SPECIAL REPORT 95-22

Evaluation of Clean Solid Phases for

Extraction of Nitroaromatics and

Nitramines from Water

Thomas F. Jenkins, Philip G. Thorne, Karen F. Myers,

Erika F. McCormick, Don E. Parker and B. Lynn Escalon September 1995
Abstract

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.

Salting-out solvent extraction (SOE) was compared with cartridge and membrane solid-phase extraction (SPE) for preconcentration of nitroaromatics,

nitramines, and aminonitroaromatics prior to determination by reversed-phase

high-performance liquid chromatography. The solid phases used were manufacturer-cleaned materials: Porapak RDX for the cartridge method and Empore

SDB-RPS for the membrane method. Thirty-three groundwater samples from

the Naval Surface Warfare Center, Crane, Indiana, were analyzed using the

direct analysis protocol specified in SW846 Method 8330, and the results

were compared with analyses conducted after preconcentration using SOE

with acetonitrile, cartridge-based SPE, and membrane-based SPE. For highconcentration samples, analytical results from the three preconcentration techniques were compared with results from the direct analysis protocol; good

recovery of all target analytes was achieved by all three preconcentration methods. For low-concentration samples, results from the two SPE methods were

correlated with results from the SOE method; very similar data was obtained

by the SOE and SPE methods, even at concentrations well below 1 μg/L. The

large chromatographic interferences observed for the SPE methods in an earlier study using less clean materials were largely absent here. A small interference was observed for both SPE methods at the retention time of RDX on the

primary analysis column that translated to concentrations ranging from 0.2 to

0.6 μg/L RDX. Detection limits for RDX should be raised to 0.6 μg/L if the SPE

methods are used for preconcentration due to this potential interference. We

recommend that solid-phase extraction be included as an option in SW846

Method 8330 as well as SOE.
US Army Corps

of Engineers®

Cold Regions Research &

Engineering Laboratory

Special Report 95-22

Evaluation of Clean Solid Phases for

Extraction of Nitroaromatics and

Nitramines from Water

Thomas F. Jenkins, Philip G. Thorne, Karen F. Myers,

Erika F. McCormick, Don E. Parker and B. Lynn Escalon September 1995

Prepared for

U.S. ARMY ENVIRONMENTAL CENTER

SFIM-AEC-ET-CR-95037

Approved for public release; distribution is unlimited.
ii

PREFACE

This report was prepared by Dr. Thomas F. Jenkins and Philip G. Thorne, Geological

Sciences Division, Research and Engineering Directorate, U.S. Army Cold Regions Research

and Engineering Laboratory (CRREL), Hanover, New Hampshire; Karen F. Myers, Biologist, and Erika F. McCormick, Chemist, Environmental Chemistry Branch, Environmental

Engineering Division, Environmental Laboratory, U.S. Army Engineer Waterways Experiment Station (WES), Vicksburg, Mississippi; and Don E. Parker and B. Lynn Escalon, AScI

Corporation, McLean, Virginia.

Funding was provided by the U.S. Army Environmental Center, Aberdeen Proving

Ground, Maryland, Martin H. Stutz, Project Monitor.

This report was technically reviewed by Dr. C.L. Grant, Professor Emeritus, Chemistry

Department, University of New Hampshire, and Thomas E. Myers, Environmental Engineer, WES. In addition, the authors acknowledge Roy Wade (WES) for collection of all

groundwater samples and Linda Stevenson for sample management.

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 the 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.
iii

CONTENTS

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

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

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

Experimental ........................................................................................................................... 2

Results and discussion ........................................................................................................... 4

Conclusions and recommendations ..................................................................................... 10

Literature cited ........................................................................................................................ 10

Appendix A: Holding-time study results ........................................................................... 13

ILLUSTRATIONS

Figure

1. Breakthrough curve for HMX and RDX with SDB-RPS membrane ........................ 4

2. Plot of HMX concentrations determined for groundwater samples...................... 7

3. Plot of RDX concentrations determined for groundwater samples ....................... 7

4. Plot of TNT concentrations determined for groundwater samples....................... 8

5. LC-18 RP-HPLC chromatograms for sample 30 preconcentrated using SOE,

SPE-C, and SPE-M with initial less-clean SPE materials .................................. 8

6. LC-18 RP-HPLC chromatograms for sample 30 preconcentrated using SOE,

SPE-C, and SPE-M with new manufacturer-cleaned SPE materials showing small RDX interference for SPE-C and SPE-M............................................... 9

7. LC-18 RP-HPLC chromatograms for sample 30 preconcentrated using SOE,

SPE-C, and SPE-M with new manufacturer-cleaned SPE materials showing small RDX interference for SPE-C and SPE-M............................................... 9

TABLES

Table

1. Retention times for various RP-HPLC separations .................................................. 2

2. Comparison of results from analysis of duplicate samples .................................... 5

3. Comparison of recoveries from fortified samples .................................................... 6

4. Ratio of concentrations obtained for the various preconcentration methods

relative to that from the direct method.............................................................. 6

5. Results of regression analyses of SPE-C and SPE-M vs. SOE for lowconcentration determinations ............................................................................. 8
Evaluation of Clean Solid Phases for Extraction of

Nitroaromatics and Nitramines from Water

THOMAS F. JENKINS, PHILIP G. THORNE, KAREN F. MYERS,

ERIKA F. MCCORMICK, DON E. PARKER AND B. LYNN ESCALON

INTRODUCTION

One of the U.S. Army’s most serious environmental problems is associated with sites contaminated with residues of secondary explosives. Contamination at these sites was chiefly caused by

manufacture of the explosives, loading of explosives

into ordnance, and disposal of off-specification or

out-of-date material. Residues from these activities contain the explosives, manufacturing impurities, and environmental transformation products

(Walsh et al. 1993). Unlike many other organic

chemicals, these compounds are quite mobile in

the soil and have resulted in serious groundwater

contamination (Kayser and Burlinson 1982, Pugh

1982, Rosenblatt 1986, Maskarinec et al. 1986,

Spaulding and Fulton 1988). Plumes of contaminated groundwater, often miles in length, have

been identified at military sites, with some extending beyond installation boundaries.

