrometry device and method that is efficient, fast, continuous, automatic, and can be used for the direct analysis of the surfaces of samples with different shapes. Summary of the Invention

[0008] In view of this, the technical problem to be solved by the present invention is that the existing DART-MS devices cannot continuously analyze the surface of the sample, have low detection efficiency, have high requirements for the shape and size of the sample, and poor universality.

[0009] The object of the present invention is achieved through the following technical solutions:

[0010] On the one hand, the present invention provides an in-situ ionization mass spectrometry system, including:

[0011] An ionization device for ionizing the compounds to be measured on the surface of the sample;

[0012] A mass spectrometry device for detecting and analyzing the ionized compounds to be measured; and

[0013] A sample platform disposed between the ionization device and the mass spectrometry device for placing the sample; the sample platform includes a sample plate and a fixing device, the sample plate is used to support the sample, and the fixing device is used to fix the sample plate and enable the sample plate to move in the horizontal direction.

[0014] Optionally, the horizontal direction includes the X-axis direction and / or the Y-axis direction. The X-axis direction is the direction approaching the gas flow outlet of the ionization device and the gas flow inlet of the mass spectrometry device, and the Y-axis direction is the direction approaching the gas flow outlet of the ionization device and away from the gas flow outlet of the mass spectrometry device.

[0015] By providing a sample platform that can move along the X-axis and Y-axis directions in the horizontal direction, the present invention can not only perform multiple measurements continuously, but also be applicable to samples of different shapes and sizes, having the advantages of high detection efficiency and good universality.

[0016] Optionally, the ionization device is a DART ion source, which is installed in a reflection mode at a certain inclination angle with respect to the sample surface, and both the horizontal and vertical distances of the DART ion source relative to the sample are adjustable.

[0017] Optionally, the fixing device includes a horizontally arranged first bracket and a vertically arranged second bracket. A guide rail is provided on the first bracket, and a slider is provided on the second bracket. The slider cooperates with the guide rail to enable the second bracket to move along the guide rail, and the sample plate is fixed on the second bracket, thereby enabling the sample plate to move in the X-axis direction.

[0018] Optionally, a plurality of protrusions are provided on the second bracket, and an opening is provided at one end of the sample plate. The opening can be sleeved on the protrusions. Further, the size of the opening is slightly larger than the size of the protrusions, so that the opening on the sample plate is tightly connected to the protrusions on the second bracket, thereby ensuring the overlap between the two.

[0019] Optionally, the plurality of protrusions are linearly arranged in a direction perpendicular to the guide rail. Further, the distance between the plurality of protrusions is 2 - 4 mm. By changing the connection position between the opening and the protrusions, the movement of the sample plate in the Y-axis direction is realized.

[0020] Optionally, scales are provided in the length and / or width direction of the sample plate.

[0021] Optionally, the material of the sample plate is stainless steel. Compared with plastic materials, stainless steel materials are cleaner, easier to clean, and do not volatilize impurities like plastic and other materials, which may affect the test results.

[0022] Optionally, a flow restrictor is provided at the gas flow outlet of the ionization device. The flow restrictor has a channel for gas flow, and the outlet aperture of the channel is smaller than the gas flow outlet aperture of the ionization device. The function of the flow restrictor is to concentrate the hot metastable particle flow generated by the ionization device onto the surface of the sample to be measured.

[0023] Further, there are multiple current limiters, and the outlet apertures of their channels are designed to have different sizes, such as 2.5 mm, 1.0 mm, and 0.5 mm. By changing the outlet apertures of the current limiters, the resolution of sample surface analysis is improved.

[0024] Optionally, the current limiter is made of ceramic and is tightly connected to the gas flow outlet of the ionization device through the internal threads thereof.

[0025] Optionally, the mass spectrometry device has an inlet transfer tube for sucking the ionized compound to be measured into the mass spectrometry device. The inlet transfer tube can be a straight tube or a bent tube, and the bending angle is 120° - 150°.

[0026] Further, the mass spectrometry device has an interface part. The interface part is provided with an inlet transfer tube and a negative pressure generating part. After the compound to be measured on the sample surface is ionized by the ionization device, it is sucked into the mass spectrometry device through the inlet transfer tube by the negative pressure generated by the negative pressure generating part for analysis and detection. The inlet transfer tube is tightly connected to the interface part through a nut and a gasket.

[0027] On the other hand, the present invention also provides an in-situ ionization mass spectrometry analysis method, including the following steps:

[0028] Place a number of samples equidistantly on the sample plate, and use the in-situ ionization mass spectrometry system of the present invention to perform real-time direct analysis on the compounds to be measured on the surface of the samples in turn.

[0029] Optionally, the moving speed of the sample plate is 0.2 mm / s - 7.0 mm / s.

