United States
Environmental Protection
Agency
Atmospheric Research and Exposure
Assessment Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S3-90/010 May 1990
SEPA Project Summary
Efficiency of Dioxin
Recovery from Fly Ash
SamplesDuring Extraction and
Cleanup Process
Joe M. Finkel, Ruby H. James, and Kim W. Baughman
The data from investigations of the
efficiency of dioxin recovery from fly
ash samples during sample
extraction and subsequent column
cleanup of sample extracts are
discussed in this report. Each step of
the extraction and the column
cleanup procedures was evaluated
by using radiolabeled 14C-dioxins as
tracers. Sample extracts and eluate
fractions were analyzed by liquid
scintillation counting (LSC) and the
results confirmed by gas
chromatography/ mass spectrometry
(GC/MS). Recovery data of spiked
2,3,7,8-tetrachlorodibenzo-p-dioxin-
i4c (TCDD-1"C) and octa-
chlorodibenzo-p-dioxin-14C (OCDD-
14C) in carbon-free fly ash and fly ash
containing from 0.1 to 10% carbon
are discussed. The data indicate that
the amount of carbon in the fly ash
may affect the efficiency of dioxin
recovery. Also, procedural details
and analytical techniques are
extremely important in the
quantification of PCDDs and PCDFs.
This Project Summary was
developed by EPA's Atmospheric
Research and Exposure Assessment
Laboratory, Research Triangle Park,
NC, to announce key findings of the
research project that is fully
documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction
Currently, several different analytical
procedures are being used for the
extraction, cleanup, and analysis of
PCDDs and PCDFs (1, 2). RCRA Method
8280 and ASME's draft method entitled
"Analytical Procedures to Assay Stack
Effluent Samples and Residual
Combustion Products for Polychlorinated
Dibenzo-p-Dioxins (PCDD) and
Polychlorinated Dibenzofurans (PCDF),"
have been applied to fly ash samples for
the determination of PCDDs and PCDFs.
Using these procedures, significantly
different levels of PCDDs and PCDFs
have been found in similar fly ash
samples. These differences may be due
to changes in combustion parameters or
inherent errors in the analysis methods
such as nonreproducible extraction and
cleanup procedures Many investigators
(3, 4, and 5,) have noted differences in
the apparent recovery efficiencies of
dioxin by different extraction procedures.
The sorptivity of different fly ash
samples for organic compounds in
general has been shown to vary greatly.
Studies with 14C-labeled PAHs as
radiotracers demonstrated that the
extraction recoveries of PAHs from fly
ash are inversely proportional to the
number of rings in the PAH molecule and
that aromatic compounds are more
strongly adsorbed than aliphatic
hydrocarbons (6). These results indicate
that analyses of some fly ash samples for
PCDDs and PCDFs may be seriously
biased if not corrected for extraction
recoveries or sorptivity losses as the
concentration levels of PCDDs/PCDFs
decrease, the number of chlorines added
to the ring structures increases, or the
nature of the fly ash changes.
This report describes an effort to
evaluate various extraction techniques to
remove dioxins from fly ash and to clean-
up sample extracts by column
chromatography. General chroma-
tographic media and eluting solvents
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were evaluated. Each step in the sample
preparation was evaluated by using 14C-
radiolabeled 2,3,7,8-tetrachlorodibenzo-p-
dioxin and octachlorodibenzo-p-dioxin as
tracers. Radiolabeled dioxins allowed the
analyst to stop and evaluate each step of
the procedure, each extract, and each
column eluate fraction by liquid
scintillation counting. To validate the
radioassay, dioxin was confirmed by gas
chromatography/mass spectrometry.
Technical Approach
A single source of fly ash that was
generated from a medium-sulfur,
bituminous coal was used in this study.
