SPECIAL REPORT 95-20

Development of a Field Method for

Quantifying Ammonium Picrate and

Picric Acid in Soil and Water

Philip G. Thorne and Thomas F. Jenkins August 1995
Abstract

Methods for the detection and quantification of ammonium picrate and picric acid in soil and water were developed. Picrate ions were extracted from

water directly or from acetone extracts of soil by solid-phase, acidic, ionexchange materials. Elution from the ion exchangers was accomplished by

converting the retained picrate to picric acid using strong aqueous, acid–

organic solvent mixtures. The resulting colorless solution was then converted back to a colored picrate solution by dilution with water. Quantification and correction for background interferences were based on spectrophotometric measurements. A colorimetric, chemical confirmation of picrate was possible for the water method. The method detection limits were

determined to be 1.3 μg/g for soil and 3.6 μg/L for water. Both methods

can be implemented under field conditions.

For conversion of SI units to non-SI units of measurement consult ASTM

Standard E380-93, Standard Practice for Use of the International System

of Units, published by the American Society for Testing and Materials,

1916 Race St., Philadelphia, Pa. 19103.

This report is printed on paper that contains a minimum of 50% recycled

material.
Special Report 95-20

Development of a Field Method for

Quantifying Ammonium Picrate and

Picric Acid in Soil and Water

Philip G. Thorne and Thomas F. Jenkins August 1995

Prepared for

U.S. ARMY ENVIRONMENTAL CENTER

SFIM-AEC-ET-CR-95010

Approved for public release; distribution is unlimited.

US Army Corps

of Engineers

Cold Regions Research &

Engineering Laboratory
PREFACE

This report was prepared by Philip G. Thorne, Research Physical Scientist, and Thomas

F. Jenkins, Research Chemist, 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, Aberdeen Proving Ground, Maryland, Martin H. Stutz, project monitor.

The authors gratefully acknowledge Dr. Clarence L. Grant, Professor Emeritus, University of New Hampshire, and Marianne E. Walsh, CRREL, for their technical reviews of this

manuscript.

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.

ii
CONTENTS

Page

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

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

Source, fate and toxicology of ammonium picrate and picric acid ...................... 1

Previous analytical methods ....................................................................................... 2

Objectives ....................................................................................................................... 3

Experimental methods...................................................................................................... 3

Results ................................................................................................................................. 3

Field screening in soil .................................................................................................. 3

Field screening in water .............................................................................................. 7

Performance evaluations ............................................................................................. 8

Coordination with existing methods ......................................................................... 9

Immunoassays for picrate in soil and water ................................................................. 10

Conclusions ........................................................................................................................ 10

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

Appendix A: Method documentation: Field method for determination of

ammonium picrate and picric acid in soil ........................................................... 13

Appendix B: Method documentation: Field method for determination of

ammonium picrate and picric acid in water ....................................................... 18

Abstract ............................................................................................................................... 22

ILLUSTRATIONS

Figure

1. Chemical structures of picric acid, picrate ion and ammonium picrate ......... 1

2. Chemical structure of Dinoseb ............................................................................... 3

3. Absorbances for picrate in acetone and water ..................................................... 4

4. Recoveries of picrate from Hawthorne soils by sequential 10-mL

extractions ............................................................................................................... 4

5. Dependence of picrate absorbance on water content of acetone. ..................... 5

6. Absorbance curves for humic acid and picrate ion in 75% acetone–H2SO4 ... 6

7. Calibration curves for soil and water methods ................................................... 7

8. Formation of the colored Meisenheimer anion from picric acid ...................... 8

9. Comparison between field methods and RP-HPLC determination of

picrate ...................................................................................................................... 9

TABLES

Table

1. Recovery of 4.8 μg/mL picrate from water–acetone mixtures ......................... 5

2. Comparison of picric acid determinations between field screening

method and HPLC ................................................................................................ 9

3. Cross-reactivities of commercial TNT immunoassays ....................................... 10

iii
OH

O 2 NO2

NO2

Picric Acid

O 2

NO2

NO2

ONH 4

Ammonium Picrate

H or NH +

4

+

Picrate Ion

O 2

NO2

NO2

O ––

INTRODUCTION

Source, fate and toxicology of

ammonium picrate and picric acid

Ammonium picrate (ammonium 2,4,6-trinitrophenoxide, CAS 131-74-8)—Explosive D—was

used in armor-piercing shells, bombs and rocket

warheads by the U.S. military from the turn of the

century to after World War II. It is no longer manufactured but now represents 8% of the demilitarization inventory. Picric acid (2,4,6-trinitrophenol,

CAS 88-89-1) was used as a grenade and mine

filling (Meyer 1987) (Fig. 1).

Layton et al. (1987) reported comprehensively

on the production, toxicology and environmental

fate of ammonium picrate and its parent compound, picric acid. When dissolved in water, both

ammonium picrate and picric acid dissociate to

the picrate ion. Aqueous solubilities for both compounds are over 10 g/L, and they appear to present

an extremely mobile environmental contaminant.

Goodfellow et al. (1983) showed that the partitioning of picrate from estuarine water to organic

sediment was very low. This follows from the low

octanol–water partition coefficient for picric acid

(log Kow = 1.6) (Layton et al. 1987).

On the other hand, Layton et al. (1987) predicted

that picrate will act like phenolic pesticides

and become incorporated into or bound to

humic substances. Chang and Anderson

(1968) studied the flocculation of clays by

picric acid and found that the degree of flocculation depended on the nature of the clay

and associated ions. When picric acid was

mixed with solutions containing calcium ion

and calcium clays, flocculation occurred rapidly and completely, removing picrate from

solution. Mixtures containing sodium ions

and sodium clays formed stable suspensions,

Development of a Field Method for Quantifying

Ammonium Picrate and Picric Acid in Soil and Water

PHILIP G. THORNE AND THOMAS F. JENKINS

Figure 1. Chemical structures of picric acid, picrate ion and

ammonium picrate.

with picrate remaining in solution. Mixtures of

sodium ions with calcium clays or calcium ions

with sodium clays produced intermediate effects.

These experimental studies suggest that transport

of picrate in the environment will be highly variable, depending on the organic and mineral composition of each soil. Kayser and Burlinson (1988)

found that picrate migrated through four soils in

lysimeter studies. Van Denburgh (reported in

Layton et al. 1987) found that picrate had migrated

from a disposal bed at an ammunition plant.

Ruchholt and Norris (1946) reported finding one

soil that retained “appreciable” amounts of picrate.

Most of the toxicological work reported by

Layton et al. (1987) was on skin adsorption and

inhalation of ammonium picrate dust. Few data

were available on the chronic effects of ingestion

of picrate. The most recent research (Wyman et al.

1992) deals with lethal-dose determinations. The

EPA has not set an action level for ammonium

picrate or picric acid in soil or water. Layton et al.

(1987) estimated an Allowable Daily Intake (ADI)

of 1–37 μg/kg-d. Since the estimated ADI is similar to other secondary explosives, similar field detection limits were sought in this research (i.e.,

low μg/g in soil and low μg/L in water). There is

potential for picric acid to be transformed to

OH

H or NH4

+ +

N N N
picramic acid (2-amino-4,6-dinitrophenol) by

adapted bacteria under the anaerobic conditions

that might be found at some waste sites. This compound has ten times the mutagenicity of picric

acid (Wyman et al. 1979). The toxic effects on

aquatic organisms are also greater for picramic

acid than for picric acid (Goodfellow et al. 1983).

Picramic acid is also a mammalian metabolic transformation product of picric acid (Barral 1915,

Wyman et al. 1992) and is excreted in the urine. It

will be introduced into the environment if picric

acid is ingested.

Unlike many of the other high explosives that

are no longer manufactured and that present environmental clean-up problems unique to the military, picric acid is a ubiquitous industrial chemical. It is widely used as a metal-etching chemical

and as feed stock in many processes in the dye,

leather and glass industries (Wyman et al. 1992).

Picrate is also an environmental transformation

product of tetryl, another obsolete military explosive (Kayser et al. 1984). Picrate was detected in a

leachate from soil columns spiked with tetryl

(Kayser and Burlinson 1988) and was recently detected as a transformation product of tetryl in water (Jenkins et al. 1995). A rapid screening method

for the detection of picrate in soil and water will

have broad utility. Indications are that it is not

degraded in the environment, either biologically

or photochemically (Layton et al. 1987), although

some strains of adapted organisms may make

bioremediation a possibility (Wyman et al. 1979,

Lenke and Knackmuss 1992).

Previous analytical methods

Detection of picric acid has been a goal of analytical chemists since the early 20th century, when

malingerers ingested picric acid to mimic the

symptoms of jaundice to avoid military service.

Early detection schemes used colored precipitates

(Barral 1915), colored solvent interfaces (Rodillon

1915) or colored solutions (Ydrac 1916) to identify

picric acid and its metabolic by-product, picramic

acid. In 1923, Deniges investigated the unique

color-changing behavior of the picric acid–picrate

system in aqueous and strongly acidic, organic

solutions.

Forensic analysts have been required to identify and quantify picric acid in complex mixtures

of other nitroaromatic explosives. Paper chromatography (Barnabas 1954, Colman 1962) or thinlayer chromatography (Parihar et al. 1966, Bagnato

and Grasso 1986) were used to separate picric acid

from other explosives, where it was detected by

color-forming reagents. Quantification was possible using a photodensitometer (Wyman et al. 1979).

