Preparing a FTIR sample with KBr involves mixing the sample with potassium bromide (KBr) and pressing it into a transparent disc. This process is crucial for obtaining clear and accurate spectra. Here’s a detailed step-by-step guide to help you through the process.
How do you prepare a FTIR sample with KBr? – 4 Essential Steps
1. Sample and KBr Preparation
Use a 100:1 ratio of KBr to sample by weight. This dilution helps in obtaining clear spectra by minimizing the absorption and scattering of infrared light by the sample.
KBr should be finely powdered but not excessively ground to avoid absorption of humidity, which can increase background noise in the spectra. KBr is hygroscopic, meaning it absorbs moisture from the air.
2. Mixing and Grinding
Quickly transfer KBr from an oven (at 100°C) into a mortar to avoid exposure to air for too long.
Add about 1 to 2 percent of the sample to the KBr in the mortar.
Mix and grind the mixture to a fine powder. For hard samples, add the sample first, grind, then add KBr and grind again.
3. Pellet Formation
Use a 13 mm Pellet Die for pressing. The pressing load should be around 10 tons, although for 7 mm pellets used in FTIR, a load as little as 2 tons might be sufficient.
The mixture is then compressed in a hydraulic press within the pellet die chamber. This process forms a solid pellet that is transparent to infrared light, allowing for effective spectroscopic analysis.
4. Considerations for Humidity and Environment
Since KBr is hygroscopic, it’s important to minimize its exposure to air, especially in humid environments. This can be done by working quickly or using a glovebox for grinding and pressing.
If the KBr absorbs a lot of moisture, it can affect the FTIR measurement. Therefore, it might be necessary to perform the grinding and pressing in a controlled environment like a glovebox or use a vacuum die.
This method ensures that the sample is adequately prepared for FTIR analysis, minimizing interference and ensuring accurate spectral readings.
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