Services: Electrical testing and certification, environmental or chemical testing

language
- English
- 中文

400-9269-886

NEWS CENTER

Industry News

Company News

Knowledge

Summary of Testing Methods for Atmospheric Metal Pollutants

Time：

2022-07-21

The testing methods of metal elements in atmospheric particles mainly include atomic fluorescence spectroscopy, atomic absorption spectroscopy, inductively coupled plasma emission spectroscopy, laser-induced breakdown spectroscopy, X-ray fluorescence spectroscopy, etc.

For heavy metal pollution, due to the invisible and colorless air pollutants, it is easier to be ignored than heavy metals in water. The annual emission of pollutants has reached about 9,500 tons. These heavy metal pollutants may enter the human body through the food chain through respiration, or after migrating to water and soil.

In the detection of metal elements in atmospheric particles, atomic absorption spectrometry (AAS), inductively coupled plasma emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), X- Detection methods such as ray fluorescence spectrometry, neutron activation analysis and proton induced X-ray emission spectrometry, among which AAS method, ICP-AES method and XRF method are widely used in China.

Spectrophotometry, graphite furnace atomic absorption spectrophotometry, etc. can only detect one metal element in one detection process, and the detection limit of general elements can only reach ppb level or sub-ppb level. The output limit can reach ppt level, but also only one metal element can be detected. The ICP-AES method can detect a variety of elements at the same time, and its detectable element types are also more than that of the AAS method. It is a relatively mature method. Such elements often cannot meet the requirements of the corresponding control limit concentration, and the analysis requirements of most elements can only be met by combining with graphite furnace atomic absorption (GF-AAS) and mercury cold atomic absorption (CV-AAS) techniques. The advantages of the XRF method are that the detection is fast, simple, no complicated pretreatment work, non-destructive detection, and simultaneous detection of multiple elements, so it can realize on-site and online monitoring, but the shortcomings of the XRF method are also obvious, the detection limit is only up to At the ppm level, the detection is dependent on the standard sample, and the requirement for sample volume makes it require a certain enrichment time, which partially offsets its field advantage. The ICP-MS method can realize multi-element analysis, and has the advantages of high sensitivity, low detection limit, and small sampling amount. /L) or parts per trillion (ppt) level, but it also has the disadvantages of high instrument price, high difficulty in use and high maintenance and use costs, and poor reproducibility when used for atmospheric particulate metal detection.

◉ Atomic Fluorescence Spectrometry

Atomic fluorescence spectrometry is an emission spectroscopic analysis method that analyzes the energy of atoms in radiation. The characteristic emission light emitted by the excitation light source is used to irradiate the atomic vapor of a certain concentration of the element to be tested to generate atomic fluorescence. Under certain conditions, the relationship between the fluorescence intensity and the concentration of the element to be tested in the tested solution follows the Lambert-Beer law. The content of the element in the sample to be tested can be obtained by measuring the intensity of fluorescence.

Atomic fluorescence spectrometry has the advantages of two analytical methods, atomic absorption and atomic emission, and overcomes the shortcomings of these two methods in some places. The advantage of this method is its high sensitivity. At present, the detection limit of more than 20 elements is better than that of atomic absorption spectrometry and atomic emission spectrometry; the spectral line is simple; the linear range of the calibration curve is as wide as 3 to 5 at low concentration order of magnitude, especially when laser is used as the excitation light source, but it has problems such as fluorescence quenching effect and scattered light interference.

This method is mainly used for the determination of metal elements, and has a wide range of applications in environmental science, high-purity substances, minerals, water quality monitoring, biological products and medical analysis.

◉ Atomic Absorption Spectroscopy

Atomic absorption spectrometry, also known as atomic absorption spectrophotometry, is an analytical method based on the quantitative determination of the content of the measured element based on the absorption intensity of the outer electrons of the gaseous ground state atoms to the corresponding atomic resonance radiation in the ultraviolet and visible light ranges. is a method of measuring the absorption of light radiation by specific gaseous atoms.

