CN110132943B - Method for improving laser-induced breakdown spectroscopy repeatability based on mixed gas environment - Google Patents
Method for improving laser-induced breakdown spectroscopy repeatability based on mixed gas environment Download PDFInfo
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- CN110132943B CN110132943B CN201910467429.4A CN201910467429A CN110132943B CN 110132943 B CN110132943 B CN 110132943B CN 201910467429 A CN201910467429 A CN 201910467429A CN 110132943 B CN110132943 B CN 110132943B
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- G—PHYSICS
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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
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
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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
- G01N21/718—Laser microanalysis, i.e. with formation of sample plasma
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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
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
- G01N2021/0106—General arrangement of respective parts
- G01N2021/0112—Apparatus in one mechanical, optical or electronic block
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2201/00—Features of devices classified in G01N21/00
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Abstract
The method for improving the repeatability of laser-induced breakdown spectroscopy based on a mixed gas environment comprises the steps of firstly placing a sample to be tested in a cavity, and vacuumizing the gas in the cavity by using a suction pump; then introducing mixed gas into the vacuum cavity, and recording the composition proportion of the mixed gas when the pressure in the cavity reaches one atmosphere; detecting a laser-induced breakdown spectrum signal of a sample to be detected in the gas environment, and calculating the relative standard deviation of the signal as an index of repeatability; then, continuously changing the proportion of the mixed gas for detection, and calculating the corresponding relative standard deviation; and comparing the relative standard deviations of the spectrum signals in various mixed gas environments to obtain the optimal mixed gas composition proportion, wherein the optimal mixed gas composition proportion is used as the gas environment of the sample to be detected. The invention can obviously reduce the relative standard deviation of the spectrum signal, improve the repeatability of laser-induced breakdown spectroscopy and further improve the measurement precision of the LIBS. Has the characteristics of simplicity, practicability, economy, practicability and the like.
Description
Technical Field
The invention relates to a method for improving laser-induced breakdown spectroscopy repeatability based on a mixed gas environment, and belongs to the technical field of atomic emission spectroscopy measurement.
Background
The Laser Induced Breakdown Spectroscopy (LIBS) technology is a new element analysis technology. The working principle of the technology is as follows: adopting pulse laser to ablate the sample to be measured to form laser induced plasma; the plasma radiates photons with specific frequency to generate a characteristic spectrum; and qualitatively and quantitatively analyzing the element composition of the sample to be detected by analyzing the characteristic spectrum. The LIBS technology has the advantages of no need of sample pretreatment, small damage to samples, high analysis speed, capability of realizing multi-element measurement and the like, and has great development potential.
However, the amount of ablated substances in the detection process of the LIBS technology is small, formed plasma is rapidly degraded, a series of fluctuations and interferences occur to experimental conditions, a series of fluctuations occur to parameters such as total ion number density, temperature, electron density and the like of the plasma, so that the repeatability of the spectrum is low, and the Relative Standard Deviation (RSD) value of the signal is high and usually exceeds 10%. This affects the detection accuracy of LIBS to some extent, making it inferior when competing with the similar techniques, limiting the further development of the techniques.
In the process from generation, expansion to attenuation and disappearance of the laser-induced plasma, a series of complex interactions can be generated with surrounding environment gas, so the environment gas can generate important influence on the signal of the plasma. Different gas environments have different properties such as molecular weight, thermal conductivity, ionization energy and the like, and the characteristics of interaction are changed accordingly. At present, an LIBS system usually detects a sample to be detected in an atmospheric environment or a pure inert gas environment (such as helium, neon and argon), and the obtained spectrum signal has high relative standard deviation and poor repeatability.
Disclosure of Invention
The invention aims to provide a method for improving the repeatability of laser-induced breakdown spectroscopy based on a mixed gas environment, which is used for solving the problems of higher relative standard deviation and poorer repeatability of a spectral signal obtained in an atmospheric environment or a pure inert gas environment, so that the repeatability of the laser-induced breakdown spectroscopy is improved, and the measurement precision of an LIBS is improved.
The technical scheme of the invention is as follows:
1. a method for improving laser-induced breakdown spectroscopy repeatability based on a mixed gas environment is characterized by comprising the following steps:
1) placing a sample to be tested in a cavity, and sealing the cavity;
2) pumping the gas in the cavity by using a suction pump; when the pressure in the cavity reaches a vacuum state, stopping pumping;
3) introducing mixed gas into the vacuum cavity after gas extraction; the mixed gas is composed of at least two of inert gas, air, nitrogen and carbon dioxide; recording the composition ratio of the several gases; in the process of introducing the mixed gas, stopping introducing the gas when the pressure in the cavity reaches an atmospheric pressure, and enabling the sample to be detected to be in the mixed gas environment;
4) under the mixed gas environment, detecting a sample to be detected by using a laser-induced plasma spectroscopy system to obtain a laser-induced breakdown spectroscopy signal of the sample to be detected, and calculating the relative standard deviation RSD of the signal1As an index of reproducibility:
wherein, the sigma I represents the standard deviation of the spectrum signal under the mixed gas environment,
the average value of the spectrum signals under the mixed gas environment is represented;
5) continuously changing the composition proportion of several gases in the mixed gas, repeating the steps 2) -4), detecting the sample to be detected in a new mixed gas environment to obtain a corresponding spectrum signal, and calculating a corresponding Relative Standard Deviation (RSD)i；
6) Comparing the relative standard deviation of the sample spectrum signals in various mixed gas environments to find out the minimum value; and taking the composition proportion corresponding to the minimum value as an optimal proportion, and detecting the sample by adopting the gas environment, thereby improving the repeatability of the laser-induced breakdown spectroscopy.
