line of origin (about 23 cm above the bottom of
ration of nitroaromatic compounds such as TNT,
the plate) and the solvent front line (10 cm from
TNB, DNT, tetryl, and the isomers of amino-DNTs.
the line of origin). Using capillary micropipettes,
The evaluated mobile phase systems using labo-
samples were spotted along the line of origin ap-
ratory-grade solvents included hexane : chloro-
proximately 1 cm apart. Spotting volumes ranged
form (4 : 1), chloroform, petroleum ether : acetone
from 0.5 to 30 L, but in most cases, samples were
(3 : 1) and (2 : 1), petroleum ether : isopropanol (4
spotted 1 L at a time. The plates were then placed
: 1), xylene, and Stoddard solution : isopropanol
in the developing tank (containing the freshly pre-
(2 : 1) and (1 : 1). These solvents were chosen
pared mobile phase) and developed in an ascend-
according to their eluting strength. The combina-
ing manner until the mobile phase had reached
tion of four parts petroleum ether with one part
the solvent front line. The plates were removed
isopropanol resulted in the best distinguish-
from the tank and either air dried or dried with
able separation of nitroaromatic compounds com-
hot air from a heat gun prior to observation. The
pared to the other evaluated mobile phase sys-
fluorescence-containing plates were observed un-
tems (Table 1). The solvent system of hexane : chlo-
der the UV lamp (set at 254 nm) and/or sprayed
roform (4 : 1) resulted in no movement of the
with visualizing agents. Nonfluorescence-contain-
compounds. Chloroform, by itself, resulted in
ing plates were sprayed with visualizing agents.
identifiable separation of TNT, TNB, DNT, and
The position of the resulting nonfluorescing spots
tetryl, but the Rf values of the amino-
(observed under the UV light) or colored spots was
DNTs were nearly identical. The combination
marked and the retention factor (Rf) values were
solvents of petroleum ether and acetone at vari-
determined by dividing the distance traveled by
ous ratios also failed to separate the compounds
the compound by the distance traveled by the sol-
efficiently. Xylene, by itself, and Stoddard solution
vent front. When analyzing soil samples, analytes
(a clear petroleum distillate) with isopropanol
were identified by comparing the Rf values to the
were fairly effective in separating the
Rf values of the standards that were spotted on
nitroaromatic compounds, but their develop-
the same plate.
ment times were considerably longer compared
to the other laboratory-grade solvent systems
(Table 2).
Commercial-grade paint thinners and alcohols,
RESULTS AND DISCUSSION
which are readily available in any local hardware
or paint store, were also evaluated for their ability
Separation of nitroaromatics using laboratory-
to separate nitroaromatic compounds. However,
grade and commercial-grade solvents
Numerous mobile phase systems were tested to
because of the high water content in commercially
determine the best solvent or combination of sol-
available alcohols (i.e., Woolworth-brand 70% iso-
vents that would result in a distinguishable sepa-
propanol and Sterling solvent alcohol), all mobile
Table 1. Separation of nitroaromatics with laboratory-grade solvents.
Solvent
TNT
TNB
2,4-DNT
Tetryl
2-A-DNT
4-A-DNT
Rf S.D.
Rf S.D.
Rf S.D.
Rf S.D.
Rf S.D.
Rf S.D.
systems
1
0.52
0.36
0.48
0.20
0.16
0.14
2
0.42
0.40
0.40
0.27
0.22
0.23
3
0.47
0.46
0.45
0.33
0.30
0.30
0.64 0.02
0.58 0.02
0.52 0.02
0.37 0.02
0.23 0.02
0.27 0.02
4
5
0.75
0.71
0.63
0.62
0.55
0.55
6
0.74
0.72
0.65
0.67
0.62
0.62
7
0.54
0.50
0.47
0.28
0.1
Solvent system key:
1--Chloroform
2--Petroleum ether : acetone (3 : 1)
3--Petroleum ether : acetone (2 : 1)
4--Petroleum ether : isopropanol (4 : 1), n = 3
5--Stoddard solution : isopropanol (2 : 1)
6--Stoddard solution : isopropanol (1 : 1)
7--Xylene
5
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