Diffuse reflectance accessories

A Perkin Elmer Diffuse Reflectance Accessory Cat. L127-5000 was used on a Perkin Elmer Spectrum 1000 FT-IR. 

Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT).6 When IR radiation is directed onto the surface of a solid sample, two types of energy reflectance can occur specular and diffuse. The specular component is the radiation that reflects directly off the sample surface (i.e., not absorbed by the sample). Diffuse reflectance is the radiation that penetrates into the sample and then emerges. Diffuse reflectance accessories are designed to optimize the diffuse reflected energy and suppress the specular component. The optics therefore selectively directs the scattered radiation to the IR detector. 

Diffuse reflectance FTIR spectra of the ground Mo03/Al203 catalysts were recorded on an FTIR instrument (Nicolet, Model 740, MCT detector). The microreactor in the flow system was replaced by an FTIR cell. The cell used a Harrick diffuse reflectance accessory (DRA-2CO) fitted with a controlled environmental chamber (HVC-DRP). Spectra (500 scans, 4 cm 1 resolution) were presented in Kubelka-Munk units and recorded at RT. 

Reflectance spectra are usually measured using a diffuse reflectance accessory with an integrating sphere attached to a spectrophotometer. Spectra are referenced against a reflectance standard, such as smoked MgO, barite or Halon powder. The latter is a commercial fluorocarbon that does not absorb water or suffer radiation damage as does MgO. Each of these standards is virtually free of spectral features in the wavelength range 0.3 to 2.5 pm. 

Figure 12 The Spectra-Tech Collector diffuse reflectance accessory. A typical accessory for the study of particles and powders by diffuse reflectance FTIR. 

Fig. 4.1.4. Diffuse reflectance accessory (Spectra-Tech Inc.). / Movable stage with Blocker device to diminish the specular component of reflectance 2 two movable parts of the hemiellipsoidal mirror. The mirror opens for sample positioning 3 mirror system to reflect the IR beam from the source to the detector A macro sample holder B micro sample holder...

Figure 6.4-19 Optical schemes of different diffuse-reflection accessories, (a) in-plane configuration, usable with blocker (b) out-of-plane configuration (c) attachment for large samples (Korte and Otto, 1988).

Figure 12.9 Diffuse reflection accessory (with the permission of the Harhck Scientific Corporation. Croton Dam Road. Ossining. New York).

R. Marbach and H. M. Heise, Optical Diffuse Reflectance Accessory for Measurements of Skin Tissue by Near-Infrared Spectroscopy, Appl. Optics, 34(4), 610 (1995). 

Figure 9.24 Optical diagram of a diffuse reflectance accessory for an FTIR instrument.

NH3-DRIFT (Diffuse Reflectance Infrared Fourier Transform) spectra were collected with a Brucker IF S88 spectrometer performing 200 scans with a resolution of 4 cm. Pure samples were placed inside a commercial controlled environmental chamber (Spectra-Tech 0030-103) attached to a diffuse reflectance accessory (Spectra-Tech collector). To investigate the stability of the adsorbed ammonia species during temperature elevation, the spectra were recorded under helium (30ml/min) at room temperature, 373, 473, and 573 K, after exposure to an ammonia flow for 30 min at room temperature. 

Diffuse reflection spectroscopy (UV-DRS). UV-Vis diffuse reflectance spectra were recorded in a Varian Cary 5 spectrophotometer (Harrick Scientific) with a diffuse reflectance accessory of Praying Mantis geometry. The samples were set in holds with 2 mm thickness. The spectra were recorded in the 200 nm and 800 nm range with a scanning speed of 1800 mm.min at room temperature against supports as reference. 

Diffuse reflectance infrared Fourier transform (DRIFT) spectra are obtained when IR radiation is incident on a scattering sample at a specific angle and is reflected at all angles. The diffuse reflectance process involves transmission, scattering, and reflection [67]. The technique is used to analyze an intact lignin sample without modification [65]. To study a sample by DRIFT, the sample is either dispersed in KBr (e.g., MWL) or is analyzed directly (e.g., paper sheet) and placed at the focal point of the diffuse reflectance accessory. The scattered light from the sample is collected... 

