United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Las Vegas NV 89193-3478
Research and Development
EPA/600/S4-91/011 Sept. 1991
EPA Project Summary
Molecular Optical Spectroscopic
Techniques for Hazardous Waste
Site Screening
DeLyle Eastwood and Tuan Vo-Dinh
The U.S. Environmental Protection
Agency is interested in field screening
hazardous waste sites for pollutants in
surface water, ground water, and soil.
This report Is an initial technical over-
view of the principal molecular spectro-
scopic techniques and instrumentation
and their possible field-screening appli-
cations at hazardous waste sites. The
goal of this overview is to describe the
power and utility of molecular spectro-
scoplc techniques for hazardous waste
site screening and to define the main
strengths, weaknesses, and applica-
tions of each major spectroscopic tech-
nique. These spectroscopic methods
include electronic (ultraviolet-visible ab-
sorption and luminescence) and vibra-
tional (infrared absorption and Raman
scattering) techniques. A brief discus-
sion is also given for some other tech-
niques that rely *on spectroscopic
detection (colorimetry and fluorometry
as well as Imrnunoassay and fiber-optic
chemical sensors).
The cost of Instrumentation and
analysis and the time needed for analy-
sis are briefly addressed, and broad
guidelines are given for three catego-
ries of instrumentation: portable, field
deployable, and semi-field deployable.
An outline of the spectroscopic prin-
ciples and instrumentation for each par-
ticular spectroscopic technique is
presented, and state-of-the-art ap-
proaches are described. Advantages,
limitations, sensitivities, and examples
of specific techniques and their appli-
cations to environmental pollutants are
also discussed.
This Project Summary was devel-
oped by EPA's Environmental Monitor-
ing Systems Laboratory, Las Vegas, NV,
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
. The U.S. Environmental Protection
Agency (EPA) is interested in field screen-
ing of hazardous waste sites for pollutants
in surface and ground water as well as
soil. Major reasons for this interest are to
achieve improved cost effectiveness and
to expedite remedial investigations at Su-
perfund sites and thus reduce the time lag
between sampling and the receipt of ana-
lytical data. Field analytical screening can
also help to confine a detailed field investi-
gation to those areas of a site which are
truly contaminated and thus reduce the
number of samples sent to the analytical
laboratory, thereby providing more com-
prehensive environmental studies as well
as more relevant data with reduced cost
and time.
Often, for field screening, optical spec-
troscopic methods and experiments that
are field deployable or portable provide
attractive alternatives to more common EPA
methods such as gas chromatography and
mass spectrometry. Optical spectroscopic
methods permit large number of samples
to be screened, characterized, and priori-
tized in the field with little or no sample
preparation. These screening techniques
permit rapid response and considerable
Uf} Printed on Recycled Paper
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cost savings because detailed analyses
are required only for a selected subset of
samples. Spectroscopic techniques may
sometimes provide information on unusual
sample types or on nonvolatile compounds
that are of high-molecular weight or ther-
mally labile. For functional groups or geo-
metrical isomers, these techniques may
also provide specific structural information
complementary to methods such as gas
chromatography. Spectroscopic techniques
may also offer advantages for in situ mea-
surements (with fiber optics), remote mea-
surements, flow-through analyses, and
nondestructive testing.
Each Spectroscopic technique has cer-
tain advantages and disadvantages.
Some may be more widely applicable,
may be more feasible for field deploy-
ment using current technology, or may be
more specific or sensitive for trace identi-
fication or classification. All of the tech-
niques discussed in this report have the
potential for field application either by
themselves or in conjunction with appro-
priate separation or chromatographic
steps. Recent rapid advances in com-
puter hardware and software, chemomet-
rfcs, and pattern recognition algorithms,
although beyond the scope of this report,
have also been combined with advances
In Spectroscopic Instrumentation to improve
the analysis of complex environmental pol-
lutant mixtures and extract maximum infor-
mation from data sets.
