CN110887710A - Sample preparation method for analyzing elements in water body based on laser-induced breakdown spectroscopy technology - Google Patents
Sample preparation method for analyzing elements in water body based on laser-induced breakdown spectroscopy technology Download PDFInfo
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- CN110887710A CN110887710A CN201911085297.5A CN201911085297A CN110887710A CN 110887710 A CN110887710 A CN 110887710A CN 201911085297 A CN201911085297 A CN 201911085297A CN 110887710 A CN110887710 A CN 110887710A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/71—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited
Abstract
The invention belongs to the field of laser material detection, and discloses a sample preparation method for analyzing elements in a water body based on a laser-induced breakdown spectroscopy technology, which comprises the following steps: (1) selecting a substrate without elements to be detected; (2) selecting an adhesive tape without elements to be detected, and punching by using a puncher; (3) the adhesive tape with the holes is adhered to the upper surface of the substrate, the adhesive tape is completely adhered to the surface of the substrate by pressing, and no gap exists between the edge area of the holes and the surface of the substrate; (4) dripping the water to be detected to the surface area exposed by the plurality of adhesive tape holes on the substrate, so that the water is limited to the surface area of the holes; and heating the substrate to evaporate water, and analyzing elements in the water body to be detected based on the laser-induced breakdown spectroscopy technology by using the obtained sample. The invention solves the problems of poor spectral stability and poor repeatability in quantitative analysis caused by nonuniform diffusion due to different liquid sample diffusion in the conventional liquid-solid displacement sample preparation method through a quick and simple sample preparation method.
Description
Technical Field
The invention belongs to the field of laser material detection, and particularly relates to a sample preparation method for analyzing elements in a water body based on a laser-induced breakdown spectroscopy technology.
Background
Water is a source of life, and the content of elements in the water body is closely related to the health of organisms. For example, the content of heavy metal elements in the water body exceeds the standard, the ecological environment balance can be directly influenced. If drinking water containing heavy metals for a long time, various diseases can be caused, and the human health is directly harmed. Therefore, the method is important for detecting the content of elements in the water body. Laser-induced breakdown spectroscopy (LIBS) is an element analysis technique, and is widely applied to element detection in water due to its advantages of rapidness, no damage, in-situ, remote, multi-element detection and the like.
However, when the LIBS technology is used to directly detect water, the spectral intensity is often weak due to the influence of liquid splashing, plasma quenching and other factors, the plasma lifetime is short, and finally, the spectral fluctuation is large, and the stability and the detection sensitivity are poor. In response to the above problems, researchers have proposed many solutions, which mainly include: (1) special liquid treatment devices such as capillary tubes, peristaltic pumps, atomizers and the like are introduced to convert static liquid into flowing or atomized liquid, so that the influence of factors such as liquid splashing is reduced, but the method not only adds extra equipment, but also has poor repeatability and is difficult to apply to actual detection due to the particularity of the devices such as fragility, precision and the like; (2) an improved laser-induced breakdown spectroscopy device is adopted, such as a double-pulse laser-induced breakdown spectroscopy device or a laser-induced fluorescence spectrum-assisted laser-induced breakdown spectroscopy device and the like, but the method not only adds extra equipment, but also does not substantially solve the problems of plasma quenching, liquid splashing and the like; (3) and (4) detecting by combining liquid-solid conversion with a laser-induced breakdown spectroscopy technology. The method has the advantages that the liquid is converted into the solid, so that the problems of liquid splashing, plasma splashing and the like are solved essentially, and meanwhile, no additional device is needed for assistance, so that the method reduces the cost and solves the key problem when the LIBS detects the liquid. For the third liquid-solid conversion method, researchers have proposed a different treatment method. Chen et al use wood chips as solid phase to achieve liquid-solid conversion, but this method requires a large amount of solution to be measured for adsorption, and the substrate cannot be reused; sobral et al use liquid nitrogen freezing to achieve liquid-solid conversion, but this method is only suitable for laboratory analysis, requires strict test environment, and is not suitable for actual field test; wang et al use a nano-graphite material as an adsorbent to achieve dispersed solid phase microextraction, which reduces the detection limit to a certain extent, but the method requires an expensive nano-graphite material, and the treatment steps of adding an adhesive to the extracted adsorbent to perform tabletting and the like, resulting in a complicated treatment process. Bae et al drop wise a drop of water onto a silicon wafer substrate etched with