Infrared spectrometer dispersive

Advantages of Fourier transform infrared spectrometers are so great that it is nearly impossible to purchase a dispersive infrared spectrometer. Fourier transform visible and ultraviolet spectrometers are not commercially available, because of the requirement to sample the interferometer at intervals of S = l/(2Av). For visible spectroscopy, Av could be 25 000 cm 1 (corresponding to 400 nm), giving S = 0.2 im and a mirror movement of 0.1 xm between data points. Such fine control over significant ranges of mirror motion is not feasible. 

Block diagram of a dispersive infrared spectrometer. The sample beam passes through the sample cell while the reference beam passes through a reference cell that contains only the solvent. A rotating mirror alternately allows light from each of the two beams to enter the monochromator where they are compared. The chart recorder graphs the difference in light transmittance between the two beams. 

A typical IR spectrometer consists of the following components radiation source, sampling area, monochromator (in a dispersive instrument), an interference filter or interferometer (in a non-dispersive instrument), a detector, and a recorder or data-handling system. The instrumentation requirements for the mid-infrared, the far-infrared, and the near-infrared regions are different. Most commercial dispersive infrared spectrometers are designed to operate in the mid-infrared region (4000-400 cm ). An FTIR spectrometer with proper radiation sources and detectors can cover the entire IR region. In this section, the types of radiation sources, optical systems, and detectors used in the IR spectrometer are discussed. 

Figure 1 illustrates a data path in a typical ratio-recording, dispersive infrared spectrometer. The digitization of the analogue signal produced by the detector M.A. Ford, in Computer Methods in UV, Visible and IR Spectroscopy , ed. W.O. George and... 

Of the several advantages of FT over dispersive infrared spectrometers [23], two are particularly important in the in-situ study of the near-electrode region. 

Those aspects of modern dispersive infrared spectrometers which are necessary for understanding the principles of operation and the capabilities and limitations of typical instrumentation were discussed. 

Analysis The analyses were performed on-line by infiured spectroscopy (IR) and mass spectrometry (MS). The former method used a dispersive infrared spectrometer (Perkin-Elmer 580B) with a multiple path cell (2.4m total path length) and a control... 

The chemist often obtains the spectrum of a compound by dissolving it in a solvent (Section 2.6). The solution is then placed in the sample beam while pure solvent is placed in the reference beam in an identical cell. The instrument automatically subtracts the spectrum of the solvent from that of the sample. The instrument also cancels out the effects of the infrared-active atmospheric gases, carbon dioxide and water vapor, from the spectrum of the sample (they are present in both beams). This convenience feature is the reason most dispersive infrared spectrometers are double-beam (sample -I- reference) instruments that measure intensity ratios since the solvent absorbs in both beams, it is in both terms of the ratio h / 4 and cancels out. If a pure liquid is analyzed (no solvent), the compound is placed in the sample beam and nothing is inserted into the reference beam. When the spectrum of the liquid is obtained, the effects of the atmospheric gases are automatically canceled since they are present in both beams. 

The data collection protocol employed to pick out the absorptions of interest is generally a difference data manipulation, which varies according to the type of spectrometer employed. The early in situ infrared studies were carried out using dispersive infrared spectrometers with their attendant low power sources and noisy detectors. The simplest approach to the sensitivity problem is exemplified by the first in situ infrared paper by Mark and Pons [39], which reported a study of the reduction of 8-quinolinol solution by electrolysis at —1.8V until sufficient... 

Perkin-Elmer introduced in 1975 the first microprocessor-controlled commercial dispersion infrared spectrometer, and advantage was taken of this facility for lipid studies a few years later (Chapman et aL, 1980). The monochromator is synchronized with the recorder drive by the abscissa microprocessor for accurate reproduction of wavenumber settings. The source radiation is split in two, one beam passing through the sample, whilst the other serves as a... 

Figure 2 Examples of liquid cells for mId-Infrared transmission measurements (A) sealed vacuum tight liquid cell with an amalgam spacer for FT-IR, (B) exploded view of a liquid cell design with a rectangular aperture for use with a dispersive infrared spectrometer, and (C) semipermanent (demountable) liquid cell for FT-IR with Teflon spacer, and fitted with a Luer fitting and Teflon plugs.

Goddu and Delker [71] reported that terminal epoxides exhibit sharp absorbances relatively free of spectral interferences in the near IR at 2.2 pm and 1.65 pm (4532 cm and 6060 cm ). These absorptions result from overtones and/or combinations of fundamental vibrations found in the mid-IR. Using a dispersive infrared spectrometer, Dannenburg [72] conducted a study of epoxides in solution. Sensitivity was restricted by the capabilities of instrumentation available at that time. These investigations were limited to epoxide resins with an equivalent weight <1000 g resin/g-eq epoxy. Concentration levels for these resins were >1.0 eq/1. 

Time-Resolved Measurements Using a Dispersive Infrared Spectrometer... 

Infrared spectroscopy has been applied to the characterization of molecules. Conventional dispersive infrared spectrometers have been replaced by Fourier-transform infrared equipment, which incorporates a Michelson interferometer and presents a series of advantages over dispersive systems, such as an improvement of energy and the simultaneous measurement of the whole spectral range. 

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