EPA/600/A-96/120
A fiber optic multichannel laser spectrometer system for remote fluorescence detection
in soils
Sean J. Hart, Yu-Min Chen, Bob K. Lien, and Jonathan E. Kenny*
Tufts University, Department of Chemistry, Medford, MA 02155
BL, U.S. EPA National Risk Management Research Lab, Ada, OK 74820
ABSTRACT
Fiber optic probes employing single channel laser excitation and fluorescence collection
have been seeing increasing use for remote sensing applications. However, multi-
channel systems offer enhanced capacity for qualitative and quantitative determination
of analytes. We describe a system which employs simultaneous delivery of laser
excitation wavelengths arising from stimulated Raman scattering (SRS). Separate
fluorescence responses for each excitation channel are imaged through a spectrograph
onto a CCD array detector. Each channel has a dedicated fiber optic pair to deliver and
collect light. Results will be presented which evaluate the capabilities of this type of
spectrometer for determination of organic contaminant mixtures in various sample
matrices.
Keywords: Fluorescence, remote sensing, fiber optic, laser, soils, in-situ, field test, EEM,
LIF
1. IN SITU FLUORESCENCE SENSING
In situ soil monitoring via fiber optics using laser induced fluorescence has become
popular in recent years with the advent of CPT (Cone penetrometer technology)
vehicles. Several groups have demonstrated and continue to develop systems capable
of being installed in a CPT vehicle for onsite, in-situ measurements of fluorescent
contaminants.1-2-3 The ROST (Rapid optical screening tool) system, developed by
Gillispie et al., has been commercialized and represents the advanced state of in-situ LIF
measurement technology.4 In earlier systems1-2 only one pair of optical fibers is used:
one for the delivery of laser excitation light and the other for the collection of
contaminant fluorescence. The lack of other excitation wavelengths to measure the
contaminant*s absorbtion profiles imposes a limit on the amount of analyte speciation
that can be accomplished. Often the calibration procedure employs a known
contaminant mixture as a standard such as DFM (Diesel fuel marine) or a standard jet
fuel.4 While this allows the soil contamination measured with a system to be expressed
as equivalents of the calibrant, it does not normally identify or quantify particular
species. In some applications, the identity of the fluorescent species in a mixture is as
important as knowing the relative total concentration.

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The ROST system offers a way to further characterize a particular contaminant plume
by stopping the advancement of the probe to scan the emission wavelengths and collect
lifetime data at many emission wavelengths. Such data is organized into a WTM
(Wavelength time matrix) which aids in the identification of species when the lifetimes
of species in a mixture are different.4
Our system for in-situ remote sensing simultaneously delivers up to ten different
excitation wavelengths to the sample and collects and disperses the emission due to
each. Thus, three dimensional data, i.e. excitation-emission matrices or EE Ms, are
collected in real time during a push. This system offers more complete real-time
screening capabilty than earlier systems, as well as the possibility of at least partial
speciation without stopping the push to scan.
There are several different analyte / media systems in which our instrument must be
able to function. These include aqueous systems, organic liquids such as LNAPL (Light
non aqueous phase liquid) and DNAPL (Dense non aqueous phase liquid), and a
myriad of soil types. In this communication we report laboratory and field
measurements of analytes in different media and solvent systems, including ethanol,
cyclohexane, and aqueous solutions, Ottawa sand and a silty clay type soil. In addition,
selected results from a recent field test conducted at Hanscom Air Force Base in
Lexington, MA will be discussed.
2. MULTICHANNEL REMOTE SENSING SYSTEM
2.1	Excitation source
The use of multiple channels without the need to stop and scan a light source allows
the rapid excitation and collection of fluorescence from in-situ contaminants. Our
system employs a Nd:YAG laser with second and fourth harmonic generating crystals.
The output of the fourth harmonic generating crystal, at 266.0 nm, is used to pump a
Raman shifter filled with methane and hydrogen gas (45:55 ratio). "Most of the beams
generated are Stokes shifted (longer wavelengths) but a few are anti-Stokes shifted
(shorter wavelengths). The simultaneous generation of multiple excitation wavelengths
using this source has been described in detail.5-6
2.2	Light delivery and collection
The light generated with the laser/Raman shifter combination is launched into
400/440/470mm diameter core/cladding/jacket silica-clad-silica fiber optics. There are
two main sections to the fiber optic bundle: one contains fibers for the delivery of the
ten excitation wavelengths to the soil through sapphire windows and the other contains
fibers for the collection and return of contaminant fluorescence to the detection sub-
system. The fibers are divided into two sections (10 and 20 meters respectively), for
modularity, and are connected by standard ST-style fiber optic connectors.
To reduce scattered excitation light, a different cutoff filter (Schott WG series) is used
for each channel Due to the small core diameter (400|j,m) of the fiber optics, arranging
10 filters at the spectrograph entrance slit (commonly done with a single filter) is highly

