CN114354737A - Mass spectrum imaging device with normal pressure laser desorption ionization and secondary photoionization - Google Patents
Mass spectrum imaging device with normal pressure laser desorption ionization and secondary photoionization Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/62—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode
- G01N27/64—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode using wave or particle radiation to ionise a gas, e.g. in an ionisation chamber
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Abstract
The invention relates to a mass spectrum imaging device with normal-pressure laser desorption ionization and secondary photoionization, and belongs to the technical field of mass spectrum imaging. Comprises a laser desorption ionization mechanism, a secondary light ionization mechanism and a gas-phase dopant introduction mechanism. The improvement lies in that: a secondary photoionization mass spectrometry mechanism and a gas phase dopant introduction mechanism are additionally arranged. The secondary photoionization mechanism comprises a tubular photoionization chamber and a vacuum ultraviolet discharge lamp; the vacuum ultraviolet discharge lamp comprises a discharge tube filled with rare gas; the gas-phase dopant introducing mechanism comprises a bubbling tank, a first conduit and a second conduit; the bubbling tank is internally provided with a dopant. During detection and analysis, the object to be detected in the biological tissue enters the sampling capillary after being analyzed by normal pressure laser, wherein unionized neutral components can be further ionized by photoinduced direct ionization and photoinduced ion molecule reaction, and high-resolution and high-sensitivity mass spectrum imaging under normal pressure is realized. The imaging technology of the invention can be used for analyzing the action mechanism of the medicine, the tumor tissue, the cell metabolism and the like.
Description
Technical Field
The invention belongs to the technical field of mass spectrum imaging, and particularly relates to a mass spectrum imaging device combining normal-pressure laser desorption ionization and secondary photoionization.
Background
The mass spectrometry imaging technology is an imaging method that a sample platform moves according to a certain rule under the control of a software program, biological samples are directly scanned and imaged through mass spectrometry, and the spatial distribution of biomolecules is analyzed according to the measured mass-to-charge ratio (m/z). Compared with the traditional optical biological imaging technology, the mass spectrum imaging technology belongs to molecular information imaging and is a novel analysis technology for researching molecular imaging in biological tissues and living animals. Compared with the traditional fluorescent molecular imaging and immune labeling molecular imaging technologies, the mass spectrum imaging can realize molecular imaging under the conditions of no labeling and no complex pretreatment, can simultaneously analyze the spatial distribution characteristics of hundreds of biomolecules on the same tissue slice, and can be used for the biopathology research by being contrasted with the biopathology analysis result. At present, mass spectrometry imaging technology has been widely applied to the fields of proteomics, lipidomics, pharmacogenomics and the like, and has also shown great application potential in pathology, clinical medicine and disease diagnosis.
At present, the main mass spectrometry imaging technology mainly comprises Matrix Assisted Laser Desorption Ionization (MALDI) mass spectrometry, desorption electrospray ionization (DESI) mass spectrometry and secondary ion ionization (SIMS) mass spectrometry, and the three technologies are respectively used for desorbing and ionizing an object to be detected from the surface of a tissue through laser, charged small droplets and ion beams, and belong to analysis methods of direct desorption ionization. A photoionization mass spectrum imaging device combined with desorption electrospray ionization is characterized in that a solid measured object is analyzed through a solvent sprayed by an electrospray needle, enters a photoionization chamber through a sampling capillary tube, and enters a mass spectrometer for analysis after secondary ionization of a light source. However, the spatial resolution of the charged droplet-based analytical electrospray ionization mass spectrometry imaging technology can only reach 200 μm, and the high-spatial-resolution mass spectrometry imaging technology has very important significance for researching the tissue micro-region and even the spatial structure at the cell level. The mass spectrum imaging technology based on laser can realize the spatial resolution of about 10-50 μm and can meet most requirements, and meanwhile, the laser desorption ionization technology is a softer ionization technology than secondary ion ionization, so the application is the most extensive. However, in the field of mass spectrometry, sensitivity and resolution are mutually restricted, and achieving the same sensitivity under higher spatial resolution conditions is extremely challenging. Furthermore, due to the complex matrix environment of biological tissues themselves, the laser desorption ionization efficiency of endogenous chemical components in biological tissues is still less than 1/1000, even with matrix assistance. Furthermore, compounds with high abundance and strong ionization efficiency inhibit ionization of other compounds. For example, in the positive ion mode, the MALDI mass spectrum of biological tissues contains mainly Phosphatidylcholine (PC) as lipid compounds, while sugar esters (glycolipids) that are also abundant are rarely detected.
