The optical path system and signal processing flow of an atomic absorption spectrophotometer are the core of achieving high-precision metal element detection. Its complete process can be divided into four major steps: optical path conduction, atomic absorption, spectral separation, and signal conversion.
In the stage of optical path conduction, the light source system uses a hollow cathode lamp to emit a characteristic wavelength beam corresponding to the element to be tested (such as lead element emitting 283.3nm characteristic light). The light beam is refracted by the reflector and enters the atomizer. During this process, the optical path is adjusted to parallel light by the collimating mirror to ensure concentrated energy transmission.
In the atomic absorption stage, the sample is converted into ground state atomic vapor in the atomizer. When the characteristic beam passes through atomic vapor, the ground state atoms selectively absorb light of a specific wavelength, resulting in a decrease in light intensity. For example, in copper element detection, the ground state copper atoms absorb 324.8nm characteristic light, which reduces the transmitted light intensity.
In the spectral separation stage, the attenuated beam enters the Cherny Turner monochromator and is diffracted and separated by 1800/mm high-precision gratings. The monochromator only allows the characteristic wavelength of the tested element to pass through (with a bandwidth adjustable to 0.1nm), effectively eliminating interference from other wavelengths of light and ensuring detection specificity.
In the signal conversion stage, the photomultiplier tube converts the transmitted light signal into an electrical signal, with a gain of up to 10-10 times, which can capture weak changes in light intensity. The electrical signal is input into the computer after analog-to-digital conversion, and the system calculates the absorbance value based on Lambert Beer's law (A=KCL), where A is the absorbance, K is the molar absorptivity, C is the sample concentration, and L is the optical path length. Determine the metal element content in the sample using the standard curve method or standard addition method.
This system achieves high selectivity through grating spectroscopy and combines with photomultiplier tubes to enhance detection sensitivity (flame detection limit up to 0.004 μ g/L). It can accurately determine more than 40 elements in geological samples and is widely used in environmental monitoring, food testing, metallurgical analysis and other fields.