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impractical. Our solution was to cut and file the filters into circles small enough
(diameter < 2 mm) to fit into a fiber optic connector between the fibers. The details
regarding the use of filters in fiber optic connectors can be found elsewhere.7
At the probe end, the fiber tips (light delivery and collection) are fixed at 16.4°, and
are epoxied (Tra-con, Bedford, MA) inside a stainless steel tube, and then the fiber ends
are polished flat on lapping paper.8 The polished fibers (in stainless steel tubes) are
spring mounted so that they push out against the sapphire window holders. The
details of the probe body design have been given elsewhere.5
2.3 Detection subsystem
The fibers returning from the probe, propagating fluorescence from analytes, are
interfaced to an imaging spectrograph (Acton Spectropro 150, Acton Research Corp.,
Acton, MA) via a fiber optic plug. The fluorescence is detected with a CCD detector
(Princeton Instruments, Princeton, NJ) interfaced to a PC for data acquisition and
analysis. The CCD integration time for all measurements was 1-2 seconds and the
spectrograph resolution was 2.4 - 3.6 nm.
3. PROBE MEASUREMENTS
3.1 Lab measurements
The performance of the probe can be assessed by examining the EEMs (Excitation
emission matrices) of several analytes and mixtures taken in several different media. A
variety of samples have been measured and will be discussed in order to understand
the probe's performance in a wide range of media. All lab measurements utilized ten
excitation channels, with wavelengths: 257.7, 266.0, 278.4, 288.5, 299.1, 314.5, 327.3,
341.6, 362.1,378.8 nm, the full capacity of the instrument.
For solution measurements, the sample container used was a tube with one end
capped. The probe was inserted into the solution contained within. For solid sample
measurements, the probe was laid in a trough style container with the sapphire
windows in contact with the sample.
3.1.1. 3-component mixture in cvclohexane
An important measurement made was a 3 component mixture of representative 1, 2,
and 3 ring compounds. This measurement allows us to clearly examine the
instrumental response from three important classes of compounds. The standard
mixture measured contained: 3 % (v/ v) benzene, 86 ppm (w/w) naphthalene and 86
ppm (w/w) anthracene in cyclohexane.

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'5	30000
J	23750'
O	17500
_	11250
*	5000
Figure 1. EEM of 3% Benzene, 86 ppm naphthalene, 86 ppm
anthracene mixture
The EEM of the 3-component mixture measured is shown in figure 1, with the
characteristic quadruplet of anthracene dominating and to shorter excitation and
emission wavelengths the naphthalene doublet (330 ran peak) and finally the emission
of benzene (280 nm peak) can be seen in the 266.0 nm excitation channel. The single
spectrum for the 266.0 nm excitation channel for the standard mixture is shown in
figure 2, While the anthracene fluorescence in the long wavelength excitation channels
of the EEM in figure 2 is still the most intense, the smaller naphthalene and benzene
signals can clearly be seen.
90i
§
B
s
e
to
e
u
2000 -r
1800 ¦¦
1600 ¦¦
1400 ••
1200 ¦¦
1000 ••
800 ••
600 ¦¦
400
200 ••
220.0
270.0
320.0
370.0
420.0
470.0
X (nm)
Figure 2. Fluorescence spectrum (266.0 nm excitation) from 3 %
benzene, 86 ppm naphthalene, 86 ppm anthracene mixture EEM

