Infrared salt plates

Anderson et al. (30) have been developing a technique for weathering neat samples of suspect oils (i.e., with total absence of water) in a thin film under long-wavelength ultraviolet radiation with air passed over the surface. This technique permits convenient accelerated weathering of small samples—from approximately 1 mL in a small petri dish to 30 mg on an infrared salt plate. Under these conditions, the ultraviolet becomes an important factor in weathering, particularly in the generation of carbonyl. 

Which of the following solvents cannot be used on an infrared salt plate Explain. 

Infrared Spectra. Films of the polymer samples were prepared by casting from a DMSO or a dimethylacetamide solution unto a salt plate. These were then examined for their infrared spectral properties in a Beckman AccuLab A spectrophotometer. Basically, as the degree of substitution increased, the OH peak (3300-3A00 cm-- -) diminshed in intensity and the C=0 peak (1710 cm-- -) increased in intensity-. Peaks due to the NH (3120-31A0 cm-l) and phenyl groups (3030-3050 cm-l) also developed as the substitution increased and the relative intensity of the aliphatic CH (backbone chain) (2910-29A0 cm-l) decreased at the same time. Some of these results are summarized in Table I where the ratios of the C = O/OH and phenyl/aliphatic CH peaks are reported for various degrees of substitution. 

An infrared spectrum of a film of peroxide between rock salt plates showed the presence of carbonyl and hydroxyl absorption from decomposition products. There was a wide region of C—O stretching absorption... 

The problem of getting uniform thin samples of catalyst on salt plates is serious when attempts are made to correlate infrared intensity measurements with quantitative chemisorption measurements obtained on bulk samples. An improvement in the technique of depositing small catalyst particles on salt plates has been developed which has considerable advantage over the simple evaporation of slurries. In the improved method isopropyl alcohol is used as the suspending liquid in the sedimentation step and the portion of the liquid containing the desired particles is sprayed onto a heated salt plate (30). 

Identification The infrared absorption spectrum of a film of the sample between two salt plates exhibits relative maxima at the same wavelengths as those of a similar preparation of USP Docusate Sodium Reference Standard. 

A. The infrared absorption spectrum of a thin film of the sample, formed between salt plates, exhibits relative maxima... 

Identification An infrared absorption spectrum of the sample contained in a sodium chloride cell or between salt plates exhibits maxima at the same wavelengths as the typical spectrum, as shown in the section on Infrared Spectra. 

Infrared and NMR Spectra. Infrared spectra were measured as thin films using ultramicro salt plates with a Perkin Imer Model 197 instrument. Proton nuclear magnetic resonance ( HNMR) spectra... 

The infrared cell is filled by inclining it slightly and placing about three drops of the solution in the lower hypodermic port with a capillary dropper. The liquid can be seen rising between the salt plates through the window. In the most common sealed cell, the salt plates are spaced 0.1 mm apart. Make sure that the cell is filled past the window and that no air bubbles are present. Then place the Teflon stopper lightly but firmly in the hypodermic port. Be particularly careful not to spill any of the sample on the outside of the cell windows. 

For these reasons, a reference absorber is often dispensed with entirely in qualitative infrared work, and the intensity of the radiation passing through the sample is simply compared with that of the unobstructed beam alternatively, a salt plate may be used as a reference. Either way, the resulting transmittance is often less than 1, even in regions of the spectrum where the sample is totally transparent. 

Infrared Measurements. In Figure 12, the infrared spectra of two foam formulations are shown which have been quenched on cold salt plates 20-30 seconds after the end-of-mixing. The first formulation is "A" the second,a similar formulation also at 105 isocyanate index but with 4 phr water. In each, the strong... 

Figure 12. Infrared spectra of two formulations, quenched on cold salt plates.

Table 1 summarizes the analytical results obtained for the thermal reaction of I and of VI. With the exception of the experiment in which methanol was added to VI, the extent of phthalocyanine formation was very small. Moreover, the infrared spectra of these reacted samples exhibited absorptions characteristic of amide or imide carbonyl as well as those for tria-zine. Under these conditions, phthalocyanine formation is not favored. For example, the yield of phthalocyanine ring formation, based on the consumption of starting material, was less than 5% for the model phthalonitrile VI, and less than 10% for the bis-phthalonitrile I. In a separate experiment a thin film of I deposited on a salt plate was allowed to cure while exposed to the atmosphere. Periodic infrared examination of the curing film showed that as the cyano absorbance diminished the absorbance in the carbonyl region increased until the latter was the predominant infrared band. These results demonstrate that... 

