and nitrocellulose turn pink. An orange color in-
from other nitroaromatics because cleanup steps
dicates that both TNT and RDX are present. An-
(solid phase extraction and liquidliquid transfer)
other advantage of the broad response of some
are used.
colorimetric methods is they may be used to de-
When several polynitroaromatic analytes are
tect compounds other than the primary target
present in soil, the EnSys and CRREL colorimetric
analyte. For example, the colorimetric RDX meth-
field results sum the analytes that respond to that
ods may be used to screen for HMX when RDX
test. For example, if a soil sample (as analyzed by
levels are relatively low, and for NQ, NC, NG, and
Method 8330) contains TNT, TNB, RDX, HMX, and
PETN in the absence of RDX and HMX. The
tetryl, the concentration estimate from the CRREL
USACE and ENVIROL colorimetric procedures
and EnSys RISc colorimetric methods for TNT
are more specific to TNT than the CRREL and
would sum contributions from TNT, TNB, and
EnSys RISc colorimetric methods, but have not
tetryl, and the RDX test kit would sum contribu-
been as thoroughly evaluated. If a secondary tar-
tions from RDX and HMX. Because response fac-
get analyte is present at only low concentrations
tors are not identical for each compound, the re-
in a sample, the effect on the analytical result is
sulting concentrations will not quantitatively sum
minimal. If the objective is to determine the con-
the analytes, but will provide an estimate that is
centration of TNT or RDX when relatively high
adequate in light of the substantial spatial hetero-
levels of other nitroaromatics and nitramines are
geneity always encountered for these analytes in
present, immunoassay or the USACE or ENVIROL
soil.
methods may be appropriate.
Extremes of temperature, pH, and soil water
Immunoassay methods
content can interfere with on-site analytical meth-
For TNT kits, the primary target analyte is TNT,
ods. According to the California Military Environ-
and the secondary target analytes are other
mental Coordination Committee, the following
nitroaromatics, such as TNB, DNTs, Am-DNTs,
physical conditions are generally not recom-
and tetryl. For the RDX kit, the primary target
mended for both colorimetric and immunoassay
analyte is RDX, and there is cross-reactivity with
methods: temperatures outside the 4 to 32C range,
HMX (3%). If the primary target analyte is the
pH levels less than 3 or greater than 11, and water
only compound present in soil, the immunoassay
content greater than 30% (CMECC 1996). Specific
methods measure the concentration of that com-
product literature should be consulted for more
pound.
information.
If multiple analytes are present in soil, the im-
munoassay kits measure the primary target
Colorimetric methods
analyte plus some percentage of the cross-reactive
For TNT methods, the primary target analyte
secondary target analytes. The response of immu-
is TNT, and the secondary target analytes are other
noassay kits to the secondary target analytes is not
nitroaromatics, such as TNB, DNB, 2,4-DNT, 2,6-
equivalent to that of the primary target analyte.
DNT, and tetryl. For RDX methods, the primary
Also, the response does not remain constant
target analyte is RDX, and the secondary target
throughout the concentration range of the kits. In
analytes are nitramines (HMX and NQ), and ni-
addition, different immunoassay kits have differ-
trate esters (NC, NG, and PETN). If the primary
ent cross-reactivities to secondary target analytes
target analyte is the only compound present in soil,
based on the antibodies used to develop each
the colorimetric methods measure the concentra-
method. Cross-reactivities for immunoassay kits
tion of that compound. If multiple analytes are
are usually reported at the 50% response level
(IC50), typically the midpoint of the concentration
present in soil, the CRREL and EnSys field meth-
range of the kits. Table 5 shows the reported cross-
ods measure the primary target analyte plus the
reactivities at IC50 for the immunoassay kits. A
secondary target analytes: nitroaromatics for the
complete cross-reactivity curve for the entire con-
TNT test kit, and nitramines plus nitrate esters for
centration range should be obtained from the
the RDX test kits. Also, the response of the CRREL
manufacturers for the immunoassay kits being
and EnSys colorimetric methods to the secondary
considered. Where multiple analytes exist in soil
target analytes is similar to that of the primary tar-
samples, immunoassay results may not directly
get analyte, and remain constant throughout the
compare with EPA Method 8330 results. For ex-
concentration range of the methods, although the
ample, an immunoassay kit may have cross-reac-
observed colors may be different. The ENVIROL
tivities of 23% for TNB and 35% for tetryl for the
method is much less susceptible to interference
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