Potassium bromide pellet method

The potassium bromide-pellet method provides the most convenient way to detect a slight polymerizability at room temperature using the following operation a few milligrams of the monomer are embedded in a KBr pellet, and the change upon irradiation is followed by IR spectroscopy. All the polymers thus obtained, their properties and the polymerization conditions are listed in Table 1. 

Calcium was determined by an EDTA method carbon and hydrogen by the combustion method total nitrogen by the Kjeldahl method sulfur by the Eschka method infrared spectra by the potassium bromide pellet technique. 

A group in Latvia and Russia [78] analysed microbial cell mass by a fairly simple classical infrared spectroscopic method, recording spectra of dried biomass embedded in potassium bromide pellets with a dispersive IR spectrometer. They could calibrate the evaluation for four major groups of cellular... 

Solid Samples. The easiest way to hold a solid sample in place is to dissolve the sample in a volatile organic solvent, place several drops of this solution on a salt plate, and allow the solvent to evaporate. This dry film method can be used only with modern FT-IR spectrometers. The other methods described here can be used with both FT-IR and dispersion spectrometers. A solid sample can also be held in place by making a potassium bromide pellet that contains a small amount of dispersed compound. A solid sample may also be suspended in mineral oil, which absorbs only in specific regions of the infrared spectrum. Another method is to dissolve the solid compound in an appropriate solvent and place the solution between two sodium chloride or silver chloride plates. 

Polycrystalline or powdered samples can be prepared as a suspension in mineral oil (Nujol mull), as a potassium bromide disk (pellet), or as thin films deposited on infrared-transparent substrates. The potassium bromide pellet is the most common way of preparing powder samples in this method a small amount, usually 1 mg, of finely-ground solid sample is mixed with powdered potassium bromide, usually 300 mg. and then pressed in an evacuated die under high pressure. The resulting disks are transparent and yield excellent spectra. The only infrared absorption in the potassium bromide matrix is due to small amounts of adsorbed water, which can. however, be confused with OH-containing impurities in the sam-... 

Based on this finding, they proposed a method for determining the tacticity of amorphous samples of PVC. Because some samples cannot be easily transformed into an amorphous state, Schneider and co-workers [68] devised an IR method of tacticity determination which is independent of sample crystallinity. From the temperature dependence of IR spectra of PVC samples prepared by different methods, the intensity of the band at 14.40 pm (proportional to the number of isotactic diads in the sample), as well as that of the tacticity-independent C-H stretching band, was found to be independent of sample crystallinity. These lines were applied to the tacticity determination in PVC, measnred in potassium bromide pellets. The numerical tacticity value was obtained from the known values of absorbance coefficients of S h and S h type C-Cl stretching bands in solution, and from the shape of the spectrum. 

The infrared analysis was performed on dried potassium bromide pellets containing 0.5 mg sample in 200 mg potassium bromide. An infrared spectrum of a methyl methacrylate - glycolymethyacrylate copolymer is shown in Figure 3.7. The peaks at the wave numbers 11.02 and 5.82 jim are the most suitable ones for analysis of epoxy and carbonyl groups, respectively. Using the base line density method, the values of the absorbances at 11.02 and 5.82 xm have been determined in triplicate. The average values of the absorbances, their ratio and the glycidylmethylacrylate mole fraction determined chemically are presented in Table 3.10. 

Solid samples or solid extracts can be mixed and ground with potassium bromide (KBr),pressed to form a transparent pellet, and a spectrum obtained from the pellet (see C in Figure 14.3). There are gas cells for obtaining spectra of gases and many other methods for obtaining spectra from liquid and solid samples that are not as frequently used as these [13-17],... 

Dispersed in an infrared transparent powder. Pellets are made with I to 2% by weight of the sample, usually in dry potassium bromide. A pellet of approximately 300 mg is prepared in a mould called a matrix using a laboratory press. This method produces pellets 1 to 2 mm thick for a diameter of approximately 13 mm. This technique can be used for quantitative studies but the spectra may sometimes differ ftom those obtained via dispersion in a liquid. This is because, under the effect of the high pressure to which the powder is subjected, the solid may undergo certain modifications. 

Solids are usually ground with a material such as potassium bromide and compressed into a pellet. Moisture must be absent, and the transparent disk is placed in the window of the spectrometer. In general, however, measurement of intensity of absorption in the solid phase is unreliable due to scattering and reflection losses, and a uniform distribution of sample in the pellet is difficult to achieve. One method of handling solutions is to allow them to soak into a KBr wedge, evaporate the solvent, and compress the tip into a microdisk or pellet (C26) alternatively the sample (1 /tl) may be either placed directly on the KBr disk (B13) or mixed with a little KBr powder and subsequently incorporated in the disk. These microdisk techniques can be used for the examination of gas chromatograph effluent. For multiple analyses, an enclosed turntable system loaded with the disks can be used. 

Spectroscopic examination in the infrared was often used as a ready if somewhat rough method of assessing the degree of crystallinity. Chromia and potassium bromide (1 10) were ground together and compressed into a pellet for spectroscopic examination. Typical residts are shown in Fig. 11. As one can see, a wide band at about 525 cm in... 

Solids. There are several methods for determining infrared spectra for solids. One method of choice has been to mix a finely ground sample with powdered potassium bromide and press the mixture under high pressure. Under pressure, the potassium bromide melts and seals the sample into a matrix. The resulting KBr pellet is inserted in the instrument. If a good pellet is prepared, the spectrum obtained will have no interfering bands since potassium bromide is transparent down to 400 cm . ... 

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