A number of laboratory methods have been

developed to characterize water samples potentially contaminated with secondary explosives. At

present, however, the method most often used by

contract laboratories conducting analyses for the

Army is SW846 Method 8330 (EPA 1992). This is

a reversed-phase, high-performance liquid chromatographic (RP-HPLC) method that specifies 14

target nitroaromatic and nitramine analytes and

two protocols for water analysis. When detection

limits ranging between 4 and 14 μg/L are adequate for project requirements, a direct injection

procedure can be used that does not require sample preconcentration prior to RP-HPLC determination. When lower detection limits are needed, a

protocol including a salting-out solvent extraction

(SOE) preconcentration step is specified (Miyares

and Jenkins 1990, 1991). Winslow et al. (1991,

1992) have proposed the use of solid-phase extraction (SPE) as an alternative to SOE and reported excellent recovery and detection limits that were

very similar to those for SOE. Winslow’s results

were obtained using Porapak R, a divinylbenzene

n-vinylpyrrolidone co-polymer, in the cartridge

format. LeBrun et al. (1993), using SPE in the membrane format, reported excellent recoveries of the

analytes in Method 8330 using a membrane composed of styrene-divinylbenzene. Recently Bouvier

and Oehrle (1995) reported on the use of Porapak

RDX for cartridge SPE preconcentration of nitroaromatics and nitramines.

Because of a number of potential advantages of

SPE over SOE, we conducted a three-way comparison of SOE, cartridge-based SPE using Porapak R

(SPE-C), and membrane-based SPE (SPE-M) using

styrene-divinylbenzene membranes (Empore SDVB)

for preconcentration of waters containing nitroaromatics and nitramines (Jenkins et al. 1992, 1994).

This evaluation included estimating detection

capability and analyte recovery using fortified

reagent-grade water, and analyte recovery for a

series of field-contaminated groundwater samples

from the U.S. Naval Surface Warfare Center

(NSWC), Crane, Indiana. Overall, the results can

be summarized as follows:

1) The three methods were comparable with

respect to low-concentration detection capability,

ranging from 0.05 to 0.30 μg/L.

2) Percent recoveries generally exceeded 80%,

except for HMX (octahydro–1,3,5,7-tetranitro–

1,3,5,7-tetrazocine) and RDX (hexahydro–1,3,5-trinitro–1,3,5-triazine) by membrane SPE where recoveries were lower.

3) Large interferences were found on about half

of the groundwater samples from the NSWC using

the two SPE methods but none were found by SOE.

4) The SPE interferences were traced to a matrix

interaction of the SPE polymers with low pH
2

groundwaters that apparently caused the release

of unreacted monomers or other contaminants

from the interior of the polymeric materials.

At least partly in response to the problems

identified above, several manufacturers of SPE

materials sought to improve the retention of SPE

materials for very polar organics such as HMX

and RDX and experimented with new cleaning

procedures to better remove interferences from

the SPE materials. As a result, Waters Corporation released a new ultra-clean SPE material for

use in cartridge SPE under the name Porapak

RDX (Bouvier and Oehrle 1995), and 3M Corporation developed a new surface-modified styrenedivinylbenzene membrane that also had been

cleaned more extensively (Empore SDB-RPS). Initial tests at the U.S. Army Cold Regions Research

and Engineering Laboratory (CRREL) and elsewhere indicated that these materials were indeed

cleaner than the original SPE materials.

OBJECTIVE

The objective of this study was to reassess SPE

for preconcentration of nitroaromatic and nitramine

explosives from water, using the newly released,

manufacturer-cleaned SPE materials. Special attention was given to recovery of HMX and RDX, because of the low recoveries found for these analytes

with membrane SPE in the initial study. Assessment

of the level of contamination resulting from use of

these manufacturer-cleaned materials was conducted

using both reagent water samples and some groundwaters from the Naval Surface Warfare Center

(NSWC). These groundwaters included some of the

low-pH waters that had revealed the contamination

problem with the initial SPE materials.

EXPERIMENTAL

Conduct of study

This work was jointly conducted by the U.S.

Army Engineer Waterways Experiment Station

(WES), Vicksburg, Mississippi, and CRREL, using

fortified reagent-grade water and actual groundwater samples from the NSWC.

Collection of groundwater samples

Groundwater samples were taken with bailers

that were rinsed once with isopropyl alcohol and

three times with distilled water between samples.

Wells were purged with a PVC bailer to a depth

midway down the well stream, allowed to recharge a minimum of 2 hours, then sampled with

Teflon bailers. Samples were collected in 1-liter precleaned amber glass bottles and were stored and

shipped at 4°C.

RP-HPLC analysis

All water samples were analyzed by RP-HPLC

at WES. Depending on the specific test conducted,

water samples were either analyzed using the

direct method specified in SW846 Method 8330

(EPA 1992) or were preconcentrated using either

SOE, SPE-C, or SPE-M as described below (Jenkins et al. 1992).

Primary analysis was conducted on a 25-cm ×

4.6-mm (5-μm) LC–18 column (Supelco) eluted

with 1:1 methanol/water (v/v) at 1.2 mL/min.

Injection volume was 50 μL introduced using a

200-μL sample loop. Concentration estimates were

obtained from peak heights from a Waters 820

Maxima chromatography workstation. The identity of target analytes and transformation products

was confirmed by analysis of the samples on a

25-cm × 4.6-mm (5-μm) LC-CN column from

Supelco eluted with 1:1 methanol/water (v/v) at

1.2 mL/min (EPA 1992). Quantitative results for

the 2-amino- and 4-aminodinitrotoluenes (2ADNT

and 4ADNT) were also taken from the LC-CN determination, since better separation of these two

analytes were obtained on this column. Retention

times of the analytes of interest for both separations are shown in Table 1.

Table 1. Retention times for various RPHPLC separations.