Contemporary analytical methods for the determination of picrate in the environment have

focused on extraction, separation from matrix components and analysis in the laboratory. U.S. Geological Survey methods (Goerlitz 1979) used benzene or methylene chloride for extraction from soils

and water, followed by concentration, solvent exchange and reverse-phase, high-performance liquid chromatography (RP-HPLC) with eluents containing an ion-pairing reagent. U.S. Army Environmental Center (USAEC) Method LW-13 (1989)

used a 10% aqueous methanol solution for extraction from soil, followed by analysis by RP-HPLC.

Methylene chloride was used to extract picric acid

from acidified water samples, followed by concentration, solvent exchange and analysis by RPHPLC using a buffered, acidic aqueous–acetonitrile eluent. Midwest Research Institute methods

(Conrad 1990a,b) used ion-pairing and solid-phase

extraction of picrate ion pairs from water, followed

by ion-pair analysis using HPLC with a polycyclic

aromatic hydrocarbon column. Picrate was extracted from soils with an acidic methanol–water

mixture and analyzed by RP-HPLC using ion-pairing conditions. Lloyd (1985) used RP-HPLC with

a buffered, acidic aqueous–methanol eluent to detect picrate and other high explosives from forensic samples. Voyksner and Yinon (1986) used

thermospray HPLC-mass spectrometry with

chemical ionization to analyze acetone wipes of

skin contaminated with six high explosives, including picric acid. Munder et al. (1990) developed a capillary supercritical fluid chromatographic technique that could resolve picric acid

from other explosives in complex mixtures.

Ammonium picrate and picric acid are not currently target analytes in SW846 Method 8330

(USEPA 1990). If the standard conditions for extraction and analysis of explosives in soil from

Method 8330 are used, picrate would be extracted

by overnight sonication in acetonitrile but would

not be retained by the RP-HPLC with a 50% aqueous–methanol eluent. Method 8330 for water uses

the same separation, and hence, picrate would not

be detected using this protocol.

A field screening method for Dinoseb (2-secbutyl-4,6-dinitrophenol, CAS 88-85-7) in soil was

developed by Anderson et al. (1993). Dinoseb is a

pesticide that is structurally similar to picric acid

but is less acidic and more hydrophobic (Fig. 2). In

this method, soil is extracted with methylene chloride and the extract is mixed with Florisil, a basic,

2
vironmental Center. Field-contaminated soils from

Hawthorne Army Ammunition Plant (AAP),

Hawthorne, Nevada; Naval Surface Warfare Center (NSWC), Crane, Indiana; and Nebraska Ordinance Plant, Mead, Nebraska, were used to test

the methods. Well waters from NSWC were also

used.

All solvents used for extraction, collection and

elution were HPLC-grade from Baker. Reagentgrade water was prepared using a Milli-Q Type 1

Reagent-Grade Water System (Millipore). The

solid-phase extraction (SPE) materials were Florisil

(Supelco), Alumina-A SPE cartridges (3 mL-1 g,

Supelco) and Anion-Empore SPE membranes (47

mm, 3M-Varian). The syringe filters were Millex

SR (0.45 μm, 25 mm, Millipore). Immunoassay kits

for TNT were EnviroGard (Millipore) and D-TECH

(EM Science). The color reagent for nitroaromatics

was from the TNT kit from EnSys (Research Triangle Park, North Carolina).

Analyses of picrate and other explosives were

performed by RP-HPLC on a 25- × 4.6-cm (5 μm)

LC-18 (Supelco) column. The analytes were eluted

using 1.5 mL/min of 60:40 (v/v) aqueous

buffer:methanol. The buffer was 0.05 M KH2PO4,

adjusted to pH 3.5 with acetic acid. The analytes

were detected at 365 nm for picrate and 254 nm

for all others. The spectrophotometer used for the

field method was a battery-powered Hach DR2000 (Loveland, Colorado).

RESULTS

Field screening in soil

Extraction conditions

An initial experiment investigated the potential for adapting the Dinoseb/Florisil method

(Anderson et al. 1993) for the detection of ammonium picrate and picric acid. When picric acid was

dissolved in MeCl2, it produced a colorless solution characteristic of solvated, but undissociated,

picric acid (Majersky and Dybalova 1975). When

white Florisil powder was added, the solution remained colorless while the powder turned a brilliant yellow. The color was due to the formation of

picrate ion pairs on the basic sorption sites of the

Florisil.

The application of this ion-exchange reaction

to soil samples was then investigated using 2 g of

soil mixed with 5 mL of MeCL2 in a 22-mL glass

vial. When wetted soils were extracted, phase separation of the MeCL2 was difficult to achieve if there

O 2

NO2

OH CH3

CH – CH – CH 2 2 3

Figure 2. Chemical structure of

Dinoseb.

normal-phase extraction material. When Dinoseb

is present, the white Florisil turns yellow. A visual

detection limit of 5 μg/g was reported; however,

quantification of contamination at higher levels

was not suggested.

Objectives

The major goal of this effort was to develop a

field screening method for ammonium picrate and

picric acid that could be used in conjunction with

field screening methods already established for

the high explosives RDX, TNT and 2,4-DNT

(Jenkins and Walsh 1992, Jenkins et al. 1994). If

detection limits and action levels are similar, qualitative identification and confirmation of picrate in

soil and water is a reasonable stopping point for a

screening method. However, if the screening can

be semiquantitative or quantitative, then site managers can be alerted to contaminant levels that

might produce a significant release if the site is

further disturbed. This is particularly true in the

case of picrate, where it could conceivably be exposed to water after having been sequestered in

clay or sheltered from rain by pavement or buildings. Furthermore, it is hoped that a rapid and

inexpensive field test will allow screening for

picrate at nonmilitary sites.

The strategy that was employed in this research

was to investigate the adaptability of some existing screening methods that detect related compounds and to develop new methods based on

the behavior of picric acid as it changes from a

colorless, undissociated acid to a yellow picrate

ion. The other characteristic of picrate that might

allow selective separation from other yellow compounds discussed below is its high acidity. Ion

exchange materials and binding and elution conditions were sought that would retain, then release,

picrate ions selectively, free from interferences.

EXPERIMENTAL METHODS

Analytes used for spikes were Standard Analytical Reference Material from the U.S. Army EnN

3
was any fresh plant material or humus present.

This problem could be overcome with larger volumes of solvent, but this seemed environmentally

unwise. Since MeCl2 is denser than water, it collects at the bottom of extraction vessels, dictating

the use of separatory funnels. These are expensive

and difficult to use and clean in the field. Several

other less-toxic solvents with densities less than

water were tried to see if they would extract picric

acid and exchange it onto Florisil. Isooctane produced a clear extract that, when picric acid was

present, turned Florisil yellow, but the extraction

efficiency of picric acid from a field-contaminated

soil was very low. Ethyl ether was an efficient extractant but resulted in a yellow extract, since it

also dissolves some aqueous picrate ions. No exchange with Florisil was apparent. No further experiments were conducted using nonpolar solvents and Florisil.

Several polar solvents (acetone, methanol, isopropanol, acetonitrile and water) were used to

extract a soil from Hawthorne AAP known to be

contaminated with picric acid. All extracts were

yellow. By far the brightest yellows resulted from

the acetone and water extractions. This soil had a

moisture content of 4%, so standard curves for

picrate in 96% acetone/4% water and 100% water

were constructed and showed a linear relationship between absorbance at 400 nm and concentration (Fig. 3). The visual detection threshold for

picrate in an acetone or water extract corresponds

to a soil contamination value of approximately 5

μg/g. The extraction efficiencies of acetone and

water were then determined. A 2-g sample of soil

was placed in a 22-mL glass vial with 10 mL of

extractant and shaken manually for three minutes.

The vials were then centrifuged for three minutes

and the extractant decanted and filtered through

a 0.45-μm Millex SR syringe filter. The quantity of

picrate extracted was determined spectrophotometrically. Further aliquots (10 mL) of extractant

were added to the soil and the procedure repeated

until no more yellow color was extracted. Since

the acetone extractions appeared to reach a plateau, the vial containing the tenth aliquot was

placed in a sonic bath overnight. This process removed the remaining picrate. Recoveries of picrate

from this soil were calculated as a normalized percentage based on the total amount recovered from

each sample. The percent recoveries in the first

10-mL aliquot were 89% for acetone and 90% for

water (Fig. 4).

Selection of ion exchange materials and

binding and elution conditions

Two ion-exchange materials were chosen for

investigation. Alumina-A solid-phase extraction

cartridges are used in the RDX field method

(Jenkins and Walsh 1992). Empore Anion extraction membranes were selected because they have

an allowable flow rate approximately 20 times

greater than the extraction cartridges and would

provide a different exchange chemistry. Solutions

containing 1 μg/mL of picric acid in acetone or

water were passed over Empore Anion membranes

and Alumina-A cartridges. For the acetone solutions, both sorbants became yellow, indicating the

retention of picrate ions. The Anion membrane

Overnight Sonic Extraction

88

90

92

94

96

98

100

Percent Recovery

0 20 40 60 80 100 120

Extractant (mL)

Water

Acetone

Figure 4. Recoveries of picrate from Hawthorne soils

by sequential 10-mL extractions.

Figure 3. Absorbances for picrate in acetone and

water.

0.2

0.4

0.6

0.8

1.0

1.2

Absorbance/cm @400 nm

0 10 20 30

Picrate (μg/mL)

Water

96% Acetone

4
was more intensely yellow than the Alumina-A

since all the picrate was sorbed on the top surface,

as opposed to being distributed within the sorbant

bed of the cartridge. The Alumina-A did not retain picrate from water only, whereas the Anion

membrane showed its greatest retention from

water.

