Atmospheric pressure laser dissociation-secondary electrospray ion source for micro-plastic mass spectrometry

Abstract

The invention belongs to the technical field of mass spectrometry, and particularly relates to an atmospheric pressure laser dissociation-secondary electrospray ion source for micro-plastic mass spectrometry. The device comprises a laser light source, a sample table and an electrospray ion source, the sample table is used for placing a detection sample; the laser light source comprises a laser element and a laser controller, the laser element emits near-infrared laser to act on a sample, and a light absorption substance in the sample absorbs laser energy and transmits the laser energy to the micro-plastic, so that the micro-plastic generates gas; the electrospray ion source generates primary charged micro-droplets, the micro-droplets collide with gas generated by laser dissociation to generate ionization, and the micro-droplets enter the mass spectrometer to be analyzed and detected. The ion source provided by the invention is a normal-pressure ion source, sample analysis can be carried out in an open environment, and high-flux and real-time online analysis can be realized without complicated pretreatment. The method is mainly applied to analysis of micro-plastics in an environment or a living body, and a feasible technology is provided for the fields of environment analysis, biological toxicology analysis and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of mass spectrometry analysis, and in particular to an atmospheric pressure laser dissociation-secondary electrospray ion source for microplastic mass spectrometry analysis. Background Art

[0002] Plastic products are widely used in daily life due to their low price and light weight. However, with the increase in the use of plastics, plastic waste in the environment is also accumulating. These plastic wastes discharged into the environment are constantly broken into smaller plastic fragments after physical, chemical and biological effects. In 2004, the concept of microplastics was first proposed and was later defined as plastic particles with a particle size of less than 5mm. As an emerging persistent organic pollutant, microplastics are widely present in water, atmosphere and soil, and can enter organisms through breathing, drinking water and food chains. However, the research on microplastics and their toxicology in the environment and organisms is still immature, and there is a lack of rapid qualitative and quantitative methods.

[0003] There are many methods for analyzing microplastics, mainly visual method, microscopy, spectroscopy and mass spectrometry, but these methods require complex pre-treatment and separation and transportation of samples, which is time-consuming and labor-intensive. Therefore, it is necessary to develop a real-time online analysis method, namely atmospheric pressure mass spectrometry, which can accurately and quickly detect microplastics under atmospheric pressure. In recent years, more and more environmental ionization technologies have been continuously developed. Among them, the combination of efficient ionization methods based on laser dissociation sampling such as near-infrared laser and direct mass spectrometry analysis has been realized, namely the secondary ionization technology of laser dissociation. The ionization principle is: the laser emits a strong laser beam, which acts on the solid sample. The solid sample absorbs the energy of the laser and converts it into heat energy, so that the solid sample instantly dissociates into gaseous small molecules, and the gas expands and diffuses outward. Under atmospheric pressure, it collides with the charged ions of the ion source to achieve the purpose of post-ionization. However, the premise of this method is that the solid sample can absorb the laser energy of the corresponding laser wavelength. Summary of the invention

[0004] In response to the problems existing in the above-mentioned prior art, the present invention proposes an atmospheric pressure laser dissociation-secondary spray ion source for microplastic mass spectrometry analysis which has a simple structure, low production cost, easy operation, and can be used in conjunction with mass spectrometry technology. The present invention performs laser dissociation on the sample to be tested in an open environment (solid samples are dissociated to generate gas phase molecules with smaller molecular weight) and combines charged microdroplets to achieve ionization of microplastic samples that are difficult to ionize and difficult to vaporize to achieve subsequent mass spectrometry analysis; its pre-treatment is simple, environmental interference is small, and it can achieve rapid and accurate qualitative and quantitative analysis of polymers such as microplastics that are difficult to ionize and difficult to vaporize.

[0005] The technical solution of the present invention is specifically described as follows.

[0006] An atmospheric pressure laser dissociation-secondary electrospray ion source for microplastic mass spectrometry analysis, comprising a laser light source, a sample stage and an electrospray ion source; wherein: A sample table is used to hold samples, wherein the samples include microplastic samples to be tested and light-absorbing substances, wherein the light-absorbing substances are substances that easily absorb near-infrared laser energy; The laser light source emits near-infrared laser to act on the sample on the sample stage. The light-absorbing substances in the sample absorb the laser energy and transfer the energy to the microplastic sample to be tested, and the microplastic is dissociated into gaseous small molecules; The electrospray ion source comprises an electrospray ion source capillary and a high voltage power supply. High voltage is applied to the liquid in the electrospray ion source capillary to generate primary charged micro-droplets at the tip of the capillary. The primary charged micro-droplets collide with gaseous small molecules generated by laser dissociation samples to ionize the gaseous small molecules, which then enter the mass spectrometer injection port of the mass spectrometer for analysis and detection.