Retention time (min)

Analyte LC–18* LC-CN*

HMX 2.4 11.4

RDX 3.5 7.3

TNB 4.6 4.3

DNB 5.6 4.4

3,5-DNA 6.1 5.6

tetryl 6.2 9.2

NB 6.6 4.0

TNT 7.4 5.2

4ADNT 8.0 6.0

2ADNT 8.4 6.4

2,6-DNT 8.8 4.9

2,4-DNT 8.9 5.2

2NT 10.6 4.5

4NT 11.8 4.7

3NT 12.4 4.8

tetryl breakdown product 4.6 8.1

2-amino-4-nitrotoluene 5.6 4.2

3-nitroaniline 4.2 3.8

2,4-diamino-6-nitrotoluene 4.0 6.3

2,6-diamino-4-nitrotoluene 2.1 4.8

4-amino-2-nitrotoluene 8.1 4.3

*Separations were conducted at 1.2 mL/min

with an eluent of 1:1 methanol/water.
Primary analyses were conducted using a

Waters Model 600 system controller, Model 610

fluid unit, Model 717 plus auto injector set for a

50-μL injection, a 486 UV variable wavelength

detector set at 245 nm, and a Maxima chromatography work station. Confirmation analysis was

conducted on a Waters LC Module 1 with a 486

UV variable wavelength detector (245 nm), a 717

plus auto injector (50 μL), and a Maxima 820 chromatography work station.

Salting-out solvent extraction/nonevaporative

preconcentration procedure

 A 251.3-g portion of reagent-grade sodium

chloride was added to a 1-L volumetric flask. A

770-mL sample of water was measured with a 1-

L graduated cylinder and added to the flask. A

stir bar was added and the contents stirred at maximum rpm until the salt was completely dissolved. A 164-mL aliquot of acetonitrile (ACN),

measured with a 250-mL graduated cylinder, was

added while the solution was being stirred, and

stirring was continued for at least 15 minutes. If

the ACN was slow in dissolving due to poor mixing, a Pasteur pipette was used to withdraw a

portion of the undissolved ACN layer and reinject it into the vortex of the stirring aqueous phase.

After equilibrium has been established, only about

5 mL of ACN should remain in a separate phase.

The stirrer was turned off and the phases allowed

to separate for 15 min. If no emulsion was present,

the ACN phase was removed and placed in a 100-

mL volumetric flask and 10 mL of fresh ACN was

added to the 1-L flask. The 1-L flask was again

stirred for 15 min, followed by 15 min for phase

separation. The ACN was removed and combined

with the initial extract in the 100-mL volumetric

flask. When emulsions were present, that portion

of the sample was removed from the volumetric

flask with a Pasteur pipette, placed in a 20-mL

scintillation vial and centrifuged for 5 min at 2000

rpm. The supernate was also pipetted into the 100-

mL volumetric flask, the scintillation vial was

rinsed with 5 mL of acetonitrile, and the acetonitrile was added to the 100-mL volumetric flask.

For the first extraction, the pellet that formed after centrifugation was added back to the 100-mL

flask, but if it occurred in the second extraction, it

was discarded.

To reduce the volume of ACN, an 84-mL aliquot of salt water (325 g NaCl per 1000 mL of

water) was then added to the 100-mL volumetric

flask. The flask was placed on a vertical turntable

and rotated at about 60 rpm for 15 min. After

3

allowing the phases to separate for 15 min, the

ACN phase was carefully removed using a Pasteur pipette and placed in a 10-mL graduated cylinder. An additional 1.0-mL aliquot of ACN was

then added to the 100-mL volumetric flask, and

the flask was rotated on the turntable for 15 min.

Again the phases were allowed to separate for 15

min, and the resulting ACN phase was added to

the 10-mL graduated cylinder. The volume of the

resulting extract was measured and diluted 1:1

with reagent-grade water prior to analysis.

Cartridge solid-phase extraction

Prepacked cartridges of Porapak RDX (Sep-Pak,

6 cc, 500 mg) were obtained from Waters Corporation. The cartridges were cleaned by placing them

on a Visiprep solid-phase extraction manifold (Supelco) and passing 15 mL of acetonitrile through

each using gravity flow. The acetonitrile was then

flushed from the cartridges using 30 mL of reagentgrade water. Care was taken to ensure that the

cartridges were never allowed to dry after the initial cleaning.

A connector was placed on the top of each cartridge and fitted with a length of 1/8-in.-diameter

Teflon tubing. The other end of the tubing was

placed in a 1-L fleaker containing 500 mL of sample. The vacuum was turned on and the flow rate

through each cartridge was set at about 10 mL/

min. If the flow rate declined significantly due to

partial plugging from suspended material, it was

readjusted. After the sample had been extracted,

the top plug containing the fitted tubing was removed from each cartridge, and 10 mL of reagentgrade water was passed through the cartridge,

using gravity flow unless the cartridges were

sufficiently plugged to require vacuum. A 5-mL

aliquot of acetonitrile was used to elute retained

analytes from the cartridges under gravity flow.

The volume of the recovered ACN was measured

and diluted 1:1 with reagent-grade water.

Membrane solid-phase extraction

Empore styrene-divinylbenzene membranes

(47 mm) were obtained from 3M Corporation. The

membranes were designated SDB-RPS and were

not commercially available at the time the study

was conducted. The styrene-divinylbenzene used

in these membranes had been modified to provide extra retention for polar organics such as

HMX.* The membranes were precleaned by cen-

* Craig Markell, 1995, 3M Corporation, personal communication.
tering them on a 47-mm vacuum filter apparatus

and adding several mL of acetonitrile to swell the

membrane before clamping the reservoir in place.

A 15-mL aliquot of ACN was then added and

allowed to soak into the membrane for 3 min. The

vacuum was then turned on and most (but not

all) of the solvent was pulled through the membrane. A 30-mL aliquot of reagent-grade water

was then added and the vacuum resumed. Just

before the last of this water was pulled through

the membrane, the vacuum was removed, the reservoir filled with a 500-mL sample, and the vacuum resumed. This sample extraction took from 5

minutes to an hour, depending on the amount of

suspended matter present. Once the water was

eluted, air was drawn through the membrane for

1 min to remove excess water. These extractions

were conducted six at a time using an Empore

extraction manifold (3M Corporation). Vials (40

mL) were placed below the outlets of the six membranes, a 5-mL aliquot of ACN was added to each

reservoir, the acetonitrile was allowed to soak into

the membrane for 3 min, and then the vacuum

was applied to pull the acetonitrile through the

membranes into the vials. Each resulting extract

was removed with a Pasteur pipette, the volume

was measured in a 10-mL graduated cylinder, and

it was diluted 1:1 with reagent-grade water before analysis.

