Obtaining and Transferring Soils for

In-Vial Analysis of Volatile Organic

Compounds

Alan D. Hewitt and Nicole J.E. Lukash February 1996

SPECIAL REPORT 96-5
Abstract

The ability to retain volatile organic compounds (VOCs) while collecting

and transferring intact soils for in-vial analysis was evaluated with field

and laboratory samples. Experiments were designed to assess if VOC concentrations are maintained in an intact soil sample when 1) held for under

an hour in a metal core liner, 2) held for days in a metal core liner sealed

with TFE–flourocarbon sheets or aluminum foil (ASTM D4547-91), 3) held

for less than 2 minutes in a plastic bag after extruding from a sampling

device, and 4) immediately transferred to an empty vial to which a solvent

was added later. Results indicate that these procedures are all highly susceptible to volatilization losses. To maintain site-representative VOC concentrations, collection of soil samples for in-vial analysis should occur

within minutes of exposing a fresh surface by using a device that limits soil

structure disruption and exposure.

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 96-5

Obtaining and Transferring Soils for

In-Vial Analysis of Volatile Organic

Compounds

Alan D. Hewitt and Nicole J.E. Lukash February 1996

Prepared for

U.S. ARMY ENVIRONMENTAL CENTER

SFIM-AEC-ET-CR-96002

Approved for public release; distribution is unlimited.

US Army Corps


of Engineers

Cold Regions Research &


Engineering Laboratory
PREFACE

This report was prepared by Alan D. Hewitt, Research Physical Scientist, and Nicole

Lukash, Physical Science Aid, Geological Sciences Division, Research and Engineering

Directorate, U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, New

Hampshire.

Funding for this work was provided by the U.S. Army Environmental Center, Martin H.

Stutz, Project Monitor. The authors thank Dr. Thomas F. Jenkins and Thomas Ranney for

critical review of the text, and Dr. T.M. Spittler for providing information about handling and

collecting soil samples.

This publication reflects the view of the author and does not suggest or reflect policy,

practices, programs, or doctrine of the U.S. Army or of the Government of the United States.

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

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

Core liner experiments ................................................................................................. 2

Extruded soil cores ....................................................................................................... 3

Collection vessel preparation ...................................................................................... 3

Analysis ............................................................................................................................... 4

Results ................................................................................................................................ 4

Core liners ...................................................................................................................... 4

Extruded samples ......................................................................................................... 7

Collection vessel experiment....................................................................................... 8

Discussion ........................................................................................................................... 8

Conclusions ........................................................................................................................ 9

Literature cited ................................................................................................................... 9

Abstract ............................................................................................................................... 11

ILLUSTRATIONS

Figure

1. Sampling pattern for core line experiments .......................................................... 2

2. Sample collection pattern for extruded soil cores ................................................ 3

3. Sampling pattern for composite samples .............................................................. 4

4. Concentrations of TCE established exterior to and within uncovered core

liners ...................................................................................................................... 4

TABLES

Table

1. Concentration of TCE determined for soil samples collected around

and within core liners ......................................................................................... 5

2. Concentration of TCE determined for soil samples collected around

 and within core liners

3. Analyte concentrations (μg/g) in modified core liners laboratory

experiments, before and after covering with TFE sheets or

 aluminum foil and storing at 4°C .................................................................... 6

4. Extruded samples ..................................................................................................... 7

5. Comparison of pairs of composited samples added to VOA vials with

and without solvent present .............................................................................. 8

iii
INTRODUCTION

An in-vial method of preparing and analyzing

soils for volatile organic compounds (VOCs) requires soil to be transferred directly to a vessel with

hermetic seals. This approach differs from those

often used under the guidelines of Method 5030

of the SW-846 (U.S. EPA 1986) by using only a

single transfer process and a vessel that is compatible with the instrumentation on which the

analysis will be performed. In-vial soil sample

preparation and analysis methods address much

of the past criticism regarding the volatilization

losses of VOCs caused by repeated exposures and

uncontrolled disturbance of soil samples when

transferred to and from receptacles of various

shapes and sizes (Urban et al. 1989, Seigrist and

Jenssen 1990, Hewitt et al. 1993, Illias 1993, Voice

and Kolb 1993, Lewis et al. 1994).

The U.S. Environmental Protection Agency has

proposed Methods 5021 and 5035, two in-vial

preparation and analysis procedures for the third

update of the Test Methods for Evaluating Solid

Waste, SW-846. The first is designed for low level

(<1-μg VOC/g) analysis by purge-and-trap, gas

chromatography/mass spectrometry (Method

8240 or 8260). The second is an equilibrium

headspace (HS) approach to analysis that can be

used in conjunction with Methods 8015, 8021, or

8260. Both of these of methods use volatile organic

analysis (VOA) vials (22 and 44 mL), which rely

on a Teflon-faced septum with bonded silicon or

rubber backing, compressed by a rigid plastic or

aluminum cap, to form a hermetic seal with a glass

rim. This septum also forms a vapor-tight seal

around the needles used to remove VOCs from the

vial during sample analysis.