In 2015, Soltwisch et al suggested that in order to increase the ionization efficiency of the difficult-to-ionize compounds in MALDI, the laser resolved diffusion particles were overlapped with the secondary photoionization laser under nitrogen cooled medium pressure (2.0-2.5 mbar), and after secondary ionization, they were detected by time-of-flight mass spectrometry through ion transport system, which was called MALDI-2 (Science) 2015, 348 (6231), 211-.
Disclosure of Invention
The invention provides an imaging device with normal-pressure laser desorption ionization and secondary photoionization mass spectrometry, which aims to realize high-resolution and high-sensitivity imaging of different compounds in biological tissues based on the combination of laser desorption ionization technology and photoinduced ion molecule reaction secondary ionization under normal-pressure conditions.
A mass spectrum imaging device with normal pressure laser desorption ionization and secondary photoionization comprises a laser desorption ionization mechanism, wherein the laser desorption ionization mechanism comprises a mass spectrometer, a laser 1, a beam expander 3, a reflector 4, a focusing mirror 5, an objective table 6 and a sampling capillary 8;
the device also comprises a secondary photoionization mechanism 9 and a gas phase dopant introduction mechanism 10;
the secondary photoionization mechanism includes a tubular photoionization chamber 95 and a vacuum ultraviolet discharge lamp;
a coaxial guide pipe 97 is arranged in the upper end of the photoionization chamber 95, the upper port of the guide pipe 97 corresponds to the outlet of a transmission capillary 98 of the mass spectrometer, and one end of a vacuumizing pipe 96 is communicated with one side of the photoionization chamber 95 corresponding to the periphery of the guide pipe 97; one end of the sampling capillary 8 is communicated with one side of the lower part of the photoionization chamber 95; the lower end of the photoionization chamber 95 is connected with a coaxial lower cover plate 91, and one side of the lower cover plate 91 is communicated with the outlet end of a dopant introduction pipe 94;
the vacuum ultraviolet discharge lamp comprises a discharge tube 99, an annular cathode 910 and a window 911; the annular cathode 910 is arranged at the upper end of the discharge tube 99, the window 911 is arranged at the through hole at the center of the annular cathode 910, and the annular anode bumps 93 are uniformly distributed on the outer circumference of the lower part of the discharge tube 99; the voltage difference between the annular positive electrode bump 93 and the annular negative electrode 910 causes the rare gas in the discharge tube 99 to discharge to generate vacuum ultraviolet light, and the vacuum ultraviolet photons enter the photoionization chamber 95 through the window 911; a coaxial annular upper cover plate 92 is arranged on the outer circumference of the annular cathode 910, and the photoionization chamber 95 and the discharge tube 99 are hermetically connected through the fixed connection of the lower cover plate 91 and the upper cover plate 92; rare gas is filled in the discharge tube 99 to obtain vacuum ultraviolet light with different energy;
the gas-phase dopant introduction mechanism includes a bubbling tank 104, a first conduit 103, and a second conduit 106; a dopant 105 is arranged in the bubbling tank 104; one end of the first conduit 103 and one end of the second conduit 106 are inserted into the bubbling tank 104, a port of the first conduit 103 is inserted into the doping agent 105, and a port of the second conduit 106 is located in the bubbling tank 104 above the doping agent 105; the other end of the first conduit 103 is connected with an air inlet pipe 101;
a first flow controller 102 is connected in series with the first conduit 103, and a second flow controller 107 is connected in series with the second conduit 106;
during work, a slide 7 carrying a sample 11 to be detected is placed on an objective table 6; the temperature of the photoionization chamber 95 is 250-380 ℃, and the vacuum degree is 2 multiplied by 103～5×104 Pa。
The further technical scheme is as follows:
the connection part of the inner diameter of the photoionization chamber 95 and the inner diameter of the draft tube 97 is in smooth transition connection with a horn-shaped tube; the distance between the inner diameter of the photoionization chamber 95 and the outer diameter of the draft tube 97 is 1-2 mm; the inner diameter of the photoionization chamber 95 is 4-8 mm; the inner diameter of the draft tube 97 is 1.2-1.6 mm, and the inner diameter of the sampling capillary 8 is 0.5-1.5 mm.
