The analysis principle of the spectrum analyzer is to absorb the characteristic spectrum of the element to be tested radiated by the light source through the ground state atoms of the element to be tested in the vapor of the sample, and the extent of the emission spectrum is weakened, thereby obtaining the content of the element to be tested in the sample. . It conforms to Langper-Beer's law A= -lg I/I o= -LgT = KCL where I is the transmitted light intensity, I0 is the emitted light intensity, T is the transmittance, and L is the light passing through the atomizer optical path due to L Is a constant value so A = KC. Physical Principles The atoms of any element are composed of nuclei and electrons moving around the nucleus. The electrons outside the nucleus are layered according to the level of their energy to form different energy levels. Therefore, a nucleus can have multiple energy levels. The lowest energy level is called the ground state level (E0 = 0), the other energy level is called the excited state level, and the lowest excited state is called the first excited state. Under normal conditions, the atoms are in the ground state, and the extranuclear electrons move in the orbit with the lowest energy. If a certain external energy, such as light energy, is supplied to the ground state atom, when the external light energy E is exactly equal to the energy level difference E between the ground state and a higher energy level in the ground state atom, the atom will absorb light of this characteristic wavelength. The outer electrons transition from the ground state to the corresponding excited state to produce an atomic absorption spectrum. After the electron transition to the higher energy level, it is in the excited state, but the excited state electron is unstable. After about 10^-8 seconds, the excited state electron will return to the ground state or other lower energy level, and will absorb the electron transition. Energy is released in the form of light, a process called atomic emission spectroscopy. It can be seen that the atomic absorption spectroscopy process absorbs radiant energy, while the atomic emission spectroscopy process releases radiant energy. Physical interference Physical interference refers to the interference effect caused by any physical factors in the transfer and evaporation process of the sample. The factors that are involved in such interference are: the viscosity of the test solution, the vapor pressure of the solvent, and the pressure of the atomizing gas. Physical interference is non-selective interference and the effects on the elements of the sample are essentially similar. Preparing a standard sample similar to the sample being tested is a common method of eliminating physical interference. Standard addition or dilution methods can be used to reduce and eliminate physical interference when the sample composition is unknown or the sample cannot be matched. Chemical interference Chemical interference refers to the interference effect caused by the chemical interaction between the element to be tested and other components. It mainly affects the atomization efficiency of the element to be tested and is the main source of interference in the atomic absorption spectrophotometry. It is due to the formation of a thermodynamically more stable compound between the atoms of the measured element in the liquid or gas phase and the composition of the interfering substances, thereby affecting the dissociation and atomization of the compound of the element to be tested. Methods for eliminating chemical interference include: chemical separation; use of a high temperature flame; addition of a release agent and a protective agent; use of a matrix modifier. Ionization interference Atomic ionization at high temperatures reduces the concentration of ground-state atoms, causing the atomic absorption signal to decrease. This type of interference is called ionization interference. The ionization effect increases with increasing temperature and increasing ionization equilibrium constant, and decreases as the concentration of the measured element increases. The addition of more easily ionized alkali metal elements can effectively eliminate ionization interference. Spectral interference Spectral interference includes spectral line overlap, non-absorption lines in the spectral passband, DC emission in the atomization cell, molecular absorption, and light scattering. When adopting the sharp line source and AC modulation technology, the first three factors can generally be disregarded, mainly considering the influence of molecular absorption and light scattering, which are the main factors that form the spectral background. Molecular absorption interference Molecular absorption interference refers to the interference caused by the absorption of radiation by gas molecules, oxides and salt molecules generated during atomization. Light scattering refers to the scattering of light by solid particles generated during atomization, so that the scattered light is deflected from the optical path and not detected by the detector, resulting in a high absorbance value. 1, argon The main function of argon blowing is to drive off the air in the spark chamber when the sample is excited, and to reduce the absorption of the ultraviolet light in the ultraviolet region. Mainly because the oxygen and water vapor in the air have a strong absorption band in the far ultraviolet region, which has a great influence on the analysis result, and is not conducive to the excitation stability, forming or strengthening the diffusion discharge, and generating white spots upon excitation. In addition, the alloying elements in the sample may react with airborne components at high temperatures to form molecular compounds, which may interfere with the atomic spectrum we require. Therefore, the purity of argon must be required to reach 99.999% or more. In addition, the pressure and flow rate of argon also have an effect on the quality of the analysis. It determines the impact of argon on the discharge surface. This excitation capability must be appropriate and too low to adequately generate oxygen during the excitation of the sample and it. The formed oxide is washed away, and these oxides agglomerate on the surface of the electrode, thereby suppressing the continued excitation of the sample; the flow rate of the argon gas is too large, causing unnecessary waste. Second, there is also a certain damage to the spectrometer. Therefore, the argon pressure and flow rate must be appropriate. According to practice, the pressure and flow rate of argon should be adjusted according to different materials. For the analysis of medium and low alloy steel, the argon pressure of the input spectrometer should reach 0.5-1.5 MPa, and the flow rate of dynamic argon should be 12-20 readings. The flow rate of static argon is 3 to 5 readings. 