This document describes several techniques for sampling materials for infrared spectroscopy analysis. The mull technique involves grinding a solid sample into a fine powder and mixing it with mineral oil or Nujol to create a paste that is squeezed between IR transmitting windows. The pressed pellet technique mixes a solid sample with potassium bromide at a ratio of 300:1 and presses it into a pellet under high pressure. Gases are sampled using large cells from 10 cm to 1m in length to account for the small particle size, while liquids are directly placed into rectangular cells made of materials like potassium bromide or sodium chloride.

1. IR Sampling Technique
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2. Content
 Solids run in solution
 Mull technique
 Pressed pellet technique
 Sampling for gases
 Sampling for liquids
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3. Solids may be dissolved in non-aqueous inert solvent
drop of this solution is placed on an alkali metal disc and
solvent is allowed to evaporate
leaving a thin film of solute
which is then mounted in spectrometer.
If the solution of solid can be prepared in a suitable solvent
then the solution is run in concentration of cells for liquids.
Some solvents used are chloroform, carbon tetrachloride,
acetone, Cyclohexane etc
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4. Mull technique:
 In this technique a small quantity of sample is thoroughly
ground in a clean mortar until the powder is very fine.
 After grinding, the mulling agent (mineral oil or Nujol) is
introduced in small quantities just sufficient to take up the
powder (mixture approximates the consistency of a toothpaste).
 The mixture is then transferred to the mull plates & the plates
are squeezed together to adjust the thickness of the sample
between IR transmitting windows.
 This is then mounted in a path of IR beam and the spectrum is
run.
 The mineral oil itself exhibits a number of intense absorption
bands (observed at 2952, 2923, 2853, 1458, and 1376 cm21)
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5. Pressed pellet technique:
 Potassium bromide + Drug (300 : 1)
 pressed under very high pressure (25000 p sig)
in evacuable die or mini press to form a small
pellet (about 1-2 mm thick and 1cm in
diameter).
 it is placed in path of the beam of IR
spectrometer and a blank KBr pellet of identical
thickness is kept in the path of reference beam
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6. Sampling for gases:
 Small size particles hence the cells are
large.
 •10 cm to 1m long
 •Multiple reflections can be used to
make the effective path length as long
as 40 cm
 •Lacks sensitivity
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7. Sampling for liquids:
 Liquid samples taken.
 •Put it into rectangular cells of KBr, NaCl etc.
 •I R spectra obtained.
 •Sample thickness … such that transmittance
lies between 15 – 20 % i.e., 0.015 – 0.05 mm
in thickness.
 •For double beam, matched cells are generally
employed
 •One cell contains sample while other has
solvent used in sample.
 •Matched cells should be of same thickness,
protect from moisture.
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