Determination of tin in ores by atomic absorption spectrometry: Atomic absorption spectrometry is also called atomic absorption spectrometry in photometric analysis. It is an instrumental analysis method to determine the content of the element in the sample according to the absorption intensity of its vibration radiation by the ground state atoms in the vapor phase. This is an effective method for the determination of trace and ultra-trace elements. It has the advantages of high sensitivity, less interference, good selectivity, simple and fast operation, accurate and reliable results, wide application range, simple instrument and low price. Moreover, it can automate the whole operation and atomize the elements to be detected in the sample solution. At the same time, it needs a light source with stable light intensity, which can give light radiation with the same atomic characteristics through an atomic region to be detected, so as to measure its absorbance, and then measure the concentration of the standard solution according to the absorbance. Therefore, it has developed rapidly in recent years and is a new instrument analysis technology with wide application. It can determine almost all metal elements and some metalloid elements. This method has been widely used in metallurgy, chemical industry, geology, agriculture, medicine and health, biology and other departments, especially in environmental monitoring, food hygiene and the determination of trace metal elements in organisms. 1. Overview: Tin ore in the mines under Yunxi Group Company is mainly cassiterite. With the continuous development of tin ore resources, the dilution rate of the deposit is increasing, which has great demand for the search and development of new ore sources, and puts forward more requirements for the analysis method of the original ore. Although there is an extensive and classical analysis method "iodometry" in the analysis of tin, it has certain limitations on raw ore, especially low-grade raw ore. Therefore, this paper intends to make some preliminary discussions on the determination of tin by atomic absorption spectrophotometry. At present, atomic absorption spectrometry has been widely used in various fields, which has played a positive role in the development of industry, agriculture, medical students, teaching and scientific research. With the development of atomic absorption technology, the continuous updating and development of atomic absorption instruments have been promoted, while other scientific and technological progress has also provided technical and material basis for the continuous updating and development of atomic absorption instruments. In recent years, a microcomputer-controlled atomic absorption spectrophotometer has been designed by using continuous light source, step grating, light pipe and diode array multi-element analysis detector, which opens up a new prospect for simultaneous determination of multi-elements. The microcomputer-controlled atomic absorption spectrometry system simplifies the instrument structure, improves the automation degree of the instrument, improves the determination accuracy, and greatly changes the face of atomic absorption spectrometry. Coupled technologies (chromatography-atomic absorption spectrometry, flow injection-atomic absorption spectrometry) have attracted more and more attention. Chromatography-atomic absorption spectrometry (GC-AAS) has an important application not only in solving the chemical speciation analysis of elements, but also in the determination of complex mixtures of organic compounds, which is a promising development direction. There have been many studies and reports on the atomic absorption analysis method of tin. 196 1 year, B.M.Gatahous et al. proposed to obtain the measured characteristic concentration of tin at 286.3 nm * * vibration line with air-acetylene rich flame. Then tin in hydrogen peroxide was determined by oxygen-hydrogen flame at 286.3nm with a long absorption tube, and the characteristic concentration was 0.025ug/ml. 1968 once again reported the determination of tin by nitrous oxide-acetylene flame, and the characteristic concentration was 1.6ug/ml. In recent years, the method of hydride generation separation for the determination of tin has improved the selectivity and sensitivity of the analytical method. Determination of tin by atomic absorption spectrometry has been widely used in the analysis of various substances in China. For example, see table1-1. Serial number method is used to analyze materials. The method shows that: 1 air-acetylene flame ore is decomposed with sodium peroxide or ammonium iodide, 2 air-acetylene flame tin concentrate is decomposed with sodium peroxide, 2% hydrochloric acid is decomposed with 3 oxygen to protect air-acetylene flame ore with sodium peroxide, 4 argon-hydrogen flame ore is decomposed with sodium peroxide, hydrochloric acid-citric acid-ascorbic acid medium, thiosemicarbazone, cinchonine and nitroso red salt are used as masking agents. Sodium peroxide decomposition, benzene extraction and sodium hydroxide solution back extraction of argon hydrogen flame ore II. Basic principles of atomic absorption spectroscopy 2. 1 Overview of atomic absorption spectroscopy: When radiation passes through free atomic vapor and the frequency of incident radiation is equal to the energy frequency required for electrons in atoms to transition from the ground state to a higher energy state (usually the first excited state), atoms will absorb energy from the radiation field and produce * *. 