Sensitive determination of triacetone triperoxide explosives using electrogenerated chemiluminescence

Article abstract of DOI:10.1021/ac401962b

Sensitive and selective detection and quantification of high explosive triacetone triperoxide (TATP) with electrogenerated chemiluminescence (ECL) at a glassy carbon electrode in water-acetonitrile solvent mixture were reported. In the presence of ruthenium(II) tris(bipyridine), TATP or hydrogen peroxide derived from TATP via UV irradiation or acid treatment produced ECL emissions upon cathodic potential scanning. Interference from hydrogen peroxide on TATP detection was eliminated by pretreatment of the analyte with catalase enzyme. Selective detection of TATP from hexamethylene triperoxide diamine (HMTD, another common peroxide-based explosive) was realized by comparing ECL responses obtained from the anodic and the cathodic potential scanning; TATP produced ECL upon cathodic potential scanning only, whereas HMTD produced ECL upon both cathodic and anodic potential scanning. The hydroxyl radical formed after the electrochemical reduction of TATP was believed to be the key intermediate for ECL production, and its stability was strongly dependent on the solution composition, which was verified with electron paramagnetic resonance spectroscopy. A detection limit of 2.5 μM TATP was obtained from direct electrochemical reduction of the explosive or hydrogen peroxide derived from TATP in 70/30% (v/v) water-acetonitrile solutions, which was ～400 times lower than that reported previously based on liquid chromatography separation and Fourier transform infrared detection.

Full text of DOI:10.1021/ac401962b

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Article
Sensitive Determination of Triacetone Triperoxide (TATP)
Explosives Using Electrogenerated Chemiluminescence
Suman Parajuli, and Wujian Miao
Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/ac401962b • Publication Date (Web): 26 Jul 2013
Downloaded from http://pubs.acs.org on August 1, 2013
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Sensitive Determination of Triacetone Triperoxide (TATP)
Explosives Using Electrogenerated Chemiluminescence
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Suman Parajuli and Wujian Miao
Department of Chemistry and Biochemistry, The University of Southern Mississippi,
Hattiesburg, MS 39406
 Corresponding author. Phone: +1 601-266 4716; Fax: +1 601-266 6075; E-mail: wujian.miao@usm.edu
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ABSTRACT
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Sensitive and selective detection and quantification of high explosive triacetone
triperoxide (TATP) with electrogenerated chemiluminescence (ECL) at glassy carbon electrode
in water-acetonitrile mixture solvents were reported. In the presence of ruthenium (II)
tris(bipyridine), TATP or hydrogen peroxide derived from TATP via UV irradiation or acid
treatment produced ECL emissions upon cathodic potential scanning. Interference of hydrogen
peroxide on TATP detection was eliminated by pre-treatment of the analyte with catalase
enzyme. Selective detection of TATP from hexamethylene triperoxidediamine (HMTD, another
common peroxide-based explosive) was realized by comparing ECL responses obtained from the
anodic and the cathodic potential scanning; TATP produced ECL on cathodic potential scanning
only, whereas HMTD produced ECL on both cathodic and anodic potential scanning. The
hydroxyl radical formed after the electrochemical reduction of TATP was believed to be the key
intermediate for ECL production, and its stability was strongly dependent on the solution
composition, which was verified with electron paramagnetic resonance spectroscopy. A
detection limit of 2.5 µM TATP was obtained from direct electrochemical reduction of the
explosive or hydrogen peroxide derived from TATP in 70-30% (v/v) water-acetonitrile solutions,
which was ~400 times lower than that reported previously based on liquid chromatography
separation and Fourier transform infrared detection method.
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INTRODUCTION
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The increasing numbers of illegal use of homemade explosives, such as the very recent
Boston marathon explosions near the finish line, have caught the attention of the media
especially legal authorities.1,2 Among these, organic peroxide explosives, namely triacetone
triperoxide (TATP, Figure 1a) and hexamethylene triperoxide diamine (HMTD, Figure 1b),3
have become very popular with terrorists because these compounds can be readily made from
off-the-shelf ingredients,4 and can easily pass through common screening devices designed to
detect nitrogen-based explosives. TATP, a white solid first synthesized by Wolffenstein in
1895,5 is one of the most sensitive explosives known with significant sensitivity towards friction,
heat, and impact. Its impact sensitivity is equal to that of another high explosive, trinitrotoluene
(TNT).6 The London bombing in 2005 that killed 52 and injured around 700 people and the
attempt to bring down trans-Atlantic flight in 2001 by a ‘shoe bomber’ are the examples of the
terrorist use of TATP.7,8
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Several analytical techniques have been used to detect peroxide-based explosives,9,10
which include (a) mass spectrometry (MS), e.g., gas chromatographic separation coupled with
mass spectrometric detection (GC/MS),11-14 desorption electrospray ionization MS
(DESI/MS),8,15,16 and electrospray or laser ionization17 time of flight (TOF) MS (TOF/MS); (b)
ion mobility spectrometry (IMS);18-21 (c) infrared absorption spectroscopy (IR), e.g., liquid
