Enhanced biosensor performance for on‐site field analysis of explosives in water using solid‐phase extraction membranes

Biosensors, over the past decade, have demonstrated their utility in a number of environmental applications. One application has been trace-level detection of energetic materials (i.e., explosives) in the soil, sediment, and waterways as a result of unexploded ordnances from past military exercises. A promising biosensor, developed at the Naval Research Laboratory, has been designed to detect the explosives 2,4,6-trinitrotoulene (TNT) and 1,3,5-hexahydro-1,3,5-trinitrotriazine (RDX), utilizing a displacement immunoassay format. The fundamental principle of the biosensor relies on the specificity of the recognition element (e.g., antibody) to recognize and bind the explosive molecule, with subsequent release and fluorescence signal response by a cyanine-5 labeled reporter complex. In recent analytical tests performed on environmental samples, erroneous signal responses and inaccurate quantitative measurements were obtained with the biosensor as a result of interference components in the environmental matrices. In this paper, we investigated the use of solid-phase extraction (SPE) membranes for their efficiency to extract the explosives TNT and RDX in water samples to improve quantitative measurements conducted with the biosensor. Three SPE membranes were evaluated: (1) styrenedivinylbenzene-extra clean (SDB-XC) copolymer, (2) styrenedivinylbenzene-reverse phase sulfonated (SDB-RPS) copolymer, and (3) C-18 octadecyl bonded silica (C18). Each SPE membrane was exposed to media containing the explosives TNT, RDX or both. Initial experiments were conducted to determine which SPE membrane and what elution solvent was most effective in the extraction of both TNT and RDX from water samples. Solvent extracts from the SPE membranes containing the explosive molecules were also analyzed using a reverse-phase high performance liquid chromatography method (EPA SW846-Method 8330). Experimental results using the SDB-RPS membrane to extract TNT or RDX from groundwater or seawater consistently produced extraction efficiencies between 80 and 100%. Results also confirmed that combining the extraction capabilities of the SPE membrane improved the fluorescence signal response and accuracy of the biosensor twofold in comparison to previous analysis © 2002 Wiley Periodicals, Inc.* Field Analyt Chem Technol 5: 272–280, 2001; DOI 10.1002/fact.10007