Dionex ASE 150, Руководство оператора

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E • Theory of ASE
Doc. 065207-02 9/08
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Dispersing
The aggregation of sample particles may prevent efficient extraction. In
these cases, dispersing the sample with an inert material such as sand or
diatomaceous earth will assist in the extraction process. Dispersing is also
recommended with samples that tend to compact in the sample cell outlet.
These samples normally contain very small particles that can adhere
tightly to each other when under pressure. It is important to periodically
run blank extractions of the dispersing agent to verify its cleanliness.
Some samples may compact in the sample cell due to the high pressures
used in ASE. In these cases, mixing the sample with sand or
diatomaceous earth will prevent this compacting of the sample that can
lead to occlusion of the sample cell. When extracting soil or sediment
samples, it is important to mix the samples with a dispersing agent unless
the samples are completely dry. If the soil or sediment samples are wet or
high in clay, the samples can be mixed with either sand or diatomaceous
earth, but the latter is preferred because it will adsorb some of the water
and make the sample easier to handle.
Drying
Samples do not have to be completely dry to achieve efficient extractions
with ASE. This depends on the analytes and the solvent used for
extraction. High levels of water can prevent nonpolar organic solvents
from reaching the target analytes. The use of more polar solvents (for
example, acetone and methanol) or solvent mixtures (for example,
hexane/acetone and methylene chloride/acetone) can assist in the
extraction of wet samples. Elevated temperatures can also improve the
extraction efficiency of wet samples (10). In addition, the solvent being
used will impact the type of drying that needs to be done to a sample and
whether it need to be done at all. With nonpolar solvents, the need for
drying is more important. One can also use a bridge solvent such as
acetone (for example, hexane/acetone, 1:1) mixed with a nonpolar solvent
to improve the extraction efficiency of wet samples.
Sample drying prior to extraction is an efficient way to handle wet
samples. Drying can be accomplished by direct addition of a drying agent
such as diatomaceous earth. The use of magnesium sulfate is not
recommended with ASE due to the extremely hard, concrete-like material
that can be produced. Sodium sulfate should be used
only with nonpolar
solvents (hexane, heptane, toluene, etc.). Sodium sulfate can become