In Diffuse Reflection Mode

These three main classes of process sample streams are in increasing order of difficulty for near-infrared process analysis. In general, liquid streams are best measured in a transmission sampling mode, solids (powders) in diffuse reflectance mode, and slurries in either diffuse reflectance or diffuse transmission according to whether the liquid phase or the suspended phase is of greater analytical signihcance. If the... 

Figure 8.1 Schematic representation of NIR chemical imaging instrument operating in diffuse reflectance mode. Radiation from the illumination source interacts with the sample. Light reflected off of the sample is focused onto a NIR sensitive 2D detector after passing through a solid-state tunable wavelength selection filter.

Clearly, both vibrational and UV-visible spectroscopy also play an important role in materials chemistry, and are well described in other texts. The principles involved in carrying out these experiments on solids rather than in solution are similar, but often experimental methods vary. For example, an IR spectrum of a zeolite would be carried out by dispersing the solid in a matrix of potassium bromide and pressing into a disk, rather than in solution. Typically, a UV-visible spectrum of a solid would be carried out in diffuse reflectance mode, where the solid is dispersed in a white matrix (such as barium carbonate) and the UV light is reflected off the surface rather than passing through a solution. 

The above provides a broad overview of some of the areas of study to which the technique of laser flash photolysis, in diffuse reflectance mode, has been applied with respect to opaque samples. It is hoped that this chapter in conjunction with other published review material [13,14,43,44] provide a complete picture of "the state of the art" of laser flash photolysis of solid surfaces, and reiterates the great potential of this new mode for flash photolysis studies at interfaces. 

The FTIR spectra of nanosilica were recorded in the mid-IR region using a ThermoNicolet FTIR spectrometer in diffuse reflectance mode. The FTIR spectra of PVA/silica films were recorded using a FT/IR-4100 (JASCO Benelux B.V.) spectrometer in transmittance mode. 

Inert sampling could be done when desired. Zr, W and Ni were determined by XRF, Ti and Cr by neutron activation analysis (NAA), Mg by AAS, C with a Leco carbon analyzer and Cl by potentiometric titration. FTIR in diffuse reflectance mode was used to follow the chemisorption and to detect possible decomposition of the reactant. Scanning electron microscopy with an energy dispersive spectrometer (SEM/EDS) was used to determine element concentrations through the particles. The specific surface area and pore volume were determined by means of nitrogen adsorption and condensation with Micromeritics ASAP 2400 equipment. Detailed experimental conditions used in the characterization are in Ref. 16. 

Full NIR spectra of a set of 74 neat polymer additives, measured with an optical fibre probe and taken in diffuse reflectance mode, have been used for qual-... 

Cost-effective, non-invasive, quantitative and simultaneous determination of low level Tlnuvin 770 (0.05 to 0.4 wt.%) and Irganox 225 (0.1 to 0.45 wt.%) contents in PP pellets by NIRS in diffuse reflection mode using MLWR and PLS spectroscopic models has been reported [287]. Seven samples were used for calibration and two for validation. Spectral bands attributable to Tinuvin 770 and Irganox 225 appear at 1560 nm and 1390 nm, respectively. For Tinuvin 770 a two factor PLS model from 1500 to 1600 nm was developed for Irganox 225 a four factor PLS model in the 1360 to 1460 nm region. A quotient-term multiple linear least-squares spectroscopic model was derived that characterises analyte concentration and corrects for spectroscopic differences within the matrix due to the extruder/pelletisers. Reported standard deviations of ca. 25 ppm for Tinuvin 770 and ca. 80 ppm for Irganox 225, or relative standard errors of 0.01 wt.% for Tinuvin 770 and 0.03 wt.% for Irganox 225, approach the accuracy of the reference analytical method. 

Ciurczak [350] has reviewed general analytical appUcations of NIRS. Applications of NIR spectroscopy to polymers [259,294] and textiles [315] have also been described. Siesler [278] has recently reviewed the quantitative determination of the additive content in plastics by means of NIR in diffuse reflection mode. 

FTIR analyses were done on Nicolet Nexus FTIR Raman spectrometer at room temperature in diffusion-reflectance mode (2 wt% HPC in KBr). Solid-state NMR analyses were carried out on a Bruker 400 MHz spectrometer. TGA-DSC analyses were performed on Setaram TGA-DSC 111 apparatus by heating the samples up to 600°C in N2 at heating rate of 5°C/min. The mass changes and heat flow were recorded against the temperature. HR-TEM and EDX analyses were performed using a JEOL 2010 microscope, operating at 200 kV. 

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