Preparation of analytical standards

All standards were prepared from standard

analytical reference materials (SARMs) obtained

from the U.S. Army Environmental Center, Aberdeen Proving Ground, Maryland. Individual stock

standards were prepared in HPLC-grade acetonitrile (Baker). Combined working standards were

in acetonitrile and were diluted 1:1 with Milli-Q

Type I water (Millipore Corp.).

RESULTS AND DISCUSSION

Determination of retention capacity of the

SDB-RPS membrane for HMX and RDX

The retention of HMX and RDX by the SDB-RPS

membranes was tested by extracting a 2-L aliquot

of reagent-grade water that had been spiked with

100 μg/L of HMX and RDX using aqueous stock

standards. Samples of the water passing through

the membrane were collected every 250 mL and

analyzed by RP-HPLC using the direct analysis

protocol. Results are plotted in Figure 1. No detectable breakthrough occured for either analyte

until more than 1 L of water had been extracted.

Thus, it appears that the SDB-RPS membranes

have an increased retention capacity for the very

polar nitramines relative to that observed with the

initial SDB membranes used in an earlier study

(Jenkins et al. 1992, 1994).

Cleanliness of Porapak RDX cartridges

and SDB-RPS membranes

Aqueous solutions of individual analytes were

prepared by placing several hundred milligrams

of each SARM into brown glass bottles and stirring for 2 days at room temperature. Each solu4

Figure 1. Breakthrough curve for HMX and RDX with SDB-RPS membrane.

100

80

60

40

20

0 400 800 1200 1600 2000

Volume of Effluent (mL)

Concentration in Effluent (μg/L)

HMX

RDX
Table 2. Comparison of results from analysis of duplicate samples.

Relative percent difference*

Sample HMX RDX TNB DNB DNA TNT 24D 4A 2A

4 Dir 0 24

SOE 0 15 6 100 8 18 11

SPE-C 1 12 0 45 8 5

SPE-M 3 8 0 17 2 1

29 Dir

SOE

SPE-C 26

SPE-M 7

B (spike) Dir 1 0 0 1 1

SOE 4 4 4 3 3

SPE-C 6 1 7 6 6

SPE-M 5 7 7 13 6

* Relative percent difference calculated by subtracting the two values obtained

from duplicates, dividing by the mean value, and multiplying by 100.

5

tion was then filtered through a 0.45-μm nylon–

66 membrane (Supelco) into clean brown glass

bottles and stored at room temperature. Test solutions were made by diluting these stocks with

reagent-grade water.

The retention of HMX and RDX by the modified SDB membranes was tested by extracting a

2-L aliquot of reagent-grade water that had been

spiked with 100 μg/L of HMX and RDX using

aqueous stocks. Samples of the membrane runthrough were taken every 250 mL and analyzed

by RR-HPLC. The results are plotted in Figure 1.

No breakthrough occured for either analyte until

more than 1 L had been extracted. This is a substantial improvement in retention of these two

polar analytes compared with that experienced

with the original SDB membranes.

Quality control

QC spiking stock solutions were prepared in

acetonitrile. Spikes for the direct injection method were made to produce an added concentration about 5 times the average method detection

limit (MDL) at 100 μg/L. Spikes for the samples

to be preconcentrated using SOE and SPE were

made to produce an added concentration of 2.00

μg/L, approximately 100 times the average MDL

reported for the SOE method. Blanks and matrix

spikes were prepared in 1-L volumetric flasks,

then subsampled for the appropriate method. Two

groundwater samples from NSWC were collected in sufficient quantity to allow analysis of matrix duplicates and spikes. In addition, two sets

of reagent-grade water blanks (one on each day

samples were preconcentrated), blank spikes, and

blank spike duplicates were analyzed.

Analytical precision was assessed by computing the relative percent difference (RPD) between

duplicate samples based on a single analysis of

each (Table 2). In only four cases were the RPD

values greater than 20%: sample 4, RDX–direct

analysis; sample 4, DNA–SOE; sample 4, TNT–

SPE-C; and sample 29, RDX–SPE-C. In all of these

cases, the concentration values were near MDL

values where errors calculated on a percentage

basis are magnified. Otherwise, analytical precision was excellent for both the direct and

preconcentration methods, even at low concentration.

Accuracy was assessed from spike recovery

data. For spiked reagent-grade water (blank

spikes), recoveries of all analytes, for both the direct and preconcentration methods, ranged from

78 to 102%, with the majority of the recoveries

above 90% (Table 3). Recoveries of matrix spikes

for the direct analysis protocol were also excellent for all analytes in both sample 4 and 29 with

recoveries ranging from 92.8 to 105.5% (Table 3).

Recoveries for matrix-spiked sample 29 ranged

from 65 to 107% for the three preconcentration

methods, again indicating excellent recovery. Recoveries for matrix-spiked sample 4 are quite variable, with values ranging from 23 to 191% for the

SOE method, 49 to 308% for the SPE-M method,

and 91 to 351% for SPE-C (Table 3). However, to

interpret these results, one must remember that

spike recovery is calculated by subtracting the

concentration obtained for the original sample

from the concentration obtained from the spiked

sample and expressing the result as a ratio of the

spike recovered relative to the spike added. This

procedure is useful when the concentration of the
6

Table 3. Comparison of recoveries from fortified samples.

