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By
Susan S. Sorini, John F. Schabron, and Joseph F. Rovani, Jr.
Introduction
Sample collection and handling
procedures for volatile organic analysis of soils must be
designed to minimize loss of volatile organic compounds (VOCs)
due to volatilization and biodegradation. Laboratory data can
grossly underestimate the actual VOC concentrations in a soil
if great attention is not paid to sampling and handling
techniques (Siegrist and Jenssen 1990, Turriff and Klopp
1995).
Current guidance provided by
the U.S. Environmental Protection Agency (U.S. EPA) in Method
5035 (U.S. EPA 1996a) and by the American Society for Testing
and Materials (ASTM) in D 4547-98, Standard Guide for Sampling
Waste and Soils for Volatile Organic Compounds (ASTM 2001),
gives two options for sample handling for VOC analysis. One
option is for immediate transfer of a sample after collection
in the field to a weighed volatile organic analysis (VOA) vial
that contains either VOC-free water or an aqueous preservative
solution for vapor partitioning analysis or methanol for
methanol extraction in preparation for analysis. In both
cases, samples are to be transported to the laboratory at a
temperature of 4 ± 2°C. The second option given is for storage
of an intact sample in an airtight container at 4 ± 2°C for up
to two days prior to sample preparation in the laboratory.
It has been suggested that an
empty VOA vial can be used as an airtight container to store a
soil sample during transportation to the laboratory for
analysis (Hewitt 1999). The proposed technique involves sample
collection using a coring device, such as a modified,
disposable plastic syringe from which the lower end with the
needle attachment and the plunger cap is removed. The sample
is collected in the modified syringe and then immediately
extruded into an empty VOA vial for storage during
transportation to the laboratory (Sorini et al. 2001). This
method, if accepted, would be used for high-level (>200 g/Kg)
samples with addition of methanol to the samples in the
laboratory by injection through the VOA vial septum. This
method would not be used for low-level samples, because the
closed system purge-and-trap equipment used for
low-concentration samples is not appropriate for analysis of
soil samples in methanol (U.S. EPA 1996a). As a result,
low-level samples would require injection of water or aqueous
preservative solution through the VOA vial septum, and there
is concern that VOCs would be lost when the VOA vial septum is
pierced and water or preservative solution is added to the
sample. It is assumed that similar losses would not be seen
for high-level samples when methanol is injected through the
septum, because of rapid dissolution of the VOCs into the
methanol. Questions have
been posed concerning the assumption that VOCs will not be
lost when methanol is injected into a VOA vial containing a
soil sample and also concerning possible losses associated
with storage of samples in VOA vials having pierced septa
after methanol injection. As a result, a series of tests was
performed to evaluate possible loss of VOCs when a high-level
sample is extruded into an empty VOA vial, and methanol is
injected into the sample through the septum of the vial.
First Series of Tests
Objective:
The first series of tests were
performed to compare VOC concentrations in soil samples in
40-mL VOA vials into which methanol was injected through the
septum after sample collection. For this testing, soil samples
were stored in VOA vials having pierced septa or having had
their caps replaced following methanol injection. VOC
concentrations determined for both conditions were compared to
VOC concentrations in samples directly extruded into methanol.
Technical Approach:
In the testing, 5-gram river bank
soil samples were used. The river bank soil is 49% sand, 26%
silt, 24% clay, 5.3% organic material, and approximately 14%
moisture. It has a dehydrogenase (microbial) activity of 22 mg
total product formed (TPF)/g/24 hr. Twenty-three river bank
soil samples were spiked in 5-gram En Core® samplers (ASTM
2001) to give VOC concentrations ranging from ~300 g/Kg to
~750 g/Kg (high level). The analytes of interest were vinyl
chloride, MeCl2, MTBE, 1,1-dichloroethane, CDCE, chloroform,
benzene, TCE, toluene, PCE, ethyl benzene, and o-xylene. Each
sample was spiked with 100 L of spiking solution that was
prepared by adding a methanol solution containing the analytes
of interest to gasoline-saturated water. After all 23 samples
were spiked, 5 samples were randomly selected for extrusion of
each directly into 5 mL of methanol in a 40-mL VOA vial. After
24 hours in the methanol at 4 ± 2°C, the samples were analyzed
to determine the time-zero analyte concentrations. The
remaining 18 samples were extruded into empty VOA vials for
the following series of tests, which began after the soil
samples in the VOA vials were stored for 48 hours at 4 ± 2°C.
