Philip G. Thorne

A Field Method for Quantifying Ammonium Picrate and Picric Acid in Soil

A simple field method for the determination of ammonium picrate and picric acid in soil was devel- oped. Picric acid is a strong acid with a pKa 5 0.80, and is colorless when dissolved in an organic solvent, whereas its anion ( picrate) is bright yellow. Picric acid and picrate ions were extracted from undried soil by shaking with acetone; any picric acid extracted was rapidly converted to picrate in the wet acetone. Picrate was extracted from the acetone soil extracts by passing the solutions through a solid-phase anion exchanger to remove interferences. Acidified acetone was used to convert the picrate to picric acid and elute it from the ion exchanger. The absorbance of the solution at 400 nm was measured; then the picric acid was converted to the colored picrate ion by diluting the eluent with wa- ter. Absorbance at 400 nm was measured again and the concentration of picrate was obtained from the differ- ence in the absorbance measurements, corrected for di- lution. The method detection limit is 1.3 mg g 2 1 of soil. Field-contaminated soils were assayed, and the results compared favorably to those from HPLC analyses in the range of 10 - 4400 mg g 2 1 . The method is simple to use, can be implemented under field conditions, and com- plements on-site methods for TNT, RDX, and 2,4-DNT.

Laboratory and analytical methods for explosives residues in soil

Abstract Standard analytical methods have been developed to characterize explosives residues in soil at U.S. Department of Defense installations. The laboratory analysis is conducted using RP-HPLC, and the most commonly found analytes are TNT and RDX. Other analytes commonly detected are the environmental transformation products of TNT including TNB, dinitroaniline, and the isomers of amino-DNT, and the manufacturing by-products DNB and the isomers of amino-DNT. Field methods designed to detect TNT and RDX have enhanced site characterization by providing rapid on-site results for a greater number of samples than would be economically feasible by depending solely on off-site laboratory analyses for all samples. Attempts may be made to use both laboratory and field methods to analyze treatment matrices such as incinerator ash and compost, but further analytical method development is needed to enhance extraction and minimize interferences.

Development of colorimetric field screening methods for munitions compounds in soil

Simple colorimetric tests have been developed to screen for the presence of TNT, TNB, DNT, DNB, tetryl, RDX, HMX, nitroglycerine (NG), PETN, nitrocellulose (NC), nitroguanidine (NQ), picric acid and ammonium picrate in soil. Soils are extracted by manual shaking with acetone. For the nitroaromatics, the extracts are reacted with potassium hydroxide and sodium sulfite to form their colored Janowsky complexes. For RDX, HMX, NG, PETN, NC and NQ, extracts are passed through an anion exchange resin to remove nitrate, and then acidified with acetic acid; the nitramines and nitrate esters are reduced with zinc to form nitrous acid. The nitrous acid is detected by the Griess reaction using a Hach Nitriver 3 powder pillow, which produces a highly colored azo dye. Detection of these analytes can be obtained visually and concentrations estimated from absorbance measurements at 540 nm for TNT, TNB and tetryl, 570 nm for DNTs and DNB, and at 510 nm for RDX, HMX, NG, PETN, NC and NQ. For picric acid/ammonium picrate, the acetone extract is passed through a basic ion-exchange column that retains picrate ion. The column is rinsed with methanol to elute interferences, and the picrate is desorbed with acetone containing several drops of sulfuric acid. The extract is diluted with deionized water, and the concentration of picrate is obtained from the absorbance at 400 nm. Detection limits are about 1 (mu) g/g for all analytes except NG, NC and NQ, which are slightly higher. Results from field screening at a number of sites have been correlated with laboratory analyses for TNT and RDX. The results indicate that the field screening methods do not suffer from false negatives and the rate of false positives is low. Concentration estimates from field screening compared favorably with results from the standard laboratory methods.

Analytical methods for characterization of explosives-contaminated sites on U.S. Army installations

The U.S. Army manufactures munitions at facilities throughout the United States. Many of these facilities are contaminated with residues of explosives from production, disposal of off- specification, and out-of-data munitions. The first step in remediating these sites is careful characterization. Currently sites are being characterized using a combination of on-site field screening and off-site laboratory analysis. Most of the contamination is associated with TNT (2,4,6-trinitrotoluene) and RDX (hexahydro-1,3,5-tri-nitro-1,3,5-triazine) and their manufacturing impurities and environmental transformation products. Both colorimetric and enzyme immunoassay-based field screening methods have been used successfully for on-site characterization. These methods have similar detection capabilities but differ in their selectivity. Although field screening is very cost-effective, laboratory analysis is still required to fully characterize a site. Laboratory analysis for explosives residues in the United States is generally conducted using high-performance liquid chromatography equipped with a UV detector. Air-dried soils are extracted with acetonitrile in an ultrasonic bath. Water is analyzed directly if detection limits in the range of 10 - 20 (mu) g/L are acceptable, or preconcentrated using either salting-out solvent extraction with acetonitrile or solid phase extraction.