Abstract: A continuous-flow immunoassay for the plastic explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was developed using anti-RDX antibodies and a sulfoindocyanine dye-labelled analog of RDX. Anti-RDX antibodies were immobilized onto Emphaze beads (50-80 µm diameter) and 100 µL of the coated beads was transferred to a microcolumn (2 cm x 5 mm i.d.). The column was incorporated into a FIA system consisting of a pump, 100 µL injection loop and a fluorimetric detector. A 100 µL 2.5-5 µM-RDX-dye conjugate in PBS was loaded onto the column and incubated overnight at room temperature to allow the dye-labelled RDX to bind with the immobilized antibody. The column was then washed with a carrier stream (2 ml/min) containing 12% ethanol/0.1% Triton X-100 in PBS to remove unbound dye and produce a stable baseline. Solutions containing RDX (samples or standards) were then injected into the carrier stream. The displacement of the RDX-dye conjugate with RDX was monitored by measuring the change in fluorescence at 663 nm (excitation at 632 nm). The calibration graph for 15-1200 ng/ml RDX is presented. The linear range was 18-300 ng/ml. Fifty analyzes were performed with each column.

Abstract: A field method for quantitative analysis of explosives in contaminated soil samples is described. The method is based on a displacement immunoassay performed in a commercial instrument, the FAST 2000, engineered by Research International Inc. The method can be used on-sire to measure 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) within 5 min. For this study, replicate analyzes were performed on soil extracts prepared from each field sample as well as appropriate controls, blanks, and laboratory standards. Statistical analyzes were done to assess accuracy, bias, and predictability of the method. The results demonstrated that the immunosensor could be used effectively to screen environmental samples for the presence or absence of explosives. In most samples, the method also provided quantitative values that were in good agreement with standard laboratory analyzes using HPLC. A limited number of sample matrices interfered with the immunoassay and produced results that varied significantly from the laboratory data. In each case, the compounds causing the problem have been identified and efforts are being made to minimize these matrix interferences in future field evaluations.

Abstract: Groundwater was mixed with phosphate buffer of pH 7.4, ethanol and surfactant and analyzed by continuous-flow immunosensors CFI), combining the highly selective antibody-antigen binding interaction with the sensitivity of fluorescence spectroscopy as the signal generation mechanism. The CFI was a semi-automated system in which the groundwater was pumped through a column containing antibodies raised against the analyte which were covalently attached to small plastic beads. As the analyte passed through the antibody matrix, some of the fluorescent dye-labelled explosive analogue was displaced from the antibody in favour of binding the analyte. The two most commonly used military explosives: 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) were detected by the method and quantified fluorimetrically. Field testing of the immunosensor proved its usefulness as a faster, less expensive and portable alternative to HPLC.