laser, which method reduces the liquid diffusion to some extent but does not guarantee that each drop is the same size. Cortex et al, which uses a flow injection-like system to spread liquid on filter paper to form a coffee ring to realize liquid-solid conversion, reduces detection limit and spectral volatility, but introduces additional sample preparation equipment, increases sample preparation complexity, and cannot be applied to actual sample detection. The metal ions to be detected are deposited on the anode electrode by utilizing an electrodeposition technology, and the detection limit is obviously reduced, but the method needs additional electrodeposition equipment and a large number of samples to be detected, needs strict operation and is not suitable for field actual detection. Papai et al use molten paraffin in combination with a chemical adsorbent as an extractant to achieve liquid-solid conversion of heavy metals in water, which can significantly reduce detection limit and spectral stability, but this method requires the use of chemical reagents, and the extraction process is complicated and difficult to apply in practical applications. In summary, in the process of detecting elements in a water body by combining liquid-solid conversion with LIBS technology, the following problems still exist in sample pretreatment: (1) when the liquid is dripped on the surface of the substrate, the liquid has different diffusion sizes due to the fact that the liquid has diffusion properties and the roughness difference of different substrate surfaces is large; (2) due to different diffusion sizes, the uniformity of liquid diffusion on the metal surface is poor. Finally, the spectrum stability and the repeatability are poor when the liquid-solid conversion is combined with the LIBS for detection.
Disclosure of Invention
In view of the above defects or improvement requirements of the prior art, an object of the present invention is to provide a sample preparation method for analyzing elements in a water body based on a laser-induced breakdown spectroscopy, wherein a tape constraint structure is obtained by improving the shape and structure of a substrate used in the sample preparation process, and the viscosity of the tape is used to ensure that a constraint area is formed on the substrate, and when the water body is dripped on the substrate, the water body is well constrained in the constraint area, so that the water body sample preparation is more convenient, and the repeatability and stability are better. The invention solves the problems of poor spectral stability and poor repeatability in quantitative analysis caused by nonuniform diffusion due to different liquid sample diffusion in the conventional liquid-solid displacement sample preparation method through a quick and simple sample preparation method.
In order to achieve the above object, according to the present invention, there is provided a sample preparation method for analyzing elements in a water body based on a laser-induced breakdown spectroscopy, comprising the steps of:
(1) referring to a chemical element to be detected, selecting a substrate which does not contain the element to be detected and does not absorb water; keeping the surface of the substrate clean and free of impurity residue, and keeping the upper surface of the substrate horizontal;
(2) selecting an adhesive tape which does not contain the element to be detected and does not absorb the water body by referring to the chemical element to be detected, and punching the adhesive tape by using a puncher, wherein the size of each hole is the same, so as to obtain the adhesive tape with holes; for any hole on the adhesive tape with the hole, the size of the hole is smaller than the minimum width of the adhesive tape, and meanwhile, the area of the hole is smaller than the surface area of the upper surface of the substrate;
(3) adhering the adhesive tape with holes obtained in the step (2) to the upper surface of the substrate obtained in the step (1), pressing the adhesive tape part of the adhesive tape with holes to be completely adhered to the surface of the substrate, wherein no gap exists between the edge area of the hole in the adhesive tape with holes and the surface of the substrate, so that the substrate restrained by the adhesive tape with holes is obtained;
(4) dropping the water body to be detected to the surface area exposed by the plurality of adhesive tape holes on the substrate aiming at the substrate restrained by the adhesive tape with holes obtained in the step (3), so that the water body is limited to the surface area of the substrate corresponding to the plurality of adhesive tape holes and simultaneously completely covers the whole hole; then, heating the substrate to evaporate water; after the heating treatment is finished, a dry layer sample which is uniform in size and distribution and is obtained from a water body to be detected can be formed in a plurality of hole exposed areas on the surface of the substrate, so that sample preparation is finished; the obtained sample can be used for analyzing elements in the water body to be detected based on the laser-induced breakdown spectroscopy technology.
In a further preferred aspect of the present invention, in the step (4), the heat treatment is performed at a temperature of 50 to 70 ℃.
As a further preferred aspect of the present invention, the chemical elements to be detected exclude carbon, chlorine and hydrogen, and the adhesive tape in step (2) is a PVC adhesive tape.
As a further preferable aspect of the present invention, in the step (2), the thickness of the adhesive tape is not less than 0.6 mm.