In addition to using the in-vial preparation and

analysis methods described in Methods 5021 and

5035, attention must also be given to how the

sample is obtained and transferred prior to this

treatment. The necessity to limit disruption and

exposure of the unsaturated soil sample, while it

is being transferred to an analysis vial, is imperative because the analytes of concern have high vapor pressures, allowing them to either partly or

largely exist as gases under environmental conditions. For instance, to avoid the volatilization losses

incurred by using utensils that allow the soil to

randomly fracture and expose an uncontrolled

amount of surface area (stainless steel spoons,

spatulas, garden trowels, etc.), small coring tools

have been used. Examples of such devices are common laboratory plastic syringes with their tips removed (Griffith et al. 1988) and specially designed

stainless steel samplers (Associated Design and

Manufacturing Co., EN CHEM, Inc.). The use of

these coring tools is addressed in the current draft

of Method 5021, and the inclusion of these devices

is anticipated for the final version of Method 5035.

The merit of using a limited-disruption singletransfer and in-vial approach to soil sample collection, handling and analysis is to achieve more

representative estimates of the in-situ environmental VOC concentrations than possible using

previous approaches.

The purpose of this study is to look closely at

some collection and transfer procedures that may

be used with in-vial methods of analysis. Experiments were designed to assess if VOC concentrations are maintained in an intact soil sample when

1) held for less than an hour in a metal core liner,

2) held for days in a metal core liner sealed with

TFE–flourocarbon sheets or aluminum foil (ASTM

D4547-91), 3) held for less than 2 minutes in a plastic bag after extruding from a sampling device,

and 4) immediately transferred to an empty vial

to which a solvent was added later.

Obtaining and Transferring Soils for

In-Vial Analysis of Volatile Organic Compounds

ALAN D. HEWITT AND NICOLE J.E. LUKASH
EXPERIMENTAL

All of the field samples used during the following experiments were obtained from rectangular

holes approximately 25 × 25 cm and extending to

depths between 20 and 46 cm below the ground

surface. At the site where the holes were excavated,

trichloroethylene (TCE) contamination has been

present for about 25 years. The soil at this location

(Hanover, N.H.) is characterized as a cohesive

silty-clay with an organic carbon content of less

than 0.5% (Hach method 8097), ranging in moisture from 13 to 16% (ASTM D2216-66).

Each experiment was performed as rapidly as

possible after exposing a smooth flat surface in the

native substrate. Except where noted, samples

taken for analysis were obtained and transferred

to VOA vials using 3-, 5-, or 10-cm3 plastic syringes

with their injection tip and rubber plunger-cap removed. The open end of these corers were pushed

approximately 2.5 cm into the exposed surface,

resulting in soil plugs of approximately 2, 4, and 6

g. When transferring the soil sample, care was

taken to remove soil adhering to the exterior of

the corer before inserting it into the mouth of a

collection vial, so that the sealing surfaces would

not be compromised. The mass of the collected

sample was obtained by the weight difference of

the collection vial before and after adding the

sample. Samples collected with either the 3- or 5-

cm3 syringe were transferred to 22-mL auto sampler vial (Wheaton), containing either 10 or 15 mL

of Type 1 water, and capped with a Teflon-faced

gray butyl septum and aluminum crimp top.

Samples obtained with the 10-cm3 syringe were

transferred to 44-mL VOA vials (Eagle Picher) containing 30 mL of Type 1 water and capped with a

Teflon-faced silicone septum and plastic screw top.

Soil samples, collected immediately after exposing a fresh surface and transferred as described

above, served as the reference samples to which

others were compared.

Core liner experiments

Field samples

In all, four separate field experiments were performed using 3.6-cm-i.d. × 5.1-cm brass core liners (Environmental Instruments). Uncovered intact soils obtained in these core liners have an exposed surface area/sample mass ratio of approximately 0.27 cm2/g. In each experiment, six core

liners were inserted vertically into the bottom of

the hole, creating a 3 × 2 array. A wooden block

I II III

IV V VI

1234

5678

9 10 11 12

and hammer were used to push each core liner to

a 5.1-cm depth. These core liners were numbered

I–VI, denoting their position and orientation. Once

positioned, 12 reference soil samples were taken

in a pattern, so that four sampling locations surrounded each of the core liners (Fig. 1).

In the first experiment, samples were sequentially collected by inserting a 5-cm3 syringe into

the freshly exposed surface 1.2 cm, removing and

discarding the soil, followed by a second insertion

into the same sampling hole, 2.5 cm beyond the

first insertion, and removing a plug of intact soil.

This subsurface sample was immediately transferred to a VOA vial containing water. After all

the reference samples (exterior to the core liners)

were taken, the core liners were removed from the

hole and, without covering, placed in a large plastic bag. Each core liner was then sequentially subsampled in the same manner, after periods of 1,

10, 20, 30, 40 and 60 minutes (one sample/core

liner).

The second experiment followed the same format as the first, except four of the core liners were

individually covered and stored. Once the samples

exterior to the core liners had been collected, the

core liner in the lower right-hand corner (VI) was

removed with the soil intact and sampled as described for the before-mentioned reference

samples. The next four core liners were then removed, one at time, going from right to left. Once

removed their exteriors and rims (top and bottom)

were wiped clean with a paper towel, both ends

were then covered with either a single 7.6-cm-wide

sheet of TFE (Environmental Instruments) or

heavy duty aluminum foil, followed by press fitting plastic end caps. The last core liner (I) was

Figure 1. Sampling pattern for core liner experiments.