- 3 samples: 5 mL methanol
injected through septum, stored at 4 ± 2°C for 24 hours,
analyzed
- 3 samples: 5 mL methanol
injected through septum, cooled for one hour to 4 ± 2°C, VOA
vial cap replaced with a new cap, stored at 4 ± 2°C for 23
hours, analyzed
- 3 samples: 5 mL methanol
injected through septum, stored at 4 ± 2°C for 48 hours,
analyzed
- 3 samples: 5 mL methanol
injected through septum, cooled for one hour to 4 ± 2°C, VOA
vial cap replaced with a new cap, stored at 4 ± 2°C for 47
hours, analyzed
- 3 samples: 5 mL methanol
injected through septum, stored at 4 ± 2°C for 7 days,
analyzed
- 3 samples: 5 mL methanol
injected through septum, cooled for one hour to 4 ± 2°C, VOA
vial cap replaced with a new cap, stored at 4 ± 2°C for 7
days, analyzed
The smallest size needle that
is commercially available on a gas-tight syringe having a 5-mL
capacity is a 22-gauge needle. As a result, this size of
needle was used for methanol injection in the tests described
above. The needle that was used was designed for non-coring
septum penetration. All analyses were performed using guidance
given in EPA Methods 5035 (U.S. EPA 1996a) and 8260B (U.S. EPA
1996b).
Discussion of Results: Analyte concentrations in the samples extruded into the empty
VOA vials with subsequent methanol injection were compared to
those in the time-zero samples extruded directly into methanol
by calculating average percent recovery values. These values
are listed in Table 1. The data given in
Table 1 show that for
many of the compounds of interest, the average percent
recovery values are less than 80% for both storage in VOA
vials having pierced septa and storage in VOA vials having had
the caps replaced. Secondly, the average percent recovery
values are very similar for the samples stored in the VOA
vials having pierced septa and for the samples stored in the
vials with new caps. In addition, storage time does not seem
to be a variable.
Second Series of Tests
Objective:
A second series of tests was performed to examine the effect
of needle gauge on the loss of VOCs from samples into which
methanol has been injected after sample collection. In the
testing described above, methanol was injected through the VOA
vial septa using a gas-tight syringe having a 22-gauge needle.
As mentioned above, the smallest size needle that is
commercially available on a gas-tight syringe having a 5-mL
capacity is a 22-gauge needle. As a result, in the second
series of tests, methanol was injected into VOA vials using
5-mL glass syringes having luer connectors fitted with 23, 25,
and 26-gauge luer lock needles designed for non-coring septum
penetration.
Technical Approach: In the testing, 23 5-gram river bank soil samples were spiked
to give VOC concentrations of ~250 g/Kg to ~500 g/Kg (high
level). The analytes of interest were vinyl chloride, MeCl2,
MTBE, 1,1-dichloroethane, CDCE, chloroform, benzene, TCE,
toluene, PCE, ethyl benzene, and o-xylene. Each sample was
spiked with 100 L of spiking solution that was prepared by
adding a methanol solution containing the analytes of interest
to gasoline-saturated water. After all samples were spiked, 5
samples were randomly selected for extrusion of each directly
into 5 mL of methanol in a 40-mL VOA vial. After 24 hours in
the methanol at 4 ± 2°C, the samples were analyzed to
determine the time-zero analyte concentrations. The remaining
18 samples were extruded into empty VOA vials for the
following series of tests, which began after the soil samples
in the VOA vials were stored for 48 hours at 4 ± 2°C. All
analyses were performed using guidance given in EPA Methods
5035 (U.S. EPA 1996a) and 8260B (U.S. EPA 1996b).
