CN112986219B - Electrode sample introduction DBD micro plasma atomic emission spectrum detection system and method - Google Patents
Electrode sample introduction DBD micro plasma atomic emission spectrum detection system and method Download PDFInfo
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Abstract
An electrode sample introduction DBD micro plasma atomic emission spectrum detection system and method belong to the field of atomic emission spectrum detection equipment and analysis. The detection system comprises a DBD microplasma excitation source and a spectrum detection system; a sample electrode in the DBD micro-plasma excitation source is used for enriching an object to be measured; one end of the sample electrode, which is enriched with the object to be detected, is inserted into the tube of the quartz tube; the output end of the neon lamp power supply connected with the voltage regulator is respectively connected with the high-voltage lead and one end of the sample electrode, which is not enriched with the object to be measured; the branch pipe arranged on the quartz tube is connected with the air circuit system; the spectrum detection system comprises a lens, an optical fiber and a micro spectrometer, wherein the lens is connected with the micro spectrometer through the optical fiber. The method comprises the following steps: the sample solution containing the analyte is pre-concentrated by flowing it over the surface of the sample electrode at a constant flow rate by means of a peristaltic pump, dried, and then measured. The system and the method can analyze the object to be detected adsorbed on the surface of the electrode in situ, and are very suitable for the rapid high-throughput analysis of batch samples.
Description
Technical Field
The invention belongs to the technical field of atomic emission spectrum detection equipment and analysis, and particularly relates to an electrode sample injection DBD micro-plasma atomic emission spectrum detection system and method.
Background
The atomic emission spectrometry is a very common analysis technology for detecting element content in scientific fields such as food, environment and the like, and is also an important means for ecological construction and environmental protection. The large-scale spectral analysis instrument in the laboratory can realize the stable, accurate and high-sensitivity detection of elements, but the analysis and detection can only be carried out in the laboratory due to the defects of high energy consumption, large volume and the like, and the requirement of field analysis and detection cannot be met. The harm of heavy metal pollution to human health has attracted extensive attention from countries throughout the world due to the toxicity, carcinogenicity, and bioaccumulation of heavy metals. Heavy metal contamination accidents occur, such as external leaks or illegal discharges, and even treated purified water may contain heavy metals due to leaching from the pipeline. Detection of heavy metal contamination in environmental water typically requires collection, storage and transport of large volumes of water samples (250-. Not only does this mode of detection increase the pressure of the logistics, but the contact of the sample with oxygen, the container walls, or physical changes in temperature and pressure will inevitably lead to loss of analyte and contamination of the sample during storage of the sample, which will seriously affect the accuracy and reproducibility of the analysis results. Therefore, the development of portable analytical instruments is urgently needed to meet the requirement of on-site analysis of heavy metal pollution.
At present, some heavy metal analysis methods based on portable detectors, such as Anodic Stripping Voltammetry (ASV) and Colorimetry (Colorimetry), can be used for detecting field trace heavy metals, but cannot be completely suitable for detecting heavy metals in complex and real water samples due to the interference of unknown coexisting metal ions. X-ray Fluorescence Spectroscopy (XRF) and Laser Induced Breakdown Spectroscopy (LIBS) can analyze elemental characteristics when directly sampling, are particularly suitable for rapid on-site analysis of heavy metals, but are limited by sample heterogeneity and insufficient detection sensitivity.