chromatography separation-IR detection (LC/IR),6,22 GC/IR,13 and mid-IR laser spectroscopy
with quantum cascade laser (QCL);23-26 (d) Raman spectroscopy;12,27 (e) luminescent techniques,
e.g., fluorescence28-32 and chemiluminescence;33 (f) UV-vis spectrophotometry;34-37 and finally
(g) electrochemistry.7,38-40
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Methods based on MS are very sensitive and can detect trace amounts of explosives but
instruments are expensive and often inappropriate for field test. The results from IMS are
affected by the matrices such as temperature and moisture, whereas fluorescence suffers from
scattering light of luminophore impurities. Infrared, UV-vis detection techniques are often time
consuming in sample preparation and are not appropriate for detection of trace amounts of
explosives. As a result, there is still a pressing need to investigate other alternative methods for
sensitive detection and identification of these peroxide explosives, especially in the security
checkpoints of the mass-transit facilities as well as in the forensic and environmental testing
laboratories.41
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Electrogenerated chemiluminescence (ECL), a technique which produces light as a result
of electrochemical reactions that take place at the electrode surface, has been considered as a
powerful analytical technique because of its good selectivity, high sensitivity and fast sample
analysis.42-45 ECL can detect target molecules down to picomolar concentration levels.46
In this study, ECL detection and quantification of TATP as well as the differentiation of
TATP from HMTD are explored at glassy carbon electrode in water-MeCN mixture solvents in
2+
the presence of added ECL emitter Ru(bpy)3 (ruthenium(II) tris(bipyridine)) ions. The method
is based on the fact that TATP contains peroxide functional groups, which, upon cathodic
potential scanning, produce strong oxidizing species hydroxyl radicals (•OH) that could oxidize
+
2+
electrogenerated Ru(bpy)3 cations to form Ru(bpy)3 * excited states that emit photons.47 The
ECL intensity as a function of solvent compositions is found to be directly correlated to the
stability of hydroxyl radicals in the solvent as revealed by electron paramagnetic resonance
(EPR) spectroscopy.
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EXPERIMENTAL SECTION
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Chemicals. The following materials were used in the study: acetonitrile (MeCN, 99.8% ,
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HPLC grade), acetone (99.5+%, ACS reagent), sulfuric acid (95-98%, ACS reagent), sodium
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phosphate,
dibasic
(99.0%),
tris-(2,2'-bypyridine)dichlororuthenium(II)
hexahydrate
(Ru(bpy)3Cl2•6H2O, 99.95%), ammonium iron(II) sulfate hexahydrate ((NH4)2Fe(SO4)2 •6H2O,
ACS reagent), sodium azide (NaN3, ≥99.0%), and 5,5′-dimethyl-pyrroline-N-oxide (DMPO,
≥97% for ESR-spectroscopy) from Sigma-Aldrich (St. Louis, MO); hydrogen peroxide (H2O2,
30%) from Fisher Scientific (Fair Lawn, NJ); sodium phosphate, monobasic monohydrate from
J.T. Baker Chemicals Co. (Phillipsburg, NJ); silver nitrate (99.5%) and tetra-n-butylammonium
perchlorate (TBAP, 99+%, electrochemical grade) from Fluka (Milwaukee, WI); catalase
(filtered, 30,000 units/mL) from Worthington Biochemical Corp. (Lakewood, NJ) were used as
received. Hexamethylene triperoxide diamine (HMTD) was synthesized as described in our
previous report.3
Synthesis and Characterization of TATP. TATP was synthesized by mixing an
appropriate amount of hydrogen peroxide and acetone (both ice-cooled) in an ice-bath.
Concentrated sulfuric acid was added drop wise with constant stirring in order to maintain the
solution temperature below 4 °C. The reaction mixture was kept in a refrigerator for 24 h, and
the white solid was then filtered, washed with water, and allowed to dry at room temperature
before stored in a refrigerator for further use. Dried TATP was characterized with FT-IR and
proton NMR spectroscopy, where a characteristic C-O stretch band at 1175 cm-1 and a singlet 1H
NMR peak at 1.48 ppm were observed,48 respectively. This chemical shift is very close to 1.41
ppm estimated theoretically using ChemBiodraw Ultra 11 (CambridgeSoft Corp., Cambridge,
MA) (see the Supporting Information for more details). [CAUTION: TATP is very sensitive to
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heat, friction and impact so it has to be handled in small amount. Dry compound is volatile and
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more likely to explode so it must be stored as solution in MeCN at ~0 °C.]
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Instruments Used for Electrochemical and ECL Studies. Cyclic voltammetry (CV)
was performed with an electrochemical workstation (Model 660A, CH Instruments, Inc., Austin,
TX). The ECL and CV responses were simultaneously recorded with a homemade ECL
instrument,43,49 where the CHI electrochemical workstation was combined with a photo-
multiplier tube (PMT, Hamamatsu R928, Japan, biased at 700 V DC). A conventional three-
electrode electrochemical cell system was used with a glassy carbon disk (GC, 3 mm diameter)
as the working electrode, a platinum gauge as the counter electrode, and a Ag/Ag+ (with 10 mM
AgNO3 and 0.10M TABP in MeCN) as the reference electrode. The GC working electrode was
polished before every run with 0.3-0.05 µm alumina slurry, washed with water and dried with
Kim wipes tissue. The solution was degassed with nitrogen gas (Ultrapure, Nordan Smith,
Hattiesburg, MS) at least 5 min to remove dissolved oxygen that could produce background ECL
as the electrode was scanned in a negative potential region.