2.2 Conditions for the generation of atomic absorption spectrum: ① Radiation energy: hν=Eu-E0② There are effective absorption particles, namely ground-state atoms. The content of the element to be measured is determined according to the absorption degree of the ground state atoms in the sample to the characteristic spectral lines of the element. Generally speaking, atoms are in the ground state. When the characteristic radiation passes through the atomic vapor, the ground atoms absorb energy from the radiation, and the outermost electrons transition from the ground state to the excited state. The degree to which atoms absorb light depends on the concentration of ground-state atoms in the optical path. Generally speaking, it can be approximated that all atoms are in the ground state. Therefore, the content of the elements to be measured in the sample can be judged according to the attenuation degree of the absorbed light. This is the theoretical basis of quantitative analysis by atomic absorption spectrometry. 2.3 Characteristics of atomic absorption spectrometry: Atomic absorption spectrometry is established according to the fact that the ground state atoms of the element under test have a strong absorption effect on the atomic vibration radiation of the element in the gaseous state. This method has the advantages of low detection limit, high accuracy, good selectivity and fast analysis speed. The absorbance (a) is directly proportional to the concentration (c) of elements in the sample. That is, A=KC, where k is a constant. Accordingly, by measuring the absorbance of the standard solution and the unknown solution, the concentration of the standard solution can be used as a standard curve to obtain the concentration of the elements to be measured in the unknown solution. 2.4 Calculation of analytical results of atomic absorption spectrometry: Standard curve method, standard addition method, internal standard method, etc. Among them, standard curve method and standard addition method are widely used. The standard curve method is used for samples with non-interference components. Standard addition method, also known as incremental method or linear extrapolation method, is a commonly used determination method to eliminate matrix interference and is used for the analysis of a small number of samples. In this paper, the standard curve method is adopted. The method is to prepare a series of standard solutions with different concentrations, analyze them from low concentration to high concentration in turn, and make a standard curve of absorbance versus concentration. Under the same conditions, determine the absorbance of the sample to be tested, and find the corresponding concentration value on the standard curve. This method should pay attention to the following points: ① The concentration of the prepared standard solution should be in the range of linear relationship between absorbance and concentration. ② The pretreatment methods of standard solution and sample solution are the same. ③ Blank value should be deducted. ④ The operating conditions should remain unchanged during the whole analysis. 3. Selection of conditions for determination of tin by atomic absorption spectrometry The determination of tin by atomic absorption spectrometry is a method to measure the absorption degree of characteristic vibration spectrum of tin radiated by light source based on the ground state atoms of tin. Atomic fluorescence analysis is to determine the content of tin by measuring the fluorescence emission intensity of tin vapor excited by radiant energy. The most sensitive absorption line wavelength of tin is 224.6nm, and the less sensitive absorption line wavelengths are 286.3, 284.0 and 270.6nm. The determination of tin content in ore by flame atomic absorption spectrometry is that tin -TOPO-MIBK is sucked into nitrous oxide-acetylene flame at the wavelength of 286. 3 nm。 Selection of optimum conditions for determination of tin by atomic absorption spectrometry: (1) Selection of absorption wavelength: The * * * vibration line of this element is usually selected as the analysis line. (2) Selection of working conditions of the hollow cathode lamp: The preheating time of the hollow cathode lamp should be longer than 65438 05 minutes, and the sharp light energy radiated is stable. The working current of the lamp is 40% ~ 60% of the maximum working current of (5 ~ 10 mA). (3) Selection of operating conditions for flame atomization: In order to maintain high atomization efficiency, the lifting amount of test solution is about 4 ~ 6 ml per minute, and the atomization rate reaches 65,438 00%. Select the appropriate flame according to the properties of the measured elements. In order to improve the measurement sensitivity, the height of the burner flame and its angle with the incident optical axis can be properly adjusted. (4) Selection of spectral passband: the spectral passband is usually 0. 1 ~ 5 mm..(5) Selection of negative high voltage of photomultiplier tube: the working voltage is about 1/3 ~ 2/3 of maximum working voltage, maintaining good stability and high signal-to-noise ratio. ? Interference of atomic absorption spectrometry and its elimination: Interference effects in atomic absorption spectrometry can be roughly divided into spectral interference, ionization interference, chemical interference, physical interference and chemical interference according to their nature and reasons. 4. 1 Spectral interference: (1) Near the measuring wavelength, there are adjacent lines of the element to be measured that cannot be separated by the monochromator-reduce the slit width (2) There are radiation of the non-element to be measured that cannot be separated by the monochromator in the lamp-High-purity element lamp (3) The analysis line of the element to be measured may be very close to the absorption line of the storage element-select another analysis line. 4.2 Ionization interference: interference caused by ionization of the element to be measured during high-temperature atomization (mainly existing in flame atomization) and: ① Ionization potential of the element to be measured-generally: ionization potential.