The main objective of this report is to
provide a technical overview and assess-
ment of the principal molecular spectro-
scoplc techniques and Instrumentation with
applications for field screening at hazard-
ous waste sites. These methods currently
Include U V-visib!e absorption and lumines-
cence (electronic) spectroscopy as well as
infrared absorption and Raman (vibrational)
spectroscopy. For each method, a brief
outline of the Spectroscopic principles and
Instrumentation considerations is given to
familiarize the reader with the present state-
of-the-art approach. Advantages, limita-
tions, sensitivities, and examples of specific
techniques and their applications to envi-
ronmental analyses are also discussed.
Specific highlights are also given for ad-
junct techniques such as colorimetric and
fluorometric analysis with chemical
dorivatlzatJon, Spectroscopic immunoassay
techniques, and fiber-optic chemical sen-
sors. The range of possible applications of
spectroscopfc methods for field analysis is
very broad and might include uses for
identification, classification, semiquant'rta-
tion, and quantitation.
This report is meant as a technical
assessment and source document. This
document can provide a basis for early
decision-making on potential Spectroscopic
techniques for field screening.
A table summarizes the applicability of
each Spectroscopic technique for field and
laboratory use, together with advantages,
limitations, sensitivity, current field avail-
ability, and estimated cost and time. It is
hoped that this overview will allow an ap-
preciation of the power and utility of mo-
lecular Spectroscopic techniques for
hazardous waste site screening.
Discussion and Conclusions
Spectroscopic approaches can pro-
vide valuable qualitative and quantitative
information with substantial savings of
time and money. Instruments and meth-
ods, developing rapidly in this growing
area, can greatly improve environmental
analytical technology. All of the Spectro-
scopic methods have specific advantages
and shortcomings and have potential ap-
plicability for particular environmental
problems. Table 1 summarizes the ad-
vantages, limitations, and sensitivities with
examples of specific techniques and their
application to environmental pollutants.
This table also includes definitions of por-
table, field-deployable and semi-field-de-
ployable instruments and includes relative
estimates of cost and time factors.
Ultraviolet-visible absorption spectros-
copy is a mature technique that has good
quantitative accuracy for single compounds
after separation, or for simple mixtures. If it
is used in conjunction with high-perfor-
mance liquid chromatography using an op-
tical multichannel analyzer as a detector,
the entire spectrum for each chromato-
graphic peak can be recorded Its sensitiv-
ity is moderate and its specificity is low.
Colorimetric reagents can greatly increase
the specificity of the method and improve
sensitivity by moving the spectrum of the
reaction product into the visible region with
high absorption coefficients. Ultraviolet-vis-
ible absorption spectroscopy is most use-
ful for unsaturated compounds (aromatic
or heterocyclic).
Ultraviolet-visible luminescence (fluo-
rescence and phosphorescence), when
applicable, can be the most sensitive spec-
troscopic technique for trace and ultralrace
analysis, especially with laser excitation. It
is useful in aqueous solutions to the part-
per-billion to part-per-trillion level. Specific
techniques most useful in the field include
synchronous luminescence and room tem-
perature phosphorescence. Luminescence
is applicable to most polyaromatic com-
pounds and their derivatives and can be
made applied to many other compounds
by using fluorometric reagents for chemi-
cal derivatization reactions. It can also be
used with high performance liquid chroma-
tography and multichannel detection. Lu-
minescence is much more selective for
identification or classification purposes than
ultraviolet-visible absorption but less se-
lective than infrared or Raman spectros-
copy. Its selectivity can be enhanced using
various excitation and emission wave-
lengths and by time or phase resolution
methods, and indirect detection methods
such as fluorescence quenching or energy
transfer.
Infrared absorption spectroscopy (dis-
persive and Fourier transform) has been
used in field applications, especially for
monitoring air pollutants using a gas cell,
for characterizing oil or hazardous chemi-
cals where structural information from group
frequencies is useful and where sensitivity
is not the critical factor. Infrared devices
are also useful as real-time detectors with
GC-FTIR and for specific quantitation ap-
plications such as oil and grease. Dis-
advantages include the need for sample
preparation to eliminate water, which is the
major interferent, some difficulties related
to quantitation, and the moderate sensitiv-
ity of the technique. Lately, more compact,
rugged instruments along with better
sample preparation and signal processing
techniques that are designed to increase
the sensitivity of this method have made it
more attractive for field use.
