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Guide for Characterization of Sites Contaminated with Energetic Materials
43
then sprayed with the third aerosol can. If a pink color appears only after
applying the third aerosol, then the presence of an inorganic nitrate (ammonium,
potassium, sodium, barium, strontium nitrate, or black powder) is indicated.
To estimate the explosives concentrations in soil or water sample extracts, a
visual calibration scale can be prepared by spraying 5-L aliquots of 10, 100, and
1000 mg/L standards of TNT and RDX that have been placed on separate test
sheets (all six aliquots can be placed on the same sheet, but the TNT standards
need to be covered when applying the second aerosol). This screening method
can detect the presence of 0.05 g of explosive analyte when concentrated in a
discrete location (5 L) on a white surface (test paper or filter paper). Screening
sample extracts using this method complements the on-site spectrophotometric
colorimetric, immunoassay, and GC methods of analysis (see the following
sections and Appendixes I and J) by alerting the analyst to when sample extract
dilution is necessary.
Spectrophotometric Colorimetric Methods Extraction
To characterize EM in soil, a 20-g portion of undried or dried material is
mixed with 100 mL of acetone containing 3% distilled water. Extraction is
performed over a 30-min period facilitated by 3-min intervals of vigorous shak-
ing. Typically, this extraction procedure is sufficient to achieve complete recov-
ery of the EM (Jenkins et al. 1997c). After extraction, the sample is allowed to
settle and is then filtered with a syringe filter. Very heavy clays might need more
time to settle, but sandy and loamy soils require as little as 3 minutes to settle. To
prepare a water sample for analysis, see Appendix G, Solid-Phase Cartridge
Extraction. The extracts are then subjected to TNT and RDX screening proce-
dures (see below). It should be noted that these acetone extracts can also be
analyzed by Methods 8330 (Jenkins et al. 1997b) and 8095 (Walsh and Ranney
1998, 1999).
TNT On-Site Determination
In the TNT procedure, the initial absorbance of the acetone extract at 540 nm
is obtained using a portable spectrophotometer. Potassium hydroxide and sodium
sulphite are added to the extract, it is agitated for 3 minutes, and then filtered.
Extracts are evaluated visually. If the extract has a reddish or pinkish color, it
contains TNT; if it has a bluish color, it contains 2,4-DNT; if it is orange, it
contains tetryl; if it has a reddish-orange color, it contains picric acid. The
absorbance peak at 540 nm is used to verify the presence of TNT and represents
the optimal wavelength to minimize interference from humics. The field spectro-
photometer recommended is the HACH DR/2010 Portable Data Logger. The
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