Circles with crosses show location of samples taken exterior to core liners.

2
removed and immediately sampled as described

for core liner VI. Shortly thereafter, the core liners

covered with aluminum foil were wrapped with

PVC tape, sealing both the edges of the foil and

plastic cap to the core liners’ exterior walls.

The third and fourth experiments used the same

general format as the second, except that the reference samples and those taken from the core liners were collected without discarding the top 1.2

cm of soil. The last experiment used 18, 3-cm3 syringes: 12 were positioned exterior to the core liners, and 3 each into core liners I and VI. Once they

all were in position (pushed 2.5 cm into the exposed soil surface) they were sequentially removed

and the plug of soil obtained in each syringe was

transferred to a prepared VOA vial.

For all of these field experiments the entire sampling operation, from the point of inserting the core

liners until the last sample was collected, took

approximately 15 minutes. Covered core liners

were stored in a refrigerator (4°C) for either 5 or

10 days before being sampled in the laboratory

using the same procedure that had been used in

the field.

Laboratory experiment

Three laboratory experiments were performed

with modified core liners (3.6-cm-i.d. × 3.4 cm

high) made by soldering a brass cap onto one end,

making a cup. The matrix used was a sandy soil

desiccated with CaSO4 or moistened with water

to 1% or 10%. In each case 50 g of the soil was

packed (1.4 g/cm3) into 12 brass cups, leaving <2

mm of space between the soil surface and rim. Uncovered, the surface area to sample mass ratio was

approximately 0.20 cm2/g. Handling one sample

at a time, we then spiked each of the 12 replicates

by inserting the needle (gauge 26s) of a 10-μL syringe to the bottom of a soil-filled cup and injecting 5 μL of a methanol (MeOH) standard containing trans-1,2-dichloroethylene (TDCE), trichloroethylene (TCE), benzene (Ben) and toluene (Tol).

Upon removing the needle, the soil was tamped

down filling the injection channel. These experiments were performed in conjunction with others

not reported here; thus, for convenience, different

methanol standard solution was used for the 10%

moisture experiment than was used for the desiccated and 1% moisture experiments. Of the 12 replicates, five were covered with two sheets of TFE,

and five were covered with aluminum foil, then

capped and taped as described previously. The

remaining two samples were immediately taken

for analysis, by submersing the entire cup into 300

mL of water contained in a 500-mL jar and capped

with a Teflon-backed silicone septum top. These

jars have a special opening in the cap to allow for

syringe penetration. All covered samples were

stored at 4°C until the day of analysis, whereupon

the caps and coverings were removed and the cups

quickly submersed into 300 mL of water contained

in 500-mL jars.

Extruded soil cores

This study initially compared soil samples obtained with 10- and 3-cm3 syringes and extruded

directly into 44- or 22-mL VOA vials containing

water, respectively. Samples for this initial comparison were collected at a depth of 33 cm after

inserting five of each size of the syringes into the

bottom of the hole. The syringes were positioned

in a tight array (12 × 5 cm) in two rows (Fig. 2). A

second experiment, performed in the same hole at

a depth of 38 cm, collected two separate arrays of

eight soil samples, using first the 10-cm3 then the

3-cm3 syringes. Again all eight syringes were positioned, prior to being sequentially removed, placing alternating soil plugs into VOA vials containing water, or into small (7.5-cm × 5-cm) plastic

Ziploc bags and sealing. Those transferred to the

Ziploc bags were held for 1 to 2 minutes; then the

bags were cut open with scissors so that the plugs

of soil could be easily transferred (Ziploc bags have

a lip that interfered with the sliding of a plug of

soil). Special care was taken for those plugs extruded into the plastic bags so that they would

remain intact until immersed in the water present

in the VOA vials. Once extruded into the plastic

bags the soil samples had a surface area/mass exposure ratio of approximately 2.0 and 3.6 cm2/g

for the 10- and 3-cm3 syringes, respectively.

Collection vessel preparation

This experiment assesses the effect of introducing a solvent to a sample after it has been transferred to an empty VOA vial compared to samples

transferred to VOA vials with water present. Six-

~5 cm

Figure 2. Sample collection pattern for extruded

soil cores.

3
composed of a HS auto sampler (Tekmar 7000)

coupled to a GC (SRI, model 8610-0058). Additional information concerning sample analysis and

the operating conditions used with these instruments can be found elsewhere (Hewitt et al. 1992,

Hewitt 1995a).

Concentration estimates were established on

moist weight basis relative to working standards,

which were prepared by spiking analysis vials

(jars) that contained the same amount of water as

the samples with small volumes (<100 μL) of a

methanol stock standard. The stock standards

were prepared on a weight basis, then volumetrically diluted as necessary. Samples and standards

were hand shaken for at least two minutes prior

to analysis. This approach to the analysis establishes VOC concentration estimates that often are

not significantly different than more rigorous

purge-and-trap procedures when the soil matrix

has a low (<1%) organic carbon content (Hewitt et

al. 1992).

