Atomic Absorption Spectroscopy: An analytical method based on the absorption of ultraviolet and visible light by the outer electrons of the ground state atom of the gaseous state. (A method for quantitative analysis of elements based on the absorption of atomic vapor generated by a substance on a characteristic line (usually a characteristic line of an element to be tested).
Atomic Emission Spectroscopy: Atomic Emission Spectroscopy is the measurement of the chemical composition of a substance based on the spectrum emitted by the atom. Spectral analysis is to identify the presence of elements (qualitative analysis) from the characteristic spectra of the identified elements, and the intensity of these spectral lines is related to the content of the elements in the sample, so the intensity of these lines can be used to determine the content of the elements. (Quantitative analysis). This is the basic basis for emission spectroscopy.
Atomic Fluorescence Spectroscopy: An emission spectrometric method for quantitative analysis of the intensity of fluorescence emitted by an atom under the action of optical radiant energy.
The difference and connection between the three
Similarities
1. From the principle, the frequency involved in the transition between the corresponding energy levels is the same;
2, both involve the atomization process, and its evaporation, atomization and other conditions are similar.
3. The intensity of absorption or emission has similar or identical dependence on elemental properties, spectral properties and external conditions.
the difference
1. AAS is mostly limited to resonance absorption, and the spectral line is relatively simple; AFS is more limited to the resonant line with higher intensity, and the spectral line is simpler.
2. Different principles, different production methods, different temperatures, different instrument structures, different operating conditions, different analysis objects and purposes.
Can be simple / approximate: 1, flame AAS advantages: precision, high accuracy, simple operation; disadvantages: sample consumption, can not be multi-element analysis; 2, electric AAS and AFS advantages: absolute detection limit is low, The sample consumption is small, but the accuracy is poor. 3. The classical arc method AES mainly has good multi-element simultaneous analysis ability, and others are not prominent enough. 4. ICP advantages: high precision and accuracy, multi-element analysis, linearity is divided into width and AFS (less than 1.0ng / g); 2, flame AAS (1 ~ 104ng / mL) 3, ICP (1 ~ 100ng / mL) 4, arc AES (1 ~ 103ng / g)
Comparison of analytical objects: 1. AAS and AFS have good detection limits for easily ionized alkali metals, volatile Zn and Cd, and poor detection limits for Zr, Hf, Ta, Nb and rare earth elements; 2. ICP is sensitive The elements of the ion line (such as Zr above) have good detection limits. The detection limit of the easily ionized alkali metal; 3, the arc AES is similar to the flame AAS, but the ionization element is not as good as the flame method, and the detection limit of the atomic element which is difficult to volatilize is better than the flame method.
Characteristics of atomic absorption spectrometry
High sensitivity: flame atom method, ppm level, sometimes up to ppb level; graphite furnace up to 10-9~10-14 (ppt level or lower);
High accuracy: FAAS's RSD can reach 1~3%. The measurement range is wide and 70 elements can be measured.
Limitations: Difficulties in simultaneous determination of multiple elements; refractory elements (such as W), non-metallic elements are difficult to measure, and interference with complex samples is also severe; graphite furnace atomic absorption analysis is less reproducible.
Characteristics of atomic emission spectroscopy
High sensitivity (10-3~10-9g); good selectivity; can analyze dozens of elements at the same time; linear range is about 2 orders of magnitude. If an inductively coupled plasma source is used, the linear range can be extended to 6 to 7 orders of magnitude, allowing direct analysis of high, medium and low levels of components in the sample. Qualitative analysis is available, which is superior to atomic absorption. Disadvantages: 1). In the classical analysis, there are many factors affecting the intensity of the line, especially the influence of the sample components is significant, so the requirements for the standard reference components are higher. 2). When the content (concentration) is large, the accuracy is poor. 3). It can only be used for elemental analysis, and the structure and morphology cannot be measured. 4). Most non-metallic elements are difficult to obtain sensitive spectral lines.
Characteristics of atomic fluorescence spectrometry
High sensitivity and low detection limit. High-intensity light source can further reduce the detection limit; less spectral interference, can be made into non-dispersive AFS; wide range of calibration curve (3~5 orders of magnitude); easy to make multi-channel instruments - simultaneous determination of multiple elements; fluorescence Quenching effect, complex matrix effect, etc. can reduce the sensitivity of measurement; disperse light interference; few elements can be measured, and the application is not extensive (the main applications of AES and AAS are widely used, compared with them, AFS has no obvious advantage) . Most people say that there are more atomic fluorescence and atomic absorption. Almost every laboratory will be equipped with these two instruments, and most of them are arranged in a laboratory. What is the difference between the two?
The difference between atomic fluorescence and atomic absorption
1, the light path is different:
The atomic absorption source, the atomizer, and the detector are on one optical path; the atomic fluorescence is a vertical path.
2, the principle is different:
Atomic absorption utilizes the characteristic absorption spectrum of an atom; atomic fluorescence utilizes the excitation-transition spectrum (fluorescence) of an atom.
3. Different sensitivity:
For atomic absorption, increasing the intensity of the light source will increase the background absorption, and the intensity of the atomic fluorescence signal is proportional to the intensity of the excitation source, so the sensitivity can be greatly improved.
In general, the atomic fluorescence detection project has limitations in its use, and it is now only possible to detect eleven elements such as arsenic and mercury. The detection surface of atomic absorption is relatively wide. Atomic fluorescence in most laboratories has so far only detected both arsenic and mercury. The remaining heavy metals are either atomic absorption or graphite furnaces. This is the biggest flaw in atomic fluorescence. It can only detect elements that are capable of generating gaseous hydrides at room temperature and can emit fluorescence, so the elements are limited, but coincidentally, those elements are important, and it is very laborious to use atomic absorption to detect them, so there is a promotion value. . Atomic absorption belongs to the absorption spectrum. Although atomic fluorescence is similar in structure to atomic absorption, atomic fluorescence belongs to the emission spectrum, but it belongs to photoluminescence. This is the difference in principle.
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