CN117517038A - High-sensitivity detection method and device for heavy metal elements in water - Google Patents
High-sensitivity detection method and device for heavy metal elements in water Download PDFInfo
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- 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
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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Abstract
The application discloses a high-sensitivity detection method and a device thereof for heavy metal elements in water, which combine an electrodeposition method with SD-LIBS, and comprise the preparation of a solution to be detected, the establishment, measurement and calculation of an electrodeposition device and a spark discharge auxiliary laser-induced breakdown spectroscopy device, the sensitivity analysis of the heavy metal elements is realized through the plasma spectrum intensity, and finally the accuracy of trace elements in quantitative analysis aqueous solution is evaluated, so that the detection sensitivity of the heavy metal elements in the aqueous solution can be greatly improved, the detection limit of the heavy metal elements is reduced, and the quantitative analysis of the heavy metal elements in water is realized.
Description
Technical Field
The application relates to a high-sensitivity detection method and device for heavy metal elements in water, and belongs to the field of detection of heavy metal elements in water.
Background
Water is a source of life and heavy metal contamination of water is increasingly attracting attention. When the heavy metal in water exceeds a certain level, it can create a significant health risk to the life of the earth. Therefore, it is necessary to monitor the heavy metal content in the aqueous environment. The laser-induced breakdown spectroscopy (LIBS) can provide portable equipment, and can conveniently, quickly, in-situ and fixed-point detect heavy metal elements in aqueous solution, so that the LIBS can be widely applied to analysis of trace elements in water. In addition, the work has been primarily applied in many fields such as environmental pollution detection, hazardous material detection, artware detection, universe exploration, archaeological exploration, etc. Researchers can refer to the development experience of LIBS in various fields and combine the advantages of LIBS in water detection to realize the monitoring of water environment.
However, LIBS has some technical bottlenecks when used for direct detection of liquid samples. For example, laser light acts on the surface of a liquid to cause problems such as liquid sputtering, liquid level fluctuation, etc., resulting in poor stability of spectrum and weak spectrum intensity. In order to reduce the detection limit (LoD) of elements and improve the accuracy of quantitative analysis, students at home and abroad have developed a plurality of researches, which mainly comprise three aspects: in a first aspect, converting a liquid from static to dynamic, e.g., flowing liquid, liquid jet, liquid droplet, laminar flow, and liquid aerosol; in a second aspect, additional instrumentation is added, such as, for example, double pulse LIBS, laser induced fluorescence LIBS, magnetically constrained LIBS, and microwave assisted LIBS; in a third aspect, a liquid is converted to a solid, for example: freezing, adsorption, surface enhancement, and the like.
Among them, electrodeposition is also one of the methods of converting liquid into solid. The electro-deposition method adopts a conductive electrode replacement technology to enrich cations in the aqueous solution to be detected on the surface of an electrode, so that a liquid phase sample is converted into a solid phase. The solid phase sample has a lower breakdown threshold than the liquid phase sample, and the solid phase sample has a stronger spectral intensity. However, in the actual use process, the detection sensitivity of the element is low and the detection limit is high only by adopting the method, so that the ideal measurement effect cannot be achieved.
In addition, spark Induced Breakdown Spectroscopy (SIBS) is an atomic spectroscopy technique similar to LIBS that uses high-pressure spark discharge to decompose a sample for spectroscopic analysis. SIBS systems are more economical and more adaptable than LIBS systems. However, SIBS technology also has its inherent drawbacks, such as that background radiation generated by high voltage and high current spark discharge is strong and discharge stability is greatly affected by sample surface roughness. Therefore, researchers ablate the sample to be tested using a pulse laser of a certain energy, and then further break down the laser plasma using spark discharge to achieve the purpose of improving the spectral intensity, the signal-to-back ratio and the analysis sensitivity, and this method is called spark discharge assisted LIBS (SD-LIBS for short).
In summary, the electrodeposition method and the SD-LIBS have advantages and disadvantages, and few students combine the two methods to improve the detection sensitivity of heavy metal elements in aqueous solution in practical application, so it is necessary to discuss the influence of the electrodeposition method and the SD-LIBS on the detection sensitivity of heavy metal elements in aqueous solution, and reduce the detection limit of heavy metal elements, which has important significance for further development of monitoring trace heavy metals in water environment and further guaranteeing the living environment of human beings.
