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MB62 Instruction Manual
EN-21
5.1.1. Good Practices of Sample Preparation
Characteristics, preparation and size of the sample are all important contributing factors in
increasing speed and the quality of the measurement process. Sampling and the sample
preparation have a great influence on the reproducibility of the measured results. It is also
important that the sample being investigated is a representative part of the total amount
of the sample under test.
The final results of a moisture determination depends on a carefully thought out sample
preparation. The part of the sample used for analysis must always be representative of
the total quantity. The sample preparation includes work processes such as sampling,
sample division, size reduction, homogenization and others. All of these processes should
be carried out as quickly as possible and without loss or uptake of moisture.
As with most products, the lab samples are not homogenous. As a result, random sampling
will not lead to a representative sample. The appropriate standards and directions must
be consulted to determine the method of sampling as this is dependent upon the product,
consistency and the amount used.
Number of samples
An increase in the number of samples always leads to an improvement in the statistical
reliability of the analysis results. The size depends on the homogeneity of the test material,
the accuracy of the test material, the accuracy of the measurement method and the desired
accuracy of the measurement result.
Mechanical size reduction
Sample division is usually accomplished by specific types of mills influenced by the sample
characteristics. Hard, brittle samples are mainly reduced in size by pressure, impact or
friction action, whereas, soft and viscoplastic substances can be comminuted only by
shearing or cutting action. Whatever the operating principle of a mill may be, for the
subsequent moisture determination, there must be no loss of moisture during the milling
operation. If this cannot be avoided, it should at least be calculable. The quantitative
recovery of the mill chamber should also be simple and complete.
Use of quartz sand
To ensure an optimum drying process, samples should always have as large an area
as possible. Results of substances 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 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.
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