CN113758895B - Full detection method for plastic microfibers based on focal plane array infrared technology - Google Patents
Full detection method for plastic microfibers based on focal plane array infrared technology Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3563—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor
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Abstract
A full detection method for plastic microfibers based on focal plane array infrared technology relates to the detection of microplastic. Adding synthetic fibers with different diameter materials into seawater to be detected; the double-layer metal screen is combined with the vacuum filtering sand core, and the plastic fiber suspension is filtered under negative pressure; back flushing the metal mesh screen to collect eluent; vacuum filtering the eluent by a small-caliber long-neck sand core filter, and intercepting plastic fibers by a filter membrane; placing the filter membrane into a zinc selenide pressure tank, flattening the fiber by a barium fluoride window, and placing the filter membrane on an infrared microscope objective table to focus and shoot the image of the filter membrane; coaxial confocal adjustment of different backgrounds is carried out for 2 times in an infrared spectrum transmission mode, an infrared spectrum is collected, a undistorted high-precision imaging picture is obtained, and a filter membrane area is analyzed; and performing dimension reduction analysis on characteristic peaks of the plastic fibers by using OPUS processing software, marking colors after integrating peak areas, calculating RGB images on the surfaces of the filter membranes, evaluating three-dimensional spectrogram data by combining visible light in-situ pictures, and integrating fiber full-scale chemical images. Short time consumption and high accuracy.
Description
Technical Field
The invention relates to the technical field of micro-plastic detection and application, in particular to a full detection method for plastic microfibers based on focal plane array infrared technology for detecting plastic fibers with diameters smaller than 20 mu m in seawater.
Background
Plastic products that are not properly treated and discharged into the environment contaminate various areas of the marine ecosystem, while fibrous microplastic is one of the most widely distributed microplastics on coastlines. Especially, fibers in textile production and washing wastewater are difficult to control and measure, and the current sewage treatment process does not have the capability of specifically capturing and removing micro-plastic fibers, so that the micro-plastic fibers finally escape into the sea. Therefore, the detection and evaluation of the fiber-state microplastic in the seawater are of far-reaching significance.
At present, no mature detection method is available for the micro plastic fiber in the seawater. The microfiber has the characteristic of large length-width ratio, and has complex three-dimensional structures such as bending, superposition, upturned and the like, so that problems such as difficult overall recognition, low detection signals, signal interference and the like are caused, the difficulty of manual screening and identification is increased, real sample data are difficult to obtain, in addition, fibers in the environment are extremely easy to introduce into a sample, especially a fibrous filter membrane, the impurity abundance in the sample is increased, and the recognition error rate is obviously increased.
Therefore, in the pretreatment process, a combined metal screen is adopted to replace a filter membrane, so that the sample pollution risk is reduced. The zinc selenide pressure tank and the barium fluoride window sheet are used for pressing the filter membrane, so that the problems of superposition, upwarp, suspension and the like of fibers are solved, and the problem of difficulty in overall view identification is effectively solved by matching with characteristic focusing. The optimal infrared detection parameters are debugged, a large amount of spectrum data of high-intensity signals are collected in a short time, and a pseudo-color image with clear outline and simulated morphology is automatically constructed. Realizes the identification, quantification and qualitative of the microfibers with the diameter of 10-20 mu m in the filter membrane.
Disclosure of Invention
The invention aims to provide a full detection method for plastic microfibers based on a focal plane array infrared technology with high sensitivity, wherein the full detection diameter of the fibers can be reduced to 10 mu m by virtue of a focal plane array wide-area imaging and high-automation measurement system, and the secondary coaxial confocal method in a transmission mode ensures that the fibers in a seawater sample are accurately identified and imaged in a clear manner while the consumption is shortened by tens of times compared with that of conventional infrared detection by matching a zinc selenide pressure tank with a barium fluoride window.