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Electron Paramagnetic Resonance (EPR) Spectrometry. EPR spectra of hydroxyl
radicals were recorded at a resonant frequency of 9.83 GHz, a modulation frequency of 100 kHz,
and the microwave power of 20 mW using a Bruker EMX microX EPR spectrometer equipped
with an ER 4119HS standard cylindrical resonator (Bruker BioSpin Corp.). The instrument was
pre-calibrated using the manufacturer’s DPPH calibration sample. Hydroxyl radicals (•OH) were
freshly produced chemically by Fenton reaction from 0.50 mM H2O2 and 75 µM ferrous
ammonium sulfate in different H2O-MeCN compositions, and were trapped by 200 mM 5,5′-
dimethyl-pyrroline-N-oxide (DMPO) “spin trapping” agent to form DMPO/•OH “spin adduct”
for EPR detection (Scheme 1). Experimentally, DMPO was mixed with H2O2 before ferrous
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ammonium sulfate was added to the system. Note that the concentrations listed above were all
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final values in a total reaction volume of 400 μL.
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•
Scheme 1. Formation of OH radical by Fenton reaction and the DMPO/•OH adduct, where k1
and k2 are the rate constants of Fenton reaction and the spin trapping reaction, respectively.
Samples of the DMPO/•OH adduct in H2O-MeCN mixture were measured using a
standard glass capillary (10 cm long, 2/1.2 OD/ID (mm), World Precision Instruments, Inc.,
Sarasota, FL) filled with the solution to a height of ~4 cm and sealed with “Permanent Avery
Glue Stic” (Office Depot, Hattiesburg, MS) at the bottom. This capillary was then placed in a
normal EPR tube for spectra acquisition which took place exactly after 5 min of the solution
preparation, unless otherwise stated. Such a “5 min time window” was necessary for solution
transfer and instrument setup and tuning. The experimentally obtained EPR spectra were
simulated using PEST Winsim Software (National Institute of Environmental Health Sciences,
National Institute of Health, Research Triangle Park, NC) for calculating of hyperfine coupling
constants.
RESULTS AND DISCUSSION
Cyclic Voltammetry (CV) of TATP. The CV of 1.0 mM TATP (Figure 2a) shows that
reduction of TATP is very difficult (unrecognizable reduction peak at ~ -1.0 V vs Ag/Ag+, inset
2+
+
in Figure 2). The ECL luminophore, Ru(bpy)3 , however, can be readily reduced to Ru(bpy)3
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with a peak potential at -1.8 V vs Ag/Ag+ (Figure 2b), suggesting that ECL could be produced
only after Ru(bpy)32+ reduction.
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2+
ECL Behavior of TATP. Because TATP has a poor solubility in water and Ru(bpy)3
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reduction occurs at a very negative potential region (see Figure 2b), ECL studies of TATP were
first conducted in MeCN. As proposed in Scheme 2, up on the cathodic potential scanning,
TATP could form H2O2 intermediate that could be reduced further to form hydroxyl radical
•
(•OH) (Eq. 1). The newly formed OH, which is a powerful oxidant as indicated by its standard
2+
3+
redox potential ( EO0H /OH - = 1.77~1.91 V vs NHE50-52), could oxidize Ru(bpy)3 to Ru(bpy)3
+
2+
2+
(Eq. 3) and Ru(bpy)3 (electrochemically reduced from Ru(bpy)3 , Eq. 2) to Ru(bpy)3 * excited
2+
state (Eq. 4). Alternatively, the excited state of Ru(bpy)3 * could be generated by ion
annihilation reaction (Eq. 5). Note that, MeCN always contains a trace amount of water (e.g.,
~0.01% or ~4 mM H2O for HPLC grade MeCN) that should meet the need for H2O2 production
from electrochemical reduction of TATP.
TATP + e  [H2O2 ]e OH
(1)
2+
+
(2)
(3)
(4)
(5)
(6)
Ru(bpy)3 + e  Ru(bpy)3
2+

3+
Ru(bpy)3 + OH  Ru(bpy)3 + OH-
+

2+*
Ru(bpy)3 + OH  Ru(bpy)3
+
3+
2+*
2+
Ru(bpy)3 + Ru(bpy)3  Ru(bpy)3 + Ru(bpy)3
2+*
2+
Ru(bpy)3
 Ru(bpy)3 + hv
Scheme 2. Proposed ECL mechanism of TATP in the presence of Ru(bpy)32+ upon the cathodic
potential scanning.
2+
Experimentally, however, no ECL was observed from the Ru(bpy)3 /TATP system in
0.10 M TBAP MeCN at bare Pt or GC electrode. To verify if the problem was really due to the
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poor reduction of TATP or H2O2 at the electrode in this solvent, several efforts were made. First,
UV irradiation (254 nm UV lamp, Model ENF-40C, 0.20 AMPS from Spectronics Corp., New
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York) was applied to the system so that TATP can be decomposed to H2O2 prior to ECL
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detection. Second, the working electrode (Pt or GC) modified with crystalline Prussian blue
40
(ferric ferrocyanide) which could catalytically reduce H2O2 was employed in the ECL testing.
2+
Neither helped the ECL generation. Surprisingly, in MeCN even the Ru(bpy)3 /H2O2 system
did not produce any notable ECL signals. Scheme S1 in the Supporting Information summarizes
the above observations.
