KBr pellet technique

At infrared wavelengths extinction by the MgO particles of Fig. 11.2, including those with radius 1 jam, which can be made by grinding, is dominated by absorption. This is why the KBr pellet technique is commonly used for infrared absorption spectroscopy of powders. A small amount of the sample dispersed in KBr powder is pressed into a pellet, the transmission spectrum of which is readily obtained. Because extinction is dominated by absorption, this transmission spectrum should follow the undulations of the intrinsic absorption spectrum—but not always. Comparison of Figs. 10.1 and 11.2 reveals an interesting discrepancy calculated peak extinction occurs at 0.075 eV, whereas absorption in bulk MgO peaks at the transverse optic mode frequency, which is about 0.05 eV. This is a large discrepancy in light of the precision of modern infrared spectroscopy and could cause serious error if the extinction peak were assumed to lie at the position of a bulk absorption band. This is the first instance we have encountered where the properties of small particles deviate appreciably from those of the bulk solid. It is the result of surface mode excitation, which is such a dominant effect in small particles of some solids that we have devoted Chapter 12 to its fuller discussion. 

Crystalline or solid samples (ca. 10 mg) are ground with 5 drops of nujol in an agate mortar to form a paste for subsequent CD or MCD measurement. Perfluoro-butadiene can also be used instead of nujol. Otherwise, the KBr pellet technique, for which KBr and sample should be completely dried in vacuo and ground into a fine powder, can be used conveniently. On using the KBr technique, one can often observe a different CD spectrum from that of the nujol-mull method. 

Tetrakis(acetato)di- U-amido-diborane is a white crystalline compound which is not too sensitive to moisture. It can be stored in a nitrogen atmosphere in a refrigerator for long periods without decomposition. It is sparingly soluble in most organic solvents and slowly dissolves in glacial acetic acid and acetic anhydride. Monoclinic and triclinic crystalline forms were obtained by recrystallization from acetic anhydride and glacial acetic acid, respectively.1 The infrared spectrum recorded (Beckman i.r.-12) by the KBr pellet technique contains major absorption bands (at frequencies cm.-1) 3280(s), 3230(s), 3100(s), 1740(w,sh),... 

Fig. 3. The 3 to 13 micron emission spectrum from the Orion Bar compared with the absorption spectra of the PAHs chrysene, pyrene and coronene suspended in KBr pellets. (Orion, Ref. [47] Chrysene, Ref. [38] Pyrene, Ref. [37] Coronene, Ref. [39].) A schematic representation for the absorption spectrum is used because the KBr pellet technique alters the spectrum compared to that of a free species...

Infrared spectra. IR absorption spectra in the framework vibration region (400-1400 cm-1, resolution 1 cm 1) were obtained with a Nicolet MX-1 Fourier transform spectrometer using the KBr pellet technique. 

Fig. 4.1.7. Baseline-corrected and normalized FTIR spectra illustrating spectral types G, GS 1-GS 4, and HGS. G Norway spruce (Picea abies)-, GS I (Gnetum venosum) GS 2 lauan (Shorea polysperma), GS 3 dabema (Piptadeniastrum africanum) GS 4 birch (Betula sp.) HGS a bamboo (Bambusa sp.) b barley (Hordeum vulgare). (Instrument FTS 40 Bio-Rad, Digilab, 4cm 1 resolution, 32 scans, KBr pellet technique). According to Faix 1991...

Kg. 4.1.9. Difference spectrum of oak (Quercus obtusata) obtained by subtracting the spectrum of MWL from the spectrum of the same MWL after NaBH4 reduction. (Instrument Nicolet 20SX D, 4cm 1 resolution, 32 scans, KBr pellet technique)... 

Fig. 4.1.11. FTIR spectra of spruce, beech, and bamboo MWL before and after deconvolution (Faix and Beinhoff 1988). (Instrument) Bio-Rad, Digilab FTS 40, resolution 4cm 1, 64 scans, bandwith for deconvolution 15cm1, KBr pellet technique). By courtesy of Marcel Dekker Inc.

Fig. 4.1.13. IR spectrum (dotted line) and second derivative IR spectrum of tulip tree (Liriodendron tulipifera sapwood MWL. (Resolution 4 cm-1, 64 scans, KBr pellet technique)...

Other researchers have evaluated the crystallinity index by using IR spectrophotometry. This method requires the KBr pellet technique of sampling. The X-ray diffraction method was investigated for its potential as a nondestructive technique for recording changes in cellulose as it ages. 

