Measurement principle and our measuring range |
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The measurement principle of an IR spectrometer lies in the absorption of infrared light by IR-ACTIVE molecules. The more these molecules are present, the more lights one swallows. The infrarotspektrometer permits therefore only the proof of IR-ACTIVE molecules, what concerns nearly all organic compounds and a multiplicity of inorganic compounds. |
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Range Wavecount [cm-1] Wavelength [µm] Close infrared 13300 ... 4000 therefore 0.75 ... 2.5 Middle infrared 4000 ... 400 therefore 2.5 ... 25 Far infrared 400 ... 10 therefore 25 ... 1000 |
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For the analytic spectroscopy the middle infrared is the most useful range. The infrared theory means that a molecule can absorb infrared radiation by suggestion of oscillation and/or rotation conditions. If a sample with infrared radiation of a far wavelength coverage is through-radiated, the energy is absorbed with certain frequencies. The system is: Source of infrared optical system detector |
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The appropriate range, wavelength can be represented exactly: | |||||||||||
This measuring method began in such a way: | |||||||||||
Today the measuring instruments look in such a way: |
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Here as example a Perkin Elmer | |||||||||||
One can measure evenly very much with the equipment. But for each application the sample is to be prepared accordingly. To select the correct absorption cell and to look for then the appropriate wavelength. With our IR spectrometer of the OMS-Systems we developed an analytic unit, which considers only a certain range. We look only for oil in the sample. In the technical language NDIR method. The task is to be found first the total hydrocarbon in the sample. But we adjusted our devices to the following wavelength: CH - Bande 3030 cm-1 or 3,30 µm CH2 - Bande 2924 cm-1 or 3,42 µm CH3 - Bande 2958 cm-1 or 3,38 µm Of course also can our analysis unit (optical bank) be when desired in such a way laid out that it the CH? Ranges (aromatics) filter. Then the equipment recognizes only the CH2/CH3 gang By the exact design of our IR spectrometer we can automate the entire process. The risk, which error rate in the sample preparation likewise minimized, since also this equal necessity with one automated. Of course also the possibility exists other certain desired wavelengths, which an IR spectrometer can seize, to adjust into our analysis unit particularly. |