Tech Team · Kintek Solution

In IR spectroscopy, different sampling techniques are employed depending on the state of the sample (solid, liquid, or gas). For solid samples, techniques include the mull technique, solid run in solution, cast film technique, and pressed pellet technique. For liquid samples, methods such as diffuse reflection and attenuated total reflection are utilized.

Sampling of Solids:

1. Mull Technique: This involves mixing a finely crushed solid sample with Nujol (a mulling agent) to form a thick paste. This paste is then spread as a thin film onto salt plates and analyzed.
2. Solid Run in Solution: The solid sample is dissolved in a non-aqueous solvent that does not interact chemically with the sample. A drop of this solution is placed on an alkali metal disc, and the solvent is evaporated, leaving a thin film of the solute.
3. Cast Film Technique: Used for amorphous solids, this method involves depositing a sample on a KBr or NaCl cell by evaporating a solution of the solid. The film must be thin enough to allow IR radiation to pass through.
4. Pressed Pellet Technique: Finely ground solid is mixed with potassium bromide and compressed into a pellet using a hydraulic press. These pellets are transparent to IR radiation and are suitable for analysis.

Sampling of Liquids:

• Diffuse Reflection Method: This method is suitable for powder samples and has gained popularity with the advent of FTIR. It involves the reflection of IR radiation from the surface of the sample.
• Attenuated Total Reflection (ATR): This technique allows direct measurement of powder samples by reflecting IR radiation internally within a crystal, enabling analysis without the need for sample preparation.

These techniques ensure that the samples are prepared in a manner that allows effective interaction with IR radiation, facilitating accurate analysis of the chemical bonds present in the sample.

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