Integrating sphere attachments

Recording spectrophotometer with integrating sphere attachment, with ports for sample and standard... 

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. 

Ultraviolet spectra measurements were performed with a Shimadzu UV-200 spectrophotometer equipped with a holder for KBr pellet. To attenuate the scattered light ultraviolet absorption spectra were measured by the method of an integrating sphere attached to a spectrophotometer. 

Most high-accuracy spectrophotometers incorporate an integrating sphere attachment to collect diffuse reflections or transmissions from specimens. 

Fig. 1.1. Integrating sphere attachment. After Burgess [9]. Reprinted with permission from Spectroscopy in Process and Quality Control (SPQ), 1998. Proceedings SPQ-98 is a copyrighted publication of Advanstar Communications Inc. All rights reserved.

Spectral hemispherical transmittance of samples is measured using a Perkin-Elmer Lambda-9 dual-beam UV-VIS-NIR spectrophotometer with an integrating-sphere attachment. Use of such a device allows the absolute transmittance to be measured as po- ASTM E903. Such spectral measurements can then be eonvolved with an appropriate standard terrestrial spectrum (as specified by ASTM G173) to compute a solar-weighted hemispherical transmittance, T2 (>.=200 nm to 2600 nm), as a meaningful single measure of optical performance. 

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. 

UV-VIS-NIR diffuse reflectance (DR) spectra were measured using a Perkin-Elmer UV-VIS-NIR spectrometer Lambda 19 equipped with a diffuse reflectance attachment with an integrating sphere coated by BaS04. Spectra of sample in 5 mm thick silica cell were recorded in a differential mode with the parent zeolite treated at the same conditions as a reference. For details see Ref. [5], The absorption intensity was calculated from the Schuster-Kubelka-Munk equation F(R ,) = (l-R< )2/2Roo, where R is the diffuse reflectance from a semi-infinite layer and F(R00) is proportional to the absorption coefficient. 

Attach an integrating sphere to a spectrophotometer, turn on the spectrophotometer, and allow it to warm up for 30 min prior to use. 

Fig. 18. A Schematic representation of a diffuse reflectance spectrometer. For (i) nondiffuse dispersed illumination the source at the left and the detector at the integrating sphere are used. For (ii) diffuse nondisperse illumination (in the case of fluorescent samples) a source directly attached to the sphere and the detectors on the left upper side are applied. B Temperature-regulated and evacuable diffuse reflectance sample cell according to [32]. Reprinted from [32] with permission of Academic Press, Inc...

Diffuse reflectance UV-Vis spectra were obtained with a Shimadzu UV-2401PC UV-Vis spectrometer equipped with an integration sphere diffuse reflectance attachment. The samples were used as powders and a halon white (PTFE) reflectance standard used to record the baseline. The reflectance spectra were taken over the range 200 to 800 nm and converted into Kubelka-Munk function F(R). 

The accessories usually attached to commercially available NIR spectrometers are considered first. As NIR spectra depend sensitively on temperature, thermostats to stabilize the temperature of samples, mainly liquid samples in an optical cell, are usually provided. An integrating sphere is necessary for measurements of diffuse reflection. Attachments for measuring transmission spectra from samples outside the body of the spectrometer are used for samples that cannot be put into the sample compartment of the spectrometer, or are used with an automatic sampler. Ports for the optical fibers are of especial practical importance, because optical fibers of many kinds are used to measure NIR spectra of samples in various shapes and states, including high pressure and high temperatures an appropriate optical fiber should be used for the sample to be studied. 

Likewise, there are a vast array of attachments for solid samples, whether for transmission studies or for surface reflectance investigations. In particular, many attachments provide either a method of integrating total reflectance (as in integrating spheres to surround the sample) or to orientate the surface with respect to the light beam and detector so as to probe specular and diffuse reflectance. 

ATP synthase actually consists of two principal complexes. The spheres observed in electron micrographs make up the Fj unit, which catalyzes ATP synthesis. These Fj spheres are attached to an integral membrane protein aggregate called the Fq unit. Fj consists of five polypeptide chains named a, j3, y, 8, and e, with a subunit stoichiometry ajjSaySe (Table 21.3). Fq consists of three hydrophobic subunits denoted by a, b, and c, with an apparent stoichiometry of ajbgCg.ig- Fq forms the transmembrane pore or channel through which protons move to drive ATP synthesis. The a, j3, y, 8, and e subunits of Fj contain 510, 482, 272, 146, and 50 amino acids, respectively, with a total molecular mass... 

In the liner approximation, we see thus that the NHIM is made of periodic/ quasi-periodic orbits, organized in the usual tori characteristic of the integrable systems. Because the NHIM is normally hyperbolic, each point of the sphere has stable/unstable manifolds attached to it. This situation is exactly parallel to the one described earlier for PODS. The equation for it is... 

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