The KBr method of IR, specifically known as the KBr pellet method, is a technique used in infrared spectroscopy for analyzing solid samples.
This method involves the preparation of a thin, transparent pellet containing the sample of interest dispersed in potassium bromide (KBr), which is transparent in the infrared region.
The typical procedure involves mixing a small amount of the solid sample (usually 2-5 mg) with KBr powder, pressing this mixture under high pressure to form a pellet, and then analyzing the pellet using Fourier Transform Infrared Spectroscopy (FTIR).
4 Key Steps Explained
1. Sample Preparation
The first step in the KBr pellet method is the preparation of the sample.
A small quantity of the solid sample is mixed with KBr powder.
The ratio of KBr to sample is typically 100:1, ensuring that the pellet is predominantly composed of KBr, which is transparent to infrared radiation.
2. Pellet Formation
The mixture of sample and KBr is then subjected to high pressure.
This causes the KBr to become plastic and form a thin, transparent sheet or pellet.
This pellet is designed to be compatible with the specific requirements of the FTIR equipment, typically ranging from 3 mm to 13 mm in diameter.
3. FTIR Analysis
The prepared pellet is then placed in the FTIR spectrometer for analysis.
The FTIR technique is sensitive enough to analyze the sample within the KBr matrix, detecting the specific infrared absorption bands of the sample.
This analysis helps in identifying the functional groups and molecular structure of the sample.
4. Diffuse Reflectance and Kubelka-Munk Transformation
In some cases, the diffuse reflectance method might be used alongside the KBr pellet method, especially for samples that are difficult to pelletize.
In diffuse reflectance, the sample is mixed with KBr powder and packed into a sample plate.
The infrared spectrum is measured, and the data is transformed using the Kubelka-Munk function to compare it with transmission spectra.
This transformation is necessary because the diffuse reflectance method involves multiple transmissions of light through the sample, which can emphasize low absorption bands.
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