RESULTS

Core liners

A greater than 90% decrease in TCE concentration resulted in less than 40 minutes for the

samples collected and stored in core liners, when

compared to the mean of the four reference

samples obtained around the liners’ exterior (Table

1). In addition, the rate of TCE loss during the first

30 minutes was greater than the subsequent 30

minutes of exposure (Fig. 4). Therefore it is rea0 10 20 30 40 50 60

Exposure Time (min)

100

80

60

40

20

TCE Concentration (%)

Figure 4. Concentrations of TCE established exterior to and within uncovered core liners.

Figure 3. Sampling pattern for composite samples.

teen, 3-cm3 tipless syringes were inserted vertically

in a 4 × 4 array (Fig. 3) into the bottom of a 38-cm

hole. Once all the syringes had been positioned,

one from each row and column of the 4 × 4 array

was randomly removed and its contents quickly

composited (4 separate plugs) into either a VOA

vial containing 10 mL of water or empty VOA that

was then covered with Parafilm. For the vials covered with Parafilm, this temporary covering was

removed after a 2-minute period and 10 mL of

water was added. The 4 × 4 sampling array allowed for duplicates of the composited samples

to be compared. This series of steps was repeated

in the same hole at depths of 40, 43, and 46 cm. At

the next two depths (40 and 43 cm) the vials without water were sealed with Teflon-faced gray butyl rubber septa and aluminum crimp tops, and

they were opened after 20 or 200 minutes to add

10 mL of water and then recapped. At the depth

of 46 cm, 10 mL of water was added immediately

after the last soil plug of four being

composited had been transferred to

the empty VOA vial. In all cases,

the plugs of soil remained intact

during collection process; i.e., they

remained in the cylindrical shape

created by the coring tool even after they were transferred to the

analysis vials.

ANALYSIS

All samples were analyzed by

equilibrium headspace (HS) analysis. Samples transferred to 44-mL

VOA vials or 500-mL jars were analyzed on a model 10S10 PhotoVac

gas chromatograph (GC). Samples

transferred to 22-mL VOA vials were

analyzed on an automated system

~2.5 cm

4
aggregate micropores (Sawhney and Gent 1990,

Pavlostathis and Mathavan 1992).

Core liners are devices designed to prevent VOC

volatilization losses from intact soil samples so

that the soil can be shipped from the field to an

off-site laboratory prior to sampling for analysis.

During transportation and storage this device is

covered with either sheets of TFE or aluminum foil

(ASTM, D 4547-91). Ideally, when using core liners, sample exposure would be limited to two short

periods: when the sample is first retrieved and

covered, and when it is opened in the laboratory

to prepare a sample for analysis. For this approach

to be useful, VOC concentrations must be maintained for at least several days to allow time for

samples to be shipped to the analytical laboratory.

Table 2 shows results of field samples stored in

core liners and covered with either TFE or aluminum foil. As in Table 1, samples taken from core

liners immediately after they were removed from

the hole showed TCE concentration estimates comparable to the means obtained for adjacent

samples. However, regardless of the covering or

Table 2. Concentration (μg/g) of TCE determined for soil samples collected around

and within core liners. Core liners covered with either TFE sheets or aluminum foil

were stored at 4°C.

Reference soil samples

Core liner no. Storage period** from around the

covering Day 0 Day 5 Day 10 core liner

Second experiment

I/None 2.9 3.2±0.4† (1,2,5,6)

II/Aluminum 0.15 3.4±0.7 (2,3,6,7)

III/TFE 0.18 3.6±0.5 (3,4,7,8)

IV/TFE 0.049 3.4±0.8 (5,6,8,10)

V/Aluminum 0.16 3.3±0.6 (6,7,10,11)

VI/None 2.5 3.5±0.4 (7,8,11,12)

Third experiment

I/None 0.63 0.79±0.17 (1,2,5,6)

II/Aluminum 0.018 0.70±0.28 (2,3,6,7)

III/TFE 0.018 2.4±2.5 (3,4,7,8)

IV/Aluminum 0.017 0.62±0.25 (5,6,8,10)

V/TFE 0.006 0.70±0.33 (6,7,10,11)

VI/None 0.82 1.2±0.7 (7,8,11,12)

Fourth experiment

I/None 0.86±0.01* 1.2±0.4 (1,2,5,6)

II/Aluminum 0.14±0.08 1.6±0.8 (2,3,6,7)

III/TFE 0.069±0.014 1.6±0.8 (3,4,7,8)

IV/TFE 0.059±0.016 0.86±0.18 (5,6,8,10)

V/Aluminum 0.072±0.001 1.4±0.9 (6,7,10,11)

VI/None 0.64±0.21 1.4±0.9 (7,8,11,12)

* Mean and standard deviation, n = 3 † Mean and standard deviation, n = 4

** Samples taken from within core liner.

Table 1. Concentration (μg/g) of TCE determined

for soil samples collected around and within core

liners.