In the above technical scheme, the method for continuously changing the composition ratio of several gases in the mixed gas in the step 5)Comprises the following steps: changing according to gradient, i.e. selecting a positive integer n greater than or equal to 5, to obtain
In order to change the gradient, the composition ratio of the mixed gas is gradually changed.
The invention has the following advantages and prominent technical effects: in an atmospheric environment or a pure inert gas environment (such as helium, neon and argon), the repeatability of a laser-induced breakdown spectroscopy signal is poor, and the relative standard deviation value is usually over 10 percent; moreover, when the spectrum signal is weak and the experimental condition fluctuation is large, the relative standard deviation even exceeds 20%; under the optimal mixed gas environment of the method, the relative standard deviation of spectral line signals can be effectively reduced to be below 10 percent, and the repeatability of the spectrum is obviously improved; moreover, the improvement effect of the method is not only effective on one or more spectral lines in the spectrum, but also universally effective on most spectral lines, namely the method has universality; the process of determining the optimal proportion basically does not involve complicated experimental operation and mathematical operation, is simple and practical and is convenient to master; after the optimal proportion is determined, the method basically only needs to add an air blowing nozzle on the original LIBS system, the required instruments and devices are very simple, and the whole system is compact in structure and economical and practical.
Drawings
FIG. 1 is a block flow diagram of the method of the present invention.
FIG. 2 shows the Relative Standard Deviation (RSD) of the Ti 498.2nm line in 22 gas environments.
Detailed Description
The invention is further described below with reference to the figures and examples.
The invention provides a method for improving laser-induced breakdown spectroscopy repeatability based on a mixed gas environment, which specifically comprises the following steps:
1) placing a sample to be tested in a cavity, and sealing the cavity;
2) pumping the gas in the cavity by using a suction pump; when the pressure in the cavity reaches a vacuum state, stopping pumping;
3) introducing mixed gas into the vacuum cavity after gas extraction; the mixed gas is composed of at least two of inert gas, air, nitrogen and carbon dioxide; recording the composition ratio of the several gases; in the process of introducing the mixed gas, stopping introducing the gas when the pressure in the cavity reaches an atmospheric pressure, and enabling the sample to be detected to be in the mixed gas environment;
4) under the mixed gas environment, detecting a sample to be detected by using a laser-induced plasma spectroscopy system to obtain a laser-induced breakdown spectroscopy signal of the sample to be detected, and calculating the relative standard deviation RSD of the signal1As an index of reproducibility:
wherein, the sigma I represents the standard deviation of the spectrum signal under the mixed gas environment,
the average value of the spectrum signals under the mixed gas environment is represented;
5) continuously changing the composition proportion of several gases in the mixed gas, repeating the steps 2) -4), detecting the sample to be detected in a new mixed gas environment to obtain a corresponding spectrum signal, and calculating a corresponding Relative Standard Deviation (RSD)i(ii) a The method for continuously changing the composition ratio of the gases in the mixed gas is preferably as follows: changing according to gradient, i.e. selecting a positive integer n greater than or equal to 5, to obtain
In order to change the gradient, the composition ratio of the mixed gas is gradually changed.
6) Comparing the relative standard deviation of the sample spectrum signals in various mixed gas environments to find out the minimum value; and taking the composition proportion corresponding to the minimum value as an optimal proportion, and detecting the sample by adopting the gas environment, thereby improving the repeatability of the laser-induced breakdown spectroscopy.
Example (b):
a method for improving the repeatability of laser-induced breakdown spectroscopy based on a mixed gas environment is explained by taking LIBS detection for measuring a titanium alloy sample TC4-2 as an example.
