Analysis of the basic principles of atomic absorption spectroscopy

1. Generation of atomic absorption spectra

As we all know, atoms of any element are composed of atomic nuclei and electrons orbiting the nucleus. The electrons outside the atomic nucleus are distributed in layers according to their energy levels to form different energy levels. Therefore, an atomic nucleus can have multiple energy levels. The energy level with the lowest energy is called the ground state energy level (E0=0), the remaining energy levels are called excited state energy levels, and the lowest excited state is called the first excited state. Under normal circumstances, atoms are in the ground state, and the electrons outside the nucleus move in their respective lowest energy orbits. If a certain external energy such as light energy is provided to the ground state atom, when the external light energy E is exactly equal to the energy level difference ?E between the ground state and a higher energy level in the ground state atom, the atom will absorb the light of this characteristic wavelength, and the outer electrons will transition from the ground state to the corresponding excited state, and an atomic absorption spectrum will be generated. After the electrons jump to a higher energy level, they are in an excited state, but the excited state electrons are unstable. After about 10-8 seconds, the excited state electrons will return to the ground state or other lower energy levels, and release the energy absorbed during the electron transition in the form of light. This process is called atomic emission spectroscopy. It can be seen that the atomic absorption spectroscopy process absorbs radiation energy , while the atomic emission spectroscopy process releases radiation energy. The spectrum line absorbed by the extranuclear electrons from the ground state to the first excited state is called the resonance absorption line, or resonance line for short. The spectrum line emitted when the electron returns to the ground state from the first excited state is called the first resonance emission line. Since the energy level difference between the ground state and the first excited state is the smallest and the probability of electron transition is the largest, the resonance absorption line is most likely to be generated. For most elements, it is the most sensitive of all absorption lines, and the resonance line is usually used as the absorption line in atomic absorption spectroscopy analysis.

2. Principle of atomic absorption spectroscopy analysis The wavelength region of atomic absorption spectroscopy analysis is in the near-ultraviolet region. The analysis principle is to absorb the characteristic spectrum of the element to be measured radiated by the light source through the ground state atoms of the element to be measured in the vapor of sample a, and then calculate the content of the element to be measured in the sample according to the degree of attenuation of the emission spectrum. It conforms to the Lamper-Beer law A=-lgI/Io=-lgT=KCL , where I is the intensity of transmitted light, I0 is the intensity of emitted light, T is the transmittance, and L is the optical path of light through the atomizer. Since L is a constant value, A=KC.