As a further preferable mode of the present invention, in the step (1), when the chemical element to be detected is chromium, cadmium or lead, the substrate is a zinc substrate;
when the chemical element to be detected is zinc or copper, the substrate is a silicon substrate.
In a further preferred embodiment of the present invention, in the step (1), the substrate surface is kept clean and free of impurities, and the substrate surface is cleaned and free of impurities by washing the substrate with industrial alcohol at least 3 times.
As a further preferred aspect of the present invention, in the step (2), the holes are circular holes.
Compared with the prior art, the technical scheme of the invention limits the irregular diffusion of the liquid by using the adhesive tape with holes as the geometric constraint area of the liquid, so that the sample preparation is more convenient to control and convenient to prepare, and the drying layer with consistent size and uniform distribution can be obtained. At the same time the tape can mark the diffusion area so that the position of the drying layer is better distinguished. The method can effectively inhibit the problems of large spectral fluctuation and poor repeatability and stability of the LIBS technology in liquid detection.
Specifically, the invention has the following technical characteristics:
(1) the adhesive tape with the holes is combined with the substrate, and liquid is dripped on the surface of the substrate restrained by the holes, so that liquid-solid conversion of liquid drops is quickly and effectively realized, and meanwhile, the sizes of all the liquid drops are ensured to be consistent and the liquid drops are uniformly distributed. The method avoids the problems that the traditional liquid-solid conversion operation is complex, additional auxiliary equipment is needed and the like, and solves the problems that liquid drops are not uniformly diffused and the diffusion size is not consistent in the traditional liquid-solid conversion method.
(2) The adhesive tape selected by the method is low in cost, free of impurity interference of chemical reagents and the like, simple and rapid in sample preparation and good in repeatability.
(3) The liquid diffusion area can be well limited and marked by the constraint of the adhesive tape with holes, so that the diffusion position can be better distinguished, and the use of chemical reagents such as color developing agents and the like is avoided.
(4) The method is not limited to the types of the substrates and the types of the elements to be detected, can be suitable for various substrates and various detection elements, can simultaneously prepare a plurality of samples, and improves the detection efficiency.
(5) In addition, the temperature of the heating treatment is preferably controlled to be 50-70 ℃ so that water in the water body is evaporated, adverse effects of liquid splashing and the like caused by too low temperature, too low drying speed and too high temperature can be avoided, and deformation of the adhesive tape caused by too high temperature is avoided.
In summary, the liquid-solid conversion sample preparation method disclosed by the invention utilizes the adhesive tape with holes to be adhered on the surface of the substrate so as to limit the liquid diffusion and ensure the uniformity of the diffusion area. The method is simple to operate, low in cost, rapid in sample preparation, good in repeatability and good in spectral stability, and can be used as a rapid and simple liquid-solid conversion method for LIBS liquid detection.
Drawings
Fig. 1 is a schematic diagram of a sample preparation method and a detection device for analyzing elements in a water body based on a laser-induced breakdown spectroscopy technology, which are provided by the invention.
Fig. 2 is a graph comparing the direct liquid-solid conversion effect and the tape-constrained liquid-solid conversion effect, wherein (a) in fig. 2 corresponds to the direct liquid-solid conversion method, and (b) in fig. 2 corresponds to the tape-constrained liquid-solid conversion method.
Figure 3 is a graph of intensity fluctuations versus single pulse acquisition.
Figure 4 is a graph of intensity fluctuations versus multi-pulse cumulative acquisition.
FIG. 5 is a comparison of LIBS detection quantification after direct liquid-solid conversion of non-metallic phosphorus and tape liquid-solid confinement in the present example, where the direct liquid-solid conversion corresponds to a fitted straight line R20.976, the adhesive tape restrains the fitting straight line R corresponding to the liquid-solid conversion2＝0.997。
FIG. 6 is a comparison of the compliance of LIBS measurements with predicted and standard levels of phosphorus in the present invention using direct liquid-solid conversion and tape-constrained liquid-solid.