Percent recovery*

Sample HMX RDX TNB DNB DNA TNT 24D 4A 2A

B (spike) Dir 99.5 98.5 95.6 96.5 98.1

SOE 94.2 91.2 92.9 83.2 92.1

SPE-C 99.0 101.0 96.6 94.1 95.1

SPE-M 92.5 95.6 89.3 88.6 86.9

B (spike) Dir 98.8 98.2 95.9 97.2 99.2

SOE 91.0 95.0 89.0 81.0 89.0

SPE-C 93.5 100.0 89.8 89.1 89.3

SPE-M 88.0 102.0 83.0 78.0 82.0

29 Dir 95 95.5 95.2 92.8 93

SOE 107 89 85 89 65

SPE-C 103 107 104 105 102

SPE-M 80 78 76 78 77

4 Dir 105.5 105 103 104 105

SOE 23† 191† 76.0 83 76

SPE-C 351† 95† 92.2 91.1 93.7

SPE-M 308† 49.5† 87.4 85.6 90.8

* % recovery calculated by subtracting the value obtained from the analysis of

the unspiked sample from the value obtained for analysis of the fortified

sample, dividing by the concentration spiked and multiplying by 100.

† For an explanation of these unreliable estimates, see text.

Table 4. Ratio of concentrations obtained for the

various preconcentration methods relative to that

from the direct method.

Concentration-preconc./Concentration-direct

Analyte n SOE SPE-C SPE-M

HMX 11 0.870±0.188 0.957±0.147 0.833±0.129

RDX 13 0.800±0.184 0.975±0.192 0.882±0.158

TNT 4 1.010±0.252 1.143±0.331 1.015±0.244

4ADNT 5 0.909±0.128 0.996±0.106 0.925±0.095

2ADNT 5 0.865±0.106 1.021±0.066* 0.871±0.057

n = number of ratios in each mean.

* Value significantly different at the 95% confidence level.

spike added is greater than that already present

in the matrix. If, on the other hand, the spike concentration is small relative to the matrix concentration, a situation encountered here, the result is

obtained by subtraction of two similar concentrations to obtain a much smaller value. This can result in widely ranging percent recoveries. This

problem has been discussed in detail by Provost

and Elder (1983) who stated “Regardless of how

percent recovery is defined, it can be shown that

percent recovery data tend to be unreliable when

the spike/background ratio is small.” In sample

4, for example, the concentrations determined in

the unspiked sample for HMX were 45.7, 48.0, and

40.8 μg/L for the SOE, SPE-C, and SPE-M methods, respectively. Sample fortification added only

another 2 μg/L and hence it is not surprising that

percent recoveries, calculated as described above,

were 23, 351, and 308% for SOE, SPE-C, and SPE-M,

respectively. As shown by Provost and Elder (1983)

this is not a surprising result and does not indicate that the methods were out of control. The

excellent results for the other QC samples provide convincing evidence that both the direct and

preconcentration procedures were in-control and

providing very reliable concentration estimates.

Comparison of results using groundwater

samples from Naval Surface Warfare Center

Analytical results for 33 groundwater samples

from NSWC are presented in Appendix A. These

samples were all analyzed by the direct RP-HPLC

method (without preconcentration) and by RPHPLC after preconcentration using salting-out

solvent extraction (SOE), cartridge solid-phase

extraction (SPE-C), and membrane solid-phase

extraction (SPE-M). The following target analytes

were detected in these samples (the number of

samples where the analytes were detected in at

least one of the four analyses is given in parentheses): HMX (19), RDX (22), TNB (4), DNB (5), 3,5-

DNA (6), TNT (11), 2,4-DNT (2), 4ADNT (15), and

2ADNT (15). Concentrations measured for HMX

and RDX in these groundwater samples were generally much higher than for the nitroaromatics and

aminonitroaromatics.

Although results from the direct method are

certainly not error free, they are subject to many fewer sources of error than methods employing a
7

preconcentration step. For that reason, we treated the results from the direct analysis as “true values” for purposes of comparison with results from

the three preconcentration techniques. Table 4

summarizes results for samples where analytes

were detected by the direct RP-HPLC method. Of

the 33 groundwater samples analyzed, 11 had detectable HMX using direct analysis, with concentrations ranging from 25 to 325 μg/L. Likewise,

RDX was detected in 13 groundwaters using the

direct method with concentrations ranging from

13 to 608 μg/L; TNT in four samples with concentrations ranging from 14 to 180 μg/L; 4ADNT and

2ADNT in five samples with concentrations ranging from 9 to 59 μg/L and 7 to 65 μg/L, respectively; and TNB was detected in two samples at 5

and 8 μg/L. For a given analyte, the ratio of the

concentration obtained for each preconcentration

technique relative to that for the direct method was

computed, and the mean and standard deviation

was obtained (Table 4). Mean ratios ranged from

0.800 for RDX using the SOE method to 1.143 for

TNT using the SPE-C method. Only for 2ADNT

was a significant difference among methods detected (by ANOVA) at the 95% confidence level

(SPE-C was different from SOE and SPE-M, which

were not significantly different from each other).

The results of this analysis indicate that, for relatively high concentrations, all three preconcentration techniques produced concentrations similar

to that from the direct analysis method, with analyte recoveries in all cases at or above 80%. These

results demonstrate a marked improvement in the

recovery of HMX and RDX using the SDB-RPS

membrane relative to that observed in our original study where the SDB membrane was used

(Jenkins et al. 1992, 1994). This improvement is

particularly striking for HMX, where recoveries

improved from about 49% to 83%, and appears to

be due to an improvement in retention for polar

compounds resulting from sulfonation of the styrene-divinylbenzene. Recovery of HMX and RDX

using the Porapak RDX cartridge remains excellent at 96 and 98%, respectively.

Since the value of a preconcentration technique

is to enable determination at concentrations below those that can be determined directly, it is important to evaluate its performance when concentrations are below the detection limits of the direct method. Since the SOE method is the procedure currently recommended in SW846 Method

8330, results for SPE-C and SPE-M were compared

with those obtained for SOE for samples with analyte concentrations below the detection limits of

14

12

10

8

6

4

2

0 2 4 6 8 10 12 14

HMX Concentration by SOE (μg/L)

HMX Concentration by SPE-C and SPE-M (μg/L)

SPE-C vs. SOE

SPE-M vs. SOE

SPE-C

vs. SOE

SPE-M

vs. SOE

14

12

10

8

6

4

2

0 2 4 6 8 10 12 14

RDX Concentration by SOE (μg/L)

RDX Concentration by SPE-C and SPE-M (μg/L)

SPE-C vs. SOE

SPE-M vs. SOE

SPE-C

vs. SOE

SPE-M

vs. SOE

Figure 3. Plot of RDX concentrations determined for

groundwater samples using SOE with those using SPE-C

and SPE-M.

