DEl
innovations in chemical detection
Reactor Thermionic IonizationAnalysis (RTIA)
selectiveTID/NPD transducer screening of vapors evolved from
THERMAL DESORPTION/OXIDATION
of nonvolatile liquid residues or solid sample constituents
Background:
Thermal desorption continues to be an
increasinglypopularmeansof preparing realworldsamples
for subsequent analysis by gas chromatography. Among
the many different types of GC detectors, TID and NPO
detectors have the distinctive characteristic that they can
provide chemical species selectivity using Air as the
primary detector gas. Consequently, these detectors are
well suited to non-GC chemical screening applications
where the gas environment is simply ambient Air drawn
through aTIO/NPOtransducer by a sampling pump. Inan
RTIA
configuration, such a transducer is preceded by a
heated reactor chamber into which are inserted solid
samples packed intoaglass tube or liquid sample residues
on a ceramic rod. The TID or NPO transducer provides
selective responses to vapors evolved from thermal
desorption and/or oxidation of the samples. At low reactor
temperatures, thermal desorption usuallyaccounts formost
detected signals, while at high temperatures oxidative
sampledecompositionproductsoftenprovide largesignals.
Good examples of the oxidative detection processes are
large T10-1 signals from oxidation of sugars and proteins.
For T10-1 and T10-3 thermionic detection, only Air is
required as theoperating gas,while for NPOasmall flowof
Hydrogen has to also be introduced into the incoming Air.
HEATING
CURRENT
THERMIONIC
SOURCE
HEATED
REACTOR
GLASSWOOL
ORFRJT
-4- _
HYDROGEN (NPD)
ORCAPPED (TID-')
i-Propanol Wipe Transfer of Surface Residue to 1/16 in.
. CeramicRod· Rod inserted into 140 deg C Reactor
Malathion Residue on Quartz Rod
NPD, 160 pA f.s., Hydr.=4.3, Air=200
rod dipped into sample –
Methanol evaporated –
rod residue inserted into
140deg C reactor
- 0.1 mg/mL
Malathion
in Methanol
rod out of
reactor
I
2ndWipe of
I
Residual TNT
on Table Top
rod taken
out of
reactor
I
Wipe of
/ TNT residue
on Table Top
TID-1-Air
80 pA f .a.
Wipe of Clean
Table Top
I
Air-600 mUmin
dried TNT residue on a table top wiped with an
iso-propanol pad and transferred to ceramic rod.
small quartz rod dipped into a
0.1
mg/mL
solution
ofMalathion in Methanol.