Reference soil samples

Core liner/exposure Within core from around the

period (min.) liner core liner

I/60 0.27 9.7±1.0* (1,2,5,6)†

II/40 0.99 11±0.7 (2,3,6,7)

III/30 2.1 12±1.0 (3,4,7,8)

IV/20 4.7 11±0.5 (5,6,8,10)

V/10 6.5 10±0.9 (6,7,10,11)

VI/1 11 12±1.0 (7,8,11,12)

* Mean and standard deviation, n = 4 † Sample positions exterior to core liner (Fig. 1)

sonable to assume that these samples, which had

been removed from the middle of the core liners

(1.2 cm below/above the exposed surfaces), had

experienced large volatilization losses, due to gaseous diffusion. The observed faster rate of desorption has been attributed to processes occurring at

the mineral surfaces (macropores), whereas the

slower rate may result from diffusion from intra5
Table 3. Analyte concentrations (μg/g) in modified core liners laboratory experiments,

before and after covering with TFE sheets or aluminum foil and storing at 4°C.

Condition/covering/ Storage period

analyte Day 0 Day 1 Day 2 Day 3 Day 7 Day 14

Desiccated/TFE/

TDCE 3.1/3.1 1.9 1.5 1.3 0.56 ND*

Ben 4.4/4.3 4.4 4.2 4.3 4.0 2.9

TCE 7.1/7.0 7.3 6.3 6.3 5.3 2.4

Tol 6.7/6.6 7.0 6.8 7.0 6.4 6.1

Desiccated/aluminum/

TDCE 3.1/3.1 3.0 0.92 0.97 2.2 1.5

Ben 4.4/4.3 4.4 4.2 4.3 4.3 4.4

TCE 7.1/7.0 7.3 6.2 6.8 6.9 6.4

Tol 6.7/6.6 7.0 6.9 7.0 6.8 7.1

10% Moisture/TFE/

TDCE 1.8/1.8 0.074 0.028† 0.010 ND

Ben 7.9/8.1 0.45 0.20 0.10 0.040

TCE 5.1/5.2 0.24 0.12 0.071 0.032

Tol 7.2/7.2 0.31 0.26 0.13 0.056

10% Moisture/aluminum/

TDCE 1.8/1.8 0.41 0.21/0.21 0.24 0.053

Ben 7.9/8.1 2.5 1.1/1.1 1.5 0.37

TCE 5.1/5.2 1.1 0.35/0.36 0.65 0.14

Tol 7.2/7.2 2.0 0.49/0.46 1.3 0.19

1% Moisture/TFE/

TDCE 3.0/3.1 0.064±0.02**

Ben 4.5/4.3 0.17±0.5

TCE 7.2/7.1 0.25±0.08

Tol 6.7/6.7 0.39±0.08

1% Moisture/aluminum/

TDCE 3.0/3.1 0.50±0.11

Ben 4.5/4.3 1.2±0.5

TCE 7.2/7.1 1.4±0.3

Tol 6.7/6.7 2.6±0.6

* ND not detected

† Sample replicate lost

** Mean and standard deviation, n = 5; 1-day storage.

how the samples were collected, after five or more

days of storage at 4°C, the TCE concentration estimates were consistently lower than the mean of

the adjacent samples by more than 90%. In addition, all of the samples covered with aluminum

foil and wrapped with PVC tape showed concentrations of Tol ranging from 0.1 to 0.3 μg/g after

five days of storage. Since Tol was not observed in

any of the other field samples collected for this

study, its source was most likely the adhesive used

in the PVC tape. This assumption was confirmed

by the analysis of this material.

The results of the laboratory experiments performed with modified core liners are shown in

Table 3. These samples differed from those obtained in the field by being laboratory fortified,

held in a brass cup (smaller exposed surface/mass

ratio), and using two layers of TFE for the samples

covered with this material. Two trends established

by these experiments were 1) analyte concentration stability was markedly better for the desiccated condition and 2) aluminum foil was superior to TFE as a barrier for the prevention of volatilization losses. The first trend can be explained

by a dry mineral surface’s greater affinity for the

sorption of VOCs (Chiou and Shoup 1985, Smith

et al. 1990). This is a condition under which physical processes, perhaps involving van de Waals

forces, help retain the VOCs (Sawhney and Gent

1990). The stability of the analytes on the desiccated soil can, therefore, be attributed to the condition of grain surfaces prior to treatment. The second trend can be explained by the observation that

sheets of pliable TFE, used for covering ends of

6
core liners, can be permeated by many gases.

This phenomenon has been established for

oxygen (Barbeau et al. 1995), and although not

yet documented, has been demonstrated using a vapor fortification process (Hewitt and

Grant 1995) to treat a soil with TDCE, Ben,

TCE, Tol, ethyl benzene, and para- and orthoxylene, held in glass ampoules covered with

TFE.

A closer look at the results in both Tables 2

and 3 shows a fairly continuous decreasing

trend in analyte concentration with time for

the TFE covered samples, but a more sporadic

trend for aluminum foil. An explanation for

this discrepancy between the coverings: while

TFE allows for uniform rate of loss by penetration through the entire covered end of the

core liner, vaporization losses occur only

around the rim when aluminum foil is used.

The tightness of the seal between these two

metal surfaces was variable from sample to

sample, resulting in variable rates of loss for

individual samples.

The most important finding of these two experiments (Table 2 and 3) is that VOC volatilization

losses are not prevented by covering the open ends

of core liners with either of these two materials.