Figure 2. Plot of HMX concentrations determined for

groundwater samples using SOE with those using SPE-C

and SPE-M.

the direct method. In Figures 2, 3, and 4 the concentrations of HMX, RDX, and TNT, determined

using SPE-C and SPE-M, are plotted against the

concentrations obtained using SOE. In the absence

of bias, the plots should have a slope of 1.00 and

an intercept of 0. Regression analyses were conducted for the SPE-C vs. SOE and SPE-M vs. SOE

individually for each analyte, and the resulting
1.2

0.8

0.4

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

TNT Concentration by SOE (μg/L)

TNT Concentration by SPE-C and SPE-M (μg/L)

SPE-C vs. SOE

SPE-M vs. SOE

SPE-C

vs. SOE

SPE-M

vs. SOE

1.6

Figure 4. Plot of TNT concentrations determined for

groundwater samples using SOE with those using SPE-C

and SPE-M.

Table 5. Results of regression analyses of SPE-C and

SPE-M vs. SOE for low-concentration* determinations.

SPE-C vs. SOE SPE-M vs. SOE

Analyte m b r2 m br2

HMX 1.083 0.125 0.999 0.972 0.113 0.999

RDX 1.255 –1.044 0.987 1.160 –0.850 0.980

TNT 1.264 –0.052 0.933 1.325 –0.085 0.972

4ADNT 1.400 –0.448 0.994 1.208 –0.360 0.992

2ADNT 1.270 0.110 0.981 1.484 0.875 0.974

3,5–DNA 0.972 0.007 0.996 0.930 0.014 0.996

* Concentrations below that detectable using the direct method.

m — Slope.

b — Intercept.

r2 — Correlation coefficient squared.

Salting-out

Cartridge-SPE

048 12 16 20

Retention Time (min)

Membrane-SPE

slopes, intercepts, and correlation coefficients

squared are presented in Table 5. Similarly, regression analyses were conducted for 4ADNT, 2ADNT,

and 3,5-DNA (Table 5). Slopes for these 12 regression analyses range from 0.930 to 1.400, with intercepts ranging from –1.044 to +0.875. Values for the

square of the correlation coefficients range between

0.933 and 0.999. The results from these regression

analyses indicate that the two SPE methods are producing data that are very similar to those obtained

from SOE, even at concentrations below 1 μg/L. The

TNT data for concentrations below 0.5 μg/L is particularly striking in this respect (Fig. 4).

Examination of chromatograms for

groundwater samples

In our initial comparison of SOE, SPE-C, and SPEM, we found a series of groundwater samples that

caused the solid-phase materials to release high concentrations of interferences. This is illustrated for the

chromatograms obtained for sample 20641 (Well

10C40P2) in 1992 using SOE, Porapak R (SPE-C), and

Empore SDB (SPE-M) (Fig. 5). Chromatograms for

this same sample obtained using the new, manufacturer-cleaned Porapak RDX and SDB-RPS are shown

8

Figure 5. LC–18 RP-HPLC chromatograms for sample

30 preconcentrated using SOE, SPE-C, and SPE-M with

initial less-clean SPE materials.
9

Figure 7. LC-CN RP-HPLC chromatograms

for sample 30 preconcentrated using SOE,

SPE-C, and SPE-M with new manufacturercleaned SPE materials showing small RDX

interference for SPE-C and SPE-M.

Salting-out

Cartridge-SPE

0 4 8 12 16

Retention Time (min)

Membrane-SPE

RDX Interference

Cartridge -SPE

Salting-out

0 4 8 12 16 Retention Time (min) RDX Interference

Membrane -SPE

Figure 6. LC–18 RP-HPLC chromatograms for

sample 30 preconcentrated using SOE, SPE-C,

and SPE-M with new manufacturer-cleaned SPE

materials showing small RDX interference for

SPE-C and SPE-M.
10

in Figure 6. Clearly there is a vast decrease in interferences released from the two solid phases.

There remains, however, a small interference peak

at the retention time for RDX in the two chromatograms for the SPE methods that is not observed

for the SOE (Fig. 6) and does not confirm as RDX

using the LC-CN confirmation column (Fig. 7).

This peak was observed in the LC-18 chromatograms for both SPE-C and SPE-M for the same six

well waters that resulted in release of interferences

in the original study. Observation of these peaks

would require that a confirmation analysis be conducted and would result in quantitative RDX estimates ranging from 0.2 to 0.6 μg/L if careful

scrutiny of an LC-CN confirmation analysis had

not been done. Thus, when SPE preconcentration

is used, the detection limit for RDX should be

raised to about 0.6 μg/L to eliminate the chance

for misidentification due to this small interference

peak.

CONCLUSIONS AND RECOMMENDATIONS

Solid-phase extraction, in both the cartridge

(SPE-C) and membrane (SPE-M) formats, was

evaluated for the ability to preconcentrate nitroaromatics, nitramines, and aminodinitroaromatics

from water samples prior to analysis by RP-HPLC

(SW846 Method 8330). A series of 33 groundwater samples from the Naval Surface Warfare Center was used for comparison. New, manufacturercleaned solid-phase materials (Porapak RDX for

SPE-C and SDB-RPS for SPE-M) were compared

to salting-out solvent extraction with respect to

their recovery of target analytes and their production of chromatographic interferences.

Based on these results, we recommend that

solid-phase extraction, in either the cartridge or

membrane format, be included as an option along

with salting-out solvent extraction for the preconcentration step in SW846 Method 8330. Comparison of the results of this study and earlier work

(Jenkins et al. 1992, 1994) demonstrates the necessity of using carefully cleaned solid phases for

this purpose, or interferences will be released for

certain water matrices.

LITERATURE CITED

Bouvier, E.S.P. and S.A. Oehrle (1995) Analysis and

identification of nitroaromatic and nitramine explosives in waters using HPLC and photodiodearray detection. LC-GC, 13(2): 120–130.