- 3 samples: 5 mL methanol injected through septum using a
23-gauge needle, stored at 4 ± 2°C for 24 hours, analyzed
- 3 samples: 5 mL methanol injected through septum using a
25-gauge needle, stored at 4 ± 2°C for 24 hours, analyzed
- 3 samples: 5 mL methanol injected through septum using a
26-gauge needle, stored at 4 ± 2°C for 24 hours, analyzed
- 3 samples: 5 mL methanol injected through septum using a
23-gauge needle, stored at 4 ± 2°C for 48 hours, analyzed
- 3 samples: 5 mL methanol injected through septum using a
25-gauge needle, stored at 4 ± 2°C for 48 hours, analyzed
- 3 samples: 5 mL methanol injected through septum using a
26-gauge needle, stored at 4 ± 2°C for 48 hours, analyzed
Discussion of Results: Analyte concentrations in the samples extruded into the empty
VOA vials with subsequent methanol injection were compared to
those in the time-zero samples extruded directly into methanol
by calculating average percent recovery values. These values
are presented in Table 2, along with the 22-gauge/24-hour and
48-hour average percent recovery values determined in the
first series of tests.
As shown in Table 2, no data were generated for the
25-gauge/24 hr. samples. The reason for this is that the
methanol leaked from the luer fitting between the syringe and
needle during methanol injection into these samples. It should
be noted that methanol injection into the sealed VOA vials
using syringes having luer fittings is difficult because of
leaking problems. The pressure inside the VOA vial and the
back pressure of the needle require significant manual
pressure to be applied to the syringe piston. If the luer
fittings do not seal well enough, leaking will occur.
The data presented in
Table 2 show that for many of the
compounds of interest, the average percent recovery values are
less than 80%, regardless of the needle gauge used for
methanol injection. In addition, the average percent recovery
values are very similar regardless of needle gauge and storage
time.
Discussion of Results Shown in
Tables 1 and 2: The average percent recovery values given in
Tables 1 and 2
are very similar despite the variables involved in the
testing. These variables include different storage times, 24
hours, 48 hours, and 7 days; storage with and without pierced
septa; and methanol injection using 22, 23, 25, and 26-gauge
needles. These values show a consistent VOC loss regardless of
storage time, needle gauge, and replacement of the VOA vial
cap with a new one having an intact septum.
There are two possible sources of VOC loss in the series of
tests that were performed. One possibility is that VOCs were
lost from the samples during their extrusion into the empty
VOA vials. As previously mentioned, the proposed technique
involves sample collection using a coring device, such as a
modified plastic syringe, to collect and extrude the sample
into the empty VOA vial for storage during transportation to
the laboratory. In the series of tests described above,
samples of spiked soil were extruded into empty VOA vials and
stored for 48 hours at 4 ± 2°C prior to methanol injection. A
second possibility is that the VOCs were lost from the VOA
vials during methanol injection. To determine if the VOC
losses seen in the testing described above can be attributed
to extrusion of the samples into empty VOA vials, a third
series of tests was performed.
Third Series of Tests
Objective:
The third series of tests were performed to compare VOC
concentrations in spiked soil samples extruded into 40-mL
empty VOA vials versus VOC concentrations in spiked soil
samples extruded into 40-mL VOA vials containing 5 mL of
methanol.
Technical Approach: In the testing, 5-gram river bank soil samples were used.
Spiking was performed to give VOC concentrations of ~250 g/Kg
to ~600 g/Kg (high level). The analytes of interest were
vinyl chloride, MeCl2, MTBE, 1,1-dichloroethane, CDCE,
chloroform, benzene, TCE, toluene, PCE, ethyl benzene, and o-xylene.