The meaning of the reference symbols in fig. 1 is as follows: 1 is foraminiferous sticky tape, 2 is the base plate, 3 is the pipette, 4 is the base plate of foraminiferous sticky tape restraint, 5 is spectral signal acquisition head, 6 is optic fibre, 7 is the spectrum appearance, 8 is the chronogenesis synchronizing signal transmission line, 9 is time schedule controller (like LDG3.0), 10 is time schedule controller signal transmission line, 11 is the dichroic mirror, 12 is CMOS imaging camera, 13 is spectrum appearance spectral signal transmission line, 14 is camera signal transmission line, 15 is the chronogenesis synchronizing signal transmission line, 16 is laser instrument control signal transmission line, 17 is Nd: YAG pulse laser, 18 is a focusing mirror, 19 is a displacement platform control signal transmission line, 20 is a substrate with a sample to be measured, 21 is a displacement platform, and 22 is a computer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention utilizes the combination of the perforated adhesive tape and the substrate to realize the geometric constraint on the liquid. The sticky tape has certain thickness to when guaranteeing that liquid drips the base plate that limits to the hole on, liquid can not irregularly spread, but is retrained downtheholely, and the sticky tape has viscidity simultaneously, can paste on the base plate, guarantees that liquid can not follow the edge and oozes out. The advantages ensure the size consistency and uniformity of a drying layer formed after liquid-solid conversion, and overcome the problems of random liquid diffusion and uneven diffusion existing in the existing liquid-solid conversion technology.
Fig. 1 is a schematic diagram of a sample preparation method and a detection apparatus for analyzing elements in a water body based on a laser-induced breakdown spectroscopy technology in the present invention, which is detailed below with reference to fig. 1:
the sample preparation method mainly comprises the following steps:
(1) selecting a substrate without the element to be detected (the specific type of the element to be detected is preset), wherein the upper surface and the lower surface of the substrate should be kept parallel, and the surface of the substrate should be clean and free of impurities. The flat substrate needs not to contain elements to be detected, and the substrate should be made of a non-water-absorbing material so as to prevent water to be detected from permeating into the substrate.
(2) Selecting an adhesive tape without the element to be detected, punching the adhesive tape by using a puncher, wherein the hole size is smaller than the minimum width of the adhesive tape, the hole area is smaller than the surface area of the substrate, and the hole diameter can be selected to be different in size according to the volume of the liquid to be detected. The diameter of the hole can be selected to have different sizes according to the volume of the liquid to be measured, for example, the size of the hole can be selected according to the amount of the water to be measured, but the diameter of the hole is smaller than the minimum size of the substrate.
(3) And (3) adhering the adhesive tape with the holes on the surface of the substrate, wherein the adhesive tape is completely adhered to the surface of the substrate, and no gap is formed at the adhesion part of the edge area of the holes on the adhesive tape and the surface of the substrate. The reason is that the liquid is randomly diffused, and when the adhesive tape is completely adhered to the surface of the substrate, the liquid cannot penetrate into the lower side of the adhesive tape, so that the repeatability of sample preparation is ensured.
(4) The liquid to be measured is dripped to the surface of the substrate limited by the upper hole of the adhesive tape, the dripped liquid is ensured to completely occupy the whole hole (for example, the water to be measured is dripped to the surface of the substrate in the middle of the hole and completely fill the hole), and then the substrate is heated, wherein the temperature is generally controlled to be 50-70 ℃. When the temperature is too low, the drying speed is too slow, and when the temperature is too high, liquid can splash, and meanwhile, the adhesive tape can deform due to too high temperature, so that the temperature is preferably 50-70 ℃.
(5) After heating, a drying layer containing the substance to be detected with uniform size and uniform distribution can be formed on the exposed area of the holes on the surface of the substrate. The adhesive tape can also play a role in marking the position of the dry layer in the detection process, thereby eliminating the interference of the application of indicators such as ink or methylene blue and the like on the matrix.
(6) And finally, detecting and analyzing the drying layer by directly utilizing a laser-induced breakdown spectroscopy device, thereby obtaining the content of the sample to be detected in the water body sample.
The detection device, as shown in fig. 1, may mainly include: spectral signal acquisition head 5, optic fibre 6, spectrum appearance 7, time sequence synchronization signal transmission line 8, time schedule controller (LDG3.0) 9, time schedule controller signal transmission line 10, dichroic mirror 11, CMOS imaging camera 12, spectrum appearance spectral signal transmission line 13, camera signal transmission line 14, time sequence synchronization signal transmission line 15, laser instrument control signal transmission line 16, Nd: YAG pulse laser 17, focusing mirror 18, displacement platform control signal transmission line 19, substrate 20 with sample to be measured, displacement platform 21 and computer 22.