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3.1.2. Measurement of jet fuel in soil
In preparation for our field work at Hanscom AFB, lab measurements of JP8 were
made in soil samples taken from the site. Pure JP8 was mixed with the soil samples
(silty clay). The EEM of this mixture is shown in figure 3, with the large fluorescence
intensities expected for pure fuel product even with a small particle size soil system
such as silty clay.8
30000'
22750'
« 15500
8250-
Figure 3. EEM of silty clay from Hanscom AFB mixed with JP8.
3.1.3 Aqueous phenol: linearity and detection limits
The measurement of truly aqueous aromatic compounds is an important goal
towards successful in-situ measurement of groundwater plumes. Toward that goal we
have begun work on probe measurements of species in water. The most simple starting
point is phenol due to its high solubility in water. Figure 4a is an EEM of aqueous
phenol (940 ppm) made using the tube container described above.
The upper limit of phenol's concentration signal response linearity was determined to
be 471 ppm. By extrapolation with the minimum detection signal set to baseline counts
plus 3 times the baseline standard deviation, the LOD (limit of detection) for phenol in
water was determined to be 9.7 ppm.
3.1.4. Aqueous phenol in Ottawa sand
The aqueous phenol solution was also measured in Ottawa Sand (EM Science,
Gibbstown, NJ). The EEM of phenol in Ottawa sand is shown in Figure 4b. The
absolute peak signal in solution was 860 counts vs. 554 counts when the phenol solution
was mixed with sand. This 36 % loss of signal is at least partly due to the excitation
light penetration depth being reduced in Ottawa sand (particle size 420-595 nm) vs. that
in solution.2'8

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*
'35
s
£
B
EE
s
4*
Figure 4. a) Aqueous phenol (940 ppm), b) Aqueous phenol (940 ppm) mixed with Ottawa
sand.
3.2. Field measurements
Field measurements have recently been made at Hanscom AFB (6/28/96 - 6/30/96).
During the field test, 14 pushes were made in a 2.5 day period with successful system
operation and data collection using 8 channels in all cases. The two excitation
wavelengths not used were 362.1 and 378.8 nm. The average depth pushed was
approximately 17 feet with the deepest hole at 21 feet. While the system was
configured to allow pushes to 30 feet, an exceptionally hard glacial till prevented us
from pushing deeper. Future publications will discuss the work done at that site in
more detail.
3.2.1. Quinine sulfate for calibration and power normalization
A system calibration was performed before each push to accomplish two goals: 1)
confirm system operation and channel integrity and 2) act as a measurement of beam
energy for power normalization. The compound used was quinine sulfate, well known
as a fluorescence standard and to a lesser extent as a quantum counter. This calibrant
was dissolved in ethanol and not the usual dilute H2SO4 due to damaging reaction of
the latter with the steel probe body.
All of the probe channels report fluorescence, although not uniformly. This is due to
several factors including the fiber optic attenuation of the strongest UV beams, and the
small energy (before fiber optic launch) of the high order Stokes and first anti-Stokes
beam. The net result is that the central channels (288.5 nm - 314.5 nm) have the largest
signal. The emission spectra at the excitation wavelengths measured for standard
quinine sulfate solution in ethanol (0.2 g/L) is shown in Figure 1.
According to Kasha's rule, fluorescence emission is independent of excitation
wavelength and therefore the wavelength of fluorescence peaks of quinine sulfate at the
different excitation wavelengths should be identical. This is not the case for the spectra

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Excitation X (nm)
zifto au
257.7
C
3
o
o
266.0
278.4
C/3
© IT
+2 o
c S
—H O
0>
o X
C w
CD
o
CO

O
288.5
299.1
314.5
327.3
341.6
Emission X (nm)
Figure 5. Emission spectra of quinine sulfate in ethanol, 0.2 %/L for the 8 excitation
wavelengths used in the field.

