The quality of water directly affects people's health condition. Water quality monitoring has become an important part of our environmental protection. A good water quality detection method has become the direction that researchers pursue, and atomic absorption spectrometry has become the first choice in water quality analysis.

I. Basic principles of atomic absorption spectrometry

First, atomic absorption spectrometry (AAS) is based on the phenomenon that gaseous atoms can absorb light radiation of a certain wavelength, making the electrons in the outer layer of the atom transition from the ground state to the excited state. When radiation passes through the free atomic vapor, and the frequency of the incident radiation is equal to the energy frequency required by the electrons in the atom to transition from the ground state to a higher energy state (generally the first excited state), the atom will absorb energy from the radiation field and produce resonance absorption, and the electrons will transition from the ground state to the excited state, accompanied by the generation of the atomic absorption spectrum. In general, atoms are in the ground state. When the characteristic radiation passes through the atomic vapor, the ground state atom absorbs energy from the radiation, and the outermost electron transitions from the ground state to the excited state. The degree to which an atom absorbs light depends on the concentration of ground state atoms in the optical path. In general, it is possible to approximate that all atoms are in the ground state. Atomic absorption spectrometry is based on the fact that the ground state atoms of the tested element in the gaseous state strongly absorb the atomic resonance radiation of the element.

In water analysis, atomic absorption spectrometry is a kind of instrumental analysis method to measure the absorption intensity of electromagnetic radiation by atoms in the vapor produced by substances. Atomic absorption spectrometer is composed of light source, atomization system, optical system, detection system and display device. The atomization system plays an important role in the whole device. Specific cathode lamp, wavelength range, slit width, lamp current value and so on have been determined for different elements. In order to reach a higher order of magnitude or improve the quality of detection, the key lies in the sample pretreatment and sampling technology.

2. Application field of atomic absorption spectrometry

In the application of element analysis, atomic absorption spectrometry with its own characteristics, has been widely used in industry, agriculture, biochemical pharmaceutical, geology, metallurgy, food inspection and environmental protection and other fields. The method has become one of the most powerful means of metal element analysis. And in many fields has been used as a standard analysis method, such as cement analysis in the chemical industry, glass analysis, petroleum analysis, plating solution analysis, salt electrolyte impurity analysis, coal ash analysis and polymer inorganic element analysis; Agricultural plant analysis, fertilizer analysis, feed analysis; Biochemistry and pharmacology in body fluid composition analysis, viscera and sample analysis, drug analysis; Steel analysis and alloy analysis in metallurgy; Water quality analysis, air pollutant analysis, soil analysis, rock and mineral analysis in geochemistry; Analysis of trace elements in food.

Applications in the analysis of organic matter, The indirect method of atomic absorption spectrometer can be used to determine a variety of organic matter, such as 8-hydroxyquinoline (Cu), alcohols (Cr), esters (Fe), amino acids (Cu), vitamin C(Ni), halogen containing organic matter (Ag) and other organic matter, can be measured indirectly through stoichiometric reaction between the corresponding metal elements.

Application in theoretical research, atomic absorption can be used as an experimental means of physics or physical chemistry to measure and study some basic properties of substances, but also can study the different forms of metal elements in different compounds.

Application in element analysis: atomic absorption spectrometry with its own characteristics, has been widely used in industry, agriculture, biochemical pharmaceutical, geology, metallurgy, food inspection and environmental protection and other fields. The method has become one of the most powerful means of metal element analysis. And in many fields has been used as a standard analysis method, such as cement analysis in the chemical industry, glass analysis, petroleum analysis, plating solution analysis, salt electrolyte impurity analysis, coal ash analysis and polymer inorganic element analysis; Agricultural plant analysis, fertilizer analysis, feed analysis; Biochemistry and pharmacology in body fluid composition analysis, viscera and sample analysis, drug analysis; Steel analysis and alloy analysis in metallurgy; Water quality analysis, air pollutant analysis, soil analysis, rock and mineral analysis in geochemistry; Analysis of trace elements in food.

3. The use of atomic absorption spectrometry

In analytical chemistry, the combination or combination of different analytical means is often used to improve the analytical sensitivity and detection limit. If the characteristic concentration of electrochemical and flame atomic absorption method is greatly reduced, the sensitivity of the determination is increased by more than 2 orders of magnitude. For example, electrodeposition technology and atomic absorption spectrometry are widely used in the detection of heavy metals. Flame atomic absorption has also become an important method for the morphology analysis of organometallic compounds. It can detect both atoms and ions at the same time and realize the highly sensitive synchronous determination of trace organometallic compounds and their co-existing organic compounds. Yin Xuefeng et al. studied four chemical forms of arsenic by factor analysis and hydride generation atomic absorption method. As (Ⅲ),As (Ⅴ), Monomethyl-arsenic and dimethyl-arsenic have different toxicity in environmental water samples. The previous on-line determination by chromatographic separation and atomic spectrometry is limited by the dilution effect of chromatographic separation, and the lower limit of detection is high, which is limited in practice. However, this method is simple to operate, does not require treatment, has high density, and has good qualitative and quantitative ability.

In recent years, foreign researchers are still trying to combine some special separation and enrichment methods and sampling methods with atomic absorption spectrometry, so as to solve many difficult problems in research. For example, different types of plasma have been combined with the thermal discharge of spectroscopy for stoichiometric research and basic research. At the same time, there has been a significant increase in the study of speciation processes. Some people use microcolumn preconcentration atomic absorption spectrometry to determine trace elements and matrix elements. Gasper,Attlia et al. proposed the low pressure injection sample column flame atomic absorption spectrometry method for the determination of silver, cadmium, mercury, lead, selenium and zinc. The results showed minimal relative deviation and could be used as an element analysis method for water quality standard and pollution measurement. Electrothermal atomic absorption spectrometry (ETAAS) has been used to directly atomize solid samples for the determination of trace elements in steel. The detection limit of cadmium was 217ng/ L by electrothermal atomic absorption spectrometry, and the relative deviation was reduced from 312 % to 118 % by direct extraction. Mercury content in seafood has been determined by wet microwave digestion and flow injection atomic absorption spectrometry. Thallium in wine has been determined by extraction - preconcentration - electrothermal atomic absorption spectrometry. The above examples demonstrate the practical and efficient application of atomic absorption spectrometry in combination with other methods.

4.The development trend of atomic absorption spectrometry

In recent years, some people at home and abroad are committed to studying the application of laser in atomic absorption analysis: using tunable laser instead of hollow cathode light source; Atomize the sample with a laser. It will provide a new method for microzone and thin film analysis and a new method for atomization of refractory elements. The application of Zeeman effect makes the determination can be achieved smoothly even in very high background. The introduction of high efficiency separation technology gas chromatography, liquid chromatography, separation instrument and determination instrument combined, will make atomic absorption spectrophotometry
The face of degree method has changed greatly, microsampling technique and solid direct atomic absorption analysis have received people's attention. The significant advantages of solid direct atomic absorption analysis are that it eliminates the step of sample decomposition, does not add reagents, does not go through any separation and enrichment procedures, and reduces the possibility of contamination and loss, which will be of particular interest in such fields as biology, medicine, environment, chemistry, etc., where only a small number of samples are available for analysis. All these new developments deserve our attention. In recent years, with the application of microcomputer to atomic absorption spectrophotometer, the performance and automation of the instrument have reached a new stage.