The rate of VOC losses from intact soils held in a

core liner thus would be more dependent on the

rate of analyte diffusion in a given matrix. Therefore, grain size, soil type, moisture content, organic carbon content, transportation conditions,

etc., would all be variables. Based on the experiments performed, unsaturated soils with low organic carbon and clay contents would be suspect

after very short periods of storage, perhaps even

less than a single day. In contrast to the poor performance of TFE sheets of <0.02 mm thickness,

the formulation and ≥ 0.13 mm thickness of the

material used to seal VOA vials serves as an adequate barrier for the prevention of VOC volatilization losses over a period of a couple of weeks

(Hewitt 1995c). Indeed, solutions of several VOCs

(TDCE, TCE, perchloroethylene, Ben, Tol,

ethylbenzene, and para- and ortho-xylene) showed

only a 5% to 15% reduction in concentrations when

held in Teflon-lined gray butyl rubber-capped

VOA vials for 28 days under similar conditions as

the covered core liners.

Extruded samples

Table 4 presents TCE concentration variations

for samples collected with different size plastic

syringes and as a function of whether samples

Table 4. Extruded samples.

a. Comparison of samples collected with 3- and 10-cm3

syringes and transferred directly to VOA vials.

3-cm3 syringe 10-cm3 syringe

(μg TCE/g) (μg TCE/g)

3.4±0.4* 4.0±0.4

* Average and standard deviation, n = 5

b. Comparison of samples collected with either 3- or

10-cm3 syringes, half of the samples being extruded directly into VOA vials, the other half extruded into a plastic bag, stored for 1- to 2-minute period and then transferred to a VOA vial.

3-cm3 syringe 10-cm3 syringe

VOA vial plastic bag VOA vial Plastic bag

(μg TCE/g) (μg TCE/g) (μg TCE/g) (μg TCE/g)

1.6±0.4† 0.14±0.09 3.1±0.6 0.72±0.16

† Average and standard deviation, n = 4

were extruded directly into a vial or were temporarily stored in a plastic bag. The two samplers used in these experiments were 10- and 3-

cm3 plastic syringes with 1.4- and 0.8-cm i.d., respectively. A statistical comparison of the mean

TCE concentrations estimates for these samplers,

when transferred immediately to VOA vials containing water, found a small but significant difference at the 95% confidence level. On the average the samples collected with the 3-cm3 syringe were 15% lower in estimated TCE concentration.

The second experiment looked at the effect of

extruding an intact soil core into a plastic bag for

temporary storage. When samples passed through

this additional step were compared to samples

transferred directly to prepared VOA vials, those

extruded from a 3-cm3 syringe showed a loss of

greater than 90% in TCE concentration, while those

transferred with the 10-cm3 syringe showed a loss

of 77%. Both of these experiments suggest that

sample size (i.e., surface area to mass ratio) is an

important variable, and that large volatilization

losses are likely when an extruded soil sample is

exposed for less than 2 minutes, even if placed inside a plastic bag. Based on these findings both

the diameter of the soil collection device (i.e.,

Geoprobe, Veihmeyer tube, etc.), and the method

by which an extruded sample is transferred to a

prepared vial can significantly influence the VOC

concentrations present.

7
Collection vessel experiment

From the data in the last table (Table 5) we can

assess the effect of adding a soil sample to a VOA

vial containing water vs. adding soil to an empty

vial and then adding water. These experiments

used composited samples to minimize effects of

spatial variability. The results of these experiments

show that even if the water is added immediately

after the soil sample, measurable TCE was lost.

When the period between addition of soil and

water was increased, and temporary covers were

used, greater than 60% loss of TCE resulted. Similar findings have also been reported for laboratory

experiments comparing treated and field-contaminated soils transferred to vials with and without

solvent (Jenkins and Schumacher 1987, Hewitt et

al. 1995). Therefore, vials into which soils are transferred for in-vial handling and analysis methods

cannot have their hermetic seals broken to introduce a solvent, or for any other reason, without

significant VOC loss. An exception to this statement is when the soil sample is immersed into a

solvent in which the VOCs are highly soluble (i.e.,

methanol, etc.), then the VOA vial can be repeatedly opened and aliquots withdrawn without

significant VOC losses (Hewitt 1995b).

The results in Table 5 also show that the amount

of TCE lost did not appear to change when the

addition of water was varied between 2 to 200 minutes. One explanation for this is that the TCE in

the soil plugs rapidly achieved an equilibrium condition with the air inside the vial. Therefore, when

the water was introduced, TCE was lost due to displacement (10 mL of water/10 cm3 of air) and other

air exchange processes. The rapid attainment of

equilibration for these soil plugs (3.6 cm2/g, surface area to mass ratio) agrees with the previous

experiment, showing that 90% of the TCE was lost

in less than 2 minutes when similar plugs of soil

were temporarily stored in plastic bags.

DISCUSSION

Once in-vial methods are used for site investigations, samples with VOC concentration more

representative of their environment will be

handled and analyzed by off-site laboratories. Reducing volatilization losses by using in-vial methods, samples that better represent the site conditions will often equate to higher concentrations.

Therefore, laboratories will have to be better informed of the site conditions and the sampling and

analysis plan. The reason for increased awareness

Table 5. Comparison of pairs of composited

samples added to VOA vials with and without

solvent present.