The carbon content of the fly ash was
5%. A carbon-free fly ash was prepared
by heating the native fly ash for 16 hours
in a muffle furnace set at 750°G. Fly ash
samples were spiked with either 2,3,7,8-
tetrachlorodibenzo-p-dioxin-Ring-UL-14C
(TCDD-HC) or octachlorodibenzo-p-
dioxin-Ring-UL-^C (OCDD^C). Also, fly
ash samples were spiked with carbon
which came from three commercial
sources.
The samples were extracted with a
Soxhlet extraction apparatus. Fly ash
samples (10 g) in the extraction thimbles
were spiked with either TCDD-14C (88.5
ng; 9,145 pCi) or OCDD-14C(230 ng;
10,304 pCi). Extraction times were either
24 or 48 hours, and the extracting
solvents were 150 mL of methylene
chloride or toluene. Also, some samples
were extracted sequentially with
methylene chloride followed by toluene.
Three types of chromatography media
were used in the column cleanup
procedures (basic alumina, AGIO; silica
gel, Bio-Sil A; and a mixture of activated
carbon, AX-21 grade/Celite 545).
The selection of these columns and
solvents was based on the
recommendations of the ASME's
analytical procedures to assay stack
effluent samples for PCDDs and PCDFs.
All eluate fractions were either saved or
solvent exchanged with toluene or n-
nonane and submitted for liquid
scintillation counting (LSC) and, in some
cases, were analyzed by gas
chromatography/mass spectrometry.
Results and Discussion
In this study, radiolabeled TCpD-^C
and OCDD-14C with liquid scintillation
counting (LSC) were used to trace the
PCDDs through each of the steps
associated with an analytical method
based on ASME's analysis of stack
effluents from combustion processes.
The quantification of TCDD-14C and
OCDD-14C by LSC allows for lower
detection limits than does quantification
by GC/MS. Also, the use of radiolabeled
PCDD is more time and cost effective
because separation from impurities
(those not radiolabeled) is relatively
unimportant, especially in preliminary
screening or evaluation of analytical
procedures.
Soxhlet Extraction
Three types of fly ash samples were
prepared from a single source of fly ash
for this investigation: native fly ash, zero-
carbon fly ash, and carbon-spiked fly ash.
Elemental analysis of the.native fly ash
indicated the presence of approximately
5% carbon (wt/wt). Both the native fly ash
and the zero-carbon fly ash were spiked
with various amounts of carbon. Thus, fly
ash samples containing from 0% to 10%
carbon (wt/wt) were extracted for 24
hours with methylene chloride followed
by an additional 24 hours with toluene or
were extracted with only one of the two
solvents for 24 hours. The recovery
efficiencies for TCDD-14C from fly ash
spiked at 8.85 ppb and for OCDD-14C
from fly ash spiked at 23.0 ppb indicate
that the carbon content of the fly ash and
the nature of the carbon may affect the
extraction efficiencies of PCDDs if
methylene chloride is used as the
extracting solvent in the Soxhlet
extraction procedure. Also, the data
demonstrate that the recovery of OCDD-
14C with toluene was less than that of
TCDD-14C.
Column Cleanup
Chromatography Methods
When dioxins and furans are
determined at parts per trillion levels
(ppt), concentration of the sample extract
is required and extensive sample
preparation ^prpcedures^are needed.,.J,hjs
is due to the increased ratio of interfering
substances to the compounds of interest
in the concentrated extract. Many
environmental samples, after they
undergo an initial extraction or separation
such as liquid-liquid or liquid-solid
extraction may require one or more
column chromatography cleanup
procedures.
The selected column cleanup
procedures, as individual columns and as
columns in sequence, were evaluated
with TCDD-14C and OCDD-14C. The
elution sequences that were used for
TCDD-14C were based on the ASME's
procedures. However, difficulties were
noted and several changes were made
when we evaluated the cleanup
procedures for OCDD-14C. A 5 mL
standard of TCDD-14C (88.5 ng) or
OCDD-14C (230 ng) was solvent
exchanged into either toluene (n-nonane
was used with OCDD-14C) or hexane and
was concentrated to 1 mL. The resulting
concentrate was applied to the
appropriate column.
