US Army Corps 
 of Engineers® 
 
 Cold Regions Research & 
 Engineering Laboratory 
 
 On-Site Method for Measuring 
 Nitroaromatic and Nitramine Explosives 
 in Soil and Groundwater Using GC-NPD 
 
 Feasibility Study 
 
 Alan D. Hewitt and Thomas F. Jenkins 
 
 August 1999 
 
Abstract: 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 Mlllex SR (0.5-pm) 
 filter. Groundwater samples (1 L) were passed through 
 SDB-RPS extraction disks that were subsequently ex¬ 
 tracted with 5 ml of acetone. A 1 -|irL volume of a soil or 
 water extract is manually injected into a field-transport¬ 
 able 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 mlVmin. 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 |Lig/L for groundwater. 
 One of the major advantages of this method, over cur¬ 
 rently available colorimetric and enzyme immunoassay 
 on-site methods, is the ability to quantify individual target 
 analytes that often coexist in soils and groundwater con¬ 
 taminated 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. 
 
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Special Report 99-9 
 
 US Army Corps 
 of Engineers® 
 
 Cold Regions Research & 
 Engineering Laboratory 
 
 On-Site Method for Measuring 
 Nitroaromatic and Nitramine Explosives 
 in Soil and Groundwater Using GC-NPD 
 
 Feasibility Study 
 
 Alan D. Hewitt and Thomas F. Jenkins August 1999 
 
 Prepared for 
 
 OFFICE OF THE CHIEF OF ENGINEERS 
 and 
 
 U.S. ARMY ENVIRONMENTAL CENTER 
 SFIM-AEC-ET-CR-99044 
 
 Approved for public release: distribution is unlimited. 
 

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I 
 
 PREFACE 
 
 This report was prepared by Alan D. Hewitt, Research Physical Scientist, and 
 Dr. Thomas F. Jenkins, Research Chemist, Geological Sciences Division, U.S. Army 
 Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire. 
 
 Funding for this work was provided by the U.S. Army Environmental Center, 
 Martin H. Stutz, Project Monitor, and from the U.S. Army Corps of Engineers In¬ 
 stallation Restoration Program, Work Unit AF25-CT-006, Dr. M. John Cullinane, 
 Program Manager. The authors thank Dr. C.L. Grant and Dr. PH. Miyares for tech¬ 
 nical review of the text. 
 
 This publication reflects the view of the author and does not suggest or reflect 
 policy, practices, programs, or doctrine of the U.S. Army or of the Government of 
 the United States. 
 
 I 
 
 ft 
 
 11 
 
CONTENTS 
 
 Preface. ii 
 
 Introduction. 1 
 
 Deficiencies with current methods and objectives of this study. 2 
 
 Experimental methods. 3 
 
 Calibration standards. 3 
 
 Instrumentation and separations. 3 
 
 RP-HPLC analyses. 4 
 
 Sample preparation—soil. 4 
 
 Sample preparation—water. 4 
 
 Miscellaneous variables. 5 
 
 Results and discussion. 5 
 
 GC separations. 5 
 
 Response factors. 7 
 
 MDL tests. 8 
 
 Comparison of results for GC-NPD vs. RP-HPLC for field-contaminated 
 
 soils. 10 
 
 Miscellaneous variables. 11 
 
 Summary. 12 
 
 Literature cited. 12 
 
 Abstract. 13 
 
 ILLUSTRATIONS 
 
 Figure 
 
 1. Chromatogram of 2.4-DNT, TNT, RDX, 4ADNT, 2ADNT, and HMX 
 
 by GC-NPD analysis. 6 
 
 2. Chromatogram of 2,4-DNT, TNT, RDX, 4ADNT, and 2ADNT by 
 
 GC-ECD analysis. 6 
 
 3. Calibration curve obtained for RDX by GC-NPD analysis. 8 
 
 4. Calibration curve obtained for RDX by GC-ECD analysis. 9 
 
 5. Comparison of target analyte concentrations established by HPLC and 
 
 GC-NPD analysis of field samples. 11 
 
 TABLES 
 
 Table 
 
 1. Concentration ranges for the working standards of TNT, 2,4-DNT, 
 
 RDX, 2ADNT, and 4ADNT prepared for the evaluation of the 
 
 nitrogen-phosphorus (NP) and electron capture (EC) detectors. 4 
 
 2. Response factors for the GC-NPD, based on the average of triplicate 
 
 measurements of both peak area and height. 7 
 
 3. Response factors for GC-EC detector, based on the average of duplicate 
 
 measurements. 7 
 
 4. Response factors for RP-HPLC analysis, based on duplicate measurements 8 
 
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5. Method detection limit study of blank soil spiked with five target 
 
 analytes and analyzed by GC-NPD. 9 
 
 6. MDL study of 1-L reagent grade water samples fortified with five target 
 
 analytes and analyzed by solid phase extraction and GC-NPD. 10 
 
 7. Comparison between GC-NPD and RP-HPLC results for the solvent 
 
 extracts of field-contaminated soil samples. 10 
 
 8. Assessment of the effect of soil moisture on GC-NPD response. 11 
 
 9. Retention times for explosives using different oven temperature programs 
 
 for NPD and ECD. 12 
 
 
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On-Site Method for Measuring Nitroaromatic 
 and Nitramine Explosives in Soil and 
 Groundwater Using GC-NPD 
 
 Feasibility Study 
 
 ALAN D. HEWITT AND THOMAS F. JENKINS 
 
 INTRODUCTION 
 
 Until the last several years, almost all sites po¬ 
 tentially contaminated with toxic and hazardous 
 wastes were characterized by shipping soil and 
 water samples to off-site laboratories for analysis. 
 These off-site laboratories utilized powerful labo¬ 
 ratory instrumentation and followed methods 
 such as those that have been standardized through 
 the U.S. Environmental Protection Agency’s 
 SW846 Methods compendium. In general the data 
 obtained in this way were adequate to make deci¬ 
 sions on whether sites were contaminated at lev¬ 
 els that required remedial activities. Action levels 
 for explosives, although not universally accepted, 
 have generally been based on water quality crite¬ 
 ria. The interim EPA guidance indicates that con¬ 
 centrations as low as 2 |ig/L for 2,4,6-trinitrotolu¬ 
 ene (TNT) may have some level of human toxicity 
 (U.S. EPA 1989). Action levels for soil have gener¬ 
 ally been in the milligram/kilogram range. 
 
 A major downside of this approach is the time 
 involved in producing the data for making these 
 decisions. It often takes weeks to months after 
 samples were collected before data become avail¬ 
 able to project personnel. Secondly, this approach 
 was extremely expensive on a per sample basis, 
 resulting in the analysis of a relatively few samples 
 to characterize large geographical areas. Recogni¬ 
 tion of these problems led to the development of 
 analytical methods that could be used on site to 
 provide adequate characterization when rapid de¬ 
 cisions were required. Because of lower analysis 
 costs, these methods allowed more samples to be 
 
 analyzed resulting in a more spatially detailed 
 characterization. 
 
 The first on-site method for detecting explosives 
 residues in water was reported by Heller et al. 
 (1982) and later improved by Erickson et al. (1984), 
 who extended its application to include soils. This 
 method was specifically aimed at the detection of 
 TNT and utilized a detection tube that had two 
 sections. The first section contains a basic oxide 
 that converts TNT to its Meisenheimer anion. This 
 colored species migrates to the second section of 
 the tube, where it is retained on a quaternary am¬ 
 monium chloride ion exchange resin. Water 
 samples were pumped through this tube, and TNT 
 was detected visually by the development of a 
 reddish stain on the second section of the tube. 
 The concentration of TNT was estimated from the 
 length of the stain produced. Soil samples are first 
 extracted with methanol, and then this solvent is 
 passed through the tube. The tubes have been 
 independently evaluated at CRREL and found to 
 provide reliable detection of the presence of TNT 
 at concentrations greater than 40 pg/L, but the 
 ability to precisely and accurately quantify TNT 
 concentrations in water or soil was poor (Jenkins 
 and Schumacher 1990). Moreover, the 1-minute 
 extraction time specified for soil was insufficient 
 for field samples. 
 
