Common analytical methods

In the qualitative analysis of X-ray fluorescence spectrum, the X-ray fluorescence emitted by the sample is split by a splitting crystal. According to Bragg equation, X-ray fluorescence with wavelength λ is incident on the crystal with spacing d, and interference can only occur if the incident angle θ satisfies the equation. That is to say, λ can be known by measuring angle θ, and the measured element can be determined by Moseler formula.

The qualitative analysis of X-ray spectrum includes the recording of sample X-ray spectrum and the identification of peak. The sample is placed in the sample room of an X-ray spectrometer, irradiated by primary X-rays, and secondary X-rays are emitted, and the secondary X-rays contain the characteristic lines of each component element of the sample. After the secondary beam is collimated and scanned, the curve of intensity changing with θ angle is actually the X-ray spectrum. Then analyze the spectral lines in the spectrogram to know the elements contained in the sample. At present, the characteristic X-rays of most elements have been accurately measured. The new X-ray fluorescence spectrometer has input all the spectral lines into the computer for storage, and the scanned spectrogram can be directly matched with the spectral lines by application software.

The spectrum of X-ray fluorescence is relatively simple, but there are some interference phenomena, so the following X-ray characteristics should be observed in the process of analyzing the spectrum:

1) Determine the intensity ratio of a series of spectral lines of each element, such as the K series characteristic spectral lines of Mo, Kα 1, Kα2, Kβ2 and Kβ3, and their intensity ratio is100: 50:14:.

2) The wavelength of spectral lines with the same name of different elements decreases with the increase of atomic number, which is because the distance between electrons and nuclei becomes shorter and the combination of electrons becomes stronger.

3) To judge the existence of an unknown element, it is best to use several spectral lines, such as Kα and Kβ, to confirm the existence of the element.

4) The interference of spectral lines should be judged from the relative intensity of peaks. If a strong peak is Cu(Kα), then the intensity of Cu(Kβ) should be 1/5 of Kα. When the intensity of Cu(Kβ) is very weak and does not conform to the above relationship, other spectral lines may overlap on Cu(Kα).

Semi-quantitative analysis of 10.3

With the continuous development of science and technology, the emerging new materials also need to be analyzed. The traditional wet chemical method is time-consuming and laborious, and the legislation of harmful elements in industrial waste increases the demand for rapid semi-quantitative analysis methods. In some cases, it is necessary to carry out nondestructive analysis on samples. When there is no suitable standard sample and the semi-quantitative analysis results can meet the requirements, further accurate quantitative analysis is not needed. Therefore, the semi-quantitative analysis method of X-ray fluorescence is gradually developed.

Qualitative analysis and semi-quantitative analysis do not need standard samples, and nondestructive analysis can be carried out. The accuracy of semi-quantitative analysis is related to the sample itself, such as the uniformity of the sample, whether the surface of the block sample is smooth, the particle size of the powder sample, etc. The accuracy of semi-quantitative analysis of different elements may be different. The accuracy of semi-quantitative analysis may be different for the same element in different samples.

The relative uncertainty of semi-quantitative analysis results of most principal elements can reach below 10% (95% confidence level), and even close to the accuracy of quantitative analysis in some cases, which can completely meet the detection tasks with low accuracy requirements.

Semi-quantitative analysis is suitable for the following situations: the accuracy is not very high; The analysis speed is required to be particularly fast (the results can be obtained within 30min minutes); Lack of suitable standard samples; Nondestructive analysis, etc.

Quantitative analysis10.3.10.3

X-ray fluorescence spectrum quantitative analysis is a relative analysis technology, which requires a set of standard sample series with known content (chemical analysis or artificial synthesis). By measuring and comparing the X-ray intensities of standard sample series and unknown samples, quantitative analysis can be made in the following ways.

(1) standard curve method

Measure a group of (generally not less than 5) standard samples similar to the analytical samples, draw the calibration curve of the relationship between the content of analytical elements in the standard samples and the X-ray intensity, and obtain the content of analytical elements in the unknown samples. When applying this method, we should pay attention to the influence of the existing elements, and if necessary, choose a suitable mathematical model to obtain the influence coefficient and make corrections.

(2) Internal standard method

For the sample that is easy to be mixed evenly after adding a certain component such as solution, the internal standard method can be adopted, that is, a certain amount of internal standard elements are added to the sample with known analytical element content as the standard sample, and the X-ray intensity ratio of analytical elements to internal standard elements in the standard sample is determined, and the calibration curve is drawn based on this intensity ratio relative to the analytical element content. Add the same internal standard and the same amount to the analysis sample, get the X-ray intensity ratio by the same method, and get the content from the calibration curve. The internal standard method is suitable for the determination of elements with content higher than 10%, and attention should be paid not to cause selective absorption, selective excitation or overlapping interference to the analytical line due to the addition of internal standard elements. The spectral lines and scattering lines of appropriate matrix elements can also be used as internal markers.

(3) Standard addition method

The standard addition method is also called incremental method, that is, a certain amount of analytical elements are added to the sample, and the content of analytical elements in the sample is obtained according to the change of X-ray intensity. Using this method, it is required that the content of analytical elements has a linear relationship with the corresponding X-ray intensity, and the increment value should not be less than 2. This method is suitable for the determination of elements with content less than 10%.

In order to obtain accurate quantitative analysis results, we should pay attention to the following points: (1) Use standard samples with reliable or verified content data; The components of standard samples and analytical samples should be as consistent as possible, and the sample preparation methods should be exactly the same; In order to eliminate the influence of * * * storage elements, the correct correction method should be selected; The content of analytical elements should not exceed the range specified in the standard sample; The drift of the instrument will lead to the displacement of the calibration curve, so before the daily analysis, the instrument should be calibrated with standardized samples.