SPECIAL REPORT 96-10

On-Site Analysis for High

Concentrations of Explosives in Soil

Extraction Kinetics and Dilution Procedures

Thomas F. Jenkins, Patricia W. Schumacher, Jane G. Mason

and Philip G. Thorne May 1996
Abstract: Soils containing high concentrations

(>10%) of secondary explosives might detonate from

shock or flame, resulting in human injuries or equipment damage during remediation activities. In lieu of

expensive and time-consuming protocols involving

impact tests, friction tests, and shock gap tests, compositional analysis has been recommended as an expedient method to assess the risk of detonation from

heavily contaminated soils. A number of methods now

available allow determination of TNT and RDX on site.

All of these methods spe-cify solvent extraction with

either acetone or methanol to transfer the analyte from

the soil matrix to a solvent as the first step in the determination. The rate of extraction of TNT and RDX, when

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present at percent levels in soil, has not been determined. Protocols currently in use specify very short extraction times (one to three minutes) and results could

be biased low if extraction kinetics are slow. The objective of this work was to document the rate of extraction of

secondary explosives by acetone and methanol and

make recommendations for possible modification of

current protocols if warranted. Because solvent extracts

from highly contaminated soils will have very high concentrations of secondary explosives, compared with the

range of concentrations that can be determined using

the various on-site methods, large dilutions will be required. Recommendations are made for a field-expedient method making appropriate dilutions.
Special Report 96-10

On-Site Analysis for High

Concentrations of Explosives in Soil

Extraction Kinetics and Dilution Procedures

Thomas F. Jenkins, Patricia W. Schumacher, Jane G. Mason

and Philip G. Thorne May 1996

Prepared for

U.S. ARMY ENVIRONMENTAL CENTER

SFIM-AEC-ET-CR-96158

Approved for public release; distribution is unlimited.

US Army Corps


of Engineers

Cold Regions Research &


Engineering Laboratory
PREFACE

This report was prepared by Dr. Thomas F. Jenkins, Patricia W. Schumacher, Jane G.

Mason, and Philip G. Thorne, Geological Sciences Division, Research and Engineering

Directorate, U.S. Army Cold Regions Research and Engineering Laboratory (CRREL),

Hanover, New Hampshire. Funding was provided by the U.S. Army Environmental Center (USAEC), Aberdeen Proving Ground, Maryland, Martin H. Stutz, Project Monitor.

The authors gratefully acknowledge Marianne E. Walsh, Environmental Engineer,

CRREL; Wayne Sisk, Senior Scientist, USAEC; and Martin H. Stutz, Senior Chemist,

USAEC, for their technical review of this manuscript. The authors also acknowledge

Stephen Schnitker, U.S. Army Corps of Engineers, Missouri River Division Laboratory;

Douglas Peery, Quantera Corporation; and Clarkson Merideth, Versar Corporation, for

supplying soil samples with high concentrations of explosives.

This publication reflects the personal views of the authors and does not suggest or

reflect the policy, practices, programs, or doctrine of the U.S. Army or Government of the

United States. The contents of this report are not to be used for advertising or promotional

purposes. Citation of brand names does not constitute an official endorsement or approval of the use of such commercial products.

ii
iii

CONTENTS

Preface ........................................................................................................................................ ii

Introduction ............................................................................................................................... 1

Background ........................................................................................................................... 1

Objective................................................................................................................................ 2

Overiew of on-site methods ............................................................................................... 2

Experimental ............................................................................................................................. 5

Chemicals and reagents ...................................................................................................... 5

RP-HPLC analyses............................................................................................................... 5

Field-contaminated soils .................................................................................................... 6

Protocol for kinetic extraction studies .............................................................................. 6

Colorimetric field-screening analysis ............................................................................... 6

Results and discussion ............................................................................................................ 7

Kinetic extraction tests ........................................................................................................ 7

Extract dilution study ......................................................................................................... 9

Recommendations .................................................................................................................... 11

Literature cited .......................................................................................................................... 11

Abstract ...................................................................................................................................... 13

TABLES

Table

1. Extraction techniques used with on-site analysis methods ....................................... 2

2. Extraction techniques used with on-site analysis methods for RDX ........................ 5

3. High concentration extraction rate study for archived soils ...................................... 7

4. Extraction rate data for TNT from field-moist soils .................................................... 8

5. Syringe dilution study—precision and accuracy ......................................................... 10

6. Recommended modifications of methods for commercial kits for high-level

determination of explosives ....................................................................................... 10

On-Site Analysis for High Concentrations of Explosives in Soil

Extraction Kinetics and Dilution Procedures

THOMAS F. JENKINS, PATRICIA W. SCHUMACHER, JANE G. MASON

 AND PHILIP G. THORNE

INTRODUCTION

Background

For the greater part of this century, the U.S. Army has manufactured explosives and munitions

and demilitarized munitions at Army facilities throughout the United States. Disposal of wastes

generated in these manufacturing operations has contaminated some Army lands with residues of

explosives. For example, the Army utilized unlined evaporation/percolation lagoons for disposal

of wastewaters from manufacturing, demilitarization, and load, assemble, and pack operations.

After many years of operation, explosives tended to accumulate at the soil surface of these lagoons,

sometimes at concentrations in the percent range. Whether sampling for site characterization or

conducting remediation activities, these areas of very high explosives concentration are a major

concern relative to the potential for detonation.

