contained similar levels of TNT (14 g/g) and TNB
tems such as petroleum ether and isopropanol (4 :
(9.4 g/g), was used. Soil samples were extracted
1) and petroleum ether and acetone (1 : 1),
nitroaromatic, nitramine, and nitrate ester com-
in acetone as described above, but to maximize
pounds could be effectively separated. In most
the extract concentration, the soil-to-solvent ratio
cases, commercial-brand solvents (which are
was increased to 1 : 2 (1 gm of soil to 2 mL of
acetone). A volume of 20 L (which was equiva-
readily available in hardware stores) were also
lent to 0.14 g of TNT and 0.094 g of TNB) was
effective in giving good-to-fair separation of com-
ponents of explosives. However, as mentioned at
spotted and developed in the solvent system of
the onset of this report, the detection capability of
Sterling VM & P naphtha and laboratory-grade
conventional TLC methods is poor, and this re-
isopropanol (4 : 1). Plates were sprayed with TiCl3,
mains the major limitation of this method. The con-
NaNO2, and Bratton-Marshall reagent (Jork et al.
ventional TLC method evaluated in this report is
1994b). Two spots, light purple in color, were iden-
capable of detecting 0.1 g of TNT or RDX with
tified as TNT and TNB. These results seemed to
either UV, TiCl3 spray followed by DMACA, or
indicate that TLC could be used to separate and
distinguish different explosives components in
Griess reagent followed by UV exposure. This is
equivalent to spotting a volume of 1 L of sample
actual field samples when appropriate solvent sys-
extract containing 100 g/mL of TNT or RDX, and
tem and visualizing procedures are utilized.
if the sample extract was prepared using the soil-
to-solvent ratio used in the on-site colorimetric
Recommendations for specific separations and
methods (20 g of soil to 100 mL of acetone), the
visualizing reagents
The solvent system of petroleum ether and iso-
concentration of TNT or RDX in soil would
correspond to approximately 500 g/g. This is
propanol (4 : 1) is recommended to separate vari-
ous species of nitroaromatic compounds, includ-
about 500 times above the minimum detection
limit for TNT (1.1 g/g) and RDX (1.4 g/g) colo-
ing TNT, TNB, and DNT. The most sensitive
visualizing agents tested for nitroaromatics are
rimetric on-site tests. Even if the maximum spot-
ting volume of 30 L is used, the detection capa-
TiCl3 followed by DMACA spray. For the separa-
bility remains at about 17 g/g if the
tion of nitramines such as RDX and HMX, and
nitrate esters PETN and NG, the solvent system
soil-to-solvent ratio is maintained at 20 g and 100
of petroleum ether and acetone (1 : 1) is recom-
mL. If a larger soil-to-solvent ratio is used to ob-
mended with visualization with Griess reagent
tain an extract for TLC analysis, the detection ca-
followed by UV exposure. Optimal separation
pability could be further improved. More experi-
occurs with laboratory-grade solvents; however,
ments aimed at optimizing detection capability by
in cases where laboratory-grade solvents are not
either concentrating sample extracts and/or uti-
readily available, commercially available solvents
lizing higher soil-to-solvent ratios are needed to
fully assess the practical limit of detection for the
such as paint thinner and acetone may be substi-
TLC method.
tuted. If sensitivity is not an issue, commercially
available solvents will be more cost-effective and
more readily available in the field.
LITERATURE CITED
Bagnato, L., and G. Grasso (1986) Two-dimen-
CONCLUSIONS
sional thin-layer chromatography for the separa-
For the purposes of this evaluation, the conven-
tion and identification of nitro derivatives in ex-
tional TLC approach was used rather than the
plosives. Journal of Chromatography, 357: 440444.
modern TLC techniques for the following reasons:
Carlson, M., and R. Thompson (1986) Thin-layer
1) the conventional TLC techniques involve less
chromatography of isosorbide dinitrate, nitroglyc-
equipment, and so are less expensive and are field
erin and their degradation products. Journal of
portable, and 2) the purpose of this report was to
Chromatography, 368: 472475.
evaluate a method that can be used in conjunc-
Coker, R.D., A.E. John, and J.A. Gibbs (1993)
tion with on-site colorimetric methods. The results
Techniques of thin layer chromatography. Journal
indicate TLC methods could indeed be used to
of Chromatography Library, 54: 1235.
separate various components of explosives such
DiCarlo, F.J., J.M. Hartigan, and G.E. Phillips
as TNT, TNB, DNT, RDX, HMX, PETN, and NG
(1964) Analysis of pentaerythritol tetranitrate and
from soil samples. Using appropriate solvent sys-
its hydrolysis products by thin layer chromatog-
12
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