The distance between the slide 7 and the outlet of the sampling capillary 8 is not more than 5 mm; the distance between the inlet of the sampling capillary tube 8 and the surface of the window 911 is less than 8mm, and the distance between the outlet of the dopant introducing tube 94 and the surface of the window 911 is also less than 8 mm; the laser wavelength is ultraviolet light, visible light or infrared light wave band.
The object stage 6 is a conductor, and when the surface of the glass slide 7 is sprayed with a conductive material indium tin oxide, a voltage of 0V to 10KV is selectively applied in a positive ion mode, and a voltage of-10 KV to 0V is selectively applied in a negative ion mode.
The window 911 material is magnesium fluoride (Mg 2F) or lithium fluoride (LiF).
During detection, a matrix is sprayed on the surface of the sample 11 to be detected to increase laser desorption ionization efficiency, and the matrix is alpha-cyano-4-hydroxycinnamic acid or 2, 5-dihydroxybenzoic acid or titanium dioxide.
The flow rate of the first flow rate controller 102 is smaller than that of the second flow rate controller 107, and the introduction amount of the gas phase dopant can be adjusted by controlling the difference between the flow rates of the first flow rate controller and the second flow rate controller.
The dopant is one of toluene, acetone, anisole, chlorobenzene, bromobenzene and carbon disulfide.
The rare gas is one of helium, neon, krypton, xenon and nitrogen.
The beneficial technical effects of the invention are embodied in the following aspects:
1. compared with a photoionization mass spectrum imaging device combining desorption electrospray ionization, the invention has the advantages that: (1) the dopant is directly introduced into the photoionization chamber in a gas phase form through a dopant bubbling system, so that the efficiency is higher and the stability is higher; (2) in the photoionization mass spectrometry imaging device for desorption electrospray ionization, the horizontal distance between the outlet end of an electrospray needle and a sampling capillary is 10-40 mm, however, the distance between the sampling port and a laser analysis site is less than 2mm, and the sampling efficiency is high; (3) the photoionization mass spectrum imaging device for desorption electrospray ionization needs high-speed atomizing gas to be sprayed out from an atomizer to atomize a solvent, the temperature at the inlet of a sampling capillary can be obviously reduced under the blowing of the high-speed atomizing gas, and the sampling efficiency is influenced, but the photoionization mass spectrum imaging device does not have the problems; (4) the imaging spatial resolution of the photoionization mass spectrometry imaging technology of desorption electrospray ionization can only reach 200 mu m, and as shown in figure 6, the invention can realize mass spectrometry imaging with the spatial resolution less than or equal to 20 mu m.
2. Compared with MALDI-2: (1) MALDI-2 is a kind of analysis ionization technology in vacuum, need to take out the sample from the vacuum while changing the sample, but the invention is the laser analysis of the ordinary pressure, it is more convenient to operate; (2) although MALDI-2 and the present invention both use ultraviolet light as the secondary ionization mode, MALDI-2 utilizes photo-induced direct ionization, the present invention utilizes the sum of photo-induced ion molecular reaction and photo-induced direct ionization to realize secondary ionization, and the ion molecular reaction can significantly improve the photo-ionization efficiency, which has been reported in the previous literature (anal. Chim. Acta, 2015, 891, 203-); (3) secondary ionization chamber in the invention (2X 10)2～5×104Pa) can realize higher vacuum degree than MALDI-2 (2.0-2.5 mbar), and the higher the vacuum degree P is, the larger the amount n of the molecular substance to be detected is, i.e. the larger the volume density of the molecule to be detected is, the more ionizable the ion to be detected with higher density is, according to the ideal gas state equation PV = nRT, the same temperature and the same volume space.