Time (min.) lapse before addition

of water/temporary cap/depth Immersed Solvent added

(cm) of samples collected (μg TCE/g) (μg TCE/g)

0.1/None/45 1.7/1.6 1.3/1.1

2/Parafilm/38 1.7/1.6 0.50/0.50

20/VOA septum/40 1.7/1.5 0.53/0.69

200/VOA septum/43 1.9/2.1 0.60/0.59

Note: Four samples collected at a depth of 35 cm with a 5-

cm3 syringe established mean and standard deviation of

2.0±0.4 μg TCE/g.

is to avoid the potential problem that could occur

when samples that require purge and trap gas

chromatography mass spectrometry (PT/GC/MS)

analysis have concentrations of 1 ppm or greater,

as that would damage the detection system.

Samples with these high VOC concentrations will

become a common occurrence on those sites where

VOCs can be easily detected (smelled) by field

personnel. To address this issue, Methods 5021 and

5035 recommend that two or more colocated

samples be collected, thus allowing for a screening analysis to be performed prior to PT/GC/MS.

One logical solution would be to always collect

one colocated sample for equilibrium HS analysis

(Hewitt et al. 1995). The concentrations established

by HS would inform the analyst how to prepare a

colocated sample, or which colocated sample

should be then taken for PT/GC/MS analysis.

However, as pointed out earlier, the sample is

likely to be compromised with regard to VOC concentration, unless a nondisruptive and limited

exposure transfer is made to a VOA vial that is

either prepared for in-vial handling and analysis

or that contains an appropriate solvent.

If PT/GC/MS analysis is required, VOC concentrations exceed 1 ppm, and an organic solvent

such as methanol cannot be used on-site. At

present there is no effective way of storing an intact soil sample so that it can be placed in a solvent off-site, without allowing for uncontrolled

volatilization losses. Collection of samples in core

liners that are then covered with either sheets of

TFE or aluminum foil fail to maintain a VOC concentration representative of the field condition, as

would VOA vials requiring their hermetic seal be

broken so as to introduce a solvent after sample

collection.

However, a device is under development that

shows promise for allowing colocated samples to

8
be held for a couple of days without altering the

VOC concentration present (Turriff et al. 1995).

This sampling tool maintains the soil structure

during collection, storage and transfer as would a

plastic syringe; however, it is made out of either

stainless steel and proprietary composite material,

and uses Viton O-rings for hermetic seals. These

materials are believed to rival that of the currently

accepted VOA vial with regard to inertness and

preventing volatilization losses. In its current design, once an undistrubed soil core has been obtained by pushing the core barrel into an exposed

surface and removing it, a gas tight cap is used to

seal the opening. After estimating the concentration of VOC present for a colocated sample, the

soil can then be extruded after moving the cap

from this temporary holding chamber, and transferred directly into an appropriately prepared

VOA vial.

Another topic that this study addressed was

sample size. Subsurface sample collection is both

a very costly and time-consuming activity. Efforts

to minimize the impact of these two factors has

led to use of smaller and more rapid sampling systems. The results of this study show that as the

surface area/mass ratio increases for intact soil

cores, time of exposure needs to decrease in order

to maintain VOC concentrations representative of

the in-situ conditions. When samples are retrieved

from intact core liners or from recently excavated

pits, samples should be collected and transferred

within a few minutes. However, if subsurface soils

are retrieved in the barrel of a device with a diameter of less than 1.5 cm, and the soil has to be extruded prior to subsampling, the subsequent collection and transfer most likely cannot be performed without substantial volatilization losses.

In general, as the diameter and cohesiveness of the

matrix decreases and vapor pressure of the analyte

increases, the ability to obtain samples that are

representative of the in-situ conditions diminishes.

Furthermore, with time playing such a critical variable for small diameter extruded soil cores, it becomes unlikely that even sequentially collected

colocated samples, would be representative of one

another.

CONCLUSIONS

Soil samples retained in core liners covered with

either sheets of TFE-fluorocarbon or aluminum foil

are subject to volatilization losses. Uncontrollable

volatilization losses occur within seconds of exposure for samples with a large surface/mass ratio. Thus, soils obtained in small diameter coring

devices should be extruded directly into appropriately prepared analysis vials. Sample vials that

do not contain a organic solvent before soil sample

collection cannot have their hermetic seals broken

without incurring volatilization losses. To maintain site-representative VOC concentrations in soil

samples, any collections and transfers for in-vial

analysis must occur rapidly with limited structure

disruption and exposure.

LITERATURE CITED

Barbeau, D.S., T.G. Ellis and C.P.L. Grady Jr.

(1995) Oxygen leakage during respirometric measurement: A caution on the use of PTFE tape. Water Research, 29(4): 1211–1212.

Chiou, C.T. and T.D. Shoup (1985) Soil sorption

of organic vapors and effects of humidity on sorptive mechanism and capacity. Environmental Science and Technology, 19: 1196–1200.

Griffith, T.J., G.A. Robbins and T.M. Spittler

(1988) A new method for field analysis of soils

contaminated with aromatic hydrocarbon compounds. In FOCUS Conference on Eastern Regional

Water Issues, National Water Well Association, September, Stamford, Connecticut, p. 223–248.