 Stevanovic and Mitrovic (1990) developed a 
 method for TNT and 1,3,5-hexahydro-1,3,5- 
 trinitrotriazine (RDX) that could be adapted for 
 on-site analysis. In this method, water is passed 
 through a porous disk coated with a thin film of 
 silica gel, and TNT and RDX are adsorbed on the 
 
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surface. The (disk is dried and sprayed with a color 
 forming solution of o-toluidine for TNT and Griess 
 reagent for RDX. Measurement is made by reflec- 
 tometry, and detection limits of about 200 pg/L 
 were estimated. 
 
 Seitz and coworkers at the University of New 
 Hampshire developed a fiber-optic-based ap¬ 
 proach for on-site measurement that utilizes 
 the reaction of TNT with an amine-loaded 
 poly(vinyl)chloride (PVC) membrane to form a 
 colored product (Zhang et al. 1989, Zhang and 
 Seitz 1989). This approach was specific for TNT, 
 and has a detection limit of about 100 pg/L. 
 
 In another approach, TNT and RDX were ab¬ 
 sorbed into a cellulose acetate membrane contain¬ 
 ing pyrenebutyric acid, and concentrations were 
 estimated via fluorescence quenching by the nitro 
 groups Qian and Seitz 1990). Detection limits were 
 estimated at 2 and 10 mg/L. 
 
 A photometric method for RDX was developed 
 by Hass and Stork (1989) and Hass et al. (1990) 
 that involves evaporation of a 500-mL water 
 sample to dryness, followed by reaction of the 
 residue with diphenylamine in sulfuric acid. A 
 colored product is produced and the concentra¬ 
 tion of RDX is estimated from the absorbance at 
 596 nm. The detection limit of about 5 pg/L 
 is nearly adequate for this application, but the 
 procedure is cumbersome and impractical for on¬ 
 site use. 
 
 Colorimetric-based methods for TNT and RDX 
 in water and soil were developed at CRREL 
 Genkins 1990, Walsh and Jenkins 1991, Jenkins et 
 al. 1994, Jenkins and Walsh 1998). Soil samples (20 
 g) are extracted with 100 mL of acetone. Water 
 samples are passed through two solid-phase ex¬ 
 traction membranes, and the retained compounds 
 were eluted from each membrane with acetone. 
 The acetone extract of the first membrane is re¬ 
 acted with a base, producing highly colored 
 Janowsky anions. The acetone soil extracts are pro¬ 
 cessed in an identical manner. The concentration 
 of TNT is estimated from the absorbance measured 
 with a field-portable spectrophotometer at 540 nm. 
 The acetone extract of the second membrane or 
 that from soil extraction is acidified and reacted 
 with zinc powder to convert RDX to nitrous acid. 
 The solution is filtered and further reacted with a 
 Griess reagent to produce a highly colored azo 
 dye. RDX concentration is estimated from the ab¬ 
 sorbance measured at 510 nm. Detection limits for 
 TNT and RDX using these colorimetric methods 
 were 1 pg/L and 4 pg/L, in water, respectively, 
 and 1.0 and 1.4 mg/kg for soil. These methods 
 
 have been available commercially from EnSys 
 (now Strategic Diagnostics) for several years and 
 have been widely used. 
 
 Keuchel et al. (1992a,b and 1994) was the first to 
 report on the development of an enzyme immunoas¬ 
 say (EIA) method for TNT in water and soil. Com¬ 
 mercial test kits for TNT using EIA were first intro¬ 
 duced by Strategic Diagnostics Corporation (SDI) 
 in 1993 (Hotter et al. 1993). Subsequently, SDI pro¬ 
 duced a commercial EIA method for RDX as well 
 (Teaney and Hudak 1994). These methods are 
 known commercially as the D TECH™ piA meth¬ 
 ods. Detection limits for TNT and RDX in water 
 using the D TECH were reported as 5 pg/L. Detec¬ 
 tion limits for soil were 0.5 mg/kg for both TNT 
 and RDX. Along with the colorimetric methods, the 
 D TECH methods have been used extensively in the 
 past several years for on-site determination of TNT 
 and RDX in groundwater and soil. 
 
 The U.S. Naval Research Laboratory (NRL) has 
 developed a continuous flow immunosensor (CEI) 
 for on-site determination of TNT and RDX in water 
 (Bart et al. 1997). This method is an extension of the 
 EIA methods and uses either TNT or RDX antibod¬ 
 ies that are immobilized on a membrane saturated 
 with a fluorescent-labeled antigen. An aqueous 
 buffer is pumped across the membrane and samples 
 are injected into the flowing buffer. If the appropri¬ 
 ate analyte is present, binding occurs with the mem¬ 
 brane, thereby releasing the labeled antigen that is 
 detected using a fluorometer. Detection limits ap¬ 
 pear to be about 10 pg/L using this system. 
 
 Another approach for on-site determination of 
 TNT and RDX, developed at NRL, is the fiber op¬ 
 tic biosensor (Shriver-Lakeetal. 1995,1997). These 
 are also EIA-based methods. Eor TNT, fluorescent- 
 labeled trinitrobenzene (TNB) is exposed to an 
 antibody-coated optical fiber, producing a refer¬ 
 ence signal. When the fiber is then placed in a so¬ 
 lution containing TNT, the signal is reduced as 
 TNT competes for sites on the fiber. The reduc¬ 
 tion in signal is used to estimate TNT concentra¬ 
 tion. Estimates of RDX concentrations are obtained 
 similarly. Detection limits for this method have 
 been estimated at 10 pg/L. 
 
 DEFICIENCIES WITH CURRENT METHODS 
 AND OBJECTIVES OF THIS STUDY 
 
 A summary of the performance characteristics 
 of the various on-site methods for TNT and RDX 
 in soil is presented by Crockett et al. (1996, 1998), 
 and the performance characteristics in groundwa- 
 
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ter are summarized by Crockett et al. (in press). 
 Currently available on-site methods for explosives 
 residues in water and soil generally can inexpen¬ 
 sively provide reliable estimates for the concen¬ 
 trations of TNT and RDX. To our knowledge no 
 on-site methods for explosives analytes other than 
 TNT or RDX have been reported except colorimet¬ 
 ric-based methods for 2,4 DNT (Jenkins and Walsh 
 1992) and ammonium picrate (Thorne and Jenkins 
 1995): the RDX colorimetric method has been used 
 to estimate octahydro-1,3,5,7-tetranitro-l,3,5,7- 
 tetrazocine (HMX) concentrations at antitank fir¬ 
 ing ranges where the concentration of HMX was 
 several orders of magnitude higher than that of 
 RDX (Jenkins et al. 1997, 1998). Therefore, no on¬ 
 site methods currently provide comprehensive 
 data for the suite of other manufacturing impuri¬ 
 ties and environmental transformation products 
 that are often present at explosives-contaminated 
 sites (Walsh et al. 1993). In addition, for antitank 
 ranges, neither colorimetric nor immunoassay- 
 based methods are capable of estimating concen¬ 
 trations of RDX when HMX is present at equal or 
 higher concentrations Qenkins et al. 1998). Simi¬ 
 larly, the concentration of TNT cannot be estimated 
 accurately using these methods when DNT, TNB 
 or 2,4,6- trinitrophenylnitramine (tetryl) is present. 
 Moreover, no currently available on-site method 
 provides for the determination of the major 
 biotransformation products of TNT, 4-amino-2,6- 
 dinitrotoluene (4ADNT) and 2-amino-4,6- 
 dinitrotoluene (2ADNT), which are sometimes 
 present at higher concentrations than TNT itself 
 Qenkins et al. 1998). Thus there is a need for an 
 on-site analytical method that can provide simul¬ 
 taneous estimates of the entire suite of analytes 
 that are commonly present at explosives-contami¬ 
 nated sites. 
 