EPA (1989) Trinitrotoluene Health Advisory. Office

of Drinking Water. Washington, D.C.: U.S. Environmental Protection Agency.

EPA (1988a) Health Advisory for RDX. Criteria and

Standards Division, Office of Drinking Water.

Washington, D.C.: U.S. Environmental Protection

Agency.

EPA (1988b) Health Advisory for HMX. Criteria and

Standards Division, Office of Drinking Water.

Washington, D.C.: U.S. Environmental Protection

Agency.

EPA (1988c) Health Advisory for 1,3-Dinitrobenzene.

Criteria and Standards Division, Office of Drinking Water. Washington, D.C.: U.S. Environmental

Protection Agency.

EPA (1992a) Nitroaromatics and Nitramines by HPLC.

Second Update SW846 Method 8330. Washington,

D.C.: U.S. Environmental Protection Agency.

EPA (1992b) Dinitrotoluene Health Advisory. Criteria and Standards Division, Office of Drinking

Water. Washington, D.C.: U.S. Environmental Protection Agency.

Etnier, E.L. (1987) Water quality criteria for 2,4-dinitrotoluene and 2,6-dinitrotoluene. AD-ORNL–6312.

Oak Ridge National Laboratory Report, Oak Ridge,

Tennessee.

Jenkins, T.F., P.H. Miyares, K.F. Myers, E.F. McCormick and A.B. Strong (1994a) Comparison of solidphase extraction with salting-out solvent extraction

for preconcentration of nitroaromatic and nitramine

explosives from water. Analytica Chimica Acta, 289:

69–78.

Jenkins, T.F., P.G. Thorne and M.E. Walsh (1994b)

Fieldscreening method for TNT and RDX in

groundwater. USA Cold Regions Research and

Engineering Laboratory, Special Report 94-18.

Jenkins, T.F., P.H. Miyares, K.F. Myers, E.F. McCormick and A.B. Strong (1992) Comparison of cartridge and membrane solid-phase extraction with

salting-out solvent extraction for preconcentration

of nitroaromatic and nitramine explosives from

water. USA Cold Regions Research and Engineering Laboratory, Special Report 92-25.

Kayser, E.G. and N.E. Burlinson (1982) Migration

of explosives in soil. Naval Surface Weapons Center Report TR 82–566.

LeBrun, G., P. Rethwill and J. Matteson (1993) Determination of explosives in surface and groundwater. Environmental Laboratory, p. 12–15.

Miyares, P.H. and T.F. Jenkins (1990) Salting-out

solvent extraction method for determining low levels of nitroaromatics and nitramines in water. USA

Cold Regions Research and Engineering Laboratory, Special Report 90–30.

Miyares, P.H. and T.F. Jenkins (1991) Improved salt-
11

ing-out extraction–preconcentration method for

the determination of nitroaromatics and nitramines in water. USA Cold Regions Research and

Engineering Laboratory, Special Report 91-18.

Provost, L.P. and R.S. Elder (1983) Interpretation

of percent recovery data. American Laboratory, December, p. 57–63.

Pugh, D.L. (1982) Report DRXTH-FR–8213, Milan

Army Ammunition Plant contamination survey.

USA Toxic and Hazardous Materials Agency,

Aberdeen Proving Ground, Maryland.

Rosenblatt, D.H. (1986) Contaminated soil cleanup objectives for Cornhusker Army Ammunition

Plant. Technical Report 8603, USA Medical

Bioengineering Research and Development Laboratory, Fort Detrick, Maryland.

Spaulding, R.F. and J.W. Fulton (1988) Groundwater munition residues and nitrate near Grand

Island, Nebraska, U.S.A. Journal of Contaminant

Hydrology, 2: 139–153.

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

of SW846 Method 8330 for characterization of sites

contaminated with residues of high explosives.

USA Cold Regions Research and Engineering Laboratory, CRREL Report 93-5.

Winslow, M.G., B.A. Weichert and R.D. Baker (1991)

Determination of low-level explosives residues in

water by HPLC: Solid phase extraction vs. salting-out extraction. In Proceedings of the 7th Annual

Waste Testing and Quality Assurance Symposium, 8–

12 July, Environmental Protection Agency, Washington D.C.

Winslow, M.G., B.A. Weichert, R.D. Baker and P.F.

Dumas (1992) A reliable and cost-effective method for the determination of explosives compounds

in environmental water samples. In Proceedings of

the 8th Annual Waste Testing and Quality Assurance

Symposium, 13–17 July, Environmental Protection

Agency, Washington D.C.
13

Table A1. Comparison of results for direct analysis (Dir) with those using

salting-out (SOE), cartridge SPE (SPE-C) and membrane SPE (SPE-M) for

groundwater samples from NSWC.

Concentration (μg/L)