Several years ago, the U.S. Army Toxic and Hazardous Materials Agency (now the U.S. Army

Environmental Center) sponsored a study to document the reactivity (propagation of a detonation)

hazard associated with high concentrations of secondary explosives in soil (Kristoff et al. 1987). A

series of tests was conducted to define the reactivity of explosives-contaminated soils to flame and

shock as a function of explosives composition. The results of this work indicated that soils containing concentrations of TNT (2,4,6-trinitrotoluene) and RDX (1,3,5-hexahydro-1,3,5-trinitrotriazine)

below 15% were not reactive to shock stimuli, and soil concentrations below 12% could not be

detonated by flame initiation. To provide a margin of safety, the U.S. Army Environmental Center

has established a level of 10% as the concentration of secondary explosives in soil at which a detonation would not propagate. Any concentration above 10% would be considered an explosive operation and would require the approval of the Department of Defense Explosive Safety Board. Because

of the cost and specialized nature of these reactivity tests, it was recommended that compositional

analysis be used to identify potentially reactive soils (those above the 10% criteria). Because of the

explosive hazard involved, a simple, rapid method for on-site analysis is useful in order to allow

decisions to be made expeditiously or to screen samples prior to shipment to off-site laboratories.

Three approaches have been developed for rapid on-site analysis: colorimetric methods, immunoassays, and ion mobility spectrometry (Table 1). All of these methods rely on an initial step involving rapid extraction of the soil with an organic solvent. Acetone or methanol have been the solvents

of choice because of the large solubility of these compounds in these polar solvents, and their compatibility with on-site methods of determination. However, the applicability of these solvents to

extraction of soil samples with very high concentrations of nitroaromatics and nitramines has not

been evaluated.
Table 1. Extraction techniques used with on-site analysis methods.

Concentration

TYPE Extraction range

Method Solvent time Soil/solvent (μg/g)

Colorimetric

EnSys Acetone 3 min 10 g/50 mL 1 to 30

Erickson Methanol 1 min 6 g/20 mL 0.3 to 30

Jenkins Acetone 3 min 20 g/100 mL 1 to 22

Medary Methanol 1 min 6 g/35 mL 4 to 90

Immunoassay

EM Science (D TECH) Acetone 3 min* 4.5g†/9 mL 0.5 to 5.0

Idetek (Quantix) Acetone 3 min 4.2g/21 mL 0.25 to 100

Millipore (EnviroGard) Acetone 2 min 2 g/8 mL 1 to 100

Ohmicron Methanol 1 min 10 g/20 mL 0.07 to 5

Ion mobility spectrometry

Barringer Acetone-hexane 3 min 1 g/1 mL Low ppb

* Shaking several times over three-minute period.

† Actual mass of soil will vary depending on soil density.

Objective

The main objective of our study was to determine the rate of extraction of secondary explosives

from highly contaminated soil to ensure that on-site methods currently available can provide sufficiently accurate results for soils contaminated with percent levels of TNT and RDX. Field-contaminated soils from a number of installations were utilized in these assessments. Because the most

commonly used on-site methods for explosives in soil specify either acetone or methanol as the

extraction solvent, much of the work evaluated extraction using these solvents. Based on these

results, recommendations will be made on modifications to established protocols for available onsite methods for determining whether concentrations exceed the 10% safety criterion. Since large

dilution factors (about 1 to 10,000) are required to reduce extract concentrations to the range suitable for these tests, a dilution procedure that is simple and sufficiently accurate and precise will be

provided.

Overview of on-site methods

Colorimetric TNT methods

The first on-site screening method for TNT in environmental matrices was reported by Heller et

al. (1982). This method was initially developed for water analysis and utilized a detection tube

containing two sections. The first section contained a basic oxide that converted TNT to its Meisenheimer anion (eq 1), which was retained by the anion exchanger in the second section of the tube.

Since the Meisenheimer anion for TNT is highly colored, detection is achieved visually and quantitation is made by measuring the length of the colored region of the tube. The use of these tubes for

detection of TNT in soil was reported by Erickson et al. (1984). Their method specifies extraction of

about 6 g of soil with 20 mL of methanol by manually shaking for one minute followed by filtering

2

Equation 1. MEISENHEIMER ANION

 CH 3

+ OH 

2

 NO 2 O2N

3

2

2 O2N

 OH 

H

 NO 

 NO 

 NO 

 CH 

 TNT 
3

through filter paper. The detection tubes used for this method have been available as a special order

item from Supelco (Bellefonte, Pennsylvania).

In 1990 we reported a colorimetric-based method for TNT in soil (Jenkins 1990). In this method,

20-g samples of field-moist soils are extracted with 100 mL of acetone by shaking manually for three

minutes (Table 1), allowing the soil to settle, and filtering the extract through a 0.5-μm syringe filter.

The resulting extract is then reacted with potassium hydroxide and sodium sulfite to form the highly colored (reddish for TNT) Janowsky anion (eq 2),

Equation 2. JANOWSKY ANION

 CH 3

+

2

 NO 2 O2N

3

2

2 O2N

H

2 C R

O CH 

 NO 

 CH 

 NO 

 NO 

2 C R

O

 CH 

 TNT 

and the TNT concentration is estimated from absorbance measurements at 540 nm. A similar method was developed by Medary (1992) at about the same time. Medary’s method uses a 6-g portion of

field-moist soil and 35 mL of methanol, and requires manual shaking for one minute for extraction

(Table 1). The extracted TNT is reacted with a 10% aqueous solution of sodium hydroxide. TNT is

estimated from the absorbance of the colored Meisenheimer anion produced at 516 nm (eq 1). The

method developed by Medary is sometimes referred to as the Corps of Engineers method.

