IR spectroscopy is a technique used to identify and analyze the chemical composition of solid, liquid, or gas samples.
It does this by measuring the absorption of infrared radiation by the sample.
This technique is based on the principle that different chemical bonds within a molecule absorb specific wavelengths of infrared light.
These wavelengths correspond to the vibrational and rotational energy levels of the molecule.
By analyzing the absorption spectrum, chemists can determine the types of bonds present in an unknown molecule.
What is the Technique of IR Spectroscopy? (5 Key Points Explained)
1. Sample Preparation
IR spectroscopy requires that the sample be transparent to infrared radiation.
Commonly used materials for sample preparation include salts like NaCl and KBr.
The preparation methods vary depending on the type of sample.
Solid Samples
Mull Technique: Finely crushed solid samples are mixed with Nujol (a mulling agent) to form a thick paste.
The paste is then spread onto salt plates.
The sample is placed in the path of the IR beam, and the spectrum is recorded.
Diffuse Reflection Method: This method is used for powder samples.
The sample is diluted in an alkali halide like KBr.
The spectrum is obtained from the diffuse reflected light.
This method does not require forming pellets, simplifying pretreatment.
KBr Pellet Method: Samples are mixed with KBr and compressed into a pellet using a hydraulic press.
This pellet is then analyzed in the spectrometer.
ATR (Attenuated Total Reflection) Method: This method allows direct measurement of powder samples.
The samples are pressed against a high-refractive-index prism (e.g., ZnSe or Ge).
The infrared spectrum is measured using light that is totally internally reflected in the prism.
2. FTIR Spectroscopy
Fourier Transform Infrared (FTIR) spectroscopy is a specific type of IR spectroscopy.
It uses an interferometer to split and recombine infrared light.
This technique enhances the resolution and sensitivity of the spectral data.
It allows for more detailed analysis of the chemical bonds and their vibrations.
3. Analysis of Results
When an IR spectrometer is used, the sample is exposed to infrared light.
Each type of chemical bond within the molecule absorbs specific wavelengths of this light.
This light is converted into vibrational energy.
For example, a C=O double bond typically absorbs light at 5800 nm.
By examining the wavelengths of light absorbed, chemists can deduce the types of bonds present in the molecule.
This aids in the identification and characterization of the chemical composition of the sample.
4. Versatility of IR Spectroscopy
IR spectroscopy is a versatile analytical tool.
It utilizes the absorption of infrared radiation by chemical bonds.
It identifies and analyzes the molecular structure of various types of samples.
Different preparation methods are tailored to the physical state of the sample.
It provides valuable insights into the chemical composition of materials.
5. Power of IR Spectroscopy
IR spectroscopy is a powerful analytical tool.
It provides valuable insights into the chemical composition of materials.
The technique is versatile, with different preparation methods tailored to the physical state of the sample.
It offers valuable insights into the chemical composition of materials.
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