Field Screening Method for TNT and RDX in Groundwater

摘要

Two field screening methods were developed to determine TNT and RDX ingroundwater. Both methods rely on solid phase extraction to remove analytes from the water and effect preconcentration. For the first method, a 500-mL water sample is passed through a 3-mL solid phase extraction cartridge packed with HayeSep R. TNT and RDX are then eluted from the cartridge with acetone and the extract divided into two portions. One portion of the extract is reacted with acetic acid and zinc to convert RDX to nitrous acid. The nitrous acid is converted to an azo dye with a Griess reagent and the concentration estimated by the absorbance at 507 nm (Griess method). The second portion of the extract is reacted with a pellet of KOH and about 0.3 mg of sodium sulfite. The concentration of TNT is estimated from the absorbance at 540 nm of the Janowsky anion (Janowsky method). Using these methods, and visual detection of the colored solutions produced, samples containing 5 ug L(-1) of either TNT or RDX can be reliably distinguished from uncontaminated water. In the second method, a 2-L water sample is passed through a stack of two 47-mm Empore SDVB disks to preconcentrate TNT and RDX. The top disk is removed, the bottom disk eluted with 5 mL of acetone and the extracted RDX determined using the Griess method described above. The top disk is then replaced and eluted with 20 mL of acetone and the extracted TNT determined by the Janowsky method described above.