Infrared Spectroscopy Analysis Method

Infrared spectroscopy analysis is a common method of structural analysis of substances. When molecules absorb infrared radiation of specific frequencies, their vibrational state changes, producing an infrared spectrum. Through infrared spectroscopy, we can learn about the functional groups, structure, and other related information of a substance.

 

Principle of Infrared Spectroscopy

The theory of infrared spectroscopy takes advantage of the concept that molecules tend to absorb light of specific frequencies, which are characteristic of the corresponding molecular structures. The energy depends on the shape of the molecular surface, the related electronic vibration coupling, and the mass corresponding to the atoms. For example, a molecule can absorb the energy contained in the incident light, resulting in faster rotation or more apparent vibrations.

 

Infrared Spectroscopy Samples

Samples used in infrared spectroscopy can be in solid, liquid, or gaseous states.

 

1. Solid samples can be prepared by grinding the sample with an oil-like grinding agent. Now, a thin layer of this paste can be coated on a salt plate to be measured.

2. Liquid samples are usually kept between two salt plates and measured, as salt plates are transparent to infrared light. Salt plates can be made of sodium chloride, calcium fluoride, or even potassium bromide.

3. Since the concentration of gaseous samples can be one in a million, the sample pool must have a relatively long path length, i.e., the light must propagate a relatively long distance within the sample pool.

 

Hence, samples of various physical states can be used for infrared spectroscopy analysis.

 

FAQ

1. Can Water Be Used in Infrared Spectroscopy?

Water cannot be used as a solvent in infrared spectroscopy because it has two high infrared absorption peaks. Moreover, water is a polar solvent that can dissolve alkali metal halide pans, which are widely used in infrared.

 

2. What Is the Sensitivity of Infrared Spectroscopy?

Infrared spectroscopy can now identify samples as small as 1 to 10 grams. Almost all organic and some inorganic molecules can be analyzed using infrared spectroscopy. It can be used for both qualitative and quantitative analysis, with a wide range of applications.

 

3. What Are the Necessary Conditions for Infrared Spectroscopy Analysis?

The necessary condition for a molecule or sample to show an infrared spectrum based on the selection rules of infrared transitions is that there is a change in the dipole moment during the vibration of the functional groups in the molecule or sample.

 

4. What Solvents Are Used in Infrared Spectroscopy?

Carbon tetrachloride (CCl4) and carbon disulfide (CS2) are the most commonly used solvents. Polar material solvents include chloroform, dichloromethane, acetonitrile, and acetone. Solid reduced to fine particles can be analyzed as a thin paste or slurry.