Interpretation of technical terms in spectral photometric analysis

Spectral analysis is a method to identify substances and determine their chemical composition and relative content according to their spectra. This is an analytical method based on molecular and atomic spectra.

Its advantages are sensitivity and rapidity. Many new elements such as rubidium, cesium and helium have been discovered through spectral analysis in history.

According to the analysis principle, spectral analysis can be divided into emission spectral analysis and absorption spectral analysis. According to the morphology of the tested components, it can be divided into atomic spectrum analysis and molecular spectrum analysis. Spectral analysis is called atomic spectrum when the measured component is an atom, and molecular spectrum when the measured component is a molecule.

Physical principles:

Atoms of any element are composed of nucleus and electrons moving around the nucleus, and electrons outside the nucleus are distributed in layers according to their energy levels, forming different energy levels. Therefore, a nucleus can have multiple energy levels.

The energy level state with the lowest energy is called the ground state (E0=0), the remaining energy levels are called the excited state, and the excited state with the lowest energy is called the first excited state. Under normal circumstances, the atom is in the ground state, and the electrons outside the nucleus move in their respective orbits, with the lowest energy.

If the ground state atom is provided with certain external energy, such as light energy, when the external light energy E is exactly equal to the energy level difference E between the ground state atom and the higher energy level in the ground state atom, the atom will absorb the light with this characteristic wavelength, and the outer electrons will transition from the ground state to the corresponding excited state. After splitting, some characteristic spectral lines are missing from the spectral lines of the original energy-supplying light, resulting in atomic absorption spectra.

After the electrons jump to a higher energy level, they are in an excited state, but the excited electrons are unstable. After about 10-8 seconds, the excited electrons will return to the ground state or other lower energy levels, and the energy absorbed during electron transition will be released in the form of light. This process is called atomic emission spectroscopy.

It can be seen that the atomic absorption spectrum process absorbs radiant energy, while the atomic emission spectrum process releases radiant energy.