When a 5 to 45 min UV-irradiated TATP MeCN solution was transferred to a water-
2+
MeCN mixture medium containing Ru(bpy)3 and a phosphate supporting electrolyte, strong
ECL signals were observed. For example, in 70:30 (v/v) water-MeCN mixture containing 1.0
mM Ru(bpy)32+ and 70 mM phosphate buffer, 0.50 mM TATP (with UV irradiation for 30 min)
starts to produce ECL at ~-1.5 V vs Ag/Ag+ and reaches the maximum at ~-1.8 V vs Ag/Ag+
+
(Figure 3a). The ECL profile is coincident with the reduction of Ru(bpy)32+ to Ru(bpy)3 (Figure
3b), suggesting that TATP (or H2O2) must be reduced at a less negative potential region as
2+
revealed earlier in Figure 2. ECL generation from the Ru(bpy)3 /H2O2 system in water-MeCN
has been reported previously.47
2+
Since the concentration of Ru(bpy)3 could influence the ECL production, its optimum
concentration was determined. When 0.50 mM of TATP is used (with UV irradiation), 0.60 mM
2+
Ru(bpy)3 produces the maximum ECL response in 70:30 (v/v) water-MeCN mixture (Figure
4a). As shown in Figure 4b, with the exposure of TATP MeCN solution to UV irradiation, the
ECL intensity of the irradiation product (i.e., H2O2) increases within the first 25 min, and then
remains essentially unchanged within the next 15-20 min. This suggests that under present UV
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irradiation conditions, i.e., with a 0.20 AMPS UV lamp at 254 nm and an experimental time
scale of 45 min, TATP was gradually decomposed and H2O2 was relatively stable. The
decomposition of H2O2 under UV irradiation has been reported previously.35
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Effect of Solvent Composition on ECL Intensity. Figure 5a shows the effect of solvent
composition on the ECL peak intensity of 0.5 mM TATP (with UV irradiation for 30 min). With
the addition of water to MeCN, ECL intensity increases and maximizes at a water volume of
70 % (i.e., 70:30 (v/v) water-MeCN). Because TBAP supporting electrolyte is sparely soluble in
water-MeCN mixture solvent, a final concentration of 70 mM phosphate buffer was used as the
supporting electrolyte. This buffer was prepared from 71 mL 0.10 M disodium phosphate and 29
mL of 0.10 M sodium phosphate, resulting in 100 mL of 0.10 M phosphate buffer solution
having pH 7.5. When the irradiated 0.50 mM TATP solution was replaced with 1.0 mM H2O2, a
very similar profile of the ECL intensity versus solution composition was obtained (Figure 5b).
At 70:30 (v/v) water-MeCN solutions, the ECL intensity ratio of 0.50 mM TATP to 1.0 mM
H2O2 has a value of 1.4, which is consistent with the TATP UV irradiation decomposition
reaction shown in Eq. 7.
TATP [(CH ) CO ] + 3H O  3H O + 3(CH ) O
3
(7)

3
2
2
2
2
2
3 2
Limit of Detection of TATP. In this section, three different modes of ECL detection of
TATP, namely, UV irradiation-ECL detection, acid treatment-ECL detection, and direct ECL
detection, are employed and compared.
As shown in Figure 6, for TATP UV irradiation-ECL detection mode, as low as 2.5 µM
TATP can be detected, which is 400 times lower than that from a LC/IR based detection35 and
more than three times lower than that from a horseradish peroxidase treatment-based UV-vis
detection method,35 respectively.
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ECL detection of TATP can also be achieved after TATP is treated with acid, resulting in
the formation H2O2.7,40 The ECL signal produced from obtained H2O2, however, was found to be
acid concentration related. In highly concentrated acidic media, ECL was greatly quenched. With
12 mM HCl pretreatment, TATP produces ECL responses which are comparable to the direct
detection (see below) and the limit of detection is also similar, i.e., 2.5 µM (Figure 7A).
Interestingly, as shown in Figure 7B, acid treated TATP produces two ECL peaks: the first one at
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2+
-1.8 V vs Ag/Ag+ is believed to be associated with the first electron reduction of Ru(bpy)3 to
+
Ru(bpy)3 , and the second one at -2.0 V vs Ag/Ag+ remains unclear, although it might be related
+
0
to the Ru(bpy)3 /Ru(bpy)3 electron-transfer process. Both ECL peaks show good linear
relationship with TATP concentration (Figure 7A).
In water-MeCN mixture solvents, TATP can produce ECL directly without need of any
treatment, as shown in Figure 8A. The ECL intensity, however, is relatively weak as compared
with results obtained from UV irradiation. Figure 8B illustrates the relationship between the ECL
peak intensity and TATP concentration, where a limit of detection of 2.5 µM is evident.
Although the three ECL detection modes give the same TATP detection limit of 2.5 µM, direct
detection can be completed within 5 min. In contrast, two- and seven times longer time would be
required to detect the same TATP sample, should the acid treatment and the UV irradiation
modes be chosen, respectively.