Drawings
FIG. 1 is a schematic view of the structure of the present invention.
Fig. 2 is a partially enlarged view of fig. 1.
Fig. 3 is a cross-sectional enlarged view of the secondary photoionization mechanism of fig. 1.
Fig. 4 is an enlarged cross-sectional view of the gas-phase dopant introduction mechanism of fig. 1.
Fig. 5 is a positive ion mode mass spectrogram obtained by coating a red water color pen on a glass slide and analyzing by normal pressure laser desorption ionization and normal pressure laser desorption ionization-secondary light ionization mass spectrometry, wherein a in fig. 5 is a normal pressure laser desorption ionization diagram, and B in fig. 5 is a mass spectrogram of rhodamine 6G in the red water color pen by normal pressure laser desorption ionization-secondary light ionization mass spectrometry.
FIG. 6 is a graph showing the distribution of cholesterol (m/z 369) in the mouse cerebellum tissue by the analysis of the atmospheric pressure laser desorption ionization and the atmospheric pressure laser desorption ionization-secondary photoionization mass spectrometry according to the present invention.
Sequence numbers in FIGS. 1-4: the device comprises a laser 1, a laser 2, a beam expander 3, a reflector 4, a focusing mirror 5, an object stage 6, a glass slide 7, a sampling capillary 8, a secondary photoionization mechanism 9, a gas-phase dopant introduction mechanism 10, a sample 11 to be detected, a lower cover plate 91, an upper cover plate 92, an annular positive bump 93, a discharge tube 99, an annular negative electrode 910, a window 911, a dopant introduction tube 94, a photoionization chamber 95, an evacuation tube 96, a draft tube 97, a mass spectrum transmission capillary tube 98, an air inlet tube 101, a first flow controller 102, a first conduit 103, a bubbling tank 104, a dopant 105, a second conduit 106 and a second flow controller 107.
Detailed Description
The invention will now be further described by way of example with reference to the accompanying drawings.
Examples
Referring to fig. 1, a mass spectrometry imaging device with atmospheric pressure laser desorption ionization and secondary photoionization includes a laser desorption ionization mechanism; the laser analysis ionization mechanism comprises a mass spectrometer, a laser 1, a beam expander 3, a reflector 4, a focusing mirror 5, an objective table 6 and a sampling capillary 8; the device also comprises a secondary photoionization mechanism and a gas-phase dopant introduction mechanism.
Referring to fig. 2, 349nm ultraviolet light output by the laser 1 is firstly expanded by the expander lens 3 to obtain laser 2, which is reflected by the reflector 4 and then focused to the back side of the biological tissue 11 by the focusing lens 5. The glass slide 7 is made of quartz glass coated with conductive indium tin oxide material, and 90% of 349nm ultraviolet light can penetrate through the glass slide 7. The objective table 6 is made of conductive material, 5KV voltage is applied, the distance between the surface of the sample 11 to be measured and the sampling port of the sampling capillary 8 is 1mm, and when the sample 11 to be measured is a biological tissue slice, the thickness of the sample is 10 μm.
Referring to fig. 3, the secondary photoionization mechanism includes a tubular photoionization chamber 95 and a vacuum ultraviolet discharge lamp.