Disclosure of Invention
Aiming at the defects of the prior art, the application provides the high-sensitivity detection method and the device for the heavy metal elements in water by combining electrodeposition with spark discharge auxiliary laser-induced breakdown spectroscopy, which can effectively improve the detection sensitivity of the heavy metal elements in aqueous solution, reduce the detection limit of the heavy metal elements and realize quantitative analysis of the heavy metal elements in water. The method comprises the steps of enriching heavy metal elements in water by an electrodeposition method, inducing to generate plasma by a spark discharge auxiliary laser-induced breakdown spectroscopy method, realizing sensitivity analysis of the heavy metal elements by plasma spectral intensity, and finally evaluating the accuracy of quantitatively analyzing trace elements in an aqueous solution.
Specifically, according to one aspect of the present application, there is provided a high-sensitivity detection method for heavy metal elements in water, including the steps of:
s1: determining target elements and obtaining corresponding spectral line information thereof to prepare a solution to be measured;
s2: building an electrodeposition device, and electrodepositing the target element in the solution to be detected to obtain a first metal plate formed after electrodeposition;
s3: building a spark discharge auxiliary laser-induced breakdown spectroscopy device, and fixing the first metal plate on the spark discharge auxiliary laser-induced breakdown spectroscopy device;
s4: measuring and analyzing spectral information of the target element;
s5: and calculating the concentration of the target element.
Optionally, the preparing the solution to be tested in the step S1 includes:
preparing mother liquor by using deionized water and solid powder containing target elements;
and diluting the mother solution into a plurality of parts of solutions to be tested with different concentrations.
Preferably, the method for acquiring the spectral line information in step S1 is specifically to search the NIST database for the corresponding spectral line information.
Optionally, the building an electrodeposition device in step S2 specifically includes:
s2-1: carrying out ultrasonic treatment on the metal plate to remove surface impurities and greasy dirt;
preferably, the ultrasonic treatment time is 15-30 min;
preferably, the sheet metal purity is higher than 99.99%.
S2-2: the ultrasonically treated metal plates are used as the cathode and anode for the electrodeposition process.
Optionally, the electrodepositing the target element in the step S2 specifically includes:
s2-3: and applying direct-current voltage between the cathode and the anode, and under the action of an electric field, moving cations in the solution to be detected to the surface of the cathode metal plate, obtaining electrons, reducing the electrons into atoms and depositing the atoms on the surface of the cathode metal plate to form a first metal plate.
Optionally, the step S4 specifically includes:
s4-1: ablating the first metal plate by using pulse laser so as to generate plasma, wherein electrons in the plasma generate spark discharge under the action of high voltage, and meanwhile, the plasma spectrum information is acquired;
preferably, ablation is carried out on different positions of the first metal plate, plasma spectrum information is acquired, each position is recorded as a data point, and the sampling frequency of each data point is more than or equal to 20 times;
s4-2: and comparing the spectrum information with the spectral line information, and searching the spectral line of the target element so as to determine whether the element is contained in the solution to be detected.
Optionally, the step S5 specifically includes:
according to the spectrum information, determining a scaling relation between the concentration of the target element and the spectral line intensity, and calculating to obtain the concentration of the target element;
preferably, the method for determining the scaling relationship specifically comprises:
preparing a plurality of standard solutions containing the target element at different concentrations;
measuring the spectral line intensity of the target element in each standard solution, wherein the power supply voltage used at the moment is the same as the power supply voltage used for measuring the solution to be measured;
and (5) establishing a spectral line intensity-element concentration calibration curve.
The application also provides a high-sensitivity detection device for heavy metal elements in water, which comprises an electrodeposition device for enriching the heavy metal elements and a spark discharge auxiliary laser-induced breakdown spectroscopy device.