The basic principle is that a beam of incident light with a specific wavelength is emitted from a hollow cathode lamp or light source. When it passes through the atomic vapor of the element to be measured in the atomizer, part of it is absorbed, and the part that passes through can pass through the spectroscopic system and the detection system. The degree of absorption of the characteristic spectral line is measured, that is, the absorbance. According to the linear relationship between the absorbance and the atomic concentration of the element, the content of the analyte can be obtained.

In agriculture, atomic absorption spectrometry is mainly used in the analysis of medium and trace elements in soil, fertilizers and plants, water quality analysis, soil heavy metal environmental pollution analysis, soil background value investigation and agricultural environmental evaluation analysis. The advantages of this method are: strong selectivity, high sensitivity, wide analysis range, strong anti-interference ability and high precision. The disadvantage is that it is difficult to measure multiple elements at the same time, it is still difficult to measure non-metallic and refractory elements, the interference to the analysis of complex samples is also serious, and the reproducibility of graphite furnace atomic absorption analysis is poor.

◉ Inductively Coupled Plasma Emission Spectroscopy

Inductively coupled plasma emission spectroscopy is based on the atoms or ions of the element to be measured, which are excited in the light source to generate characteristic radiation. By judging the existence and intensity of this characteristic radiation, each element is qualitatively and quantitatively analyzed.

Inductively coupled plasma emission spectrometry is applied to the analysis of trace elements in environmental water samples and soil samples. The application technology in elemental analysis and testing is simple, fast, and fast in analysis; the detection limit is low, most of which can reach 0.005μg/ Below ml; the measurement dynamic linear range is wide, generally up to 5 to 6 orders of magnitude, and the analysis of high-content elements and low-content elements can be carried out at the same time, which can reach the partial detection level of graphite furnace atomic absorption spectrometer; multiple elements can be analyzed simultaneously , It can qualitatively and quantitatively analyze metal elements, and can also analyze some non-metal elements, which improves the analysis efficiency, has the advantages of small matrix effect, low background interference, high signal-to-noise ratio, high precision and good accuracy.

◉ Laser Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy is one of the most commonly used laser ablation spectroscopy techniques. Its working principle is: the laser is converged by a converging lens, and the high peak power density vaporizes and ionizes the material on the surface of the unknown sample, and excites it to form a high-temperature, high-energy plasma (temperature up to 10000K), and the atomic spectrum and ion spectrum radiated by the plasma are The optical system is collected, coupled to the incident slit of the spectrometer through the input fiber, and the spectral data is transmitted to the computer through the data acquisition controller, and the composition and concentration of the measured substance can be analyzed and calculated by studying the spectrum.

The wavelengths of atomic spectrum and ion spectrum correspond to specific elements one-to-one, and the spectral signal intensity has a certain quantitative relationship with the content of the corresponding elements. Therefore, this technology can realize the qualitative and quantitative analysis of chemical elements in real time and quickly.

Laser-induced breakdown spectroscopy can truly achieve rapid on-site analysis without sample preprocessing, which is convenient for analysis and is not limited by research objects. However, the cost of the measuring instrument is high, the fluctuation of laser pulse energy, the inhomogeneity of the sample, and the characteristics of the sample will directly affect the stability of the measurement, that is to say, the characteristics of the studied sample have a great influence on the accuracy of the results.

◉ X-ray Fluorescence Spectrometry

X-ray fluorescence spectroscopy is a method of qualitatively or quantitatively determining the components in the sample by using the absorption of X-rays by the sample to change with the composition and how much in the sample.

The structure of X-ray fluorescence spectrometer is basically composed of several parts such as light source, dispersion, detection, spectrometer control and data processing to excite the sample. The difference between the elemental analysis results of the X-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry, and emission spectrometry showed that their differences were not significant. It can meet the experimental requirements in terms of detection limit, accuracy, precision and recovery.

◉ Summarize

Heavy metal detection is a long-term task, requiring various detection methods to develop in the direction of higher sensitivity, higher selectivity, and more convenience and speed, and constantly introduce new methods to solve new analytical problems encountered. With the establishment of various analytical methods and the continuous advancement of science and technology, analytical instruments have gradually developed from simplification to complexity. It is foreseeable that various analytical instruments will develop in the direction of multi-function, automation, intelligence and miniaturization. , and the detection accuracy and sensitivity will also be improved to a certain extent.