EPR Spectroscopy of Hydroxyl Radical (•OH). The stability of hydroxyl radical •OH in
various compositions of water-MeCN solvent was estimated by EPR spectroscopy. The rate
constants for Fenton reaction (k1, Scheme 1) and for hydroxyl radical trapping with DMPO (k2,
Scheme 1) have a value of 76-84,53,54 and 3.4×109 M-1 s-1,55 respectively. The rate constants for
•
hydroxyl radical quenching with various species such as OH itself, OH-, Fe(II), and many
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organic molecules are reported to be in the range of 109-1010 M-1 s-1,56,57 which is comparable to
or larger than k2. As a result, the stability of hydroxyl radical in solution could be reflected on the
stability of the spin trapping adduct DMPO/•OH (Scheme 1), assuming that the adduct is
sufficiently stable and its stability is independent of the solvent composition.
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Figure 9A shows the EPR spectra of DMPO/•OH adduct produced in a series of solution
composition of water-MeCN mixture. As expected, the spectra consist of a characteristic, 1:2:2:1
quartet.55 Very weak EPR signals are observed from solutions containing 5-20% (v/v) of water.
With the increase in water contents, the EPR signal gradually increases and maximizes at a
mixture solvent containing 70% (v/v) of water (Figure 9B). This EPR intensity of DMPO/•OH
versus H2O volume% profile coincides with the ECL intensity of TATP and H2O2 versus H2O
•
volume% profile shown in Figure 5. This suggests that the stability of OH is solvent
composition dependent, which is a determining factor for ECL generation from TATP or H2O2.
In MeCN, •OH could hardly survive, so no ECL was observed from TATP or H2O2. On the other
hand, TATP and H2O2 showed their highest ECL responses in 70:30 (v/v) water-MeCN solution,
because in such a medium, the •OH radical possesses its highest stability.
The stability of the DMPO/•OH adduct in different water-MeCN mixture solvents was
also monitored over time. The adduct was relatively stable and well-defined EPR spectra could
be recorded even after Fenton reaction occurred for 2 h in 100%-50% (v/v) water-MeCN
solutions. Quantitative analysis of the decay in EPR intensity after 5 and 20 min Fenton reaction
reveals that ~30% decrease for every solution composition is obtained (see Table S1 in the
Supporting Information), implying that the DMPO/•OH adduct had the similar stability
irrespective of solvent composition, as we assumed earlier.
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Simulations of the experimentally obtained EPR spectra confirmed that the 1:2:2:1
quartet is representative of virtually identical coupling of the free electron to the nitroxide
nitrogen (aN = 14.85 G) and the beta hydrogen of the pyrroline ring (aH = 14.85 G) in the
DMPO/•OH adduct (Scheme 1). Figure S2 in the Supporting Information shows an example of
such a simulation.
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Elimination of Trace Amounts of H2O2 from TATP. Trace amounts of H2O2 from the
laundry detergent could lead to the false positive ECL response. This undesired H2O2 is likely to
be found in travelers’ baggage as well as in some forensic samples, and has to be removed before
the experiment. As demonstrated in Figure S3 in the Supporting Information, strong ECL signals
2+
from 1.0 mM H2O2-0.60 mM Ru(bpy)3 system are almost completely suppressed after the
addition of catalase enzyme to the solution, in which unwanted H2O2 is decomposed to H2O and
O2 (Eq. 8),58 thus removing false positive ECL.
2H2O2 Catalase 2H2O + O2
(8)
Note that before TATP ECL measurements, the remaining catalase must be deactivated
by sodium azide (NaN3, which was found to have no effect on the ECL generation of TATP), so
that the electrogenerated H2O2 from TATP reduction would not be decomposed by the enzyme
(see Scheme S2 and Figure S4 in the Supporting Information for more details)..
Detection of TATP in the Presence of HMTD. HMTD, another common peroxide-
based explosive, also has peroxide functional groups which could produce ECL in the same
fashion as TATP (Figures 10A(a) and (b)). Moreover, cathodic ECL responses from HMTD and
TATP mixture are expected to be additive, as shown in Figure 10A(c).
In addition to peroxide functional groups, HMTD contains tertiary amine functional
groups which are capable of producing ECL in anodic potential scanning3 (Figure 10B). In other
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words, TATP could produce ECL on cathodic potential scanning only, whereas HMTD could
produce ECL on both cathodic and anodic potential scanning (Figure 10).
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CONCLUSIONS
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The highly explosive TATP was determined with cathodic scanning ECL in the presence
2+
of Ru(bpy)3 at glassy carbon working electrode. Solvent composition has profound effect on
the ECL generation, which was found to be associated with the stability of electrogenerated
hydroxyl radicals. Optimum ECL can be produced when water-MeCN mixture solvent has a
volume ratio of 70:30, which corresponds to the strongest EPR signal observed from the
DMPO/•OH adduct generated in the same solvent composition. Although UV irradiation, acid
treatment, and direct ECL methods provide the same TATP detection limit of 2.5 μM, direct
ECL approach is much fast (~5 min) and easy to operate. Elimination of contaminated H2O2
from TATP with catalase, and the differentiation of TATP from HMTD have also been
accomplished in the present studies.
ACKNOWLEDGEMENT
The abstract was presented at the 2011 PITTCON, March 13-18, Atlanta, GA. Financial
support from the NSF CAREER award (CHE-0955878) and the NSF Chemical Instrumentation
grant (CHE-0741991) is gratefully acknowledged.
SUPPORTING INFORMATION AVAILABLE.