Hewitt, A.D. (1995a) Determining volatile organic

compound concentration stability in soil. In Proceedings of 11th annual Waste Testing and Quality Assurance Symposium, 23–28 July, Washington, D.C.,

1995.

Hewitt, A.D. (1995b) Preservation of volatile organic compounds in soil subsamples. American

Environmental Laboratory, 16–18 August.

Hewitt, A.D. (1995c) Enhanced preservation of

volatile organic compounds in soil with sodium

bisulfate. USA Cold Regions Research and Engineering Laboratory, Special Report 95-26.

Hewitt, A.D. and C.L Grant (1995) Round-robin

study of performance evaluation soils vapor-fortified with volatile organic compounds. Environmental Science and Technology, 29: 769–774.

Hewitt, A.D., T.F. Jenkins and C.L. Grant (1995)

Collection, handling, and storage: Keys to improved data quality for volatile organic compounds in soil. American Environmental Laboratory,

January–February.

Hewitt, A.D., P.H. Miyares and R.S. Sletten (1993)

Determination of two chlorinated volatile organic

compounds in soil by headspace gas chromatrography and purge-and-trap gas chromatography

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mass spectrometry. Hydrocarbon Contaminated Soils,

3: 135–145. Chelsea, Michigan: Lewis Publishers.

Hewitt, A.D., P.H. Miyares, D.C. Leggett and T.F.

Jenkins (1992) Comparison of analytical methods

for determination of volatile organic compounds.

Environmental Science and Technology, 26: 1932–8.

Illias, A.M. and C. Jaeger (1993) Evaluation of

sampling techniques for the analysis of volatile and

total recoverable petroleum hydrocarbons (TRPH)

by IR, GC, and GC/MS methods. Hydrocarbon Contaminated Soils, 3: 147–165. Chelsea, Michigan:

Lewis Publishers.

Jenkins, T.F. and P.W. Schumacher (1987) Comparison of methanol and tetraglyme as extraction

solvents for the determination of volatile organics

in soil. USA Cold Regions Research and Engineering Laboratory, Special Report 87-22.

Lewis, T.E., A.B. Crockett, R.L. Siegrist and K.

Zarrabi (1994) Soil sampling and analysis for volatile organic compounds. Environmental Monitoring

and Assessment, 30: 213–246.

Pavlostathis, S.G. and G.N. Mathavan (1992)

Desorptive behavior of trichloroethylene in contaminated soil. Environmental Science and Technology, 26: 532–79.

Sawhney, B.L. and M.P.N. Gent (1990) Hydrophobicity of clay surfaces: Sorption of 1,2-dibromoethane and trichloroethylene. Clays and Minerals,

38: 14–20.

Siegrist, R.L. and P.D. Jenssen (1990) Evaluation

of sampling method effects on volatile organic

compounds measurements in contaminated

soils. Environmental Science and Technology, 24:

1387–1392.

Smith, J.A., C.T. Chiou, J.A. Kammer and D.E.

Kile (1990) Effects of soil moisture on the sorption

of trichloroethylene vapor to vadose-zone soil at

Picatinny Arsenal, New Jersey. Environmental Science and Technolology, 24: 676–683.

Turriff, D., C. Reitmeyer, L. Jacobs and N. Melberg (1995) Comparison of alternatives for sampling and storage of VOCs in soil. In Proceedings of

11th Annual Waste Testing and Quality Assurance

Symposium, 23–28 July, 1995, Washington, D.C., p.

51–58.

U.S. Environmental Protection Agency (1986)

Test methods for evaluating solid waste. Vol. 1B.

SW-846.

Urban, M.J., J.S. Smith, E.K. Schultz and R.K.

Dickinson (1989) Volatile organic analysis for a

soil, sediment or waste sample. In: 5th Annual

Waste Testing and Quality Assurance Symposium, U.S.

Environmental Protection Agency, Washington,

D.C., p. II-87–II-101.

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headspace analysis of volatile organic compounds

in soils. Environmental Science and Technology, 27:

709–713.

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February 1996

Obtaining and Transferring Soils for In-Vial Analysis of

Volatile Organic Compounds

Alan D. Hewitt and Nicole J.E. Lukash

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road Special Report 96-5

Hanover, New Hampshire 03755-1290

U.S. Army Environmental Center

Aberdeen Proving Ground, Maryland 21010-5401 SFIM-AEC-ET-CR-96002

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17

Collection procedures Soil sampling Volatile organic compounds

In-vial analysis Transfer procedures

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

The ability to retain volatile organic compounds (VOCs) while collecting and transferring intact soils for in-vial

analysis was evaluated with field and laboratory samples. Experiments were designed to assess if VOC

concentrations are maintained in an intact soil sample when 1) held for under an hour in a metal core liner, 2)

held for days in a metal core liner sealed with TFE–flourocarbon sheets or aluminum foil (ASTM D4547-91), 3)

held for less than 2 minutes in a plastic bag after extruding from a sampling device, and 4) immediately

transferred to an empty vial to which a solvent was added later. Results indicate that these procedures are all

highly susceptible to volatilization losses. To maintain site-representative VOC concentrations, collection of

soil samples for in-vial analysis should occur within minutes of exposing a fresh surface by using a device that

limits soil structure disruption and exposure.