COMPARISON OF SOLID-PHASE EXTRACTION WITH SALTING-OUT SOLVENT-EXTRACTION FOR PRECONCENTRATION OF NITROAROMATIC AND NITRAMINE EXPLOSIVES FROM WATER

Residues of high explosives are a significant pollution problem at U.S. military facilities. Because TNT, RDX and HMX, as well as several manufacturing impurities and environmental transformation products, are mobile in the soil and have caused groundwater pollution, there is an increasing demand for low-concentration analysis of these compounds in water from installation boundary wells. Because RDX and HMX are polar, conventional liquid-liquid extraction with nonpolar solvents yields poor recovery. Two techniques have been reported that appear to offer improved recovery and adequate preconcentration: solid phase extraction (SPE) and salting-out solvent extraction (SOE). This paper compares resin based cartridge-SPE, membrane-SPE, and SOE using fortified reagent grade water samples and a set of 58 groundwater samples from an explosives-contaminated military facility. The three methods were comparable with respect to low-concentration detection capability, which ranged from 0.05 to 0.30 mu Lg/l. Percent recoveries generally exceeded 80%, except for HMX and RDX by membrane-SPE. Interferences were found in extracts from half of the groundwater samples preconcentrated using the two SPE procedures, but were not found in any of the extracts from the SOE. These interferences were traced to matrix interaction of the polymeric resins with low-pH groundwater containing high levels of dissolved solids.