EnSys (Research Triangle Park, North Carolina) commercialized a colorimetric method for TNT

in soil using an approach similar to that developed by Jenkins (1990). The EnSys method (RisC)

specifies that a 10-g portion of dried soil is extracted with 50 mL of acetone. Extraction is conducted

by manually shaking for three minutes, allowing the soil to settle for five minutes, and filtering the

extract through a 0.5-μm Millex SR syringe filter. This method has been issued as SW846 Method

8515, “Colorimetric Screening Method for Trinitrotoluene (TNT) in Soil,” by the USEPA Office of

Solid Waste.

Enzyme immunoassay (EIA) methods for TNT

Keuchel et al. (1992a, b) and Keuchel and Neissner (1994) were the first to report the development of a competitive enzyme immunoassay (EIA) method to detect TNT in water. The immunoassay used polystyrene microtiter plates coated with antibodies. Enzyme-analyte conjugate was

synthesized from 2,4,6-trinitrobenzene sulfonic acid conjugated to the enzyme horseradish peroxidase.

A commercially available enzyme immunoassay for TNT in water and soil was issued in 1993 by

EM Science (Gibbstown, New Jersey) as D TECH Environmental Detection Systems (Hutter et al.

1993, Teaney et al. 1995). This assay makes use of a competitive reaction between enzyme-labeled

TNT and free TNT for binding sites on antibody-coated latex particles. The particles are trapped on

a membrane, washed clean of unbound enzyme conjugate, and treated with a substrate to induce a

color change inversely proportional to the amount of free TNT in the sample. Homogenized, fieldmoist soils are collected in a calibrated 3-mL syringe, transferred to a plastic bottle, and extracted

with 6.5 mL of acetone. Extraction is conducted by manually shaking several times over a threeminute period, allowing the soil to settle for one minute, and pipetting off a 1.0-mL aliquot of the

supernatant. Results are quantitated with a hand-held, dual-beam reflectometer that measures the

difference between the sample and the reference control.

Three other commercial enzyme immunoassay methods are currently available for TNT. The

EnviroGard TNT kit (Millipore ImmunoSystems, Scarborough, Maine) is intended to be a laboratory assay for semi-quantitative analysis of TNT in both soil and water. Field-moist soil samples are
4

extracted with acetone, and the diluted acetone extracts are incubated with TNT-enzyme conjugate

in microtiter wells coated with antibody. Upon completion of the incubation, the unbound analytes

are rinsed away, substrate is added, and the developed color is measured with an ELISA plate-reading spectrophotometer at 450 nm. The extraction step specifies a 2-g portion of soil and 8 mL of

acetone and two minutes of mechanical shaking.

Enzyme immunoassay methods for TNT are also available from Ohmicron (RaPID Assay, Newtown, Pennsylvania) and Idetek (Quantix, Sunnyvale, California). The Ohmicron method is a magnetic particle-based method run in test tubes; it specifies extraction of a 10-g portion of undried soil

with 20 mL of methanol in a special extraction container by manually shaking for one minute followed by a five-minute settling time prior to filtration with a filter cap. The Idetek method, which is

functionally very similar to the EnviroGard method described above (Table 1), specifies that a volumetric portion of soil (corresponding to about 4.2 g of soil) is added to a soil extraction bottle with 21

mL of acetone; the sample is shaken manually for three minutes and is used without filtration.

Field methods for RDX

Considerably less attention has been devoted to field screening for RDX than for TNT. RDX does

not respond to either the TNT colorimetric or EIA-based screening methods and is one of the compounds most often found at munitions-contaminated sites in the U.S. (Walsh et al. 1993). Forensic

chemists have used colorimetric-based tests for RDX for many years to identify RDX in post-blast

residues (Yinon and Zitrin 1981), and in 1991 we reported the development of a colorimetric field

screening method for RDX in soil (Walsh and Jenkins 1991) utilizing a similar approach. This method

was based on two classical chemical reactions that have been known since the nineteenth century.

Using the Franchimont reaction (eq 3),

RDX, in the acetone extract described above, is reacted with zinc under acidic conditions to produce

nitrous acid, and the nitrous acid is converted to an azo dye using the Griess reaction (eq 4). The

reddish-colored product can be detected visually and quantified using absorbance measurements at

507 or 510 nm.

Equation 4. GRIESS REACTION (1864)

This method utilizes the same acetone extract described above for the TNT test (Jenkins 1990) and

thus allows a single soil extract to be screened for both TNT and RDX. A similar colorimetric approach has been commercialized by EnSys.

A commercial EIA-based test for RDX has also been developed by Strategic Diagnostics (Newark,

Delaware) and is available from EM Science as the D TECH RDX Test. This method uses the same

Equation 3. FRANCHIMONT REACTION (1897)

N

 NO 2

2 2

RDX

+ Zn 3 HNO2 N

O N

N

Acetic Acid

 NO 

N2

+

R

NR'2

N N

R

Azo Dye

NR' + 2

Griess Reaction (1864)
Table 2. Extraction techniques used with on-site analysis methods

for RDX.

Extraction

Method Type Solvent time Soil/solvent

Barringer IMS* Acetone 3 min

EM Science (D TECH) Immunoassay Acetone 3 min† 3 mL**/15 mL

EnSys Colorimetric Acetone 3 min 10 g/50 mL

Walsh & Jenkins Colorimetric Acetone 3 min 20 g/100 mL

* Ion Mobility Spectrometry.

† Shaking several times over three-minute period.

