Diffuse reflectance spectroscopy spectrometers

In diffuse reflection spectroscopy, the spectrometer beam is reflected from, scattered by, or transmitted through the sample, whereas the diffusely scattered light is reflected back and directed to the detector. The other part of the electromagnetic radiation is absorbed or scattered by the sample [124,125]. Changes in band shapes or intensity as well as signal shifts can be affected by morphological and physicochemical properties of the sample or combinations thereof (e.g., chemical absorptions, particle size, refractive index, surface area, crystallinity, porosity, pore size, hardness, and packing density [126]). Therefore, NIR diffuse reflection spectra can be interpreted in dependence of various physical parameters [127]. 

As illustrated by the examples discussed here, the use of FT spectrometers for the observation of surface structures is favored by situations in which the flux of radiation coming from the sample is very low or the data acquisition time is limited. Such cases arise in transmission spectroscopy using strongly absorbing or scattering samples, specular and diffuse reflectance spectroscopy from opaque samples, and emission spectroscopy from low temperature sources. FT spectroscopy is also well suited for observing the dynamics of surface species during adsorption, desorption, and reaction. 

A steady-state diffuse reflectance spectroscopy instrument typically includes a broadband fight source, intermediate optics, spatially separated delivery-collection optical fiber probes,77 and a CCD-based grating spectrometer. Frequency-based approaches have also been pursued.78 Correlations between the glucose concentration and the tissue transport scattering coefficient have been observed.77,78... 

Fig. 1 Accessories for diffuse reflectance spectroscopy (A) Integrating sphere with hemispherical radiation collection (B) Accessory based on ellipsoidal mirrors, used within the sample compartment of the spectrometer (C) Rotational ellipsoidal mirror device with dedicated detector and (D) Bifurcated fiber optic-based accessory (also shown is the random mixture of fibers for illumination and detection compared with devices based on reflection optics the acceptance cone for radiation delivery and collection is limited and depends on the refractive indices of the core and cladding material).

CW-EPR X-band measurements were performed on a Bruker ESP 300E Spectrometer at a temperature of 120 K. The CuHis complexes are paramagnetic due to the S=l/2 spin of the Cu " ion. Nitrogen physisorption was performed with a Micromeritics ASAP 2400 apparatus. Measurements were done at 77 K. Prior to the measurements the zeolite samples were degassed for 24 hours at 373 K in vacuum. Micropore volumes and pore size distributions were determined with standard BET and BJH theory. Diffuse Reflectance Spectroscopy of the CuHis complex encapsulated zeolite samples were taken on a Varian Cary 5 UV-Vis-NIR spectrophotometer at room temperature. The DRS spectra were recorded against a halon white reflectance standard in... 

Diffuse Reflectance Measurements. Adequate amounts of the sample were packed in sealed quartz glass sample cuvettes and the diffuse reflectance spectroscopy (DRS) measurements were made from 200 to 1100 nm at a resolution of 2 mn using a Perkin-Elmer Lambda 2S UV-Vis spectrometer at room temperature. A BaS04 disc was used as the reference standard. The dehydrated zeolite samples were initially transferred under an argon atmosphere in a glove box in order to exclude ambient humidity from the samples and the cuvettes were filled and sealed in the glove box. 

Spectroscopy. FT-IR spectra were recorded on a Nicolet F-730 spectrometer equipped with an in-situ flow-cell. Electron Paramagnetic Resonance (EPR) spectra were recorded in X-band with a Bruker ESP-300 with a fE (,4 cavity. Diffuse Reflectance Spectroscopy (DRS) spectra were recorded on a Cary-5 spectrofotometer with a BaS04 integration-sphere in the UV-VIS-NIR. Molecular graphics analysis was done with Hyperchem 3.0 for Windows (Hypercube Inc.). 