2, the slit The spectrometer uses a complex and sensitive optical system. The ambient temperature, humidity, mechanical vibration, and changes in atmospheric pressure of the spectrometer cause small changes in the line that cause spectral line shifts. Changes in air pressure and humidity change the refractive index of the medium, which causes the line to shift. The increase in humidity not only increases the refractive index of the air, but also corrodes the optical parts, reducing the light transmittance and humidity of the instrument. Generally should be controlled below 55% -60%. The effect of temperature on the grating mainly changes the grating constant, which causes the amplitude of the character to change, resulting in spectral line drift. These changes can cause the spectral lines to not be perfectly aligned with the corresponding exit slits, thereby affecting the analysis results. Therefore, the optical system is adjusted at least once a day if the indoor temperature control is constant. Even if the weather does not change much, adjust the slit twice a week. 3. The lens of the incident window The lens that leads to each chamber, especially the lens that leads to the air chamber, causes argon to be blown when the sample is excited, so that the dust generated when the sample is exposed is blown onto the lens to prevent the transmission of light, which affects the accuracy of the measurement result. Sex. Therefore, it should be cleaned frequently, usually twice a week, to keep it clean, to ensure that all light passes through the lens and enters the light chamber for measurement. It is especially reminded that after cleaning the lens, several waste samples should be excited, and the standardization operation should be performed after the strength is stabilized, otherwise the quality of the analysis will be affected. 4, the excitation table Cleaning the inner surface of the excitation table is mainly to avoid the influence of the dust discharge on the residual inner wall. Usually it should be cleaned once every 100-200 times. The distance between the electrode and the excitation surface must be adjusted according to the pole distance requirement. If the distance from the excitation surface is too large, the sample is not easy to be excited. If the distance between the electrode and the excitation surface is too small, the discharge current during exposure is too large, so that the discharge current is too large. Does not match the parameters of the instrument, so there is a difference between the measured results and the actual results, affecting the accuracy of the measurement. Therefore, the distance between the electrode and the excitation surface must be adjusted accurately. After cleaning the excitation stage and the electrode, this problem must be taken seriously. 5, the correction of the working curve Although the photoelectric direct reading spectrometer method is not limited by the photosensitive plate, after the working curve is drawn, the curve will change after a period of time. For example, the pollution of the lens, the contamination of the electrode, the change of temperature and humidity, the influence of argon, the fluctuation of the power supply, etc., can change the curve. The position of A in the original graph, after a period of time, the curve may drift to the position of B. In order to use the curve for analysis, we must try to restore curve B to the position of curve A. To do this, the work curve must be standardized. In the standardization of curves, the following points must be noted: (1) After cleaning the sample excitation stage, it must be excited more than 10 times or argon gas for one hour before daily standardization work can be done. (2) The standardized sample should be uniform, the sample preparation should be careful, the surface of the sample should be flat, and the grain should be cleaned. The analysis gap is accurate and the sample holder is kept clean. (3) The normalized frequency is determined according to the number of samples analyzed. Generally, it must be standardized twice a day. 6, control sample In actual work, the working curve often changes due to the metallurgical process of the sample and the standard sample and some physical conditions. Usually, the standard sample is mostly forged and rolled, and the daily analysis is cast. In order to avoid the influence of the metallurgical state change on the analysis results, it is often necessary to use a control sample with the same metallurgical state and physical state as the analytical sample to control the analysis results. The element content of the controlled sample should be within the range of the working curve. And the closer to the content of the analytical sample, the better. At the same time, the element content of the control sample should be accurate and reliable, the composition of the composition is uniform, and the appearance is free of physical defects such as pores, blisters and cracks. 7, sample The quality of the spectral analysis depends largely on the sample, and attention should be paid to the preparation and processing techniques of the sample. The lack of a flat surface due to stomatal segregation or the absence of sample placement, as well as errors due to operational errors, can have a significant impact on the quality of the analysis. Therefore sample processing must meet the following requirements: (1) The entire sample surface should be uniform (the shape is suitable for the excitation table so that the gas flushing chamber can be sealed). (2) There is no blisters. (3) Clean the scale and oil on the back of the sample to ensure good contact between the sample and the excitation table. (4) The surface of the sample should not be contaminated, and the sample should have a grain. (5) When the sample is excited, the excitation point is generally located at 1/2 of the sample radius, where the chemical composition is relatively uniform, the result is representative, and the measurement accuracy is high. In summary, through years of practice, several factors affecting direct reading spectrometry have been summarized, which have important application value for improving the quality of elemental analysis. Converters And Extenders, Video Converters And Extender,CCTV Converters And Extender Chinasky Electronics Co., Ltd. , https://www.cctv-products.com