** Actual mass of soil will vary depending on soil density.

5

* J. Avolio, Applications Chemist, Barringer Instruments, Inc., New Providence, New Jersey.

extract as their TNT test and hence a single extract can be tested for both TNT and RDX. Soil extraction methods for these RDX tests are summarized in Table 2.

Ion mobility spectrometry

Ion mobility spectrometry (IMS) has been used extensively for the detection of explosives associated with potential terrorist activities. Recently there has been interest in the use of this technology for

rapid on-site analysis of explosives in soil. Rodacy and Leslie (1993) presented an initial investigation

of the use of IMS for this purpose.

Avolio et al. (1995), from Barringer Instruments Inc. (New Providence, New Jersey), have also

described the use of IMS for rapid on-site analysis of TNT, DNT, and RDX. The best results were

obtained when acetone extracts were deposited on a PTFE filter and thermally desorbed into the IMS.

A 1-g soil sample is extracted with a 1-mL portion of acetone by shaking for three minutes. A 1-mL

portion of hexane is added and an aliquot of the acetone-hexane extract is used for thermal desorption (Avolio, pers. comm.*). An advantage of the IMS approach is that it provides an estimate of TNT

and RDX in a single analysis.

EXPERIMENTAL

Chemicals and reagents

All standards for TNT, DNT, and RDX were prepared from Standard Analytical Reference Materials (SARMS) obtained from the U.S. Army Environmental Center, Aberdeen Proving Ground, Maryland. Stock standards of TNT, DNT, and RDX in acetone were prepared using HPLC-grade acetone.

Working standards in the field were prepared using hardware-store-grade acetone.

All acetone used for soil extraction and glassware cleaning was hardware grade obtained locally.

Methanol used for soil extraction was HPLC grade. Acetonitrile and methanol used in the laboratory

for preparation of HPLC eluents and extract dilution were Baker, EM, or Mallinckrodt HPLC grade.

Water used for preparation of HPLC eluents, and for addition to extracts to ensure that an adequate

water content was present for the color-forming reaction, was reagent-grade water prepared from a

Millipore Milli-Q Type 1 reagent-grade water system.

RP-HPLC analyses

Reversed phase HPLC analysis was conducted as described in EPA SW846 Method 8330. Primary

analysis was conducted on a Supelco LC-18 column eluted with 1:1 methanol/water at 1.5 mL/min.

Absorbance was recorded at 254 nm on a Spectra Physics Model 8490 variable-wavelength detector,

and peaks were recorded on a Hewlett Packard 3396 Digital Integrator in the peak height mode.

Selected samples were subjected to second-column confirmation on a Supelco LC-CN column using

either 35:65 methanol/water or 23:12:65 acetonitrile/methanol/water, depending on the specific analytes detected in the primary analysis (Jenkins and Golden 1993).
6

Because the extracts had very high concentrations of TNT, DNT, or RDX, they were diluted by

introduction of microliter volumes of the acetone or methanol extracts into a measured volume of 1:1

methanol/water. Dilutions ranged from 1:100 to 1:10,000.

Field-contaminated soils

Several high-concentration field-contaminated soils from a number of installations were utilized

for this study. Initial experiments used archived soil samples that had been air dried, ground, and

thoroughly homogenized. These samples were rewetted with water prior to extraction to simulate

field conditions. To do so, about 4 mL of water was added to each 20-g sample of soil, mixed, and

allowed to stand for 30 minutes before adding the extracting solvent. Archived samples from Weldon Springs Army Ammunition Plant (AAP), Nebraska Ordnance Works, Iowa AAP, Volunteer

AAP, and Hawthorne AAP were used in this portion of the study.

Kinetic extraction tests were also conducted with undried soils from Volunteer AAP. These fieldmoist samples were processed by removing large stones and thoroughly mixing prior to removing a

20-g subsample for extraction.

Protocol for kinetic extraction studies

A 20-g portion of field-moist soil was placed in a 125-mL (4 oz) polypropylene bottle containing

five stainless steel balls. A 100-mL aliquot of either acetone or methanol was added and the bottle

was capped and vigorously shaken for three minutes on a mechanical shaker. After the shaking

period, the soil was allowed to settle for about five minutes; a 2-mL aliquot was then removed and

passed through a 0.5-μm Millex SR filter unit into a labeled autosampler vial. The Nalgene bottle was

then recapped and shaken for additional time increments. After each shaking time increment, soils

were allowed to settle and samples of the supernatant were collected and processed as above. When

all the kinetic samples were collected, portions of the filtered extracts were diluted into 1:1 methanol/water and analyzed by RP-HPLC as described above.

Colorimetric field-screening analysis

Colorimetric analysis of the acetone extracts was conducted using the EnSys reagent. A reference

standard of TNT in acetone (containing 3% water) was prepared with a concentration of 3 mg/L.

This standard was analyzed with each set of samples and was used to establish the response factor

(RF-TNT) for estimating TNT concentration for the sample extracts. The filtered sample extracts

were diluted with acetone (containing 3% water) using a microliter syringe. A 25-mL portion of the

diluted extract was placed in a spectrophotometer cuvette and the initial absorbance (ABS-initial)

obtained at 540 nm on a Hach DR/2000 battery-operated spectrophotometer. The cuvette was then

removed from the spectrophotometer and one drop of the EnSys developer solution (referred to as

the EnSys reagent) was added. The contents of the vial were mixed thoroughly and allowed to stand

for one minute. The absorbance at 540 nm was then obtained (ABS-final) as described above. Dilutions were made to obtain final absorbances below 1.0 A.U. after addition of the EnSys reagent. The

TNT concentration in the sample was calculated as follows:

TNT (μg/g) = {[ (ABS-final) – 2 × (ABS-initial)] / RF-TNT} × 5.