[0030] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0031] 1. The in-situ ionization mass spectrometry system provided by the present invention includes an ionization device, a mass spectrometry device, and a sample platform disposed between the ionization device and the mass spectrometry device. The sample platform includes a sample plate and a fixing device. The sample plate is used to support the sample to be measured, and the fixing device is used to fix the sample plate and enable the sample plate to move in the horizontal direction. This enables the mass spectrometry system of the present invention to not only perform multiple measurements continuously, but also be applicable to samples of different shapes and sizes, having the advantages of high detection efficiency and good universality.

[0032] 2. The in-situ ionization mass spectrometry system provided by the present invention sets a current limiter at the gas flow outlet of the ionization device, and the outlet aperture of the gas flow channel of the current limiter is smaller than the outlet aperture of the gas flow of the ionization device. Thus, the hot metastable particle flow generated by the ionization device can be concentrated and guided to the surface of the sample to be measured, thereby improving the resolution of sample surface analysis.

[0033] 3. The in-situ ionization mass spectrometry system provided by the present invention can efficiently transmit the ionized compound to be measured into the mass spectrometry device for real-time analysis by setting the inlet transfer tube of its mass spectrometry device as a bent tube with different angles.

[0034] 4. The in-situ ionization mass spectrometry system provided by the present invention can be applied to the direct, efficient, and continuous analysis of the chemical components on the surfaces of samples with different shapes and sizes by configuring current-limiting components with different apertures and inlet transfer tubes with different bending angles, and both the current-limiting components and the inlet transfer tubes are easy to build and disassemble, can be flexibly replaced, and in addition, the sample platform can move in the horizontal two-dimensional direction.

[0035] 5. In the in-situ ionization mass spectrometry system provided by the present invention, components such as the sample plate and the inlet transfer tube are all made of stainless steel, which are easy to clean, easy to obtain, and can be reused.

[0036] 6. The in-situ ionization mass spectrometry system provided by the present invention does not require sample pretreatment processes such as solvent extraction, extraction, concentration, centrifugation, and purification, and can directly and quickly analyze the chemical components on the surface of the sample, with simple, fast analysis steps and accurate results. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required to be used in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0038] Figure 1 It is a schematic structural diagram of the in-situ ionization mass spectrometry system in Example 1;

[0039] Figure 2 It is a schematic structural diagram of the sample platform in Example 1;

[0040] Figure 3 It is a comparison diagram of ionization effects of ceramic caps with different apertures and at different temperatures;

[0041] Figure 4 It is a comparison diagram of mass spectrometry signals using inlet transfer tubes with different shapes;

[0042] Figure 5 It is a total ion current diagram of direct surface analysis of ginseng slices;

[0043] Figure 6 It is a mass spectrometry diagram of ginseng slices.

[0044] Among them, the description of the reference numerals is as follows:

[0045] 1 - Ionization device; 11 - Current limiting component; 2 - Mass spectrometry device; 21 - Inlet transfer tube; 22 - Negative pressure generating component; 3 - Sample platform; 31 - Sample plate; 32 - Fixing device; 321 - First bracket; 322 - Second bracket; 323 - Guide rail; 324 - Protrusion; 4 - Sample; 5 - Mounting rack. Detailed implementation mode

[0046] The following embodiments are provided to better further understand the present invention. They are not limited to the best implementation mode, and do not limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with those of other existing technologies falls within the protection scope of the present invention.

[0047] For those not specifying specific experimental steps or conditions in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For reagents or instruments not indicating the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0048] Embodiment 1

[0049] As Figure 1 shown, the in-situ ionization mass spectrometry system provided in this embodiment includes:

[0050] Ionization device 1, used for desorbing and ionizing the compound to be measured on the surface of sample 4. This ionization device 1 is specifically a DART ion source, which is installed on the mounting rack 5 in a reflection mode to make it form a certain inclination angle with the surface of sample 4. The horizontal and vertical distances of the ion source relative to sample 4 can both be adjusted. A current limiting component 11 is also provided at the gas flow outlet of the DART ion source. The current limiting component 11 has a channel for gas flow, and the outlet aperture of the channel is smaller than the gas flow outlet aperture of the DART ion source. Thus, the hot metastable particle flow generated by the DART ion source can be concentrated and guided to the surface of the sample to be measured. The current limiting component 11 in this embodiment is specifically a ceramic cap, which is tightly connected to the gas flow outlet of the DART ion source through the internal thread. The number of ceramic caps can be multiple, and the outlet apertures of their channels are designed to be different sizes respectively. For example, they can be 2.5 mm, 1.0 mm, 0.5 mm. Of course, the size of the outlet aperture is not limited to these several sizes and can be changed and varied within the range allowed by the process. By changing the outlet aperture, the resolution of surface analysis of the sample is improved.

