Proper sample preparation is essential for obtaining accurate IR spectra.
Techniques vary based on the sample's physical state: solid, liquid, gas, or solution.
1) Solid Sampling:
a) KBr Pellet Technique:
Solid is ground with potassium bromide (transparent to IR) and pressed into a pellet.
b) Mull Technique:
Solid is mixed with mineral oil to form a mull, then spread between NaCl salt plates.
c) Diffuse Reflectance (DRIFT):
Used for solids unsuitable for other methods. The sample is mixed with a reflective medium, and the reflected IR radiation is analyzed.
2) Liquid Sampling:
a) Thin Film:
A thin liquid film is placed between NaCl plates for analysis, suitable for non-corrosive liquids.
b) Solution Technique:
Sample dissolved in an IR-transparent solvent and analyzed in a liquid cell or between salt plates.
3) Gas Sampling:
a) Gas Cells:
Special cells with salt windows and variable path lengths are used. The gas is sealed in the cell for analysis.
4) Solution Sampling:
a) Salt Plates:
A drop of solution is placed between plates. After solvent evaporation, the remaining solute is analyzed.
b) Liquid Cells:
Two salt plates, separated by a thin spacer, form a liquid cell. The solution is added for spectrum measurement.