The invention comprises the following steps:
1) Adding known quantity of synthetic fibers with different diameters and materials into the seawater in the environment to be detected to prepare a plastic fiber suspension;
2) Adopting a double-layer metal screen to be combined with a vacuum filtering sand core, and filtering the plastic fiber suspension prepared in the step 1) under negative pressure to enrich the plastic fibers;
3) Back flushing the metal mesh screen with ultrapure water and collecting the eluent;
4) Vacuum filtering the eluent obtained in the step 3) by using a small-caliber long-neck sand core filter, and intercepting plastic fibers by using a filter membrane;
5) Naturally airing the filter membrane, putting the filter membrane into a zinc selenide pressure tank, flattening and superposing or tilting fibers by a barium fluoride window sheet, directly putting the whole pressure tank on an infrared microscope objective table, and focusing to shoot an image of the whole filter membrane;
6) Coaxial confocal adjustment of different backgrounds is carried out for 2 times under an infrared spectrum transmission mode, an infrared spectrogram is rapidly and accurately stamped and collected in a large scale based on a focal plane array infrared detector, a distortion-free high-precision imaging picture is obtained, and a filter membrane area is completely analyzed;
7) And (3) performing dimension reduction analysis on characteristic peaks of the plastic fibers by utilizing OPUS processing software, marking colors after peak area integration, calculating RGB images on the surfaces of the filter membranes, evaluating three-dimensional spectrogram data by combining visible light in-situ pictures, and integrating synthetic fiber overall chemical images.
In the step 1), the synthetic fibers with different diameters and materials comprise, but are not limited to, polyamide fibers (PA), polyethylene terephthalate fibers (PET) and polyacrylonitrile fibers (PAN), wherein the diameters of the synthetic fibers can be 10 mu m, 14 mu m and 20 mu m respectively, and the lengths of the synthetic fibers can be 1-4 mm; the specific method for preparing the plastic fiber suspension liquid can be as follows: taking 1L of surface seawater, adding PA fiber with the diameter of 10 μm and the length of 4mm, PET fiber with the diameter of 14 μm and the length of 4mm, and PAN fiber with the diameter of 20 μm and the length of 3mm, and uniformly mixing.
In the step 2), the double-layer metal screen mesh is combined with the vacuum filter sand core, two metal screen meshes made of stainless steel materials can be nested with the vacuum filter sand core, the specification of the screen mesh above the vacuum filter sand core is 100 meshes, the 200-mesh screen mesh above the 100-mesh screen mesh is nested, and the diameters of the metal screen mesh and the filter sand core can be 6cm.
In step 3), the back flushing with ultrapure water may be performed at least 3 times to avoid as much as possible the loss of fibres due to sticking to the screen.
In step 4), the filter membrane may be an alumina filter membrane having a diameter of 13mm and a pore size of 0.2 μm; the diameter of the sand core part of the small-caliber long-neck sand core filter can be 8mm so as to reduce the area of a filter cake, the infrared permeability of the alumina filter membrane is good, and the time cost of manually sorting fibers is saved.
In the step 5), the gap specification of the zinc selenide pressure cell is 100 mu m, and a barium fluoride window sheet with the diameter of 13mm and the thickness of 1mm is used for integrally pressing the filter membrane and the fiber on the filter membrane; preferably, a 36X objective lens equipped with a microscope is adopted, an assembled visual overview image of the whole surface of the filter membrane is obtained after focusing clearly, and the approximate distribution of the fibers on the filter membrane is visually and preliminarily observed;
in step 6), the 2 times of coaxial confocal adjustment on different backgrounds in the infrared spectrum transmission mode is to sequentially adjust 2 times of coaxial confocal adjustment by taking air, a film and a window as backgrounds in the focal plane array transmission mode respectively so as to eliminate signal deviation caused by refraction due to different materials and thicknesses of the film and the window;
the acquisition condition for acquiring the infrared spectrogram can be that a water-cooled high-performance mid-infrared light source is adopted, the spectral information is recorded in an FPA transmission mode, and the resolution is set to be 8cm -1 The scanning times are 64 times, and the scanning wave band number is 1200-3300cm -1 The number of single FPA test spectrograms is 4096, and the time is about 60 seconds; the whole-area scanning of the filter membrane can be shortened to 48 hours.