 Gas chromatography has been used extensively 
 for many years in on-site methods to identify and 
 quantify specific target chemicals associated with 
 fuels and solvents (U.S. ERA 1997). The availabil¬ 
 ity of the nitrogen-phosphorus detector (NPD) and 
 the electron capture detector (ECD) on field trans¬ 
 portable instruments provides selective detectors 
 for nitrogen containing organic compounds and 
 electron deficient compounds, respectively. Both 
 detectors are selective and sensitive for the most 
 commonly encountered explosives such as TNT, 
 RDX and tetryl, as well as their manufacturing 
 impurities and environmental transformation 
 products. Recently, Walsh and Ranney (1998) dem¬ 
 onstrated that gas chromatography with a fused 
 silica macrobore column (0.53 mm) provides ad¬ 
 
 equate separation for the suite of analytes com¬ 
 monly encountered at explosives-contaminated 
 sites. Gas chromatography has not received wide 
 use for these analytes because of their thermal in¬ 
 stability, but this analysis is possible by using a 
 deactivated injection port and setting high linear 
 velocities for the carrier gas with short fused silica 
 macrobore columns. 
 
 It was the intent of this work to evaluate the 
 potential for using a field-transportable gas chro¬ 
 matograph (GC) equipped with NP and EC de¬ 
 tectors for on-site determination of individual ex- 
 plosives-related analytes. In particular an 
 emphasis was placed on the ability to determine 
 (1) RDX in the presence of HMX for use at anti¬ 
 tank firing ranges, (2) the biotransformation prod¬ 
 ucts of TNT, which are 2ADNT and 4ADNT, and 
 (3) simultaneous estimates for the suite of analytes 
 commonly encountered at explosive-contami¬ 
 nated sites, since no currently available on-site 
 method can perform these three tasks. 
 
 EXPERIMENTAL METHODS 
 Calibration standards 
 
 Analytical standards of 2,4-dinitrotoluene (2,4- 
 DNT), TNT, RDX, 4ADNT, 2ADNT, and HMX 
 were prepared from standard analytical reference 
 materials (SARMs) obtained from the U.S. Army 
 Environmental Center, Aberdeen Proving Ground, 
 Maryland. A primary stock standard of approxi¬ 
 mately 1000 mg/L for each analyte was prepared 
 by transferring a weighed amount into acetone 
 and diluting to 100 mL in a glass volumetric flask. 
 Combined analyte secondary stock standards 
 ranging from approximately 0.25 to 200 mg/L 
 were prepared by transferring up to 1.00 mL of 
 each primary stock standard with either glass sy¬ 
 ringes or glass pipettes into prepared bottles and 
 volumetric flasks containing acetone. Both the 
 primary and secondary stock standards were 
 stored in a refrigerator at 4°C and removed only 
 for brief periods while in use. Moreover, because 
 of the instability of some of these compounds at 
 low concentrations, working standards for the lev¬ 
 els shown in Table 1 were prepared daily (Walsh 
 and Ranney 1998). Henceforth 2,4-DNT, TNT, 
 RDX, 4ADNT, and 2ADNT will be collectively 
 called target analytes. 
 
 Instrumentation and separations 
 
 A field-transportable SRI model 8610 gas chro¬ 
 matograph, equipped with a heated on-column 
 
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Table 1. Concentration ranges for the working 
 standards of TNT. 2,4-DNT, RDX, 2ADNT, and 
 4ADNT prepared for the evaluation of the nitro¬ 
 gen-phosphorus (NP) and electron capture (EC) 
 detectors. 
 
 Detector Concentration range 
 
 (tng/L) 
 
 NPD 0.25-10.0 
 
 ECD 0.01-1.00 
 
 injector (8690-0025) and two detectors, a NPD 
 (8690-0015) and ECD (8690-0020, Ni®^), was used 
 for this study. Separations were performed on a 
 Crossbond 100% dimethyl polysiloxane column, 
 6 m X 0.53 mm i.d., 1.5 gm (Restek MXT-1). The 
 injection-port temperature was 250°C and the ni¬ 
 trogen carrier gas was set at about 9.5 mL/min 
 (36-40 psi). Injections (1 gL) were made manually 
 with a 10-gL glass syringe (Hamilton) equipped 
 with an extra long needle (7.5 cm). 
 
 When the NPD detector was used, the oven 
 temperature was initially held at 100°C for 2 min; 
 then the temperature was programmed at 20°C per 
 minute to 240°C, and held at 240°C for 0.5 min¬ 
 utes. Air from the onboard purification system was 
 supplied at 6 psi (41 kPa) and zero grade hydro¬ 
 gen was supplied at 7 psi (48 kPa) (flow rate was 
 approximately 2 mL/min). The voltage setting for 
 the NPD was 350 V and this detector was un¬ 
 heated. 
 
 When the ECD was used, the nitrogen makeup 
 gas was supplied at 36-40 psi (248-276 kPa) by 
 splitting the flow from the carrier gas supply line. 
 For ECD analyses the oven temperature was ini¬ 
 tially held at 140°C for 6 min, then temperature 
 programmed at 20°C per minute to 180°C, while 
 the detector was maintained at 250°C. 
 
 RP-HPLC analyses 
 
 Confirmation analyses, by reversed phase high 
 performance (RP-HPLC), were performed on the 
 working standards, stock aqueous solutions (used 
 for the aqueous method detection limit [MDL] 
 study), and field-contaminated soil samples. The 
 acetone-based standards and soil extracts were 
 diluted 1:5 (0.300 mL acetone + 1.200 niL water) 
 with reagent-grade water prior to analysis. Con¬ 
 firmation analyses of the target analytes was con¬ 
 ducted on a C-8 column, 15 cm x 3.9 mm (Nova 
 Pak). The eluent was 85:15% water/isopropanol 
 
 flowing at 1.4 mL/min. Retention times for the five 
 target analytes were RDX—2.9 min., TNT—5.3 
 min, 2,4-DNT—10.3 min, 2ADNT—13.5 min, and 
 4ADNT—15.4 min. Determination of HMX was 
 conducted using a 25-cm x 4.6-mm CN column 
 (Supelco) using 50:50% water/methanol flowing 
 at 1.4 mL/min. The retention time for HMX was 
 11.1 min. 
 
 Sample preparation—soil 
 
 All soils were obtained from near-surface loca¬ 
 tions and air dried. While transferring subsamples 
 of soil to 40-mL amber VOA vials, pebbles larger 
 than 2 mm in diameter or any large pieces of veg¬ 
 etation were excluded. For the MDL study we used 
 an explosive-free soil obtained at Ft. Ord, Califor¬ 
 nia. All other field soils analyzed were removed 
 from bulk samples in which detectable explosive 
 residues had been identified. These field-contami¬ 
 nated samples had been obtained at firing ranges 
 and ammunition production plants. 
 
 Soil samples were prepared for the MDL study 
 by placing 20 g into seven separate amber 40-mL 
 VOA vials. These samples were each spiked by 
 adding 1.00 mL of an acetone solution containing 
 the five target analytes and HMX, using a glass 
 pipette. This volume of spiking solution wetted 
 the top three-quarters of the soil and created a soil 
 concentration of approximately 0.5 mg/kg, for 
 each analyte. After standing uncovered for 1 hour 
 inside an exhaust hood, 20 mL of acetone was 
 transferred to each vessel using a graduated cyl¬ 
 inder. Each bottle was capped and shaken several 
 times over a 5-minute period. The suspended soil 
 was allowed to settle for 30 minutes then a 3-mL 
 aliquot of the supernatant was pulled into a 5-cm^ 
 Luer-Lok syringe (Becton Dickinson & Co.) while 
 leaving a pocket of air between the plunger 
 and solvent extract. The air pocket prevented the 
 acetone extract from coming into contact with 
 the rubber plunger, which could compromise 
 the analysis. The extract was filtered through a 
 Millex-SR 0.5-pm disposable filter unit (Millipore), 
 discarding the first 1-mL portion and collect¬ 
 ing the remainder into an amber 2-mL vial for 
 subsequent instrumental analysis. Likewise, por¬ 
 tions of eight field-contaminated soils were ex¬ 
 tracted with acetone and filtered in preparation 
 for analysis. 
 
