Page 125 - Modern Derivatization Methods for Separation Sciences

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Fig. 1.3.1.
Scheme of pre-treatment for chromatographic analysis of
environmental contaminants in gas sample.
including adsorbents (the adsorbent method) and the method directly sampling the gas (the direct gas
sampling method). Fig. 1.3.1 shows the flow from sampling through to chromatography. Refer to the
explanation by DeGraff [2].

Solution Trapping Method

This method bubbles the sample gas into the trapping solution using an impinger to trap the desired
components (Fig. 1.3.2). Although accompanied by complications related to the use of many tools and
the problem of processing the exhausted gas when using organic solvent as the trapping solution, the
method is suitable for chemicals which do not achieve a satisfactory trapping or recovery rate with the
adsorbent method described below.

With regard to the post-treatment, since the trapping solution is often relatively clean, the solution is
directly or after being concentrated measured in quantity of trapping solution, and then subjected to GC
or LC methods either directly or after derivatization. When the sample with unknown concentration of
analytes is to be trapped using the solution trapping method, it is important to connect the multiple
impingers in series and to pay attention to any possible break-through of the analytes.

Adsorbent Method

This method passes samples through a trapping tube packed with an appropriate adsorbent (carbon
molecular sheave, porous polymer, florisil etc.) to adsorb the desired components (Fig 1.3.3), and then
measures them using heating desorption or solvent extraction. This method is useful because it allows
for very compact sampling. It does, however, require equipment for heating desorption and adsorbent
clean-up, which makes the total system expensive. For the selection and combination of appropriate
adsorbents for individuals analytes used in this method, it is recommended that you contact the
manufactures of adsorbents, who have numerous experience and information in this area.

With regard to post-treatment, the adsorbed analytes are either subjected to heating desorption and then
directly introduced into GC with the heating desorption equipment combined with

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