In the step 7), the peak area integration is bottom-removing integration, namely, integration is carried out by taking the connecting lines of the wave troughs at the two sides of the characteristic peak as a base point, and the influence of the base signal intensity is removed; the integral wave band is: PA (1532-1608 cm) -1 )、PET(1409～1514cm -1 )、PAN(1709～1766cm -1 ) RGB mark colorIncluding but not limited to red, yellow and blue.
Compared with the prior art, the method has the following outstanding advantages:
(1) Because of the special physicochemical properties of the fiber, the detection difficulty is higher, and the existing detection of the microplastic in the environment mainly focuses on fragments and particle states, however, researches show that the toxicity of the plastic fiber to water fleas and part of filter feeding shellfish is stronger than that of particles and microbeads, so that the detection and monitoring of the plastic fiber in the seawater are needed to be enhanced. The PA, PAN, PET plastic fiber added in the invention is a fiber which is prepared by reprocessing the primary and secondary synthetic materials for fitting an environmental sample, and can meet the actual needs.
(2) In the enrichment and concentration process of plastic fibers in seawater, a metal screen mesh is combined with a negative pressure suction filtration method, so that fiber pollution in the treatment process is reduced, the slope length of a filter cup is increased, the slope gradient is increased, the process loss of the plastic fibers is reduced, the filtration speed is increased, and the recovery rate is ensured to be higher than 90%;
(3) In the microscope field of view, microfibers are easy to overlap, bend, upwarp and hang, the overall view cannot be focused clearly, information such as the positions, the number and the like of the fibers are difficult to distinguish in the visual overview image, and the subsequent spectrum signals are also greatly influenced. The invention creatively selects the zinc selenide pressure tank and the barium fluoride window sheet to realize the integral pressing of the filter membrane and the fiber, further focuses according to the material and thickness characteristics of the zinc selenide pressure tank, the barium fluoride window sheet and the aluminum oxide membrane, ensures that the photographed fiber is clear and real, simultaneously uses different backgrounds for secondary coaxial confocal in sequence, corrects the optical signal path and ensures the accurate collection of the infrared signal;
(4) Compared with the conventional infrared single-point detection, under the condition of acquiring the same spectrum data volume, the single FPA (coverage area is 70 mu m multiplied by 70 mu m, acquisition spectrum is 4096 pieces) detection only needs 60s, and the acquisition time of a single spectrum is only 0.01s, so that the efficiency is effectively improved. The method does not miss any region on the filter membrane, and the detection result is more complete and comprehensive.
Drawings
Fig. 1 is a schematic flow chart of an embodiment of the present invention.
Fig. 2 is a photograph of the fiber in a rolled and suspended state (photographed by an FT-IR microscope, 36 times magnification) taken without using a zinc selenide pressure cell in example 1 of the present invention.
FIG. 3 is a photograph of fibers taken in an overlapped state (FT-IR microscopy at 36 times magnification) without using a zinc selenide pressure cell in example 2 of the present invention.
Fig. 4 is a photograph of a fiber taken with a large range of shadows (FT-IR microscopy at 36 x magnification) using a zinc selenide pressure cell without feature adjustment in co-axial confocal in example 2 of the invention.
FIG. 5 is a photograph (FT-IR microscopy, 36 times magnification) of a 20 μm diameter PET fiber pressed using a 100 μm zinc selenide pressure cell and a barium fluoride window in example 2 of the present invention.
FIG. 6 is a photograph of an 8mm small bore sand core filter apparatus used in examples 1 and 2 of the present invention.