 Sample preparation—water 
 
 The MDL study for aqueous samples was per¬ 
 formed using a 1-L volume of reagent-grade wa¬ 
 ter fortified with the target analytes. An aqueous 
 
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 appropriate volumes of individual aqueous stock 
 standards after verifying their concentrations by 
 RP-HPLC analysis (Grant et al. 1993). One-millili¬ 
 ter aliquots of this solution were then diluted up 
 to 1.00 L, to make seven 1-L water samples. The 
 resulting analyte concentrations in these 1-L 
 samples ranged from 2.08 to 2.71 |ig/L. These 
 samples were preconcentrated (200 fold) using 
 membrane solid phase extraction (SPE, [Empore 
 3M, SDB-RPS, 47 mm]) and eluted with 5 mL of 
 acetone, following the procedure outlined by 
 Jenkins et al. (1994). 
 
 For this study an apparatus was used that con¬ 
 sisted of three filtering funnels attached to a 
 common manifold. The manifold allowed three 
 samples to be prepared simultaneously and 
 all the filtrate to be collected in a 2-L vacuum flask. 
 Briefly, after rinsing the extraction funnels 
 (Kontes), collection vessels, and tongs with 
 acetone, 47-mm membrane disks was placed on 
 each support screen and wetted with acetone 
 before centering each funnel and clamping in 
 place. Each membrane was precleaned with two 
 10-mL aliquots of acetone. Prior to the sec¬ 
 ond aliquot being pulled completely through 
 the membrane, a 30-mL aliquot of organic- 
 free water was added to a funnel. Near the 
 completion of filtering this aliquot of water, a sec¬ 
 ond 30 mL aliquot was added. With a small vol¬ 
 ume remaining from the second water rinse, a 1-L 
 fortified water sample was added to the funnel. A 
 small vacuum was applied throughout these 
 cleaning and rinsing cycles, then adjusted during 
 a sample preconcentration step so that the solu¬ 
 tion passed through the membrane at approxi¬ 
 mately 100 mL/min. After the sample had com¬ 
 pletely passed through a membrane the vacuum 
 remained on for an additional 10 minutes to help 
 remove all of the water. 
 
 Once dried, the entire funnel and membrane 
 support was removed from the manifold and wa¬ 
 ter drops were removed from the tip of the drain 
 tube with a clean acetone wetted towel. Before 
 returning a funnel and membrane support to the 
 manifold, a 25- x 200-mm test tube was positioned 
 to collect any further solution passing through a 
 membrane in the filter assembly. Then 5 mL of 
 acetone was poured over the interior surface of a 
 funnel and allowed to cover the membrane for 
 three minutes before applying a small vacuum and 
 slowly pulling through. The volume of acetone 
 recovered during a membrane extraction step was 
 4.2±0.2mL. 
 
 Miscellaneous variables 
 
 For many soils, the use of acetone and vigor¬ 
 ous agitation (hand shaking) results in near-quan¬ 
 titative recovery of explosive compounds within 
 3 minutes Genkins 1990, Walsh and Jenkins 1991). 
 Noted exceptions, however, are heavy clays or 
 high organic soils, which have demonstrated slow 
 extraction kinetics. For this reason, extraction time 
 for a given soil must be verified at each location 
 Genkins and Walsh 1998). Initially, when devel¬ 
 oping field screening methodologies, a 20-g soil 
 sample (undried) was extracted with 100 mL of 
 acetone at a soil to solvent ratio 1:5, so as to en¬ 
 sure that the water content of the final extract was 
 not too high for the colorimetric based methods 
 of determination. Subsequent studies with this 
 field screening method determined that the water 
 content in the acetone extract was not an issue. 
 Therefore, to maximize delectability in soil, a 
 sample weight (g) to acetone volume (mL) ratio 
 of 1:1 could be used. 
 
 Following the same logic, sample preparation 
 for the on-site analyses of explosive residues by 
 GC also used a 1:1 ratio. To assess if soil moisture 
 would affect instrumental responses, solutions 
 were prepared to simulate the extracts that would 
 be obtained when a 1:1 ratio of sample weight to 
 acetone volume was used with soils of 5, 10, 20, 
 30, 40, 50% moisture by dry weight. Furthermore, 
 to assess the range of application of the method 
 and potential use of non-reagent-grade acetone, 
 the following experiments were performed to (1) 
 determine the detectability and retention times of 
 other common explosives, (2) estimate the upper 
 limit of linearity for the target analytes, and (3) 
 examine the feasibility of using hardware-store 
 grade acetone for sample extraction. The addi¬ 
 tional explosives determined were nitrobenzene; 
 ortho-, para-, and meta- nitrotoluene; 1,3-dini¬ 
 trobenzene; 2,6-dinitrotoluene; 1,3,5-trinitro- 
 benzene; and methyl-2,4,6-trinitrophenyl 
 nitramine (tetryl). Acetone-based standards of 
 these analytes were prepared from archived stock 
 standards. 
 
 RESULTS AND DISCUSSION 
 GC separations 
 
 The GC and its configuration was selected 
 based on the works of Walsh and Ranney (1998). 
 Here, we strived to meet the following goals; easy 
 field implementation, minimal consumable sup¬ 
 port, and rapid analysis time (less than 15 min.). 
 
 PROPERTY OF 
 
 WMRC LIBRARY 
 

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 1 
 
In the study by Walsh and Ranney (1998), they 
 injected solvent extracts into the heated injection 
 port of a Hewlett-Packard 5890 GC equipped with 
 an ECD and a 6-m, 0.53-mni-i.d. polydimethyl- 
 siloxane column. They established that responses 
 for analytes with low vapor pressures were en¬ 
 hanced by increasing the linear velocity of the car¬ 
 rier gas and the injection port temperature. Fol¬ 
 lowing their lead, we chose on-column injections 
 into a heated injector and a carrier gas flow rate of 
 9.5 mL/min that produced a linear velocity of 70 
 cm/sec. The two detectors used different chro¬ 
 matographic conditions because, while tempera¬ 
 ture programming was feasible with the NPD, 
 excessive baseline drift limited the ECD to isother¬ 
 mal operation during the elution of the target 
 analytes. 
 
 Typical chromatograms of the target analytes 
 for the NP and EC detectors, are shown in Figures 
 
 Time (min) 
 
 Figure I. Chromatogram of 2,4-DNT, TNT. RDX, 
 4ADNT 2ADNT and HMX by GC-NPD analysis. 
 Chromatogram is of one of the MDL samples (approxi¬ 
 mately 0.5 mg/kg). 
 
 1 and 2, respectively. Analysis of samples with high 
 concentration of HMX confirmed that the latest 
 eluting peak(s) (retention time > 7.5 min) was in¬ 
 dicative of this compound (Fig. 1). However, ei¬ 
 ther the low vapor pressure of HMX caused it to 
 rapidly condense once leaving the column, or it 
 was thermally degraded, and consequently these 
 late eluting peaks could only be used to qualita¬ 
 tively identify its presence. The GC manufacturer 
 suggested that upgrading the NP detector to one 
 with a heater would eliminate this quantitation 
 problem. We have not yet verified this possibility. 
 HMX was not detected by the ECD. Here a long 
 metal transfer line exists between the column 
 and detector, and HMX compound is known to 
 be very reactive with hot metal surfaces (Walsh 
 and Ranney 1998). More work is underway to find 
 a way to include HMX determination in this 
 method. 
 
 Time (min) 
 
 Figure 2. Chromatogram of 2,4-DNT TNT, RDX. 
 4ADNT, and 2ADNT by GC-ECD analysis. Analyte 
 concentrations approximately 0.5 mg/kg. 
 
 6 
 
Table 2. Response factors for the GC-NPD, based on the average 
 of triplicate measurements of both peak area and height. 
 
