Salt plates

The most common fused salt baths are complex mixtures of alkah chlorides, rigorously purified and dried. Fused salt plating must be done under an inert atmosphere. Often argon is used because nitrogen can react with some metals. Inert anodes, eg, Pt-coated titanium or graphite, are used and the plating metal is suppHed by additions of an appropriate metal salt. 

Ordinarily, you put the sample between two salt plates. Yes. Common, ordinary water-soluble salt plates. Or mix it with potassium bromide (K Br), another water-soluble salt. 

Place the sandwich in the IR salt plate holder and cover it with a holddown plate. 

Put at least two nuts on the posts of the holder (opposite corners) and spin them down GENTLY to hold the plates with an even pressure. Do not use force You ll crack the plates Remember, these are called salt plate holders and not salt plate smashers. 

Spread the mull on one salt plate and cover it with another plate. There should be no air bubbles, just an even film of the solid in the oil. 

In any case, if the peaks are too large, with the baseline in the proper place, your sample is just too concentrated. You can wipe some of your liquid sample or mull off one of the salt plates or remake the KBr pellet using less compound or more KBr. Sorry. 

Demountable cells can be disassembled and may or may not use a spacer. Without a spacer, the liquid sample is simply applied to one salt plate, and the second plate is positioned over the first to smear the liquid out between the plates. Such a method cannot be useful for quantitative analysis because the pathlength is undefined and not reproducible. Also, the two salt plates may be positioned in the path of the light without a frame if there is a way to hold them there. If a spacer is used, it is positioned over one of the plates. The sample is applied to this plate in the cutout space in the spacer reserved for it, and the second plate is then positioned over the first with both spacer and sample in between. There are no inlet and outlet ports since the sample is not introduced that way. However, the plates, with sample, are placed in a frame, or holder, similar in appearance to the sealed cell, but without the ports. See Figure 8.18. Such a cell is also undesirable for quantitative analysis because of the difficulty in obtaining an identical pathlength each time the cell is reassembled. 

FIGURE 8.22 A solid may be prepared by dissolving it in an organic solvent, placing it on a salt crystal (left), and allowing the solvent to evaporate such that the film of the solid is cast on the surface of the salt plate, which can then be placed in the path of the light (right). 

The solvent evaporation method is especially useful for polymers that can be cast onto the surface of the salt plate. Casting involves dissolving the polymer in an appropriate solvent at an elevated temperature and evaporating the solvent on the salt plate by heating the salt plate on a hot plate or under a heat lamp. 

Dissolve in a solvent and then use a liquid sampling cell to measure the solution 2) dissolve in a solvent, place several drops of the solution on a salt plate, evaporate the solvent, and measure the residue 3) KBr pellet 4) Nujol mull and 5) reflectance. 

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. 

For the measurements of extent of cure (3), the monomer mixture was melted onto a salt plate, then cured in a closed can under conditions identical to those used for the mixtures in the sol/gel experiments. The plate was removed from the oven periodically and the spectrum recorded on a Perkin-Elmer Model 267 spectrometer. 

The type of arrangement of the monomeric units in polymeric dienes can be determined qualitatively and quantitatively by IR spectroscopy. For this purpose thin films are prepared by dropping an approximately 2% solution in carbon disulfide (spectroscopically pure) on to suitable rock salt plates and allowing the solvent to evaporate at room temperature.The plates are placed in the spectrometer beam and the IR spectrum is recorded.The different types of chemical linkages are associated with characteristic IR bands as summarized in Table 3.9. 

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... 

Quickly place a small amount of material between two IR salt plates and run the IR immediately (time = 0). Run the IR spectrum every 15 min by scanning only the absorption peaks at 3226 and 912 cm-1 to follow the reaction. 

Place a small amount of the diethylenetriamine between the IR salt plates. 

Quickly place a small amount of the mixture between two IR salt belts and place inside the IR spectrometer. (Note To protect the salt plates use the protective film strips). 

These polymers are of potential interest as photoresists. Accordingly, their photochemistry was also studied in very thin (1-4 jtm) films which were spin-coated onto polished salt plates. After irradiation in a standard xenon arc photoilluminator, the loss of carbonyl could be determined from FTIR measurements. Experiments were carried out both at 254 nm (deep-UV) and 313 nm (mid-UV). Typical rate curves are shown in Figures 2 and 3. The... 

Liquids may be examined neat or in solution. Neat liquids are examined between salt plates, usually without a spacer. Pressing a liquid sample between flat plates produces a film 0.01 mm or less in thickness, the plates being held together by capillary action. Samples of 1-10 mg are required. Thick samples of neat liquids... 

A commercial cracking catalyst was used in this work, so that it was necessary to obtain small particles by grinding and water sedimentation. The sample was deposited on a salt plate by evaporation of an alcohol slurry. The average thickness was 1.5 mg./cm.2, but the intensity of the Si—O bands near 5.0 p indicated that the thickness was about 4 mg./cm.2 in the area penetrated by the infra-red beam. 

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... 

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