Heavy metal water pollution refers to a relative density of 45. The abnormal concentration of more than 5 metal elements and their compounds in water makes the water quality decrease or deteriorate. The relative density is 45. Heavy metals above copper, lead, zinc, nickel, chromium, cadmium, mercury and non-metallic arsenic. Methods for detecting heavy metals in water include flame atomic absorption spectrophotometry, graphite furnace atomic absorption spectrophotometry, atomic fluorescence spectroscopy, and inductively coupled plasma emission spectrometry.
1. Atomic fluorescence spectrometry.
Atomic fluorescence spectroscopy is an emission spectrometry method that analyzes atoms in radiation energy. Under certain conditions, the relationship between the fluorescence intensity and the concentration of the element to be measured in the measured solution follows the Lambert-Beer law, and the content of the element in the sample to be measured 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 that it is highly sensitive, and the detection limits of more than 20 elements are better than those of atomic absorption spectrometry and atomic emission spectrometryThe spectral lines are simple;At low concentrations, the linear range of the calibration curve is as wide as 3 5 orders of magnitude, especially when using laser 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.
2. Atomic absorption spectrometry.
Atomic absorption spectrophotometry, also known as atomic absorption spectrophotometry, is an analytical method based on the absorption intensity of the corresponding atomic resonance radiation in the ultraviolet and visible range of the ground atom in the gaseous state to quantify the content of the measured element, and is a method to measure the absorption of optical radiation by specific gaseous atoms.
The basic principle is that a beam of incident light of a specific wavelength is emitted from the hollow cathode lamp or light source, and when it passes through the atomic vapor of the element to be measured in the atomizer, part of it is absorbed, and the degree of absorption of the characteristic spectral line can be measured through the spectroscopic system and the detection system, that is, the absorbance, and the content of the analyte can be obtained according to the linear relationship between the absorbance and the atomic concentration of the element.
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. Its shortcomings are that it is difficult to determine multiple elements at the same time, it is still difficult to determine non-metallic and refractory elements, and the interference is serious for the analysis of complex samples, and the reproducibility of atomic absorption analysis in graphite furnace is poor.
3. Inductively coupled plasma emission spectrometry.
Inductively coupled plasma emission spectroscopy is based on the atoms or ions of the measured element, which are excited in the light source to produce characteristic radiation, and by judging the existence of such characteristic radiation and the magnitude of its intensity, qualitative and quantitative analysis of each element.
Inductively coupled plasma emission spectrometry is applied to the analysis of trace elements in environmental water samples and soil samples, and the application technology in elemental analysis and testing is simple, fast and fastThe detection limit is low, most can reach 0005 g ml or less;The dynamic linear range of measurement is wide, generally up to 5 6 orders of magnitude, and the analysis of high and low elements can be carried out at the same time, and the partial detection level of the graphite furnace atomic absorption spectrometer can be reachedIt can analyze a variety of elements at the same time, qualitatively and quantitatively analyze metal elements, and can also analyze some non-metallic elements, which improves the analysis efficiency, small matrix effect, low background interference, high signal-to-noise ratio, high precision, good accuracy and other advantages.
4. X-ray fluorescence spectroscopy.
X-ray fluorescence spectroscopy is a method for qualitatively or quantitatively determining the composition of a sample by using the absorption of X-rays in the sample as the composition in the sample changes with how much it changes.
The structure of X-ray fluorescence spectrometer is basically composed of several parts, such as light source, dispersion, detection, spectrometer control and data processing of the excited sample. The difference between the results of elemental analysis between X-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry and emission spectrometry showed that the difference between them was not significant. It can meet the experimental requirements in terms of detection limit, accuracy, precision and rate.
Heavy metal detection is a long-term work, which requires various detection methods to develop in the direction of higher sensitivity, higher selectivity, and more convenient and fast, and constantly introduce new methods to solve new analytical problems encountered. With the establishment of various analytical methods and the continuous progress of science and technology, analytical instruments have gradually developed from simplification to complexity, and 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.