Synthesis, spectroscopic characterization of TATP, experimental and simulated EPR
spectra of hydroxyl radical and its stability in various water-MeCN mixtures, as well as ECL
data shown the elimination of trace amounts of H2O2 from TATP. (PDF) This material is
available free of charge via the Internet at http://pubs.acs.org.
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REFERENCES
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7
8
(1) Marshall, M.; Oxley, J. C., Eds. Aspects of Explosive Detection; Elsevier B. V.:
Amsterdam, 2009.
9
(2) Yinon, J., Ed. Counterterrorist Detection Techniques of Explosives; Elsvier, B. V.:
Amsterdam, 2007.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(3) Parajuli, S.; Miao, W. Anal. Chem. 2009, 81, 5267-5272.
(4) Dubnikova, F.; Kosloff, R.; Almog, J.; Zeiri, Y.; Boese, R.; Itzhaky, H.; Alt, A.; Keinan, E.
J. Am. Chem. Soc. 2005, 127, 1146-1159.
(5) Wolffenstein, R. Chem. Ber. 1895, 28, 2265-2269.
(6) Schulte-Ladbeck, R.; Edelmann, A.; Quintas, G.; Lendl, B.; Karst, U. Anal. Chem. 2006,
78, 8150-8155.
(7) Munoz, R. A. A.; Lu, D.; Cagan, A.; Wang, J. Analyst 2007, 132, 560-565.
(8) Cotte-Rodriguez, I.; Chen, H.; Cooks, R. G. Chem. Commun. 2006, 953-955.
(9) Burks, R. M.; Hage, D. S. Anal. Bioanal. Chem. 2009, 395, 301-313.
(10) Miao, W.; Ge, C.; Parajuli, S.; Shi, J.; Jing, X. In Trace Analysis with Nanomaterials;
Pierce, D., Zhao, J., Eds.; Wiley-VCH Verlag: Weinhcim, 2010, pp 161-189.
(11) Stambouli, A.; El, B. A.; Bouayoun, T.; Bellimam, M. A. Forensic Sci. Int. 2004, 146,
S191-S194.
(12) Jimmie, O.; James, S.; Joseph, B.; Faina, D.; Ronnie, K.; Leila, Z.; Yehuda, Z. Applied
Spectroscopy 2008, 62, 906-915.
(13) Pena, A. J.; Pacheco-Londono, L.; Figueroa, J.; Rivera-Montalvo, L. A.; Roman-
Velazquez, F. R.; Hernandez-Rivera, S. P. Proc. SPIE-Int. Soc. Opt. Eng. 2005, 5778, 347-
358.
(14) Kende, A.; Lebics, F.; Eke, Z.; Torkos, K. Microchim. Acta 2008, 163, 335-338.
(15) Cotte-Rodriguez, I.; Cooks, R. G. Chem. Commun. 2006, 2968-2970.
(16) Cotte-Rodriguez, I.; Hernandez-Soto, H.; Chen, H.; Cooks, R. G. Anal. Chem. 2008, 80,
1512-1519.
(17) Sigman, M. E.; Clark, C. D.; Caiano, T.; Mullen, R. Rapid Commun. Mass Spectrom. 2008,
22, 84-90.
(18) Oxley, J. C.; Smith, J. L.; Kirschenbaum, L. J.; Marimganti, S.; Vadlamannati, S. J.
Forensic Sci. 2008, 53, 690-693.
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6
(19) Rasanen, R.-M.; Nousiainen, M.; Perakorpi, K.; Sillanpaa, M.; Polari, L.; Anttalainen, O.;
Utriainen, M. Anal. Chim. Acta 2008, 623, 59-65.
7
8
9
(20) Koyuncu, H.; Seven, E.; Calimli, A. Turk. J. Chem. 2005, 29, 255-264.
(21) Buttigieg, G. A.; Knight, A. K.; Denson, S.; Pommier, C.; Bonner, D. M. Forensic Sci. Int.
2003, 135, 53-59.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
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30
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41
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45
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47
48
49
50
51
52
53
54
55
56
57
58
59
60
(22) Schulte-Ladbeck, R.; Vogel, M.; Karst, U. Anal. Bioanal. Chem. 2006, 386, 559-565.
(23) Bauer, C.; Sharma, A. K.; Willer, U.; Burgmeier, J.; Braunschweig, B.; Schade, W.;
Blaser, S.; Hvozdara, L.; Mueller, A.; Holl, G. Appl. Phys. B: Lasers Opt. 2008, 92, 327-
333.
(24) Hildenbrand, J.; Herbst, J.; Woellenstein, J.; Lambrecht, A. Proc. SPIE 2009, 7222,
72220B/72221-72220B/72212.
(25) Herbst, J.; Hildenbrand, J.; Woellenstein, J.; Lambrecht, A. Proc. SPIE 2009, 7298,
72983W/72981-72983W/72912.
(26) Dunayevskiy, I.; Tsekoun, A.; Prasanna, M.; Go, R.; Patel, C. K. N. Appl Opt 2007, 46,
6397-6404.
(27) Ko, H.; Chang, S.; Tsukruk, V. V. ACS Nano 2009, 3, 181-188.
(28) Sanchez, J. C.; Trogler, W. C. J. Mater. Chem. 2008, 18, 5134-5141.
(29) Germain, M. E.; Knapp, M. J. Inorg. Chem. 2008, 47, 9748-9750.
(30) Malashikhin, S.; Finney, N. S. J. Am. Chem. Soc. 2008, 130, 12846-12847.
