Preparing a Sample
Selecting a Sample
§ 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
$ 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
§ 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.
$ 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.
$ Mix the condensed moisture back in with a sample, if necessary.
Preparing a sample
§ When crushing a sample, avoid any contact with heat: heat results in moisture loss.
§ Crush a sample with
– a pestle
– a shredder (see below)
For liquids containing solids, use
– a glass stirrer
– a spoon or
– a magnetic stirrer.
$ Use an appropriately designed tool for shredding a sample.
Using disposable sample pans
§ 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
22
To Next Page
Loading...
Need help?
General
