Research is underway at CRREL to evaluate the
Table 7 presents some of the important physi-
use of solid-phase microextraction (SPME) for
cal and chemical properties for TNT and RDX, and
sampling the headspace vapor above a potentially
some of their commonly encountered manufactur-
contaminated soil for nitroaromatics. Initial re-
ing impurities and environmental transformation
sults, where this sampling method is combined
products. The unique properties that differentiate
with gas chromatography with an electron cap-
these chemicals from other semivolatiles such as
ture detector, look promising, but the method will
PCBs and polynuclear aromatic hydrocarbons
not work for nitramines such as RDX and HMX,
(PNAs) are their thermal lability and polarity.
because of their very low vapor pressures. The
Many of these compounds thermally degrade or
explode at temperatures below 300C. Thus, meth-
combination of SPME with IMS detection looks
like a promising field option.
ods based on gas chromatography are not recom-
Another study at CRREL is investigating the use
mended for routine use. In addition, log Kow val-
of gas chromatography with either a nitrogen-
ues range from 0.06 to 2.01 compared with values
phosphorus detector or an electron capture detec-
of 4 to 5 for PCBs and PNAs, indicating that these
tor as a method for analyzing acetone extracts in
compounds are quite polar and that normal non-
the field. The major advantage of this method
polar extraction solvents used for other
would be the ability to determine the presence of
semivolatile organics may not elute successfully.
the amino-dinitro transformation products. They
For most routine analyses, environmental soil
are currently not detectable using the colorimet-
samples are extracted with polar solvents. The
ric or immunoassay methods.
sample extracts are analyzed using RP-HPLC,
often using SW-846 Method 8330 (EPA 1995).
SUMMARY OF THE EPA REFERENCE
Soil extraction
Extraction of TNT and RDX from soils has been
METHOD FOR EXPLOSIVES
studied in terms of process kinetics and recovery
COMPOUNDS, METHOD 8330
using methanol and acetonitrile with several ex-
traction techniques including Soxhlet, shaking,
Properties of secondary explosives
TNT and RDX have been the two secondary
and ultrasonication (Jenkins and Grant 1987). Ac-
explosives used to the greatest extent by the U.S.
etone, while an excellent solvent for these com-
pounds, was not included in this study because
military over the past 70 years. With their manu-
extracts were to be analyzed using RP-HPLC-UV,
facturing impurities and environmental transfor-
and acetone absorbs in the ultraviolet region used
mation products, the two compounds account for
for detection of the contaminants of interest.
a large part of the explosives contamination at ac-
Overall, methanol and acetonitrile were found
tive and former U.S. military installations. While
to be equally good for extraction of TNT, but ac-
all of these explosives compounds can all be clas-
etonitrile was clearly superior for RDX. Equilibra-
sified as semivolatile organic chemicals, their
tion of the soil with solvent using ultrasonication
physical and chemical properties require different
or a Soxhlet extractor appears to provide equiva-
analytical approaches than normally used for other
lent results; however, a subsequent investigation
semivolatiles.
Table 7. Physical and chemical properties of predominant nitroaromatics and
nitramines.
Water
Vapor
Molecular
Melting pt.
Boiling pt.
solubility
pressure
(C)
(C)
(mg/L at 20)
(torr at 20)
Compound
weight
log Kow
80.1-81.6
5.5106 at 25
TNT
227
240 (explodes)
130
1.86
2.2104
TNB
213
122.5
315
385
1.18
69.5-70.5
1.4104
2,4-DNT
182
300
270
2.01
(decomposes)
5.7109
Tetryl
287
129.5
(decomposes)
80
1.65
4.1109
RDX
222
204.1
(decomposes)
42
0.86
5 at 25
3.31014
HMX
296
286
(decomposes)
0.061
2.1 at 25
5.4109 at 25
PETN
316
141
--
3.71
24
Previous Page