The light outlet of the YAG laser 17 and the dichroic mirror 11 are sequentially arranged on the same horizontal light path, the dichroic mirror 11 and the horizontal light path are arranged at an angle of 45 degrees, and the CMOS imaging camera 12, the dichroic mirror 11 and the focusing mirror 18 are sequentially arranged on the same vertical light path;
the spectrum signal acquisition head 5 is connected with a spectrometer 7 through an optical fiber 6, the spectrometer 7 is connected with a time sequence controller (LDG3.0) 9 through a time sequence synchronous signal transmission line 8, the spectrometer 7 is connected with a computer 22 through a spectrometer spectrum signal transmission line 13, the time sequence controller (LDG3.0) 9 is connected with the computer 22 through a time sequence controller signal transmission line 10, the time sequence controller (LDG3.0) is connected with a Dd, namely a YAG laser 17, through a time sequence synchronous signal transmission line 15, and the Dd, namely the YAG laser 17, is connected with the computer 22 through a laser control signal transmission line 16;
the CMOS imaging camera 12 is used primarily to image the sample surface to determine the ablation location and the relative location of the laser focal point to the sample surface. Wherein the instrument should ensure that the clearest imaging position of the CMOS imaging camera 12 is the laser focusing focal point position.
The function of the YAG laser 17 is to generate high-energy pulse laser, and the substrate 20 with the sample to be detected is ablated after being focused by the focusing mirror 18 to generate plasma.
The displacement platform 21 is used for controlling the moving speed of the substrate 20 with the sample to be measured, so that the laser is ensured to be in a new position during each ablation, and the same position is prevented from being ablated.
The dichroic mirror 11 mainly functions to reflect the pulsed laser light on one hand and to realize the imaging of the sample surface through visible light on the other hand.
The spectrum signal collecting head 5 is used for collecting the plasma emission spectrum signal.
The spectrometer 7 is used for splitting the spectrum signal transmitted by the optical fiber 6 through the grating, decomposing the spectrum signal into characteristic spectral lines with different wavelengths, amplifying the signal through a configured enhanced inductively coupled amplifier (ICCD) and realizing imaging, and meanwhile, the acquisition delay and the gate width can be adjusted.
The focusing mirror 18 functions to focus the pulsed laser light generated by the Dd YAG laser 17.
The computer 22 is used for controlling the Dd YAG laser 17, the time sequence controller (LDG3.0) 9, the spectrometer 7 and the displacement platform 21 and realizing the functions of imaging, processing, qualitative analysis, quantitative analysis and the like of the spectrum.
The apparatus of the present invention will be described in further detail with reference to specific examples.
Example 1:
taking the non-metal element phosphorus (P) as an example, the substrate 2 selected in the experiment is a pure aluminum metal substrate. The perforated adhesive tape 1 is selected to be a PVC adhesive tape with the thickness of 0.6 mm. The water solution to be detected is non-metal phosphorus solution, and is prepared by analyzing pure chemical reagent dipotassium hydrogen phosphate (K)2HPO4) 10000 mug/mL of mother liquor is prepared in advance with deionized water, and then the mother liquor is diluted into standard solutions with the concentrations of 50, 80, 100, 200, 400, 500 and 800 mug/mL respectively. Then, the standard solution was sampled according to the sampling method shown in FIG. 1. Wherein the sampling volume is 40 μ L, the heating temperature is 70 ℃, and the preparation time is about 4 minutes.
Fig. 2 (a) and (b) show the states of the direct liquid-solid conversion method and the tape-constrained liquid-solid conversion method after liquid dropping, respectively. 7 spots were prepared on each substrate. Compared with a direct liquid-solid conversion method, the adhesive tape restrains the liquid dropping of the liquid-solid conversion method to form points with consistent size, and the repeatability of sample preparation is ensured.
The substrate 20 with the sample to be measured prepared above was placed on a displacement stage 21, and then spectrum collection was performed using the LIBS apparatus shown in fig. 1, in which the laser 17 was a Brilliant B type Nd: YAG pulse laser (pulse width: 5ns, repetition frequency: 10Hz, wavelength: 1064nm) from Quantel corporation, and then reflected by a dichroic mirror 11, and focused using a focusing mirror 18 (f: 100mm), and the focal point of the laser was located on the substrate 20 with the sample to be measured. To prevent air breakdown, the surface of the substrate 20 with the sample to be measured is optionally placed 2mm above the focal point of the laser. The time sequence between the YAG laser 17 and the spectrometer 7 is controlled by a time sequence controller (LDG3.0) 9, so that the Q-Switch triggering synchronization of the spectrometer 7 and the laser 17 is ensured. Plasma radiation signals generated by laser ablation of a sample are collected by a spectral signal collecting head 5 and transmitted to a spectrometer 7(Princeton Instruments, Isoplane SCT320) through an optical fiber 6 for light splitting, signal amplification and photoelectric conversion are realized by a matched ICCD (Princeton Instruments, Max3,1024 x 256 pixels), and finally, display analysis of spectral data and the like are completed by a computer 22.
