United States
Environmental Protection
Agency
Environmental Monitoring Systems
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S4-84-016 Feb. 1984
Project Summary
Survey of Direct Analysis
Methods for Organic Compounds
in Particulate Matter
C. A. Alexander, J. R. Hoyland, R. H. Barnes, and J. S. Ogden
Spark source, secondary ion and direct
probe mass spectroscopy and infrared,
Raman and photoacoustic optical
spectroscopy were evaluated for their
present and potential usefulness in
direct (i.e., without prior concentra-
tion) qualitative and semiquantitative
analysis of aromatic hydrocarbons in
particulate matter. It was found that
spark source and secondary ion mass
spectroscopy, and Fourier-Transform
infrared, Raman and photoacoustic
spectroscopy did not provide sufficient
sensitivity for the determination of
environmental levels (low ppm by
weight) of polycyclic aromatic
hydrocarbons in particulate matter.
Direct probe thermal desorption mass
spectroscopy was found to be capable
of detection and quantification of
organic compounds, particularly high
molecular weight species not detected
with the usual extraction and gas
chromatography or gas chromatogra-
phy/mass spectroscopic analysis. The
National Bureau of Standards (NBS)
Standard Reference Material 1648 was
used to evaluate the various techniques.
It is further concluded that the organic
material absorbed on ambient particu-
late matter may be much more complex
than previously suspected.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems 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' in-
formation at back).
Introduction
Current methodology for analysis of
organic material in particulate matter
involves extraction procedures which are
tedious, time consuming, and may
contaminate the sample. Analytical
techniques normally employed for
determining the identity and concentra-
tion of extracted species include gas
chromatography (GC), liquid chromatog-
raphy (LC), or GC combined with mass
spectrometric detection (GC/MS). The
utility of GC and GC/MS techniques is
limited by the low volatility of many of the
organic species of interest, and the
efficiency of extraction is thermodynami-
cally limited by the relative free energies
of adsorption and solution. Because the
current state-of-the-art of quantitative
analysis is time consuming, costly, and
can yield uncertain or incomplete results,
a study was undrtaken of experimental
methods currently available which might
prove capable of yielding such
information without prior sample
extraction. There are several emerging
techniques which may be used to
determine organic compounds in
particulate matter without extraction,
i.e., direct methods. The present study
addresses the question of whether these
direct methods have sufficiently low
detection limits (i.e., low ppm by weight)
and quantitative capabilities to be useful
in monitoring applications.
The objective of this particular program
was to evaluate five candidate direct
methods and to make recommendations
for further development of the most
promising ones. A direct method is
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defined as one for which the sample
preparation involves no liquid extraction
or other concentration steps. The
techniques which were evaluated were
(a) temperature-programmed direct
probe mass spectrometry; (b) spark
source mass spectrometry; (c) photoa-
coustic spectroscopy; (d) Fourier
transform infrared absorbance and
Raman spectroscopy; and (e) Fourier
transform reflectance spectroscopy. The
NBS Standard Reference Material 1648,
ambient particulate matter, was used in
the evaluations. These techniques were
evaluated for qualitative and semiquanti-
tative analyses of polynuclear aromatic
hydrocarbons. Additionally, a limited
investigation was made of the
applicability of secondary ion mass
spectroscopy (SIMS) to organic
compounds adsorbed on the surface of
particulate samples.
Fluorescence spectroscopy, which is
expected to have greater sensitivity than
the optical techniques covered here, was
not evaluated since it was being studied
in another project.
Conclusions and
Recommendations
The results of this experimental
assessment of presently available direct
analysis techniques show that only the
thermal desorption mass spectrometry
technique has much chance of being of
general applicability. The spark source
MS technique does not work in enough
cases to be of practical value. Fast atom
bombardment and molecular secondary
ion mass spectrometry are both sensitive
but are not always effective for
particulate samples because the
polycyclic aromatic material in the
particulate sample is not readily
accessible at the surface exposed to the
ion beam. The optical techniques studied
suffer from the same problem since the
organic compounds have selected ener-
getically favorable sites in the particulate
phase, and these sites can be optically
shielded from the probing radiation.
Therefore the thermal desorption mass
spectrometry technique is the most likely
candidate for successful direct analysis of
organic compounds in particulate matter.
This technique can yield quantitative
data. Results obtained on the National
Bureau of Standards SRM 1648
generally duplicated those obtained by
extraction procedures, but thermal
desorption is more efficient. It was shown
that significant quantities of polycyclic
aromatics with heteroatoms, which are
generally missed by the usual extraction-
GC-MS technique, are present in
particulate matter. Whether these occur
in nature or were formed on the particles
after sample collection cannot be
ascertained at this time. However, their
presence in such abundance needs to be
addressed in any overall protocol
involving extraction and subsequent GC-
MS analysis.
Some preliminary experiments with a
state-of-the-art quadrupole mass spec-
trometer have indicated that the number
and quantity of organic species in
particulate matter may be even higher
than indicated by the mass-limited scans
made with the quantitative direct probe
mass spectrometric technique.
It is recommended that direct probe
thermal desorption mass spectrometer
studies should be continued in order to
better define the limitations of the
technique and to develop temperature
programming which will enhance
thermal fractionation of organic species.
It does not seem possible at this time to
fully identify and quantify all the therm-
ally desorbed species in particulate
matter. Consequently, future efforts
should be directed toward simplification
of the mass spectra by careful
temperature control. Possible simplifica-
tion in compound identification should be
explored through the utilization of
chemical ionization with several different
reagent gases. Additional studies directly
comparing the thermal desorption/MS
approach with conventional extraction/
GC or GC/MS approaches should be
conducted.
C. A. Alexander, J. R. Hoyland, R. H. Barnes, and J. S. Ogden are with Battelle
Columbus Laboratories. Columbus. OH 43201.
D. R. Scott and R. G. Lewis are the EPA Project Officers (see below).
The complete report, entitled "Survey of Direct Analysis Methods for Organic
Compounds in Particulate Matter." (Order No. PB 84-154 723; Cost: $10.00.
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 Officers can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park. NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 452G3
Official Business
Penalty for Private Use S300
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