United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S2-85/125 Dec. 1985
Project Summary
Effects of Residual Organic
Matter on Elemental
Analyses by Spark Source
Mass Spectrography (SSMS)
David Stern
A research program was designed
and conducted to define the effect of
organics in SSMS and to evaluate
several sample preparation methods for
their removal. Samples of known or-
ganic content were fabricated by dilut-
ing NBS SRM 1633 fly ash with a
mixture of organic compounds. The
SRM 1633 fly ash was spiked with
several trace elements prior to this
mixing. Samples containing 0. 10, 50,
and 90 percent organic material were
developed. These fabricated samples
and NBS SRM 1632 coal were analyzed
by three laboratories using SSMS with-
out prior pretreatment (neat) and after
processing by several preparation pro-
cedures. The effects of organic material
on neat SSMS analysis were assessed
for the various concentration levels.
Samples containing < 50 percent or-
ganic material could be successfully
analyzed by SSMS without pretreat-
ment. Difficulties were encountered
with 90 percent organics. Four prepara-
tion procedures (Parr oxygen bomb, HF
bomb, low temperature ashing, and
mineral acid extraction) were evaluated
for removal of organic interference and
maintenance of sample integrity for
SSMS, AAS (primarily Hg), and ICP
analyses. Conclusions were drawn re-
garding their suitability for use in the
Level 1 and/or Level 2 analysis schemes
and the benefits of further research.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory. Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
A three-phased approach to the envi-
ronmental assessment of stationary
sources of pollution has been developed
by EPA's Air and Energy Engineering
Research Laboratory at Research Triangle
Park (AEERL-RTP). The first phase. Level
1, is devoted to comprehensiveness and
employs broad survey techniques to
define the hazard potential of source
em issions a nd to identify possible control
needs. Level 2 seeks more specific ele-
mental composition and compound identi-
fication information, while Level 3 uses
process and control monitoring to define
temporal variation of source emissions.
Although the Level 1 sampling and ana-
lytical scheme has been used for several
years by the EPA and its contractors,
questions still exist regarding the per-
formance of the techniques in meeting
Level 1 criteria of precision and accuracy.
Of particular concern is the multielement
analytical technique, spark source mass
spectrography (SSMS), used for Level 1
elemental surveys. SSMS can determine
70 elements simultaneously with an
accuracy (combined with sampling ac-
curacy) of a factor of 2 or 3, a criterion set
for Level 1 environmental assessment
measurements. In conducting Level 1
studies, however, questions arose as to
whether such limits could be achieved for
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all of the elements measured in all of the
sample matrices encountered in station-
ary source assessments. The effect of
organic matter on SSMS analyses and if
interference of such organic matter could
be eliminated by various sample prepara-
tion techniques were unknown, but ad-
verse effects were suspected.
A research program was designed and
conducted to define the effect of organics
on SSMS and to evaluate several sample
preparation methods for their removal.
Major work elements required to accom-
plish this were:
1. Fabrication of test samples from
National Bureauof Standards(NBS)
Standard Reference Material (SRM)
1633 (fly ash), additionally spiked
with nine metals and an organic
mixture of L-ascorbic acid, benzoic
acid, and graphite.
2. Preparation of samples for SSMS
analysis by three techniques (Parr
oxygen bomb, low temperature
ashing, and hydrofluoric acid
bombs) and for inductively coupled
argon plasma (ICP) and atomic
absorption (AA) analysis by Level 1
acid extraction.
3. Elemental analysis of neat and
prepared samples by SSMS at three
laboratories, and m-house analysis
of the acid extracted material bylCP
and AA.
4. Evaluation of quantitative data for
Level 1 and 2 applications and
assessment of SSMS photoplate
quality.
Experimental Procedures
Fabrication of Test Samples
The fabricated test samples were pre-
pared from spiked NBS SRM 1 633 fly ash
and an organic mixture of 80 percent L-
ascorbic acid (Fisher Scientific Co.), 10
percent benzoic acid (Fisher Scientific
Co.), and 10 percent spectral grade graph-
ite (National brand-Union Carbide). The
NBS fly ash was chosen because it
represents a well characterized sample.
Prior to mixing with the organics, it was
spiked with nine elements (U, Pb, Ce, I,
Ag, Se, As, Sc, and Cl) to disguise its
identity and to obtain information on the
recoverability of these elements. The
organic mixture was chosen because it
contributed only oxygen, hydrogen, and
carbon to the test samples. Also, it formed
an abundance of molecular spectral lines
on the ion sensitive photoplates which
were typical of those that might be caused
by residual organic material in environ-
mental samples.