[0051] The mass spectrometry device 2 is provided with an interface part, and the interface part is provided with an inlet transfer tube 21 and a negative pressure generating member 22. After the compound to be measured on the sample surface is ionized by the DART ion source, it is sucked into the mass spectrometry device 2 through the inlet transfer tube 21 by the negative pressure generated by the negative pressure generating member for analysis and detection. The inlet transfer tube 21 is tightly connected to the interface part through nuts and gaskets. In this embodiment, the inlet transfer tube 21 can be a straight tube or a bent tube made of stainless steel, and its bending angle can be, for example, 120° or 150°.

[0052] The sample platform 3 is arranged between the ionization device 1 and the mass spectrometry device 2 and is used for placing the sample 4. The sample platform 3 includes a sample plate 31 and a fixing device 32. The sample plate 31 is used to support the sample 4. The size of the sample plate 31 is, for example, 12 cm × 5.5 cm. Of course, the size of the sample plate 31 can be changed according to actual needs. Scale marks are provided in both the length and width directions of the sample plate 31 to facilitate equidistantly placing multiple samples 4 to be measured on the sample plate 31. The sample plate 31 is made of stainless steel. Compared with plastic materials, stainless steel is cleaner, easier to clean, and does not volatilize impurities like plastic materials, which may affect the test results. The fixing device 32 is used to fix the sample plate 31 and enable the sample plate 31 to move in the horizontal direction. In this embodiment, the horizontal direction includes the X-axis direction and the Y-axis direction. Among them, the X-axis direction is the direction close to the gas flow outlet of the ionization device 1 and the gas flow inlet of the mass spectrometry device 2, and the Y-axis direction is the direction close to the gas flow outlet of the ionization device 1 and away from the gas flow outlet of the mass spectrometry device 2.

[0053] Please refer to Figure 2 , in this embodiment, the fixing device 32 includes a horizontally arranged first bracket 321 and a vertically arranged second bracket 322. A guide rail 323 is arranged on the first bracket 321, and a slider (not shown in the figure) is arranged on the second bracket 322. The slider is matched with the guide rail 323 to enable the second bracket 322 to move along the guide rail 323. The sample plate 31 is fixed on the second bracket 322, so that the sample plate 31 can be moved in the X-axis direction. In addition, a plurality of protrusions 324, such as 5 protrusions, are arranged on the second bracket 322. These protrusions are linearly arranged along the direction perpendicular to the guide rail 323, and the distance between adjacent two protrusions is 2 - 4 mm, for example, it can be 3 mm. At the same time, an opening is arranged at one end of the sample plate 31, and the size of the opening is slightly larger than the size of the protrusion 324, so that the opening on the sample plate 31 can be tightly connected to the protrusion 324 on the second bracket 322, thereby ensuring the lap joint of the two. By changing the connection position between the opening and the protrusion 324, the sample plate 31 can be moved in the Y-axis direction.

[0054] In this embodiment, by setting a sample platform that can move in the horizontal direction along the X-axis and Y-axis directions, the entire system can not only perform multiple sample measurements continuously, but also be applicable to samples of different shapes and sizes, having the advantages of high detection efficiency and good universality.

[0055] A method for mass spectrometry analysis using the in-situ ionization mass spectrometry system in this embodiment includes the following steps:

[0056] Before the test, install the ceramic cap at the gas flow outlet of the DART ion source, fix the inlet transfer tube at the ion inlet of the interface part of the mass spectrometry device, then install the sample plate on the fixing device, and fix the sample to be analyzed on the sample plate. When analyzing multiple samples, the samples can be placed on the sample plate in sequence at the same interval. Finally, adjust the position of the DART ion source so that the gas flow outlet of the ceramic cap faces the sample to be analyzed.

[0057] During the test, set the relevant working parameters of the DART ion source and the mass spectrometry device. By controlling the movement of the slider in the guide rail, the sample to be analyzed on the sample plate automatically reaches the DART ionization region at a set moving speed, for example, 0.2 mm / s to 7.0 mm / s. The substances on the sample surface are ionized by the DART ion source, and then enter the mass spectrometry device through the inlet transfer tube under the negative pressure generated by the mass spectrometry device for analysis and detection, thereby obtaining a mass spectrometry analysis signal.

[0058] Test Example 1

[0059] Select ginseng slices and astragalus slices as samples to be analyzed. Using the in-situ ionization mass spectrometry system in Example 1, according to the optimized parameter conditions for direct analysis of the sample surface, set the temperature of the DART ion source to 350 °C and 400 °C, and the pump pressure to -65 MPa for analysis and detection.