Sample Type HMX RDX TNB DNB DNA TNT 24D 4A 2A

1 Dir

SOE 1.04 2.45 0.47 0.36 0.32

SPE-C 1.00 1.33 0.44 0.29 0.3

SPE-M 0.93 1.35 0.57 0.28 0.56

2 Dir 94 79

SOE 54.2 63.8 0.3 0.33 3.08 1.36

SPE-C 64.0 83.1 0.3 0.34 3.34 2.27

SPE-M 57.1 71.8 0.3 0.29 2.89 2.05

3 Dir 93 91

SOE 85.7 75.3 0.2 0.19 0.08 2.43 1.31

SPE-C 93.1 88.8 0.2 0.17 0.11 2.49 1.65

SPE-M 78.9 74.7 0.2 0.13 0.07 1.99 1.89

4 Dir 45 14

SOE 45.7 16.4 0.17 0.3 0.13 2.18 1.21

SPE-C 48.0 21.6 0.2 0.19 2.31 1.42

SPE-M 40.8 18.9 0.2 0.13 2.07 1.64

5 Dir

SOE 0.76 5.77 0.13 0.05

SPE-C 1.16 6.48 0.16 0.05

SPE-M 1.19 6.11 0.16 0.14

6 Dir

SOE 10.5 6.17 0.10 0.71 0.33

SPE-C 11.5 7.03 0.10 0.79 0.40

SPE-M 10.3 6.34 0.07 0.82 0.70

7 Dir 134 365

SOE 75.4 202 0.98 8.12 1.80

SPE-C 115 308 1.51 11.3 3.44

SPE-M 109 291 1.41 9.81 3.30

8 Dir

SOE 0.61 10.9

SPE-C 0.64 11.9

SPE-M 0.64 11.0

9 Dir 25 13

SOE 30.2 12.1 1.14 0.56

SPE-C 31.2 12.7 1.50 0.79

SPE-M 27.5 11.0 1.34 0.79

10 Dir

SOE 0.33 7.12

SPE-C 0.62 8.23

SPE-M 0.26 7.60

11 Dir

SOE

SPE-C

SPE-M

12 Dir

SOE

SPE-C

SPE-M

APPENDIX A: HOLDING-TIME STUDY RESULTS
14

Table A1 (cont’d). Comparison of results for direct analysis (Dir) with those

using salting-out (SOE), cartridge SPE (SPE-C) and membrane SPE (SPE-M) for

groundwater samples from NSWC.

Concentration (μg/L)

Sample Type HMX RDX TNB DNB DNA TNT 24D 4A 2A

13 Dir

SOE

SPE-C

SPE-M

14 Dir 13

SOE 5.98

SPE-C 12.0

SPE-M 11.6

15 Dir

SOE

SPE-C

SPE-M

16 Dir 40

SOE 0.58 28.7 0.04 0.39 0.13

SPE-C 0.77 33.8 0.03 0.43 0.17

SPE-M 0.66 32.7 0.03 0.44 0.22

17 Dir

SOE

SPE-C

SPE-M

18 Dir 165 58 9 7

SOE 141 39.1 0.80 0.96 8.5 5.62

SPE-C 152 44.4 0.93 0.88 9.5 7.01

SPE-M 138 40.9 0.90 0.9 99.3 6.03

19 Dir 173 76 17 59 54

SOE 172 69.5 2.6 23.1 1.20 65.2 56.4

SPE-C 142 75.6 0.11 2.5 20.9 1.08 57.7 50.5

SPE-M 136 72.7 0.11 2.4 20.3 1.23 55.0 48.0

20 Dir

SOE

SPE-C

SPE-M

21 Dir 252 157 5 110 47 65

SOE 227 132 6.62 0.30 102 42.6 56.5

SPE-C 238 146 6.90 0.33 104 48.0 63.5

SPE-M 226 141 6.45 0.31 102 47.0 61.8

22 Dir 218 40

SOE 201 35.9 2.20 1.90

SPE-C 203 36.5 2.74 2.24

SPE-M 199 35.8 2.78 2.08

23 Dir

SOE

SPE-C

SPE-M

24 Dir

SOE 2.15 7.54

SPE-C 2.47 8.91

SPE-M 2.34 8.84

25 Dir

SOE

SPE-C 0.59

SPE-M 0.63
Table A1 (cont’d).

Concentration (μg/L)

Sample Type HMX RDX TNB DNB DNA TNT 24D 4A 2A

26 Dir

SOE

SPE-C

SPE-M

27 Dir 112 608 8 180 10 8

SOE 82.8 429 4.45 0.79 137 7.71 6.20

SPE-C 91.0 510 9.53 0.90 149 8.25 7.67

SPE-M 77.3 445 7.37 0.79 128 8.16 6.33

28 Dir 325 102 14 51 40

SOE 290 87.5 0.37 0.10 5.6 13.9 42.3 33.5

SPE-C 319 109 0.87 0.17 7.5 22.0 56.2 45.0

SPE-M 249 85.7 0.65 0.13 6.1 17.2 43.0 34.5

29 Dir

SOE

SPE-C 0.43

SPE-M 0.28

30 Dir

SOE

SPE-C

SPE-M

31 Dir

SOE 0.21

SPE-M 0.23

32 Dir

SOE

SPE-C

SPE-M 0.38

33 Dir

SOE

SPE-C

SPE-M

15
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Analysis RDX TNT

Explosives Salting out Water

Preconcentration Solid-phase extraction

September 1995

Evaluation of Clean Solid Phases for Extraction of

Nitroaromatics and Nitramines from Water

Thomas F. Jenkins, Philip G. Thorne, Karen F. Myers, Erika F. McCormick,

Don E. Parker and B. Lynn Escalon

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road Special Report 95-22

Hanover, New Hampshire 03755-1290

U.S. Army Environmental Center SFIM-AEC-ET-CR-95037

Aberdeen, Maryland

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161.

Salting-out solvent extraction (SOE) was compared with cartridge and membrane solid-phase extraction (SPE) for

preconcentration of nitroaromatics, nitramines, and aminonitroaromatics prior to determination by reversed-phase

high-performance liquid chromatography. The solid phases used were manufacturer-cleaned materials: Porapak

RDX for the cartridge method and Empore SDB-RPS for the membrane method. Thirty-three groundwater samples

from the Naval Surface Warfare Center, Crane, Indiana, were analyzed using the direct analysis protocol specified

in SW846 Method 8330, and the results were compared with analyses conducted after preconcentration using SOE

with acetonitrile, cartridge-based SPE, and membrane-based SPE. For high-concentration samples, analytical results from the three preconcentration techniques were compared with results from the direct analysis protocol;

good recovery of all target analytes was achieved by all three preconcentration methods. For low-concentration

samples, results from the two SPE methods were correlated with results from the SOE method; very similar data

was obtained by the SOE and SPE methods, even at concentrations well below 1 μg/L. The large chromatographic

interferences observed for the SPE methods in an earlier study using less clean materials were largely absent here.

A small interference was observed for both SPE methods at the retention time of RDX on the primary analysis column that translated to concentrations ranging from 0.2 to 0.6 μg/L RDX. Detection limits for RDX should be raised

to 0.6 μg/L if the SPE methods are used for preconcentration due to this potential interference. We recommend that

solid-phase extraction be included as an option in SW846 Method 8330 as well as SOE.