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shown in figure 5, where there are apparent shifts in the emission maxima. The spectral
shifts are due to the different cutoff filters used in each channel to reject scattered light,
3.2.2. Pushes at Hanscom AFB
The summed fluorescence signal vs. cone tip depth for a typical push is shown in figure
6. One can see two depth regions of fluorescence, with peaks at 9 feet and 15 feet. Also
shown in figure 6 is the EEM corresponding to the summed fluorescence maximum.
The EEM in figure 6 has all channels reporting fluorescence with the highest intensity in
the central excitation wavelength channels. Qualitatively this may indicate the presence
of more two ring class compounds at this particular depth. In addition, the lower
fluorescence signals extending off the long wavelength emission scale may indicate the
existence of smaller amounts of three and possibly four ring species.
As an initial verification of our in situ measurements, the groundwater and fuel depth
were measured with an oil / water interface probe (ORS Co.) immediately after the
push in a nearby monitoring well (MW-9). The fuel depth measured from the ground
surface was 14 feet and the top of the water table was 17.0 feet. The monitoring well
was approximately 15 feet down gradient from the push site and therefore the amount
of fuel product and the actual depths may differ. Nevertheless, the LIF depth profile
contains signal from 11 to 14 feet (the probe windows begin 1 foot above the cone tip
and are 1.5" apart) with a maximum signal seen at 14 feet which correlates well with the
measurement of fuel product at 14 feet. From 11 to 14 feet, the LIF signal increases
gradually and this may be due to contamination in the unsaturated zone or capillary
fringe above the free fuel product. In addition, there is a small amount of signal at 18
feet which may be due to species in the groundwater at much lower concentration than
in the fuel product layer.
Signal (counts)
t> 1250-
! ;ooo-
f 750-
"" 500-
E 250-1
Figure 6. Summed fluorescence depth profile and EEM for the peak. LIF data taken at Hanscom
AFB.

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4. CONCLUSION
We have described and demonstrated our multichannel laser spectrometer system
and probe in a variety of media. Lab measurements have been made for a three
component mixture (Benzene, naphthalene and anthracene), jet fuel in silty clay, and
aqueous phenol neat and in Ottawa sand. Field measurements have been made for
quinine sulfate in ethanol as a standard calibrant and finally, we have presented the
results for a selected push location from our recent field work at Hanscom AFB with a
summed fluorescence depth profile and an EEM from that push. We have
demonstrated the capacity of our system to measure fluorescent analytes in several
media including water, NAPLs such as jet fuel, cyclohexane and ethanol. The
simultaneous detection of our 3 component mixture demonstrates our system's ability
to discriminate among 1, 2 and 3 ring aromatics. The calibration procedure using
quinine sulfate has been tested in the field and has proven to be quick and convenient
to implement. Finally, the operation of the system and the collection of field data has
been demonstrated with a sample from our very recent field work.
5. ACKNOWLEDGEMENTS
This project was funded by the Robert S. Kerr Laboratory of U.S. Environmental
Protection Agency. Additional support was provided by the Northeast Hazardous
Substance Research Center at New Jersey Institute of Technology (NJIT project number
R-43). Although the research described in this article has been funded wholly or in part
by the United States Environmental Protection Agency under assistance agreement No.
CR-821856 to Tufts University and agreement No. R-819679 to New Jersey Institute of
Technology, it has not been subjected to the Agency's peer and administrative review
and therefore may not necessarily reflect the views of the Agency and no official
endorsement should be inferred. The authors would like to extend thanks to John
Macey and Jane Pepper for their help with the lab measurements and Susan Mravik
and John Hoggatt for their roles in operating the CPT vehicle and handling the probe
during the field measurements. The authors would like to extend special thanks to
Tom Best, site manager, at Hanscom AFB for all of his efforts to accommodate us
during the field work. In addition, the fuel and water depth data presented were taken
by him during the site investigation.
6. REFERENCES
1.	R. W. StGermain, G. D. Gillispie, "Transportable tunable dye laser for field analysis
of aromatic hydrocarbons in groundwater," Proc. Second International Symposium of
Field Screening Methods for Hazardous Waste Site Investigations, Las Vegas, NV, Feb.
11-13,1991.
2.	S. H. Lieberman, S. E. Apitz, L. M. Borbridge, G. A. Theriault, "Subsurface
screening of petroleum hydrocarbons in soils via laser induced fluorometry over
optical fibers with a cone penetrometer system", International Symposium on
Environmental Sensing, EOS/SPIE Proceeding, Vol. 1716,1992.

