Expray 1: The presence of nitroaromatics (TNT) immediately exhibited a
dark brown color and was discernable by a distinct boundary that was coincident
with the wetted perimeter immediately after blotting.
Expray 2: The application of the second spray is slower to indicate than
Expray 1. In the presence of a nitramine (RDX or HMX) or nitrate-ester (NG),
the color change resolved in 5 to 10 seconds where time was dependent on
concentration. The color change was pink and varied in intensity according to
the concentration. In both cases there was a distinct boundary coincident with
TNT is detectable down to 20 ppm and very intense at 750 ppm. The color
gradation from 20 ppm to 100 ppm is not dramatic, and there is a distinct jump in
intensity with the 500-ppm concentration. The color gradation between 500 ppm
and 1000 ppm is not dramatic as well. The faint color intensity, 20 to 100 ppm,
would suggest a tenfold dilution. The medium intensity from 100 to 500 ppm
would suggest a hundredfold dilution. Finally, the brightest color intensity, from
500 to 1000 ppm, would suggest a thousandfold dilution (Fig. 3a, Table 1).
RDX was discernable down to 30 ppm and very intense at 500 ppm. The
color gradation from 30 to 100 ppm was not dramatic and would suggest a ten-
fold dilution. The medium intensity color occurred at 250 ppm so 100 ppm to
500 ppm would require a hundredfold dilution. The color intensity from 500 to
1000 ppm was dramatic; however, the gradation was not very discernable. This
would require a thousandfold dilution (Fig. 3b, Table 1).
HMX was discernable down to 100 ppm with only a slight gradation to 1000
ppm. Great care would need to be taken if it were known that the samples were to
contain only HMX. The first indication would immediately require a hundredfold
dilution with the brightest intensity requiring a thousandfold dilution. The bright-
est intensity was very faint in comparison with RDX (Fig. 3b, Table 1).
NG was discernable down to 40 to 50 ppm with only a slight gradation up to
100 ppm. A tenfold dilution would be required for this intensity range. From 100
to 1000 ppm is the medium color intensity with little gradation, where a hundred-
fold dilution would be required. The color intensity was greatest at 1000 ppm;
however, not as intense as RDX, but greater than HMX, and this would require a
thousandfold dilution (Fig. 3b, Table 1).