Dionex ASE 150, Руководство оператора

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E • Theory of ASE
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lipids that extracted with the analytes. Then the samples were placed in a freezer
to allow them to separate and harden. The samples were centrifuged and aliquots
were removed and analyzed. This is a case in which the analytes were polar, the
solvent was polar (water), and the matrices (baby food and meat) were polar. This
is in contrast to several publications in which the analytes were relatively
nonpolar (PCBs, PCDDs, OCPs, etc.) and the solvents were nonpolar (like
hexane). In this case, the adsorbents have higher capacity than in the case where
the extraction solvent is polar.
Ion-exchange resins can be used to remove unwanted ionic species (22). For
example, Dionex has been involved in projects to determine perchlorate in soils
and vegetation samples. Water at 80 °C was used as the extraction solvent.
Alumina was used to remove colored compounds such as chlorophyll. Ion-
exchange resins were placed in the ASE cells that removed chloride and sulfate.
This allowed the determination of perchlorate at the sub-ppb levels.
Björklund and his coworkers have published many articles on the use of
adsorbents in-line in ASE cells to improve selectivity (25–31), especially for PCB
and PCDD analysis. One article discusses the results of the development of a
scheme that allows the separation of non-ortho PCBs and PCDD/Fs from the bulk
of the PCBs, gravimetric fat determinations, and minimum post-extraction clean-
up prior to analysis (25). This can be an obvious savings in time, labor, and
solvent costs as compared to traditional extraction procedures followed by clean-
up methods such as GPC.