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How does the direct reading spectrometer choose the excitation light source?
Release time: 2019-12-20 10:42:17 Click: 624
，这些过程非常重要，是衡量元素含量是否准确的几个主要技术指标，如光谱分析的检出限，精密度和准确度等，只有放直读光谱仪的激发光源做好了，才能得到好的分析结果。 There is a partial excitation light source in the direct-reading spectrometer, which is responsible for the main processes of material vaporization, dissociation, and excitation . These processes are very important. They are several major technical indicators to measure the accuracy of element content, such as detection of spectral analysis Limits, precision and accuracy, etc., only when the excitation light source of the direct-reading spectrometer is completed, can a good analysis result be obtained.
The excitation light source has two processes. This effect is to evaporate the sample and generate the spectrum of excited atoms. These two effects occur simultaneously and together determine the intensity of the spectral line. Evaporation and dissociation of the elements in the sample will involve the physical and chemical properties of the sample components. The excitation of the evaporated element atoms is naturally related to the nature of the light source generator, and more closely related to the electrical characteristics of the generator. Therefore, it can be said that the excitation light source determines the spectral analysis method. Therefore, the understanding of the current situation of the light source is What spectrum workers need.
Because there are many types of samples for spectral analysis, different shapes of samples, different elements are difficult to be excited, etc. It is very difficult to use an excitation light source to meet various tasks for various analyses. Therefore, each type of light source has its characteristics and application range. Different types of light sources should be selected according to different analysis purposes.
Electric discharge characteristics are different from arcs. In an arc, electrode materials are vaporized into the arc column by hot evaporation, which is excited by collision between particles. Electric sparks are composed of both the conductive pipe and the vapor moment of fire of the electrode material. When the spark breaks down between the electrodes, the gas is strongly ionized in the very thin conductive pipe formed between the electrodes. 10 °～ 10A/cm2，使管道具有很高的温度（10000℃以上）。 After the pipeline is formed, the capacitor discharges through the pipeline and releases a lot of energy in a short time. The maximum current density can reach 10 ° ~ 10A / cm2, which makes the pipeline have a very high temperature (above 10000 ° C). After the pipeline is formed, it expands violently at a speed of 1 ~ 5000m / s, and the temperature of the shock wave front drops rapidly. We can hear the crackling sound of electric spark discharge.
After the electrical breakdown, the voltage drops sharply, the current density decreases, and the nature of the light source actually turns into an arc. The capacitor releases a large amount of energy in the area where the electrode surface contacts through the pipeline, so that the electrode substance appears as a luminous vapor ejected at a speed of about 10 cm / s, which is usually called a torch. Each discharge generates a new tube at a different surface on both ends of the electrode, so a torch is also generated at a different surface. Electrode diameter per unit on the electrode is about 0.2mm. In the actual analysis, exposure time of 1 ~ 2min will cause thousands of breakdowns, so the area of effect is not small. Although the temperature of the pipeline is high, the torch spray makes the electrode material intensely hot, but due to the breakdown area It is not large, the time is short, the electrode tip is not significantly hot, and the amount of material entering the discharge area per unit time is not as much as an arc.
How to choose a direct-reading spectrometer
From the perspective of quantitative analysis, the requirements for the light source are as follows:
1 . ppm 或 ppb 数量级。 High analytical sensitivity, and can analyze trace and trace element analysis, the sensitivity can reach the order of ppm or ppb .
2 . C 有小的变化时，相应的分析线强度 2 变化要大，即 dI ／ dc 要大。 The concentration sensitivity is high, that is, when there is a small change in the analysis element content C , the corresponding analysis line intensity 2 changes to be large, that is, dI / dc needs to be large.
3 ． During the excitation process, the light source should have good stability and reproducibility, which is the basic requirement to ensure the accuracy of the analysis.
4 . The matrix effect is small. When the matrix content in the sample changes, the results of analyzing elements are not affected by the matrix change. The influence of the third element, the structure of the structure, and the shape and quality of the sample are less affected.
5 . ( 积分 ) 要短，可提高分析效率和分析速度。 Pre-ignition time and exposure time ( integral ) should be short, which can improve analysis efficiency and analysis speed.