Tech Team · Kintek Solution

Preparing a sample for FTIR spectroscopy using potassium bromide (KBr) involves creating a transparent pellet that allows infrared light to pass through while containing a diluted sample for analysis. The process requires precise mixing of the sample with KBr powder, followed by compression using a hydraulic press to form a solid pellet. This method ensures the sample is sufficiently diluted to avoid overwhelming the FTIR instrument while maintaining transparency for accurate infrared analysis.

Key Points Explained:

1. Sample and KBr Ratio:

   • The typical ratio for preparing an FTIR sample with KBr is 1 part sample to 100 parts KBr. This ensures the sample is sufficiently diluted to avoid excessive absorption of infrared light, which could lead to inaccurate readings.
   • The small amount of sample ensures that the pellet remains mostly transparent to infrared light, allowing the FTIR instrument to detect the sample's characteristic absorption peaks effectively.

2. Mixing the Sample and KBr:

   • The sample and KBr powder must be thoroughly mixed to ensure homogeneity. This can be done using a mortar and pestle or a mixing device.
   • Proper mixing is critical to avoid localized concentrations of the sample, which could result in uneven absorption of infrared light and distorted spectra.

3. Pellet Die and Hydraulic Press:

   • The mixture is placed into a pellet die, which is a specialized tool designed to compress the powder into a solid pellet.
   • A hydraulic press is used to apply high pressure to the mixture, typically in the range of 8-10 tons, to form a transparent pellet. The pressure ensures the KBr particles bind together, creating a solid and uniform pellet.

4. Transparency and Dilution:

   • The primary purpose of using KBr is to create a matrix that is transparent to infrared light. KBr is chosen because it is optically clear in the infrared region and does not interfere with the sample's absorption spectrum.
   • The dilute concentration of the sample within the KBr matrix ensures that the FTIR instrument can detect the sample's absorption bands without saturation or distortion.

5. Handling and Storage:

   • After pressing, the pellet should be handled carefully to avoid contamination or damage. It is typically stored in a desiccator to prevent moisture absorption, as KBr is hygroscopic and can absorb water from the air, which may interfere with the FTIR analysis.
   • If the pellet is not used immediately, it should be kept in a dry environment to maintain its integrity.

By following these steps, you can prepare a high-quality KBr pellet for FTIR spectroscopy, ensuring accurate and reliable results. The process requires attention to detail, particularly in the mixing and pressing stages, to achieve a transparent and homogeneous pellet suitable for infrared analysis.

Summary Table:

Step	Key Details
Sample and KBr Ratio	1 part sample to 100 parts KBr for optimal dilution and transparency.
Mixing	Use a mortar and pestle or mixing device for thorough homogenization.
Pellet Formation	Apply 8-10 tons of pressure using a hydraulic press and pellet die.
Transparency	KBr ensures infrared light passes through, enabling accurate FTIR analysis.
Handling and Storage	Store in a desiccator to prevent moisture absorption and maintain pellet integrity.

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