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3.	J.E. Kenny, A.H. Kinney, "Spectroscopy in the field", Spectroscopy, 10, 7, 32,1995.
4.	Gregory D, Gillispie and Randy W. St. Germain, "Performance characterization of
the rapid optical screening tool (ROST™), preprint from author.
5.	J. Lin, S. J. Hart, T. A. Taylor, J. E. Kenny, "Laser fluorescence EEM probe for cone
penetrometer pollution analysis", A&WMA/SPIE Symposium on Optical Sensing for
Environmental and Process Monitoring, Vol. 2367, 70-79,1994.
6.	J. Lin, S. J. Hart, W. Wang, D. Namytchkine, and J. E. Kenny, "Subsurface
contaminant monitoring by laser fluorescence excitation-emission spectroscopy in a
cone penetrometer probe", A&WMA/SPIE European Symposium on Optics far
environmental and public safety, Vol. 2504, 59-67,1995.
7.	S. J. Hart, J. Lin, J. E. Kenny, "Filters in fiber-optic connectors", to be submitted to
Applied Spectroscopy, 8/96,
8.	J. Lin, S. J. Hart, J. E. Kenny, "Improved two-fiber probe for in-situ spectroscopic
measurements", to be published in Analytical Chemistry, Sept. 15 or Oct 1,1996.

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TECHNICAL REPORT DATA
1. REPORT NO.
E P A/600/A-96/120
2 .
3. RI
4. TITLE AND SUBTITLE A FIBER OPTIC MULTICHANNEL LASER SPECTROMETER
SYSTEM FOR REMOTE FLUORESCENCE DETECTION IN SOILS
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR (S) SEAN J. HART1, YU-MIN CHEN1, BOB K. LIEN!,
JONATHAN E. KENNY1
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
TUFTS UNIVERSITY, DEPARTMENT OF CHEMISTRY, MEDFORD, MA 021551
USEPA NATIONAL RISK MANAGEMENT RESEARCH LAB, ADA, OK 748201
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
USEPA NATIONAL RISK MANAGEMENT RESEARCH LAB, SUBSURFACE PROTECTION
AND REMEDIATION DIVISION,
PO BOX 1196
ADA, OK 74820
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/15
15. SUPPLEMENTARY NOTES
16. ABSTRACT: Fiber optic probes employing single channel laser excitation and fluorescence collection have
been seeing increasing use for remote sensing applications. However, multichannel systems offer enhanced
capacity for qualitative and quantitative determination of analytes. We describe a system which employs
simultaneous delivery of laser excitation wavelengths arising from stimulated Raman scattering (SRS). Separate
fluorescence responses for each excitation channel are imaged through a spectrograph onto a CCD array detector.
Each channel has a dedicated fiber optic pair to deliver and collect light. Results will be presented which
evaluate the capabilities of this type of spectrometer for determination of organic contaminant mixtures in
various sample matrices.
17. KEY WORDS AND DOCUMENT ANALYSIS
A. DESCRIPTORS
B. IDENTIFIERS/OPEN ENDED TERMS
C. COSATI FIELD, GROUP
Fluorescence, remote sensing,
fiber optic, laser, soils, in-
situ, field test, EEM, LIF


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EPA FORM 2220-1 (REV.4-77) PREVIOUS EDITION IS OBSOLETE

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