The most central component of an atomic emission spectrometry instrument is an atomizer/excitation source, which directly determines the overall analytical performance, volume size and the number of accessory devices of the whole atomic emission spectrometry instrument. At present, the development of portable instruments is accelerated by the application of various microplasma excitation sources in an atomic emission spectrometry detection system, and efficient performance is shown in the field of trace element analysis. Common microplasmas include: dielectric Barrier Discharge (DBD), Point Discharge (PD), Atmospheric Pressure Glow Discharge (APGD), and the like. Since the power of microplasmas is much lower than that of conventional Inductively Coupled Plasma (ICP) and Microwave Induced Plasma (MIP) sources, and evaporation of solvents and matrixes can seriously deteriorate the atomization/excitation capability of microplasmas, the development of a sample injection mode has become an important challenge of a microplasma atomic emission spectroscopy detection system. Generally, to ensure that the microplasma has sufficient atomization/excitation capability, the ideal method for introducing a liquid sample into the microplasma is to convert the analyte into "pure" and "dry" volatile species by chemical/photochemical/electrochemical Vapor Generation (VG) or Electrothermal Evaporation (ETV). Due to the limitations of the reaction conditions, the vapor generation method for introducing a sample into microplasma will result in a limited number of detectable elements, a large reagent consumption, and difficulty in measuring multiple elements simultaneously. Electrothermal evaporation based on a tungsten wire coil for introducing a sample into microplasma is easy to realize simultaneous determination of multiple elements, but the limited sample loading amount on the tungsten wire coil prevents further improvement of the sensitivity of the tungsten wire coil, and the service life of the tungsten wire coil limits long-term use of the tungsten wire coil. Inspired by the use of microplasmas as mass spectrometry ionization sources for in situ ionization of surface samples, microplasma excitation sources, if capable of exciting analytes deposited on the surface of a substrate for elemental analysis, would provide a promising approach for efficient sample introduction and instrument miniaturization. The invention patent publication No. CN104749139A is to use microwave with high energy to induce plasma tail flame to initiate combustion of sample substrate, and use combustion heat to promote atomization and excitation of sample element to be measured attached to the substrate to realize element measurement. However, the energy of the microplasma such as DBD, PD, etc. is so low that it is not possible to ignite the paper, and the key to the effective excitation of the analyte on the substrate surface using the microplasma excitation source is how to increase the sample volume of the sample introduced into the microplasma excitation source and overcome the "coffee ring" effect caused by the non-uniform deposition of the sample. Marcus et al (anal. chem.2016,88,5579-5584.) propose proof of concept using liquid sampling APGD to volatilize and excite dry solution residues and detect heavy metals by atomic emission spectroscopy, however this system only qualitatively analyzes heavy metals.
Disclosure of Invention
The invention aims to provide a microplasma atomic emission spectrometry detection system capable of conveniently and efficiently introducing a sample for field heavy metal pollution analysis and a corresponding analysis method using the detection system. The electrode sample introduction DBD micro plasma atomic emission spectrometry detection system can analyze an object to be detected adsorbed on the surface of an electrode in situ by using the DBD micro plasma atomic emission spectrometry detection system.
The electrode sample introduction DBD micro plasma atomic emission spectrum detection system comprises a DBD micro plasma excitation source and a spectrum detection system;
the DBD micro-plasma excitation source comprises a sample electrode, a quartz tube with a branch tube, a high-voltage lead wound on the outer wall of the quartz tube, a neon lamp power supply, a voltage regulator and an air path system;
the sample electrode is made of a material with conductivity and adsorbability for enriching the object to be detected on the surface of the sample electrode;
one end of the sample electrode, which is used for enriching the object to be detected, is inserted into the tube of the quartz tube and is coaxial with the quartz tube;
the input end of the voltage regulator is connected with alternating current, the output end of the voltage regulator is connected with the input end of a neon lamp power supply, and the output end of the neon lamp power supply is respectively connected with a high-voltage lead and one end of a sample electrode, which is not enriched with a substance to be detected;
the branch pipe arranged on the quartz tube is connected with the air circuit system;
the spectrum detection system comprises a lens, an optical fiber and a micro spectrometer, wherein the lens is connected with the micro spectrometer through the optical fiber, the lens is arranged in the axial direction or the horizontal direction of the side face of the quartz tube and used for focusing the generated characteristic emission spectrum, and the micro spectrometer is used for coupling the characteristic emission spectrum focused by the lens into the micro spectrometer through the optical fiber for detection.