A response factor of 0.177 A.U./mg/L was obtained from calibration. The factor of 5 is used to convert concentration in mg/L to concentration on a μg/g basis. Results were then corrected for the

specific dilution used.

Results on moist samples from Volunteer AAP were obtained as described above except that the

soil extraction step was modified. A short kinetic study conducted at Volunteer revealed that extractions needed to be extended to get stable concentrations. Samples were shaken for three minutes,

allowed to stand for 30 minutes, and shaken for an additional three minutes. After allowing the soil

to settle, an aliquot was filtered, diluted using microliter syringes as described above, and analyzed

using the EnSys method.
7

RESULTS AND DISCUSSION

Kinetic extraction tests

Initial extraction rate studies were conducted with archived soil samples from a variety of installations. These samples had been air dried and stored for several years at room temperature. Soils

were moistened by adding water prior to adding extraction solvent to simulate the field-moist conditions that would be present when samples are subjected to on-site analysis. Results of RP-HPLC

analyses of these acetone and methanol extracts are presented in Tables 3a–3c.

Table 3. High concentration extraction rate study for archived soils.

a. TNT.

TNT concentration (μg/g)*

Weldon Nebraska

Hawthorne Hawthorne Springs Ordnance Iowa Iowa Volunteer

AAP AAP AAP Works AAP AAP AAP

 Extr. (#12) (#14) (#29) (#39) (SS-8-005) (SS-8-001) (SE-5369)

 time A† M† AM A M A M A M AM A M

3 min 921 1020 9170 10400 4360 4380 25500 28100 2240 15900 9880 6450 110000 94900

10 min 1000 1080 9470 10700 4490 4430 27200 28700 2500 15900 9780 6650 117000 95400

30 min 1040 1100 9830 10800 4640 4440 26700 27400 2590 15600 9970 6750 127000 97000

60 min 1060 1140 9870 10700 4650 4490 26700 28600 2780 16100 10100 6850 130000 101000

18 hr 1130 1360 9970 11000 4610 4600 26800 28600 2770 15900 10300 6850 130000 101000

Ratio:

3 min/ 0.82 0.75 0.92 0.95 0.95 0.95 0.95 0.98 0.81 1.00 0.96 0.94 0.85 0.94

18 hr

* Estimated by RP-HPLC.

†A = Acetone extraction, M = Methanol extraction.

b. RDX.

RDX concentration (μg/g)*

Hawthorne Hawthorne Iowa Iowa

AAP AAP AAP AAP

 Extr. (#12) (#14) (SS-8-005) (SS-8-001)

 time Acetone Methanol Acetone Methanol Acetone Methanol Acetone Methanol

3 min 318 307 7670 6240 927 1990 3200 846

10 min 336 300 7820 6550 1160 2620 3150 957

30 min 340 306 8100 6660 1210 2880 3210 954

60 min 334 310 8110 6680 1430 2960 3240 972

18 hr 343 340 8170 7070 1400 2970 3290 1000

Ratio:

3 min/18 hr 0.93 0.90 0.94 0.88 0.66 0.67 0.97 0.85

* Estimated by RP-HPLC.

c. 2,4-DNT

2,4-DNT concentration (μg/g)*

Volunteer AAP Volunteer AAP

Extraction (SE-5538) (SE-5369)

time Acetone Methanol Acetone Methanol

3 min 130000 101000 31800 24300

10 min 94500 85600 37400 24700

30 min 144000 90200 43600 25900

60 min 158000 94800 45400 27000

18 hr 150000 92800 45500 27900

Ratio:

3 min/18 hr 0.87 1.09 0.70 0.87

* Estimated by RP-HPLC.
Table 3a presents kinetic results for TNT from seven archived soil samples from five installations.

Extracted concentrations generally increase with extraction time for both acetone and methanol,

indicating that extraction is not complete in three minutes; however, the additional increase is generally small. The concentration obtained for the three-minute extraction time was always at least

75% of the value obtained after shaking for 18 hours for both solvents. Thus for these high concentration samples, the extraction rate is relatively fast for both acetone and methanol compared to that

observed for air-dried, lower concentration field-contaminated soils using acetonitrile and ultrasonic extraction (Jenkins et al. 1989).

Similar kinetic results were obtained for the extraction of RDX from these archived soils (Table

3b). For one soil (Iowa SS-8-005), only 66–67% of the RDX extractable at 18 hours was extracted in

the first three minutes. For the other three soils, at least 85% of the concentration found after 18

hours of extraction was attained after only three minutes of shaking for both methanol and acetone.

Comparison of the extraction efficiencies of acetone versus methanol cannot be made because extractions were performed on separate subsamples and the analytes were heterogeneously distributed between subsamples. This heterogeneity is evident in both samples from Iowa AAP (Table 3a).

2,4-DNT is a propellant rather than a secondary explosive and its sensitivity to shock and flame

in soil was not evaluated by Kristoff et al. (1987). Nevertheless, an on-site method for 2,4-DNT in

soil is available (Jenkins and Walsh 1991) and two samples of soil contaminated with high levels of

2,4-DNT were available. Therefore, we decided to determine the extraction rate for this compound

when present at high concentrations in soil. Kinetic extraction results for 2,4-DNT in archived soils

are presented in Table 3c. Here again, the rate of extraction was rapid with extracted concentrations

after only three minutes of shaking, at least 70% of that attained after 18 hours with either acetone or

methanol.

