Web Release Date: February 9,
Progressive Thermal Desorption of Vapor Mixtures from a Preconcentrator with a Porous Metal Foam Internal Architecture and Variable Thermal Ramp Rates
Pacific Northwest National Laboratory, Richland, Washington 99352
Received for review June 10, 2004. Accepted December 24, 2004.
Abstract:
A vapor preconcentrator has been designed with the
porous polymer (Tenax) packed into a highly porous metal
foam to facilitate thermal conductivity and temperature
uniformity throughout the bed of the preconcentrator
during heating. Vapors were desorbed using linear temperature programming from room temperature to a maximum temperature of 170 or 200 
C; the programmed
duration of the thermal ramp was varied from 10 to 180
s. The partial separation of vapor mixtures that are
thermally desorbed from the preconcentrator has been
examined in terms of a metric for resolution, using methyl
ethyl ketone, toluene, and dimethyl methylphosphonate
as a test mixture. Vapors desorbed as a sequence of
partially separated overlapping peaks, as observed with
a polymer-coated flexural plate wave sensor. It was shown
that vapor mixture resolution improved as the total time
of the thermal ramp was extended from 30 to 120 s. In
this way, the preconcentrator serves to act as a preseparator in addition to its usual functions for sampling, signal
modulation, and improving sensitivity. Overlapping peaks
were modeled, and peak areas were extracted using an
exponentially modified Gaussian model. Peak areas were
independent of the thermal ramp rate. Uses of such
preconcentrators with multivariate detectors, such as
sensor arrays, are discussed.
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