 A. Peak area response factors (SRI integrator peak area divided by mg/L 
 concentration). 
 
 Response factors (x 10^) 
 Concentration - 
 
 (mg/L) 
 
 2.4-DNT 
 
 TNT 
 
 RDX 
 
 4ADNT 
 
 2ADNT 
 
 10 
 
 6.13 
 
 5.29 
 
 23.3 
 
 8.72 
 
 11.0 
 
 5 
 
 6.21 
 
 5.18 
 
 23.6 
 
 8.74 
 
 11.1 
 
 1 
 
 5.32 
 
 4.61 
 
 21.3 
 
 8.28 
 
 10.5 
 
 0.5 
 
 4.57 
 
 4,46 
 
 19.8 
 
 8.35 
 
 10.1 
 
 0.25 
 
 5.13 
 
 3.85 
 
 17.4 
 
 9.34 
 
 11.1 
 
 B. Peak height response factors (SRI integrator peak height divided by nig/L 
 concentration). 
 
 Response factors (x lOf) 
 
 Concentration 
 
 (mg/L) 
 
 2.4-DNT 
 
 TNT 
 
 RDX 
 
 4ADNT 
 
 2ADNT 
 
 10 
 
 5.67 
 
 5.51 
 
 24.5 
 
 9.45 
 
 10.1 
 
 5 
 
 6.04 
 
 5.35 
 
 25.1 
 
 9.67 
 
 10.3 
 
 1 
 
 5.60 
 
 4.77 
 
 22.7 
 
 9.08 
 
 9.55 
 
 0.5 
 
 5.18 
 
 4.43 
 
 20.0 
 
 8.70 
 
 8.69 
 
 0.25 
 
 4.94 
 
 3.82 
 
 18.0 
 
 9.03 
 
 9.19 
 
 Response factors 
 
 Tables 2 and 3 show the response factors ob¬ 
 tained for the five target analytes on the NP and 
 EC detectors, respectively, over the concentrations 
 shown in Table 1. The response factors for the ECD 
 systematically decreased with increasing concen¬ 
 tration for all of the target analytes (Table 3) while 
 the opposite trend, to smaller extent, was observed 
 for the NPD for three of the five analytes (Table 
 2). To rule out the possibility that the slight increase 
 in response factor seen for the NPD over this con¬ 
 centration range, which is unusual, was not due 
 
 to incorrectly prepared standards, the standards 
 were also analyzed by RP-HPLC. The response 
 factors shown in Table 4 for RP-HPLC analysis 
 failed to show any relationship to concentration, 
 and resulted in much lower relative standard de¬ 
 viations (RSDs). The superior precision of RP- 
 HPLC is due to a combination of variables: better 
 sensitivity, an automated lOO-pL sample injection 
 volume, greater analyte peak symmetry, and bet¬ 
 ter peak resolution. Figure 3 and 4 show the re¬ 
 sponses of these two detection systems to RDX. 
 Because the response of the ECD is more nonlin- 
 
 Table 3. Response factors (SRI integrator peak height divided 
 by mg/L concentration) for GC-EC detector, based on the aver¬ 
 age of duplicate meaurements. 
 
 Response factors (x i(fi) 
 
 Concentration 
 
 (mg/L) 
 
 2.4-DNT 
 
 TNT 
 
 RDX 
 
 4ADNT 
 
 2ADNT 
 
 1 
 
 1.14 
 
 1.13 
 
 0.748 
 
 0.789 
 
 0.832 
 
 0.5 
 
 1.93 
 
 1.83 
 
 1.05 
 
 1.07 
 
 1.14 
 
 0.25 
 
 2.82 
 
 2.48 
 
 1.27 
 
 1.31 
 
 1.39 
 
 0.1 
 
 4.37 
 
 3.84 
 
 1.56 
 
 1.42 
 
 1.46 
 
 0.05 
 
 5,31 
 
 4.78 
 
 1.70 
 
 1.35 
 
 1.41 
 
 0.025 
 
 6.17 
 
 5.08 
 
 1.75 
 
 1.49 
 
 1.39 
 
 0.01 
 
 7.29 
 
 5.64 
 
 1.86 
 
 ND‘ 
 
 ND 
 
 ‘Not measured by integrator. 
 
 7 
 
lu.: jKi 
 
 ■ 
 
Table 4. Response factors (HP integrator peak height divided by 
 mg /L concentration) for RP-HPLC analysis, based on duplicate 
 measurements. 
 
 Response factors (x ICP) 
 Concentration - 
 
 (mg/L) 
 
 2.4-DNT 
 
 TNT 
 
 RDX 
 
 4ADNT 
 
 2ADNT 
 
 10 
 
 11.8 
 
 16.3 
 
 13.6 
 
 4.11 
 
 6.16 
 
 5 
 
 11.5 
 
 15.8 
 
 13.3 
 
 4.30 
 
 6.02 
 
 1 
 
 11.9 
 
 16.0 
 
 13.7 
 
 4.19 
 
 6.34 
 
 0.5 
 
 11.8 
 
 16.4 
 
 13.7 
 
 4.14 
 
 6.35 
 
 0.25 
 
 11.6 
 
 16.3 
 
 13.0 
 
 4.37 
 
 6.02 
 
 Mean 
 
 11.7 
 
 16.1 
 
 13.5 
 
 4.22 
 
 6.18 
 
 Std. Dev. 
 
 0.16 
 
 0.29 
 
 0.30 
 
 0.110 
 
 0 163 
 
 RSD 
 
 1.37% 
 
 1.79% 
 
 2.25% 
 
 2.60% 
 
 2.64% 
 
 ear than that of the NPD for RDX, and likewise 
 for the other target analytes, the NPD was deemed 
 more practical for field applications. Moreover, the 
 small nonlinearity for the NPD causes only a slight 
 underestimation of the low analyte concentrations 
 (less than 1 mg/L or mg/kg). For these reasons 
 only the NPD detector was evaluated during the 
 subsequent studies. 
 
 MDL tests 
 
 Table 5 shows the results of the soil MDL study 
 for the target analytes at concentrations ranging 
 
 between 0.39 and 0.51 mg/kg. The MDLs obtained 
 from this study ranged from 0.087 mg/kg for 
 4ADNT to 0.15 mg/kg for 2,4-DNT, and recover¬ 
 ies ranged from 94.7 to 113%. Table 6 shows the 
 MDL results for aqueous solutions spiked at con¬ 
 centrations ranging from 2.08 to 2.71 pg/L for the 
 five target analytes. The MDLs for these aqueous 
 samples ranged from 0.32 to 0.82 pg/L. The 
 analyte recoveries by this method SPE were lower 
 than expected (61% to 71%) and will require fur¬ 
 ther investigation. Possible explanations for these 
 low recoveries are (1) differences in performance 
 
 Figure 3. Calibration curve obtained for RDX by GC-NPD analysis. 
 
 8 
 
# 
 
Concentration (mg/L) 
 
 Figure 4. Calibration curve obtained for RDX by GC-ECD analysis. 
 
 Table 5. Method detection limit (MDL) study of blank soil spiked 
 with five target analytes and analyzed by GC-NPD. 
 
 Found concentration (mg/kg) 
 
 Rep. 
 
 2.4- DNT 
 
 TNT 
 
 RDX 
 
 4ADNT 
 
 2ADNT 
 
 1 
 
 0.429 
 
 0.451 
 
 0.510 
 
 0.438 
 
 0.461 
 
 2 
 
 0.281 
 
 0.499 
 
 0.486 
 
 0.506 
 
 0.503 
 
 3 
 
 0.359 
 
 0.493 
 
 0.548 
 
 0.477 
 
 0.498 
 
 4 
 
 0.388 
 
 0.532 
 
 0.558 
 
 0 532 
 
 0.532 
 
 5 
 
 0.411 
 
 0.538 
 
 0.478 
 
 0.499 
 
 0.521 
 
 6 
 
 0.363 
 
 0.508 
 
 0.486 
 
 0.486 
 
 0.529 
 
 7 
 
 0.327 
 
 0.456 
 
 0.558 
 
 0.484 
 
 0.444 
 
 Theoretical* 
 
 0.386 
 
 0.497 
 
 0.505 
 
 0.454 
 
 0.442 
 
 Mean 
 
 0.365 
 
 0.497 
 
 0.518 
 
 0.489 
 
 0.498 
 
 Std. dev. 
 
 0.0505 
 
 0.0338 
 
 0.0361 
 
 00289 
 
 0.0340 
 
 MDL 
 
 0.15 
 
 0.10 
 
 0.11 
 
 0.087 
 
 0.10 
 
 Recovery 
 
 94.5% 
 
 100% 
 
 103% 
 
 108% 
 
 113% 
 
 ‘Expected analyte concentration. 
 
