Basic Principles
Atomic absorption spectroscopy is used for quantitative analysis of elements based on the absorption characteristics of ground state atoms towards specific wavelengths of light. When the characteristic spectral lines emitted by the light source pass through the atomic vapor of the element under test, if the energy corresponding to the radiation wavelength is equal to the energy required for the ground state atom to transition to the excited state, the atom will absorb the light of that characteristic wavelength, and the outer electrons will transition from the ground state to the excited state. By measuring the degree of intensity reduction of characteristic spectral lines after absorption, combined with Lambert Beer's law (A=KCL, where A is the absorbance, K is a constant, C is the sample concentration, and L is the optical path length), the content of the element to be measured in the sample can be determined. This method has the characteristics of high sensitivity, strong selectivity, and high accuracy, and is suitable for trace and trace element analysis.
Optical System Design
The optical system is the core of an atomic absorption spectrometer, consisting of four modules: light source, atomizer, spectrometer, and detector
Light source: Hollow cathode lamps or electrodeless discharge lamps are used as sharp line light sources, emitting characteristic spectral lines that highly match the absorption lines of the tested element. For example, a lead hollow cathode lamp emits 283.3nm characteristic light with a half width of only 0.002nm, ensuring energy concentration on the target absorption line and avoiding background interference.
Atomizer: Convert the sample into gaseous ground state atoms. The flame atomizer atomizes and dissociates the sample using high-temperature gas (such as acetylene air flame with a temperature of 2300 ℃); The graphite furnace atomizer uses programmed heating, which is divided into three stages: drying, ashing, and atomization. The sample is heated to 3000 ℃ to achieve high-sensitivity detection of trace elements (such as 0.001 μ g/g cadmium).
Spectral system: With a grating as the core, the composite light is decomposed into monochromatic light through diffraction effect. The combination of mid step grating and prism cross dispersion technology can achieve a resolution of 0.001nm in the wavelength range of 190-900nm, accurately separating the absorption lines of the tested elements from adjacent interference lines.
Detector: Photomultiplier tube (PMT) is the core of traditional detectors. Its photocathode receives monochromatic light and emits photoelectrons, which are amplified by multi-stage multiplier electrodes and ultimately output an electrical signal inversely proportional to the light intensity, meeting the requirements of ppb level trace analysis.