The electrode sample introduction DBD micro plasma atomic emission spectrum detection system further comprises a computer and spectrum analysis software corresponding to the micro spectrometer, the micro spectrometer is connected with the computer, and the spectrum analysis software on the computer is used for analyzing the spectrum detected by the micro spectrometer. The micro spectrometer may be an Ocean Optics QE65000 spectrometer, and the spectrometer has spectral analysis software spectrasoite.
The micro plasma generated by the micro plasma excitation source is generated in the tube of the quartz tube, and the sample electrode is immersed in the micro plasma;
the sample electrode preferably comprises an electrode head and a connecting support; one end of the electrode tip is connected with the connecting support; the electrode head is used for enriching heavy metals, and the material of the electrode head is preferably active carbon, graphene, stainless steel and the like. The connecting support is preferably a hollow metal tube, such as a hollow stainless steel tube, a hollow tungsten tube, for supporting and connecting the high voltage wire. Preferably, the electrode head has a diameter of 0.4-1.2mm and a length of 2-8 mm; the inner diameter of the hollow metal pipe is 0.4-1.2mm, the thickness of the pipe wall is 0.05-0.1mm, and the length is 40-100 mm; the outer diameter of the electrode tip is the same as the inner diameter of the hollow metal tube, and after the electrode tip is inserted into the hollow metal tube, the exposed length of the electrode tip is 1-7 mm.
The sample electrode is also provided with a peristaltic pump and a heating platform in a matching way, the peristaltic pump is used for enabling solution containing the substance to be detected to flow into the sample electrode at a uniform speed, and the heating platform is used for drying the sample electrode.
The quartz tube with the branch tube has the outer diameter of 1-4mm, the tube wall thickness of 0.05-0.1mm and the length of 60-100 mm.
The voltage regulator is used for controlling the voltage loaded on the sample electrode and the high-voltage lead by the neon lamp power supply by regulating the output voltage of the voltage regulator.
The high-voltage wire is preferably a copper wire.
The invention discloses an electrode sample introduction DBD micro plasma atomic emission spectrum analysis method, which adopts the electrode sample introduction DBD micro plasma atomic emission spectrum detection system and comprises the following steps:
step 1:
enabling a sample solution containing the object to be detected to flow through the surface of the sample electrode at a constant flow rate through a peristaltic pump, and performing preconcentration to obtain the sample electrode in which the object to be detected is preconcentrated;
heating the sample electrode pre-concentrated with the object to be detected to remove water to obtain a sample electrode enriched with the object to be detected;
step 2:
inserting a sample electrode enriched with an object to be detected into a tube of a quartz tube with a branch tube, and introducing micro plasma discharge gas into the quartz tube through a gas path system;
connecting the output end of the neon lamp power supply with one end of the sample electrode far away from the enrichment object to be detected, and connecting the other output end of the neon lamp power supply with a high-voltage lead wound on the outer wall of the quartz tube;
the output end of the voltage regulator is connected with the input end of the neon lamp power supply, and the input end of the voltage regulator is connected with alternating current. Adjusting the voltage of a sample electrode and a high-voltage lead which are enriched with the object to be tested into a voltage for igniting plasma through a voltage regulator, then increasing the voltage to the voltage capable of exciting the object to be tested, exciting the object to be tested adsorbed on the surface of the sample electrode in situ by micro-plasma, finishing the excitation process of the object to be tested on the surface of the sample electrode within 3-5 seconds, and generating a characteristic emission spectrum;
and step 3:
the characteristic emission spectrum is focused by a lens and is coupled into a micro spectrometer through an optical fiber for detection.
The electrode sample introduction DBD micro plasma atomic emission spectrum analysis method further comprises the steps of displaying the spectral intensity of each object to be detected through computer spectral analysis software by using the characteristic emission spectrum detected by the micro spectrometer, and carrying out quantitative analysis by using the spectral peak height of each object to be detected to obtain the type and the corresponding content of the object to be detected in the solution.
In the step 1, the constant flow rate is preferably 3-10 mL/min.
In the step 1, the heating temperature is preferably 50-70 ℃, and the heating time is 3-10 min.