[0007] In the present invention, the light-absorbing substance is a matrix material or a light-absorbing material carried by the microplastic sample to be tested when it is sampled; the matrix material is selected from any one or both of soil or sand, and the light-absorbing material is selected from any one or more of nano-carbon copper, graphite flakes, copper sulfide, graphene powder or Prussian blue material.

[0008] In the present invention, the sample stage is made of zirconium oxide or aluminum oxide.

[0009] In the present invention, the laser light source includes a laser element and a laser controller which are connected to each other. The wavelength of the laser element is between 780-2500nm. The laser controller is used to focus and regulate the intensity of the laser element.

[0010] In the present invention, the laser element is arranged directly above the sample stage, the tip of the electrospray ion source capillary is located at the upper left of the sample stage, and the mass spectrometer injection port is located at the upper right of the sample stage.

[0011] In the present invention, the tip of the electrospray ion source capillary and the mass spectrometer injection port are respectively arranged at a horizontal distance of 5 mm on both sides of the sample stage where the sample is placed.

[0012] As described above, the present invention aims to solve the problems of complex thermal desorption components and narrow application range of plastic polymers, and selects to use laser to heat plastics; at the same time, in order to solve the problem of low laser absorption efficiency of some plastics, an indirect laser pyrolysis scheme of heat absorption medium is proposed to realize secondary electrospray mass spectrometry analysis; compared with the prior art, the beneficial effects of the present invention are: The present invention uses a substance that easily absorbs near-infrared laser energy to absorb laser energy and raise its own temperature, and then transmits it to the target microplastics by heat conduction to make them reach the pyrolysis temperature, thereby solving the problem that some microplastics are difficult to absorb laser energy when directly irradiated by laser due to their own physical properties, such as light transmittance, and microplastics in complex solid samples and liquids are difficult to vaporize and ionize, and cannot be directly ionized; The present invention introduces a laser dissociation method to gasify microplastics. This method does not require or only requires simple pre-treatment to obtain gas molecules generated by the dissociation of microplastics. Combined with the electrospray ion source secondary ionization technology, real-time and in-situ analysis and detection of complex samples can be achieved. The device of the present invention has a simple structure, is easy to implement, and can be well combined with a mass spectrometer; a portable laser light source can be used to dissociate samples and instantly dissociate microplastics; the samples after laser dissociation are post-ionized under the action of charged micro droplets sprayed by electrospray and detected by mass spectrometry. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the structure of the atmospheric pressure laser dissociation-secondary electrospray ion source used for microplastic mass spectrometry analysis of the present invention.

[0014] Figure 1 The reference numerals are: 1-mass spectrometer inlet, 2-laser element, 3-laser controller, 4-capillary, 5-high voltage power supply, 6-sample stage. DETAILED DESCRIPTION

[0015] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. Example

[0016] An atmospheric pressure laser dissociation-secondary electrospray ion source for microplastic mass spectrometry analysis, which is a normal pressure ion source, can perform sample analysis in an open environment, does not require complex pretreatment, and achieves high throughput and real-time online analysis; Figure 1 As shown, it includes a laser light source, a sample stage 6 and an electrospray ion source.

[0017] The laser light source includes a laser element 2 and a laser controller 3; the laser controller 3 is connected to the laser element 2 through a circuit, and the laser element 2 is placed directly above the sample stage 6. It emits laser light vertically to act on the sample on the sample stage 6. The wavelength range of the laser light is mainly near-infrared wavelength, and the wavelength is between 780-2500nm.

[0018] The electrospray ion source includes a capillary 4 and a high-voltage power supply 5. The high-voltage power supply is connected to the capillary 4 through a circuit. The tip of the capillary 4 is 5 mm above and to the left of the sample stage 6 where the sample is placed. The high-voltage power supply acts on the liquid path in the capillary, causing a Coulomb explosion at the tip of the capillary to form primary charged micro-droplets. The mass spectrometer inlet 1 is 5 mm above and to the right of the sample stage 6 where the sample is placed.

