Infrared spectrophotometer dispersive

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. 

Traditional infrared spectrophotometers were constructed with mono-chromation being carried out using sodium chloride or potassium bromide prisms, but these had the disadvantage that the prisms are hygroscopic and the middle-infrared region normally necessitated the use of two different prisms in order to obtain adequate dispersion over the whole range. 

The infrared spectrophotometer is the principal instrument used by scientists for ihcse measurements. Most laboratory spectrophotometers are of a dispersive design, i.e.. a prism or grating is used to separate the spectral components in the source radiation. Modern infrared spectrophotometers base it wide wavelength range from 2 to 50 micrometers. They lind use in research, quality control, and analytical service laboratories. 

The infrared spectrum of pantoprazole sodium was obtained in a KBr pellet (2% dispersion level) using a Perkin-Elmer 410 infrared spectrophotometer. The spectrum is shown in Figure 6, and the assignments for the major absorption bands are found in Table 2. 

Fig. 10. Improvement of the infrared spectrophotometer. Infrared spectra of fully oxidized bovine heart cytochrome c oxidase cyanide derivatives measured with (A) a dispersive infrared spectrophotometer (Perkin-Elmer Model 180) and (B) a FTIR spectrometer equipped with a mercury/cadmium/tellurium detector (Perkin-Elmer Model 1800). Concentrations of the enzyme (O.VmM) and cyanide (19.4 M) were identical in both measurements.

Since this is a book concerned primarily with applications, no further details are given concerning instrumentation. The reader is referred to Alpert et al. (1970), in which are discussed an optical diagram of a double-beam spectrophotometer operating variables (resolution, photometric accuracy) components of infrared spectrophotometers (sources, types of photometers, dispersing elements, detectors, amplifiers, and recorders) special operating features, such as optimization of scan time and available instruments and their specifications. The books by Martin (1966), Conn and Avery (1960), and Potts (1963), and the chapter by Herscher (1966) are also recommended for details on some of these topics. 

The infrared spectrum of hydralazine hydrochloride (Figure 1) was obtained with a Beckman IR-12 spectrophotometer. A mineral oil dispersion between potassium bromide plates was scanned from 420 to 4000 cm-1, and a thicker layer of the dispersion, supported on polyethylene film,... 

The infrared spectrum of pseudoephedrine hydrochloride is shown in Figure 1. It was obtained as a 0.2% dispersion of pseudoephedrine hydrochloride in KBr with a Nicolet Model 7199 FT-IR spectrophotometer.2 Table I gives the infrared assignments consistent with the structure of pseudoephedrine hydrochloride. 

Samples of both fulvic and humic acids were suspended in methanol and methylated with diazomethane. Both H and spectra of the free acids were obtained, at 299.94 MHz and 75.42 MHz respectively, on a Varian XL-300 spectrometer having a Nicolet TT-100 PET accessory. Spectra were obtained in D2O, in a 12-mm tube, with deuterated TSP (sodium 3-(trimethylsilyl)propionate-, , 3,3- 4) added as internal reference. GC/MS of methylated acids was conducted on a Hewlett-Packard Model No 5995 GC/MS/DA system equipped with a fused silica capillary column (12 m x. 020 mm ID, Hewlett Packard) internally coated with crosslinked methylene silicone. Infrared spectra were obtained with solid samples dispersed in KBr pellets, by using a Beckman IR-33 spectrophotometer. The various absorption peaks in IR and NMR were interpreted conventionally (9-10). 

This instrument has evolved from ihe laboratory spectrophotometer to satisfy the specific needs of industrial process control. While dispersive instruments continue to be used in some applications, the workhorse infrared analyzers in process control are predominantly nondispersive infrared (NDIR) analyzers. The NDIR analyzer ean be used for either gas or liquid analysis. For simplicity, the following discussion addresses the NDIR gas analyzer, hut it should be recognized that the same measurement principle applies to liquids. The use of infrared as a gas analysis technique is certainly aided by the fact that molecules, such as nitrogen (N ) and oxygen tO , which consist of two like elements, do not absorb in the infrared spectrum. Since nitrogen and oxygen are the primary constituents of air. it is frequently possible to use air as a zero gas. 

The infrared absorption spectrum of gemifloxacin mesylate was recorded on FT-IR model Spectrum BX spectrophotometer (Perkin-Elmer, USA) using a KBr disc ( 2 mg of gemifloxacin mesylate was dispersed in 200 mg KBr). The obtained infrared spectrum is shown in Fig. 4.3, and the assignments of the characteristic bands are tabulated in Table 4.2. 

Three types of infrared instruments are found in modem laboratories dispersive spectrometers (or spectrophotometers), Fourier-transform (FTIR) spectrometers, and fdter photometers. The first two are used for obtaining complete spectra for quali-... 

Figure 10.7 Schematic diagram of spectrometers and analysers in the infrared, (a) Single beam analyser containing a fixed monochromator or a filter used when a measurement at a single wavelength will suffice (b) dispersive spectrometer, double beam system. In contrast to spectrophotometers in the UV/Vis, the sample, located prior to the monochromator is permanently exposed to the full radiation of the source, knowing that the energy of the photons in this region is insufficient to break the chemical bonds and to degrade the sample (c) Fourier transform single beam model.

---