In the step 1, a plurality of sample electrodes can be simultaneously fed according to the multichannel property of the peristaltic pump.
In the step 2, the input power supply of the neon lamp power supply is 220V, and the output voltage is 6kV and 30mA high-voltage power supply.
In the step 2, the microplasma discharge gas is preferably an inert gas, and more preferably argon or helium.
In the step 2, the voltage for igniting the plasma is determined according to the thickness of the quartz tube and the relative position of the sample electrode and the high-voltage wire, and is preferably 3.4-3.6 kV.
In the step 2, the voltage for exciting the object to be measured is determined according to the condition that the quartz tube is not broken down and the object to be measured can generate a characteristic emission signal, and the voltage is preferably 3.6-6.0 kV.
In the step 3, the distance between the microplasma and the lens is preferably 6-12 cm.
Compared with the prior art, the electrode sample introduction DBD micro plasma atomic emission spectrum detection system and method provided by the invention have the advantages that:
(1) the invention most importantly integrates sampling, pre-concentration and micro-plasma excitation on a sample electrode, thereby not only simplifying the pretreatment steps of the sample and improving the portability, but also obviously improving the sensitivity of the micro-plasma atomic emission spectroscopy detection system for analyzing the object to be detected, particularly the detection limit of cadmium and lead elements can reach the sub-ppb level under the optimized condition, and the detection limit can reach the pollution detection standard.
(2) The dielectric barrier discharge micro-plasma is adopted as an excitation source, the operation can be carried out under the atmospheric pressure, and the energy consumption is low; the micro spectrometer is adopted for detection, the size is small, and the cost is low. The system lays a foundation for miniaturization and field analysis of the atomic spectrum instrument.
(3) The device and the method provided by the invention are adopted to carry out detection and analysis on the sample, have higher analysis speed, and the time required for detecting the sample electrode enriched with the substance to be detected once is only 3-5 seconds, so that the device and the method are very suitable for the rapid high-throughput analysis of batch samples.
(4) The device and the method provided by the invention can provide a convenient and efficient sample introduction method for the pollution analysis of the on-site object to be detected. The invention uses the sample electrode as the capture carrier of the object to be detected through simple liquid-solid phase transformation. The object to be detected adsorbed on the surface of the sample electrode can be quantitatively analyzed by a micro plasma atomic emission spectrometry detection system by simply adjusting the electric field intensity without any sample transmission channel.
Drawings
FIG. 1 is a diagram of an apparatus of an electrode-fed DBD microplasma atomic emission spectrometry detection system, wherein 1-a sample electrode, 2-a quartz tube with a branch tube, 3-a high-voltage lead, 4-a neon lamp power supply, 5-a voltage regulator, 6-a gas path system, 7-a lens, 8-an optical fiber and 9-a micro spectrometer.
Fig. 2 is a sample introduction unit of an electrode-fed DBD microplasma atomic emission spectroscopy detection system, wherein: 10-activated carbon rod, 11-hollow stainless steel tube, 12-peristaltic pump and 13-heating table.
FIG. 3 is an emission spectrum of a standard solution containing no cadmium and 6. mu.g/L of cadmium element measured by the apparatus and method of the present invention.
FIG. 4 is an emission spectrum of a standard solution containing no lead and 70. mu.g/L of lead element measured by the apparatus and method of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and embodiments, which are provided for illustration only and are not intended to be limiting.
The equipment and equipment used in the following examples are commercially available, except as otherwise indicated.
