Infrared spectroscopy is a powerful tool that can analyze various types of samples, including solids, liquids, and gases. This technique involves preparing the samples in a way that allows them to be transparent to infrared radiation. Commonly, salts like NaCl or KBr are used for this purpose.
What types of samples can be analyzed by infrared spectroscopy? (7 Key Methods)
1. Solid Samples
Solid samples can be analyzed using several techniques:
1.1 Mull Technique
In this method, finely crushed solid samples are mixed with Nujol, a mulling agent, to form a thick paste. This paste is then spread as a thin film onto salt plates and placed in the path of an IR beam for spectral recording.
1.2 Solid Run in Solution
Here, 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 for IR analysis.
1.3 Nujol Mull Method
An alternative method involves creating Nujol mulls between KBr plates. The solid is ground to a particle size of 1 to 2 microns, mixed with Nujol, and spread between KBr plates. This method is effective if the particle size is smaller than the wavelength of the light to be transmitted.
2. Liquid Samples
Liquid samples are typically analyzed by placing a thin film of the liquid between salt plates or by using a liquid cell with a path length adjusted to the sample's absorbance properties.
3. Gas Samples
Gas samples are analyzed using gas cells with known path lengths, where the gas is sealed inside and exposed to the IR beam.
4. Infrared Spectrometer
The IR spectrometer detects the absorption of specific wavelengths of infrared light by the bonds in the sample. Each type of bond absorbs a characteristic wavelength, allowing the identification of the functional groups present in the molecule.
5. Measurement Methods
Different methods are employed based on the sample form:
5.1 Diffuse Reflection Method
Suitable for powder samples, where the light is scattered by the sample.
5.2 Attenuated Total Reflection (ATR)
Allows direct measurement of powder samples by reflecting light internally multiple times within a crystal, interacting with the sample.
These methods ensure that the sample is prepared and analyzed in a way that maximizes the transmission and absorption of IR radiation, providing accurate spectral data for chemical analysis.
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