Tech Team · Kintek Solution

To prepare a KBr sample for infrared spectroscopy, the following steps are crucial:

1. Preparation of KBr and Sample Mixture: Start by taking finely powdered KBr from an oven set at 100 °C, being cautious to avoid burns. Transfer the KBr into a mortar and add between 1 to 2 percent of your sample. Mix and grind the mixture to a fine powder. For hard samples, it's advisable to grind the sample first, then add KBr and grind again. This ensures a homogeneous mixture that minimizes scattering losses and absorption band distortions.

2. Formation of Pellets: The finely ground mixture is then used to form pellets. This involves pouring the KBr-sample matrix into a pellet-forming die. The die is then subjected to a pressing load, typically around 8 tons under a vacuum of several mm Hg for a few minutes. This process forms transparent pellets. It's important to note that the KBr powder should be pulverized to a maximum of 200 mesh and dried at approximately 110 °C for two to three hours before pellet formation. Rapid heating can oxidize KBr to KBrO3, causing discoloration.

3. Pellet Handling and Analysis: After the pellets are formed, they are retained inside a collar. This collar can be placed in a V-shaped sample holder compatible with standard spectrometer slide mounts. After analysis, the pellet can be rinsed out with water or ejected from the collar for storage or further analysis.

4. Special Considerations for Liquids and Solids in Solution: For liquid samples, a small drop is placed on a KBr plate, and another plate is placed on top, rotated to create an even film. These plates are then inserted into a sample holder for spectroscopy. For solids in solution, a concentrated solution of the compound is prepared in a suitable solvent like CH2Cl2.

Throughout these processes, it's essential to work quickly to minimize the hygroscopic KBr's exposure to humidity, which can increase background noise in certain spectral ranges. Additionally, proper cleaning of KBr plates and tools is necessary to prevent contamination of future samples.

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