IR diffuse reflectance

Quantitation of one polymorphic form within another by mid-IR diffuse reflectance has also been performed on SC-41930 [14]. The high melting point form (HM) was spiked with low melting point form (LM) between 0 and 25% w/w. The 1670 cm-1 absorbance feature in the LM was used for quantitation. Based upon the spectral data, a detection limit of approximately 1% w/w of LM in HM was estimated. 

CE European certification DRIFT-IR diffuse reflectance Fourier-transform... 

Quantitative FT-IR diffuse reflectance analysis of vinyl silanes on an aluminum hydroxide substrate... 

Abstract—This study extends previous work on silanized kaolin clays to other substrates, such as aluminum hydroxide. It will also show that high precision quantitative Fourier Transform Infrared Spectroscopy (FT-IR) diffuse reflectance measurements can be performed on this vinyl silanized substrate and predict that other silanized finely divided powders can be analyzed using these techniques. 

FT-IR diffuse reflectance measurements have been used to quantitatively determine the amount of silane deposited on a substrate. The advantages of FT-IR are speed and sensitivity, the latter relating to the ultimate analytical precision or the smallest amount of the analyte one can determine. Other classical uses of infrared spectroscopy are as a qualitative identification or structure elucidation tool. 

Hanning [4], Miller and Ishida [5], and McKenzie and Koenig [6] favored transmission measurements using FT-IR for monitoring silanized mica quantitatively. Berger and Desmond [3] demonstrated the ability of FT-IR diffuse reflectance measurements to quantitate various silanized substrates including mercapto silane on hydrous clay and epoxy silane on alumina trihydrate. Later Vagberg el at. 

To elucidate the nature of the bonded states of the main hydrogen mass that is retained up to high temperatures, the IR diffuse reflection spectra were measured for GNF and SWNT powders in the initial state, after the treatment under hydrogen pressure, and after the degassing annealing. Measurements were performed in the range 400-5,000 cm-1 at room temperature. The results are presented in Fig. 11.5. 

Fig. 11.5 IR diffuse reflection spectra of graphite nanofibers and single-walled carbon nanotubes in the initial state, after saturation with hydrogen at 9 GPa, after removal of about 40% of absorbed hydrogen, and after degassing annealing. T = 300 K...

T. Chopin and E. Whalen, A new and rapid method for carrageenan identification by FT IR diffuse reflectance spectroscopy directly on dried, ground algal material, Carbohydr. Res., 246 (1993) 51-59. 

Determination of infra-red crystallinity index at different wavelengths (1429 cm V893 cm ) by the usual base line technique can be used [38]. When cellulose-II samples are considered, the 1372 cm 72900 cm" ratio is more reliable index [39, 40]. A rapid method for estimation of the degree of mercerization has been developed using a near IR diffuse reflection technique [41]. 

A series of Diffuse Reflection measurements was performed, subsequently, on partly decomposed CPC (system B) samples to check the decomposition pattern given in Figure 6.21. Four samples were (under the same conditions) heated to different, previously selected temperatures, see Figure 6.22. The measured IR Diffuse Reflection spectra of the TGA residues of these four samples offer the possibility to monitor the changes in the molecular structure in an independent way. 

Metal phthalocyanine complexes (MPc M = V, Co and Cu) encapsulated in zeolite-Y were prepared by in-situ ligand synthesis and characterized by chemical and thermal analyses and FT-IR, diffuse reflectance UV-vis and EPR spectroscopic techniques. The studies provided evidence for the encapsulation of MPc inside the supercages of zeolite-Y. The Pc moiety distorts from square planarity as a consequence of encapsulation. The encapsulated complexes exhibited enhanced styrene epoxidation activity with /e/-/-butylhydroperoxide compared to the neat complexes in homogeneous medium. The activity and product selectivity of the encapsulated complexes varies with the central metal atom. 

ON-LINE MEASUREMENT OF POLYVINYL ALCOHOL SIZE ON WARP YARNS USING A NEAR-IR DIFFUSE REFLECTANCE SPECTROSCOPY METHOD... 

