Test methods and key points of X-ray fluorescence spectrometer are introduced in detail
- Source: Unknown
- Date: 2021-04-28
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X-ray fluorescence spectrometer is a common type of spectrometer, which has the advantages of good reproducibility, fast measurement speed, high sensitivity, good stability and so on. Users need to master the test methods and key points when using the X-ray fluorescence spectrometer, which is helpful for users. Here are the test methods and key points of the X-ray fluorescence spectrometer, hoping to help you.
1、 Test method of X-ray fluorescence spectrometer:
1. Sample preparation for X-ray fluorescence spectrometer
The samples for X-ray fluorescence spectrum analysis can be solid or aqueous. Whatever the sample, the sample preparation has a great influence on the determination error. For metal samples, attention should be paid to the mistakes caused by component segregation; With the same chemical composition, samples with different heat treatment processes have different counting rates; Metal samples with nonuniform composition shall be remelted and rapidly cooled to form discs; The sample with uneven surface shall be polished; For the powder sample, grind it to 300 mesh - 400 mesh, and then press it into a disc, or put it into the sample tank for determination. If the solid sample cannot get a uniform and flat surface, the sample can be dissolved with acid and then precipitated into salt for determination. The liquid sample can be dropped on the filter paper, evaporated with an infrared lamp, and then measured, or sealed in the sample tank. In a word, the tested sample shall not contain water, oil, volatile components, nor corrosive solvents.
2. Qualitative analysis of X-ray fluorescence spectrometer
Fluorescent x-rays of different elements have their own specific wavelength or energy, so the composition of elements can be determined according to the wavelength or energy of fluorescent x-rays. If it is a wavelength dispersive spectrometer, for the crystal with a certain spacing between crystal planes, the wavelength of the x-ray can be calculated from the 2e angle rotated by the detector, so as to determine the element composition. For the energy dispersive spectrometer, the energy can be judged by the channel, so as to determine what kind of elements and components are. However, if the element content is too low or there is spectral line interference between elements, manual identification is still required. First, the characteristic x-ray of the x-ray tube target and the accompanying line of the strong peak are identified, and then the residual spectral lines are marked according to the energy. When analyzing unknown spectral lines, the source, nature and other elements of the sample should be considered at the same time for comprehensive judgment.
3. Quantitative analysis by X-ray fluorescence spectrometer
The basis for quantitative analysis by X-ray fluorescence spectrometry is that the fluorescent x-ray intensity ii of the element is proportional to the content ci of the element in the sample: ii=is × ci, where is is ci=100%, the fluorescent x-ray intensity of the element. According to the above formula, standard curve method, incremental method, internal standard method, etc. can be used for quantitative analysis. However, these methods should make the composition of the standard sample and the sample as the same or similar as possible. Otherwise, the matrix effect of the sample refers to the influence of the basic chemical composition of the sample and the changes in the physicochemical state on the X-ray fluorescence intensity. The change of chemical composition will affect the absorption of the sample to the primary x-ray and x-ray fluorescence, and will also change the fluorescence enhancement effect. For example, in the determination of elements such as fe and ni in stainless steel, nika fluorescent x-ray will be generated due to the excitation of a single x-ray, and nika may be absorbed by fe in the sample, so that fe will be excited to generate feka. When determining ni, the result is lower because of the absorption effect of fe, and higher because of the fluorescence enhancement effect when determining fe.
2、 Importance of correctly establishing application oriented standard sample for X-ray fluorescence spectrometer
From the above, we know that the standard sample should be as same as the actual test sample. However, in fact, the standard samples of general standard sample companies, in order to ensure their market universality, mostly deviate from the actual testing materials. This has greatly affected the use of the X-ray fluorescence spectrometer, and sometimes the measured value deviates dozens or even hundreds of times. According to the theory of x-ray fluorescence spectrometer, it is possible to carry out relatively more accurate quantitative analysis. Users of many devices are small and medium-sized enterprises, and it is often impossible to afford the more expensive and expensive icp_oes. How to give full play to the best performance of hundreds of thousands of devices is the most urgent concern of their users.
In fact, application oriented standard samples are classified according to the identity of their main components according to the materials they need to test, and several groups of standard samples with different contents of hazardous substances need to be tested are established. Since the components of this standard sample and the actual product are basically the same, the degree of segregation is very small. During sample testing, the data with small deviation can be accurately measured. To a certain extent, it increases the certainty of detection. Ensure that user detection is high and accurate.
3、 How to establish application oriented standard sample for X-ray fluorescence spectrometer
How to establish application oriented standard samples? It can be implemented in the following steps:
1. First, classify the sample materials to be tested by the user, and divide the samples of different materials into different categories.
2. Materials of the same kind shall be classified according to their base materials and main components.
3. Materials with the same base material shall be normalized and classified according to their main components.
4. Confirm that the component difference of the normalized material is controlled within the allowable range, and confirm that there should be no uncertain characteristic interference elements affecting the spectral line, or classify according to the supplier.
5. On the basis of steps 1-4 (users can choose which step to go to according to their own needs for accuracy and operability), the final subdivided categories are quantitatively analyzed with instruments such as icp_oes and gc_ms for the main components, related components and components to be tested. According to the content of the component to be measured, a certain amount of the element to be measured can be added manually. In order to ensure the stability of the added element, its stable compound should be added as far as possible. The standard sample of the given classification material is thus established, and the standard curve is established on the X-ray fluorescence spectrometer using the standard sample.
6. According to the needs of users, the types of standard samples are constantly expanded, and the corresponding material number or user number is used for the corresponding material user, so that the operator can accurately use the corresponding standard curve to test this type of material.