The amounts of TCDD-14C recovered
in each fraction for the various cleanup
steps are summarized in the report.
Approximately 80% or more of the
TCDD-14C was recovered or was
accountable. However, several potential
problem areas were noted. Over 70% of
the TCDD-14C immediately eluted from
the silica gel column in the first 10 mL of
hexane. If the analyst is not aware of this,
a major portion of the dioxin may be lost.
Thus, all effluent from the silica gel
column should =be.collected,, pooled,: and
concentrated to 1 mL. The data indicate
that about 90% of the TCDD-14C was
recovered from the silica gel column.
Nonpolar polychlorinated compounds
will be absorbed on the basic alumina
column; thus, this column is often used
as a second step in the cleanup
procedure. Also, this column allows for
the separation of PCBs from dioxins.
Approximately 90% of TCDD-14C was
associated with the 15% methylene
chloride in hexane fraction. This step
must be monitored closely because the
activity and uniformity of the alumina
may vary with each lot and some of the
dioxin may elute in the 8% methylene
chloride in hexane fraction.
If additional cleanup is required on a
sample extract, the carbon/ced'fe column
may be used. Chlorinated dibenzo-p-
dioxins are initially adsorbed on this
column and the interferences are
removed by eluting with solvents of
increasing polarity. The PCDDs can then
be backwashed from the column by
jnyerting the column and eluting with
toluene. ThV analyst must monitor this
procedure carefully. Approximately 20%
of TCDD-14C may be lost if a second 4-
mL portion of toluene were not collected.
After evaluating the column cleanup
procedures using TCDD-14C, we made a
few modifications in the cleanup
procedures. The report gives details of
the modifications and the effect on
recovery efficiency of dioxin. Also, we
increased the volume of toluene from 4
mL to 10 mL as the last step of the AX-21
Carbon/Celite 545 cleanup procedure.
Because the first two fractions collected
from this column in our initial evaluation
were free of TCDD-14C, the 1 mL of
hexane wash was combined with the 2
mL of 50% methylene chloride in hexane
wash.
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The total recovery or accountability of
OCDD-14C varied from 40 to 100%. and
>95% of the spiked OCDD-14C was
recovered from the silica gel column.
The cleanup procedures for OCDD-14C
with the basic alumina column were
identical with those used for TCDD-14C.
Although a small amount, if any, of
OCDD-14C remained on the column, the
elution with 10 mL of 8% methylene
chloride in hexane did contain various
amounts of the OCDD-14C. If this fraction
were discarded, >20% of OCDD-14C
may be lost.
The cleanup procedures for OCDD-14C
with the AX-21 Carbon/Celite 545
retained various amounts of the spiked
standard. Approximately 80% of the
spiked OCDD-14C was recovered.
....Although we made a few changes in
the ASME's cleanup procedures, the
evaluation of these changes with OCDD-
14C revealed additional areas for possible
problems. A major concern is the
possible loss of dioxins, especially those
that are highly chlorinated, during the
basic alumina column cleanup procedure.
In an attempt to reduce the amount of
OCDD-14C eluted from the basic alumina
column with 10 mL of 8% methylene
chloride in hexane, we changed to 10 mL
of 5% methylene chloride in hexane.
About 3% of OCDD-14C eluted with the
5% methylene chloride in hexane
fraction. This is a problem that may not
be easily resolved. Certainly this fraction
must be analyzed for the presence of
trace amounts of dioxins, especially
those that are highly chlorinated and
when recovery of surrogate standards are
low. The results obtained in one study
demonstrate another problem that must
be addressed. The technical skills and
experience of the analyst may bias the
data. We recommend that the procedures
in this report be implemented by or under
the close supervision of analysts with
considerable experience in trace
analyses.
