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ERDC/CRREL TR-02-1
site determination of explosives in soil as compared to water, because of the time
and equipment necessary to extract and concentrate explosives from an aqueous
matrix.
All of these methods are simple, portable, rapid (especially for soils), use
only low-toxicity solvents, work over a large linear analytical range, and have
low detection limits. Moreover, the two spectrophotometric field colorimetric
analytical methods have shown strong correlations when compared to standard
laboratory methods. The major attribute of the visual method is its ability to
rapidly screen for the presence and estimate the concentration of EM in soil or on
surfaces. The following sections will separately discuss the visual screening
methods and the spectrophotometric colorimetric methods.
Visual Colorimetric Screening Method
Simple qualitative and semi-quantitative visual colorimetric tests to screen
for explosive residues on-site can be performed using the Expray kit (e.g., avail-
able from Plexus Scientific, Silver Spring, Maryland). The Expray kit comes in a
small, lightweight (less than 1.4 kg) case that contains three aerosol cans for dis-
pensing chemical reagents and some test paper. To screen surfaces, e.g., range
scrap, the first step is to wipe (rub) exposed surfaces with a white sheet of paper
(100 test sheets are supplied with the kit, or any white filter paper or cotton swab
could be used). For direct analysis of soils (or other materials comprised of small
particles), a small quantity (0.5 to 1 g) is placed in the middle of 47-mm glass
fiber filter paper and soaked with acetone (approximately twice the volume as
weight). The filter paper is folded over and placed on a clean white paper surface.
For soil or water sample extracts, a small aliquot (5 L) of solvent extract (ace-
tone or ACN) is transferred to a test sheet. Actually, several (6 to 12) sample
extracts can be screened simultaneously by carefully arranging the placement of
each aliquot on the test sheet.
The next step is to spray the surface of the test sheet, wipe, or folded filter
paper, following the kit instructions. If a color appears after application of the
first aerosol, then polynitroaromatics (e.g., TNT, TNB, DNT, picric acid, tetryl,
etc.) are present. Some of the colors that may appear upon the application of this
first aerosol are blue, red, or orange. A bluish color appears when 2,4-DNT or
2,6-DNT is the dominant compound, a reddish-brown color appears for TNT and
TNB, and an orange color for tetryl and picric acid. After application of spray
from a second aerosol can, the formation of a pink color indicates the presence of
nitramines or nitrate esters (e.g., RDX, HMX, NG, PETN, NC, NQ, and tetryl).
Application of the first two aerosol cans allows for the sequential detection of
both polynitroaromatics and nitramines. If no color has appeared, the sample is
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