 9 
 
J 
 
 'i ,fj 
 
 * 
 
Table 6. MDL study of 1-L reagent grade water samples fortified 
 with five target analytes and analyzed by solid phase extraction 
 and GC-NPD. 
 
 Found concentration (\ig/L) 
 
 Rep. 
 
 2.4-DNT 
 
 TNT 
 
 RDX 
 
 4ADNT 
 
 2ADNT 
 
 1 
 
 1.55 
 
 2.11 
 
 2.08 
 
 2.33 
 
 1.83 
 
 2 
 
 1.66 
 
 1.98 
 
 1.73 
 
 1.91 
 
 1.57 
 
 3 
 
 1.88 
 
 2.16 
 
 1.82 
 
 2.11 
 
 1.74 
 
 4 
 
 1.61 
 
 1.74 
 
 1.72 
 
 1.82 
 
 1.51 
 
 5 
 
 1.67 
 
 1.82 
 
 2.02 
 
 1.68 
 
 1.42 
 
 6 
 
 1.65 
 
 1.91 
 
 1.91 
 
 1.66 
 
 1.43 
 
 7 
 
 1.74 
 
 1.68 
 
 2.08 
 
 2.27 
 
 1.88 
 
 Mean 
 
 1.68 
 
 1.91 
 
 1.91 
 
 1.97 
 
 1.63 
 
 Std. dev. 
 
 0.106 
 
 0.181 
 
 0.156 
 
 0.273 
 
 0.190 
 
 MDL 
 
 0.32 
 
 0.54 
 
 0.47 
 
 0.82 
 
 0.57 
 
 between batches of the extraction disks, or (2) a 
 need to reduce the flow of the aqueous solutions 
 through these membranes. 
 
 Compeu'ison of results for GC-NPD vs. RP-HPLC 
 for field-contaminated soils 
 
 A method comparison was performed by ana¬ 
 lyzing the same acetone extracts of field-contami¬ 
 nated soil samples by both RP-HPLC and GC- 
 NPD. To obtain determinations for all of the 
 analytes of interest, two RP-HPLC analyses were 
 performed. With the exception of HMX, the com¬ 
 pounds were quantified by RP-HPLC analysis 
 using a C8 column. The RP-HPLC determination 
 
 of HMX was performed using a CN column. The 
 results in Table 7 show that there was usually very 
 good agreement between these two methods of 
 analysis, particularly for TNT and RDX. The 
 highly significant correlation (r^ = 0,998) between 
 these instrumental methods for all explosive 
 analytes is also shown in Figure 5. In a few cases, 
 there was poor agreement between the methods 
 and the failure of the GC-NPD analysis to iden¬ 
 tify a compound that was determined by RP- 
 HPLC analysis. This occurred for 2ADNT and 
 4ADNT when HMX was present at some two to 
 four orders of magnitude higher in concentration, 
 and therefore they were not completely resolved 
 
 Table 7. Comparison between GC-NPD and RP-HPLC results for the solvent extracts of 
 field-contaminated soil samples. 
 
 Found concentration (mg/kg) 
 
 Sample 
 
 2.4 DNT 
 GC/HPLC 
 
 TNT 
 
 GC/HPLC 
 
 RDX 
 
 GC/HPLC 
 
 4ADNT 
 
 GC/HPLC 
 
 2ADNT 
 
 GC/HPLC 
 
 HMX 
 
 GC/HPLC 
 
 E 
 
 BDLt/ 0.027 
 
 1.3/0.72 
 
 0.50/0.43 
 
 ND / 0.43 
 
 0.38 / 0.45 
 
 NQ / 3000t 
 
 F 
 
 BDL / 0.032 
 
 2.4 / 2.1 
 
 0.25/0.22 
 
 ND/0.52 
 
 0.27 / 0.53 
 
 NQ / 2800t 
 
 K 
 
 BDL / 0.045 
 
 28t / 25t 
 
 0.48/0.30 
 
 0.52 / 0.39 
 
 ND /0.31 
 
 NQ / 1500t 
 
 M 
 
 5.5/45 
 
 140t / 150t 
 
 13t / 10 
 
 ND/0.34 
 
 ND / 0.43 
 
 ND/NA 
 
 N 
 
 1.3 / 2.0 
 
 250t / 300t 
 
 1201 / 130t 
 
 ND / 1.4 
 
 ND / 3.5 
 
 ND/NA 
 
 O 
 
 2.5 / 2.8 
 
 440t / 540t 
 
 1.7 / 2.1 
 
 2.7/0.93 
 
 2.5 / 1.6 
 
 ND / NA 
 
 T 
 
 0.92 / 1.2 
 
 0.39 / 0.68 
 
 0.28/0.30 
 
 ND /0.16 
 
 ND /0.19 
 
 NQ / 1800t 
 
 U 
 
 1.6 / 1.7 
 
 0.43 / 0.28 
 
 0.10 / 0.085* 
 
 ND/0.11 
 
 ND /O il 
 
 NQ / 1100 
 
 ‘Below GC-NPD detection level, 
 t Above calibration curve. 
 
 ND Not detected. 
 
 NA Not analyzed. 
 
 NQ Not quantitated. 
 
 10 
 
I 
 
 
 i 
 
0.01 0.1 1 10 100 1000 
 
 HPLC (mg/kg) 
 
 Figure 5. Comparison of target analyte concentrations (mg/kg) established by HPLC and 
 GC-NPD analysis of Field samples. 
 
 from this later eluting compound. On the other 
 hand, excellent agreement between the methods 
 was achieved for the determination or RDX at 
 near-detection-limit concentrations even in the 
 presence of high HMX concentrations. 
 
 Miscellaneous variables 
 
 The effect of soil moisture on GC-NPD response 
 is shown in Table 8. TNT and 2,4-DNT do not ap¬ 
 pear to be significantly affected by moisture over 
 
 the range tested, but the other three, less volatile, 
 analytes show suppressed responses at the high 
 soil moisture contents (> 30% by dry weight). Per¬ 
 haps upgrading the detector with a heater would 
 overcome this apparent suppression. 
 
 Table 9 shows that in addition to the five target 
 analytes, several other compounds associated with 
 the manufacturing and degradation of explosives 
 can be detected by GC-NPD analysis. The only 
 analytes not detected by the NPD were the ortho. 
 
 Table 8. Assessment of the effect of soil moisture on GC-NPD 
 response. 
 
 Soil 
 
 moisture* 
 
 Percent average (h 
 
 = 2) response (pkht) relative to standardf 
 
 2.4-DNT 
 
 TNT 
 
 RDX 
 
 4ADNT 
 
 2ADNT 
 
 5% 
 
 111 
 
 102 
 
 104 
 
 107 
 
 106 
 
 10% 
 
 102 
 
 100 
 
 96 
 
 104 
 
 100 
 
 20% 
 
 108 
 
 105 
 
 90 
 
 94 
 
 88 
 
 30% 
 
 102 
 
 98 
 
 81 
 
 89 
 
 84 
 
 40% 
 
 108 
 
 102 
 
 82 
 
 87 
 
 81 
 
 50% 
 
 105 
 
 100 
 
 72 
 
 83 
 
 77 
 
 *Dry weight basis. 
 
 tRcspon.scs were corrected for a proportional, volumetric dilution of acetone by water. 
 These corrected responses were divided by the re.sponse obtained for a standard that did 
 not contain water. 
 
 11 
 
A 
 
 \ 
 
 
 I» V* 
 
 J j 
 
Table 9. Retention times for explosives using 
 different oven temperature programs for NPD 
 and ECD. 
 