Additional kinetic extraction studies were conducted with four field-moist soil samples from

Volunteer AAP that contained high levels of TNT (Table 4). The rate of extraction for these samples

was quite rapid. At least 88% of the TNT concentration obtained after 18 hours of shaking was

attained after only a three-minute extraction time using either acetone or methanol. Concentrations

extracted after the three-minute acetone or methanol extraction were at least 70% of the values

obtained using the standard laboratory extraction procedure of 18 hours of ultrasonic extraction

8

Table 4. Extraction rate data for TNT from field-moist soils.

TNT concentration (μg/g)

Volunteer AAP Volunteer AAP Volunteer AAP Volunteer AAP

(7R-1) (7R-4) (7R-6) (8-3)

Time Acetone Methanol Acetone Methanol Acetone Methanol Acetone Methanol

3 min 85300 84000 88800 83500 101000 102000 24600 26700

10 min 88400 85000 91300 82500 97500 102000 28700 26700

30 min 90900 85000 94300 83000 118000 101000 27100 26400

60 min 87700 85500 94800 82500 101000 102000 26900 26300

18 hrs 85800 85500 96300 85500 102000 104000 28000 27000

Ratio:

 3 min/18 hr 0.99 0.98 0.92 0.98 0.99 0.98 0.88 0.99

Method 109000 119000 100000 21300

 8330* (ACN) (ACN) (ACN) (ACN)

Ratio:

 3 min/8330 0.78 0.77 0.75 0.70 1.01 1.02 1.15 1.25

EnSys† 82000 76200 78200 23200

Ratio:

 EnSys/8330 0.75 0.64 0.78 1.09

* Method 8330 results from acetonitrile ultrasonic extraction for 18 hr followed by RP-HPLC

determination.

† EnSys results determined in the field prior to laboratory sample homogenization using acetone

extraction and colorimetric determination.
using acetonitrile (Table 4). Also, concentrations obtained in the field using acetone extraction and

the EnSys colorimetric method ranged from 64% to 109% of the value obtained after subsequent

laboratory homogenization and determination by SW846 Method 8330. These field determinations

utilized a three-minute shaking period with acetone followed by a 24-minute rest period and another three-minute period of shaking.

These kinetic extraction experiments indicate that a short three-minute extraction of TNT and

RDX from highly contaminated soils is incomplete, whether using acetone or methanol. For the

soils we tested, however, extract concentrations after a three-minute extraction were at least 70% of

those attained after 18 hours of shaking. The rate of extraction into acetone and methanol appear to

be comparable.

It is possible that the rate of extraction of TNT and RDX from other highly contaminated soils

could be slower, resulting in a smaller percentage extracted after the short three-minute extraction.

However, contaminants present at these high (%) concentrations far exceed the amount required to

form a mono-layer on soil surfaces, and so most of the contaminant must be present in crystalline

form. Differences in the rate of extraction of crystalline material from soil to soil should be small

since it is controlled by the rate of dissolution of the crystalline material. It appears that a value of

70% can be used to represent the percentage of TNT or RDX that would be extracted from a highconcentration sample in a short three-minute extraction. Therefore, field analyses that result in concentrations above 7% should be considered potentially explosive.

Extract dilution study

Because all of the current on-site methods for TNT and RDX in soil were developed to detect low

levels (low μg/g) in soil, all these methods, when used for high concentration samples, require that

the extracts be diluted substantially before they can be analyzed by colorimetric, immunoassy, or

IMS methods. For the EnSys colorimetric method, for example (Table 1), the concentration of TNT

in acetone extract from a soil containing 10% TNT is 20,000 mg/L. The linear range for the EnSys

method extends from about 0.2 to 10 mg/L, so a dilution of at least 1:2000 is necessary to allow

accurate determination. Similar dilutions are necessary for the other colorimetric and immunoassay methods and are probably required for the IMS method as well, although this is yet to be determined. In the laboratory, dilutions of this magnitude are generally conducted using volumetric

pipets and serial dilution techniques. In the field, however, this approach is cumbersome and produces a significant amount of solvent waste that requires costly disposal. A simple one-step approach is possible using glass syringes that can deliver microliter quantities of extract. The following experiments were conducted to assess whether the precision and accuracy of this approach is

acceptable for this application.

Three experiments were conducted to assess the precision of the syringe dilution. Acetone soil

extracts from three field-contaminated soils from Volunteer AAP were used. Five replicate dilutions

for each extract were made using 10-μL glass microliter syringes (Hamilton #701, Reno, Nevada).

For one sample, a 1:2000 dilution was made by diluting 10.0 μL of the filtered acetone extract into

20.0 mL of 1:1 methanol/water. In another, a 1:10,000 dilution was made by diluting 2.0 μL of the

acetone extract to 20.0 mL of 1:1 methanol/water. For the third, a 4.0-μL aliquot was diluted with

20.0 mL of 1:1 methanol/water (1:5000). The methanol/water diluent was selected because analyte

concentrations for the diluted samples were determined using RP-HPLC.

The analyte concentrations obtained in the 1:5000 syringe dilution study were compared with a

1:5000 dilution obtained using a two-step serial dilution with glass volumetric pipets and volumetric flasks to assess the accuracy of the syringe dilution approach. This was a two-step dilution: 5.00

mL of extract diluted to 100.0 mL with acetone followed by a 1.00 mL dilution to 250.0 mL with

methanol/water. The diluted extracts were determined using RP-HPLC.