In example 1, the parameters involved in the detection device are mainly: the laser energy is 50mJ, and the acquisition delay and the gate width of the spectrometer are both 2 mus. The analytical line chosen in the experiment was the atomic line for phosphorus P I213.62 nm. In order to ensure that each laser pulse can ablate a new position, the moving speed of the displacement platform is set to be 2mm/s by computer software. Because the drying layer is circular, the displacement platform moves concentrically, the diameter of the circle gradually increases until the drying layers are ablated (the interval between the concentric circles can be 0.5mm, for example), the plasma emission spectrum signals of the whole drying layer are accumulated to be used as one spectrum, 100 pulses are accumulated at each position, and 7 spectra are repeatedly collected for each sample.
To verify the uniformity of liquid diffusion by the tape-constrained liquid-solid conversion method of the present invention, the Relative Standard Deviation (RSD) of the spectral intensity after single-pulse acquisition and multi-pulse accumulation was compared. Fig. 3 shows a graph of spectral intensity fluctuations for a single pulse acquisition of 100 pulses. As shown in the figure, RSD obtained by direct liquid-solid conversion and adhesive tape-constrained liquid-solid conversion is 20% and 12%, respectively, and the spectral intensity fluctuation is reduced after the adhesive tape is utilized for constraining. Fig. 4 is a plot of spectral intensity fluctuations versus thirty repetitions of multiple pulse accumulation (accumulation of 40 pulses). As shown in the figure, RSD obtained by direct liquid-solid conversion and adhesive tape-constrained liquid-solid conversion is 15% and 9%, respectively, and the spectral intensity fluctuation is reduced after the adhesive tape is utilized for constraining. Fig. 3 and 4 show that the adhesive tape constrained liquid-solid conversion method can reduce the spectral intensity fluctuation and effectively solve the problem of uneven liquid distribution in direct liquid-solid conversion.
In order to verify the accuracy of the sample preparation method in quantitative detection in LIBS element detection, the phosphorus element in the water body is quantitatively analyzed, and a coefficient R is determined by using quantitative linear fitting2And RSD to evaluate the quantitative effect. Simultaneously obtaining a comparison curve of the standard content and the predicted content of the phosphorus element, and using the comparison curveAverage Relative Error (ARE) and predicted value cross-validation Root Mean Square Error (RMSECV) to evaluate the prediction effect.
FIG. 5 is a graph showing the comparison of the quantitative effect of the quantification of phosphorus solutions of different concentrations. As can be seen from the graph, the linear fit of the sample concentration and the spectral intensity in the tape-constrained liquid-solid conversion method determines the coefficient R, compared to the direct liquid-solid conversion method2From 0.976 to 0.997.
FIG. 6 is a graph showing the comparison between the standard content and the predicted content of phosphorus, and it can be seen that the coefficient R is determined by linear fitting2The method is improved from 0.977 of the direct liquid-solid conversion method to 0.998 of the adhesive tape constraint liquid-solid conversion method.
Table 1 shows RSD, ARE and RMSECV obtained by the direct liquid-solid conversion method and the tape-constrained liquid-solid conversion method for phosphorus elements according to the examples of the present invention and analyzed by LIBS. Compared with the direct liquid-solid conversion method, the RSD of the phosphorus element in the tape-constrained liquid-solid conversion method is reduced from 10.2% to 7.2%, the ARE is reduced from 21.8% to 5.6%, and the RMSECV is reduced from 36.44 mu g/mL to 11.98 mu g/mL. The results of fig. 5, fig. 6 and table 1 show that the liquid-solid conversion method using tape constraint can ensure the consistency of liquid sample preparation, thereby improving the stability of the spectrum and the accuracy of quantitative analysis.