Both sorbants that retain picrate are ion-exchange materials; therefore, elution and quantification of the picrate is feasible. For the Anion disk,

10% concentrated sulfuric acid/methanol (v/v),

and for the Alumina-A cartridge 2% concentrated

sulfuric acid/acetone (v/v), were the mildest conditions that resulted in elution. Lower concentrations of acids, different acids or different solvents

were not successful. Under conditions of such high

acidity, the picrate is converted to undissociated

picric acid and is colorless, as it is in MeCl2. The

eluted solution is filtered through a Millex SR

syringe filter placed on the tip of the cartridge,

then diluted with water until the pH was raised

above the pKa of picric acid, resulting in the formation of the colored picrate anion. This enabled

both quantification using a field-portable spectrophotometer and confirmation by the unique colorchanging behavior of picric acid to picrate (Deniges

1923). The eluent from the Empore Anion membrane did not require additional filtration.

Optimization of conditions

Although the Empore Anion membrane did

retain picrate from both acetone and aqueous extracts, it was not chosen for the soil method because one membrane costs nearly ten times as

much as one Alumina-A cartridge.

Acetone extracts of field-moist soils will contain variable amounts of water. Since the initial

retention experiments showed that the AluminaA cartridge did not retain picrate from water alone,

an additional test was run to determine what percentage of water in acetone would result in the

maximum retention of picrate. The results are

listed in Table 1. The maximum occurred at a broad

plateau around 50% water. The sharp rise in recovery from low water contents to 50% indicated

that extracts of field-moist soils would produce

unpredictable results if not diluted with water up

to the 50% plateau.

The field methods for TNT, 2,4DNT and RDX

specify the use of 100 mL of acetone to extract 20 g

of soil. These methods use about 60 mL of the

common extract for analyses. This leaves 40 mL

for the picrate assay. Since it is difficult to remove

all of the remaining acetone from the extraction

bottle, 30 mL of acetone extract diluted one-to-one

with water was chosen for subsequent tests.

Further increases in recovery were realized by

optimizing extraction and elution conditions.

Breakthrough tests were conducted at different extraction rates using 60 mL of a 50% aqueous–acetone solution fortified with picric acid. At a flow

rate of 10 mL/min, about 4% of the picrate was

not retained. The loss increased from 4% to 13%

when the flow rate was increased to 40 mL/min.

Elution with a 10-mL aliquot of 2% H2SO4–acetone

at a flow rate of 5 mL/min was sufficient to recover 88–91% of the retained picrate.

To achieve the brightest color for quantification, as much acetone as possible should be used

with the minimum water to drive the ionization

and subsequent color change. The absorbance of

picrate in acetone is highly dependent on the water content (Fig. 5). Once sufficient water is present,

additional water only dilutes the sample and reduces the color. However, the amount of water

that gives the highest absorbance is in a very narrow peak of the curve. Precise measurement

would then be critical to duplicate the predicted

Table 1. Recovery of 4.8 μg/mL picrate from water–acetone mixtures.

Water–acetone Recovery of picrate

(%) (%)

8 4

25 38

50 86

75 85

Figure 5. Dependence of picrate absorbance on water content of acetone.

0.5

1.0

1.5

Absorbance/2.5 cm @ 400 nm

0 20 40 60 80 100 120

Percent Water

2 μg/mL

4 μg/mL

6 μg/mL 

10 μg/mL

5
calibration. A water content of 25% will give a

reasonable value while being at the least sensitive

part of the curve. Thus, small measurement errors

that may occur under adverse field conditions

would not have large effects on calculated results.

Potential interferences

Three environmental transformation products

of TNT that produce yellow acetone extracts are

3,5-DNA, 2ADNT and 4ADNT. Maximum reported concentrations of these chemicals in explosives-contaminated soils (373 μg/g for 2ADNT

and 14 μg/g for 3,5-DNA) were obtained from a

report documenting analytical results for a number of soil samples from explosives-contaminated

sites in the U.S. (Walsh et al. 1993). When these

chemicals in an acetone–water solution at concentrations above the maximum reported levels were

extracted with an Alumina-A cartridge, the yellow color was retained on the sorbant. A rinse with

3 mL of methanol removed all traces of the color.

An additional rinse with 3 mL of acetone removed

the methanol and returned the cartridge to the

original extraction conditions, ready for the elution step. When subsequent eluents were analyzed

by RP-HPLC, none of these analytes were detected.

Thus these compounds do not interfere in this

method.

Another source of yellow in acetone soil extracts is elemental sulfur.* The yellow color from a

sulfurous acetone extract from an anaerobic Eagle

River Flats, Alaska, sediment was not retained on

Alumina-A.

The presence of humic materials in soil extracts

was found to be a problem because these compounds are also highly colored acids which are

retained by acidic ion exchangers. Some humic

substances were eluted along with the picrate. The

quantity of eluted humic color was highly variable (from 14 to 45% of the applied material) and

absorbed strongly in the 400-nm region, where

picrate absorbance is at its maximum for the

HACH spectrophotometer (Fig. 6). However, since

the development of the picrate color requires a

dilution of the eluent with water, a background correction scheme was used. As previously optimized,

3.3 mL of water was needed to maximize the yellow color of the diluted 10 mL of eluent (producing a 13.3-mL mixture of 25% aqueous–acetone).

This dilution would reduce the absorbance of the

* M.E. Walsh, U.S. Army Cold Regions Research and

Engineering Laboratory, personal communication, 1994.

humic materials by 25%. It was decided that a 50%

reduction in interfering absorbances would produce a more reliable correction factor. This could

be achieved by adding 5 mL of unacidified acetone followed by 5 mL of water to the 10 mL of

acidic eluent (producing a 20-mL mixture of 25%

aqueous acetone). The absorbance of the initial 10

mL of eluent is divided by the factor-of-two dilution and subtracted from the final absorbance of

the 20 mL of acetone–water mixture.

This background scheme also provides an important confirmation step to the method. The addition of 5 mL of unacidified acetone will cause a

visible decrease in the absorbance of colored eluents. The subsequent addition of 5 mL of water

will then cause a visible increase in yellow if picrate

is present.

Method detection limit

To establish the method detection limit (MDL)

(USEPA 1984) for this method, a locally acquired

sand was fortified by adding aqueous picrate solutions to the air-dried soil such that the resulting

moisture content was 10%. A standard curve was

constructed by processing 22-g samples that had

been fortified with a range of picrate concentrations plus a blank sample. The curve that was calculated using a standard regression model had a

very small, non-zero intercept. If absorbance readings were rounded to the nearest 0.01, this intercept became insignificant. Resulting picrate values should be reported using two significant digits. The quantity of picric acid based on a dry weight

of 20 g of soil, extracted with 100 mL of acetone

and quantified with a 1-cm path-length cell, was:

0

0.2

0.4

0.6

0.8

Absorbance/cm

360 460 560

Wavelength

4 μg/mL Picrate

28 μg/mL Humic Acid

Figure 6. Absorbance curves for humic acid and

picrate ion in 75% acetone–H2SO4.

6
picric acid (μg/g) = 91 (μg/g-ABS unit)

× (Final ABS @400 nm – 0.5

× Initial ABS @ 400 nm) (Fig. 7).

The computation of the MDL was based on the

replicate extractions of seven 22-g samples of locally acquired sandy loam that had been fortified

with 5 μg/g of picric acid. After a few minutes

settling time, 30 mL of the acetone extract was filtered using a 0.45-μm Millex SR syringe filter, then

diluted with 30 mL of reagent-grade water. The

diluted extract was then passed through an Alumina-A cartridge using a 60-mL syringe at 10 mL/

min. The cartridge was rinsed with 3 mL of methanol followed by 3 mL of acetone using a 10-mL

syringe. A 10-mL aliquot of 2% H2SO4–acetone was

then passed through the cartridge at 5 mL/min

using a 10-mL syringe. The eluent was collected

through another 0.45-μm Millex-SR syringe filter

attached to the tip of the cartridge. The initial absorbance at 400 nm was recorded. An additional

5-mL aliquot of unacidified acetone was added to

the extract. This dilution resulted in a visible decrease in the yellowish humus-derived color of

the initial extract. Then 5 mL of reagent-grade

water was added and the resulting deeper yellow

color measured at 400 nm. The resulting MDL was

1.3 μg/g.

A field screening method that includes a quantification step requires a daily check standard for

validation. An aqueous, unacidified standard at

10 μg/mL of picric acid is stable for at least two

weeks. A simulated soil extract is prepared by diluting a 30-mL aliquot of this standard one-to-one

with acetone. This mixture is then extracted and

eluted according to the method. The absorbance/

cm at 400 nm should be 0.56 ± 0.08.

Field screening in water

Selection of ion-exchange material

and extraction and elution conditions

Initial tests with the basic ion-exchange materials indicated that the Anion membrane retained

picrate from water but the Alumina-A cartridge

did not. Thus development of the screening

method for water utilized the Anion membrane.

A 2-L water sample fortified with 2 μg/L of

picric acid was extracted with the Anion membrane in 20 minutes. The membrane turned yellow. Microscopic examination of a cross section of

the membrane showed that all of the picrate was

retained on the top surface of the membrane. One

5-mL aliquot of 10% H2SO4–methanol was added

to the extraction apparatus and allowed to soak

the membrane for three minutes. Vacuum was applied and the extraction solution pulled into a test

tube placed beneath the membrane holder. This

procedure removed most of the yellow color from

the membrane, producing a colorless solution of

undissociated picric acid. Some picrate remained

in the ring of membrane that was clamped between the top and bottom of the extraction apparatus. This could be recovered by removing the

reservoir top and pouring a few milliliters of extraction solution on the surface of the membrane,

allowing that to soak, then pulling it through the

membrane by vacuum. This procedure required

some care and did not appear to be worthwhile

for a field method. The additional recovery was in

a more dilute solution than the original 5 mL of

extract, reducing the overall absorptivity of the

combined extracts. An addition of 5 mL of reagentgrade water produced the maximum yellow color

from the picrate ion.

