Module 8 Infrared spectroscopy (1 Viewer)

[NexusRich]

Could someone please explain what are the function of the reference and the sample cells in the set up of infrared spectroscopy ? Thanks in advance

 

[Eagle Mum]

Could someone please explain what are the function of the reference and the sample cells in the set up of infrared spectroscopy ? Thanks in advance

The sample cell is where you place the unknown substance of interest which you are interested in identifying or quantifying. The reference cell is for comparison. In qualitative analyses, the reference cell is often a blank (the cuvette container alone or with distilled water) whilst in quantitative analyses, it would contain a known concentration and serve as a reference standard.

For qualitative analyses, most substances have a unique spectral pattern of absorption (ie. absorb energy at specific electromagnetic wavelength(s)). However, there is also background spectral absorption by the cell cuvette’s glass or plastic material and by atmospheric particles, so there might be a reference ‘blank’. The infrared light beam is split in two and simultaneously projected through the sample and reference cells. The absorption spectra of the blank is subtracted from the total spectra of the unknown substance in its cuvette to isolate the characteristic spectra of the unknown substance which can be compared to published data on the absorption wavelengths of specific substances.

If the identity of the substance of interest is known, for quantitative analyses, reference cells would contain known concentrations of the substance, so that the peak heights of absorption, at known specific wavelengths, by the sample and reference cell(s) can be compared to determine the concentration of the substance of interest in the sample.