A coaxial guide pipe 97 is arranged in the upper end of the photoionization chamber 95, and the connection part of the inner diameter of the photoionization chamber 95 and the inner diameter of the guide pipe 97 is in horn-tube-shaped smooth transition connection. The upper port of the draft tube 97 corresponds to the outlet of the transmission capillary 98 of the mass spectrometer, and one end of the vacuumizing tube 96 is communicated with one side of the photoionization chamber 95 corresponding to the periphery of the draft tube 97; one end of the sampling capillary 8 is communicated with one side of the lower part of the photoionization chamber 95; the lower end of the photoionization chamber 95 is connected to a lower cover plate 91 which is coaxial, and one side of the lower cover plate 91 is communicated with the outlet end of a dopant introduction tube 94.
The vacuum ultraviolet discharge lamp comprises a discharge vessel 99, an annular cathode 910 and a louver 911; the annular cathode 910 is arranged at the upper end of the discharge tube 99, the window 911 is arranged at the through hole at the center of the annular cathode 910, and the annular anode bumps 93 are uniformly distributed on the outer circumference of the lower part of the discharge tube 99; the voltage difference between the annular positive electrode bump 93 and the annular negative electrode 910 causes the rare gas in the discharge tube 99 to discharge to generate vacuum ultraviolet light, and the vacuum ultraviolet photons enter the photoionization chamber 95 through the window 911; the outer circumference of the annular cathode 910 is provided with a coaxial annular upper cover plate 92, and the photoionization chamber 95 and the discharge tube 99 are hermetically connected through the fixed connection of the lower cover plate 91 and the upper cover plate 92. The discharge vessel 99 is filled with a rare gas helium.
The distance between the inner diameter of the photoionization chamber 95 and the outer diameter of the draft tube 97 is 1.2 mm; the inner diameter of the photoionization chamber 95 is 5 mm; the inner diameter of the flow guide pipe 97 is 1.6 mm, and the inner diameter of the sampling capillary 8 is 1.5 mm.
The distance between the outlet of the sampling capillary 8 and the louver 911 was 1.5 mm, and the distance between the outlet of the dopant introduction tube 94 and the louver 911 was 1 mm.
Referring to fig. 4, the gas-phase dopant introduction mechanism includes a bubbling tank 104, a first conduit 103, and a second conduit 106; a dopant 105 is provided in the bubbling tank 104.
One end of the first conduit 103 and one end of the second conduit 106 are inserted into the bubbling tank 104, a port of the first conduit 103 is inserted into the doping agent 105, and a port of the second conduit 106 is positioned in the bubbling tank 104 above the doping agent 105; the other end of the first conduit 103 is connected with an air inlet pipe 101; the first flow controller 102 is connected in series to the first conduit 103, and the second flow controller 107 is connected in series to the second conduit 106. Dopant 105 is toluene.
Referring to fig. 4, the gas introduced through the first conduit 103 is bubbled in the bubbling tank 104 to volatilize the liquid dopant toluene into a gas, which enters the second conduit 106, so that the dopant can enter the photoionization chamber 95 through the dopant introduction tube 94 to react with the analyte to promote ionization, and the dopant introduction tube 94 is located between the sampling capillary 8 and the light source, so as to ensure that the sample can be ionized with the aid of the dopant toluene. The flow rate of the second flow controller 107 is 8ml/min greater than the flow rate of the first flow controller 102.
The working principle of the invention is explained in detail as follows:
the sample 11 to be tested is analyzed from the surface of the glass slide 7 under the action of the focused laser spot, the ionization efficiency of the analyzed chemical substance is less than 0.1 percent, and the charged ions and the neutral molecules enter the photoionization chamber 95 from the sampling capillary 8 under the action of vacuum suction. Under the atmosphere of pressure lower than atmospheric pressure, unionized neutral molecules can be secondarily ionized by vacuum ultraviolet light emitted from the vacuum ultraviolet lamp window 911 with the aid of a doping agent toluene, and ions generated by secondary ionization and charged ions generated by laser resolution enter a mass spectrometer through the guide pipe 97 and the mass spectrum transmission capillary 98 to be detected.
