Field Gas Chromatography/Thermionic Detector System
for On-Site Determination of Explosives in Soils
ALAN D. HEWITT, THOMAS F. JENKINS, AND THOMAS A. RANNEY
INTRODUCTION
Methods 8330 and 8095 are recommended by the
U.S. EPA for the analysis of explosives samples sent to
Currently, there are two sets of on-site analytical
off-site laboratories (U.S. EPA 1994 and 1999). Both
methods--4050 and 4051, 8510 and 8515--recognized
methods are capable of detecting a large suite of explo-
by the U.S. Environmental Protection Agency (U.S.
sives analytes (Table 1). These more rigorous methods
EPA) for the determination of 2,4,6-trinitrotoluene
of instrumental analysis require analytical run times that
(TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine
exceed 15 minutes per analysis and use a soil sample
(RDX) in soil (U.S. EPA 19962000). These two
preparation protocol that includes an 18-hour extrac-
analytes are the major ingredients in nearly all military
tion in a cooled ultrasonic bath. Although these labora-
munitions and subsequently are the most frequently
tory-based instrumental methods generally provide pre-
detected nitroaromatic and nitroamine compounds in
cise and accurate results, they inhibit site investigation
soil samples taken for characterization of explosives
activities because the time between sample collection
residues (Walsh et al. 1993). The analysis of soil samples
and reporting of results often takes one or more weeks.
with these on-site methods can serve to optimize off-
In addition, there are several sample storage and trans-
site analysis (e.g., screen for sample blanks) with the
portation requirements that must be met.
knowledge that the concentration estimates for these
The ability to quickly characterize the distribution
two explosives are subject to interferences or the pos-
of contamination in a large number of samples, and to
sibility of cross-reactivity, or both (Table 1 [Crockett
reduce the number of very low concentration or
et al. 1996]). For example, neither of the on-site meth-
nondetect samples sent off site for analysis, provided
ods for TNT can estimate the concentration of this
the incentives for developing on-site methods (Jenkins
analyte accurately when 1,3,5-trinitrobenzene (TNB),
et al. 1996). These same criteria, along with the need to
2,4,6-trinitrophenylnitramine (tetryl), or the
fill the gap between the capabilities of the existing on-
dinitrotoluenes (DNTs, 2,4- or 2,6-dinitrotoluene) are
site methods and those of the rigorous laboratory-based
also present at similar concentrations. Therefore, be-
procedures, served as incentives for developing the on-
fore a definitive interpretation of on-site results can be
site analytical method described here. To meet this ana-
made, an analyte-specific analytical method of analy-
lytical need we have been evaluating a field-portable
sis has to be performed. Another concern is that these
gas chromatograph (GC) equipped with a thermionic
on-site methods cannot determine the presence of the
ionization detector (TID [SRI, Torrance, California])
major biotransformation products of TNT, 4-amino-2,6-
that is selective for compounds containing nitro (NO2)
dinitrotoluene (4AmDNT) and 2-amino-4,6-
functional groups (Hewitt et al. 2000). The instrument
dinitrotoluene (2AmDNT) (Jenkins et al. 1998). These
selection was based on the ability to determine the same
are just a couple of the analyte selectivity issues that
suite of target analytes that can be determined using
must be taken into account when determining whether
Method 8095 (GC-ECD [Walsh and Ranney 1998]),
these on-site methods can meet a project's data quality
field ruggedness, and the need for minimal auxiliary
objectives. A more comprehensive discussion of the ap-
support. Initially, both a nitrogen phosphorus detector
plications and limitations of these on-site techniques
(NPD) and electron capture detector (ECD) were also
can be found elsewhere (Crockett et al. 1996, 1999).
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