Results of the syringe dilution tests are presented in Table 5. For Volunteer sample #1, a 2.0-μL

volume of filtered extract was diluted to 20 mL and the precision, as measured by the relative stan9
10

Table 5. Syringe dilution study—precision and accuracy.

Volunteer AAP Volunteer AAP Volunteer AAP

(#1*) (#2†) (#3**)

TNT concentration TNT concentration TNT concentration DNT concentration

Replicate (mg/L) (mg/L) (mg/L) (mg/L)

1 19700 5700 13000 6230

2 20200 5760 13100 6270

3 19800 5700 12400 5980

4 20200 5700 13300 6430

5 20000 5800 13200 6390

Mean 20000 5730 13000 6260

Std Dev 241 46 354 177

RSD 2.41% 0.80% 2.72% 2.83%

106% 106%

Concentration relative to that obtained

by serial dilution.

* 1:10000 = 2 μL to 20 mL.

† 1: 2000 = 10 μL to 20 mL.

** 1: 5000 = 4 μL to 20 mL.

dard deviation (RSD), was 2.41%. For Volunteer sample #2, a 10.0-μL sample of filtered extract was

diluted to 20 mL and the calculated RSD was 0.80%. For Volunteer #3, a 4-μL sample was diluted to

20 mL and the RSD was 2.72% for TNT and 2.83% for 2,4-DNT. In all cases, the random error introduced using syringe dilution is minor compared with that due to short-range heterogeneity in soil

(Jenkins et al. 1996). Likewise, the concentration estimates for TNT and 2,4-DNT were 106% of

estimates using serial dilution, indicating that no significant bias would be introduced using this

approach.

Based on these results, we believe that extracts to be analyzed to determine whether soils are

heavily contaminated with secondary explosives can be successfully diluted using a 10-μL syringe

Table 6. Recommended modifications of methods for commercial kits for high-level determination

of explosives.

Concentration Additional

of TNT in extraction Solvent extract dilution

TYPE solvent for soil sample diluent required for Resulting concentration

Method containing 10% TNT recommended linear range of test and estimated detector response

Colorimetric

EnSys 20 g/L Acetone 1:10000 2 mg/L A ≈ 0.35*

Erickson 30 g/L Methanol 1:10000 3 mg/L Stain length ≈ 28 mm

Jenkins 20 g/L Acetone 1:10000 2 mg/L A ≈ 0.377

Medary 17.1 g/L Methanol 1:2500 6.8 mg/L A ≈ 0.28**

Immunoassay

EM Science (D TECH) 64.6 g/mL 50 μL/15 mL 50 μL/15 mL 0.71 μg/g ≈ 50 on DTechtor

Acetone (1/300) Bottle B (1/300)

Idetek (Quantix) 25 g/mL 100 μL/4 mL 100 μL/10 mL 5 μg/g ≈ 50% B/Bo†

Acetone (1/40) MQ (1/100)

Diluent tube

Millipore (EnviroGard) 25 g/mL 100 μL/25 mL 100 μL/10 mL 4 μg/g ≈ 40% B/Bo

Acetone (1/250) MQ (1/100)

user supplied

Ohmicron 50 g/mL 100 μL/25 mL 100 μL/25 mL 1.6 μg/g ≈ 40% B/Bo

MeOH (1/250) Buffer (1/250)

Diluent tube

* Absorbance.

** Estimated for 25-mL cuvette.

† Absorbance of test vs. absorbance of control.
11

to deliver quantities in the 2.0- to 10.0-μL range. Recommendations for dilution procedures for

specific on-site methods are presented in Table 6.

RECOMMENDATIONS

1. Current on-site methods for TNT and RDX in soil rely on a short (one- to three-minute) extraction of soil with either acetone or methanol, prior to determination. Kinetic extraction studies on

highly contaminated soils indicate that extraction of TNT and RDX is incomplete when a threeminute extraction period is used with either acetone or methanol. In general, however, a concentration of at least 70% of that attained after an 18-hour extraction is achieved after three minutes of

manual extraction. To account for this incomplete extraction, concentrations determined using this

short extraction and on-site analysis, at or above 7%, should be considered potentially reactive. We

also recommend that protocols that now specify a one- or two-minute extraction period be changed

to require a minimum of three minutes of shaking with the extracting solvent. When it is necessary

to pinpoint concentrations, a kinetic extraction study as detailed in this report can be carried out on

the sample.

2. Current on-site methods for TNT and RDX in soil were developed for detecting low (μg/g)

concentrations. For this reason, extracts from highly contaminated soils must be diluted by as much

as 1 to 10,000 in order to obtain concentrations in the linear range of the tests. These dilutions can be

made using a one-step procedure utilizing glass microliter syringes. The resulting precision and

accuracy is adequate for this application.

LITERATURE CITED

Avolio, J., R. DeBono, and P. Radwanski (1995) Ion mobility spectrometry (IMS) field screening

methods and analysis of explosives in contaminated soils. In Proceedings of an International Symposium, Field Screening Methods for Hazardous Wastes and Toxic Chemicals. Las Vegas, Nevada, 22–24 February 1995, p. 1037.

Erickson, E.D., D.J. Knight, D.J. Burdick, and S.R. Greni (1984) Indicator tubes for the detection of

explosives. Naval Weapons Center, China Lake, California, Report NWC TP 6569.

Heller, C.A., S.R. Greni, and E.D. Erickson (1982) Field detection of 2,4,6-trinitrotoluene in water by

ion-exchange resins. Analytical Chemistry, 54: 286–289.

