OHAUS MB45 Instruction Manual page 52

How to obtain the best results - Section 8
52
Use of quartz sand
To ensure an optimum drying process, samples should always have as large an area as possible. Results of sub-
stances which form crusts (e.g. glucose syrup) or pasty substances (e.g. butter) can be considerably improved by
mixing with quartz sand. Sample pans with a large volume and relatively high walls are needed for this.
Pasty, fat-containing and melting substances
For pasty, fat containing and melting substances, use of a glass fiber filter is advantageous to increase the surface
area of the sample. The glass fiber filter is tared together with the sample pan. The liquid contained in the substance
is uniformly and extensively distributed in the interstices between the fibers throughout the available area. The same
also applies to melting fats and fat containing samples. This increase in the surface area results in faster and com-
plete 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. Experi-
ence 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 improv-
ing 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.