Raman spectroscopy complements in-
frared spectroscopy because it also pro-
vides structural information but with different
selection rules. Raman spectroscopy is
not sensitive to water and can use visible
or near-infrared optical techniques. Until
recently, Raman was considered to have
several disadvantages for field use includ-
ing complex instrumentation, need for la-
ser excitation, fluorescence interferences
in the visible, and relatively low sensitivity.
These disadvantages have been some-
what reduced by the advent of more com-
pact Raman spectrometers, smaller and/or
near-IR lasers, and special, more sensitive
Raman techniques. The most promising
Raman technique for field use is
surface-enhanced Raman spectroscopy in
which Raman scattering efficiency can be
enhanced by factors of as much as 10" for
some compounds when a chemical is ad-
sorbed on a special roughened metal (Cu,
Ag, Au) surface. Although this technique
may be promising for future field applica-
tions, it is not yet fully understood or devel-
oped and may not apply to all chemicals.
The advantage of the technique is that it
has the potential to combine the sensitivity
of luminescence with structural information
similar to that provided by infrared spec-
troscopy.
Other techniques that rely on Spectro-
scopic detection and that greatly enhance
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the utility of spectroscopic methods include
cobrimetry, fluorometry, immunoassay, and
some fiber-optic chemical sensors. Fiber-
optic sensors may also use some change
in the optical properties of the fiber or
cladding or may be used as probes for
most of the spectroscopic techniques dis-
cussed.
Spectroscopic techniques are being
used with increasing frequency for field
screening, allowing rapid response and
reduced costs for environmental monitor-
ing programs. Such techniques also help
to optimize sampling efforts and help to
prioritize samples for more detailed analy-
sis. Some spectroscopic methods can be
used in place without sampling, e.g., fiber-
optic chemical sensors, whereas others
can be used with portable instrumentation
or field deployable instruments set up in a
mobile laboratory. Recent instrumentation
developments, such as more compact la-
sers, miniaturized optical hardware, new
types of detectors such as charge-coupled
devices, increased use of fiber optics, and
better computer software for spectral data
processing and pattern recognition have
increased the utility of these spectroscopic
methods.
Further research and development ef-
forts are heeded to improve the field ap-
plicability of current and new
spectroscopic analytical techniques, to
make instruments more portable and com-
pact. Also, new techniques that employ
field-ready instruments need to be ac-
companied by detailed analytical proto-
cols, appropriate standards, calibration
criteria, and appropriate quality assur-
ance for specific pollutant classes. Field
spectroscopic instruments and methods are
a rapidly improving and growing analytical
area which can greatly improve environ-
mental analytical technology.
A better appreciation of the conclu-
sions, relative to the applicability of these
spectroscopic techniques, can be obtained
by reviewing Table I.
Table 1. Characteristics of Spectroscopic Techniques lor Field Analysis
Applicability Advantages Limitations Sensitivity
Current Field
Applicability
Related Lab
Techniques &
Sensors
UV-vIs Absorption
Polyaromatic
Compounds (PACs)
Dyes
Colorimetric Reaction
Products
Mature Technique
Instrumentation
Readily A vailable
Good Quantitative
Accuracy for Single
Compounds and
Simple Mixtures
Few Interferences
by Nonaromatics
Spectral Data
Available
Unspecific
(Compared to IR and
Luminescence)
Extensive Sample
Preparation
Quantitation may be
Affected by Solvent,
Polarity, or Medium,
Chemical Complexation
Moderate Sensitivity
pom - ppb in
Favorable Cases
Portable
- Hand-held Colorimeter
- Colorimetric Kits
Field Deployable
Instrumentation with
Multichannel Detectors
HPLC Detectors
UV-VIS Techniques
-FT
-Derivative
LT Matrix Isolation
Reflectance
Photoacoustic
Spectroscopy
Fiberoptic
Colorimetric
Sensors
Multichannel
Detectors
- Diode Arrays
-CCDs
UV-vis Luminescence (Fluorescence and Phosphorescence)
Polyaromatic
Compounds
Fluorescent Dyes
Fluorometric Reaction
Products
PCBs
Phenols
Pesticides
Semivolatiles
Nonvolatiles
Petroleum Oils
Most Sensitive Method
for Trace and
Ultratrace Analysis
when Applicable
Instrumentation
Readily A vailable
No Interference by
Water
Few Interferences by
Nonaromatics
Some Structural
Specificity
-Enhanced by
Special Techniques
Limited to Compounds
with Fairly High
Luminescence Yields
(Usually PACs, unless
Derivatized)
Relatively Unspecific
for Structural
Information
(Compared to IR) .