Example 1
FIG. 1 is a schematic diagram of the overall structure of an apparatus of an electrode-fed DBD microplasma atomic emission spectroscopy detection system. As shown in fig. 1, the proposed device of the electrode-fed DBD microplasma atomic emission spectroscopy detection system includes a DBD microplasma excitation source, a spectroscopy detection system;
the DBD micro-plasma excitation source comprises a sample electrode 1, a quartz tube 2 with a branch tube and a high-voltage lead 3 wound on the outer wall of the quartz tube, wherein the high-voltage lead is a copper wire, a neon lamp power supply 4, a voltage regulator 5 and an air path system 6;
the sample electrode 1 comprises an activated carbon rod 10 and a hollow stainless steel tube 11, wherein one end of the activated carbon rod 10 is connected with one end of the hollow stainless steel tube 11;
one end of a hollow stainless steel tube 11 of the sample electrode 1 and one end of a high-voltage lead 3 are respectively connected with the output end of a neon lamp power supply 4. The input end of the neon lamp power supply 4 is connected with the output end of the voltage regulator 5, and the input end of the voltage regulator 5 is connected with the 220V power supply. The branch port of the quartz tube 2 with the branch tube is connected with a gas path system 6 for introducing the micro-plasma discharge gas. The DBD microplasma is generated inside the quartz tube 2 of the branch tube, and the sample electrode 1 is immersed in the DBD microplasma. The output voltage of the voltage regulator 5 is regulated to control the high voltage loaded between the sample electrode 1 and the high voltage lead 3 by the neon lamp power supply 4.
The spectrum detection system comprises a lens 7, an optical fiber 8 and a micro spectrometer 9, wherein the lens 7 is connected with the micro spectrometer 9 through the optical fiber 8, and the lens is arranged in the axial direction or the horizontal direction of the side surface of the quartz tube 2 with the branch pipe far away from the branch opening of the quartz tube. The characteristic light emission of the object to be detected generated by the excitation of DBD micro plasma on the surface of the sample electrode 1 is focused by a lens 7 along a quartz tube 2 with a branch tube and then coupled to a micro spectrometer 9 through an optical fiber 8 for signal detection and amplification, and finally, after the spectral intensity of each object to be detected is displayed by spectral analysis software on a computer, the peak height is adopted for quantitative analysis, so that the detection of the object to be detected is realized.
In this embodiment, the activated carbon rod 10 has a diameter of 0.9mm and a length of 5 mm; the inner diameter of the hollow stainless steel pipe 11 is 0.9mm, the thickness of the pipe wall is 0.05mm, and the length is 50 mm; after the activated carbon rod 10 is inserted into the hollow stainless steel tube 11, the activated carbon rod 10 extends 4mm from the hollow stainless steel tube 11. The sample electrodes 1 can be fed simultaneously according to the multichannel property of the peristaltic pump 12.
The quartz tube 2 with the branch tube has an outer diameter of 3.3mm, a tube wall thickness of 0.8mm and a length of 85 mm. The diameter of the high-voltage wire 3 is 0.5 mm. The carrier gas was argon, and the gas flow rate was 600mLmin-1. The neon lamp power supply 4 can adopt a high voltage source with the input voltage of 220V and the output voltage of 6kV and 30 mA. The voltage regulator 5 inputs 220V voltage and outputs 0-250V voltage. The distance between the microplasma discharge area and the center position of the lens is 10 cm.
The method for detecting heavy metal elements using the apparatus of the present invention is described below.
A sample introducing unit of the electrode sample introduction DBD micro plasma atomic emission spectrometry detection system is shown in figure 2, a sample solution containing an object to be detected flows through the surface of an activated carbon rod 10 at a constant flow rate of 10mL/min through a peristaltic pump 12 for preconcentration, and a sample electrode 1 with the object to be detected in the preconcentration mode is obtained. And then drying and dewatering the sample electrode 1 through a heating table 13 to obtain the sample electrode enriched with the object to be detected. The heating stage temperature is 60 deg.C, and the heating time is 5 min.
