Potassium Bromide Discs

Infrared spectra for solid organic compounds are frequently obtained by mixing and grinding a small sample of the material with specially dry and pure potassi um bromide (the carrier), then compressing the powder in a special metal die under a pressure of 15 30 tonnes to produce a transparent potassium bromide disc. As the potassium bromide has virtually no absorption in the middle-infrared region, a very well-resolved spectrum of the organic compound is obtained when the disc is placed in the path of the infrared beam. 

The infi red absorption spectrum of benzoic acid was obtained in a potassium bromide disc (using approximately 2 mg of benzoic acid dispersed in 200 mg KBr), and recorded on a Jasco 5300 FTIR spectrophotometer. The spectrum thusly obtained is shown in Figure 6, and the assignment of the characteristic bands is given in Table 3. 

The method used for sample preparation depends upon the nature of the sample. Liquids are easily examined as films formed when one drop of the liquid is squeezed between two flat sodium chloride plates, which arc transparent to IR radiation in the 4000-666 cm region. Solids can be examined as solutions, mulls in Nujol, or as potassium bromide discs. For solutions, a 5% solution of the solid is introduced into a sodium chloride cell, which is usually 1 mm thick. The solvent employed should be reasonably transparent to IR, and the background should be obtained with the cell containing the solvent only. 

The spectra were run on potassium bromide discs of the specimens at about 0.35% w/w concentration using a Perkin-Elmer Model 21 spectrometer. Microscopic examination of the discs showed that in spite of long grinding, the coal particle size was relatively large (<1(V, except for CGL 105, which contained many particles in the range 10- 50m). Consequently, a fair amount of scatter was observed in the spectra. 

Finally release the press and remove the die body (A) and the upper steel pellet from the face of the disc and then remove the disc itself with tweezers (the disc should never be handled with the fingers), and mount it in the specially designed holder. These latter operations are best conducted under a radiant heater. The disc holder is located in position in the sample beam path of the spectrophotometer if required a blank potassium bromide disc, similarly prepared, is introduced into the reference beam path. 

Reported (2) principal infrared absorption peaks of oxyphenbutazone in potassium bromide discs are 1683, 1725, 1275 and 1518 cm" . 

A method for identifying chlorinated insecticide residues in fish tissue is described. Whereas electron capture gas chromatography guides the isolation procedures and provides tentative identification and quantitative estimation, positive identification is made on the basis of the infrared spectrum of isolated insectiQides. The procedure consists of hexane extraction of fish tissue, partition between hexane and acetonitrile, column adsorption and thin layer chromatography cleanup, and micro-infrared analysis in a potassium bromide disc. The practical limit of sensitivity needed to provide excellent infrared spectra of a number of the more common chlorinated insecticides is about 1 p.p.m. in the fish tissue concentrations as low as 0.25 p.p.m. have given informative infrared spectra. 

The rate of isomerization of the sulfur-bonded dithiocyanatobis(tri-phenylarsine)palladium(II) takes place so rapidly in solution that a visible absorption spectrum cannot be obtained. In the solid state the rearrangement is much slower (30 minutes at 156°C.) and is even slower when the solid is incorporated at low concentration in a potassium bromide disc, with a half-life of 130 minutes at 150°C. This decrease on going from the... 

IR spectra of amoxicillin trihydrate and amoxicillin sodium salt in a potassium bromide disc are shown in Figures 2 and 3 respectively. The frequencies and assignments of significant bands are listed below. 

The infrared spectrum of diltiazem hydrochloride is obtained from a potassium bromide disc and is recorded at 4 cm 1 resolution. A disc is made from 1 mg of sample in about... 

Transmission spectroscopy (2) is the simplest sampling technique in IR spectroscopy and is used for routine spectral measurements on diverse samples. Resin samples such as polystyrene or TentaGel (3) beads are usually prepared as a potassium bromide disc (pellet). A small amount, usually 1-3 mg, of finely ground solid sample is mixed with approximately 400 mg powdered potassium bromide and then pressed in an evacuated die under high pressure. The resulting discs are transparent and yield good spectra. 

Stimson, M. M. (1962). Sampling for spectrophotometry with special reference to the use of the potassium bromide disc technique. In Progress in Infrared Spectroscopy, Voi. 1 (H. A. Szymanski, ed ). Plenum Press, New York. pp. 143-150. 

The infrared spectrum of a neat film obtained from methyl chloride is shown in Figure 4a. The spectrum is appreciably less definitive than the methane film spectrum (Figure 3). The spectrum of a more concentrated powdered sample contained in a potassium bromide disc is shown in Figure 4b. The insert at the low frequency end was made with a different interchange. 

The elemental analyses were carried out by the Australian Micro-analytical Service, CSIRO, Melbourne. IR spectra were recorded on a Unicam SP200 spectrophotometer in potassium bromide discs (for solids) and as thin films between sodium chloride plates (for liquids). Proton magnetic resonance (PMR) spectra of the monomers were recorded on a Varian HA100 instrument and 13C NMR spectra on a Varian CF7/20. In both cases the chemical shifts (8) are quoted in ppm with tetramethyl silane as the internal standard. 

Anthraquinones are poorly soluble in common IR solvents and in practice most spectra are measured in potassium bromide discs [1],... 

Squibb House Standard (Potassium Bromide Disc). 

The infrared absorbance specfrum of clofazimine is shown in Figure 3. The spectrum was recorded with a Nicolet 5ZDX FT-IR spectrophotometer, from a compressed potassium bromide disc. Structural assignments for some of the characteristic absorption bands in the spectrum are listed in Table I. 

IR-spectra are obtained from samples in film form, provided the film is thinner than approx. 50 pm. Thicker samples or resin granules are heated above their softening temperature and then pressed to form films thin enough to be used directly for IR-spectroscopy. Films can also be obtained by casting from solutions of the plastic. A few drops of the solution are placed on a potassium bromide disc, and after evaporation of the solvent, the IR-spec-trum can be observed directly from the disc because KBr does not show any absorption in the infrared, i.e., it is completely transparent. One has to make sure that evaporation of the solvent is complete in order to avoid interference through absorption bands due to the solvent. For this reason. 

Figure 5.21 Infrared spectrum of UV 531 (2-hydroxy-4-n-octoxy benzophenone) isolated from a polyolefin (potassium bromide discs)...

The spectra were run either as potassium bromide discs (1.5-2 pg polymer per 400 mg potassium bromide) or as polymer films of varying thickness up to 12 pm using a sodium chloride prism. 

Most early work on the vibrational spectra of inorganic ions was carried out using Raman spectra, because of the problems of sample handling in the infra-red. However, a small amount of work was done using reflection spectra [ 1 ], and the development of the nujol mull technique stimulated many studies by Lecomte and his co-workers [2—5, 10]. The introduction of the pressed potassium bromide disc technique with the associated equipment for fine grinding has led to a stimulation of interest in this field. 

There are a wide variety of dies commercially available for the preparation of potassium bromide discs. In general, a die which can be evacuated prior to pressing the disc is preferable but not mandatory. Evacuation improves the lifetime of the disk clarity. Pressures of approximately 8 tons for a press-... 

Raynor et al separated additives in complex mixtures by capillery supercritical flow chromatography and deposited the separated products in potassium bromide discs prior to measurement of their infrared spectra by FTIR spectroscopy. Supercritical flow chromatography coupled with F.T. infrared spectroscopy (SFC-FTIR) has been used to provide quantitative information on and characterization of a range of polymeric surfactants. Bartle et al and Chester also investigated this technique. 

---