Dionex ASE 100, Руководство оператора

Страница: 37 / 150

3 • Operation and Maintenance
Doc. 031842-01 5/02
3-5
3.1.3 Preparing the Sample
Some samples must be mixed with a drying or dispersing agent before
being loaded into the cell. If you have successfully followed a particular
sample pretreatment procedure for another extraction method (Soxhlet,
for example), use the same procedure with the ASE 100. If you have never
run an extraction before or if you are preparing a new sample, follow the
guidelines here.
Drying or Dispersing Agent Selection Guidelines
_
The sample preparation guidelines in the next section mention two
drying and dispersing agents: sodium sulfate (Na
2
SO
4
) and pelletized
diatomaceous earth (DE). DE is easier to work with than sodium
sulfate; it dries samples more quickly, provides a cleaner transfer of
the mixtures to the cell, and extracts well. Sodium sulfate is more
readily available, but it tends to clump the samples and this makes
transfer more difficult.
_
The use of sodium sulfate with very wet samples (30% moisture) can
clog the frits in the cell with recrystallized sodium sulfate. This is
most likely to occur when using a mixed solvent with acetone or
methanol. To prevent clogging, substitute DE as a drying agent and
mix it with the sample before loading into the extraction cell. Or, use
DE as a drying agent in the cell for all levels of moisture.
_
To ensure that very wet samples are completely dried (regardless of
which drying agent is used), add sodium sulfate to the bottles after
collection and then pass the extracts through either a drying column
or a drying cartridge. At the temperatures used during ASE 100
extractions, more water is co-extracted than with other extraction
procedures. To ensure good analyte recovery, thoroughly rinse the
sodium sulfate from the bottle and the cleanup column.