Inserting a sample electrode enriched with an object to be detected into a tube of a quartz tube, introducing DBD (double-diffused metal) micro-plasma discharge gas (argon gas in the embodiment) into the quartz tube through a gas path system, connecting the output end of a neon lamp power supply with one end of the sample electrode far away from the enriched object to be detected, and connecting the other output end of the neon lamp power supply with a high-voltage lead wound on the outer wall of the quartz tube;
the power supply is connected, the voltage of the sample electrode and the high-voltage lead which are rich in the object to be tested is adjusted to be the voltage for igniting the plasma through the voltage regulator, the voltage is increased to be the voltage capable of exciting the object to be tested, the object to be tested adsorbed on the surface of the sample electrode which is rich in the object to be tested is excited by the micro plasma in situ, the voltage for exciting the object to be tested is 5.8kV in the embodiment, and the object to be tested on the surface of the sample electrode can finish the excitation process to generate the characteristic emission spectrum within 3-5 seconds. The characteristic emission spectrum detected by the micro spectrometer displays the spectral intensity of each object to be detected through computer spectral analysis software, and the spectral peak height of each object to be detected is adopted for quantitative analysis to obtain the type and the corresponding content of the object to be detected in the solution.
Cadmium and lead are taken as examples, and feasibility of detection by adopting the electrode sample injection DBD microplasma atomic emission spectrometry detection system and the analysis method using the system is explained.
FIG. 3 is a spectrum diagram of an emission spectrum of a standard solution containing no Cd and 6 μ g/L Cd measured by the detection system and method of the present invention, wherein the abscissa represents the wavelength range and the ordinate represents the intensity of the emission signal. As can be seen from FIG. 3, the specific cadmium atom emission line at 228.8nm is clearly separated from the blank emission spectrum, and the feasibility of the detection device and method of the present invention is verified. And continuously testing cadmium with different concentrations for multiple times, and explaining the sensitivity of the established method. When the sample volume is 50mL, the peristaltic pump samples for 5min, the experimental result shows that the detection limit of cadmium (calculated by multiplying the standard deviation of 11 blank samples by 3 and dividing the standard deviation by the slope of the regression equation of the standard curve) is as low as 0.03 mu g/L, the linear range is 0.1-12 mu g/L, and the signal RSD (relative standard deviation of 11 measured values of 5 mu g/L Cd) is lower than 3%. The detection limit can reach the pollution detection standard.
FIG. 4 is a spectrum of an emission spectrum of a standard solution containing no lead Pb and containing 70. mu.g/L of lead element measured by the apparatus and method of the present invention, with the abscissa representing the wavelength range and the ordinate representing the intensity of an emission signal. As can be seen from FIG. 4, the specific lead atom emission lines at 368.3nm and 363.9nm were clearly separated from the blank emission spectrum, and the feasibility of the detection device and method of the present invention was verified. And continuously testing lead with different concentrations for multiple times, and explaining the sensitivity of the established method. When the sample volume is 50mL and the peristaltic pump is used for sampling for 5min, the experimental results show that the detection limit of lead (calculated by multiplying the standard deviation of 11 blank samples by 3 and dividing the result by the slope of the regression equation of the standard curve) is as low as 0.6 mug/L, the linear range is 2-100 mug/L, and the signal RSD (relative standard deviation of 11 measurements of 50 mug/L Pb) is lower than 4%. The detection limit can reach the pollution detection standard.
Example 2
The structure of the electrode sample injection DBD micro plasma atomic emission spectroscopy detection system is the same as that of the embodiment 1, and the difference is that an activated carbon rod 10 included in a sample electrode 1 is a hollow stainless steel pipe, namely the sample electrode 1 is an integrated hollow stainless steel pipe. At this time, the sample electrode 1 has a weaker ability to enrich the analyte than the sample electrode 1 used in example 1.
The method for detecting heavy metal elements by electrode injection DBD micro plasma atomic emission spectroscopy is the same as that in example 1, and by taking cadmium as an example, the characteristic emission spectrum of cadmium appears at 228.8nm in an emission spectrum of a standard solution containing cadmium elements measured by the detection system and the method. When the Cd concentration (6. mu.g/L) measured in example 1 was 1% of that of example 2, example 1 showed 8 times the spectral intensity of cadmium at 228.8nm as that of example 2 by computer spectroscopic analysis software.
Example 3
The structure of the electrode sample injection DBD micro plasma atomic emission spectrometry detection system is the same as that of the embodiment 1, and the difference is that the voltage for exciting the object to be detected is 4.0 kV.