Hutter, L., G. Teaney, and J.W. Stave (1993) A novel field screening system for TNT using EIA. In

Field Screening Methods for Hazardous Wastes and Toxic Chemicals, Proceedings of the 1993 U.S. EPA/

A&WMA International Symposium, vol. 1, p. 472.

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 M.E. Walsh (1991) Field screening method for 2,4-dinitrotoluene in soil. USA Cold

Regions Research and Engineering Laboratory Special Report 91-17.

Jenkins, T.F. and S.M. Golden (1993) Development of an improved confirmation separation suitable

for use with SW846 Method 8330. USA Cold Regions Research and Engineering Laboratory Special

Report 93-14.

Jenkins, T.F., M.E. Walsh, P.W. Schumacher, P.H. Miyares, C.F. Bauer, and C.L. Grant (1989) Liquid

chromatographic method for determination of extractable nitroaromatic and nitramine residues in

soil. Journal of AOAC, 72: 890–899.

Jenkins, T.F., C.L. Grant, G.S. Brar, P.G. Thorne, T.A. Ranney, and P.W. Schumacher (1996) Assessment of sampling error associated with the collection and analysis of soil samples at explosivescontaminated sites. USA Cold Regions Research and Engineering Laboratory Special Report 96-15.

Keuchel, C., L. Weil, and R. Niessner (1992a) Enzyme-linked immunoassay for the determination of

2,4,6-trinitrotoluene and related nitroaromatic compounds. Analytical Sciences, 8: 9–12.
12

Keuchel, C., L. Weil, and R. Niessner (1992b) 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. and R. Niessner (1994) Rapid field screening test for the determination of 2,4,6-trinitrotoluene in water and soil with immunofiltration. Fresenius Journal of Analytical Chemistry, 350: 538–

543.

Kristoff, F.T., T.W. Ewing, and D.E. Johnson (1987) Testing to determine relationship between explosive contaminated sludge components and reactivity. U.S. Army Toxic and Hazardous Materials

Agency, Aberdeen Proving Ground, Maryland, USATHAMA Report No. AMXTH-TE-CR-86096.

Medary, R.T. (1992) Inexpensive, rapid field screening test for 2,4,6-trinitrotoluene in soil. Analytica

Chimica Acta, 258: 341–346.

Rodacy, P. and P. Leslie (1993) Ion mobility spectroscopy as a means of detecting explosives in soil

samples. In Field Screening Methods for Hazardous Wastes and Toxic Chemicals, Proceedings of the 1993

U.S. EPA/A&WMA International Symposium, vol. 2, p. 823-829.

Teaney, G.B., R.T. Hudak, and J.M. Melby (1995) On-site soil and water analysis using D TECH immunoassays for RDX and TNT. In Proceedings of an International Symposium, Field Screening Methods

for Hazardous Wastes and Toxic Chemicals. Las Vegas, Nevada, 22–24 February 1995, p. 965.

Walsh, M.E. and T.F. Jenkins (1991) Development of a field screening method for RDX in soil. USA

Cold Regions Research and Engineering Laboratory Special Report 91-7.

Walsh, M.E., T.F. Jenkins, P.S. Schnitker, J.W. Elwell, and M.H. Stutz (1993) Evaluation of analytical

requirements associated with sites potentially contaminated with residues of high explosives. USA

Cold Regions Research and Engineering Laboratory Special Report 93-5.

Yinon, Y.J. and S. Zitrin (1981) The Analysis of Explosives. Oxford: Pergamon Press, Pergamon Series in

Analytical Chemistry, vol. 3.
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UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

May 1996

On-Site Analysis for High Concentrations of Explosives in Soil:

Extraction Kinetics and Dilution Procedures

Thomas F. Jenkins, Patricia W. Schumacher, Jane G. Mason and Philip G. Thorne

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road Special Report 96-10

Hanover, New Hampshire 03755-1290

U.S. Army Environmental Center

Aberdeen Proving Ground, Maryland SFIM-AEC-ET-CR-96158

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161.

Soils containing high concentrations (>10%) of secondary explosives might detonate from shock or flame, resulting in human injuries or equipment damage during remediation activities. In lieu of expensive and timeconsuming protocols involving impact tests, friction tests, and shock gap tests, compositional analysis has

been recommended as an expedient method to assess the risk of detonation from heavily contaminated soils.

A number of methods now available allow determination of TNT and RDX on site. All of these methods

specify solvent extraction with either acetone or methanol to transfer the analyte from the soil matrix to a

solvent as the first step in the determination. The rate of extraction of TNT and RDX, when present at percent levels in soil, has not been determined. Protocols currently in use specify very short extraction times

(one to three minutes) and results could be biased low if extraction kinetics are slow. The objective of this

work was to document the rate of extraction of secondary explosives by acetone and methanol and make

recommendations for possible modification of current protocols if warranted. Because solvent extracts from

highly contaminated soils will have very high concentrations of secondary explosives, compared with the

range of concentrations that can be determined using the various on-site methods, large dilutions will be required. Recommendations are made for a field-expedient method making appropriate dilutions.

Dilutions

DNT

Explosives

RDX

Reactive

Soils

Extraction kinetics

High concentrations

On-site analysis

For conversion of SI units to non-SI units of measurement consult Standard Practice for Use of the International System of Units (SI),

ASTM Standard E380-93, published by the American Society for Testing and Materials, 1916 Race St., Philadelphia, Pa. 19103.

TNT