Optionally, the electrodeposition device comprises a cathode metal plate and an anode metal plate which are respectively connected with the first power supply through wires;
the cathode metal plate and the anode metal plate are inserted into a beaker filled with a solution to be tested;
the beaker is placed on a magnetic stirrer, and a stirring rod of the magnetic stirrer is placed in the solution to be tested;
preferably, the cathode metal plate and the anode metal plate are each 50mm×50mm×1mm in size, and Al material is selected.
Optionally, the spark discharge auxiliary laser induced breakdown spectroscopy device comprises a pulse laser, a diaphragm, two reflectors, a first focusing lens and a three-dimensional translation stage which are sequentially arranged;
the position of the three-dimensional translation table is vertical to the laser direction, and a first metal plate is fixed on the three-dimensional translation table;
the three-dimensional translation stage is connected with a second power supply, wherein the anode and the cathode are respectively an Al plate and metal without the target element, and the Al plate and the metal without the target element are separately placed on the surface of the first metal plate;
the first metal plate is ablated by laser pulse to generate plasma, electrons in the plasma generate spark discharge under the action of high voltage, and light generated by the plasma is collected by the second focusing lens and led into a spectrometer through optical fibers;
the spectrometer is also connected with the photodiode and the computer respectively;
preferably, an ICCD detector is configured in the spectrometer, and the signal of the photodiode is considered as a zero point of the ICCD and is used as a time reference point;
preferably, the second power supply is a high-voltage power supply, and the ideal spectral line intensity is obtained by changing the voltage of the second power supply;
preferably, the metal not containing the target element is needle-shaped;
preferably, the metal not containing the target element is a Cu material;
preferably, the metal and Al plate without the target element are placed at 45 °.
Optionally, the peak power density of the pulsed laser reaches the threshold for plasma generation and is less than the breakdown threshold for atmospheric.
The beneficial effects that this application can produce include:
the high-sensitivity detection method and the device for the heavy metal elements in the water can greatly improve the detection sensitivity of the heavy metal elements in the water solution, reduce the detection limit of the heavy metal elements and realize quantitative analysis of the heavy metal elements in the water.
Drawings
FIG. 1 is a flow chart of a measurement process in one embodiment of the present application;
FIG. 2 is a schematic view of an electrodeposition apparatus according to an embodiment of the present application;
FIG. 3 is a schematic diagram of a spark discharge assisted laser induced breakdown spectroscopy device according to one embodiment of the present disclosure;
FIG. 4 is a graph showing the spectra of Cr (I) at 425.43, 427.48 and 428.90nm at different Cr concentrations at different discharge voltages in one embodiment of the present application;
FIG. 5 is a graph showing the spectra of Cr (I) at 425.43, 427.48 and 428.90nm at different discharge voltages for different Cr concentrations in one embodiment of the present application;
FIG. 6 is a calibration curve of Cr (I) at 425.43 and 428.90nm at different discharge voltages (0 and 2 kV) in one embodiment of the present application;
fig. 7 is a graph showing the correlation between the prepared concentration and the predicted concentration at different discharge voltages (0 and 2 kV) in one embodiment of the present application.
List of parts and reference numerals:
1. a first power supply; 2. a cathode metal plate; 3. an anode metal plate; 4. a beaker; 5. a stirring rod; 6. a magnetic stirrer; 7. a pulsed laser; 8. a diaphragm; 9. a reflecting mirror; 10. a first focusing lens; 11. a three-dimensional translation stage; 12. a first metal plate; 13. a second power supply; 14. a second focusing lens; 15. an Al plate; 16. a Cu needle; 17. a spectrometer; 18. ICCD; 19. a photodiode.
Detailed Description
The present application is described in detail below with reference to examples, but the present application is not limited to these examples.
As shown in fig. 1, according to one embodiment of the present application, the measurement flow includes the following steps:
s1: and determining target elements and acquiring corresponding spectral line information thereof to prepare a solution to be measured.
S2: an electrodeposition apparatus is built up, and the target element is electrodeposited to obtain a first metal plate 12 formed after electrodeposition.
S3: a spark discharge auxiliary laser induced breakdown spectroscopy device is built, and the first metal plate 12 is fixed on the spark discharge auxiliary laser induced breakdown spectroscopy device.
S4: and measuring and analyzing the spectrum information of the target element.