 Analyte 
 
 NPD 
 
 retention time 
 (min) 
 
 ECD 
 
 retention time 
 (min) 
 
 NB 
 
 0.96 
 
 NA 
 
 o-NT 
 
 ND 
 
 NA 
 
 m-NT 
 
 ND 
 
 NA 
 
 p-NT 
 
 ND 
 
 NA 
 
 1,3-DNB 
 
 2.4 
 
 NA 
 
 2,6-DNT 
 
 2.6 
 
 NA 
 
 2,4-DNT 
 
 3.0 
 
 0.97 
 
 TNB 
 
 3.9 
 
 NA 
 
 TNT 
 
 4.1 
 
 1.7 
 
 RDX 
 
 4.7 
 
 2.7 
 
 4ADNT 
 
 5.3 
 
 4.2 
 
 2ADNT 
 
 5.6 
 
 5.1 
 
 Tetryl 
 
 6.1 
 
 NA 
 
 HMX 
 
 7.9 
 
 ND 
 
 NA Not analyzed. 
 
 ND Not detected at 10 mg/L concentration. 
 
 para and meta nitrotoluenes, which are among the 
 least frequently encountered analytes found at 
 sites contaminated with explosives. Therefore, this 
 analytical method applies to most of the explo¬ 
 sives cited by SW846 Method 8830, the standard 
 laboratory method for explosives in water and soil. 
 
 An assessment of the upper range of the NPD's 
 linearity was performed using the standards con¬ 
 taining the five target analytes. This experiment 
 showed that the response of the NPD remains lin¬ 
 ear up to 100 to 200 mg/L. Therefore, the range of 
 linear response for these analytes is two to three 
 orders of magnitude. 
 
 Lastly, no impurities were detected by GC-NPD 
 analysis of hardware-store grade acetone. Further¬ 
 more, the analysis of a 1 -mg/L standard of the tar¬ 
 get analytes prepared in both hardware-store and 
 reagent-grade acetone resulted in identical re¬ 
 sponses. This finding would eliminate the need 
 to ship large quantities of acetone to the field. 
 
 SUMMARY 
 
 These preliminary findings indicate that a ro¬ 
 bust and rapid field GC-NPD analytical method 
 can be developed for the simultaneous identifica¬ 
 tion and quantification of explosive residues in 
 both soil and water matrices. When working with 
 action levels for these analytes of 0.5 mg/kg and 
 2.0 pg/L, for soil and water, respectively, a field- 
 transportable GC-NPD is a practical choice of in¬ 
 
 strumentation, even though lower levels of detec¬ 
 tion could probably be achieved by GC-ECD. The 
 GC-NPD, coupled with the sample preparation 
 methodologies described, offers the following fea¬ 
 tures: 
 
 • Simultaneous determination of multiple tar¬ 
 get analytes, 
 
 • Adequate sensitivity, 
 
 • A linear range of response (except at concen¬ 
 trations less than 1 mg/L or 1 mg/kg) that 
 exceeds current field screening technologies, 
 
 • Faster analytical runs than the currently rec¬ 
 ommended laboratory LG or GC methods, 
 
 • Compatibility with hardware-store grade ac¬ 
 etone. 
 
 One of the only limitations of this methodology is 
 that the instrumentation does require a fair 
 amount of support. In addition to a source of elec¬ 
 trical power, the NPD requires independent 
 sources of both hydrogen and nitrogen gas. 
 
 Before recommending this methodology as an 
 analytical approach for characterizing the extent 
 and type of explosive contamination in soil and 
 water, field trials need to be performed. Field veri¬ 
 fication would further establish the robustness of 
 this analytical method and provide insight as to 
 the number of samples that could be processed 
 daily and better define the logistical requirements. 
 Knowledge of all of these parameters is needed 
 before estimates of cost saving can be made. More¬ 
 over, as with other methods based on chromatog¬ 
 raphy, unanticipated interferences may be encoun¬ 
 tered during field studies. 
 
 This on-site method offers the potential to es¬ 
 tablish timely concentrations for individual explo¬ 
 sives well above and below current action levels. 
 Gurrently, this task cannot be unambiguously 
 achieved using current on-site methodologies, 
 since they either lack adequate sensitivity and/or 
 the selectivity required. Therefore, this field ana¬ 
 lytical method could fulfill a very useful function 
 in our effort to economically characterize active 
 and formerly used manufacturing plants, ord¬ 
 nance works and disposal sites, depots, proving 
 grounds, impact ranges, firing points, etc. 
 
 LITERATURE CITED 
 
 Bart, J.C., L.L. Judd, K.E. Hoffman, A.M. Wilkins, 
 and A.W. Kusterbeck (1997) Application of a por¬ 
 table immunosensor to detect explosives TNT and 
 RDX in groundwater samples. Environmental Sci¬ 
 ence Technology 31(5): 1505-1511. 
 
 Crockett, A.B., H.D. Craig, T.F. Jenkins, and W.E. 
 
 12 
 
-I .)f- • 
 
 
 m 
 
 JS 
 
 r^nm 
 
 . - ^tof 
 
 •. 
 
 .., -ii Mif* 
 
 'irvi^y 
 : .tA 
 ■ \mi ■ 
 
 •tnii 
 
 •■'i 
 
 't tJ_ 
 
 : . i9bl 
 
Sisk (1996) Field sampling and selecting on-site 
 analytical methods for explosives in soil. Federal 
 Facilities Forums Issue, ERA Report 540/R-97/501. 
 Crockett, A.B., T.F. Jenkins, H.D. Craig, and W.E. 
 Sisk (1998) Overview of on-site analytical meth¬ 
 ods for explosives in soil. USA Cold Regions Re¬ 
 search and Engineering Laboratory, Special Report 
 98-4. 
 
 Crockett, A.B., H.D. Craig, and T.F. Jenkins (in 
 press) Field sampling and selecting on-site meth¬ 
 ods for explosives in water. ERA Federal Facilities 
 Forum Issue paper. ERA Office of Research and 
 Development, Office of Solid Waste and Emer¬ 
 gency Response. 
 
 Erickson E.D., D.J. Knight, D.J. Burdick, and S.R. 
 Greni (1984) Indicator tubes for the detection of 
 explosives. Naval Weapons Center Report NWC 
 TR 6569, China Lake, California. 
 
 Grant, C.L., T.F. Jenkins, and S.M. Golden (1993) 
 Evaluation of pre-extraction analytical holding 
 times for nitroaromatics and nitramine explosives 
 in water. USA Cold Regions Research and Engi¬ 
 neering Laboratory, Special Report 93-24. 
 
 Heller, C.A., S.R. Greni, and E.E. Erickson (1982) 
 Field detection of 2,4,6-trinitrotoluene in water by 
 ion-exchange resins. Analytical Chemistry, 54: 286- 
 289. 
 
 Haas, R., and G. Stork (1989) Konzept zur 
 Untersuchung von Rustungsaltlasten: 1. Unter- 
 suchung ehemaliger TNT-Fabriken und 
 Fullstellen. Fresenius Journal of Analytical Chemis¬ 
 try. 335:839-846. 
 
 Haas, R., I. Schreiber, E. von Low, and G. Stork 
 (1990) Conception for the investigation of contami¬ 
 nated munition plant wastes: 2. Investigation of 
 former RDX-plants and filling stations. Fresenius 
 Journal of Analytical Chemistry, 338: 41-45. 
 
 Hutter, L., G. Teaney, and J.W. Stave (1993) A 
 novel field screening system for TNT using EIA, 
 p. 472 in Field Screening Methods for Hazardous 
 Wastes and Toxic Chemicals, Vol. 1, Proceedings 
 of the 1993 U.S. EPA/A and WMA International Sym¬ 
 posium. 
 
 Jenkins, T.F. (1990) Development of a simplified 
 field method for the determination of TNT in soil. 
 USA Cold Regions Research and Engineering 
 Laboratory, Special Report 90-38. 
 
 Jenkins, T.F., and P.W. Schumacher (1990) Evalu¬ 
 ation of a field kit for detection of TNT in water 
 and soils. USA Cold Regions Research and Engi¬ 
 neering Laboratory, Special Report 90-20. 
 Jenkins, T.F., and M.E. Walsh (1992) Development 
 of field screening methods for TNT, 2,4-DNT and 
 RDX in soil. Talanta, 39: 419-428. 
 