[0060] The ginseng slices and astragalus slices do not require any pretreatment and are fixed on the sample plate using double-sided tape. This sample plate can achieve continuous and automatic sample injection. The DART-MS analyzes four samples each time, and the ceramic cap and the mass spectrometry inlet transfer tube are optimized using the ginseng slices and astragalus slices respectively. When optimizing the pore diameter of the ceramic cap, a 150° bent tube is used as the mass spectrometry inlet transfer tube, and other experimental parameters are controlled unchanged. The pore diameters of the ceramic cap are changed to 2.5 mm, 1.0 mm, and 0.5 mm respectively. When optimizing the mass spectrometry inlet transfer tube, a ceramic cap with a pore diameter of 1.0 mm is used, and other experimental parameters are controlled unchanged. The mass spectrometry inlet transfer tubes are replaced with a straight tube, a 120° stainless steel bent tube, and a 150° stainless steel bent tube respectively. After continuous operation, the mass spectrometry data of the ginseng slices and astragalus slices are recorded, and the mass spectrometry data are analyzed and processed.

[0061] See the ionization effect of ceramic caps with different pore diameters and at different temperatures in Figure 3 , according to Figure 3It can be seen that ceramic caps with different pore sizes have different resolutions, and the smaller the pore size of the ceramic cap, the higher the resolution. The mass spectrometry signals of inlet transfer tubes with different shapes are as Figure 4 shown, and it can be seen from Figure 4 that the elbow form of the improved inlet transfer tube has better ion transfer efficiency and can improve the signal response of mass spectrometry detection.

[0062] Test Example 2

[0063] The in-situ ionization mass spectrometry system in Example 1 was adopted, and ginseng slices were selected as the samples to be analyzed and detected. The temperature of the DART ion source was set at 350 °C, the pump pressure was -65 MPa, the DART worked continuously, and the mass spectrometry was in a continuous recording state. Four ginseng slices could be injected and analyzed at one time.

[0064] Figure 5 is the total ion current chromatogram (TIC) of the direct surface analysis of ginseng slices, and rich substance signals can be obtained, such as Figure 6 shown. By analyzing the substance signals, it can be obtained that there are many active small molecule signals in ginseng. For example, the substance signals with mass numbers of 104.07 and 116.07 are the signals of γ-aminobutyric acid and proline respectively.

[0065] Obviously, the above-mentioned embodiments are only examples for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. An in-situ ionization mass spectrometry system, comprising: an ionization device (1) for ionizing a compound to be measured on the surface of a sample; a mass spectrometry device (2) for detecting and analyzing the ionized compound to be measured; and a sample platform (3) disposed between the ionization device (1) and the mass spectrometry device (2) for placing the sample; characterized in that the sample platform (3) includes a sample plate (31) and a fixing device (32), the sample plate (31) is used to support the sample, and the fixing device (32) is used to fix the sample plate (31) and enable the sample plate (31) to move in the horizontal direction; the fixing device (32) includes a horizontally arranged first bracket (321) and a vertically arranged second bracket (322), a guide rail (323) is provided on the first bracket (321), a slider is provided on the second bracket (322), and the slider cooperates with the guide rail (323) to enable the second bracket (322) to move along the guide rail (323), and the sample plate (31) is fixed on the second bracket (322); a plurality of protrusions (324) are provided on the second bracket (322), one end of the sample plate (31) is provided with an opening, and the opening can be sleeved on the protrusions (324); the plurality of protrusions (324) are linearly arranged along a direction perpendicular to the guide rail (323); a flow restrictor (11) is provided at the gas flow outlet of the ionization device (1), the flow restrictor (11) has a channel for gas flow, and the outlet aperture of the channel is smaller than the gas flow outlet aperture of the ionization device (1); the mass spectrometry device (2) has an inlet transfer tube (21) for sucking the ionized compound to be measured into the mass spectrometry device (2), and the inlet transfer tube (21) is a bent tube with a bending angle of 120° to 150°.

2. The in-situ ionization mass spectrometry system according to claim 1, characterized in that scales are provided in the length and / or width direction of the sample plate (31).

3. The in-situ ionization mass spectrometry system according to claim 1 or 2, characterized in that the material of the sample plate (31) is stainless steel.

4. An in-situ ionization mass spectrometry analysis method, characterized in that comprises the following steps: Placing a plurality of samples equidistantly on a sample plate, and sequentially performing real-time direct analysis on the compound to be measured on the surface of the samples by using the in-situ ionization mass spectrometry system according to any one of claims 1-3.

5. The in-situ ionization mass spectrometry analysis method according to claim 4, characterized in that the moving speed of the sample plate is 0.2 mm / s to 7.0 mm / s.

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