United States
Environmental Protection
Agency
Environmental Monitoring Systems,
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S4-82-067 Jan. 1983
SEPA Project Summary
Development of a Tunable
Zeeman Spectrometer for
Analysis of Toxic Organic
Compounds
T. Hadeishi, R. McLaughlin, and J. Millaud
This program was undertaken to
investigate the application of a new
analytical technique called tunable
atomic line molecular spectroscopy
(TALMS) to the detection of a variety
of volatile organic molecules of
concern to the Environmental Protec-
tion Agency. During the first phase of
the study a prototype instrument was
built and tested to demonstrate the
detection of both small (i.e., less than
four atoms) and complex molecules.
During the second phase a more
compact instrument was constructed
for delivery to EPA, Research Triangle
Park, NC before January, 1982. This
second instrument was optimized for
the detection of the more complex
organic molecules benzene and chloro-
benzene.
TALMS is a high resolution, molec-
ular differential absorption technique
used in the ultraviolet-visible spectral
region. It utilizes the splitting of an
atomic emission spectral line from a
lamp in a magnetic field (the Zeeman
effect). One split line (Zeeman com-
ponent) is made to overlap a rotational
line associated with an electronic
transition of the analyte molecule by
proper adjustment of the magnetic
field. Other Zeeman components of
this same atomic line that do not
overlap the absorption feature are
used as reference lines. The concen-
tration of the molecule is then deter-
mined by differential intensity mea-
surements of these two Zeeman
components. TALMS was first devel-
oped to detect inorganic diatomic and
triatomic molecules which exhibit
well defined rotational spectra in the
visible and ultraviolet spectral regions,
e.g., NO, SO2, NO2. Rationale for
expected high specificity and high
sensitivity with the TALMS instrument
for large complex, organic molecules
are discussed. Estimates of detection
limits, resolution, selectivity, and
linear range of the TALMS technique
are also given.
TALMS data on nitric oxide and
formaldehyde are presented as a part
of this study. The TALMS spectrum of
formaldehyde near 3390 A is discussed
since this data is the highest resolution
data yet obtained on this compound
and illustrates the selectivity attain-
able with the technique. During the
second phase of this work, the line
shapes of the absorption features
responsible for the benzene and
chlorobenzene TALMS signals near
2537 A were obtained. Line shape
information can be used to optimize
the sensitivity of the instrument for a
given compound. Using this informa-
tion, it was possible to build a second
instrument with a magnetic field
strength that was optimum for the
detection of benzene at 2537 A. Both
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benzene and chlorobenzene give
TALMS signals with the same mercury
line at 2537 A. The line shape informa-
tion for the compounds allowed a field
strength and configuration to be
chosen that effectively eliminated the
interference of chlorobenzene on the
benzene TALMS signal. Block dia-
grams, photographs of the prototype
instrument, and descriptions of its
components are included.
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
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Increased utilization of advanced
technologies has led to the need to
monitor a large variety of toxic organic
and inorganic species. The identifica-
tion and quantification of almost all
organic compounds are presently ac-
complished using some type of chro-
matographic technique, e.g., GC, GC/MS,
HPLC, etc. These methods are time
consuming, frequently not very selective,
and, in the case of the GC-MS, require
expensive equipment. A highly selective
technique that depends on high
resolution spectrometric principles
would be faster and reducethe likelihood
of incorrect qualitative analysis. The
goal of this study, which was performed
at the Lawrence Berkeley Laboratory, is
to develop an instrument to be used for
highly selective and sensitive organic
analysis. This instrument should ideally
be compact, relatively inexpensive, and
easy to operate.
Those methods that depend only upon
the interaction of radiation with the
sample most closely approach the ideal
case. Contamination and loss problems
are greatly reduced when the sample is
only moved into a light beam. The
technique whose development is de-
scribed in this report represents a step
in this direction for the determination of
both organic and inorganic species.
Although non-gaseous samples must be
volatilized to use this technique, this
alteration is common in other types of
organic analysis, e.g., GC, GC-MS, LC-
MS.
