Solvents infrared transmission characteristics

Table 7.29 Infrared Transmission Characteristics of Selected Solvents...

TABLE 7.29 Infrared Transmission Characteristics of Selected Solvents Transmission below 80%, obtained with a 0.10-mm cell path, is shown as shaded area. 

Table A-5. Infrared transmission characteristics of spectroquality solvents commonly used in infrared spectroscopy in the 2... 16 pm region (5000... 625 cm ) for 0.1 mm solvent thickness . ...

TabIe-2.7 Infrared Transmission characteristics of selected solvents and Mulling Oils... 

Table-2.7 Infrared Transmission characteristics of selected solvents and Mulling Oils (Transmission below 80% obtained with a 0-10 mm cell path is given in cm ) ...

Using matched cuvettes for solvent and analyte is seldom practical for infrared measurements because it is difficult to obtain cells with identical transmission characteristics. Part of this difficulty results from degradation of the transparency of infrared cell windows (typically polished sodium chloride) with use due to attack by traces of moisture in the atmosphere and in samples. In addition, pathlengths are hard to reproduce because infrared cells are often less than 1 mm thick. Such narrow cells are required to permit the transmission of measurable intensities of infrared radiation through pure samples or through very concentrated solutions of the analyte. Measurements on dilute analyte solutions, as is done in ultraviolet or visible spectroscopy, are usually difficult because there are few good solvents that transmit over appreciable regions of the infrared spectrum. 

The chalcogenides are all insoluble in water and other common solvents. ZnSe and CdTe have excellent transmission characteristics. The only problem with these materials is their high refractive index, which leads to high front-surface reflectance (see Section 13.2.2), so that transmission spectra of liquids held in cells fabricated from these materials often give rise to interference fringes (see Section 11.1.3). These materials aU make excellent internal reflection elements. AMTIR (amorphous material that transmits infrared radiation) is a mixture of several chalcogenides. Many optical fibers used for mid-infrared spectrometry are made from this material (see Section 15.4). 

Another useful technique for the qualitative and quantitative characterization of brushes inside porous membranes is transmission mode Fourier transform infrared (FTIR) spectroscopy [22,29]. If the membrane material does not appreciably adsorb light near the characteristic frequency of the C-H stretching peak, which is the footprint of carbon hydrogen bonds in polymer chains, then the measured FTIR absorbance peak can be used (after proper calibration) for the calculation of the amoimt of polymer inside the pore. As in the case of gravimetric analysis, transmission FTIR measurements are performed on dried solvent-free samples where the grafted chains are collapsed on the iimer pore surface. 

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