Infrared (IR) spectroscopy is a powerful analytical technique used to study the molecular structure of various substances. One of the most commonly used materials in this process is potassium bromide (KBr). But why is KBr so widely favored? Here are five key reasons why KBr is the go-to choice for IR spectroscopy.
5 Key Reasons Why KBr is Used in IR Spectroscopy
1. Optically Transparent for IR Radiation
KBr is optically transparent for the light in the range of IR measurement. This means it allows IR radiation to pass through it without interfering with its absorbance. KBr has a transmittance of 100% in the range of wave numbers (4000-400 cm-1), which is the range typically used in IR spectroscopy.
2. No Absorption in the IR Range
KBr does not exhibit absorption in the IR range. This ensures that it does not interfere with the accurate measurement of the sample's IR spectrum. The transparency of KBr is crucial for obtaining clear and accurate results.
3. Used as a Carrier for the Sample
KBr is used as a carrier for the sample in IR spectroscopy. The sample needs to be transparent to IR radiation to obtain an accurate IR spectrum with sharp peaks, good intensity, and high resolution. Salts like KBr, NaCl, and AgCl are commonly used to mix with the sample and create a transparent medium for the IR radiation to pass through.
4. Preparation of KBr Pellets for Solid Samples
KBr pellets are commonly used for solid samples in IR spectroscopy. The sample is dispersed in KBr by pressing it into a disc-shaped pellet. The typical conditions for KBr pellet preparation include a 100:1 KBr to sample ratio (by weight), a 13 mm pellet die, and a pressing load of 10 tons (or as little as 2 tons for FTIR applications).
5. Clear Pellets and Avoidance of Noisy Spectra
The concentration of the sample in KBr should be in the range of 0.2 to 1 percent to ensure clear pellets and avoid noisy spectra. This careful preparation ensures that the sample analysis is accurate and reliable.
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