Fourier transform infrared (FTIR) spectroscopy is a form of vibrational spectroscopy that is useful in the study of a variety of soil chemical processes. FTIR spectroscopy is preferred over dispersive method of IR spectral analysis for several reasons:  It is a non-destructive technique. Also, one can use the unique collection of absorption bands to confirm the identity of a pure compound or to detect the presence of specific impurities. Principle of FTIR spectroscopy. An FTIR spectrometer simultaneously collects high-resolution spectral data over a wide spectral range. [13] FTIR method uses the maxima of the absorbance band at about 5,200 cm−1 which correlates with the true water content in the material. The Michelson–Morley showed that the speed of light is the same in all directions; a … PART ONE THEORY AND OPERATION PRINCIPLE OF FTIR SPECTROMETER 1. Underlying principal of infrared spectroscopy is based upon the molecular vibration which is further composed of the stretching and the bending vibration of a molecule. Systems where the path difference is generated by a rotary movement have proved very successful. A typical instrument was the cube interferometer developed at the NPL[9] and marketed by Grubb Parsons. FTIR can be used in all applications where a dispersive spectrometer was used in the past (see external links). With the advent of cheap microcomputers it became possible to have a computer dedicated to controlling the spectrometer, collecting the data, doing the Fourier transform and presenting the spectrum. Fourier transform infrared spectroscopy is used in geology, chemistry, materials and biology research fields. In a Michelson interferometer adapted for FTIR, light from the polychromatic infrared source, approximately a black-body radiator, is collimated and directed to a beam splitter. Principles of FTIR Spectroscopy. In a FTIR spectrophotometer, monochromatic light (632.8 nm) from a He-Ne laser is used, together with a moving mirror, and the intensity of the output interference signal is measured as a function of time. For example, with one point per wavelength of a HeNe reference laser at 0.633 μm (15800 cm−1) the shortest wavelength would be 1.266 μm (7900 cm−1). The wavelength accuracy or Connes' advantage. There, the light is focused on the sample. cannot be more than a few tens of microns. Principle of FTIR is based on the bonds and the groups of bonds vibrates at some characteristic frequencies. Infrared spectroscopy is the study of interactions between matter Infrared spectrum is molecular vibrational spectrum. Another minor advantage is less sensitivity to stray light, that is radiation of one wavelength appearing at another wavelength in the spectrum. Types 4. A quite different approach involves moving a wedge of an IR-transparent material such as KBr into one of the beams. FTIR spectroscopy offers a vast array of analytical opportunities in academic, analytical, QA/QC and forensic labs. The difference between successive retardation values is constant. Uncooled indium gallium arsenide photodiodes or DTGS are the usual choices in near-IR systems. The form of the interferogram when no sample is present depends on factors such as the variation of source intensity and splitter efficiency with wavelength. The images contain a spectrum for each pixel and can be viewed as maps showing the intensity at any wavelength or combination of wavelengths. The Fourier transform converts one domain (in this case displacement of the mirror in cm) into its inverse domain (wavenumbers in cm−1). One notable exception is to measure chain branching as a function of molecular size in polyethylene using gel permeation chromatography, which is possible using chlorinated solvents that have no absorption in the area in question. 7  Frequency spectrum obtained from interferogram. This process is rapidly repeated many times over a short time span. This requires it to be stored in digital form as a series of values at equal intervals of the path difference between the two beams. However, as time passes (the mirror moves), destructive interference occurs and the signal strength gradually converges to zero. The wavelength scale is calibrated by a laser beam of known wavelength that passes through the interferometer. This technique then measures how much of that beam is absorbed by the sample. In FTIR spectroscopy, an interference wave is synthesized from two beams separated by a beam splitter, the detected interference waveform (interferogram) is Fourier-transformed, and a spectrum is obtained by separating each wavenumber. Principle of UV Spectroscopy Basically, spectroscopy is related to the interaction of light with matter. Fig. is to measure how much light a sample absorbs at each wavelength. This is the spectral resolution in the sense that the value at one point is independent of the values at adjacent points. Fourier-transform spectroscopy is a less intuitive way to obtain the same information. To measure the path difference a laser beam is sent through the interferometer, generating a sinusoidal signal where the separation between successive maxima is equal to the wavelength of the laser (typically a 633 nm HeNe laser is used). FTIR Analysis measures the infrared region of the electromagnetic radiation spectrum, which has a longer wavelength and a lower frequency than visible light, and is measurable in a sample when submitted to infrared radiation (IR). This confers a significant advantage over a dispersive spectrometer, which measures intensity over a narrow range of wavelengths at a time. FTIR analysis is used to determine water content in fairly thin plastic and composite parts, more commonly in the laboratory setting. In 1966 Connes measured the temperature of the atmosphere of Venus by recording the vibration-rotation spectrum of Venusian CO2 at 0.1 cm−1 resolution. This so-called centerburst is not always symmetrical in real world spectrometers so a phase correction may have to be calculated. As mentioned, computer processing is required to turn the raw data (light absorption for each mirror position) into the desired result (light absorption for each wavelength). 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