KBr Pellet
Definition
A classical solid sample mode: 1 to 2 mg analyte ground with about 200 mg dry KBr and pressed in a 13 mm die at 8 to 10 tonnes into a transparent disc.
- Analyte quantity
- 1 to 2 mg
- KBr quantity
- About 200 mg, dried
- Die diameter
- 13 mm
- Press force
- 8 to 10 tonnes
Common questions
Why must the KBr be kept dry when preparing the pellet?+
KBr is hygroscopic, and residual moisture produces broad water absorption bands around 3400 and 1640 per centimetre that obscure the sample spectrum, so the salt is usually oven-dried and handled quickly under low humidity.
When is a KBr pellet preferred over ATR-FTIR for a solid sample?+
The pellet method is chosen when a transmission spectrum with minimal band distortion is needed for library matching, or when the sample amount is too small to press flat against an ATR crystal, though ATR is faster and needs no sample preparation.
Related terms
- ATR-FTIR
- Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy: a non-destructive mid-infrared method that analyses a single drop of milk pressed against an ATR crystal....
- Fingerprint Region
- The 1500 to 400 cm⁻¹ stretch of an infrared spectrum where bending and combination bands produce a pattern unique to a given...
- FTIR
- Fourier-transform infrared spectroscopy. A Michelson interferometer modulates all wavelengths simultaneously, the interferogram is Fourier-transformed into the conventional absorbance versus wavenumber spectrum.
- Group Frequency
- A characteristic absorption band associated with a specific functional group (carbonyl about 1700 cm-1, hydroxyl 3200 to 3600 cm-1) used to read...
- Wavenumber
- The reciprocal of wavelength expressed in cm-1, the universal IR axis. Higher wavenumber means higher photon energy. The mid-IR window is 4000...