I Want to take IR spectra of sample compounds. For FTIR, KBR disc sample prepararion step can be skipped by using ATR instead, i want to to know the scientic feasibilty and validity of the ATR method compared to FTIR.
Dear Mohammad,
I believe You should not be afraid using ATR technique instead transmission. The nature of ATR is the light absorption when the electromagnetic wave penetrates to the sample in a distance of approximately one half of wavelength, so ATR spectra are very similar to classical transmission spectra obtained with KBr pellet method. The feature of ATR spectra is the intensity dependence on the wavelength, so the absorbance in short wavelength region is underesimated when compared with long wavelength. This effect can be easily compensated with so called ATR correction which performs automatically by the spectrometer software. After such correction its difficult to find the difference between ATR and transmission spectra, although the spectral bands can be shifted in 1-2 cm-1 which is camparable with sampling points interval. If You want to use ATR for quantification purposes, You should take into account the poorer repeatability of method because of the difficulty to make a constant pressure and reproducible contact of the sample with the surface of ATR element.
ATR is an accessory that is placed into an FTIR instrument. Depending on your application there are a variety of different ATR crystals that you can choose from.
Please find attached book. It explains the fundamental differences between atr-ftir and standard ftir.
When interpreting ATR-FTIR spectra where quantitative results are important, note that non-corrected ATR spectra have much stronger absorbance bands at longer wavelengths (smaller wave numbers) than at shorter wavelengths (larger wave numbers) compared to normal FTIR transmittance spectra. The reason being that the penetration depth is dependent on (in addition to refractive indices of sample and ATR crystal, and angle of incident radiation) the radiation wavelength, and increases with increasing wavelength (decreasing wave number). Various details about the ATR-FTIR technique which may be helpful may be found in the following article (may be requested through Research Gate): B. P. Jelle, T.-N. Nilsen, P. J. Hovde and A. Gustavsen, ”Accelerated Climate Aging of Building Materials and their Characterization by Fourier Transform Infrared Radiation Analysis”, Journal of Building Physics, 36, 99-112, 2012.
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