Sample Preparation
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
$ If required, homogenize the product before a sample is taken 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.
This way it will not lose or gain moisture as a result of the ambient conditions.
$ If you need to take several samples simultaneously, the samples must be sealed in air-
tight containers 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.
– Storing samples in a container may lead to moisture condensing on the walls
of the container.
– If the container is too large, moisture is passed to 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 of 92 mm). Reusing sample
pans leads to poor reproducibility of results for several reasons:
– sample residues can remain on the pan even after cleaning
– residues from cleaning agents can evaporate during the next moisture analysis
– scratches and grooves made during cleaning result in damage that forms points
of attack for hot, rising air produced during the drying process (more pronounced buoy-
ancy)
22
To Next Page
Loading...