S5: and calculating the concentration of the target element.
Examples
As shown in fig. 2, in this embodiment, al metal plates are used as the cathode metal plate 2 and the anode metal plate 3, and the measurement method provided in the present application, that is, the electrodeposition combined with the spark discharge assisted laser induced breakdown spectroscopy method, is used to implement high sensitivity analysis of Cr element in water, specifically:
first, a certain amount of CrCl is weighed by using an electronic balance (weighing range of 0.01g to 100 g) 3 ·6H 2 O powder (purity greater than 99.9% by national pharmaceutical systems chemical Co., ltd.).
Then deionized water and CrCl are used 3 ·6H 2 O powder was mixed to make a 10. Mu.g/mL stock solution and diluted to several different concentrations, as shown in Table 1.
TABLE 1
| Sample numbering | 1 | 2 | 3 | 4 | 5 | 6 |
| Concentration (ng/mL) | 25 | 50 | 100 | 150 | 200 | 250 |
Then, carrying out ultrasonic treatment on an Al metal plate (with purity higher than 99.99 percent, 50mm multiplied by 1 mm) for 15 minutes to remove surface impurities and greasy dirt;
will be filled with CrCl 3 ·6H 2 The beaker 4 of O aqueous solution is placed on a magnetic stirrer 6, the magnetic stirrer 6 continuously stirring the CrCl during the electrodeposition process 3 ·6H 2 O aqueous solution to ensure CrCl 3 ·6H 2 Uniformity of Cr ion concentration in the O aqueous solution.
The Al plate treated by ultrasonic wave is adopted as a cathode metal plate 2 and an anode metal plate 3 which are electrodeposited, the two electrodes are respectively connected with the positive electrode and the negative electrode of a first power supply 1 through wires, the first power supply 1 is a direct current power supply, and a potential difference of 8V is applied between the two electrode plates; under the action of the electric field, the cations in the aqueous solution move to the cathode Al plate surface to obtain electrons, which are then reduced to atoms and deposited on the Al plate surface. After deposition for 10 minutes, the Al plate of the cathode was removed for LIBS analysis.
FIG. 3 is a schematic diagram of an SD-LIBS experimental apparatus: the pulse laser 7 used in this example is a Q-switched Nd: YAG laser, the laser pulse energy used is 10mJ, the repetition rate is 1Hz, the laser wavelength is 1064nm, and the laser pulse width is 10ns.
Firstly, fixing an electrodeposited Al plate (namely the first metal plate 12) on a three-dimensional translation table 11 perpendicular to the laser direction so as to ensure that each pulse laser irradiates a new surface;
then, the laser pulse is focused onto the surface of the first metal plate 12 through the first focusing lens 10 (focal length 25 mm);
the anode and the cathode of the second power supply 13 are respectively provided with a Cu needle 16 and an Al plate 15, wherein the Cu needle 16 and the Al plate 15 are placed on the surface of the first metal plate 12 at an angle of 45 degrees, and the distance between the Cu needle 16 and the Al plate 15 is 3mm.
Ablating the first metal plate 12 by using laser pulses to generate plasma, wherein electrons in the plasma generate spark discharge under the action of high voltage;
the light emitted by the plasma is collected by a second focusing lens 14 of 75mm focal length and 50mm diameter and directed through a quartz fiber into a spectrometer 17 (SP 500i, pi Acton, grating 1200 lines/mm) equipped with an ICCD detector 18 (PIMAX 4, princeton Instruments, resolution 1024 x 1024 pixels); in this process, the signal of the photodiode 19 is regarded as the zero point of the ICCD18 and as a time reference point, the time delay and gate width of the ICCD18 are 0.5 μs and 20 μs, respectively.
As shown in FIGS. 4 to 7, the embodiment is directed to CrCl 3 ·6H 2 And (3) measuring the O solution to obtain an experimental result.
The spectral lines of Cr (I) were found to be 425.43, 427.48 and 428.90nm, and the measured spectra of Cr (I) at 425.43, 427.48 and 428.90nm at different discharge voltages and different Cr concentrations are shown in FIG. 4, where the line intensities of Cr (I) at 425.43, 427.48 and 428.90nm increased with increasing discharge voltage.