A breakthrough test was performed using reagent-grade water fortified with 20,000 μg/L of

picric acid. The run-through was measured using

RP-HPLC. No breakthrough was observed when

2 L of water at this concentration was extracted.

Potential interferences

The same yellow TNT transformation products

that were retained by the Alumina-A (two isomers

of amino-DNT and 3,5-DNA) were also retained

by the Anion membrane. A 5-mL methanol wash

removed these from the membrane without eluting any picrate.

Humic acids produced the same problems in

the water method as in the soil method. Humic

material was retained by the Anion membrane,

Figure 7. Calibration curves for soil and water methods. then eluted by the acidified solvent. Fortunately

0.2

0.4

0.6

0.8

0 100 200

Water (μg/L)

Soil (μg/g)

Picric Acid in Soil and Water (RP–HPLC)

Absorbance/cm @ 400 nm

7
the required 50% dilution of the 5-mL eluent provided a background correction factor similar to

the soil method.

Qualitative confirmation of picrate

The extraction of 2 L of reagent-grade water

fortified with 2 μg/L of picrate produced a visibly

yellow surface on the Anion membrane. A lack of

any yellow color on the membrane is an indication that less than 2 μg/L of picrate is present in

the sample. If there is a yellow color remaining

after the methanol rinse, it could be picrate at a

level above 2 μg/L. Since picric acid is a nitroaromatic, it forms a colored Meisenheimer anion

when exposed to the Janowsky conditions of a

basic ketone solution (Kabeya et al. 1973) (Fig. 8).

Experiments were performed to see if this reaction would occur with the sorbed picrate. A quaternary ammonium salt reagent commercially

available as part of the EnSys TNT detection kit

was used to confirm the presence of picric acid on

the surface of the Anion membrane, both with and

without brown humic interferences. An additional

acetone rinse was added after the methanol rinse.

One or two drops of EnSys reagent was then applied and the color observed. When the Anion

membrane was yellow or brown, the Ensys reagent turned a noticeable pink or dark rust, respectively, confirming that the yellow color was

due to a nitroaromatic.

This colorimetric confirmation scheme was tried

for the soil method; however, in the cartridges the

yellow was dispersed throughout a few millimeters of the sorbant bed so that the pink that was

produced was barely discernible, even when there

were no brown interferences. The presence of any

brown completely obscured the pink EnSys color

in the cartridge.

Method detection limit

A standard curve was constructed by making a

series of 2-L solutions of reagent-grade water fortified with picric acid, plus a blank. The calculated

curve that resulted had a small non-zero intercept

similar to the curve calculated for the soil method.

This became insignificant when absorbances were

rounded to the nearest 0.01. Concentrations of

picric acid should be reported using two significant digits. For a 2-L water sample and a spectrophotometer with a 1-cm path-length cell:

picric acid (μg/L) = 280 (μg/L-ABS unit)

× (Final ABS @ 400 nm – 0.5

× Initial ABS @ 400 nm) (Fig. 7).

To estimate the MDL, a series of seven replicate

2-L well-water samples fortified with 7.5 μg/L of

picric acid were extracted, rinsed with 5 mL of

methanol, then eluted with 5 mL of 10% H2SO4–

methanol and the absorbance at 400 nm of the

resulting extract recorded. The extract was diluted

with 5 mL of reagent-grade water and the absorbance at 400 nm of the diluted extract obtained.

The MDL was 3.6 μg/L.

A daily calibration standard is made by diluting 30 mL of a 10 μg/mL aqueous solution of picric

acid to 2 L with reagent-grade water and performing the method. The absorbance/cm at 400 nm

should be 0.56 ± 0.03.

Performance evaluations

Soil method

The method was tested on field-contaminated

soils. The results are listed in Table 2. Soils from

Crane, Indiana, produced “straw-colored” acetone

extracts. Analyses by HPLC showed that they contained no picrate. The field screening method produced a very light yellow Alumina-A extract that

was reduced by dilution. The soil from Hawthorne

required a 360-fold dilution to fall within the linear range of the calibration curve. The soils from

Mead had been analyzed previously by Method

8330. The only detected analyte had been tetryl.

Both the field screening method and the HPLC

method using the buffered eluent system revealed

the presence of picrate. Since picrate is a hydrolysis product of tetryl (Kayser et al. 1984, Kayser

Figure 8. Formation of the colored Meisenheimer anion from picric acid.

Colorless

O 2

NO2

OH

NO2

Pink

OH

O 2

NO2

O

CH – C – CH 2 3

NO2

H

+

O

CH – C – CH 2 3

N – N

8
color upon addition of water indicated that little

or no picrate was present. Subsequent RP-HPLC

analysis confirmed the absence of picrate in all of

the samples.

A comparison between field method and RPHPLC determinations of picrate in contaminated

or fortified environmental matrices shows reasonable agreement (Fig. 9). Rigorous statistical evaluations can be made after more field samples are

analyzed. Future tests of the water method will

have to be conducted as part of a sampling plan

that considers the 2-L sample requirement.

Coordination with

existing methods

The soil method can be easily added to accepted

screening methods for the military explosives TNT

and RDX in soil (Jenkins and Walsh 1992). A single

100-mL acetone extract can be split for each of the

three tests. The Alumina-A cartridges are required

for the RDX test to remove interfering nitrates and

nitrites.

A field screening method for TNT and RDX in

water that uses Empore SDB membranes has been

proposed (Jenkins et al. 1994). Both that method

and the one proposed in this report require a

vacuum filtration apparatus. A hand-operated

vacuum pump can be used, but it requires constant pumping for at least 20 minutes for sediment-free samples. If sediment causes partial plugging of the membrane, the hand pump is inadequate. Realistically, a powered vacuum pump is

required to supply sufficient suction to extract 2-L

samples in a reasonable time.

Table 2. Comparison of picric acid determinations

between field screening method and HPLC.

Picric acid Picric acid Tetryl

screening HPLC HPLC

Sample (μg/g) (μg/g) (μg/g)

Crane162 0.0 0.0 0.0

Crane541 0.0 0.0 0.0

Hawthorne13 25,200 23,000 0.0

Mead42 1.9 1.0 60

Mead43 14.0 24.4 1265

Mead45 6.8 9.8 397

and Burlinson 1988, Jenkins et al. 1995), it is to be

expected in environmental samples contaminated

with tetryl.

Water method

The MDL determinations were performed using fortified well waters, which produced a slightly

brown acidic extract. As a worst-case example of

background interference due to dissolved humic

substances, this method was tested on river water

that had been fortified with 125 μg/L of tetryl and

allowed to sit at room temperature in the dark for

60 days. HPLC analysis showed that 64% of the

tetryl had degraded, producing 25 μg/L of picrate

plus several other unidentified products. The Anion membrane turned a dirty brown color when

this sample was extracted. Application of a drop

of EnSys reagent did produce a rusty colored spot.

Elution with 5 mL of 10% H2SO4–methanol produced a dark yellow-brown extract with an initial

absorbance at 400 nm of 1.3. The subsequent dilution with reagent-grade water and the final absorbance reading resulted in a calculated concentration of 39 μg/L of picric acid.

Water samples from 34 monitoring wells at the

Naval Surface Warfare Center in Crane, Indiana,

were screened for picrate using the proposed

method. Since there was only one 500-mL sample

available from each well, samples were composited

to make 2-L samples for extraction. All composites had been previously extracted for nonionic

explosives using Empore SDB extraction membranes, which do not retain picrate. The samples

at that point were colorless and free of sediment.

All the composites produced pink- or salmon-colored deposits on the Anion membranes. The addition of EnSys reagent did not produce a darker

spot. These deposits were removed by the acidified methanol, producing light yellow extracts

whose colors were reduced upon dilution with

water. A spectrophotometer was not used for quantification; however, the lack of a visible increase in

20

40

60

80

Picrate in Soil and Water (field methods)

0 20 40 60 80

Water Method

Soil Method 

Picric Acid in Soil and Water (RP–HPLC)

(μg/g)

(μg/L)

Figure 9. Comparison between field methods and

RP-HPLC determination of picrate.

9
extraction materials with a 70-year-old, qualitative colorimetric assay. The chemical confirmation

reagents used were also derived from work done

by chemists around the turn of the century (reviewed in Jenkins 1990). The resulting methods

are both sensitive and relatively free from interferences produced by humic substances or other

nitroaromatics that are likely to occur at military

sites. A single extract can be used to screen for

picric acid, ammonium picrate, TNT, 2,4DNT and

RDX in soils. The estimated cost of a few dollars

per sample is very low. Single assays can be run in

about 20 minutes. Multiple samples can be processed in less time using cartridge or membrane

manifolds.

Immunoassays are gaining increased acceptance in screening applications, although the costs

and time requirements can be significantly higher

than spectrophotometric methods. The positive

response to picric acid of two TNT immunoassays

presents two interesting possibilities. When a field

site is known to contain no nitroaromatics other

than picric acid or ammonium picrate, immunoassays could be used to screen for picrate. Although

this may be unusual at military sites, it should be

the case at industrial sites contaminated with

picric acid. Conversely, if a TNT immunoassay

gives a response that is greater than the sum of

TNT and other known cross-reactive analytes as

determined by Method 8330, unsuspected contamination by picric acid may be indicated.

