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| Main Article Featured in Issue 20.2 |
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| A Tool for Selecting an Adsorbent for Thermal Desorption
Applications |
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common question asked by GC users working with thermal desorption is “Which
adsorbents trap what analytes?” To assist customers in selecting the
appropriate adsorbents for their applications, we embarked on a study to
evaluate 24 adsorbents for trapping and releasing a targeted list of 43
analytes. The results of this effort lead to the development of a color-coded
selection chart system that simplifies the decision of “Which adsorbents
trap what analytes?” |
Chart System Development
We selected 24 adsorbents for the study including Carboxen™ and
Carbosieve™ carbon molecular sieves, Carbopack™ and Carbotrap™
graphitized carbons, and several porous polymers. Each adsorbent was
packed into a tube and spiked with the 43 component gas mix. To assess
the analyte breakthrough, we conducted tests using six different sampling
volumes ranging from 0.2 to 100 liters for each tube. The collected
analytes were desorbed onto an SPB-1 capillary column and we measured
the recovered analytes at each challenge volume. We then conducted
a second desorption of each tube to observe if any carryover had occurred.
We recorded all the analyte recovery data into spreadsheets. We then
applied the analogy of a traffic light to the data with green indicating
greater than or equal to 80% recovery, yellow indicating between 21%
and 79%, and red for recoveries of 20% or less. With this color scheme,
we transformed the data into a color-coded chart system for determining
which adsorbents trap what analytes. Figure A
shows an example of one of the charts generated in the study.
Using the Selection Tool |
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Figure A. Recovery Chart from the Study
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| As an illustration of how to work with the chart system,
assume you plan to sample 10 liters of air for the presence of trichloroethene.
Examining the chart system, you learn recoveries of 80% or greater can be
achieved on several adsorbents, including Carbopack B and Carboxen-1003
(Figure B). Your decision here is easy since
either of these adsorbents will provide good trichloroethene results at
10 liters. |
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However, what if your sampling needs change? Now assume
you must monitor for vinyl chloride, methylene chloride, and 1,2,4-trichlorobenzene
in addition to trichloroethene. The color coding for each adsorbent found
in Figure B tells us neither the Carbopack B
nor the Carboxen-1003 adsorbents can be used alone for sampling. None of
the adsorbents will effectively retain all the compounds of interest. If
you want to use a single tube, you must design a multiple adsorbent bed
tube. Based on the chart information, you can achieve good results by combining
two adsorbents, Carbopack B and Carboxen-1003. The Carbopack B bed must
be the first adsorbent the sample encounters. This is because the trichloroethene
and 1,2,4-trichlorobenzene are trapped on the Carbopack B, while the vinyl
chloride and methylene chloride pass through to the Carboxen-1003 bed, where
they are collected. The data shows that the 1,2,4-trichlorobenzene may be
irreversibly adsorbed on the Carboxen-1003 if it were first.
The decision process used here to determine which adsorbents trap what analytes
can be applied to scenarios that are more complex by using the color-coded
chart system we developed. |
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To review the entire study, see |
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T402025 (1,817 KB)  "A Tool for Selecting an Adsorbent for Thermal Desorption
Applications" |
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| Other information related to this article: |
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| Trademarks and Registered Trademarks: |
| Air Toxics, PerkinElmer - PerkinElmer;
Agilent Technologies - Agilent Technologies;
GERSTEL - GERSTEL GmbH; Tekmar
- Tekmar Co.; Teflon - E.I.du Pont de Nemours
& Co., Inc. |
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