Table 2. Extraction techniques used with on-site analysis methods
for RDX.
Extraction
Method
Type
Solvent
time
Soil/solvent
Barringer
IMS*
Acetone
3 min
3 min†
EM Science (D TECH)
Immunoassay
Acetone
3 mL**/15 mL
EnSys
Colorimetric
Acetone
3 min
10 g/50 mL
Walsh & Jenkins
Colorimetric
Acetone
3 min
20 g/100 mL
* Ion Mobility Spectrometry.
† Shaking several times over three-minute period.
** Actual mass of soil will vary depending on soil density.
extract as their TNT test and hence a single extract can be tested for both TNT and RDX. Soil extrac-
tion methods for these RDX tests are summarized in Table 2.
Ion mobility spectrometry
Ion mobility spectrometry (IMS) has been used extensively for the detection of explosives associat-
ed with potential terrorist activities. Recently there has been interest in the use of this technology for
rapid on-site analysis of explosives in soil. Rodacy and Leslie (1993) presented an initial investigation
of the use of IMS for this purpose.
Avolio et al. (1995), from Barringer Instruments Inc. (New Providence, New Jersey), have also
described the use of IMS for rapid on-site analysis of TNT, DNT, and RDX. The best results were
obtained when acetone extracts were deposited on a PTFE filter and thermally desorbed into the IMS.
A 1-g soil sample is extracted with a 1-mL portion of acetone by shaking for three minutes. A 1-mL
portion of hexane is added and an aliquot of the acetone-hexane extract is used for thermal desorp-
tion (Avolio, pers. comm.*). An advantage of the IMS approach is that it provides an estimate of TNT
and RDX in a single analysis.
EXPERIMENTAL
Chemicals and reagents
All standards for TNT, DNT, and RDX were prepared from Standard Analytical Reference Materi-
als (SARMS) obtained from the U.S. Army Environmental Center, Aberdeen Proving Ground, Mary-
land. Stock standards of TNT, DNT, and RDX in acetone were prepared using HPLC-grade acetone.
Working standards in the field were prepared using hardware-store-grade acetone.
All acetone used for soil extraction and glassware cleaning was hardware grade obtained locally.
Methanol used for soil extraction was HPLC grade. Acetonitrile and methanol used in the laboratory
for preparation of HPLC eluents and extract dilution were Baker, EM, or Mallinckrodt HPLC grade.
Water used for preparation of HPLC eluents, and for addition to extracts to ensure that an adequate
water content was present for the color-forming reaction, was reagent-grade water prepared from a
Millipore Milli-Q Type 1 reagent-grade water system.
RP-HPLC analyses
Reversed phase HPLC analysis was conducted as described in EPA SW846 Method 8330. Primary
analysis was conducted on a Supelco LC-18 column eluted with 1:1 methanol/water at 1.5 mL/min.
Absorbance was recorded at 254 nm on a Spectra Physics Model 8490 variable-wavelength detector,
and peaks were recorded on a Hewlett Packard 3396 Digital Integrator in the peak height mode.
Selected samples were subjected to second-column confirmation on a Supelco LC-CN column using
either 35:65 methanol/water or 23:12:65 acetonitrile/methanol/water, depending on the specific an-
alytes detected in the primary analysis (Jenkins and Golden 1993).
* J. Avolio, Applications Chemist, Barringer Instruments, Inc., New Providence, New Jersey.
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