An atmospheric pressure laser desorption - secondary electrospray ion source for microplastic mass spectrometric analysis

Abstract

The application belongs to the technical field of mass spectrum analysis, and particularly relates to an atmospheric pressure laser desorption-secondary electrospray ion source for mass spectrum analysis of microplastics. The ion source comprises a laser light source, a sample stage and an electrospray ion source. The sample stage is used for placing a sample to be detected. The laser light source comprises a laser element and a laser controller. The laser element emits near-infrared laser to act on the sample. Light-absorbing substances in the sample absorb laser energy and transfer the energy to the microplastics, so that the microplastics generate gas. The electrospray ion source generates primary charged microdroplets. The primary charged microdroplets collide with the gas generated by laser desorption to be ionized, and then enter a mass spectrometer for analysis and detection. The ion source provided by the application is an atmospheric pressure ion source, and can be used for sample analysis in an open environment. Without complex pretreatment, the ion source can realize high-throughput and real-time online analysis. The application is mainly applied to analysis of microplastics in the environment or in organisms, and provides a feasible technology for the fields of environmental analysis and biological toxicology analysis.

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 ease of use. However, with the increasing use of plastics, plastic waste in the environment is also accumulating. These plastic wastes discharged into the environment are continuously broken into smaller plastic fragments after physical, chemical and biological reactions. In 2004, the concept of microplastics was first proposed and 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 the food chain. 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] Currently, there are many methods for analyzing microplastics, primarily visual inspection, microscopy, spectroscopy, and mass spectrometry. However, these methods require complex pretreatment and sample separation and transportation, which is time-consuming and labor-intensive. Therefore, there is a need to develop a real-time, online analytical method, namely, atmospheric pressure mass spectrometry, capable of accurately and rapidly detecting microplastics under atmospheric pressure. In recent years, a growing number of ambient ionization technologies have been developed. Among them, laser dissociation sampling, using methods such as near-infrared lasers, has been combined with direct mass spectrometry analysis to achieve high-efficiency ionization methods, known as laser dissociation secondary ionization. This ionization principle involves an intense laser beam directed at a solid sample. The sample absorbs the laser energy and converts it into heat, causing the solid sample to instantly dissociate into small gaseous molecules. The gas expands and diffuses outward, colliding with charged ions from the ion source at atmospheric pressure, resulting in post-ionization. However, this method presupposes that the solid sample can absorb the laser energy of the corresponding 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 with a simple structure, low production cost, easy operation, and the ability to be combined 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, the 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:

[0007] A sample stage 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;

[0008] The laser light source emits near-infrared laser light 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.

[0009] The electrospray ion source includes 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 microdroplets at the tip of the capillary. The primary charged microdroplets collide with the gaseous small molecules generated by the laser dissociation sample, causing the gaseous small molecules to be ionized and then enter the mass spectrometer inlet for analysis and detection.

[0010] 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 nanocarbon copper, graphite flakes, copper sulfide, graphene powder or Prussian blue material.

[0011] In the present invention, the sample stage is made of zirconium oxide or aluminum oxide.

[0012] In the present invention, the laser light source includes a laser element and a laser controller that are connected to each other. The wavelength of the laser element is between 780-2500nm, and the laser controller is used to focus and regulate the intensity of the laser element.

[0013] In the present invention, the laser element is arranged directly above the sample stage, the tip of the electrospray ion source capillary is located on the upper left of the sample stage, and the mass spectrometer injection port is located on the upper right of the sample stage.

[0014] 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.

[0015] The present invention addresses the complex composition and limited application of thermal desorption of plastic polymers by using laser heating. Furthermore, to address the low laser absorption efficiency of some plastics, an indirect laser pyrolysis scheme using a heat-absorbing medium is proposed to enable secondary electrospray mass spectrometry analysis. Compared with existing technologies, the present invention has the following advantages:

[0016] The present invention uses a substance that easily absorbs near-infrared laser energy to absorb laser energy and raise its own temperature. After that, the heat is transferred to the target microplastics through heat conduction to reach the pyrolysis temperature. This solves 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. Microplastics in complex solid samples and liquids are difficult to vaporize and ionize, and cannot be directly ionized.

