Infrared (IR) spectroscopy is a powerful analytical technique used to study the molecular structure of various materials.
KBr, or potassium bromide, plays a crucial role in this process.
Here’s why KBr is essential for IR spectroscopy.
Why do we use KBr in IR spectroscopy? 5 Key Reasons
1. Transparency to Infrared Light
KBr is transparent to infrared radiation.
This transparency ensures that infrared light can pass through the sample without significant absorption.
This allows for clear detection of the sample's absorption characteristics.
It’s essential for obtaining spectra with sharp peaks and good intensity.
2. Sample Preparation
In IR spectroscopy, the sample is often mixed with KBr and compressed into a pellet.
This method allows for the inclusion of just the right amount of sample (typically 1% by weight) to be analyzed.
The pellet formation process exploits the plasticity of alkali halides like KBr when subjected to pressure.
This forms a transparent sheet suitable for spectroscopic analysis.
3. Background Measurement and Calibration
Before measuring the sample, a background measurement is performed using pure KBr.
This step is crucial for calibrating the system.
It ensures that any signals observed are due to the sample and not the matrix.
The sample is then mixed with KBr (diluted to 0.1% to 10%) and packed into the sample plate for measurement.
This technique allows for the analysis of very small sample volumes, as little as 50 to 100 ng.
4. Handling of Moisture
KBr is hygroscopic, meaning it can absorb moisture from the air.
This property can affect the accuracy of IR measurements if not properly managed.
To mitigate this, sample preparation and pressing are often conducted in controlled environments such as gloveboxes or under vacuum conditions.
This prevents moisture absorption.
5. Comparison with Transmission Spectra
The diffuse reflectance method used with KBr pellets involves repeated transmission of light through the sample.
This can emphasize low absorption bands.
To compare these spectra with traditional transmission spectra, a Kubelka-Munk transformation is applied.
This ensures accurate and quantitative analysis.
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