Infrared spectra were run of Nujol mulls prepared in a glove box and sealed between salt plates. Samples could then be transferred to a Perkin-Elmer Model 283 spectrometer without decomposition. Visible spectra were run in stoppered glass cells on a Cary 118 spectrometer. NMR spectra were run at 180 MHz on a FT instrument. 

Modem IR instmments often have reflectance of other sampling capabilities for obtaining IR spectra that eliminate the necessity of salt plate cells and simplify sample handling. The most useful is an internal reflectance method called attenuated total reflectance (ATR). The sample is pressed on a diamond substrate and the infrared radiation penetrates the sample, being reflected internally, and then exits for detection. 

A more detailed study was made by the same Japanese workers of the static decomposition reaction with Ni as a catalyst [Hirota et al. (45)]. An infrared cell, constructed according to the principles indicated by Eischens (55), was horizontally mounted in a Hilger H 800 spectrometer. To avoid interference by adsorbed groups occurring on the carrier material, finely divided Ni particles were deposited on a thin rock-salt plate by decomposition of Ni formate suspended in ethanol. 

A second example is shown in Figure 8.12. The sample is diethyl ether, a pure liquid with a low boiling-point. The infrared spectrum is that of a capillary film of this sample between two salt plates. Notice the aliphatic CH bands (2900, 1460, CH3 at 1380). There is also an aliphatic ether band at 1130 cm . ... 

The fillers can be isolated by ashing a quantity of polyurethane to yield the desired quantity of ash for spectroscopic (or wet chemical method) analysis. Often the filler can be identified by infrared without any elemental analyses. Usable spectra of inorganic compounds may be obtained by grinding with a mortar and pestle to a powder, spreading uniformly between two salt plates, and gently moving one plate over the other until good contact between plates and sample is achieved. A demountable cell is normally required to centre the plates in the spectrophotometer beam. 

Infrared spectra of the copol)nners were obtained using a Nicolet MX-1 fourier transform infrared spectrophotometer. The spectra were taken of solvent (CHCl ) cast films of the copolymers on salt plates. 

At your instructor s option, obtain an infrared spectrum using salt plates (Technique 25, Section 25.2). Compare the spectrum with the one reproduced in this experiment and include it with your report to the instructor. If any of your sample remains after performing the determination of the infrared spectrum, submit it in a properly labeled vial along with your report. 

Obtain the infrared spectrum of the oil as a pure liquid sample (Technique 25, Section 25.2). Small amounts of water will damage the salt plates that are used as cells in infrared spectroscopy. 

It may be necessary to use a capillary tube to transfer a sufficient amount of liquid to the salt plates. If the amount of liquid is too small to transfer, add one or two drops of methylene chloride to aid in the transfer. Gently blow on the plate to evaporate the solvent. Include the infrared spectrum in your laboratory report, along with an interpretation of the principal absorption peaks. 

Spectroscopy. Obtain an infrared spectrum using salt plates (see Technique 25, Section 25.2). Determine the proton NMR spectrum using 3-4 drops of your biodiesel in 0.7 mL of deuterated chloroform. Since biodiesel consists of a mixture of different molecules, it is not helpful to perform an integration of the area imder the peaks. Compare the NMR spectrum of biodiesel to the spectrum of vegetable oil shown here. Finally, analyze your sample using gas chromatography-mass spectrometry (GC-MS). Your instructor will provide you with instructions on how to do this. 

The plan is to run the proton NMR, and then use your sample to obtain the infrared spectrum. Pour the contents of the NMR tube into a small test tube. Transfer a small amount of the CDCI3 solution to a salt plate using a Pasteur pipette, blow on the plate to evaporate the solvent, and then determine the infrared spectrum. Make... 

At your instructor s option, obtain an infrared spectrum using salt plates (Technique 25, Section 25.1). Compare your spectrum with the one reproduced in this... 

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