OHAUS MB120, Instruction Manual

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EN-50 MB120
melting fats and fat containing samples. This increase in the surface area results in faster
and complete vaporization of the moisture. Pre-drying of the glass fiber filter and storage in a
desiccator is necessary only for highly precise measurement results.
Liquid substances
Liquid substances (e.g. dispersions) often tend to form drops on the sample pan owing to the
surface tension of the liquid. This prevents a rapid drying process. The use of a commercial
glass fiber filter shortens the drying time by a factor of 2 to 3. The glass fiber filter distributes
the liquid sample over a wide area as a result of its absorbent action. Pre-drying of the glass
fiber filter and storage in a desiccator is necessary only for highly precise measurement
results.
Skin-forming and temperature sensitive substances
The use of a glass fiber filter can be useful for temperature-sensitive and skin forming
substances. In this case, the sample to be dried is covered by the filter and thus receives a
“new surface”. This shields the surface of the sample against direct IR radiation. Gentler
heating of the samples is based on convection rather than on IR radiation. Experience with
this type of preparation has been good; particularly for products containing sugar. Further,
the shielding of the sample against direct IR radiation by covering the test substance can
make a considerable contribution to improving the reproducibility with temperature sensitive
samples.
Sugar-containing substances
Samples containing a large amount of sugar tend to caramelize on the surface. In such
cases, ensure a thin layer is applied. Also select a moderate temperature.
Sample application on the drying pan
To obtain reproducible results, it is essential to ensure uniform distribution of the sample on
the pan. An uneven distribution can result in homogeneous heat distribution in the sample.
As a result, the sample could be incompletely dried in the center owing to excessive piling.
Thick layers have an adverse effect on the escape of moisture. The resulting lengthening of
the measurement time promotes decomposition at the surface of the sample by prolonged
heat action.
Film formation on the sample can prevent complete escape of the moisture. With such
samples, ensure application of a thin and uniform layer thickness.
With readily volatile samples, rapid application of the sample on the sample pan is advisable,
otherwise, moisture can escape before the initial weight is recorded; here, use of the manual
operating mode is appropriate.