Figure 12. Schematic diagram of diffuse reflectance accessory.

Cary 5 spectrometer with a diffuse reflectance accessory. The characterisation was performed before and after catalytic tests. 

The diffuse reflectance accessory (model DRA-2CN, Harrick Scientific) was modified with a three-dimensional translational stage to optimally position the sample for maximum radiation throughput (15). The sample cell (model HVC-DRP, Harrick Scientific) was heated by a resistive heater contained within a post that housed a sample cup. The base of the sample cell also contained an external connector for evacuation and a second port, which was sealed with a septum and used for the introduction of pyridine by microsyringe. The sample cell cover contained a channel and connectors for water cooling and ZnSe windows (12 mm in diameter) for the IR radiation. The base and cover of the cell were sealed vacuum-right with an O-ring. 

Diffuse—reflectance electron absorption spectroscopy was performed on a Perkin-Elmer 320 UV-VIS spectrometer equipped with a diffuse-reflectance accessory. 

Diffuse Reflectance spectra (DRS) of samples were recorded using a Caiy 5 spectrometer with a diffuse reflectance accessory in the wavelength range 200-2500 nm, covering UV, visible and near-infrared regions. 

UV/VIS-DRS measurements were performed using a Cary 400 UV/VIS spectrometer (Varian) equipped with a diffuse reflectance accessory (praying mantis, Harrick). The reflectance spectra were converted into the Kubelka-Munk function F(R) which is proportional to the absorption coefficient for low values of F(R). Spectra were deconvoluted into Gaussian bands using the GRAMS/386 program (Galactic Industries Corporation). 

Fig 1. Schematic of the Bruker Diffuse Reflectance Accessory used in the present work... 

The schematic setup of a diffuse reflectance spectrometer which is obtained by supplying a normal UV-VIS spectrometer with a diffuse reflectance accessory is shown in Fig. 18. The core is an integrating sphere coated with a highly reflective material that collects the scattered radiation and leads it to the detector. The light remitted by the sample is compared with that of a white standard as the reference. Zeolite layers of ca. 5 mm depth are generally sufficient to meet the condition of infinite thickness. A typical sample cell furnished with an evacuated Infrasil double window and designed for temperature control and evacuation is depicted in the lower part of Fig. 18 [32]. Other cell constructions have been reported by Klier [31] and Schoonheydt [34]. 

Weakly scattering solids can be investigated by transmission techniques. For strongly scattering samples, diffuse reflection accessories must be used. 

Figure 4.6. Schematic arrangement of conventionai diffuse-reflectance accessory for measuring multiple-transmission spectra of microsamples. (1,2) focusing optical system of accessory (3) sample holder (4) plate under study (5) metallic mirrors, (a) Plate with polished surfaces placed between ground metallic surfaces. (6) Plate with ground surfaces placed between polished mirrors. Reprinted, by permission, from V. P. Tolstoy, Methodsof UV-Vis and IR Spectroscopy of Nanolayers, St. Petersburg University Press, 1998, p. 130, Fig. 4.10. Copyright 1998 St. Petersburg University Press.

Figure 4.28. Optical diagram of Praying Mantis (Harrick Scientific Inc.) diffuse-reflectance accessory Mi, M2, M5, Me — plane mirrors Ms, M4 — 6 1 90° off-axis focusing and collecting ellipsoids. Sample is placed at position S. Adapted, by permission, from K. Moradi, C. Depecker, and J. Corset, Appl. Spectrosc. 48,1491 (1994), p. 1492, Fig. 2. Copyright 1994 Society for Applied Spectroscopy.

Figure 4.29. Diffuse-reflectance accessory with Blocker. Reprinted, by permission, from R. G. Messerschmidt, Appl. Spectrosc. 39, 737 (1985). Copyright 1985 Society for Applied Spectroscopy.

The samples were dried and analyzed by FTIR from 4000 to 400 cm, with 128 scans collected at intervals of 4 cm L Then, FTIR analyses were carried out in a Spectrophotometer Thermo Scientific Nicolet 6700 equipped with DTGS detector with diffuse reflectance accessory (DRIFT). 

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