LITERATURE CITED

Anderson, D., S.F. Tsang, T. Jackson and P.

Marsden (1993) Dinoseb analysis in the field and

the laboratory. In Proceedings of the 9th Annual Waste

Testing and Quality Assurance Symposium Proceedings, American Chemical Society, p. 347–359.

Bagnato, L. and G. Grasso (1986) Two-dimensional

thin-layer chromatography for the separation and

identification of nitro derivatives in explosives.

Journal of Chromatography, 357: 440–444.

Barnabas, J. (1954) Identification of phenols by

circular paper chromatography. Chemical Abstracts,

49: 10128.

Barral, E. (1915) Picric acid and malingering.

Chemical Abstracts, 10: 2100.

Colman, D.M. (1962) Paper chromatography of

nitro compounds. I. Substituted trinitrobenzenes.

Journal of Chromatography, 8: 399–403.

Deniges, G. (1923) Nature and application of the

Table 3. Cross-reactivities of

commercial TNT immunoassays.

Millipore D-TECH

Tetryl – +

2Am-DNT – +

4Am-DNT + –

TNB + +

2,6-DNT + –

2,4-DNT – +

IMMUNOASSAYS FOR

PICRATE IN SOIL AND WATER

Immunoassays are available commercially for

detecting TNT in soil extracts and water. A disadvantage of all immunoassays is that they also detect compounds that are structurally related to the

target analyte. This phenomenon is called crossreactivity. Antibodies are produced in response to

small molecules (molecular weight less than 200)

only after they have been conjugated to a large

carrier protein. Exactly how this conjugate is made

determines the sensitivity of the assay and the degree of cross-reactivity to various compounds

(Harrison et al. 1991). In the case of TNT, conjugates could be made by coupling a protein to either a reactive moiety at the 1- position (e.g.

trinitro-sulphonic acid) or at the 2- or 4- position

(2- or 4-aminodinitrotoluene). The antibody would

then tend to recognize either a trinitro-aromatic or

a dinitro-toluene, respectively. Judging from the

cross-reactivities listed on two commercial TNT

kits (Table 3), it was assumed that they were produced using these different schemes. A test of their

cross-reactivies to picrate showed that the

EnviroGard TNT plate kit was mildly responsive,

with a detection limit of about 2.5 μg/g in soil and

5 μg/L in water (the detection limit of TNT is 0.25

μg/g in soil and 0.5 μg/L in water). The D-TECH

kit was equally sensitive to TNT and picrate, with

detection limits of 0.2 μg/g in soil and 5 μg/L in

water.

CONCLUSIONS

The proposed methods (App. A and B) for field

screening for residues of picric acid or ammonium

picrate in soil and water resulted from the combined application of contemporary solid-phase

10
precipitate formed by strong acids in aqueous solutions of picric acid. Chemical Abstracts, 18: 2858.

Chang, C.W. and J.U. Anderson (1968) Flocculation of clays and soils by organic compounds. Soil

Science Society of America Proceedings, 32: 23–27.

Conrad, E. (1990a) Determination of munitions,

Group B, in water. Standard Operating Procedures

No. 103, Midwest Research Institute, St. Louis,

Missouri.

Conrad, E. (1990b) Determination of munitions,

Group B, in soils. Standard Operating Procedures

No. 104, Midwest Research Institute, St. Louis,

Missouri.

Goerlitz, D.F. (1979) Analysis of picric acid in water by high-performance liquid chromatography.

U.S. Geological Survey, Menlo Park, California,

Open-File Report 79-207.

Goodfellow, W.L., D.T. Burton, W.C. Graves,

L.W. Hall and K.R. Cooper (1983) Acute toxicity

of picric acid and picramic acid to rainbow trout,

Salmo gairdneri, and American oyster, Crassostrea

virginica. Water Resources Bulletin, 19: 641–648.

Harrison, R.O., M.H. Goodrow, S.J. Gee and B.D.

Hammock (1991) Hapten synthesis for pesticide

immunoassay development. In Immunoassays for

Trace Chemical Analysis (M. Vanderlaan, L.H.

Stanker, B.E. Watkins and D.W. Roberts, Ed.), ACS

Symposium Series 451, American Chemical Society, Washington, D.C.

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 (1992) Development

of field screening methods for TNT, 2,4-DNT and

RDX in soil. Talanta, 39(4): 419–428.

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

Field screening method for TNT and RDX in

groundwater. USA Cold Regions Research and Engineering Laboratory, Special Report 94-14.

Jenkins, T.F., P.G. Thorne, K.F. Myers and E.F.

McCormick (1995) Preservation of water samples

containing nitroaromatics and nitramines. USA

Cold Regions Research and Engineering Laboratory, Special Report 95-16.

Kabeya, T., K. Kohashi, Y. Ohkura and T. Momose

(1973) Mechanism of the color reaction of active

methyene compounds with 1,3,5-trinitrobenzene

derivatives. IV. Color reaction of picric acid and

acetone under Janovsky conditions. Chemical Pharmacology Bulletin, 21(10): 2168–2174.

Kayser, E. and N.E. Burlinson (1988) Migration of

explosives in soil: Analysis of RDX, TNT and tetryl

from 14C lysimeter study. Journal of Energetic Materials, 6: 45–71.

Kayser, E., N.E. Burlinson and D.H. Rosenblatt

(1984) Kinetics of hydrolysis and products of hydrolysis and photolysis of tetryl. Naval Surface

Weapons Center, Silver Spring, Maryland, Report

NSWC TR 84-68.

Layton, D., B. Mallon, W. Mitchell, L. Hall, R. Fish,

L. Perry, G. Snyder, K. Bogen, W. Malloch, C. Ham

and P. Dowd (1987) Conventional weapons demilitarization: A health and environmental effects data

base assessment. Explosives and their co-contaminants final report, Phase II. Lawrence Livermore

National Laboratory, Livermore, California.

Lenke, H. and H. Knackmuss (1992) Initial hydrogenation during catabolism of picric acid by

Rhodococcus erythropolis HL 24-2. Applied and Environmental Microbiology, 58(9): 2933–2937.

Lloyd, J. (1985) Microcolumn clean-up and recovery techniques for organic explosives compounds

and for propellants traces in firearms discharge

residues. Journal of Chromatography, 330: 121–129.

Majersky, P. and M. Dybalova (1975) Spectrophotometric determination of the dissociation constant

of picric acid in anhydrous solvent. Acta Facultatis

Rerum Naturalium Universitatis Comenianae Chimia

XXII.

Meyer, R. (1987) Explosives. VCH Verlagsgesellschaft

mbH, Weinheim, Germany, p. 269–271.

Munder, A., S.N. Chesler and S.A. Wise (1990)

Capillary supercritical fluid chromatography of

explosives. Journal of Chromatography, 521: 63–70.

Parihar, D., S.P. Sharma and K.C. Tewari (1966)

Thin-layer chromatography of polynitrophenols,

nitrophenols, nitrohydroquinones and related

compounds. Journal of Chromatography, 24: 230–236.

Rodillon, G. (1915) A specific reaction of picric

acid. Chemical Abstracts, 10: 3268.

Ruchholt, C. and F. Norris (1946) Estimation of

ammonium picrate in wastes from bomb- and

shell-loading plants. Industrial and Engineering

Chemistry, 18: 480–483.

USAEC (1989) Method LW-13. Picric acid in soil

samples. USA Toxic and Hazardous Materials

Agency, Aberdeen Proving Ground, Maryland.

USEPA (1984) Definition and procedure for the

determination of the method detection limit. Code

of Federal Regulations, Part 136, Appendix B.

USEPA (1990) Nitroaromatics and nitramines by

high pressure liquid chromatography (Revision 1).

Washington D.C.: US EPA Office of Solid Waste

and Emergency Response, Draft Method 8330,

SW846.

11
Voyksner, R.D. and J. Yinon (1986) Trace analysis

of explosives by thermospray high-performance

liquid chromatography-mass spectrometry. Journal of Chromatography, 354: 393–405.

Walsh, M.E., T.F. Jenkins, 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.

Wyman, J.F, H.E. Guard, W.D. Won and J.H. Quay

(1979) Conversion of 2,4,6-trinitrophenol to a mutagen by Pseudomonas aeruginosa. Applied and Environmental Microbiology, 37: 222–226.

Wyman, J.F., M.P. Serve, D.W. Hobson, L.H. Lee

and D.E. Uddin (1992) Acute toxicity, distribution, and metabolism of 2,4,6-trinitrophenol (picric acid) in Fischer 244 rats. Journal of Toxicology

and Environmental Health, 37: 313–327.

Ydrac (1916) Detection of picric acid by the formation of potassium isopurate. Chemical Abstacts, 11:

2469.

12
1.0 SCOPE AND APPLICATION

This method is suitable for the determination

of ammonium picrate and picric acid in field-moist

or dried soil, using a battery-operated spectrophotometer.

2.0 SUMMARY OF METHOD

A 20-g subsample of soil is extracted with 100

mL of acetone by manually shaking for three minutes. A 30-mL aliquot is filtered into a graduated

cylinder and diluted with 30 mL of deionized water. This converts picric acid or ammonium picrate

in the extract to picrate ions. The diluted extract is

then passed through an ion-exchange solid-phase

extraction (SPE) tube. Picrate ions are retained on

the resin. Interferences are removed by washing

the resin with methanol. Picrate ions are converted

to protonated picric acid and eluted from the resin

by washing with 10 mL of acetone containing four

drops of concentrated sulfuric acid. The initial absorbance of the eluent at 400 nm is recorded and

provides a background correction. The colorless,

protonated picric acid solution is converted to a

yellow picrate ion solution by diluting the acidified acetone extract with water. The absorbance is

measured again at 400 nm. The corrected absorbance is converted to μg/g of picric acid based on

the response from calibration standards.