Quantitation
Complicated by
Differences in Quantum
Yields, Quenching,
Microenvironments
Limited Reference
Spectra Available
Excellent Sensitivity
ppb (pptrillion or
Less with Laser
Excitation)
Dependent on
Quantum Yields
__
Portable Instruments
Available
Field Deployable
Instruments Available
Flow-through Oil-Water
Monitors and HPLC
with Multichannel
Detectors
Front Surface - RTP
Luminescence
Techniques
- Fluorescence
- Phosphorescence
- Synchronous
- Time and Phase
Resolution
- Polarization
-RTandLT
-3D
- Microscopy
Fiber Optic
Fluorometric
Sensors
Multichannel
Detectors
- Diode Arrays
-CCDs
(Continued)
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Ttblt 1. Continued
Applicability Advantages
Limitations
Sensitivity
Current Field
Applicability
Related Lab
Techniques &
Sensors
UV-vls Luminescence (Fluorescence and Phosphorescence) (continued)
Very Selective
-Enhanced by Time
and Wavelength
Variability
Can Distinguish
Geometrical Isomers
Fluorescence
Quenching or
Energy Transfer
- Indirect Ways
to Measure Non-
luminescent
Molecules
Synchronous Fluorescence
Increased Specificity
for Individual PACs
or PAC Classes in
Complex Mixture
Petroleum Oils
Creosotes
Increased Specificity
Less Spectral
Overlap
Classification ofPAHs
by Number of Rings
Useful for Screening
Combine with Other
Luminescence
Techniques
Decrease in
Sensitivity with
Narrower Bandpasses
and Wavelength Offset
Loss of Vibrational
Structure in Spectrum
Need Dual Scanning
Monochromators
Need Polychromatic
Source
Good Sensitivity
Slightly Lower than
Fluorescence Emission
Dependent on
Instrumental
Conditions
Dependent on Stokes
Shift of Compound
Portable Instruments
under Development
Field Deploy able
Instruments
Available
L T Measurements
Time and Phase
Resolution
Derivative
Remote Monitor
under Development
Synchronous
Phosphorescence
Room Temperature Phosphorescence (RTP)
Most Luminescent
PACs, PCBs,
PAHs
Directly or with
HoavyAtom
Pertufbar
Easy Sample Prep
Eliminates Scatter
and Fluorescence
Background
Longer Lifetimes
titan Fluorescence
No Need for Cryo-
genic Instrumentation
Useful for Screening
Additional Selectivity
Due to Perturber
Oxygen may Quench
in Solution
Less Structure than
LTP
Substrate/Technique
Dependent
Quantitation may be
Complicated
Limited Corrected
Spectra Available
Good Sensitivity
ppb in Favorable Cases
Dependent on Quantum
Yield of Compound
Dependent on
Efficiency of
Perturber
Portable Instruments
Under Development
Field Deployable
Instruments Available
Front Surface
Rigid Medium
-Filter Paper
- TLC Plate
Dosimetry
Easy Sample Prep
Can Compare with
LT Techniques for
Optimization
• Time Resolution
TLC
Organized Medium
- Micelle Solution
- Cyclodextrin
Low Temperature Luminescence (Fluorescence and Phosphorescence)
Luminescent PACs
PCBs
Higher Sensitivity,
Specificity than RT
Vibrational Structure
Similar to Raman
Quantitation Over 6
Orders of Magnitude
Distinguish Isomers
Very Selective
-Enhanced by Time
and Wavelength
Variability
Cryogenic Apparatus
More Complicated
Need Skilled Operator
Less Reference
Spectral Data than RT
Some Analytes Matrix
Dependent
Excellent Sensitivity
pptrillion in Optimal
Cases
Improved with Laser
,
Limited Semi-Field
Deployability
LT Techniques
- Shpolskii Spectra
- Laser-line
Narrowing
- Site Selection
- Matrix Isolation
Low Temperatures
77 K to4K
(Continued)
