33
10 Tips for the determination of the humidity content of the
substances
10.1 Preparing the sample
Prepare a sample only at a time to prevent humidity exchange with the environment.
If you want to prepare multiple samples simultaneously, make sure to store them in a
tightly closed container to prevent changes during storage.
For repeatable results, the sample should be distributed on the test plate in a
homogeneous and evenly manner with a thin layer.
If the distribution is not homogeneous even the heat will not be uniform on the substance
thus determining a drying that is not complete and longest drying time.
A substance accumulation causes a greater heating of the surface layer with the
consequent formation of a burned layer. The considerable thickness of the burnt layer
prevents the removal of humidity in the lower part of the sample. The humidity that remains
trapped in the substance leads to incorrect results that are not less repeatable.
Preparing the samples of solid substances
Arrange evenly on the sample pan powdered substances or granules.
If the samples are large seeds, chop them with special instruments.
During this process, avoid overheating the substance.
Preparing the samples of liquid substances
In the case of liquids or samples subjected to fusion, we recommend using glass fabric filters
involving the following advantages:
uniform arrangement by capillary action,
no dripping,
fast evaporation due to increased surface area.
10.2 Types of samples
A good rule for the humidity determination occurs on samples that have the following
properties:
Solid material in powder form or grains,
Thermally stable materials that evaporate easily, volatile substances without addition
of particular substances,
Evaporating liquids up to become dry matter without formation of film.
The humidity determination could be critical in the case of samples that:
are sticky and viscous,
during heating easily undergo chemical decomposition or release various
components,
have tendency to create surface film when subjected to heating.