The method for detecting heavy metal elements by electrode injection DBD microplasma atomic emission spectroscopy is the same as that in example 1, taking cadmium as an example, the emission spectrum of a standard solution containing cadmium elements measured by adopting the detection system and the method of the invention has a characteristic emission spectrum of cadmium at 228.8nm, and when the concentration (6 mug/L) of Cd measured in example 1 is the same as that in example 3, the spectral intensity of cadmium is 2.5 times that of example 3 at 228.8nm as shown in example 1 through computer spectral analysis software.
Example 4
The electrode sample introduction DBD micro plasma atomic emission spectrometry detection system is adopted to determine cadmium and lead in lake water, and the method for detecting heavy metal elements by electrode sample introduction DBD micro plasma atomic emission spectrometry is the same as the embodiment 1, and is different from the method in that the lake water sample is filtered by a 0.22-micrometer filter membrane and then is analyzed.
In this example, the obtained spectral peak heights of cadmium and lead were converted into concentrations according to a regression equation of a standard curve, and the cadmium concentration in lake water was 0.34 ± 0.01 μ g/L, lead was not detected, and the recovery rates of cadmium and lead in spiking were 96.5% and 100.5% when cadmium and lead were spiked to 3 μ g/L and 50 μ g/L, respectively.
Example 5
Cadmium and lead in drinking water are measured by adopting the electrode sample introduction DBD micro plasma atomic emission spectrometry detection system, and the method for detecting heavy metal elements by adopting the electrode sample introduction DBD micro plasma atomic emission spectrometry is the same as that in the embodiment 1.
In this example, the spectral peak heights of cadmium and lead obtained were converted into concentrations according to a regression equation of a standard curve, and neither cadmium nor lead was detected, and the recovery rates of cadmium and lead when spiked to 5. mu.g/L and 20. mu.g/L were 95.5% and 101.4%, respectively.
Compared with the existing in-situ surface analysis method, the volume type in-situ micro-plasma excitation method provided by the invention overcomes the coffee ring effect caused by non-uniform dry residues. In addition, the high-efficiency microplasma excitation capability and the use of the activated carbon carrier with the pre-concentration function on the liquid sample further improve the sensitivity of the system.
The above examples are merely illustrative of the embodiments of the present invention and are not intended to limit the scope thereof. Various modifications and improvements of the present invention can be made without departing from the spirit of the invention, and the scope of the invention is defined by the claims.
Claims (9)
1. An electrode sample introduction DBD micro plasma atomic emission spectrum detection system is characterized by comprising a DBD micro plasma excitation source and a spectrum detection system;
the DBD micro-plasma excitation source comprises a sample electrode, a quartz tube with a branch tube, a high-voltage lead wound on the outer wall of the quartz tube, a neon lamp power supply, a voltage regulator and an air path system;
the sample electrode is made of a material with conductivity and adsorbability for enriching the object to be detected on the surface of the sample electrode;
one end of the sample electrode, which is used for enriching the object to be detected, is inserted into the tube of the quartz tube and is coaxial with the quartz tube;
the sample electrode comprises an electrode head and a connecting support; one end of the electrode tip is connected with the connecting support; the electrode head is used for enriching heavy metals; the connecting support is a hollow metal pipe and is used for supporting and connecting a high-voltage lead; the diameter of the electrode tip is 0.4-1.2mm, and the length is 2-8 mm; the inner diameter of the hollow metal tube is 0.4-1.2mm, the thickness of the tube wall is 0.05-0.1mm, and the length is 40-100 mm; the outer diameter of the electrode tip is the same as the inner diameter of the hollow metal tube, and the exposed length of the electrode tip is 1-7mm after the electrode tip is inserted into the hollow metal tube;
the input end of the voltage regulator is connected with alternating current, the output end of the voltage regulator is connected with the input end of a neon lamp power supply, and the output end of the neon lamp power supply is respectively connected with a high-voltage lead and one end of a sample electrode, which is not enriched with a substance to be detected;
the branch pipe arranged on the quartz tube is connected with the air circuit system;
the spectrum detection system comprises a lens, an optical fiber and a micro spectrometer, wherein the lens is connected with the micro spectrometer through the optical fiber, the lens is arranged in the axial direction or the horizontal direction of the side face of the quartz tube and used for focusing the generated characteristic emission spectrum, and the micro spectrometer is used for coupling the characteristic emission spectrum focused by the lens into the micro spectrometer through the optical fiber for detection.