FIG. 7 is a dimensional reference of the 8mm small bore sand core filter apparatus used in examples 1 and 2 of the present invention.
FIG. 8 is a scanning electron microscope image of an alumina filter membrane having a pore size of 0.2 μm used in examples 1 and 2 of the present invention.
FIG. 9 is a photograph of an overall view of a PA fiber with a diameter of 10 μm on the surface of an alumina filter membrane and an in-situ chemical image obtained by integration (FT-IR microscopy, magnification 36 times) in example 1 of the present invention.
FIG. 10 is an in-situ chemical image (FT-IR microscopy, magnification 36) obtained by photographing original image of PET fiber with a diameter of 14 μm on the surface of an alumina filter membrane and integrating in example 2 of the present invention.
FIG. 11 is an in situ chemical image (FT-IR microscopy, magnification 36) obtained by taking an original image of a PAN fiber having a diameter of 20 μm on the surface of an alumina filter membrane and integrating it in example 2 of the present invention.
Fig. 12 is an infrared spectrum of PA, PET, PAN fibers measured in examples 1 and 2 of the present invention.
Fig. 13 is an infrared second derivative spectrum of the PA, PET, PAN fibers measured in examples 1 and 2 of the present invention.
Detailed Description
In order to more clearly illustrate the technical solution of the present invention and to embody the advantages thereof, the present invention is correspondingly depicted in the following examples, and is necessarily supplemented by the accompanying drawings, which should not be construed as limiting the invention.
The invention applies a middle infrared device with extremely high sensitivity and transverse resolution, adopts a mesh screen negative pressure rapid filtering device, combines the efficient sample preparation of a zinc selenide pressure tank and a barium fluoride window sheet, and adopts a method of secondary coaxial confocal correction in a focal plane array transmission mode. The equipment device and the sample preparation method comprise a Fourier transform infrared spectrometer, a water-cooled mercury lamp light source, a full-automatic Fourier transform infrared imaging microscope provided with a focal plane array detector, a 36X infrared objective lens, a stainless steel wire mesh screen, a zinc selenide pressure cell with a gap of 100 mu m, a 1mm thickness, a barium fluoride window with a diameter of 13mm, a data recording system and a computer. The mesh screen negative pressure rapid filtering device is formed by combining a metal mesh screen with a suction filtering device, and rapidly filtering and obtaining a mesh screen fiber sample; the zinc selenide pressure cell with the gap of 100 mu m and the barium fluoride window sheet with the thickness of 1mm can effectively flatten plastic fibers overlapped, upturned and suspended on the filter membrane, so that the accurate detection level is improved; the infrared spectrometer prepares an infrared light source in a water-cooling mercury lamp, so that the signal intensity is improved by 30% -100%, the full-automatic Fourier transform infrared imaging microscope of the prepared focal plane array detector shoots a high-definition filter film picture through a 36X infrared objective lens, a sample area with 70X 70 mu m is covered at one time, 4096 pixels with 1.1 mu m spatial resolution are measured at the same time in the sample area, and infrared images of a measured sample are further assembled automatically; the secondary coaxial confocal method effectively solves the problems of light path offset and signal loss caused by film and window thickness; the data processing system is used for collecting and combining visible sample images, and performing evaluation calculation such as integral and the like on a spectrogram of the target fiber.
