KBr is used to prepare samples for FTIR analysis because it is transparent to infrared light, allowing the light to pass through the sample and be analyzed effectively.
This transparency ensures that the sample does not block the infrared light, which would otherwise interfere with the accurate measurement of the sample's chemical bonds and their vibrations.
Additionally, KBr is commonly used to create pellets that contain a dilute amount of the sample, typically around 1% by weight, which is ideal for FTIR detection.
Why KBr is Used to Prepare Samples for FTIR Analysis? 4 Key Reasons
1. Transparency to Infrared Light
KBr is transparent to infrared light, which is the primary wavelength used in FTIR spectroscopy.
This transparency is crucial because it allows the infrared light to pass through the sample without significant attenuation.
If the sample were opaque to infrared light, it would block the light, preventing the formation of an interference pattern that is essential for analyzing the sample's molecular structure.
2. Sample Dilution and Pellet Formation
The use of KBr in pellet preparation involves mixing the sample with KBr in a ratio of approximately 1:100.
This dilution ensures that the sample does not overwhelm the FTIR system, which could lead to inaccurate readings.
The mixture is then compressed using a hydraulic press to form a solid pellet.
This pellet is primarily composed of KBr, with the sample dispersed within it.
The resulting pellet is both robust and transparent, making it ideal for FTIR analysis.
3. Hydroscopic Nature of KBr
It is important to note that KBr is hydroscopic, meaning it can absorb moisture from the air.
This property can affect the accuracy of FTIR measurements if the KBr pellet absorbs too much moisture.
Therefore, it is recommended to prepare the KBr pellets in a controlled environment, such as a glovebox or using a vacuum die, to minimize the absorption of moisture.
This precaution ensures that the FTIR measurements are not influenced by the presence of water in the sample.
4. Use of Salts in Sample Preparation
Besides KBr, other salts like NaCl and AgCl are also used in sample preparation for IR spectroscopy.
These salts are chosen because they are transparent to IR radiations and help in obtaining an accurate IR spectrum with sharp peaks, good intensity, and high resolution.
The choice of salt depends on the specific requirements of the sample and the analytical goals of the FTIR analysis.
In summary, the use of KBr in FTIR sample preparation is essential for creating a transparent, dilute sample that allows for accurate and reliable analysis of the sample's molecular structure and chemical bonds.
The careful preparation of KBr pellets ensures that the FTIR measurements are not compromised by the sample's opacity or by the absorption of moisture.
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