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Analysis of carbonaceous nanomaterials
in environmental and biological samples
P. Lee Ferguson
Nicholas School of the Environment and Department of Civil & Environmental Engineering, Duke University, Durham, NC
2012 NSF Nanoscale Science and Engineering Grantees Conference
December 3, 2012, Arlington, VA
Carbon-based nanomaterials are seeing
increased production and use
Chemical & Engineering News, (2007) v 85, no. 46 pp. 29-35
Woodrow Wilson International Center for Scholars, Project on Emerging Nanotechnologies (2010)
Nanomaterial use in consumer products
Challenges for analyzing carbon
nanomaterials in environmental media
• Both fullerenes and CNTs are expected to occur at very low
concentrations in the ambient environment (ppb to ppt)
• “Particle characterization” methods (e.g. microscopy and light
scattering) fail to perform in highly complex media with low
nanoparticle concentrations.
• Carbon nanomaterials offer a “contrast problem” for detection
against a carbon-rich environmental background.
• Fullerenes and CNTs have very limited solubility in most organic
solvents, complicating sample preparation.
• Most environmental analytical laboratories are poorly-equipped
for particle separation and detection.
Analytical methods for detecting
fullerenes in environmental samples
• Because fullerenes are molecular
species, they can be efficiently
solubilized and separated by HPLC.
• UV-vis absorbance detection is
useful for detecting fullerenes in
pure solutions and at high (ppm or
above) concentrations.
• In complex mixtures and at trace
(ppb or ppt) concentrations, HPLC-
MS is the method of choice.
X. Xia et al. 2006. HPLC-UV-vis analysis of nano-C60 in protein solution, porcine plasma, and skin extract. Journal of
Chromatography A, 1129 (2), p. 216-
222)
Quantitation of nano-C60 in drinking water
by HPLC-APCI-MS
Z. Chen, et al. 2008. Quantification of
C60 Fullerene Concentrations in Water.
Environmental Toxicology and
Chemistry, 27 (9), p. 1852-1859.
MDL = 0.30 ± 0.09 μg/L
MDL = 3.33 ± 1.06 μg/L
MDL = 2.78 ± 0.88 μg/L
Recovery from tap
water: < 35 %
• Solid phase extraction was used to isolate nano-C60 colloids from
water prior to HPLC-MS analysis.
• Recoveries were non-quantitative but ppt detection limits attained.
Analysis of fullerenes in wastewater
suspended solids by HPLC-ESI-MS
M. Farre, et al. 2010. First
determination of C60 and C70 fullerenes
and N-methylfulleropyrrolidine C60 on
the suspended material of wastewater
effluents by liquid chromatography
hybrid quadrupole linear ion trap
tandem mass spectrometry. Journal of
Hydrology, 383, p. 44-51.
• Filtration and solvent extraction was used to isolate fullerenes
from suspended solids in WWTP effluent prior to HPLC-MS.
• Excellent detection limits were achieved but with limited recovery.
C60 MDL = 0.005 μg/L
Recovery = 63 ± 7 %
C70 MDL = 0.008 μg/L
Recovery = 59 ± 7 %
N-methylfullero-pyrrolidine
MDL = 0.02 μg/L
Recovery = 58 ± 6 %
Methods for carbon nanotube
characterization
• Carbon nanotubes are challenging to analyze at trace levels in the
environment – they are not molecules and MS is of little use.
• Electron microscopy
− Provides information on size, physical state, sample purity
− Qualitative, limited sensitivity, poor performance in complex
mixtures
• Raman spectroscopy
− Distinctive bands provide purity assessment, some structural
information
− Relatively poor sensitivity, susceptible to interferences
• Near infrared fluorescence spectroscopy
− Spectra provide diameter, structural information
− Very high sensitivity, tolerant of complex background, only useful for
semiconductive SWNT species
SWNT have unique structural
characteristics
The integers (n,m) uniquely define the diameter and
chirality of the quantized SWNT species.
Semiconductive SWNT are represented with black
numbers, while conductive SWNT are shown in red.
d = 0.0794 n2 + nm+m2
Adapted from Fluorometric Characterization of SWCNT, Weisman, RB, 2009.
30°
0°
Qualitative characterization of CoMoCat
SWNT type SG65 by NIRF spectroscopy
P.A. Schierz, et al. 2012. Characterization and
Quantitative Analysis of Single-Walled Carbon
Nanotubes in the Aquatic Environment Using Near-
Infrared Fluorescence Spectroscopy, Environmental
Science & Technology, 2012. 46 (22), pp 12262–
12271
7000 8000 9000 10000 11000 12000
638 nm excitation
691 nm excitation
782nm excitation
em
iss
ion
po
we
r [
nW
cm
-1]
wave number [cm-1
]
Detection of CoMoCat SWNT type SG65
in sediment by NIRF
• CoMoCat SWNT were spiked into
estuarine sediment at 10 mg/g
concentration.
• Sequential extractions were performed
with 2% sodium deoxycholate
(ultrasonication at 40 W for 10 minutes).
