Write a short note on Non-Dispersive Infrared Spectroscopy.
In non-dispersive IR spectrophotometry, the IR radiation from a source is not dispersed according to wavelength by a prism as in a standard IR spectrometer. This technique has been used to monitor gas streams and in air pollution studies. It depends mainly on selective filtering for specificity. The radiation from an IR source is ‘chopped’ by a rotating device so that it alternately passes through a sample cell and a reference cell (See figure Below). Both the beams are incident on a detector which is filled with CO gas.
The detector is divided with two compartments by a flexible diaphragm. The relative amounts of IR radiations absorbed by CO in the two sections of the detector are determined by the CO level in the sample. The difference in the amount of IR radiation absorbed is the two compartments give rise to temperature difference so that the diaphragm even to a slight extent can be measured with relative accuracy of 5 per cent.