Each sample was spiked with 100 L of spiking solution that
was prepared by adding a methanol solution containing the
analytes of interest to gasoline-saturated water. The
following sets of samples were prepared and analyzed to
evaluate the loss of VOCs due to extrusion into empty VOA
vials. All analyses were performed using guidance given in EPA
Methods 5035 (U.S. EPA 1996a) and 8260B (U.S. EPA 1996b).
- 3 river bank soil samples in 5-gram En Core samplers:
spiked with 100 L of spiking solution, extruded into VOA
vials containing 5 mL of methanol, stored at 4 ± 2°C for 24
hours, analyzed
- 3 river bank soil samples in 5-gram En Core samplers:
spiked with 100 L of spiking solution and extruded into empty VOA vials; 5 mL methanol injected through septum of each vial
using a 23-gauge needle, stored at 4 ± 2°C for 24 hours,
analyzed
- 3 5-gram river bank soil samples in VOA vials: soil
surface spiked with 100L of spiking solution added through
opening of the vial with immediate capping after spiking; 5 mL
methanol injected through septum of each vial using a 23-gauge
needle, stored at 4 ± 2°C for 24 hours, analyzed
- 3 VOA vials each containing 5 mL of methanol: 100 L of
spiking solution injected through septum of each vial using a
23-gauge needle, stored at 4 ± 2°C for 24 hours, analyzed
Discussion of Results: The average concentration of each of the analytes of interest
in each of the various soil samples was calculated and
compared to the average concentration of the analyte in the
spiked methanol solution by calculating average percent
recovery. These values are listed in Table 3. As shown in
Table 3, the average percent recovery values for the analytes
of interest in the soil samples that were spiked directly in
the VOA vials and in the soil samples that were spiked and
extruded into VOA vials containing methanol are very similar,
except for vinyl chloride, which is the most volatile of the
analytes tested. For the VOCs, other than vinyl chloride,
these data show losses of approximately 10% for both
techniques. These losses are most likely due to the
experimental design. For the soil spiked in the VOA vials,
some loss can be expected prior to capping the vials; and for
the samples extruded into methanol, some loss can be expected
during the spiking and extrusion steps.
The average percent recovery values shown in Table 3 for the
soil extruded into the empty VOA vials are much lower than for
the other two sets of soil samples, showing a greater VOC
loss. To compare VOC loss due to sample extrusion into empty
VOA vials versus sample extrusion into vials containing
methanol, VOC concentrations in the 5-gram river bank soil
samples extruded into empty VOA vials were compared to VOC
concentrations in the samples extruded into methanol by
calculating average percent recovery values. These values are
shown in Table 4 and are very similar to those shown in
Tables
1 and 2. This suggests that the VOC losses shown in
Tables 1
and 2 are due to extrusion of the spiked samples into the
empty VOA vials. The experimental design of this testing most
likely represents a worse case scenario for possible loss of
VOCs during sample extrusion; however, it should be noted that
the data do show a significantly greater loss of VOCs from the
high-level samples extruded into empty VOA vials as compared
to VOC loss from the high-level samples extruded into
methanol. In similar studies evaluating the use of an empty
VOA vial for storage of samples during transportation to the
laboratory, soil samples were spiked directly in VOA vials
rather than extruding spiked samples into empty vials (Hewitt
1999 and Ricker 1999). As a result, VOC loss due to extrusion
into the empty VOA vials was not observed.
Conclusions
- Extrusion of high-level samples into empty VOA vials can
result in significantly greater VOC losses from the samples as
compared to losses resulting from sample extrusion directly
into methanol.
- For storage at 4 ± 2°C up to 7 days, average percent
recovery values for high-level VOC concentrations from spiked
soil samples into which methanol has been injected are very
similar for samples stored in VOA vials having pierced septa
and for samples stored in vials that were cooled and had their
caps replaced. There is also no significant difference in
average percent recovery values for storage of the samples at
4 ± 2°C for 24 hours, 48 hours, and 7 days.