Referring to fig. 1 to 13, an embodiment of the present invention includes the steps of:
(1) Sample pretreatment
a, preparing a plastic fiber suspension: taking 1L of surface seawater, quantitatively adding microfibers with different lengths and diameters, and uniformly mixing;
the invention preferably combines stainless steel metal screen mesh with the diameter of 6cm, the aperture of 100 meshes and 200 meshes up and down, and is used together with a vacuum filtering sand core (6 cm), and the prepared fiber suspension is rapidly filtered;
preferably, the front and back surfaces of the two screens are washed 3 times by ultrapure water, and the washing liquid is collected by the beaker, so that the loss of the fibers caused by adhesion of the screens is avoided as much as possible;
d, assembling the alumina filter membrane with the diameter of 0.2 mu m with a self-designed small-caliber long-neck sand core filter to filter flushing liquid again, and naturally airing the filter membrane. Preferably, the diameter of the sand core part of the filter is 8mm, the gradient and the length of the filter cup are increased correspondingly, the contact area between the fiber and the filter cup during filtration is reduced, the infrared permeability of the alumina filter membrane is good, and the time cost for manually sorting the fiber is saved;
e, after drying, preferably, the filter membrane and the fiber on the filter membrane are integrally transferred into a zinc selenide pressure tank with a gap specification of 13mm in diameter and 100 mu m in gap, and a barium fluoride window sheet of a product with a thickness of 1mm and a diameter of 13mm is flattened into irregular three-dimensional fibers, so that the fibers are ensured to be positioned on the same plane as much as possible;
(2) Obtaining fiber visual images
Preferably, a 36X objective lens equipped with a microscope is adopted, an assembled visual overview image of the whole surface of the filter membrane is obtained after focusing clearly, and the approximate distribution of the fibers on the filter membrane is visually and preliminarily observed;
(3) Spectral acquisition and evaluation
Preferably, the scanning wave band is set to 1200-3300cm during acquisition -1 Spectral resolution of 8cm -1 The air, the membrane and the window are respectively used as the background to carry out 2 times of coaxial confocal, the optical signal path is corrected, the single FPA simultaneously collects 4096 Zhang Guangpu, the superposition scanning is carried out 64 times, the image point array is 64 multiplied by 64, and the whole-domain scanning of the filter membrane can be shortened to 48 hours. After integrating the characteristic peaks of the fibers, an RGB image is calculated from the imaging information.
The main equipment involved in the example steps is referred to table 1.
TABLE 1
Specific examples are given below.
Example 1
A rapid overall inspection method of 10 mu m PA fiber based on infrared focal plane array technology comprises the following steps:
(1) Preparation and pretreatment of PET-containing fiber sample
a, preparing a plastic fiber suspension with a certain concentration: taking 1L of surface seawater, adding 30 PA fibers with the diameter of 10 mu m and the length of 4mm, and uniformly mixing;
b, vertically nesting a stainless steel metal screen with the specification of 100 meshes and 200 meshes, combining the stainless steel metal screen with a vacuum filtering sand core, filtering the prepared fiber suspension, and primarily retaining the fibers on the surface layer of the screen;
c, flushing the front and back sides of the two screens by using ultrapure water, repeating for three times until no fiber residue exists in the holes of the screens, and collecting flushing liquid by using a 1L beaker to avoid the loss of the fiber caused by adhesion to the screens as much as possible;
d, assembling the alumina filter membrane with the diameter of 0.2 mu m with a small-caliber long-neck sand core filter, fixing a bimetal clamp, filtering flushing liquid again, and naturally airing the filter membrane; as shown in fig. 6 and 7, the small-caliber long-neck glass sand core filtering device sequentially comprises a long-neck filter cup, a filter membrane, a sand core filter and a conical flask from top to bottom; the long-neck filter cup comprises a cup body and a hollow tube perpendicular to the glass; the inner diameter of the cup body can be 80mm, the height of the cup body can be 100mm, the lower part of the cup body is connected with a long-neck glass vertical hollow pipe with the length of 30mm and the aperture of 8mm by adopting a steep-slope inner wall, and the slope design can be 60 degrees, so that the water flow scouring can be accelerated, the probability of adsorbing the inner wall by micro plastic particles can be reduced, and the sample residue can be reduced; the long-neck filter cup can be tightly attached to a sand core filter with the diameter of 8mm, the filter membrane is an inorganic alumina membrane with the diameter of 13mm and the aperture of 0.2 mu m, and is overlapped on a quartz membrane with the diameter of 47mm and the aperture of 2 mu m, and when the filter membrane is assembled, the filter membrane is placed in the sand core filter and is matched with a double external metal clamp to be firmly assembled; during operation, the sand core filter is connected with the vacuum pump, and the water sample is poured from the filter bowl top, gathers the suspended solid in the water sample in 8mm diameter's circular region, high-efficient entrapment plastic granules improves the density of plastic granules on the filter membrane, reduces the screening scope when discernment. Further, the outer diameter of the long-neck glass vertical hollow tube can be 25mm, and the capacity of the conical flask can be 1.0L.
