Preparing a Sample
Selecting a Sample
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Select a representative part of the whole substance as a sample
– a representative number of individual samples for quality control
– samples which indicate a trend are sufficient for in-process control
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Homogenize the product before a sample is taken, if required, by:
– mixing or stirring,
– taking several samples from different areas of the product, or
– taking several samples at defined intervals
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Take only one sample at a time for a given analysis and prepare it as quickly as possible.
In this way, it will not lose or gain moisture as a result of the ambient conditions.
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If you need to analyze several samples at a time, the samples must be sealed in air-tight
containers, in order to ensure that the storage conditions do not alter the state or
condition of the samples:
– Warm or highly volatile substances lose their moisture very quickly.
– If you store the samples in a container, the moisture can condense on the walls
of the container.
– If the container is too big and not filled completely, the sample can exchange its
moisture with the air remaining in the container.
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Mix the condensed moisture back in with a sample, if necessary.
Preparing a sample
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When crushing a sample, avoid any contact with heat: heat results in moisture loss.
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Crush a sample with
– a pestle
– a shredder (see below)
For liquids containing solids, use
– a glass stirrer
– a spoon or
– a magnetic stirrer.
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Use an appropriately designed tool for shredding a sample.
Using disposable sample pans
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Use only Sartorius disposable sample pans (inner diameter = 92 mm). Reusing sample
pans leads to poor reproducibility of results for several reasons:
– after cleaning, sample residues can still remain on the pan
– residues from cleaning agents can evaporate during the next moisture analysis
– if scratches and grooves are inflicted during cleaning, the hot, rising air produced
during the drying process acts on these surfaces, resulting in a more pronounced
buoyancy
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