Spectrophotometer configurations

FIGURE 4.7 Diagram of a predispersive, fast-scanning, grating spectrophotometer configured for reflectance or transmittance. (Courtesy of NIR Systems, Inc.)... 

The goal of the basic infrared experiment is to determine changes in the intensity of a beam of infrared radiation as a function of wavelength or frequency (2.5-50 im or 4000—200 cm respectively) after it interacts with the sample. The centerpiece of most equipment configurations is the infrared spectrophotometer. Its function is to disperse the light from a broadband infrared source and to measure its intensity at each frequency. The ratio of the intensity before and after the light interacts with the sample is determined. The plot of this ratio versus frequency is the infrared spectrum. 

Diode-array spectrophotometers have no moving parts, or at most a shutter that moves thus they are more suited to locations near the process. However, these instruments still require the introduction of the sample into the instrument s sample cavity, as well as the necessity for a separate reference measurement. These instruments are usually only found in a single-beam configuration. 

Raman spectra were taken on a home built system, composed of Spectra-Physics 2020 series lasers, coupled with a Dilor XY-800 triple spectrometer and a Whight Instruments nitrogen cooled CCD. All samples were measured at room temperature in a backscattering configuration, with 514.53 nm Ar+ laser excitation. The laser power was tuned between 1 mW and 30 mW. UV-VIS diffuse reflectance spectra were taken on a Varian Cary 5 spectrophotometer, equipped with a specially designed Praying Mantis diffuse reflectance attachment of Harrick. 

Stewart [505, 585] was the first to investigate systematically the spectra of the rare earth aquo ions, and he reported the following absorption maxima for the Eu3+ ion. It will be seen that the absorption bands in the visible region are of very weak intensity. Later Banes and Kjlengman [586] measured the same spectra using a Cary 14 spectrophotometer and their results for the Eu3+ ion are also reproduced below. A broad band at 1880 A (53190 cm-1) has been observed [587] for 0.03 M europium perchlorate in 0.1 M HGLO4 which may possibly be due to a 4/ - 5d transition of the /8 configuration. 

After a final centrifugation, resuspend cells in fresh fixative to an optical density of about 0.3 at 600 nm (light scattering depends on the configuration of the spectrophotometer and higher or lower values may be needed) and drop about 200 p.1 from about 5 cm on slightly slanted slides. 

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