The UV-visible-near IR diffuse reflectance spectra of the en-SiOa+INi, ENien and ENien+INi samples exhibit three d-d transitions, characteristic of nickel complexes in oct edral symetry. In the following, we will only consider the Vi band due to the A2g — T2g transition, because the V2 and V3 ones are less resolved. For the samples considered, the Vi band position varies between 890 nm which is characteristic of the [Ni(en)3] complex, e.g. present in the ENien samples, and 1160 nm which is characteristic of [Ni(H20)6] complex, e.g. present in standard impregnated INi samples (Table 3) [2]. 

In a previous study [3], it was shown that the UV-visible-near IR diffuse reflectance spectra of the ENien samples calcined in air at 600°C then maintained in air at 25 C, exhibited absorption bands at 410,660 and 1160 nm attributed to isolated hexacoordinated grated nickel species, [(=Si0)2NiQ(H20)4]. An additional band at 330 nm was attributed to dimers of grafted nickel (NiP-O-NiD). The absence of bands of N-H vibrations of ethylenediamine in the near IR range, at 1530 and 2030 nm, indicates that ethylenediamine adsorbed onto silica is decomposed. An EXAFS study confirmed this interpretation [2,3]. 

Stuhlinger, T. Bidirectional reflectance distribution function of gold-plated sandpaper. Optical Eng. 22, SR-142 and Lea, T. K., and Schotland, R. M. (1988). Infrared retroreflecting lidar calibration targets. Appl. Optics 27, 208. Discuss gold-plated sandpaper, once widely used as standard for mid-IR diffuse reflectance. 

Figures 3. Typical IR specular reflectance (a), IR diffuse reflectance (b) and UV-Vis-NIR reflectance (c) electrochromic data, applied potentials as shown. The diffuse reflectance data also show the effect of y-radiation, at exposures indicated ( top group = light state, bottom group = IR dark state).

Near IR Diffuse reflectance Quantitative Solid or liquid commercial materials... 

The use of the Kubelka-Munk equation for quantitative analysis by diffuse reflectance spectroscopy is common for measurements in the visible, mid-IR and far-IR regions of the spectrum, but not in the near-IR region. As has been pointed out [187, 188], almost all near-IR diffuse reflectance spectra have been converted to log(l// ) R = reflectance of the sample relative to that of a non-absorbing sample). The use of log(l// ) instead of the K-M function provides a more linear relationship between reflectance and concentration. Olinger et al. [189] explain this behaviour by the effective penetration depth of the beam, which is very short, when absorption is strong. For many of the algorithms developed to achieve multicomponent determinations from the diffuse reflectance spectra of powdered samples, a linear dependence of band intensity on analyte concentration is not absolutely mandatory for an analytical result to be obtained. 

Diffuse reflectance is a technique where source radiation strikes a powdered sample and is diffusely reflected in different directions." This weak diffuse radiation is collected in a manner which minimizes the specular reflectance component and is measured by the spectrometer which is usually an FT-IR instrument. Usually the finely powdered sample is diluted to a concentration of 5 to 10% in powdered KBr or KCl for mid-IR diffuse reflectance spectra. No dilution is required in the near-IR region, where the bands are weaker. Pure powdered KBr or KCl is used as a reference against which the sample spectrum is ratioed as shown below, where is the reflectance of a thick scattering layer. 

IR diffuse reflectance spectroscopy seems to be the more appropriate method for observing OH stretch frequencies as well as their overtones and combination bands in the near infrared, especially with high-silica zeolites, i.e. at low hydroxyl concentrations, thus acquiring additional information on the shape of the potential curve [17,26,27]. In these papers an attempt is made to draw a unifying picture of the coinciding OH frequencies of silica-rich zeolites such as mordenites and ZSM type zeolites and the different and more complicated spectra of... 

Infrared spectroscopic method using pyridine as an adsorbate is extensively used and considered to be a most reliable method, though there are many other methods to distinguish between Brensted and Lewis acid. It was reported recently that both Bransted and Lewis acid sites can be measured by C-NMR tmd N-NMR study of adsorbed pyridine. Kazansky et al. showed that IR diffuse reflectance spectroscopy of adsorbed hydrogen molecule provided information about the nature of different Lewis acid sites in dehydroxylated H-forms of zeolites. 

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