Ohaus MB45 MOISTURE ANALYZER Manual - Manual (Page 48)

46 MB45
8.2 Sampling and 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.
Reproducibility
high
low
Sample distribution
always the same different
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 lead 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 can not be avoided, it should at least be
calculable. The quantitative recovery of the mill chamber should also be simple and complete.