Gas Chromatography/Mass
Spectrometry
Confirmation by GC/MS was used to
validate the data in this report. The
presence of TCDD was confirmed by
GC/MS. Replicate fly ash samples were
carried through the Soxhlet extraction
procedures. After the extracts were
concentrated to 1 mL, some of the
samples were submitted for LSC while
others were submitted for GC/MS
analysis. LSC indicated that
approximately 93% of the labeled
material was recovered. The recovery of
2,3,7,8-TCDD, as determined by GC/MS,
was 91%.
Conclusions
If trace compounds in complex
environmental samples are to be
accurately determined, appropriate
analytical procedures must be selected
and carefully followed by the analyst. The
extraction and cleanup procedures used
in the analyses of fly ash for the
determination of PCDD and PCDF must
be validated by the laboratory and the
individual analyst performing the
analysis. Laboratory control samples
(spiked matrix samples) must be carried
through the entire analytical method,
which includes sample preparations,
cleanup of sample extracts, and
instrumental analysis. Procedural details
and analytical techniques, such as the
cycling of solvent in the Soxhlet extractor,
transfer of the solutions, the exchange of
solvents, the packing of the
chromatographic media into columns,
and the volume and composition of the
extracting solvents, are extremely
important. Variable loss of dioxins can
occur in each of these steps. All extracts,
eluate fractions, and residues generated
during an analysis need to be saved for
additional analysis when the recovery of
spiked standards or surrogate standards
are extremely low in the initial analysis. If
there is a question about low recovery
after the final eluate is analyzed, the
other eluates may have to be analyzed.
With every set of samples that are
analyzed, laboratory control samples,
surrogate spiking standards, replicate
analyses, and method blanks must be
included. The extraction and cleanup
procedures to determine dioxins in fly
ash samples must be implemented by or
under close supervision of analysts with
experience in trace analyses.
The carbon content of fly ash and the
nature of the carbon may affect the
extraction efficiency of dioxin. As the
carbon content of fly ash increased, the
efficiency of spiked TCDD-14C and
OCDD-14C recovery decreased.
Modification and control of the extraction
and cleanup procedures improved the
efficiency of dioxin recover from the fly
ash samples. .
References
1. Albro, P.W.; Parker, C.E. General
approach to the fractionation and class
determination of complex mixtures of
chlorinated aromatic compounds. J.
Chromatogr. 197: 155-169; 1980.
2. Smith, L.M.; Stalling, D.L.; Johnson,
J.L. Determination of part-per-trillion
levels of polychlorinated dibenzofurans
and dioxins in environmental samples.
Anal. Chem. 56: 1830-1842; 1984.
3. Kooke, R.M.M.; Lustenhouwer, J.W.A.;
Olie, K.; Hutzinger, O. Extraction
efficiencies of polychlorinated dibenzo-p-
dioxins and polychlorinated
dibenzofurans from fly ash. Anal. Chem.
53:461-463; 1981.
4. Karasek, F.W.; Clement, R.E.; Viau,
A.C. Distribution of PCDDs and other
toxic compounds generated on fly ash
particulates in municipal incinerators. J.
Chromatogr. 239: 173-180; 1982.
5. Stieglitz, L; Zwick, G.; Roth, W.
Investigation of different treatment
techniques for PCDD/PCDF in fly ash.
Chemosphere 15: 1135-1140; 1986.
6. Griest, W.H.; Tomkins, B.A.; Caton,
J.E. EPRI Report 4792, September, 1986.
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Joe M. Finkel, Ruby H. James, and Kim W. Baughman are with Southern
Research Institute, Birmingham, AL 35255-5305.
Jimmy C. Pau is the EPA Prefect Officer (see below).
The complete report, entitled "Efficiency of Dioxin Recovery from Fly Ash
Samples During Extraction and Cleanup Process," (Order No. PB90-183
393 /AS; Cost: $15.00 subfect to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Research and Exposure Assessment Laboratory
U.S. Environmental Protection -Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EP/V600/S3-90/010
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