FTIR instrumentation is mature. A typical routine mid-IR spectrometer has KBr optics, best resolution of around 1cm-1, and a room temperature DTGS detector. Noise levels below 0.1 % T peak-to-peak can be achieved in a few seconds. The sample compartment will accommodate a variety of sampling accessories such as those for ATR (attenuated total reflection) and diffuse reflection. At present, IR spectra can be obtained with fast and very fast FTIR interferometers with microscopes, in reflection and microreflection, in diffusion, at very low or very high temperatures, in dilute solutions, etc. Hyphenated IR techniques such as PyFTIR, TG-FTIR, GC-FTIR, HPLC-FTIR and SEC-FTIR (Chapter 7) can simplify many problems and streamline the selection process by doing multiple analyses with one sampling. Solvent absorbance limits flow-through IR spectroscopy cells so as to make them impractical for polymer analysis. Advanced FTIR... 

The experimental system consists of three sections (i) a gas metering section with interconnected 4-port and 6-port valves, (ii) a reactor section including an in-situ diffused reflectance infrared Fourier transform spectroscopy reactor (DRIFTS) connected to tubular quartz reactor, (iii) an effluent gas analysis section including a mass spectrometer or a gas chromatograph (9). 

Samples were characterized by FTIR spectroscopy with a Perkin Elmer (Spectrum BX) spectrometer using KBr pressed disks as matrices. The DRIFT experiments were carried out with a Broker IFS 55 spectrometer equipped with a Thermo Spectra Tech reacting cell. UV-vis Diffuse Reflectance spectra were recorded on a Perkin Elmer Lambda 45 spectrophotometer equipped with a diffuse reflectance attachment. Raman spectra were collected with Perkin Elmer system 2000 NIR FT-Raman using as excitation radiation the 5th harmonic of a diode pumped Nd YAG laser (1065 nm). 

The nature and the distribution of different types of Fe species in calcined (C) and steamed (S) samples were investigated by means of UV-vis spectroscopy. UV-vis spectra of Fe species were monitored on UV-vis spectrometer GBS CINTRA 303 equipped with a diffuse reflectance attachment with an integrating sphere coated with BaS04 and BaS04 as a reference. The absorption intensity was expressed using the Schuster-Kubelka-Munk equation. 

Figure 8.7. Delayed fluorescence and diffuse reflectance transient absorption spectroscopy on scattering substrates. Example terthicnyl on silica gel excited with = 354 nm (neodymium/yttrium-aluminum-garnet) (Nd/YAG) laser pulse of 10 nsec, 20 mj), recorded with a gated diode array spectrometer.

There are several major areas of interfacial phenomena to which infrared spectroscopy has been applied that are not treated extensively in this volume. Most of these areas have established bodies of literature of their own. In many of these areas, the replacement of dispersive spectrometers by FT instruments has resulted in continued improvement in sensitivity, and in the interpretation of phenomena at the molecular level. Among these areas are the characterization of polymer surfaces with ATR (127-129) and diffuse reflectance (130) sampling techniques transmission IR studies of the surfaces of powdered samples with adsorbed gases (131-136) alumina(137.138). silica (139). and catalyst (140) surfaces diffuse reflectance studies of organo- modified mineral and glass fiber surfaces (141-143) metal overlayer enhanced ATR (144) and spectroelectrochemistry (145-149). 

Reflectance Spectroscopy. Spectra were taken from 600 -2500 nm using a Mark II 6250 Diffuse Reflectance Spectrometer obtained from Pacific Scientific. This... 

Lezna and coworkers (Juanto et al., 1994 Lezna et al., 2003) combined diffuse reflectance UV-vis spectroscopy with cyclovoltammetry, using a specially designed spectrometer with an optical multichannel analyzer. 

Binary copper-based catalysts were prepared by coprecipitation method and some components were added as promoters into the binary catalysts. The methanol synthesis reaction was carried out in a continuous flow microreactor operated at 22 atm and at various temperatures. Reaction pathway of the methanol synthesis was investigated through FT-IR spectroscopy. For the catalyst with a copper content over 15wt%, the diffuse reflectance method (DRIFT) was applied, but for fee catalyst wife a copper content of 7wt%, the transmission teclmique was used. For more information about intermediates, TPD of adsorbed methanol was carried out and the products were analyzed using mass spectrometer. 

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