[0017] The present invention introduces a laser dissociation method to vaporize microplastics. This method requires no or only simple pre-treatment to obtain gas molecules generated by the dissociation of microplastics. Combined with the secondary ionization technology of the electrospray ion source, it can achieve real-time and in-situ analysis and detection of complex samples.

[0018] The device of the present invention has a simple structure, is easy to implement, and can be well combined with mass spectrometry; a portable laser light source can be used to dissociate samples and instantly dissociate microplastics; the sample after laser dissociation is post-ionized under the action of charged micro-droplets sprayed by electrospray and detected by mass spectrometry. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic structural diagram of the atmospheric pressure laser dissociation-secondary electrospray ion source used for microplastic mass spectrometry analysis of the present invention.

[0020] Figure 1 The reference numerals are:

[0021] 1-Mass spectrometer inlet, 2-Laser element, 3-Laser controller, 4-Capillary, 5-High voltage power supply, 6-Sample stage. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments. Example

[0023] An atmospheric pressure laser dissociation-secondary electrospray ion source for microplastic mass spectrometry analysis is a normal pressure ion source that can perform sample analysis in an open environment without the need for complex pretreatment, achieving 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.

[0024] 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. The laser element 2 is placed directly above the sample stage 6, and emits laser light vertically to act on the sample on the sample stage 6. The wavelength range of the laser is mainly near-infrared wavelength, with a wavelength between 780-2500nm.

[0025] The electrospray ion source consists of a capillary 4 and a high-voltage power supply 5. The high-voltage power supply is connected to the capillary 4 via an electrical circuit. The tip of the capillary 4 is 5 mm horizontally above and to the left of the sample holder 6. The high-voltage power supply acts on the fluid path within the capillary, causing a Coulomb explosion at the capillary tip to form primary charged droplets. The mass spectrometer inlet 1 is 5 mm horizontally above and to the right of the sample holder 6.

[0026] 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 the laser energy to increase their own temperature and then conduct heat to the target plastic to make it reach the pyrolysis temperature. It 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 realizing laser desorption of polymers such as microplastics, and ionizing the products generated by subsequent desorption and secondary electrospray action for mass spectrometry analysis.

[0027] 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 when using microplastic samples, or a light-absorbing material such as nanocarbon copper, graphite sheets, copper sulfide, graphene powder and Prussian blue material.

[0028] When the atmospheric pressure laser dissociation-secondary electrospray ionization source for microplastic mass spectrometry analysis is used, the laser controller 3 controls the laser element 2 to emit laser light to the sample on the sample stage 6, and sets the laser intensity and focused laser beam. The laser light is emitted perpendicular to the sample on the sample stage 6. After absorbing the laser energy, the substances in the sample quickly transfer the energy to the microplastics that do not absorb the laser light, causing the microplastics to dissociate and vaporize, forming an expanding gas that diffuses outward. At the same time, the high-voltage power supply 5 turns on a high voltage of 3000-5000V to act on the liquid in the capillary 4. Under the action of the high electric field, the liquid at the tip of the capillary 4 undergoes a Coulomb explosion, forming primary charged microdroplets that diffuse to the right. These droplets collide with the gas formed by laser dissociation, causing secondary ionization. That is, the charge on the charged microdroplets is transferred to the gas molecules, which then enter the mass spectrometer inlet 1 for detection and analysis.

[0029] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

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 stage 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 light 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. An 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 microdroplets at the capillary tip. The primary charged microdroplets collide with gaseous small molecules generated by laser dissociation of the sample, causing the gaseous small molecules to ionize and then enter the mass spectrometer inlet for analysis and detection. The light-absorbing substance is the matrix material or 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 materials.

2. 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.

3. 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 that 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.

4. The atmospheric pressure laser dissociation-secondary electrospray ion source according to claim 3, characterized in that: The laser element is set directly above the sample stage, the tip of the electrospray ion source capillary is on the upper left of the sample stage, and the mass spectrometer inlet is on the upper right of the sample stage.

5. The atmospheric pressure laser dissociation-secondary electrospray ion source according to claim 4, characterized in that: The tip of the electrospray ion source capillary and the mass spectrometer inlet are respectively set at a horizontal distance of 5 mm on both sides of the sample stage where the sample is placed.

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