- For 24 and 48-hour storage at 4 ± 2°C, average percent
recovery values for high-level VOC concentrations from spiked
samples are very similar for samples stored in VOA vials
having septa pierced using 22, 23, 25, and 26-gauge needles to
inject methanol into the samples. There is also no significant
difference in average percent recovery values for storage of
the samples at 4 ± 2°C for 24 hours and 48 hours.
- Syringes having luer connectors fitted with luer lock
needles should not be used to inject methanol into sealed VOA
vials containing samples. If the luer fittings do not seal
well, leaking will occur. A gas-tight syringe with a 22-gauge
needle works well for this purpose.
- VOCs are not lost from samples containing high-level VOC
concentrations when methanol is injected into VOA vials
containing the samples.
References American Society for Testing and Materials, 2001, ASTM Guide D
4547-98, Standard Guide for Sampling Waste and Soils for
Volatile Organic Compounds. Annual Book of Standards, 11.04,
28-37.
Hewitt, A.D., 1999, Storage and Preservation of Soil Samples
for Volatile Organic Compound Analysis. CRREL Special Report
99-5, U.S. Army Cold Regions Research and Engineering
Laboratory, Hanover, NH. Ricker, M.J., 1999, An Easy, Cost-Effective Solution for
Sampling Volatile Organic Compounds in Soils. Proceedings of
the Fifteenth Annual Waste Testing & Quality Assurance
Symposium (WTQA ‘99), Arlington, VA. Siegrist, R.L, and P.D. Jenssen, 1990, Evaluation of Sampling
Method Effects on Volatile Organic Compound Measurements in
Contaminated Soils. Environ. Sci. Technol., 24, 1387-92.
Sorini, S.S., J.F. Schabron, and J.F. Rovani, Jr., 2001,
Validation of a New Soil VOC Sampler: Performance of the En
Core® Sampler for Storage of Low VOC Concentrations and EPA
Method 1311 Volatile Organic Analytes. Laramie, WY, WRI Report
WRI-01-R005. Turriff, D.E., and C. Klopp, 1995, Comparison of Soil
Preservation and Analysis Methods for VOC Analytes.
Proceedings of the Field Screening Methods for Hazardous
Wastes and Toxic Chemical International Symposium, Air & Waste
Management Association, pp. 1236-1237.
U.S. EPA, 1996a, Method 5035: Closed-System Purge-and-Trap and
Extraction for Volatile Organics in Soil and Waste Samples.
Test Methods for Evaluating Solid Waste: Physical/Chemical
Methods (SW-846), Vol 1B.
U.S. EPA, 1996b, Method 8260B: Volatile Organic Compounds by
Gas Chromatography/Mass Spectrometry (GC/MS). Test Methods for
Evaluating Solid Waste: Physical/Chemical Methods (SW-846),
Vol. 1B.
Acknowledgments Funding for this study was provided by the U.S. Department of
Energy, National Energy Technology Laboratory, under
Cooperative Agreement DE-FC26-98FT40323 and En Chem, Inc.,
Green Bay, Wisconsin.
Disclaimer
This report was prepared as an account of work sponsored by an
agency of the United States Government. Neither the United
States Government nor any agency thereof, nor any of their
employees, makes any warranty, expressed or implied, or
assumes any legal liability or responsibility for the
accuracy, completeness, or usefulness of any information,
apparatus, product, or process disclosed, or represents that
its use would not infringe on privately owned rights.
Reference herein to any specific commercial product, process,
or service by trade name, trademark, manufacturer, or
otherwise does not necessarily constitute or imply its
endorsement, recommendation, or favoring by the United States
Government or any agency thereof. The views and opinions of
authors expressed herein do not necessarily state or reflect
those of the United States Government or any agency thereof.
Susan S. Sorini is a senior scientist, John F. Schabron, Ph.D.
is a principal scientist, and Joseph F. Rovani, Jr. is a
senior scientist at Western Research Institute in Laramie, WY.
click image to enlarge table 1
click image to enlarge table 2
click to enlarge table 3
click image to enlarge table 4
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