Organic Structure Analysis and Infrared Chromatograph
When we first heard the name of the infrared chromatograph, it should be said in the chemistry textbook that it can be used to test the functional groups of organic matter. The principle is because different structures absorb infrared light to different extents, which is reflected in the spectrum. It can be used for analysis.
1.Prism and grating spectrometer
It belongs to a dispersive spectrometer. Its monochromator is a prism or a grating. It is a single-channel measurement, that is, only one narrow-band spectral element is measured at a time. After rotating the prism or grating and changing its orientation point by point, the spectral distribution of the light source can be measured.
2. Fourier transform infrared spectrometer
It is non-dispersive, the core part is a two-beam interference, commonly used is the Michelson interferometer. When the moving mirror moves, the optical path difference between the two coherent lights passing through the interferometer changes, and the light intensity measured by the detector also changes, thereby obtaining an interference pattern. After the mathematical operation of the Fourier transform, the spectrum B(v) of the incident light is obtained.
Fourier transform infrared spectrometer
The main advantages of the Fourier transform spectrometer are:
1 multi-channel measurement improves signal-to-noise ratio;
2 There is no entrance and exit slit limitation, so the luminous flux is high, which improves the sensitivity of the instrument;
3 With the laser wavelength of helium and neon as the standard, the accuracy of the wave value can reach 0.01 cm;
4 increase the moving distance of the moving mirror to improve the resolution;
5 working band can be extended from the visible region to the millimeter region, enabling the determination of far infrared spectroscopy
The various infrared spectrometers described above can measure both the emission spectrum and the absorption or reflection spectrum. When measuring the emission spectrum, the sample itself is used as the light source; when measuring the absorption or reflection spectrum, a tungsten halogen lamp, a Nernst lamp, a silicon carbon rod, and a high pressure mercury lamp (for the far infrared region) are used as the light source. The detectors used mainly include heat detectors and photodetectors. The former includes Gaolai pool, thermocouple, triglycine sulfate, triglyceride sulfate, etc.; the latter has mercury cadmium telluride, lead sulfide, and antimony telluride. Commonly used window materials are sodium chloride, potassium bromide, barium fluoride, lithium fluoride, calcium fluoride, which are suitable for the near and mid-infrared regions. A polyethylene sheet or a polyester film can be used in the far infrared region. In addition, metal coated mirrors are often used instead of lenses.