e, after the alumina filter membrane is dried, transferring the filter membrane and the fiber on the filter membrane into a zinc selenide pressure tank with a gap specification of 100 mu m, and compressing the thickness of the fiber by a barium fluoride window so as to ensure that the fiber is adhered to the surface layer of the filter membrane as tightly as possible;
(2) Obtaining fiber visual images
A 36-time objective lens equipped with a microscope is adopted, an assembled visual overview image of the whole area of the filter membrane is obtained after focusing is clear, the approximate distribution of the fibers on the filter membrane is visually and preliminarily observed, and the air, the membrane and the window are respectively used as background to coaxially confocal for 2 times in sequence, so that an optical signal path is optimized;
(3) Spectral acquisition and evaluation
Setting the scanning wave band of the collected spectrum to be 1200-3300cm on the operation interface of OPUS software -1 Resolution of 8cm -1 A single FPA collects 4096 Zhang Guangpu simultaneously, the stacked scan is performed 64 times, the image point combination is 64×64, and the time of the single FPA can be controlled within 60 s. For the characteristic wave band 1532-1608 cm of PA -1 And integrating, and automatically generating a distribution in-situ image of the PA fibers on the filter membrane according to an integral information processing system.
Example 2
A rapid overall inspection method of 10-20 mu m plastic fibers based on infrared focal plane array technology comprises the following steps:
(1) Sample preparation and pretreatment
a, preparing a plastic fiber suspension with a certain concentration: taking 1L of surface seawater, adding 30 PET fibers with the diameter of 14 mu m and the length of 4mm and PAN fibers with the length of 20 mu m and the length of 3mm respectively, and uniformly mixing;
b, vertically nesting a stainless steel metal screen with the specification of 100 meshes and 200 meshes, combining the stainless steel metal screen with a vacuum filtering sand core, filtering the prepared fiber suspension, and primarily retaining the fibers on the surface layer of the screen;
c, flushing the front and back sides of the two screens by using ultrapure water, repeating for three times until no fiber residue exists in the holes of the screens, and collecting flushing liquid by using a 1L beaker to avoid the loss of the fiber caused by adhesion to the screens as much as possible;
d, assembling the alumina filter membrane with the diameter of 0.2 mu m with a self-designed small-caliber long-neck sand core filter, fixing a bimetal clamp, filtering flushing liquid again, and naturally airing the filter membrane; an alumina filter membrane scanning electron microscope image of 0.2 μm is shown in FIG. 8.
e, after the alumina filter membrane is dried, transferring the filter membrane and the fiber on the filter membrane into a zinc selenide pressure tank with a gap specification of 100 mu m, and compressing the thickness of the fiber by a barium fluoride window so as to ensure that the fiber is adhered to the surface layer of the filter membrane as tightly as possible;
(2) Obtaining fiber visual images
A 36-time objective lens equipped with a microscope is adopted, an assembled visual overview image of the whole area of the filter membrane is obtained after focusing is clear, the approximate distribution of the fibers on the filter membrane is visually and preliminarily observed, and the air, the membrane and the window are respectively used as background to coaxially confocal for 2 times in sequence, so that an optical signal path is optimized;
(3) Spectral acquisition and evaluation
Setting the scanning wave band of the collected spectrum to be 1200-3300cm on the operation interface of OPUS software -1 Resolution of 8cm -1 A single FPA collects 4096 Zhang Guangpu simultaneously, the stacked scan is performed 64 times, the image point combination is 64×64, and the time of the single FPA can be controlled within 60 s. For the characteristic wave band 1409-1514 cm of PET -1 Characteristic wave band 1709-1766 cm of PAN -1 And integrating, and automatically generating a distribution in-situ image of the fibers on the filter membrane according to an integral information processing system.
