The methods of sample preparation in FTIR (Fourier Transform Infrared Spectroscopy) include:
1. Direct Placement Method: This method involves placing a small amount (2-5 mg) of the compound directly on the plates used for FTIR analysis. A drop of solvent may be added to enhance the sample's solubility.
2. Solution Method: In this method, the compound is dissolved in a small test tube using an appropriate solvent. The solution is then transferred onto the IR plates using a pipette.
3. Mull Technique: This technique is used for preparing solid samples. It involves finely crushing the sample and mixing it with a mulling agent, such as Nujol, in a mortar and pestle. The resulting thick paste is then spread as a thin film onto salt plates, which are then mounted in the path of the IR beam for spectral recording.
4. KBr Pellet Method: This method is commonly used for solid samples. It involves grinding the sample with powdered KBr (potassium bromide) to form a homogeneous mixture. The mixture is then pressed into a pellet using a hydraulic press and placed in the IR beam for analysis.
5. Nujol Method: Similar to the KBr pellet method, the Nujol method is used for solid samples. It involves mixing the finely crushed sample with Nujol, a liquid paraffin, to form a thick paste. The paste is then spread onto salt plates and analyzed using FTIR.
6. Diffuse Reflection Method: As FTIR has become more common, the diffuse reflection method has gained popularity. It is suitable for powder samples and does not require extensive sample preparation. The sample is simply placed on a diffuse reflective surface, and the IR spectrum is recorded.
7. Attenuated Total Reflection (ATR) Method: ATR is a method that allows direct measurement of powder samples. It involves placing the sample in contact with an ATR crystal, which interacts with the IR beam. This method is particularly useful for analyzing samples that are difficult to prepare or handle.
It is important to select the appropriate sample preparation method based on the sample form and the desired analysis results. Different methods may be suitable for solids, liquids, or gases. Additionally, the choice of method may depend on factors such as sample transparency to IR radiation and the level of effort required for preparation.
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