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Table 1. Continued
Applicability Advantages
Limitations
Sensitivity
Current Field
Applicability
Related Lab
Techniques &
Sensors
Infrared (Dispersive)
Organic and Inorganic
Determination of
Specific Functional
Groups
Organic and Inorganic
Determination of
Specific Functional
Groups
Routinely Used for
Real-Time GC and
Vapor Analysis
Highly Specific
Structural Data on
Group Frequencies
Mature Technique
Instrumentation Widely
Available
Spectral Libraries
Available
Mid/low Sensitivity
Water is Interferent
Requires Special
Optics/Solvents
Quantitation
Difficulties
Week Optical
Sources and
Detectors
Less Sensitive than
UV-vis Absorbance
Much Less Sensitive
than Fluorescence
ppthousand to ppm
in Favorable Cases
Portable and Field
Instruments Available
Portable Unit with
Gas Cell
Quantitation of Grease
and Oil
ATR Attachments for
Solids, Oils
FTIR
GC/LC-FTIR
Infrared (Fourier Transform)
Highly Specific
Structural Data on
Group Frequencies
Instrumentation
Widely Available
Real-Time Flow
throughVapor
Applications
- GC-FTIR
Spectral Libraries
Available
Less Sensitive than
Luminescence
Requires Special
Optics/Solvents
Can Tolerate Some
Water (Background
Subtraction)
Organics Detection
1-10 ppthousandin
Water
More Sensitive than
Dispersive IR
- Signal A veraging
ppm to subppm in
Favorable Cases
Field and Semi-field
Deployable
-With or Without GC
- Volatiles/Semivolatiles
Adaptable to Use
with SFC
GC/LC-FTIR
Matrix Isolation
- LT for Sensitivity
Microscopy
Near Infrared
Single Compounds
Simple Matrices
Organics Overtones
Sources and Optical
Materials Better than
Mid-IR
Optically Good Sensor
Materials
Can Distinguish Major
Components of Simple
Matrix
Fewer Interferences
than Mid-IR
Less Spectral
Structure than Mid-IR
- Overtone Overlap
- Less Specificity
- Interpretation
Complicated
Not Useful for Complex
Matrices
Signal Processing and
Pattern Recognition
Required
Low Sensitivity
10-1 ppthousand
_
Portable Near-IR
Instrument with Fiber
Optic Probe
Characterization of Oil
Bulk Chemical
Analysis
Surface/Pollutant
Interaction Studies
Near IR Sensors
Process Control
(Continued)
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Tibti 1. Continued
Applicability Advantages
Limitations
Sensitivity
Current Field
Applicability
Related Lab
Techniques &
Sensors
Normal Raman Spectroscopy (NfJS)
Organic and Inorganic
Aqueous Solutions
Biological Matrices
Polymers
Specific as IR for
Structural Information
Different Selection
Rules - Complements
IR
Fewer Interferences
IhanlRlnvisor
near-IR Regions
Water and Glass not
Interferences
Good Optics and
Solvents Available
Can Handle Unusual
Sample Shapes/Sizes
Fluorescence Interfer-
ence in UV-vis
Requires Laser Source
Relatively Complex
Instrumentation
Requires Skilled
Operator
Not as Mature as IR
Relatively Poor Limits
of Detection
Moderate Sensitivity
1000~20ppm
Semi-field Deploy able
Instruments under
Development
Research in:
- Aqueous Solutions
- Biological Matrices
- Polymers
Special Raman
Techniques
-SERS
- Resonance
-CARS
- Microprobes
- Microscopy
LT Applications
Surface Enhanced Raman Spectroscopy (SERS)
Many Pollutants
Demonstrated for:
-Pyridina
-Hydrazina
-PAHs
-Psstiddes
Specific in Structural
Information
More Sensitive than
Normal Raman
As Sensitive as
Luminescence in
Favorable Cases
No Interference by
Water
(See Also NRS)
Relatively New Tech.