The test samples were fabricated from
the spiked NBS fly ash and the organic
mixture. Four representative dilutions of
the fly ash were produced: 100 percent
spiked NBS fly ash/0 percent organic
mixture, 90 percent spiked NBS fly
ash/10 percent organic mixture, 50
percent spiked NBS fly ash/50 percent
organic mixture, and 10 percent spiked
NBS fly ash/90 percent organic mixture.
These classes of test samples will be
referred to throughout the remainder of
this Summary as 0,10,50, and 90 percent
organic matter, respectively. (The NBS fly
ash organic contributions were consid-
ered to be negligible with respect to the
final organic content of the test samples.)
Sample Preparation
Most of the aliquots from the four
classes of test samples were analyzed
neat (i.e., no preparation prior to making
into electrodes). The remaining aliquots
were subjected to three preparation tech-
niques: Parr oxygen bomb (PB), low
temperature ashing (LTA), and hydro-
fluoric acid bomb (HFB).
The Parr bomb was modified for trace
metal analysis by replacing the standard
electrodes with electrodes of 97 percent
platinum and 3 percent rhodium and by
fitting the bomb with a quartz liner
including a cover. Level 1 procedures
were followed. The LTA method used the
LFE Model 302 LTA. A preweighed sam-
ple, placed in a quartz dish, was ashed for
several hours. It was then reweighed and
agitated to expose fresh surface. Ashing
was continued until a constant weight
was obtained. The HFB method called for
digestion in a mixture of aqua regia and
HF. Digestion was accomplished by seal-
ing the bomb and heating in an oven at
100°C for 1 to 2 hours. All sample
preparations were conducted in-house,
and extracts were submitted to other
laboratories for SSMS analysis.
An acid extraction (AE) procedure was
performed on selected samples according
to the Level 1 acid extraction method for
solid samples and particulate filter sam-
ples to be subjected to cold vapor mercury
analysis. This procedure specifies a 6-
hour extraction with a 4:1 mixture of
HNOs and HCI, respectively. These ex-
tracts were analyzed only in-house.
Analytical Methods
The laboratories used for SSMS ele-
mental analysis represented a cross-sec-
tion of instrument types and procedural
details. SSMS analyses were performed
on SRM 1633/organic mixtures and on
NBS SRM 1632 coal samples after prepa-
ration by the PB and the LTA techniques.
Additional samples were selected and
prepared by these techniques, and the
extracts were then submitted to the partic-
ipating laboratories for analysis. Table 1
gives the number of analyses done by
each laboratory on the four classes of
samples. The electrode preparation,
SSMS operation, and photoplate analysis
procedures used by each laboratory are
similar in theory and follow the basic
guidelines of the Level 1 manual.
All AA spectrophotometry (AAS) anal-
yses were performed in-house on a Perkin
Elmer Model 460 equipped for both flame
and flameless methods. The cold vapor
technique described in the Level 1 manual
was used for all mercury determinations.
Other elemental determinations by AAS
employed either standard flame or graph-
ite furnace (Model HGA 2100) tech-
niques.
Selected elemental determinations
were also made by ICP spectroscopy. A
Jarrell-Ash Model 1160 Plasma Atom-
Comp™, equipped with 24 fixed wave-
length channels and a Mark V N+1
channel, was used for all ICP analyses.
Results
Most of the neat samples were analyzed
by SSMS with relatively few problems.
The 90 percent organic samples could
not, however, be analyzed in a neat form
by two of the participating laboratories
because sample electrodes burned too
quickly to be analyzed in their instru-
ments. The third laboratory was able to
analyze the 90 percent neat sample
because of a different instrument design,
but experienced increased pressure in
the ion source and greater difficulty in
operating the SSMS because of a slower
charge accumulation. No such problems
were encountered with 0, 10, or 50
percent samples.
The accuracy of data from neat analyses
was analyzed for elements with known
NBS or spiked values. The 0 percent
sample was used as the baseline for all
effects considered. Data reported for the
0, 10, and 50 percent samples indicate
that there is little difference in the results
for these three samples.
Several preparation methods were
evaluated with respect to their effects on
SSMS determinations. Three of the meth-
ods (PB, LTA, and HFB) effectively elim-
inated most of the interfering molecular
spectra. The neat sample plates exhibited
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Table 1. Summary of SSMS Data Collection
Number of analyses
Laboratory
A
B
C
% Organic
0
10
50
90
0
10
50
90
0
10
50
90
Neat
2
2
2"
2'
1
1
1
b
3
3
3
C
PB
1
1
1
1
--
-.
-.
-
1
1
1
1
LTA HFB
._
_.
-_
--
-_
--
-.
1h
..
..
1 1
1
'Lab A needed to dilute one run each of 50% and90% neat samples by 10 times. They were able to
give analyses for the other high percentage samples that were duplicated.
bLab B could not run the 90% organic sample neat, and used L TA instead.
