Dionex ASE 150, Operator'S Manual

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E • Theory of ASE
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Upon completion of the purge step, the cell can be removed from the oven and the
next extraction can be started.
Many features are in place to minimize safety issues with using solvents at
elevated temperatures and pressures. Flammable vapor sensors, liquid leak
detectors, checks for collection vessel overfill conditions, three levels of
overpressurization prevention (electronic and mechanical), solvent flow
monitoring, and pneumatic source pressure monitoring are among the safety
measures in place on ASE instrumentation.
E.3 Method Optimization
Method optimization consists of two main parts: sample preparation (prior to
extraction) and extraction parameters.
E.3.1 Sample Preparation
Sample preparation is an essential part of every solvent-based extraction
procedure. While many sample types can be efficiently extracted without
any pretreatment, other samples will require some manipulation for an
efficient extraction to occur. In general, the same sample preparation that
is done prior to Soxhlet or sonication extraction should be done prior to
extraction by ASE. This section discusses three sample preparation
techniques: grinding, dispersing, and drying.
Grinding
For an efficient extraction to occur, the solvent must make contact with
the target analytes. The more surface area that can be exposed in a
sample, the faster an extraction will occur. Samples with large particle
sizes should be ground prior to extraction. Efficient extraction requires a
minimum particle size, generally smaller than 1 mm. Grinding can be
accomplished with a conventional mortar and pestle or with electric
grinders and mills. Often a large, representative sample can be ground and
weighed portions of the ground sample can be used for extraction. Soil
and sediment samples generally do not need to be ground, although it may
be necessary to remove stones or sticks from the samples prior to
extraction. Polymer samples must be in a ground state for an efficient
extraction of additive compounds. Materials such as polymers and
rubbers are best ground at reduced temperatures (e.g., liquid nitrogen).