The invention adopts a multi-stage metal mesh screen with 100 meshes and 200 meshes to be nested and rapidly filtered under negative pressure; the small-caliber sand core filtering device is concentrated in the alumina filter membrane; transferring the filter membrane into a zinc selenide pressure tank, placing a barium fluoride window sheet with the thickness of 1mm, flattening the rolled and stacked fibers, and enabling the fibers to be capable of imaging in the same focal plane (figures 1-3 and 5); for a pair ofThe coaxial confocal adjustment method of 2 different backgrounds in the infrared spectrum transmission mode uses air, a film and a window sheet as backgrounds to correct (figures 4 and 5) respectively, and eliminates light path deviation and signal loss caused by refraction of materials and thickness of the film and the window sheet. The 36X infrared objective lens obtains the full view picture of the high resolution fiber (figure 9), optimizes the detection parameters, and determines the optimal parameter combination (64 times of scanning and resolution: 8 cm) of the microfiber with the one-dimensional diameter range of 10-20 μm -1 Pixel array 64×64, detection mode: transmission, detection range: 1200-3300cm -1 ) And stamping type collecting the integral spectrum of the fiber. Integrate the synthetic fiber full-scale chemical image (fig. 9-11).
Fig. 12 shows the infrared spectra of the PA, PET, PAN three fibers measured in examples 1 and 2 of the present invention. Fig. 13 shows the infrared second derivative spectra of the PA, PET, PAN three fibers measured in examples 1 and 2 of the present invention.
The multistage mesh screen filter device improves the filtration rate, reduces the introduction of membrane fibers, realizes the fiber focusing plane by matching a zinc selenide pressure tank with a barium fluoride window sheet for pressing, can detect fibers with diameters as low as 10 mu m in a full view, effectively corrects micro-fiber infrared signals by using a coaxial confocal adjusting method with different backgrounds for 2 times, and has the advantages of simple operation of a focal plane array, high detection efficiency and extremely high reliability.
The above-described embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications within the scope of the present invention are intended to be covered by the present invention.
Claims (10)
1. A full detection method for plastic microfibers based on focal plane array infrared technology is characterized by comprising the following steps:
1) Adding known quantity of synthetic fibers with different diameters and materials into the seawater in the environment to be detected to prepare a plastic fiber suspension;
2) Adopting a double-layer metal screen to be combined with a vacuum filtering sand core, and filtering the plastic fiber suspension prepared in the step 1) under negative pressure to enrich the plastic fibers;
3) Back flushing the metal mesh screen with ultrapure water and collecting the eluent;
4) Vacuum filtering the eluent obtained in the step 3) by using a small-caliber long-neck sand core filter, and intercepting plastic fibers by using a filter membrane;
5) Naturally airing the filter membrane, putting the filter membrane into a zinc selenide pressure tank, flattening and superposing or tilting fibers by a barium fluoride window sheet, directly putting the whole pressure tank on an infrared microscope objective table, and focusing to shoot an image of the whole filter membrane;
6) Coaxial confocal adjustment of different backgrounds is carried out for 2 times under an infrared spectrum transmission mode, an infrared spectrogram is rapidly and accurately stamped and collected in a large scale based on a focal plane array infrared detector, a distortion-free high-precision imaging picture is obtained, and a filter membrane area is completely analyzed;
7) And (3) performing dimension reduction analysis on characteristic peaks of the plastic fibers by utilizing OPUS processing software, marking colors after peak area integration, calculating RGB images on the surfaces of the filter membranes, evaluating three-dimensional spectrogram data by combining visible light in-situ pictures, and integrating synthetic fiber overall chemical images.
