0055im.jpg)
48
ERDC/CRREL TR-02-1
APPENDIX J: ENZYME IMMUNOASSAY FIELD METHOD
The immunoassay field method is an immunochemical detection method
based on a reaction between target analyte and a specific antibody that is quan-
titated by monitoring a color change or by measuring radioactivity or fluores-
cence. Immunochemical methods use predominantly antibodies obtained from
rabbits, sheep, or goats (for polyclonal preparations) or rats and mice (for mono-
clonal preparations). The D-Tech enzyme (EIA) test kits for RDX and TNT are
commercially available from Strategic Diagnostics, Inc. The test kits are named
D-Tech Environmental Detection Systems and were developed in 199495
(Teany and Hudak 1994, Teany et al. 1995). The components of the EIA include
RDX- and TNT-specific antibodies covalently linked to small latex particles that
are collected on the membrane of the cup assembly. A color-developing solution
added to the surface of the cup assembly reveals a color inversely proportional to
the concentration of RDX or TNT in the sample. RDX and TNT are best meas-
ured in the ranges between 0.56 ppm and between 0.55 ppm, respectively. In
the case where concentrations are higher than these upper working range limits, a
dilution of the extracts can be made to obtain a result within the effective range
of the test.
Extraction
Using the D-Tech system, soils are extracted using an equivalent ratio of
soil/acetone (1:5) as for the colorimetric procedure. However, the weight of the
soil sample is limited to approximately 2 g of material.
TNT and RDX Screening
A 1.0-mL aliquot of clear acetone extract is transferred into a bottle of buffer
solution (bottle 2 in the extraction pack). Then prescribed volumes of the buff-
ered soil extracts are added to the vials containing enzyme-labeled RDX or TNT
and antibody-coated latex particles. The mixtures are allowed to stand for 2 min
(TNT) and 5 min (RDX) to allow the explosive molecules to interact with the
binding sites of the antibodies. A control reference is processed with each analy-
sis. Samples and references receive identical treatment, and both solutions are
poured into their respective sides (test or reference) of the porous membrane of
the cup assembly. The conjugate solutions are allowed to pass through the mem-
branes, washed and treated with a color-developing solution. The reference side
of the cup is used to determine the end-point of the color development, with all
readings done at room temperature. The time for complete color development is
less than 10 min for TNT and 15 min for RDX, respectively.
Previous Page