The pulsed laser ablates Al to generate a plasma in the first metal plate 12, at this time, electrons and ions in the plasma rapidly diffuse between the Cu electrode and Al in the first metal plate 12, they are continuously accelerated by the high discharge voltage, impact ionization between particles exponentially increases, and an avalanche discharge process is formed, in which energy is rapidly transferred into the plasma, thereby reheating the plasma, so that the line strength of Cr (I) under SD-LIBS is greatly improved. In addition, as the discharge voltage increases, the energy injected into the plasma increases, and more particles are excited from a low energy level to a high energy level. Thus, the Cr (I) line at high discharge voltage is stronger than at low discharge voltage, which can be seen more clearly in fig. 5.
Further, by changing the discharge voltage, a calibration curve of Cr element concentration and spectral line intensity at 425.43 and 428.90nm of Cr (I) under different discharge voltages (0 and 2 kV) is obtained to obtain FIG. 6, and the calibration curve of the element can be obtained by the following formula
I＝S·C+b (1)
Wherein: the spectral intensity I, the element concentration C, the slope of the calibration curve S and the intercept of the calibration curve b.
In LIBS quantitative analysis, the detection limit (LoD), the Relative Standard Deviation (RSD) and the correlation coefficient (R 2 ) Is an important parameter. The calculation formula of the detection limit is as follows:
wherein σ is the standard deviation of the background.
According to experimental data, the LOD of trace heavy metal Cr is 3.86 ng/mL and 1.19ng/mL respectively under the discharge voltage of 0kV and 2kV, and the value is 1-2 orders of magnitude smaller than that of the traditional method when the LOD of 2kV is reduced to one third of that of 0 kV.
In addition, trace heavy metal Cr R 2 0.97 and 0.96, respectively, indicating a good correlation between element concentration and spectral intensity.
Finally, to evaluate the accuracy of the SD-LIBS combined with the electrodeposition method for quantitatively analyzing trace Cr elements in the aqueous solution. The prepared concentration versus predicted concentration is plotted at different discharge voltages (0 and 2 kV) as shown in fig. 7.
And calculate R 2 And cross-validated mean square error (RMSECV) values to evaluate their accuracy. R was performed at different discharge voltages (0 and 2 kV) 2 And RMSECV.
In conclusion, the high-sensitivity detection of heavy metal Cr in the aqueous solution can be better realized by combining the electrodeposition method with the SD-LIBS technology, and the accuracy of quantitative analysis of trace heavy metal Cr in the aqueous solution is improved.
The foregoing is only a few examples of the present application and is not intended to limit the present application, but the present application is disclosed in the preferred examples, and the present application is not limited to the above-described examples, and any person skilled in the art will make some changes or modifications with the technical content disclosed in the foregoing description and equivalent embodiments without departing from the scope of the technical solutions of the present application.
Claims (10)
1. The high-sensitivity detection method of the heavy metal elements in the water is characterized by comprising the following steps of:
s1: determining target elements and obtaining corresponding spectral line information thereof to prepare a solution to be measured;
s2: building an electrodeposition device, and electrodepositing the target element in the solution to be detected to obtain a first metal plate formed after electrodeposition;
s3: building a spark discharge auxiliary laser-induced breakdown spectroscopy device, and fixing the first metal plate on the spark discharge auxiliary laser-induced breakdown spectroscopy device;
s4: measuring and analyzing spectral information of the target element;
s5: and calculating the concentration of the target element.
2. The method for detecting heavy metal elements in water with high sensitivity according to claim 1, wherein the preparing the solution to be detected in the step S1 includes:
preparing mother liquor by using deionized water and solid powder containing target elements;
diluting the mother solution into a plurality of to-be-measured solutions with different concentrations;
preferably, the method for acquiring the spectral line information in step S1 is specifically to search the NIST database for the corresponding spectral line information.