[0019] The sample stage 6 is made of materials that do not change significantly when irradiated with laser, such as zirconium oxide or aluminum oxide. The samples placed on the sample stage 6 include microplastic samples to be tested and substances that easily absorb near-infrared laser energy. The substances that easily absorb near-infrared laser energy absorb laser energy to increase their own temperature and then conduct heat to the target plastic to make it reach the pyrolysis temperature. This can assist the microplastic particles in the sample that are not easy to directly absorb laser energy to reach the pyrolysis temperature for pyrolysis, thereby achieving laser desorption of polymers such as microplastics, and ionizing the products generated by subsequent desorption and secondary electrospray action for mass spectrometry analysis.

[0020] The substance that absorbs laser energy can be a matrix such as soil, sand, etc. that is easy to absorb near-infrared laser energy and has a certain thermal stability, which is often carried by microplastic samples, or light-absorbing materials such as nano-carbon copper, graphite sheets, copper sulfide, graphene powder and Prussian blue materials.

[0021] When the above-mentioned atmospheric pressure laser dissociation-secondary electrospray ion source for microplastic mass spectrometry analysis is used, the laser controller 3 adjusts the laser element 2 to emit laser light to act on the sample on the sample stage 6, and sets the laser intensity and focused laser beam, and emits laser light to act vertically on the sample on the sample stage 6. After the substance in the sample that absorbs laser energy absorbs the laser energy, it quickly transfers the energy to the microplastic that does not absorb the laser, so that the microplastic is dissociated and gasified, forming an expanded gas that diffuses outward. At the same time, the high-voltage power supply 5 turns on the 3000-5000V high voltage to act on the liquid in the capillary 4. The liquid in the tip of the capillary 4 undergoes a Coulomb explosion under the action of a high electric field, forming primary charged microdroplets and diffusing to the right, colliding with the gas formed by laser dissociation, and secondary ionization occurs, that is, the charge on the charged microdroplets is transferred to the gas molecules and then enters the mass spectrometer injection port 1 for detection and analysis.

[0022] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. An atmospheric pressure laser dissociation-secondary electrospray ion source for microplastic mass spectrometry analysis, characterized in that: It includes a laser light source, a sample stage and an electrospray ion source; wherein: A sample table is used to hold samples, wherein the samples include microplastic samples to be tested and light-absorbing substances, wherein the light-absorbing substances are substances that easily absorb near-infrared laser energy; The laser light source emits near-infrared laser to act on the sample on the sample stage. The light-absorbing substances in the sample absorb the laser energy and transfer the energy to the microplastic sample to be tested, and the microplastic is dissociated into gaseous small molecules; The electrospray ion source comprises an electrospray ion source capillary and a high voltage power supply. High voltage is applied to the liquid in the electrospray ion source capillary to generate primary charged micro-droplets at the tip of the capillary. The primary charged micro-droplets collide with gaseous small molecules generated by laser dissociation samples to ionize the gaseous small molecules, which then enter the mass spectrometer injection port of the mass spectrometer for analysis and detection.

2. The atmospheric pressure laser dissociation-secondary electrospray ion source according to claim 1, characterized in that: The absorbing substance is the matrix material or absorbing material carried by the microplastic sample to be tested when it is sampled; the matrix material is selected from any one or both of soil or sand, and the absorbing material is selected from any one or more of nano-carbon copper, graphite flakes, copper sulfide, graphene powder or Prussian blue material.

3. The atmospheric pressure laser dissociation-secondary electrospray ion source according to claim 1, characterized in that: The sample stage is made of zirconium oxide or aluminum oxide.

4. The atmospheric pressure laser dissociation-secondary electrospray ion source according to claim 1, characterized in that: The laser light source includes a laser element and a laser controller which are connected to each other. The wavelength of the laser element is between 780-2500nm. The laser controller is used to focus and regulate the intensity of the laser element.

5. The atmospheric pressure laser dissociation-secondary electrospray ion source according to claim 4, characterized in that: The laser element is arranged directly above the sample stage, the tip of the electrospray ion source capillary is located at the upper left of the sample stage, and the mass spectrometer inlet is located at the upper right of the sample stage.

6. The atmospheric pressure laser dissociation-secondary electrospray ion source according to claim 5, characterized in that: The tip of the electrospray ion source capillary and the mass spectrometer injection port are respectively arranged at a horizontal distance of 5 mm on both sides of the sample stage where the sample is placed.

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