3.0 DEFINITIONS

Ammonium picrate (ammonium 2,4,6-trinitrophenoxide)

MW: 246.14

Solubility in water at 25°C: >10 g/L

Octanol–water partition coefficient: 0.2

CAS# 131-74-8

Picric acid (2,4,6-trinitrophenol)

MW: 229.11

Solubility in water at 25°C: >10 g/L

Octanol–water partition coefficient: 4.4

CAS# 88-89-1

4.0 INTERFERENCES

Identification and quantification is based on the

absorbance of picrate ions at 400 nm. Other substances that can produce yellow extracts include

humic materials and certain nitroaromatic secondary explosives and their environmental transformation products. Extraction with ion-exchange

resins followed by a rinse with methanol removes

the nitroaromatic interferences. Background correction using the initial absorbance of the acid–

acetone eluent accounts for humic materials. Rinsing the spectrophotometer cuvette with acetone

between samples is necessary. Carry-over of any

water from the previous water–acid–acetone mixture will convert colorless, protonated picric acid

in the acid–acetone mixture to yellow picrate ions.

This will invalidate the “Initial Absorbance”

measurement that is required for background

correction.

5.0 SAFETY

The normal safety precautions associated with

the use of flammable organic solvents, strong acids and potentially toxic chemicals should be employed. Eye protection is recommended when

shaking bottles to protect against splash from

poorly sealed containers. Eye, hand and clothing

protection is recommended when handling the

concentrated sulfuric acid and acidified eluents.

6.0 EQUIPMENT AND SUPPLIES

A. Instrumentation:

1. Field-portable, battery-operated spectrophotometer with a 1-cm path-length

cell (Hach DR2000 or equivalent).

2. Mechanical or battery-operated balance

to measure soils.

3. Analytical balance for preparation of

standards.

B. Labware and equipment

1. 250-mL (Nalgene or equivalent) plastic

bottles with caps containing three 1/4-

inch steel ball bearings, one per sample.

APPENDIX A: METHOD DOCUMENTATION: FIELD METHOD FOR

DETERMINATION OF AMMONIUM PICRATE AND PICRIC ACID IN SOIL

13
2. 120-mL (Nalgene or equivalent) plastic

bottles with caps, five for calibration solutions.

3. Volumetric pipets: one each—10, 8, 6, 4, 2

mL.

4. Volumetric flasks: 100-mL (two).

5. 100-mL graduated cylinder.

6. 10-mL graduated cylinders (two).

7. Disposable eyedroppers or pasteur pipets

(one for sulfuric acid and one for each

sample).

8. Millex SR filter units, 0.5 μm, two per

sample.

9. Glass cuvettes, 1-cm path length.

10. Disposable plastic syringes: 60-mL (one

per sample), 10-mL (two per day for acidified acetone and rinses).

11. 22-mL glass vials with caps (one per

sample).

12. Supelclean Alumina-A, solid-phase extraction (SPE) tubes, 3 mL (Supelco

57082u) (one per sample).

13. Teflon-coated stir bar (10 × 15 mm).

14. 500-mL squirt bottles (three).

15. Bottle-top dispenser for acetone (highly

recommended).

16. Timer or wristwatch to measure flow rates.

7.0 REAGENTS AND STANDARDS

1. Picric acid (SARM or reagent grade).

2. Acetone, commercial grade.

3. Methanol, reagent grade.

4. Concentrated sulfuric acid, reagent grade.

5. Water, deionized.

8.0 SAMPLE COLLECTION,

PRESERVATION AND STORAGE

This method may be used with field-moist or

dried soil samples.

A soil sample is mixed as thoroughly as possible and a 20-g subsample added to a 250-mL

plastic bottle containing three 1/4-inch steel ball

bearings. The bottle is capped until extraction is

conducted. The samples should be keep cold (4°C)

and in the dark until extraction takes place.

Samples should be analyzed the same day they

are collected.

9.0 QUALITY CONTROL

9.1 GENERAL: The accuracy and precision of

this method are subject to the common errors associated with poor-quality measurements of

weights and volumes. There are a few sources of

error specific to this method. The binding and release of picrate in the solid-phase extraction (SPE)

tube is flow-rate dependent. The flow rates specified in the method (Procedure Steps 5 and 10)

should be implemented carefully. The removal of

residual water from the spectrophotometer cuvettes (Procedure Step 17) is critical for successful

application of the background correction calculation. The manufacturer’s instructions for the SPE

tubes call for a conditioning rinse. This step is not

necessary. The tubes may be used directly from

the package.

9.2 INITIAL DEMONSTRATION OF PERFORMANCE: An initial calibration curve for the

method should be performed as directed in CALIBRATION AND STANDARDIZATION. The calibration curve should be linear, with a zero intercept and a slope (response factor) of 90 ± 15. The

linear range of the method is 0.0–69 μg/g.

9.3 ASSESSING PERFORMANCE: A method

detection limit (MDL) analysis should be performed. A 150-g sample of blank soil is spiked

with 6.0 mL of the 125-mg/L working standard to

produce a picric acid concentration of 5 μg/g. The

soil is homogenized as completely as possible.

Seven 20-g subsamples are processed according

to the method. The concentration of picric acid in

the subsamples is determined using the initial calibration curve. The standard deviation (SD) of the

seven determinations is calculated. The MDL =

3.14 × SD and should be about 1.3 μg/g.

The recovery of the spiked picric acid should

be between 75 and 125%.

9.4 ASSESSING ANALYTE RECOVERY AND

DATA QUALITY: Blank and spiked soil samples

should be analyzed daily as directed in CALIBRATION AND STANDARDIZATION and records

kept. The background-corrected absorbance of a

50-μg/g soil spike should be above 85% of the

value of the 10-μg/L calibration solution processed

according to the directions for the daily calibration of response factor. The blank soil should produce a background-corrected absorbance less

than 0.01 absorbance units. The relative standard deviation of daily matrix spikes should be

less than 15%.

14
10.0 CALIBRATION AND

STANDARDIZATION

10.1 PREPARATION OF STANDARDS: About

0.2 g of solid picric acid (SARM or reagent grade)

is dried to constant weight in a vacuum desiccator

in the dark. About 0.125 g is weighed out to the

nearest 0.1 mg, transferred to a 100-mL volumetric flask and diluted to volume with deionized

water. A stir bar is added and the solution stirred

overnight in the dark. The concentration of picric acid in this stock is about 1250 mg/L. A working standard is made by diluting 10 mL of the stock

with deionized water to 100 mL in a volumetric

flask. The concentration of the working standard

is about 125 mg/L.

Calibration solutions are prepared in 125-mL

plastic bottles by diluting the working standard

with deionized water as described in Table A1.

Volumetric pipets are used to measure the working standard. A 100-mL graduated cylinder is used

to measure the dilution water.

10.2 INITIAL CALIBRATION: A 30-mL aliquot

of each aqueous calibration solution is diluted with

30 mL of acetone and processed according to the

PROCEDURE starting at Step 5. Absorbance readings of Solutions A-E should range from 0.0 to 0.7

absorbance units. The slope of the relationship between the concentration of picric acid and absorbance should be linear, with a zero intercept and a

response factor of 90 ± 15 μg/g per absorbance unit

on a wet-weight basis.

10.3 DAILY CALIBRATION: A 30-mL aliquot of

Calibration Solution D (10 μg/mL, equivalent to

50 μg/g in soil) is diluted with 30 mL of acetone

and processed according to the method. The daily

response factor is calculated:

daily response factor = (50 μg/g)/

(Absorbance @ 400 nm).

10.4 DAILY BLANK AND MATRIX SPIKE: A

blank soil is produced by adding a 100-mL aliquot

of acetone to 20 g of a soil known to be uncontaminated with picrate and performing the method. A

soil spiked at a concentration of 50 μg/g is made

by adding 8 mL of the 125-mg/L working standard to 20 g of blank soil followed by 92 mL of

acetone and performing the method.

11.0 PROCEDURE

1. A 100-mL aliquot of acetone is measured in a

graduated cylinder and added to the 250-mL

sample bottle containing 20 g of soil. The bottle is

capped and manually shaken for three minutes.

2. The soil is allowed to settle for 5 minutes.

3. The sample bottle cap is removed and a 60-

mL syringe is inserted into the extract. About 35–

40 mL of extract is pulled into the syringe. A Millex

SR filter is placed on the tip of the syringe and 30

mL of extract is expressed into a 100-mL graduated cylinder. Any remaining extract can be filtered

back into the extraction bottle. The filter is removed

and placed in a waste container.

4. The 30 mL of acetone extract is diluted in the

100-mL graduated cylinder to 60 mL with deionized water. This assures that all the picric acid and

ammonium picrate in the acetone extract is converted to picrate ion.

5. A 3-mL Alumina-A solid-phase extraction

(SPE) tube is placed on the end on the same 60-mL

syringe with the plunger removed. The aqueous–

acetone mixture is added to the syringe and the

plunger replaced. The plunger is depressed so that

the mixture flows through the SPE tube at about

10 mL/minute. The picrate ions are retained in the

SPE tube. The eluent is collected in a waste container.

6. The 60-mL syringe is removed from the SPE

tube and placed in a waste container.

7. The SPE tube is filled with methanol from a

squirt bottle (about 3 mL) and an air-filled 10-mL

syringe is used to force the methanol through the

tube into the waste container. The SPE tube is then

filled with acetone from a squirt bottle (about 3

mL) and rinsed as above into the waste container.