(31) Singh, S. J. Hazard. Mater. 2007, 144, 15-28.
(32) Sella, E.; Shabat, D. Chem. Commun. 2008, 5701-5703.
(33) Jimenez, A. M.; Navas, M. J. J. Hazard. Mater. 2004, 106, 1-5.
(34) Mills, A.; Grosshans, P.; Snadden, E. Sens. Actuators, B 2009, B136, 458-463.
(35) Schulte-Ladbeck, R.; Kolla, P.; Karst, U. Analyst 2002, 127, 1152-1154.
(36) Schulte-Ladbeck, R.; Kolla, P.; Karst, U. Anal. Chem. 2003, 75, 731-735.
(37) Apblett, A. W.; Kiran, B. P.; Malka, S.; Materer, N. F.; Piquette, A. Ceram. Trans. 2006,
172, 29-35.
(38) Lu, D.; Cagan, A.; Munoz, R. A. A.; Tangkuaram, T.; Wang, J. Analyst 2006, 131, 1279-
1281.
(39) Laine, D. F.; Cheng, I. F. Microchem. J. 2009, 91, 78-81.
(40) Laine, D. F.; Roske, C. W.; Cheng, I. F. Anal. Chim. Acta 2008, 608, 56-60.
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(41) Yinon, J. Forensic and Environmental Detection of Explosives; John Wiley & Sons, Inc.:
New York, 1999.
7
8
9
(42) Miao, W.; Bard, A. J. Anal. Chem. 2004, 76, 7109-7113.
(43) Miao, W. Chem. Rev. 2008, 108, 2506-2553.
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45
46
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53
54
55
56
57
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60
(44) Richter, M. M. Chem. Rev. 2004, 104, 3003-3036.
(45) Yin, X.-B.; Dong, S.; Wang, E. TrAC, Trends Anal. Chem. 2004, 23, 432-441.
(46) Pittman, T. L.; Thomson, B.; Miao, W. Anal. Chim. Acta 2009, 632, 197-202.
(47) Choi, J.-P.; Bard, A. J. Anal. Chim. Acta 2005, 541, 143-150.
(48) Schulte-Ladbeck, R.; Edelmann, A.; Quintas, G.; Lendl, B.; Karst, U. Anal. Chem. 2006,
78, 8150-8155.
(49) Rosado, D. J., Jr.; Miao, W.; Sun, Q.; Deng, Y. J. Phys. Chem. B 2006, 110, 15719-15723.
(50) Klaning, U. K.; Sehested, K.; Holcman, J. J. Phys. Chem. 1985, 89, 760-763.
(51) Koppenol, W. H.; Liebman, J. F. J. Phys. Chem. 1984, 88, 99-101.
(52) Schwarz, H. A.; Dodson, R. W. J. Phys. Chem. 1984, 88, 3643-3647.
(53) Walling, C. Acc. Chem. Res. 1975, 8, 125-131.
(54) Mizuta, Y.; Masumizu, T.; Kohno, M.; Mori, A.; Packer, L. Biochem. Mol. Biol. Int. 1997,
43, 1107 - 1120.
(55) Finkelstein, E.; Rosen, G. M.; Rauckman, E. J. Arch. Biochem. Biophys. 1980, 200, 1-16.
(56) Haag, W. R.; Yao, C. C. D. Envir. Sci. Tech. 1992, 26, 1005-1013.
(57) Buxton, G. V.; Greenstock, C. L.; Helman, W. P.; Ross, A. B. J. Phys. Chem. Ref. Data
1980, 17, 513-886.
(58) Kim, J.-K.; Kim, S.-M.; An, K.-W.; Choi, C.-Y.; Lee, S.-K.; Choi, K.-H. Comp. Biochem.
Physiol., Part C: Toxicol. Pharmacol. 2010, 152C, 263-269.
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Figure 1. Molecular structures of (a) triacetone triperoxide (TATP), and (b) hexamethylene
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triperoxide diamine (HMTD).
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2+
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Figure 2. CVs of (a) 1.0 mM TATP and (b) 0.60 mM Ru(bpy)3 in an electrolyte solution
containing 70% volume of 0.10 M phosphate buffer (pH 7.5) and 30% volume of MeCN (i.e.,
70 mM phosphate buffer in 70 (H2O) : 30 (MeCN) (v/v) mixture solvent) obtained from a 3-mm
diameter glassy carbon electrode at a scan rate 50 mV/s. The CV of the electrolyte solution is
displayed in (c).
Figure 3. (a) ECL and (b) CV responses of 0.50 mM TATP (with UV irradiation for 30 min) in
2+
1.0 mM Ru(bpy)3 water-MeCN (70:30, v/v) mixture containing 70 mM phosphate buffer at a
3-mm glassy carbon electrode with a scan rate of 50 mV/s.
Figure 4. (a) Effect of Ru(bpy)32+ concentration on ECL generation of 0.50 mM TATP (with UV
irradiation for 30 min). (b) Effect of UV irradiation time on TATP (0.50 M) decomposition. The
ECL was conducted in 70:30 (v/v) water-MeCN containing (a) various and (b) 0.6 mM
Ru(bpy)32+ and 70 mM phosphate buffer at a 3-mm diameter glassy carbon electrode with a scan
rate of 50 mV/s.