3. The method for detecting heavy metal elements in water with high sensitivity according to claim 1, wherein said building an electrodeposition device in step S2 specifically comprises:
s2-1: carrying out ultrasonic treatment on the metal plate to remove surface impurities and greasy dirt;
preferably, the ultrasonic treatment time is 15-30 min;
preferably, the sheet metal purity is higher than 99.99%;
s2-2: the ultrasonically treated metal plates are used as the cathode and anode for the electrodeposition process.
4. The method for detecting heavy metal elements in water with high sensitivity according to claim 3, wherein said electrodepositing said target element in step S2 comprises:
s2-3: and applying direct-current voltage between the cathode and the anode, and under the action of an electric field, moving cations in the solution to be detected to the surface of the cathode metal plate, obtaining electrons, reducing the electrons into atoms and depositing the atoms on the surface of the cathode metal plate to form a first metal plate.
5. The method for detecting heavy metal elements in water with high sensitivity according to claim 1, wherein the step S4 specifically comprises:
s4-1: ablating the first metal plate by using pulse laser so as to generate plasma, wherein electrons in the plasma generate spark discharge under the action of high voltage, and meanwhile, the plasma spectrum information is acquired;
preferably, ablation is carried out on different positions of the first metal plate, plasma spectrum information is acquired, each position is recorded as a data point, and the sampling frequency of each data point is more than or equal to 20 times;
s4-2: and comparing the spectrum information with the spectral line information, and searching the spectral line of the target element so as to determine whether the element is contained in the solution to be detected.
6. The method for detecting heavy metal elements in water with high sensitivity according to claim 1, wherein the step S5 specifically comprises:
according to the spectrum information, determining a scaling relation between the concentration of the target element and the spectral line intensity, and calculating to obtain the concentration of the target element;
preferably, the method for determining the scaling relationship specifically comprises:
preparing a plurality of standard solutions containing the target element at different concentrations;
measuring the spectral line intensity of the target element in each standard solution, wherein the power supply voltage used at the moment is the same as the power supply voltage used for measuring the solution to be measured;
and (5) establishing a spectral line intensity-element concentration calibration curve.
7. The high-sensitivity detection device for the heavy metal elements in the water is characterized by comprising an electrodeposition device for enriching the heavy metal elements and a spark discharge auxiliary laser-induced breakdown spectroscopy device.
8. The high-sensitivity detection device for heavy metal elements in water according to claim 7, wherein the electrodeposition device comprises a cathode metal plate and an anode metal plate which are respectively connected with the first power supply through wires;
the cathode metal plate and the anode metal plate are inserted into a beaker filled with a solution to be tested;
the beaker is placed on a magnetic stirrer, and a stirring rod of the magnetic stirrer is placed in the solution to be tested;
preferably, the cathode metal plate and the anode metal plate are each 50mm×50mm×1mm in size, and Al material is selected.
9. The high-sensitivity detection device for heavy metal elements in water according to claim 7, wherein the spark discharge auxiliary laser-induced breakdown spectroscopy device comprises a pulse laser, a diaphragm, two reflectors, a first focusing lens and a three-dimensional translation stage which are sequentially arranged;
the position of the three-dimensional translation table is vertical to the laser direction, and a first metal plate is fixed on the three-dimensional translation table;
the three-dimensional translation stage is connected with a second power supply, wherein the anode and the cathode are respectively an Al plate and metal without the target element, and the Al plate and the metal without the target element are separately placed on the surface of the first metal plate;
the first metal plate is ablated by laser pulse to generate plasma, electrons in the plasma generate spark discharge under the action of high voltage, and light generated by the plasma is collected by the second focusing lens and led into a spectrometer through optical fibers;
the spectrometer is also connected with the photodiode and the computer respectively;
preferably, an ICCD detector is configured in the spectrometer, and the signal of the photodiode is considered as a zero point of the ICCD and is used as a time reference point;
preferably, the second power supply is a high-voltage power supply, and the ideal spectral line intensity is obtained by changing the voltage of the second power supply;
preferably, the metal not containing the target element is needle-shaped;
preferably, the metal not containing the target element is a Cu material;
preferably, the metal and Al plate without the target element are placed at 45 °.
10. The apparatus of claim 9, wherein the peak power density of the pulsed laser reaches the threshold for plasma generation and is less than the breakdown threshold of the atmosphere.
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