8. The SPE tube is prepared for elution of picric

acid by placing a new Millex SR filter on the tip and

placing a plungerless 10-mL syringe in the barrel.

9. A 10-ml aliquot of acetone is measured in one

10-mL graduated cylinder. Four drops of concentrated sulfuric acid are added to the acetone using

an eyedropper. The tip of the dropper should be

close to the surface of the acetone to prevent splashing from the falling drop.

10. The 10-mL acid–acetone mixture is poured

into a 10-mL syringe and the plunger replaced

while the tip of the extraction tube–filter assem15
bly is held in the mouth of a 22-mL glass vial. The

plunger is depressed so that the mixture passes

through the SPE tube at about 5 mL/minute and

is collected in the glass vial. The acid–acetone mixture converts the retained picrate ions to unretained, protonated picric acid. The SPE tube and

filter are placed in a waste container.

11. A portion of the acid–acetone eluent is transferred with a disposable pasteur pipet to a glass

spectrophotometer cuvette and the absorbance at

400 nm measured and recorded as Initial ABS. The

spectrophotometer is zeroed with water.

12. The eluent is returned to the 22-mL glass

vial and the cuvette rinsed with water from a squirt

bottle and discarded.

13. If the eluent has any color, a qualitative description is recorded. A 5-mL aliquot of unacidified

acetone plus a 5-mL aliquot of water is measured

in a second 10-mL graduated cylinder and added

to the 22-mL vial. This converts any colorless, protonated picric acid to yellow picrate ions.

14. A portion of the diluted eluent is transferred

to the cuvette using the same disposable pasteur

pipet and the absorbance at 400 nm measured and

recorded as Final ABS.

15. If the Final ABS is greater than 0.7, the diluted eluent may be diluted further with water and

remeasured.

16. After measurement, the eluent is returned

to the 22-mL vial and the pipet is placed in a waste

container.

17. The cuvette is rinsed, first with water from a

squirt bottle, then with acetone from a squirt bottle.

It is critical that no residual water be present in

the cuvette when the next sample is added to the

cuvette for the Initial ABS measurement. Water will

ionize any picric acid to picrate and invalidate the

background correction.

12. DATA ANALYSIS

AND CALCULATIONS

The absorbance data are converted to picric acid

concentration in the sample by the following formula:

μg/g picric acid =

daily response factor (μg/g–ABS unit) ×

(Final ABS – 0.5 × Initial ABS).

This is based on a 20-g wet-weight subsample extracted with 100 mL of acetone and measured using the dilutions specified in the Procedure. Any

dilution that was required to bring the eluent into

the linear range of the initial calibration should be

included in the calculations using the following

formula:

μg/g picric acid =

daily rf (μg/g-ABS unit) ×

[(Final ABS × df) – 0.5 × (Initial ABS/df)]

where rf is the response factor and df is the dilution factor.

13. METHOD PERFORMANCE

The method has been applied to a series of soil

samples whose picric acid concentrations had been

determined by RP-HPLC (Table A2).

14. POLLUTION PREVENTION

All containers of organic solvents and extraction solutions should be kept capped to prevent

evaporation. A bottle-top dispenser is highly recommended to prevent acetone spillage. Alternatively, a large, deep funnel may be used when measuring the acetone into the 100-mL graduated

cylinder. A large tray should be used under the

work area to contain any spilled solvents.

15. WASTE MANAGEMENT

All solid waste contaminated with solvents, acid

and extracted chemicals should be disposed of according to Federal, state and local regulations. This

includes extraction bottles and soils, filters, syringes,

disposable pipets, SPE tubes and eluent vials.

All waste organic solvents from the extraction

procedures and rinses should be disposed of according to Federal, state and local regulations.

All acid–solvent mixtures should be treated

separately as required by Federal, state and local

regulations.

16. REFERENCE

Thorne, P.G. and T.F. Jenkins, “Development of

a Field Method for Ammonium Picrate and Picric

Acid in Soil and Water,” Special Report 95-20, USA

Cold Regions Research and Engineering Laboratory, Hanover, N.H.

16
17. TABLES AND FLOW DIAGRAM

Table A1. Preparation of calibration solutions from 125-mg/L

working standard to simulate extracts of 20-g soil subsamples

with 100 mL of acetone.

Volume of Volume of Associated

working STD water Conc. soil conc.

Solution (mL) (mL) (μg/mL) (μg/g)

A 0 100 0.0 0.0

B 2 98 2.5 12.5

C 4 96 5.0 25.0

D 8 92 10.0 50.0

E 10 90 12.5 62.5

Table A2. Comparison of picric

acid determinations between field

screening method and HPLC.

Picric acid (μg/g)

Sample Screening HPLC

1 0.0 0.0

2 0.0 0.0

3 25,200 23,000

4 1.9 1.0

5 14.0 24.4

6 6.8 9.8

SOIL SAMPLE

Extract with Acetone

Filter

Dilute with Water

Pass Through Anion Exchanger

Rinse Exchanger with Methanol, then Acetone

Elute with H2SO4 – Acetone

Obtain Initial ABS (400 nm)

Dilute with Water and Acetone

Obtain Final ABS (400 nm)

17
4.0 INTERFERENCES

Identification and quantification is based on the

absorbance of picrate ions at 400 nm. Other substances that can produce yellow extracts include

humic materials and certain nitroaromatic secondary explosives and their environmental transformation products. Extraction with ion-exchange

resins followed by a rinse with methanol removes

the nitroaromtic interferences. Background correction using the initial absorbance of the acid–

methanol eluent accounts for humic materials.

Rinsing the spectrophotometer cuvette with

methanol between samples is necessary. Carryover of any water from the previous water–acid–

methanol mixture will convert colorless, protonated picric acid in the acid–methanol mixture to

yellow picrate ions. This will invalidate the “Initial

Absorbance” measurement that is required for

background correction.

5.0 SAFETY

The normal safety precautions associated with

the use of flammable organic solvents, strong acids and potentially toxic chemicals should be employed. Eye, hand and clothing protection is recommended when handling the concentrated sulfuric acid and acidified eluents.

6.0 EQUIPMENT AND SUPPLIES

A. Instrumentation:

1. Field-portable, battery-operated spectrophotometer with a 1-cm path-length cell

(Hach DR2000 or equivalent).

2. Analytical balance for preparation of standards.

3. Vacuum source.

B. Labware and Equipment

1. 1-L (Qorpak or equivalent) amber glass

sample bottles (two per sample).

1.0 SCOPE AND APPLICATION

This method is suitable for the determination

of ammonium picrate and picric acid in well water or surface water. A battery-operated spectrophotometer and hand vacuum pump can be used;

however, a powered vacuum source is recommended.

2.0 SUMMARY OF METHOD

A 2-L subsample of water is drawn through an

anion extraction disk under vacuum. Picrate ions

are retained by the disk. Interferences are removed

by washing the disk with methanol. Picrate ions

are converted to protonated picric acid and eluted

from the disk using a mixture of 4.5 mL of methanol plus 0.5 mL of concentrated sulfuric acid. The

initial absorbance of the eluent at 400 nm is recorded and provides a background correction. The

eluted colorless, protonated picric acid is converted

to a yellow picrate ion solution by dilution with

water. The absorbance is measured again at 400

nm. The background-corrected absorbance is converted to μg/L of picric acid based on the response

from calibration standards.

3.0 DEFINITIONS

Ammonium picrate (ammonium 2,4,6-trinitrophenoxide)

MW: 246.14

Solubility in water at 25°C: >10 g/L

Octanol–water partition coefficient: 0.2

CAS# 131-74-8

Picric acid (2,4,6-trinitrophenol)

MW: 229.11

Solubility in water at 25°C: >10 g/L

Octanol–water partition coefficient: 4.4

CAS# 88-89-1

APPENDIX B: METHOD DOCUMENTATION FIELD METHOD FOR

DETERMINATION OF AMMONIUM PICRATE AND PICRIC ACID IN WATER

18
2. 120-mL (Nalgene or equivalent) plastic

bottle with cap (one for working standard).

3. Volumetric pipets: 10, 8, 5, 2 mL.

4. Volumetric flasks: 100-mL (one), 1 L (one).

5. 2-L graduated cylinder.

6. 10-mL graduated cylinder (two).

7. Disposable eyedropper (for sulfuric acid).

8. Glass fiber filters, 47 mm (for sedimentladen samples).

9. Glass cuvettes, 1-cm path length (two).

10. Vacuum filtration apparatus, 1-L vacuum

flask with 47-mm filter holder and funnel.

11. 24- × 200-mm glass test tubes with screwcaps (one per sample).

12. Empore Anion Extraction Disks, 47-mm

(Varian).

13. Pasteur pipets, 9 inch (one per sample).

14. 500-mL squirt bottles (two).

7.0 REAGENT AND STANDARDS

1. Picric acid (SARM or reagent grade).

2. Methanol, reagent grade.

3. Concentrated sulfuric acid, reagent grade.

4. Water, deionized.

8.0 SAMPLE COLLECTION, PRESERVATION

AND STORAGE

This method may be used with well water or

surface water.

A water sample is collected in two 1-L amber

glass bottles which are capped and kept cold (4°C)

in the dark until extraction. Samples should be

analyzed the same day they are collected.

9.0 QUALITY CONTROL

9.1 GENERAL: The accuracy and precision of

this method are subject to the common errors

associated with poor-quality measurements of

weights and volumes. There is a source of error

specific to this method. The removal of residual

water from the spectrophotometer cuvettes

(PROCEDURE Step 17) is critical for successful

application of the background correction calculation. The manufacturer’s instructions for the

extraction disks call for a conditioning rinse. This

step is not necessary. The disks may be used

directly from the package.