Figure 5. Effect of solvent composition on the ECL peak intensity of (a) 0.5 mM TATP (with
UV irradiation for 30 min), and (b) 1.0 mM H2O2 in an electrolyte solution containing 0.6 mM
2+
Ru(bpy)3 -70 mM phosphate buffer at a 3-mm diameter glassy carbon electrode with a scan rate
of 50 mV/s.
Figure 6. (A) ECL intensity as a function of TATP concentration for the UV-irradiation-ECL
detection scheme. (B) ECL responses obtained from different concentrations of TATP (with UV
irradiation for 30 min): (a) 0, (b) 2.5 μM, and (c) 0.50 mM. All experiments were conducted in
2+
70:30 (v/v) water-MeCN with 0.6 mM Ru(bpy)3 -70 mM phosphate buffer at a 3-mm diameter
glassy carbon electrode using a scan rate of 50 mV/s.
Figure 7. (A) ECL peak intensity as a function of TATP concentration. TATP was treated with
12 mM HCl, and the ECL measurements were conducted in 70:30 (v/v) water-MeCN mixture
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containing 0.6 mM Ru(bpy)3 -70 mM phosphate buffer at a 3-mm glassy carbon electrode using
a scan rate of 50 mV/s. (a) first ECL peak, and (b) second ECL peak as shown in (B). (B) (a) CV
and (b) ECL responses from 0.50 mM TATP (pre-treated with 12 mM HCl) using the same
experimental conditions as described in (A).
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Figure 8. (A) (a) ECL and (b) CV responses of 0.50 mM TATP directly detected in 0.60 mM
2+
Ru(bpy)3 water-MeCN (70:30, v/v) mixture containing 70 mM phosphate buffer at a 3-mm
glassy carbon electrode with a scan rate of 50 mV/s. (B) Relationship between ECL peak
intensity and TATP concentration when TATP was directly detected.
Figure 9. (A) Combined EPR spectra of DMPO/•OH produced from Fenton reaction (0.50 mM
H2O2, 200 mM 5,5′-dimethyl pyrroline-N-oxide (DMPO), and 75 µM Fe(NH4)2(SO4)2) in
different water-MeCN (v/v) solution compositions. The spectra were recorded after reactions
occurred for 5 min. (B) EPR spectra intensity of DMPO/•OH adduct (taken from (A)) as a
function of solution composition.
Figure 10. (A) Cathodic ECL of (a) 0.50 mM HMTD, (b) 0.50 mM TATP, and (c) 0.50 mM
2+
HMTD + 0.50 mM TATP in the presence of 0.60 mM Ru(bpy)3 -70 mM phosphate buffer in
70:30 (v/v) water-MeCN mixture solvent at a 3-mm glass carbon electrode with a scan rate of 50
mV/s; (B) Anodic ECL of (a) 0.50 mM TATP, (b) 0.50 mM HMTD, and (c) 0.50 mM TATP +
0.50 mM HMTD, using the same experimental conditions as in (A).
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O
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Figure 1
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- 0 .6
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E ( ( V v s A g /A g +
)
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Figure 2
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Figure 3
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TATP
H2O2
300
200
100
0
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(a)
(b)
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H2O volume % (in MeCN)
Figure 5
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Analytical Chemistry
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350
300
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150
100
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40
20
0
(A)
2.5 M TATP
9
10
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Background signal
0
30
60
[TATP] (M)
0
0
100
200
300
400
500
[TATP] (with UV Irradiation, M)
300
(B)
(c) 0.5 mM TATP
225
150
75
(b) 2.5 M TATP
(a) Background
0
0.0
-0.4
-0.8
-1.2
-1.6
-2.0
E (V vs Ag/Ag+)
Figure 6
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Analytical Chemistry
Page 26 of 30
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100
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60
40
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0
(b)
(A)
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(a)
Background
0
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300
400
500
[TATP] (M)
250
200
150
100
50
2
100
ECL,
CV
(B)
1
50
(b)
0
-50
-100
(a)
0
0.0
-0.5
-1.0
-1.5
-2.0
E (V vs, Ag/Ag+)
Figure 7
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Analytical Chemistry
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(A)
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100
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ECL,
CV
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100
50
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(a)
0
-50
-100
-150
(b)
0
0.0
-0.5
-1.0
-1.5
-2.0
E (V vs, Ag/Ag+)
150
125
100
75
30
20
10
(B)
[TATP] = 2.5 M
Background signal
0
20
40
60
[TATP] (M)
50
25
0
0
100
200
300
400
[TATP] (M)
Figure 8
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Analytical Chemistry
Page 28 of 30
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100 % water
(A)
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90 %
80 %
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70 %
60 %
50 %
40 %
30 %
20 %
10 %
5 %
3460
3480
3500
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3540
G Value/Gauss
3.0
2.5
2.0
1.5
1.0
0.5
0.0
(B)
0
20
40
60
80
100
H2O volume % (in MeCN)
Figure 9
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Analytical Chemistry
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300
250
200
150
100
50
(c)
(A)
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(b)
(a)
0
0.0
-0.5
-1.0
-1.5
-2.0
E (V vs Ag/Ag+)
125
100
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50
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0
(B)
(c)
(b)
(a)
Blank
1.5
2.0
1.0
0.5
0.0
E (V vs Ag/Ag+)
Figure 10
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