Mull
Definition and meaning of Mull in chemistry.
Mull is a paste-like suspension prepared by grinding a solid sample into a fine powder and dispersing it in an inert liquid medium, forming a homogeneous preparation suitable for analytical techniques such as infrared spectroscopy.
In more detail
In this process, a solid sample is mechanically ground, typically using a mortar and pestle, then mixed with a chemically inert liquid such as mineral oil (Nujol) or, for spectral regions where Nujol itself absorbs, a fluorinated oil such as Fluorolube. This creates a uniform suspension that allows solid samples to be properly analyzed by spectroscopic techniques, particularly infrared (IR) spectroscopy. Mulling is essential for samples that are insoluble or for analyses requiring specific physical presentations. The choice of mulling medium is critical and must not interfere with the analytical technique employed.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Common mulling mediums | Mineral oil (Nujol); Fluorolube for the low-wavenumber region |
| Primary use | Infrared spectroscopy sample preparation |
| Equipment | Mortar and pestle or ball mill |
To analyze an unknown organic solid by IR spectroscopy, a chemist might grind a few milligrams of the compound with mineral oil to create a mull that can be placed between IR-transparent salt plates for spectral analysis.
Frequently asked questions
Why can't solid samples be analyzed directly by IR spectroscopy?
Many solids are opaque or poorly suited for direct measurement, so suspending them in an inert medium creates a transparent or translucent preparation suitable for spectroscopy.
What is Nujol?
Nujol is a brand name for mineral oil commonly used as a standard mulling medium in IR spectroscopy because it is transparent to infrared radiation.