"When 90% neat sample was tried by Lab C, the electrodes eroded much too rapidly to obtain an
analysis.
multiple molecular spectra throughout
and caused suspected interferences with
Hf, Lu, Ho, Dy, Gd, Du, Br, and Zn
determinations. They were tedious to
analyze and require greater qualitative
data reduction time.
The Level 1 acid extraction procedure
extracted substantial quantities of most
elements. With some exceptions, quanti-
ties sufficient to meet Level 1 require-
ments were extracted. However, the data
clearly show a negative bias owing to
incomplete dissolution.
Accuracy analyses were also conducted
for neat and prepared samples for com-
parison to Level 1 and 2 acceptance
limits. These data revealed that many
more inaccurate determinations are low-
er than the expected values. In fact, only
12 percent of the inaccurate determina-
tions were higher than expected. There-
fore, contamination due to the prepara-
tion methods appears to be minimal.
However, a number of elemental losses
are specific to certain preparation meth-
ods. The largest contributor to the ele-
mental loss category was the PB method.
This high PB error can be attributed to
the fact that incomplete sample combus-
tion occurs frequently. When the residue
(left after the PB preparation) was re-
tained and combined with the solution
prior to SSMS analysis, better results
were obtained.
An alternative approach to the accuracy
analysis indicates that the general prob-
lem element determinations for all labor-
atories occur with Ta, I, Ag, Cl, Si, and Be.
These elements are consistently listed
outside of the precision range of SSMS.
Other problem elements that appear to be
specific to each laboratory are: Laboratory
A—RB, Fe, and Al; Laboratory B—W, Cd,
Br, and Cr; and Laboratory C—Sc.
Conclusions
Several conclusions were drawn from
the organic effects study:
• Organic components of a sample can
adversely affect, and in some cases
preclude, SSMS data collection.
• Organic molecular spectra can hinder
qualitative interpretation of the ele-
mental spectra.
• Molecular spectra produced by organic
constituents are readily discernible by
SSMS analysts.
• Interference from the coincidence of
organic and elemental spectra was not
a problem.
• For the test organic matrix used, 50
percent organic content was tolerable.
It is clear from the data obtained that, in
some cases, preparation prior to SSMS
analysis is necessary. In addition, the
delineation of sample preparation meth-
ods suitable for Level 2 elemental anal-
yses is highly desired.
Several conclusions were also drawn
from the sample preparation study:
• The Parr Oxygen Bomb (PB) eliminates
organic constituents adequately for
SSMS analysis. Although this proce-
dure can result in a mixed phase
sample, it appears to be the most
comprehensive SSMS preparation tech-
nique when all residues can be col-
lected and analyzed. While the method
is inadequate for the dissolution of
many elements, it is an excellent
preparation method for cold vapor
mercury analysis. In terms of Level 1
elemental analysis, the only significant
drawback to this method is the limited
sample size that can be accommodated
by the standard apparatus.
• L ow Temperature Plasma A shing (L TA)
is superior to any technique studied for
the elimination of organic matter.
However, when nominally volatile
elements are of interest, the method is
questionable; halogen losses repre-
sent a fundamental problem with the
method. A major advantage of the
method is its ability to accommodate
large sample sizes. Disadvantages
include its vulnerability to ambient
environmental contamination and the
long ashing times required for some
samples.
• The Modified Hydrofluoric A cid Diges-
tion Bomb (HFB) is the most compre-
hensive dissolution technique studied.
With the addition of a fuming nitric
acid step, organics can also be re-
moved. Concentration steps achieved
by solution evaporation will result in
the loss of silicon; halogen losses also
occur. While the boric acid step aids
sample dissolution, the resulting ma-
trix interferes with graphite furnace
AAS measurements.
• Level 1 Acid Extraction (AE) is ade-
quate for the preparation of paniculate
samples for cold vapor mercury anal-
ysis. Some other elements can also be
successfully extracted by this method;
however, it has limited application
potential for Level 2 analysis.
Recommendations
In summary, the Level 1 elemental
analysis scheme was found to be reliable
and to provide the kind of information
desired from the Level 1 study. Problems,
noted with some SSMS determinations,
could be eliminated by additional work in
this area. The preparation of paniculate
filter samples for SSMS analysis by the
AE procedure may bias the resulting data.
The HFB method shows great promise as
a Level 2 preparation procedure for
analytical techniques requiring solution
samples. Additional work in this area
would, no doubt, be beneficial.
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David Stern is with CCA/Technology Division, Bedford, MA 01730.
Frank E. Briden is the EPA Project Officer (see below).
The complete report, entitled "Effects of Residual Organic Matter on Elemental
Analyses by Spark Source Mass Spectrography(SSMS)." (Order No. PB 86-119
575/AS; Cost: $22.95, subject 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:
Air and Energy Engineering Research 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
EPA/600/S2-85/125
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