TABLE 1 detection of RSD, ARE and RMSECV of phosphorus element by tape-constrained liquid-solid conversion and direct liquid-solid conversion
| Index (I) | RSD(％) | ARE(％) | RMSECV(μg/mL) |
| Direct liquid-solid conversion | 10.2％ | 21.8％ | 36.44 |
| Adhesive tape for restraining liquid-solid conversion | 7.2％ | 5.6％ | 11.98 |
In conclusion, the adhesive tape constrained liquid-solid conversion method can ensure that the sizes of the drying layers are consistent and the drying layers are uniformly distributed, and finally, the stability of the spectrum and the accuracy of quantitative analysis are 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 that 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 (7)
1. A sample preparation method for element analysis in a water body based on a laser-induced breakdown spectroscopy technology is characterized by comprising the following steps:
(1) referring to a chemical element to be detected, selecting a substrate which does not contain the element to be detected and does not absorb water; keeping the surface of the substrate clean and free of impurity residue, and keeping the upper surface of the substrate horizontal;
(2) selecting an adhesive tape which does not contain the element to be detected and does not absorb the water body by referring to the chemical element to be detected, and punching the adhesive tape by using a puncher, wherein the size of each hole is the same, so as to obtain the adhesive tape with holes; for any hole on the adhesive tape with the hole, the size of the hole is smaller than the minimum width of the adhesive tape, and meanwhile, the area of the hole is smaller than the surface area of the upper surface of the substrate;
(3) adhering the adhesive tape with holes obtained in the step (2) to the upper surface of the substrate obtained in the step (1), pressing the adhesive tape part of the adhesive tape with holes to be completely adhered to the surface of the substrate, wherein no gap exists between the edge area of the hole in the adhesive tape with holes and the surface of the substrate, so that the substrate restrained by the adhesive tape with holes is obtained;
(4) dropping the water body to be detected to the surface area exposed by the plurality of adhesive tape holes on the substrate aiming at the substrate restrained by the adhesive tape with holes obtained in the step (3), so that the water body is limited to the surface area of the substrate corresponding to the plurality of adhesive tape holes and simultaneously completely covers the whole hole; then, heating the substrate to evaporate water; after the heating treatment is finished, a dry layer sample which is uniform in size and distribution and is obtained from a water body to be detected can be formed in a plurality of hole exposed areas on the surface of the substrate, so that sample preparation is finished; the obtained sample can be used for analyzing elements in the water body to be detected based on the laser-induced breakdown spectroscopy technology.
2. The sample preparation method for the elemental analysis in the water body based on the laser-induced breakdown spectroscopy technology as claimed in claim 1, wherein in the step (4), the heating treatment is performed at a temperature of 50-70 ℃.
3. The sample preparation method for elemental analysis in water based on the laser-induced breakdown spectroscopy of claim 1, wherein the chemical elements to be detected exclude carbon, chlorine and hydrogen, and the adhesive tape in the step (2) is a PVC adhesive tape.
4. The method for preparing the sample for the elemental analysis in the water body based on the laser-induced breakdown spectroscopy technology as claimed in claim 1, wherein in the step (2), the thickness of the adhesive tape is not less than 0.6 mm.
5. The sample preparation method for the elemental analysis in the water body based on the laser-induced breakdown spectroscopy technology as claimed in claim 1, wherein in the step (1), when the chemical element to be detected is chromium, cadmium or lead, the substrate is a zinc substrate;
when the chemical element to be detected is zinc or copper, the substrate is a silicon substrate.
6. The method for preparing a sample for elemental analysis in water based on laser-induced breakdown spectroscopy according to any one of claims 1 to 5, wherein in the step (1), the substrate surface is kept clean and free of impurity residues, and the substrate is cleaned with industrial alcohol at least 3 times, so that the substrate surface is clean and free of impurity residues.
7. The method for preparing the sample for the elemental analysis in the water body based on the laser-induced breakdown spectroscopy technology as claimed in any one of claims 1 to 6, wherein in the step (2), the holes are circular holes.
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Inventor after: Guo Lianbo Inventor after: Ma Shixiang Inventor after: Ma Yuyang Inventor after: Zhang Siyu Inventor after: Hu Zhenlin Inventor after: Chen Feng Inventor after: Zhang Deng Inventor after: Zeng Xiaoyan Inventor before: Guo Lianbo Inventor before: Ma Shixiang Inventor before: Ma Yuyang Inventor before: Zhang Siyu Inventor before: Hu Zhenlin Inventor before: Chen Feng Inventor before: Zhang Deng Inventor before: Lu Yongfeng Inventor before: Zeng Xiaoyan |
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