An analytical technique called Tunable
Atomic Line Molecular Spectroscopy
(TALMS) has recently been developed at
the Lawrence Berkeley Laboratory. It is
capable of the detection and measure-
ment of a large number of both organic
and inorganic molecules with high
sensitivity. The selectivity of TALMS is
such that molecules can be identified
and quantified even in the presence of a
large amount and number of interfering
substances. The number of compounds
that can be detected is almost unlimited,
depending only upon the presence of
narrow, line-like features in the ultra-
violet-visible absorption spectrum of the
compound in the gas phase. This
technique also requires minimal sample
handling.
TALM spectroscopy consists of splitting
a source atomic emission spectral line
by means of a magnetic field (Zeeman
effect) and making a differential absorp-
tion measurement between one Zeeman
component that has been magnetically
tuned to match an analyte absorption
line and an unmatched Zeeman reference
component. The difference in polariza-
tion between the Zeeman components
permits the matching and nonmatching
wavelengths to be alternately selected
and the absorption measured very
rapidly with an electrooptical device
called a Current Controlled Retardation
plate (CCR). The TALM spectrometer
detects the difference in absorption
between the Zeeman components. The
differential absorption is then propor-
tional to the amount of molecular species
whose absorption line is matched by
one of the components of the source
lamp.
One remarkable feature of TALMS is
its essential freedom from background
interference Since the difference in
wavelength between the Zeeman com-
ponents of the source emission line is
typically 0.04 nm, any particle scattering
or semi-continuous absorption will
affect both components equally. There-
fore, the differential absorption mea-
surement will remove this interference
from the total signal. Hence, this type of
interference, which is a problem in most
spectroscopic methods, does not affect
TALMS measurements.
Conclusions and
Recommendations
Tests with the TALMS system on
diatomic, triatomic, and tetratomic
molecules indicate that these molecules
contain rotational features similar in
sharpness to that of atomic lines Larger
molecules, e.g., benzene at certain
wavelengths, also show large changes
in absorption intensity within a small 60
GHz (2 cm ') spectral interval. TALMS
data, limited available data from ultra-
high resolution absorption experiments,
and theoretical considerations make it
evident that sharp line-like rotational
structure and/or very sharp changes in
the slope of absorption features are
present in larger organic compounds
and can be detected by TALMS. To
demonstrate this detection capability, a
benzene and chlorobenzene detecting
instrument has been constructed and
will be delivered to EPA, Research
Triangle Park, NC, before January,
1982
The TALMS technique has a number
of features that are useful for deter-
mining toxic organic substances. It has
an inherent resolution exceeding 500,000
It utilizes a principle of operation that is
totally different from the currently used
chromatographic methods Therefore it
provides an independent confirming
analysis. The sample pretreatment
required for the TALMS method is much
less than that required for chromato-
graphic procedures. It should be possible
to volatilize low boiling components
from a solid or liquid sample directly into
the light path of the instrument and
perform the analysis with no further
sample treatment Because the applica-
tion of TALMS analysis is simpler than
chromatographic procedures, it should
be possible to develop an instrument
that requires less skill and experience
on the part of the analyst Samples may
be sealed in previously evacuated cells
and stored in the event another deter-
mination is required at a later date.
In order to utilize the TALMS tech-
nique effectively, a data base of atomic
emission lines which match molecular
absorption features must be constructed.
The most logical way to do this is simply
to make magnetic scans using emission
lines from atoms that have the highest
possible density of spectral lines in the
region where molecular absorption is
intense Future efforts should be
directed toward fabricating high inten-
sity light sources that produce as many
emission lines as possible, toward
production of the data base required for
qualitative and quantitative analysis;
and toward analysis of complex en-
vironmental air samples
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T. Hadeishi, R. McLaughlin, and J. Millaud are with the University of California.
Berkeley. CA 94720.
D. R. Scott is the EPA Project Officer (see below).
The complete report, entitled "Development of a Tunable Zeeman Spectrometer
for Analysis of Toxic Organic Compounds," (Order No. PB 83-139 535; 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 Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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