6000 7000 8000 9000 10000 11000 12000
0.00000
0.00001
0.00002
0.00003
0.00004
0.00005
1. extraction
2. extraction
3. extraction
4. extraction
5. extraction
em
issio
n p
ow
er
[nW
cm
-1]
wave number [cm-1]
638 nm excitation wave length
SWNT extracted
from sediment:
81 ± 5 %
Quantitative performance of NIRF
spectroscopy for SWNT in 2% SDC
25 ng/mL
SWNT in mesocosm water attenuated
rapidly Water column C SWNT,0 = 2.5 mg L-1, 0.5% GA
7000 8000 9000 10000 11000 12000
0.00000
0.00005
0.00010
0.00015
638 nm excitation
691 nm excitation
782nm excitation
wave number [cm-1]
em
issio
n p
ow
er
[nW
cm
-1]
11 mg L-1
7000 8000 9000 10000 11000 12000
0.0000000
0.0000005
0.0000010
0.0000015
em
issio
n p
ow
er
[nW
cm
-1]
wave numer [cm-1]
c < DL
5 mg L-1
7000 8000 9000 10000 11000 12000
0.000000
0.000002
0.000004
0.000006
em
issio
n p
ow
er
[nW
cm
-1]
wave number [cm-1
]
670 mg L-1
0.0 0.5 1.0 1.5 2.0 2.5-5
-4
-3
-2
-1
0
time (d)
ln (
C/C
0)
SWNT t1/2 = 7.4 hours
SWNT in mesocosm water attenuated
rapidly Water column C SWNT,0 = 2.5 mg L-1, 0.5% GA
0 10 20 30-3
-2
-1
0
1
cSWNT (µg g-1)
depth
(cm
)A
D
C
B
1 cm
0.00000
0.00005
0.00010
em
iss
ion
po
we
r [n
W c
m-1]
0.00000
0.00005
0.00010
638 nm exciation wave length
691 nm exciation wave length
782 nm exciation wave length
em
iss
ion
po
we
r [n
W c
m-1
]
0.00000
0.00005
0.00010
em
iss
ion
po
we
r [n
W c
m-1]
7000 8000 9000 10000 11000 12000
0.00000
0.00005
0.00010
wave number [cm-1]
em
iss
ion
po
we
r [n
W c
m-1
]
A
B
C
D
SWNT were deposited in mesocosm
surface sediments after 6 months
NIRF imaging reveals SWNT ingestion by
mosquitofish in mesocosms
Room lighting NIR Laser illumination
Control mesocosm fish
SWNT mesocosm fish
SWNT in intestines
CNTs are resistant to chemothermal
oxidation treatment
• SWNT and MWNT survived air oxidation at
375° C for 24 hrs.
• CNTs in sediments would likely be detected
along with soot carbon using the CTO-375
method.
A. Sobek and T.D. Bucheli. 2009.
Testing the resistance of single- and
multi-walled carbon nanotubes to
chemothermal oxidation used to isolate
soots from environmental samples.
Environmental Pollution, 157, p. 1065-
1071.
SWNT 1 MWNT 4
MWNT 10
MWNT 13
Programmed thermal analysis can detect
strong CNTs in environmental matrices
• Some MWNT were sufficiently thermally
resistant that they could be separated from
background carbon in samples
• Residual black carbon in samples can cause
interferences.
MDL ~ 0.33μg
K Doudrick, et al. 2012. Detection of
Carbon Nanotubes in Environmental
Matrices Using Programmed Thermal
Analysis. Environmental Science &
Technology, 2012. 46 (22), pp 12246–
12253
TGA-MS could distinguish CNTs from
environmental matrices
• Hydrogen-assisted
thermal degradation
separated CNTs from
other carbonaceous
material
• Diagnostic ion ratios
could be used to
quantify CNTs in e.g.
sediments
D.L. Plata, et al. 2012.
Thermogravimetry–Mass Spectrometry
for Carbon Nanotube Detection in
Complex Mixtures. Environmental
Science & Technology, 2012. 46 (22),
pp 12254–12261
MDL ~ 4.0 μg
Carbon nanotubes have unique metal
catalyst compositions
• Residual metal catalyst impurities in SWNT
may prove useful as tracers for these
materials
• Ratiometric analysis may distinguish
manufacturers/synthesis processes
D.L. Plata et al. 2008. Industrailly
synthesized single-walled carbon
nanotubes: Compositional data for
users, environmental risk assessments,
and source apportionment.
Nanotechnology, 19, p. 1-13.
Research needs for carbon nanomaterial
analysis in the ambient environment
• Analytical methods for fullerenes seem to be maturing:
– Technologies (chromatography and mass spectrometry) are in-place.
– Method development efforts should focus on sample-preparation and
purification.
– Methods for qualitative analysis (e.g. modification state) are lacking.
• There are currently few methods for CNT analysis in
environmental samples:
– Thermal analysis methods lack sensitivity and specificity for CNTs.
– Only a single trace-analytical method exists for SWNT (author’s laboratory).
• Fundamental research is necessary to develop or adapt new detection methods for CNTs.
• Combination of particle-separation (e.g. field flow fractionation) methods with spectroscopic detection techniques holds particular promise.
Acknowledgement
RD83385
9
Dr. Ariette Schierz and Ashley Parks (Duke)
Dr. Tara Sabo-Attwood and Dr. Joseph Bisesi
(U. Florida)
Dr.Navid Saleh (U. South Carolina)
Dr. Phil Wallis and Dr. Samina Azad (South
West Nanotechnology)
Dr. Sergei M. Bachilo (Applied
Nanofluorescence)
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