 Jenkins, T.F., and M.E. Walsh (1998) Reagent 
 
 chemistry for on-site TNT/RDX determination. 
 Current Protocols in Analytical Chemistry, John Wiley 
 and Sons, V. Lopez-Avila, Ed., Unit 2D.2, 1998. 
 Jenkins, T.F., P.G. Thorne, and M.E. Walsh (1994) 
 Field screening method for TNT and RDX in 
 groundwater. USA Cold Regions Research and En¬ 
 gineering Laboratory, Special Report 94-14. 
 Jenkins, T.F., M.E. Walsh, P.G. Thorne, S. 
 Thiboutot, G. Ampleman, T.A. Ranney, and C.L. 
 Grant (1997) Assessment of sampling error asso¬ 
 ciated with the collection and analysis of soil 
 samples at a firing range contaminated with HMX. 
 USA Cold Regions Research and Engineering 
 Laboratory, Special Report 97-22. 
 
 Jenkins, T.F., M.E. Walsh, P.G. Thorne, P.H. 
 Miyares, T.A. Ranney, C.L. Grant, and J. Esparza 
 (1998). Site characterization at the inland firing 
 range impact area at Ft. Ord. USA Cold Regions 
 Research and Engineering Laboratory, Special 
 Report 98-9. 
 
 Jian, C, and W.R. Seitz (1990) Membrane for in 
 situ optical detection of organic nitro compounds 
 based on fluorescence quenching. Analytica 
 Chimica Acta, 237: 265-271. 
 
 Keuchel, C., and R. Niessner (1994) Rapid field 
 screening test for the determination of 2,4,6-trini¬ 
 trotoluene in water and soil with immuno-filtra- 
 tion. Fresenius Journal of Analytical Chemistry^ 350: 
 538-543. 
 
 Keuchel, C., L. Weil, and R. Niessner (1992a) 
 Effect of the variation of the length of the spacer 
 in a competitive enzyme immunoassay (ELISA) 
 for the determination of 2,4,6-trinitrotoluene 
 (TNT). Fresenius Journal of Analytical Chemistry, 343: 
 143. 
 
 Keuchel, C., L. Weil, and R. Niessner (1992b) 
 Enzyme-linked immuno assay for the determina¬ 
 tion of 2,4,6-trinitrotoluene and related nitro- 
 aromatic compounds. Analytical Sciences^ 8: 9-12. 
 Shriver-Lake, L.C., K.A. Breslin, P.T. Charles, 
 D.W. Conrad, J.P. Golden, and F.S. Ligler (1995) 
 Detection of TNT using evanescent wave fiber¬ 
 optic biosensor. Analytical Chemistry, 67: 2431-2435. 
 Shriver-Lake, L.C, B.L. Donner, and F.S. Ligler 
 (1997) On-site detection of TNT with a portable 
 fiber optic biosensor. Environ. Sci. Technol. 31(3): 
 837-841. 
 
 Stevanovic, S., and M. Mitrovic (1990) Colorimet¬ 
 ric method for semiquantitative determination of 
 nitroorganics in water. International Journal of En¬ 
 vironmental Analytical Chemistry, 40: 69-76. 
 Teaney, G.B., and R.T. Hudak (1994) Development 
 of an enzyme immunoassay based field screening 
 method for the detection of RDX in soil and wa¬ 
 ter. Proceedings of the 87th Annual Meeting and Ex- 
 
 13 
 

hibition, Air & Waste Management Association, Cin¬ 
 cinnati, Ohio, 94-RPl43.05. 
 
 Thome, P.G., and T.F. Jenkins (1995) Development 
 of a field method for ammonium picrate / picric 
 acid in soil and water. USA Cold Regions Re¬ 
 search and Engineering Laboratory, Special Report 
 95-20. 
 
 U.S. EPA (1997) Field analytical and site charac¬ 
 terization technologies summary of applications. 
 U.S. Environmental Protection Agency, Office of 
 Solid Waste and Emergency Response Technology 
 Innovation Office, Washington, DC. 
 
 U.S. EPA (1989) Trinitrotoluene health advisory. 
 U.S. Environmental Protection Agency, Office of 
 Drinking Water, Washington, DC. 
 
 Walsh, M.E., and T.F. Jenkins (1991) Development 
 of a field screening method for RDX in soil. USA 
 Cold Regions Research and Engineering Labora¬ 
 tory, Special Report 91-7. 
 
 Walsh, M.E., and T.A. Ranney (1998) Determina¬ 
 
 tion of nitroaromatic, nitramine, and nitrate ester 
 explosives in water using SPE and GC-ECD: 
 Comparison with HPLC. USA Cold Regions Re¬ 
 search and Engineering Laboratory, CRREL Report 
 98-2. 
 
 Walsh, M.E., T.F. Jenkins, PS. Schnitker, J.W. 
 Elwell, and M.H. Stutz (1993) Evaluation of ana¬ 
 lytical requirements associated with sites poten¬ 
 tially contaminated with residues of high explo¬ 
 sives. USA Cold Regions Research and 
 Engineering Laboratory, CRREL Report 93-5. 
 Zhang, Y., and W.R. Seitz (1989) Single fiber ab¬ 
 sorption measurements for remote detection of 
 2,4,6-trinitrotoluene. Analytica Chimica Acta, 221; 
 1-9. 
 
 Zhang, Y., W.R. Seitz, C.L. Grant and D.C. 
 Sunberg (1989) A clean, amine-containing 
 poly(vinyl)chloride membrane for in-situ optical 
 detection of 2,4,6-trinitrotoluene. Analytica Chimica 
 Acta, 217; 217-227. 
 
 14 
 
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REPORT DOCUMENTATION PAGE 
 
 Form Approved 
 
 OMB No. 0704-0188 
 
 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and 
 
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 1. AGENCY USE ONLY (Leave blank) 2, REPORT DATE 3. REPORT TYPE AND DATES COVERED 
 
 August 1999 
 
 4. TITLE AND SUBTITLE 
 
 On-Site Method for Measuring Nitroaromatic and Nitramine Explosives 
 in Soil and Groundwater Using GC-NPD: Feasibility Study 
 
 5. FUNDING NUMBERS 
 
 WU: AF25-CT-006 
 
 6. AUTHORS 
 
 Alan D. Hewitt and Thomas F. Jenkins 
 
 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 
 
 U.S. Army Cold Regions Research and Engineering Laboratory 
 
 72 Lyme Road 
 
 Hanover, New Hampshire 03755-1290 
 
 8. PERFORMING ORGANIZATION 
 
 REPORT NUMBER 
 
 Special Report 99-9 
 
 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 
 
 U.S. Army Environmental Center Office of the Chief of 
 
 Aberdeen Proving Ground Engineers 
 
 Maryland 21010-5401 Washington, DC 20314-1000 
 
 10. SPONSORING/MONITORING 
 
 AGENCY REPORT NUMBER 
 
 SFIM-AEC-ET-CR-99044 
 
 11. SUPPLEMENTARY NOTES 
 
 12a. DISTRIBUTION/AVAILABILITY STATEMENT 
 
 Approved for public release; distribution is unlimited. 
 
 Available from NTIS, Springfield, Virginia 22161 
 
 12b. DISTRIBUTION CODE 
 
 13. ABSTRACT (Maximum 200 words) 
 
 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-|j,m) filter. Groundwater samples (1 L) were passed through SDB-RPS extraction disks that were 
 subsequently extracted with 5 mL of acetone. A l-pL 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 con¬ 
 ducted 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 pg/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 concentra¬ 
 tions of HMX, and when the transformation products of TNT need to be identified. 
 
 14. SUBJECT TERMS Explosives On-site analysis 
 
 Gas chromatography TNT 
 
 Nitrogen-phosphorus detectors 
 
 15. NUMBER OF PAGES 
 
 22 
 
 16. PRICE CODE 
 
 17. SECURITY CLASSIFICATION 
 
 OF REPORT 
 
 UNCLASSIFIED 
 
 18. SECURITY CLASSIFICATION 
 
 OF THIS PAGE 
 
 UNCLASSIFIED 
 
 19. SECURITY CLASSIFICATION 
 
 OF ABSTRACT 
 
 UNCLASSIFIED 
 
 20. LIMITATION OF ABSTRACT 
 
 UL 
 
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