&EPA

United States
Environmental Protection
Agency

Environmental Monitoring
Systems Laboratory
P.O. Box 93478
Las Vegas NV 89193-3478

June 1991

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OFFICE OF RESEARCH AND DEVELOPMENT

J	1

TECHNOLOGY SUPPORT PROJECT

High Resolution
Mass

Spectrometry

INTRODUCTION

The identification and
quantitation of organic
compounds is a fundamental
goal of both CERCLA and
RCRA. When the identity of
the organic compound is
known, the formal CLP
methods are generally able to
address the quantitation
needs. Often, however, the
exact identity of an organic
contaminant is not obvious
and is intractable to the
commonly used low resolu-
tion mass spectrometer. In
these cases, a little chemical
detective work is needed!
Many thousands of pollutants
exist, but only a few hundred

matching standards are
available, predominantly for
the Target Compound List
(TCL) pollutants. High
resolution mass spectrom-
eters (HRMS) have been
developed to provide a closer
reading of the fingerprint of a
molecule or element. With
HRMS it is possible to isolate
specific characteristic ions,
determine their accurate
mass, and thus assign the
correct elemental composi-
tion without reference stan-
dards. Thus, HRMS is a
valuable tool for structure
determination, and has
largely replaced other

techniques such as elemental
analysis for structure verifica-
tion. Data interpretation is
complex, as is the instrumen-
tation. Expert analysts must
combine their knowledge of
chemical interactions with
super-sleuthing capabilities to
effect a complete and suc-
cessful identification. The
Environmental Monitoring
Systems Laboratory-Las
Vegas has the analytical
expertise and instrumentation
necessary to provide an-
swers to the most difficult
problems of environmental
analysis.

INSTRUMENTATION

EPA
EMSL-
T5P-
691

Mass spectrometry is a three-
phase analytical procedure
consisting of ionization,
separation, and detection.
High resolution mass spec-
trometry differs from other
techniques primarily in the
separation capability. High
resolution instruments are
able to separate ions having
the same nominal mass but
differing in specific elemental
composition and hence in
accurate mass, because
each element varies from
integral mass slightly and
differently (except carbon, set

at 12.0000). HRMS has
been applied to organic and
inorganic identification at
ultratrace levels. For ex-
ample, minor organic con-
taminants, rare earth ele-
ments, and lead isotope
ratios can be identified and
used for site-specific finger-
printing. The high resolution
instrument is much larger and
more expensive than the
commonly used quadrupole
mass spectrometer. It
contains a large magnet and
an electrostatic sector to
provide a focused beam of

ions for determinations of
mass that are accurate to
1/1000 of a mass unit. This
ability to separate com-
pounds having the same
integer mass number is a
great advantage to the
analyst who is faced with a
particularly difficult mass
assignment. High resolution
mass spectrometers are
equipped with special inlet,
ionization, and computer
systems to maximize their
capabilities.

0071SX91

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INTERPRETATION

The interpretation of high
resolution mass spectral data
is a complex procedure. A
skilfful and experienced

spectroscopist incorporates
several areas of expertise
into a thoughtful reading of
the experimental data. The
analyst uses historical
information about the site and
its contamination, early

results from low resolution
mass spectrometry, knowl-
edge of the probable chemi-
cal reactions, precursors, by-
products, and experience in
recognizing the statistical
significance of a measure-
ment that borders between
two interpretations. Some-
times the particular compo-
nent of interest has been

depleted or altered by
biodegradation,
photodegradation, or another
agent. The mass spectral
analysis must then be
thoughtfully focused upon
chemical precursors or by-
products of the original
compound.

ADVANTAGES AND
LIMITATIONS

The complexity of high
resolution mass spectrometry
interpretation demands
considerable interpretive
expertise. This level of effort
is justified for identification of
unknown toxic contaminants
during site characterization
and remediation. It can also
allow the unambiguous
correlation of off-site contami-
nation to a specific site.

MitUSil

Dependable, high sensitiv-
ity detection

Legally defensible
determinations

Ability to Identify previ-
ously unlisted compounds

Site fingerprinting

UmUMlafli

Costly Instrumentation

Expert Interpretation is
needed

REFERENCES

The Wiley/NBS Registry of Mass Spectral Data, F. W. McLafferty and D, B. Stautfer, eds., 1989.

Interpretation of Mass Spectra, 3rd Edition, F, W. McLafferty, University Science Books, 1980.

FOR FURTHER INFORMATION

The EMSL-LV will support the Regions in the determination of the identity of compounds that
are intractable to routine analysis. This assistance can aid in the identification of the Poten-
tially Responsible Party (PRP).

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For more information about specialized mass
spectrometry services available at EMSL-LV

through the Technology Support Center,
contact:

Dr. Wayne Sovocool

U.S. Environmental Protection Agency

Environmental Monitoring Systems

Laboratory
P.O. Box 93478

Las Vegas, Nevada 89193-3478

(702) 798-2212
FTS 545-2212

For information about the Technology Support
Center at EMS; L V, contact:

Mr. Ken Brown, Manager
Technology Support Center
U.S. Environmental Protection Agency
Environmental Monitoring Systems
Laboratory
P.O. Box 93478
Las Vegas, NV 89133-3478

(702) 798-2270
FTS 545-2270
FAX/FTS 545-2637

The Technology Support Center fact sheet series is developed and written by
Clare L. Gertach, Lockheed Engineering & Sciences Company, Las Vegas.

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