Fourier-transform infrared spectroscopy absorbance subtraction

Fourier transform infrared spectroscopy FT-IR. The measurement of individual degradation products with FT-IR is very simple, quick and precise. A reference sample spectrum of new oil is required to subtract electronically from the oil sample spectrum. The spectra of the fresh oil and the used oil sample are obtained individually in the same cell. The results - both spectra and the "differential" spectrum are stored in the computer in absorbance format, a form that varies linearly with concentration. 

Micro-Fourier transform infrared (FT-IR) spectroscopy was employed to examine the chemical structures by observing absorption bands at 1716 cm 1 (carbonyl group), 964 cm"1 (trans- inylene) and 910 cm 1 (end-vinyl). After 2 months from the irradiation, samples were sliced into 100-150 pm films along the direction of ion-beam penetration and the FT-IR spectra were measured as a function of depth from the surface [6]. We obtained the net absorbance AAbs. for the three bands for carbonyl group, /raws-vinylene and end-vinyl at each depth by subtraction of the measured spectrum from that of the unirradiated sample. Sliced samples were stored in the dark at room temperature. They were repeatedly measured after 4, 6 and 12 months from the irradiation to observe the effect of long-term storage. 

ATR spectroscopy in the infrared has been used extensively in protein adsorption studies. Transmission IR spectra of a protein contain a wealth of conformational information. ATR-IR spectroscopy has been used to study protein adsorption from whole, flowing blood ex vivo 164). Fourier transform (FT) infrared spectra (ATR-FTIR) can be collected each 5-10 seconds165), thus making kinetic study of protein adsorption by IR possible 166). Interaction of protein with soft contact lens materials has been studied by ATR-FTIR 167). The ATR-IR method suffers from problems similar to TIRF there is no direct quantitation of the amount of protein adsorbed, although a scheme similar to the one used for intrinsic TIRF has been proposed 168) the depth of penetration is usually much larger than in any other evanescent method, i.e. up to 1000 nm water absorbs strongly in the infrared and can overwhelm the protein signal, even with spectral subtraction applied. 

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