Referring to fig. 5, a red water color pen is coated on a slide 7, and the obtained mass spectrometry results are analyzed in two modes of atmospheric pressure laser desorption ionization and atmospheric pressure laser desorption-secondary photoionization. Compared with the normal pressure laser desorption ionization mode, in the laser desorption ionization-secondary light ionization mode, 1500V fluctuation voltage is applied between the annular positive electrode bump 93 and the annular negative electrode 910 to light the vacuum ultraviolet discharge lamp, and meanwhile, the first flow controller 102 and the second flow controller 107 of the gas phase dopant introduction mechanism are opened to introduce the dopant toluene. As shown in A in FIG. 5, in the conventional atmospheric pressure laser desorption ionization mass spectrogram, rhodamine 6G ([ M-Cl ] in a red watercolor pen]+M/z 443) only 180; however, atmospheric pressure laser desorption-secondary photoionization mass spectrometry with the assistance of secondary photoionizationIn the figure (B in FIG. 5), rhodamine 6G ([ M-Cl)]+M/z 443) reaches 180000, and the signal of the sample 11 to be measured can be improved by three orders of magnitude by using the substance as an example.
Referring to fig. 6, the secondary photoionization also has a significant effect on the spatial visualization analysis of the analyte on the surface of the sample 11 to be detected, taking the imaging result of cholesterol (m/z 369) in the mouse and cerebellum tissue as an example, the size of a single pixel point of the imaging graph is 20 μm × 20 μm, and the spatial resolution is far better than the photoionization mass spectrometry imaging resolution (about 200 μm) of desorption electrospray ionization. In addition, the cholesterol ([ M + H-H ] 369 at M/z in comparison with the conventional atmospheric pressure laser desorption ionization-secondary light ionization mass spectrum imaging (y axis is 0-1.7 mm) is realized by the atmospheric pressure laser desorption ionization-secondary light ionization mass spectrum imaging (y axis is 1.7-3.5 mm)2O]+) The signal is obviously improved, and the experiment proves that after the signal of the object to be measured on the surface of the sample to be measured 11 is enhanced by the secondary photoionization, the fine structure of the object to be measured in the surface space distribution of the sample to be measured 11 is clearer, and the imaging quality is obviously improved.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (9)
1. The utility model provides a mass spectrum image device with desorption ionization of ordinary pressure laser and secondary photoionization, includes the desorption ionization mechanism of laser, the desorption ionization mechanism of laser includes mass spectrograph, laser instrument (1), beam expanding lens (3), reflector (4), focusing mirror (5), objective table (6) and sample capillary (8), its characterized in that:
the device also comprises a secondary photoionization mechanism (9) and a gas phase dopant introduction mechanism (10);
the secondary photoionization mechanism comprises a tubular photoionization chamber (95) and a vacuum ultraviolet discharge lamp;
the photoionization chamber (95) is tubular, a coaxial guide pipe (97) is arranged in the upper end of the photoionization chamber (95), the upper port of the guide pipe (97) corresponds to the outlet of a transmission capillary (98) of the mass spectrometer, and one side of the photoionization chamber (95) corresponding to the periphery of the guide pipe (97) is communicated with one end of a vacuumizing pipe (96); one side of the lower part of the photoionization chamber (95) is communicated with one end of a sampling capillary (8); the lower end of the photoionization chamber (95) is connected with a coaxial lower cover plate (91), and one side of the lower cover plate (91) is communicated with the outlet end of a dopant introducing pipe (94);
the vacuum ultraviolet discharge lamp comprises a discharge tube (99), an annular cathode (910) and a window (911); the annular cathode (910) is arranged at the upper end of the discharge tube (99), the window piece (911) is arranged at the through hole in the center of the annular cathode (910), and annular anode lugs (93) are uniformly distributed on the outer circumference of the lower part of the discharge tube (99); the voltage difference between the annular positive electrode bump (93) and the annular negative electrode (910) enables rare gas in the discharge tube (99) to discharge to generate vacuum ultraviolet light, and vacuum ultraviolet photons enter the photoionization chamber (95) through the window sheet (911); the outer circumference of the annular cathode (910) is provided with a coaxial annular upper cover plate (92), and the photoionization chamber (95) and the discharge tube (99) are hermetically connected through the fixed connection of the lower cover plate (91) and the upper cover plate (92); rare gas is filled in the discharge tube (99) to obtain vacuum ultraviolet light with different energies;
