12
ERDC/CRREL TN-05-2
5
CONCLUSIONS
The Expray Explosives Detection Kit can be used to not only give a quali-
tative measurement, but will also provide a semi-quantitative measurement prior
to HPLC or GC analysis. TNT and RDX gave the best color intensities and gra-
dation, yielding a much clearer definition for performing orders-of-magnitude
dilutions. HMX was discernable at a concentration much higher than the other
three and with little color gradation through the range of concentrations. NG
showed little color gradation through its dynamic range. Throughout the testing it
was noted that the results were variable ( 20 ppm) at concentrations lower than
500 ppm with all analytes.
These experiments have shown that after the analyte in question reached the
upper limit of color intensity (brightest color), it was impossible to determine the
relative sample concentration. Therefore it is recommended to dilute and repeat
spraying when these high concentration extracts are encountered to ensure safe
analyzing.
Experience indicates that care should be taken when evaluating the soil
extracts, as some field samples may not react fully with the Expray solution,
yielding false negatives. Also, false positives may be encountered when
analyzing firing point samples due to the presence of nitrocellulose, which also
reacts to form a pink color with Expray 2. The location in which the sample was
taken should be scrutinized along with the results of the spraying to determine
whether an error possibly occurred. The sequence of samples should be scruti-
nized to minimize the effects of carryover, i.e., they should be analyzed in order
of increasing concentration. The recent availability of the Expray test paper in
8.5- 11-inch sheets allows it to be used for large-scale pre-screening and is
recommended; however, other cellulose filter papers can be used.
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