Diffractometer (Model PW 1710), using CuKa radiation. A thin film ( lnun) of 1.5 by 1.5 cm square sample was used for X-ray studies. Both water and gas phase permeability measurements were done with a machined 1 cm diameter thin sample ( limn). The molecular wei t distribution was obtauned using a gel permeation chromatograph (Waters) with a styragel column and using tetrahydrofuran as the solvent. Attenuated total reflectance (ATR) and KBr pellet techniques were used for FTIR. Solid state NMR was done on precipitated powdered samples. A Rayonet RPR-100 reactor at 35 C was used for UV irradiation of the samples. 

FTIR spectra of the carbon samples were obtained using a Perkin-Elmer FTIR Spectrum 2000 spectrometer. The active carbon-KBr mixtures in a ratio of 1 300 were ground in an agate mortar, desorbed under vacuum (10 - Pa), and finally pressed in a hydraulic press. Before the spectrum of a sample was recorded, the background line was obtained arbitrarily and subtracted. The spectra were recorded from 4000 to 450 cm at a. scan rate of 0.2 cm/s, and the number of interferograms at a nominal resolution of 4 cm" was fixed at 25. Figures 3 and 4 present the FTIR spectra obtained for the relevant carbon samples. The measurements applied here (KBr pellet technique) make it impossible to compare quantitatively the FTIR spectra obtained for different carbons, but they do indicate which individual chemical structures may or may not be present in the carbon [90,91,123]. 

Fig. 2 Comparison of near-infrared spectra of crystalline anhydrous glucose. Spectrum measured in transmittance using the KBr pellet technique [spectral resolution 64cm intensity data in absorbance (top trace) and diffuse reflectance spectrum using a spectral resolution of 32 cm and intensity data transformed to —log R) (bottom trace)].

Fig. 6 Spectral differences in mid-infrared spectra of caffeine measured under different conditions. Diffuse reflectance spectrum of the pure crystalline powder (top trace), diffuse reflectance spectrum of 1% of caffeine in KBr-powder (middle trace, intensity data for both spectra in K-M units), and absorbance spectrum as recorded using the KBr pellet technique (bottom trace).

Fig. 5 Comparison of mid-infrared spectra of caffeine obtained by diffuse reflectance and transmission spectroscopy. (A) Diffuse reflectance spectrum of the pure powdered substance with transformed intensity data in K-M units. (B) Same diffuse reflectance spectrum, but using —log(i ) transformation (top trace), the lower spectral range was limited by the cut-off of the MCT detector used the bottom trace shows a transmission spectrum using the conventional KBr pellet technique transformed into absorbance, i.e., —log(transmittance).

The framework IR spectra were recorded in a Nicolet (60 SXB model) instrument using KBr pellet technique. 1 l"Sn MAS NMR spectra were obtained at 111.82 MHz on a Broker MSL-300 NMR instrument. Typically around 3000 transients were signal averaged before Fourier transformation. The chemical shifts were referenced externally to tetramethyltin. 

Figure 1. Infrared spectra of natural organic materials isolated from Volo Bog obtained on solid samples by A) the KBr pellet technique and B) the diffuse reflectance method and C) in aqueous solution by CIR.

IR spectra were performed with Fourier transform spectrometer Nicolet 510 and Perkin-Elmer 2000. Samples were prepared by the KBr pellet technique unless otherwise stated. 

The application of IR spectrophotometry to the quantitative determinations of tropine alkaloids has been reported (101). The pressed KBr pellet technique was applied in these determinations. Recoveries from standard... 

Overall, the spectra of the humic substances recorded in the aqueous state are comparable to those measured by the conventional KBr pellet technique on dried samples. However, FTIR allows the samples to be observed in their native wet state and avoids the shifts in chemical equilibrium which must necessarily accompany the drying process. More detailed information on the ionization of the carboxylic acid functional groups could be obtained by measuring the spectra of the aqueous samples over a wide range of pH values. FTIR may also provide a tool for investigating the kinetics of metal-humic interactions and other reactions of humic substances in the aqueous state. 

Viscosities of the polymeric materials were obtained in tetrahydrofuran with an Ubbelohde-type viscometer at 30.00 0.02 C. The infrared absorption spectra in the region of 400-4000/cm were measured for the sample by Hitachi Model EPI-G3 infrared spectrophotometer. The samples were prepared by the KBr pellet technique. The thermal behavior of the specimens was observed with a Rigakudenki DSC-TGA apparatus. The X-ray diffraction pattern of the powdered polymer was taken in the region of 3-37 by a Rigakudenki Model 3D-F X-ray diffractometer with the use of Ni-filtered copper K radiation. 

Infrared specfra were recorded using the KBr pellet technique on a Perkin Ehner FTIR Spectrometer (Spectrum 100) from 1400 to 400 cm working with 32 number of scans and 4 cm resolution. 

Moreover, mid-infrared spectra were recorded in a Nicolet FTIR 710 using the KBr pellet technique, in order to follow the appearance of the band at - 960 cm , which is usually taken as an evidence that Ti is present in the zeolite lattice. 

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