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Published: 1999

Total Pages: 21

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An on-site method has been developed for estimating concentrations of TNT, RDX, 2,4-DNT, and the two most commonly encountered environmental transformation products of TNT, 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene, in soil and groundwater using gas chromatography and the nitrogen-phosphorus detector (NPD). Soil samples (20 g) are extracted by shaking with 20 mL of acetone, and extracts are filtered through a Millex SR (0.5-micrometers) filter. Groundwater samples (1 L) were passed through SDB-RPS extraction disks that were subsequently extracted with 5 mL of acetone. A 1-micro-L volume of a soil or water extract is manually injected into a field-transportable gas chromatograph equipped with a NPD and a heated injection port. Separations are conducted on a Restek Crossbond 100% dimethyl polysiloxane column, 6 m x 0.53-mm i.d., 1.5 mm, using nitrogen carrier gas at 9.5 mL/min. Retention times range from 3.0 min. for 2,4-dinitrotoluene (2,4-DNT) to 5.6 min. for 2-amino-4,6-dinitrotoluene. Method detection limits were less than 0.16 mg/kg for soil and less than 1.0 microgram/L for groundwater. One of the major advantages of this method, over currently available colorimetric and enzyme immunoassay on-site methods, is the ability to quantify individual target analytes that often coexist in soils and groundwater contaminated with explosive residues. This method will be particularly useful at military antitank firing ranges where it is necessary to quantify residual concentrations of RDX in the presence of high concentrations of HMX, and when the transformation products of TNT need to be identified.