Table 6. Comparison of HPTLC plates and TLC plates.
Petroleum ether : isopropanol
Petroleum ether : acetone
(4 : 1)
(1 : 1)
HPTLC
TLC
HPTLC
TLC
Rf* S.D.
Rf* S.D.
Rf* S.D.
Rf* S.D.
Compounds
0.83 0.03
0.64 0.02
TNT
0.79 0.02
0.58 0.02
TNB
0.73 0.03
0.52 0.02
2,4-DNT
0.68 0.01
0.37 0.02
Tetryl
0.57 0.00
0.23 0.02
2-A-DNT
0.62 0.02
0.27 0.02
4-A-DNT
0.32 0.02
0.30 0.02
0.65 0.05
0.72 0.01
RDX
0.57 0.06
0.62 0.01
HMX
No movement
No movement
0.82 0.02
0.84 0.03
0.82 0.04
0.91 0.03
PETN
0.75 0.02
0.79 0.02
0.79 0.04
0.88 0.02
NG
*n = 3
results is shown in Table 7. In most cases, the evalu-
DMAB, or DMACA, which react with the amines
ated visualizing agents worked well in visualiz-
to form Schiff bases. Compounds sprayed with
ing nitroaromatic compounds, but were fairly lim-
DEAB resulted in yellow-colored products,
ited in visualizing nitramines and nitrate esters.
DMAB-sprayed compounds were orange-yellow
in color, and compounds sprayed with DMACA
UV light and EnSys TNT developer
resulted in purple colors. The color developments
The simplest method for visualizing nitroaro-
were immediate after the application of DEAB,
matics and nitramines was viewing the developed
DMAB, or DMACA and were best viewed when
plate under shortwave (254 nm) UV light (Glover
the plate was still wet.
and Hoffsommer 1973, McCormick et al. 1978,
Malotky and Downes 1983, and Zou et al. 1994).
EDA : DMSO
We found the fluorescence-containing plates to
The solution of EDA : DMSO (1 : 1) reacts with
have bright green backgrounds with light-to-dark
nitroaromatic compounds to form Meisenheimer
spots representing nitroaromatic and nitramine
complexes. The results we obtained were similar
compounds. Following the UV viewing, nitroaro-
to Hoffsommer and McCullough (1968). Upon
matics could be further distinguished by placing
spraying the plate with EDA : DMSO solution, the
approximately 1 L of the EnSys TNT developer
resulting colors were purple for TNT, orange for
on the dark spots. The EnSys TNT developer re-
tetryl, red-orange for TNB, faint yellow for 2-A-
acts with the nitroaromatic compounds to form
DNT, and light green for 2,4-DNT (while the plate
Meisenheimer complexes and results in the fol-
was still wet).
lowing color formations: purple for TNT, orange
for tetryl, light yellow for 4-A-DNT, orange for
Alkaline solution (5% KOH, 1 N NaOH, 0.1 N NaOH)
TNB, light yellow for 2-A-DNT, and light green
and Griess reagent, 5% KOH and Bratton-Marshall
for 2,4-DNT. The intensity of the color varied de-
reagent, and 5% KOH and Hach NitriVer3
pending on the concentration of the compound.
These visualizing agents behave similarly in that
their reactions all follow a similar principle. The
TiCl3 and DEAB, TiCl3 and DMAB, and TiCl3 and
alkaline solution is initially used to reduce the
DMACA
compounds to form nitrite ions. These ions are
These three visualizing agents worked well in
then converted to azo compounds in the acidic
visualizing nitroaromatic compounds. They are
medium and coupled to naphthalene derivatives
grouped together due to similar reaction principle
(which are found in the Griess reagent, the Bratton-
(Yasuda 1964, 1970, Yinon and Zitrin 1981, and Jork
Marshall reagent, and the Hach NitriVer3) to form
et al. 1994b). The developed plates are initially
the characteristic colors. Slight variations in the
sprayed with the TiCl3 reagent, which reduces the
formulation of the Griess reagent resulted in dif-
nitroaromatic compounds to amines. When the
ferent color formation (Table 7). According to the
plate is dried, it is sprayed with either DEAB,
literature, nitrate esters and nitramines reacting
8
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