2. The method for fully inspecting plastic microfibers based on focal plane array infrared technology according to claim 1, wherein in the step 1), the synthetic fibers with different diameters and materials comprise polyamide fibers (PA), polyethylene terephthalate fibers (PET) and polyacrylonitrile fibers (PAN), wherein the diameters can be 10 μm, 14 μm and 20 μm, respectively, and the lengths of the fibers can be 1-4 mm.
3. The method for fully inspecting plastic microfibers based on focal plane array infrared technology according to claim 1, wherein in step 1), the specific method for preparing plastic fiber suspension is as follows: taking 1L of surface seawater, adding PA fiber with the diameter of 10 μm and the length of 4mm, PET fiber with the diameter of 14 μm and the length of 4mm, and PAN fiber with the diameter of 20 μm and the length of 3mm, and uniformly mixing.
4. The method for fully inspecting plastic microfibers based on focal plane array infrared technology as claimed in claim 1, wherein in the step 2), the double-layer metal screen is combined with a vacuum filter sand core, two metal screens made of stainless steel can be nested with the vacuum filter sand core, the size of the screen above the vacuum filter sand core is 100 meshes, the 200 meshes are nested above the 100 meshes, and the diameters of the metal screen and the filter sand core can be 6cm.
5. A method of total inspection of plastic microfibers based on focal plane array infrared technology as claimed in claim 1, wherein in step 3), said back flushing with ultrapure water is performed at least 3 times.
6. The method for fully inspecting plastic microfibers based on focal plane array infrared technology as set forth in claim 1, wherein in the step 4), the filter membrane is an alumina filter membrane with a diameter of 13mm and a pore size of 0.2 μm; the diameter of the sand core part of the small-caliber long-neck sand core filter is 8mm.
7. The method for fully inspecting plastic microfibers based on focal plane array infrared technology as set forth in claim 1, wherein in the step 5), the gap specification of the zinc selenide pressure cell is 100 μm, and the filter membrane and the fiber thereon are integrally pressed by a barium fluoride window sheet with a diameter of 13mm and a thickness of 1 mm; and a 36-multiplied objective lens arranged on the microscope, and acquiring an assembled visual overview image of the whole surface of the filter membrane after focusing clearly, and visually and preliminarily observing the approximate distribution of the fibers on the filter membrane.
8. The method for fully inspecting plastic microfibers based on focal plane array infrared technology as claimed in claim 1, wherein in the step 6), the 2 times of coaxial confocal adjustment of different backgrounds in the infrared spectrum transmission mode is to sequentially adjust 2 times of coaxial confocal adjustment by taking air, a film and a window as backgrounds respectively in the focal plane array transmission mode so as to eliminate signal deviation caused by refraction due to different materials and thicknesses of the film and the window.
9. The method for fully inspecting plastic microfibers based on focal plane array infrared technology as set forth in claim 1, whereinCharacterized in that in the step 6), the acquisition condition of the acquired infrared spectrogram is that a water-cooled high-performance mid-infrared light source is adopted, the spectral information is recorded in an FPA transmission mode, and the resolution is set to be 8cm -1 The scanning times are 64 times, and the scanning wave band number is 1200-3300cm -1 The number of single FPA test spectrograms is 4096, and the time is about 60 seconds; the whole-area scanning of the filter membrane can be shortened to 48 hours.
10. The method for fully detecting plastic microfibers based on focal plane array infrared technology as claimed in claim 1, wherein in the step 7), the peak area integration is bottom-removing integration, which is to integrate by taking the connecting lines of the trough at two sides of the characteristic peak as a base point, and remove the influence of the base signal intensity; the integral wave band is: PA (1532-1608 cm) -1 )、PET(1409～1514cm -1 )、PAN(1709～1766cm -1 )。
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