Monochromator Infrared Spectrophotometer

The various steps that may be followed sequentially to operate a double-monochromator infrared spectrophotometer are described below  

Experimental Profile of Infrared Spectroscopy Quantitative Analysis 

In usual practice, there are two methods that are frequently employed for the determination of the transmittance ratio in quantitative analysis namely  

The above two methods shall be discussed briefly with the help of certain typical examples as detailed below  

This particular method is often employed in a situation where the absorption bands of the analyte are found to be very close to those of the main constituent or the internal standard. 

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The schematic layout of a single-monochromator infrared spectrophotometer has been duly depicted in Figure 22.2. 

Figure 22.2. Optical Diagram of a Single-Monochromator Infrared Spectrophotometer.

Figure 22.3 Optical Diagram of a Double-Monochromator Infrared Spectrophotometer (Beckman Model IR-9)...

The various components of a double-monochromator infrared spectrophotometer shown in Figure 22.3 are as follows below ... 

Fig. 19.2 Layout of an infrared spectrophotometer employing a diffraction grating for monochromation. Reproduced by permission from R. C. J. Osland, Principles and Practices of Infrared Spectroscopy, 2nd edn, Philips Ltd, 1985.

The infrared spectrophotometers are based on either single monochromation or double monochromation ... 

Mirror Ml refocuses the alternate pulses of reference- and sample-beam energy on the entrance slit SI of the monochromator. The monochromator performs three functions basic to the operation of an infrared spectrophotometer ... 

Spectrometric methods Methods based on the absorption, emission, or fluorescence of electromagnetic radiation that is related to the amount of analyte in the sample. Spectrophotometer A spectrometer designed for the measurement of the absorption of ultraviolet, visible, or infrared radiation. The instrument includes a source of radiation, a monochromator, and an electrical means of measuring the ratio of the intensities of the sample and reference beams. 

The necessary instrumentation for making dichroic measurements depends on the technique used. The most common method is to use a single polarizer and an ordinary infrared or ultraviolet spectrophotometer. The sample (thin film) is then placed in the sample beam preferably before the polarizer and generally with the stretch axis at 45° to the entrance slit of the monochromator. This inclination of the stretch axis is to minimize the effect of machine polarization. Such effects have been discussed by Makus and Shareliff (42) and Jones (28). The electric vector of the polarizer is then aligned either parallel or... 

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.

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