Surface/Substrate
Material Dependent
Reproducibility
Requires Laser and
Special Substrate
Not all Analytes
Enhanced Equally
Few Spectral Libraries
(See Also NRS)
Good Sensitivity for
Selected Analytes
ppm-ppbin
Favorable Cases
Field Deployable
Instrumentation under
Development
Research to Op-
timize Techniques
Microscopy
Microprobes
Surface Studies
Fiber-Optic
Sensors
HPLC (under
Development)
Multichannel
Detectors
(Continued)
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Table 1. Continued
Applicability Advantages
Limitations
Sensitivity
Current Field
Applicability
Related Lab
Techniques &
Sensors
Resonance Raman
PACs Absorbing in UV
Phenols
Specific in Structure
May Eliminate
Fluorescence
Background
(See Also NRS)
Only Chromophore
Vibrations Enhanced
Limited,to UV Ab-
sorbing Compounds
- Mainly PACs
Quantitation 'Difficult
Not Comparable to
Other Raman
Techniques
UV Laser Source
Complex
Instrumentation
(See Also NRS)
Fair Sensitivity in
Favorable Cases with
Chromophore
Vibrations
Many Practical
Difficulties
-
Chromophore
Characterization
Biological
Application
Definitions of portable, field deployable, and semi-field deployable as used in this table are:
Portable: Field Deployable:
Battery powered
One person can carry
Little sample prep. (<10 mm.)
Instrument cost < $30,000
Analysis cost < $30
Generator powered
Compact, two people can lift (several instruments in mobile lab)
Relatively simple sample prep. (< 1 hr.)
Instrument cost $30,000 to $100,000
Analysis cost $30 - $200
Semi-field Deployable:
Can fit.in mobile lab
Complex or fragile instrument
Often considerable sample prep. (> 1 hr.)
Instrument cost >$1QO, 000
Analysis cost > $200
Definitions of abbreviations as used in this table are:
A TR Attenuated Total Reflectance
CARS Coherent Anti-Stokes Raman Spectroscopy
CCD Charge-Coupled Device
FTIR Fourier Transform-Infrared Spectroscopy
GC Gas Chromatography
HPLC High Performance Liquid Chromatography
IR Infrared Spectroscopy
LC Liquid Chromatography
LT Low Temperature
NRS Normal Raman Spectroscopy
PAC Polyaromatic Compounds
PAH Polyaromatic Hydrocarbons
PCB Polychlorinated Biphenyls
ppb/ppm part per billion/part per million (mg/mL, \ig/mL)
RTP Room Temperature Phosphorescence
SERS Surface-Enhanced Raman Spectroscopy
SFC Supercritical Fluid Chromatography
TLC Thin-Layer Chromatography
UV-vis Ultraviolet-Visible Spectroscopy
•&U.S. GOVERNMENT PRINTING OFFICE: 1991 - M8-028/40064
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DeLyle Eastwood is with Lockheed Engineering and Sciences Company, Las Vegas, NV
89119. Tuan Vo-Dinh is with Oak Ridge National Laboratory, Oak Ridge, TN 37831.
William H. Engalmann is the EPA Project Officer, (see below).
The complete report, entitled 'Molecular Optical Spectroscopic Techniques for Hazard-
ous Waste Site Screening," (Order No. PB91-195990/AS; Cost: $23.00, subject to
change) will be available onry 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
Las Vegas, NV 89193-3478
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati, OH 45268
BULKRATE
POSTAGE & FEES PAID
EPA PERMIT NO. G-35
Official Business
Penalty for Private Use $300
EPA/600/S4-91/011
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