1) Placing a titanium alloy sample in a cavity, and sealing the cavity; the titanium alloy sample takes titanium as a matrix, and the concentrations of other elements are shown in table 1;
TABLE 1 TC4-2 titanium alloy sample compositions
2) Pumping the gas in the cavity by using a suction pump; when the pressure in the cavity reaches a vacuum state, stopping pumping;
3) introducing a gas with the number 1 in the table 2 into the vacuum cavity after gas pumping, and recording the composition proportion of helium, neon and argon in the gas; in the process of introducing the gas, when the pressure in the cavity reaches 101.3KPa (namely one atmosphere), stopping introducing the gas; the sample to be detected is in the environment of the 1 st mixed gas;
4) under the environment of the 1 st mixed gas, detecting the titanium alloy sample by using a laser-induced plasma spectroscopy system to obtain a laser-induced breakdown spectroscopy signal of the sample to be detected, and calculating the relative standard deviation RSD of the signal1As an indicator of repeatability;
5) as shown in table 2, take n equal to 5 to
Namely 20 percent is a change gradient, the proportion of helium, argon and neon in the mixed gas is systematically changed, the steps 2) -4) are repeated, the 2 nd to 22 th mixed gas in the table 2 is respectively introduced, the titanium alloy sample is detected under each new mixed gas environment, the corresponding spectrum signal is obtained, and the corresponding relative standard deviation RSD is calculatedi(Note that the 1 st, 6 th, 21 st and 22 nd gas environments are pure argon, pure neon, pure helium and air, respectively, and are not mixed gases of helium, neon and argon, which is for relative indication with other mixed gas environmentsComparing the quasi-deviation results);
TABLE 2.22 Mixed gas Environment for different compositions
(Note: 1, 6, 21, 22 are respectively pure argon, neon, helium and air)
6) Comparing the relative standard deviation of the spectrum signals of the titanium alloy samples under the 22 mixed gas environments, and finding out the minimum value; here we take the atomic line of Ti 498.2nm as an example, and FIG. 2 shows the relative standard deviation values of the line under 22 gas environments; it can be found that the relative standard deviation value of the 14 th mixed gas environment is the lowest, and is only 7.7 percent and is obviously lower than 10 percent; the relative standard deviation under the environment of air, pure argon, pure neon and pure helium is respectively 14.3%, 11.9%, 16.9% and 11.7%, which are all higher than 10%; that is, in the 14 th mixed gas environment, the repeatability of the laser-induced breakdown spectroscopy is remarkably improved; then, for the titanium alloy sample, the proportion of helium, neon and argon in the 14 th mixed gas environment (40% of helium, 40% of neon and 20% of argon) is the optimal composition proportion; by using the mixed gas environment with the proportion, the relative standard deviation of the laser-induced breakdown spectrum signals of the titanium alloy sample can be effectively reduced, the repeatability of the laser-induced breakdown spectrum of the titanium alloy sample is improved, and the measurement precision of the LIBS is further improved.
Claims (2)
1. A method for improving laser-induced breakdown spectroscopy repeatability based on a mixed gas environment is characterized by comprising the following steps:
1) placing a sample to be tested in a cavity, and sealing the cavity;
2) pumping the gas in the cavity by using a suction pump; when the pressure in the cavity reaches a vacuum state, stopping pumping;
3) introducing mixed gas into the vacuum cavity after gas extraction; the mixed gas consists of at least two of helium, neon, argon and air; recording the composition proportion of several mixed gases; in the process of introducing the mixed gas, stopping introducing the gas when the pressure in the cavity reaches an atmospheric pressure, and enabling the sample to be detected to be in the mixed gas environment;
4) under the mixed gas environment, detecting a sample to be detected by using a laser-induced plasma spectroscopy system to obtain a laser-induced breakdown spectroscopy signal of the sample to be detected, and calculating the relative standard deviation RSD of the signaliAs an index of reproducibility:
wherein, the sigma I represents the standard deviation of the spectrum signal under the mixed gas environment,
the average value of the spectrum signals under the mixed gas environment is represented;
5) continuously changing the composition proportion of several gases in the mixed gas, repeating the steps 2) -4), detecting the sample to be detected in a new mixed gas environment to obtain a corresponding spectrum signal, and calculating a corresponding Relative Standard Deviation (RSD)i；
6) Comparing the relative standard deviation of the sample spectrum signals in various mixed gas environments to find out the minimum value; and taking the composition proportion corresponding to the minimum value as an optimal proportion, and detecting the sample by adopting the gas environment, thereby improving the repeatability of the laser-induced breakdown spectroscopy.
2. The method for improving the repeatability of the laser-induced breakdown spectroscopy based on the mixed gas environment as claimed in claim 1, wherein the method for continuously changing the composition ratio of the gases in the mixed gas in the step 5) comprises the following steps: changing according to gradient, i.e. selecting a positive integer n greater than or equal to 5, to obtain
For varying the gradient, the set of mixed gases being varied graduallyAnd (4) in proportion.
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| CN111398251A (en) * | 2020-03-17 | 2020-07-10 | 浙江大学 | Multi-gas-mixed L IBS signal enhancement device and heavy metal detection method |
| CN111610179B (en) * | 2020-05-20 | 2021-06-25 | 北京科技大学 | System and method for quickly detecting components LIBS of high-temperature sample in front of furnace |
| CN113310969A (en) * | 2021-04-22 | 2021-08-27 | 清华大学 | Method for improving repeatability of laser-induced breakdown spectroscopy based on time modulation |
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