2. The electrode injection DBD micro-plasma atomic emission spectrometry detection system of claim 1, further comprising a computer and a spectrum analysis software corresponding to the micro spectrometer, wherein the micro spectrometer is connected to the computer, and the spectrum analysis software on the computer is used for analyzing the spectrum detected by the micro spectrometer.
3. The electrode-fed DBD microplasma atomic emission spectrometry detection system of claim 1, wherein the sample electrode is further provided with a peristaltic pump and a heating platform in a matching manner, the peristaltic pump is used for enabling a solution containing an object to be detected to flow into the sample electrode at a uniform speed, and the heating platform is used for drying the sample electrode.
4. The electrode-fed DBD microplasma atomic emission spectrometry detection system according to claim 1, wherein the quartz tube with the branch tube has an outer diameter of 1-4mm, a tube wall thickness of 0.05-0.1mm, and a length of 60-100 mm.
5. An electrode-fed DBD microplasma atomic emission spectrometry method is characterized in that the electrode-fed DBD microplasma atomic emission spectrometry detection system of any one of claims 1-4 is adopted, and the method comprises the following steps:
step 1:
enabling a sample solution containing the object to be detected to flow through the surface of the sample electrode at a constant flow rate through a peristaltic pump, and performing preconcentration to obtain the sample electrode in which the object to be detected is preconcentrated;
heating the sample electrode pre-concentrated with the object to be detected to remove water to obtain a sample electrode enriched with the object to be detected;
step 2:
inserting a sample electrode enriched with an object to be detected into a tube of a quartz tube with a branch tube, and introducing micro plasma discharge gas into the quartz tube through a gas path system;
connecting the output end of the neon lamp power supply with one end of the sample electrode far away from the enrichment object to be detected, and connecting the other output end of the neon lamp power supply with a high-voltage lead wound on the outer wall of the quartz tube;
the output end of the voltage regulator is connected with the input end of the neon lamp power supply, and the input end of the voltage regulator is connected with alternating current; adjusting the voltage of a sample electrode and a high-voltage lead which are enriched with the object to be tested into a voltage for igniting plasma through a voltage regulator, then increasing the voltage to the voltage capable of exciting the object to be tested, exciting the object to be tested adsorbed on the surface of the sample electrode in situ by micro-plasma, finishing the excitation process of the object to be tested on the surface of the sample electrode within 3-5 seconds, and generating a characteristic emission spectrum;
and step 3:
the characteristic emission spectrum is focused by a lens and is coupled into a micro spectrometer through an optical fiber for detection.
6. The electrode-fed DBD micro-plasma atomic emission spectrometry method of claim 5, further comprising displaying the spectral intensity of each object to be tested by the characteristic emission spectrum detected by the micro spectrometer through computer spectral analysis software, and performing quantitative analysis by using the spectral peak height of each object to be tested to obtain the type and corresponding content of the object to be tested in the solution.
7. The electrode-fed DBD microplasma atomic emission spectrometry method of claim 5, wherein in step 1, the constant flow rate is 3-10 mL/min; the heating temperature is 50-70 ℃, and the heating time is 3-10 min.
8. The electrode sample introduction DBD micro plasma atomic emission spectrometry method according to claim 5, wherein in the step 2, an input power supply of a neon lamp power supply is 220V, and an output voltage is a high voltage power supply of 6kV and 30 mA.
9. The electrode-fed DBD microplasma atomic emission spectrometry analysis method of claim 5, wherein in the step 2, the ignition plasma voltage is 3.4-3.6 kV; the voltage for exciting the object to be detected is 3.6-6.0 kV.
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