the gas-phase dopant introduction mechanism comprises a bubbling tank (104), a first conduit (103), and a second conduit (106); a dopant (105) is arranged in the bubbling tank (104); one end of the first conduit (103) and one end of the second conduit (106) are inserted into the bubbling tank (104), a port of the first conduit (103) is inserted into the doping agent (105), and a port of the second conduit (106) is positioned in the bubbling tank (104) above the doping agent (105); the other end of the first conduit (103) is connected with an air inlet pipe (101);
a first flow control meter (102) is connected in series with the first conduit (103), and a second flow control meter (107) is connected in series with the second conduit (106);
in operation, a slide (7) carrying a sample (11) to be tested is placed on a stage (2)6) The above step (1); the temperature of the photoionization chamber (95) is 250-380 ℃, and the vacuum degree is 2 multiplied by 103～5×104 Pa。
2. The mass spectrometry imaging apparatus having atmospheric pressure laser desorption ionization and secondary photoionization of claim 1, wherein: the connection part of the inner diameter of the photoionization chamber (95) and the inner diameter of the draft tube (97) is in smooth transition connection with a horn-shaped tube; the distance between the inner diameter of the photoionization chamber (95) and the outer diameter of the draft tube (97) is 1-2 mm; the inner diameter of the photoionization chamber (95) is 4-8 mm; the inner diameter of the draft tube (97) is 1.2-1.6 mm, and the inner diameter of the sampling capillary tube (8) is 0.5-1.5 mm.
3. The mass spectrometry imaging apparatus having atmospheric pressure laser desorption ionization and secondary photoionization of claim 1, wherein: the distance between the slide (7) and the outlet of the sampling capillary (8) is not more than 5 mm; the distance between the inlet of the sampling capillary tube (8) and the surface of the window sheet (911) is less than 8mm, and the distance between the outlet of the dopant introducing tube (94) and the surface of the window sheet (911) is also less than 8 mm; the laser wavelength is ultraviolet light, visible light or infrared light wave band.
4. The mass spectrometry imaging apparatus having atmospheric pressure laser desorption ionization and secondary photoionization of claim 1, wherein: the object stage (6) is a conductor, and when the surface of the glass slide (7) is sprayed with a conductive material indium tin oxide, a voltage of 0V to 10KV is selectively applied in a positive ion mode, and a voltage of-10 KV to 0V is selectively applied in a negative ion mode.
5. The mass spectrometry imaging apparatus having atmospheric pressure laser desorption ionization and secondary photoionization of claim 1, wherein: the window piece (911) material is magnesium fluoride (Mg 2F) or lithium fluoride (LiF).
6. The mass spectrometry imaging apparatus having atmospheric pressure laser desorption ionization and secondary photoionization of claim 1, wherein: during detection, a matrix is sprayed on the surface of the sample (11) to be detected to increase laser analysis ionization efficiency, and the matrix is alpha-cyano-4-hydroxycinnamic acid or 2, 5-dihydroxybenzoic acid or titanium dioxide.
7. The mass spectrometry imaging apparatus having atmospheric pressure laser desorption ionization and secondary photoionization of claim 1, wherein: the flow rate of the first flow control meter (102) is smaller than that of the second flow control meter (107), and the introduction amount of the gas-phase dopant can be adjusted by controlling the difference of the flow rates of the first flow control meter and the second flow control meter.
8. The mass spectrometry imaging apparatus having atmospheric pressure laser desorption ionization and secondary photoionization of claim 1, wherein: the dopant is one of toluene, acetone, anisole, chlorobenzene, bromobenzene and carbon disulfide.
9. The mass spectrometry imaging apparatus having atmospheric pressure laser desorption ionization and secondary photoionization of claim 1, wherein: the rare gas is one of helium, neon, krypton, xenon and nitrogen.
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