The magnitude of the interference depends on the degree of overlap of the absorption lines, the concentration of the interfering elements and their sensitivity. Theoretical studies and experimental results are indicated when the wavelength difference of the absorption lines of the two elements is less than 0.03 nm. It is considered that the absorption interference of the absorption line of the atomic absorption spectrophotometer is serious. If the overlapping absorption lines are sensitive lines, even if the interference is 0.1 nm, the interference will be clearly indicated. Of course, this interference is also related to the concentration of the interfering elements and the resolution of the monochromator. There are some lines, theoretically overlapping lines, but no interference is observed in the experiment. It is possible that the interfering element has low atomization efficiency under the measurement conditions and fails to generate sufficient ground state atoms, and the absorption line sensitivity of these interfering elements may be low, so it is not normally indicated. Eliminating this interference is generally the use of other analysis lines or pre-separation of interference elements.
And easy to overcome, although the interference in atomic absorption analysis is relatively small. But in many cases it cannot be ignored. In order to get the correct analysis results, the source and elimination of the interference is very important.
1 physical interference and its elimination method
During evaporation and atomization, physical interference refers to the left shift of the sample. The effect of changes in the intensity of the atomic absorption signal due to any change in the physical properties of the sample. Physical interference is non-selective interference.
1.1 Reasons for physical interference
Then affect the rate of suction and thus affect the amount of fog and atomization. The inner diameter and length of the capillary as well as the flow of air also affect the rate of suction. The change in the external tension and viscosity of the sample will affect the fineness of the droplet, the solvent removal efficiency and the evaporation efficiency, and the final effect on the atomization efficiency. When a large amount of matrix elements are present in the sample, the evaporation and dissociation in the flame does not only consume a large amount of heat, but in the evaporation process, it is possible to wrap the element to be tested, delay the evaporation of the element to be tested, and affect the atomization efficiency. Physical interference is generally negative interference, and Zui ultimately affects the density of atoms in the flame analysis volume. In flame atomic absorption, any change in the properties of the sample solution directly or indirectly affects the efficiency of the atomic class. When the viscosity of the sample changes.
1.2 Method of eliminating physical interference
To ensure the accuracy of the analysis, in order to eliminate physical interference, the following methods are generally used:
This is a common method used by Zui. a Prepare a standard solution consistent with the liquid matrix to be tested.
A standard addition method is required. b When it is difficult to prepare a standard solution that is consistent with the liquid matrix to be tested.
Diluted solutions can be used to reduce or eliminate physical interference. c When the measured element is at a higher concentration in the test solution.
2. Spectral interference and its elimination method
It should be a resonant emission line with only the light source and an absorption line corresponding to the wavelength in the selected spectral passband. Spectral interference in atomic absorption spectrometry is much less than atomic emission spectroscopy when there is more than one absorption line or spectral passband in the spectral passband. Ideal atomic absorption. The sensitivity is reduced and the linear range of the working curve is narrowed. When the test liquid contains two elements whose absorption lines overlap, no matter which one is measured, interference will occur.
More than one absorption line in a spectral passband
More transition elements. If the wavelength difference between the multiple absorption line and the main absorption line is not very small, the interference of the multiple lines is overcome by reducing the slit. However, the wavelength difference is many hours. It is still difficult to eliminate the interference by reducing the slit, and the signal-to-noise ratio may be greatly reduced. In this case, the line is not selected. If there are several emission lines of the light source in the spectrum, and the measured elements absorb the radiation of these kinds of radiation, this causes interference. It is also called multiple line interference.
b spectrum passband memory in the non-absorption line emitted by the light source
The non-absorption line may be the line of the element to be tested, and the non-absorption line of the element to be tested appears in the spectral passband. It may also be the line of other elements. The interference generated at this time reduces the sensitivity and bends the working curve. There are several reasons for this interference:
1 Elements with complex spectra emit themselves spectral lines that are difficult to separate by the monochromator;
2 multi-element hollow core cathode lamps have non-absorption interference due to the complexity of the emission line;
3 non-absorption interference caused by impurities in the cathode material of the light source;
The spectral passband is made small enough to separate the non-absorptive line, and the non-absorptive interference caused by the radiation of the inert gas filled by the light source. A common method of overcoming this interference is to reduce the slit width. But it makes the signal to noise ratio worse. At this time, other analysis lines can be used, although the sensitivity is lower, but a larger spectral passband is allowed, which is advantageous for improving the signal-to-noise ratio.
3 absorption line overlap interference
This interference makes the result too high. When the absorption line of the analysis element and the absorption line of the coexisting element completely overlap, adjacent line interference occurs when the absorption line of two or more atoms in the flame overlaps with the analysis line emitted by the light source. When the content of the analytical element is very low, only the absorption signal of the coexisting element is measured. When the center position of the analysis line of the analysis element and the center position of the absorption line of the coexisting element are slightly deviated, there is still a considerable degree of overlap, and a large part of the absorption signal obtained at this time is still a coexisting element when the coexisting element occurs. When the absorption lines of the absorption line and the analysis element overlap slightly, a small part of the absorption signal is a coexisting element. Only the absorption line of the analysis element and the absorption line of the coexisting element are completely separated, and the coexisting element does not interfere. Co253.649 interference to Hg253.652r is a typical absorption line overlap interference.
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