9.2 INITIAL DEMONSTRATION OF PERFORMANCE: An initial calibration curve for the method should be developed as directed in CALIBRATION AND STANDARDIZATION. The calibration curve should be linear, with a zero intercept and a slope (response factor) of 280 ± 75.

The linear range of the method is 0.0–200 μg/L.

9.3 ASSESSING PERFORMANCE: A method

detection limit (MDL) analysis should be performed. A 20-L sample of deionized water is spiked

with 20 mL of the 10-mg/L working standard to

produce a picric acid concentration of 10 μg/L.

The water is stirred as completely as possible.

Seven 2-L subsamples are processed according to

the method. The concentration of picric acid in the

subsamples is determined using the initial calibration curve. The standard deviation (SD) of the

seven determinations is calculated. The MDL =

3.14 × SD and should be about 3.6 μg/L.

The recovery of the spiked picric acid should

be between 75 and 125%.

9.4 ASSESSING ANALYTE RECOVERY AND

DATA QUALITY: Blank and spiked water samples

should be analyzed daily as directed in CALIBRATION AND STANDARDIZATION and records

kept. The background-corrected absorbance of a

150-μg/L water spike should be above 80% of the

predicted absorbance based on the initial calibration curve. The blank water should produce a background-corrected absorbance less than 0.01 absorbance units. The relative standard deviation of

daily matrix spikes should be less than 27%.

10. CALIBRATION AND

STANDARDIZATION

10.1 PREPARATION OF STANDARDS: About

0.2 g of solid picric acid (SARM or reagent grade)

is dried to constant weight in a vacuum desiccator in the dark. About 0.125 g is weighed out to

the nearest 0.1 mg, transferred to a 100-mL volumetric flask and diluted to volume with deionized water. A stir bar is added and the solution

stirred overnight in the dark. The concentration

of picric acid in this stock is about 1250 mg/L. A

working standard is made by diluting 8 mL of

the stock with deionized water to 1 L in a volumetric flask. The concentration of the working

standard is about 10 mg/L.

Calibration solutions are prepared in a 2-L

graduated cylinder by diluting the working stan19
dard with deionized water as described in Table

B1. Volumetric pipets are used to measure the

working standard.

10.2 INITIAL CALIBRATION: Calibration solutions are prepared in the 2-L graduated cylinder and processed according to the PROCEDURE

starting at Step 1. Absorbance readings of Solutions A–E should range from 0.0 to 0.7 absorbance units. The slope of the relationship between the concentration of picric acid and absorbance should be linear, with zero intercept

and a response factor of about 280 μg/L per absorbance unit.

10.3 DAILY CALIBRATION: A 150-μg/L picric

acid solution is made by diluting 30 mL of working standard to 2 L with deionized water and proceeding with the method. The daily response factor is then determined:

Daily response factor = (150 μg/L)/

(Absorbance @ 400 nm).

11. PROCEDURE

1. A 47-mm Empore Anion Extraction Disk is

placed on a vacuum filter holder. A glass fiber

filter may be placed on top of that if the sample

appears cloudy. The funnel is clamped in place.

2. The water sample is measured in a 2-L graduated cylinder and a portion is added to the extraction funnel. The vacuum is applied and the funnel

refilled as needed. After the first 1-L is extracted,

the vacuum is shut off and vented and the vacuum

flask emptied into a waste container. The vacuum

is reapplied, the second liter extracted and the

vacuum flask emptied again. Picrate ions in the

sample are retained on the anion disk.

3. The glass fiber filter, if used, is removed and

placed in a waste container. The funnel is reclamped in place. Air is drawn through the Anion

disk for 5 minutes using vacuum.

4. The vacuum is turned off and vented, then 10

mL of methanol is added to the funnel. This is

allowed to soak into the disk for 2 minutes, then

pulled through with vacuum. This rinse removes

interfering compounds.

5. The vacuum is vented and the extraction

holder and funnel are removed so that the methanol rinse may be transferred to a waste container.

A 25- × 200-mm test tube is placed into the vacuum

flask. The extraction holder assembly is returned

to the vacuum flask, with its drain tube inserted

into the test tube.

6. A 4.5-mL aliquot of methanol is added to one

10-mL graduated cylinder. A 0.5-mL aliquot of concentrated sulfuric acid is added slowly with an

eyedropper. The dropper should be held close to

the surface of the methanol to prevent splashing.

7. The acid–methanol mixture is poured into

the extraction funnel and allowed to soak the disk

for 2 minutes. This converts the picrate ions to

protonated picric acid.

8. Vacuum is applied and the acid–methanol

eluent is collected in the test tube. The vacuum is

vented and the test tube withdrawn and capped.

9. The Anion disk is removed from the holder

and placed in a waste container. The holder and

funnel are assembled and returned to the vacuum

flask and rinsed with 10 mL of deionized water,

which is collected in the vacuum flask and then

transferred to a waste container.

10. A portion of the acid–methanol eluent is

transferred from the test tube to a spectrophotometer cuvette using a 9-in. pipet.

11. The absorbance at 400 nm is measured and

recorded as Initial ABS. The spectrophotometer is

zeroed with water.

12. The eluent is returned to the test tube and

the cuvette rinsed with water.

13. Any color in the eluent is qualitatively described and recorded. A 5.0-mL aliquot of deionized water is measured in a second 10-mL graduated cylinder and added to the 5.0 mL of acid–

methanol eluent in the test tube.

14. Any change in color should be qualitatively

described and recorded. An increase in yellow color

confirms the presence of picrate in the sample.

15. A portion of the diluted eluent is transferred

to the cuvette and the absorbance at 400 nm measured and recorded as Final ABS.

16. If the Final ABS is greater than 0.7, the diluted eluent may be diluted further with water

and remeasured.

17. After measurement, the eluent is returned

to the test tube.

18. The cuvette is then rinsed, first with water

from a squirt bottle, then with unacidified methanol from a squirt bottle. It is critical that no residual water be present in the cuvette when the

next sample is added to the cuvette for the Initial

ABS measurement. Water will convert any picric

acid to picrate ion and invalidate the background

correction.

20
12. DATA ANALYSIS AND

CALCULATIONS

The absorbance data are converted to picric acid

concentration in the sample by the following formula:

μg/L picric acid =

daily response factor (μg/L-ABS unit) ×

 (Final ABS – 0.5 × Initial ABS).

This is based on a 2-L subsample of water using

the dilutions specified in the PROCEDURE. Any

dilution that was required to bring the eluent into

the linear range of the initial calibration should be

included in the calculations using the following

formula:

μg/L picric acid =

daily rf (μg/L-ABS unit) ×

[(Final ABS × df) – 0.5 × (Initial ABS/df)]

where rf is the response factor and df is the dilution factor.

13. METHOD PERFORMANCE

The method was tested on 34 well waters. The

field method indicated no picrate contamination

above the detection limit. This result was confirmed using HPLC.

14. POLLUTION PREVENTION

All containers of organic solvents and extraction solutions should be keep capped to prevent

evaporation. A large tray should be used under

the work area to contain any spilled solvents.

15. WASTE MANAGEMENT

All solid waste contaminated with solvents, acid

and extracted chemicals should be disposed of

according to Federal, state and local regulations.

This includes extraction disks, glass fiber filters,

pasteur pipets and eluent test tubes.

All waste methanol from the rinses should be

disposed of according to Federal, state and local

regulations.

All acid–methanol mixtures should be treated

separately as required by Federal, state and local

regulations.

16. REFERENCES

Thorne, P.G. and T.F. Jenkins, “Development of

a Field Method for Ammonium Picrate and Picric

Acid in Soil and Water,” Special Report 95-20, USA

Cold Regions Research and Engineering Laboratory, Hanover, N.H.

17. TABLE AND FLOW DIAGRAM

TABLE B1. Preparation of calibration solutions from

the 10-mg/L working standard.

Volume of Volume of

working STD water Conc.

Solution (mL) (mL) (μg/L)

A 0 2000 0.0

B 5 1995 25

C 10 1990 50

D 20 1980 100

E 40 1960 200

WATER SAMPLE

Vacuum Filter Through Anion Disk

Rinse Disk with Methanol

Elute with H2SO4 – Methanol

Obtain Initial ABS (400 nm)

Dilute with Water

Obtain Final ABS (400 nm)

21
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NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102

REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

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August 1995

Development of a Field Method for Quantifying Ammonium Picrate

and Picric Acid in Soil and Water

Philip G. Thorne and Thomas F. Jenkins

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road Special Report 95-20

Hanover, New Hampshire 03755-1290

U.S. Army Environmental Center

Aberdeen proving Ground, Maryland SFIM-AEC-ET-CR-95010

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161

28

Ammonium picrate Picric acid

Field methods

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

Methods for the detection and quantification of ammonium picrate and picric acid in soil and water were

developed. Picrate ions were extracted from water directly or from acetone extracts of soil by solid-phase, acidic,

ion-exchange materials. Elution from the ion exchangers was accomplished by converting the retained picrate to

picric acid using strong aqueous, acid–organic solvent mixtures. The resulting colorless solution was then

converted back to a colored picrate solution by dilution with water. Quantification and correction for background

interferences were based on spectrophotometric measurements. A colorimetric, chemical confirmation of picrate

was possible for the water method. The method detection limits were determined to be 1.3 μg/g for soil and 3.6

μg/L for water. Both methods can be implemented under field conditions.