flow electrochemical sensor for trace analysis of heavy metals f. geneste umr-cnrs 6226, institute...
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Flow electrochemical sensor for trace analysis of heavy metals
F. Geneste
UMR-CNRS 6226, Institute of Chemical Sciences of RennesUniversity of Rennes 1, Team MaCSE
Beaulieu Campus, 35042 Rennes Cedex, France
6th International Conference and Exhibition onAnalytical & Bioanalytical Techniques
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Cu (mg/L)
Fe(mg/L)
Mn(mg/L)
As(mg/L)
Cd(mg/L)
Pb(mg/L)
Cr(mg/L)
Hg(mg/L)
Ni(mg/L)
2 200 50 10 5 25 (10 for 2013)
50 1 20
European communities regulation 2007, S.I. n°278 of 2007
Trace analysis
Current methodsSpectrometry, Chromatography
Portable analytical systems: colorimetry
Low sensitivity (10-3 mg L-1)
Analysis in laboratory
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Electrodeposition Rest Redissolution
Pb2+ +Hg+2e- Pb(Hg) Pb2+ + Hg + 2e-Pb(Hg)
t
t
Ed
i anod
i cat
h0
ip
Ep
Polarography:
Anodic stripping voltammetry
10-3 - 10-8 mg L-1
Electrochemical analytical systems
Advantages: - Simple- Low cost- Compatible with miniaturisation and portable
Analysis of traces but a preconcentration step is required:
Preconcentration by electrodeposition
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Preconcentration using modified electrodes : complexation
Avoid problems link to the solubility of the receptor in water
Elimination of mercury Possibility of observing electrochemical responses in positive potentials
Improvement of the selectivity by the specifically designed receptor
Possible regeneration of a fresh and reproducible surface
+ E E
L receptor : HOSTE electroactive compound : GUEST
Electrochemical response: HOST-GUEST
L L
Modified electrodes
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Flow electrochemical system
High specific surface, allowing the grafting of a high amount of receptor on the electrode in a small volume and good hydrodynamic properties
they enhance mass transport
It makes easier the automation and approaches the real-time analysis
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Preconcentration step:
-reduction at –1.4 VSCE for 5 min
____ in static mode
…. in flow (0.8 mL min-1)
---- in a standard three-electrodes cell
Scan rate: 0.1 V s-1.
LSSVs of 10-5 M zinc solution on a graphite felt electrode (0.1 M aqueous solution of NaBF4)
- Enhancement of mass-transport, leading to higher electrochemical response.
- Electrochemical flow cell appropriate for 3D electrodes led to the improvement of the electrochemical response compared with the standard three-electrodes cell.
Flow analytical system:preconcentration by electrodeposition (Zn2+)
B. Feier, D. Floner, C. Cristea, E. Bodoki, R. Sandulescu, F. Geneste, Talanta, 2012, 98, 152
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Sample Real concentration (mmol L-1)
Measured Concentrationa
(mmol L-1)
Recovery (%) RSD (n=3)
Spiked tap water 5.00 5.18 104 4
Food supplement 1.031 1.053 102 3
Determination of Zn2+ with the flow electrochemical cell in real samples
Linear in the range of 10-6 to 10-4 mol L-1 with a correlation coefficient of 0.9987
Limit of detection of 5 10-7 mol L-1 (32.7 ppb)
(French drinking water guidelines for zinc set at 7.6 10-5 mol L-1 (5 ppm))
Calibration curve:LSSV analysis with a preconcentration at -1.4 VSCE for 5 min in flow (0.8 mL min-1)
Preconcentration by electrodeposition (Zn2+)
B. Feier, D. Floner, C. Cristea, E. Bodoki, R. Sandulescu, F. Geneste, Talanta, 2012, 98, 152
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Flow electroanalytical system:Preconcentration using modified electrodes
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CCOOH
COOH
COOH
1- Complexation on residual COOH
Unmodified felt 1 L, rate 91 mL min-1
Graphite felt (Pb2+)
2- Anodic stripping voltammetry
Deposition potential
E = -1 VSCE for 5 min
-1.0 -0.8 -0.6 -0.4 -0.2
E / V vs SCE
Blank
10-7 mol L-1
0.5 mA
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Graphite felt sample was dipped in 1 L of a 10-7 M lead solution (20 mg L-1)for 11 min
Increase of the kinetic of complexation
Flowing system
Static system
Comparison with a static system
E / V vs SCE
I /
mA
Good volume control of the analyzed solution in contact with the electrode
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Gooding et coll., Electroanalysis, 18, 1141-1151 (2006).
I∞ : limiting current density
K: affinity equilibrium constant
C: lead concentration
Detection limit: 10-9 mol L-1 (0.2 mg L-1) for an analysis time of 16 min European communities regulation: 5 x 10-8 mol L-1 (10 mg L-1 )
Calibration curve and detection limit
Nonlinear curve
At the equilibrium, the calibration curve follows a Langmuir-like relation
I = I∞KC1 + KC
R. Nasraoui, D. Floner, F. Geneste, J. Electroanal. Chem., 2009, 629, 30
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0
1
2
3
4
5V
olu
me
co
nce
ntr
atio
n.1
09 /
mo
l cm
-3
Interferent ion
Réf Cu2+Cd2+ Ni2+ Zn2+ Co2+
A solution of Pb2+ (10-7 mol L-1 ) and interferent ion (10-7 mol L-1) was percolated through the porous electrode for 11 min at 91 mL min-1
Pb2+ interfered with nearly all tested ions
Ref: Pb2+ alone
Interference studies
R. Nasraoui, D. Floner, F. Geneste, J. Electroanal. Chem., 2009, 629, 30
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N N
N N
N N
N N
Cyclame derivatives
NN
N N
A B
CD
NN
N N
A B
CD
Metal detection
HOST
GUEST
HOST-GUEST
N N
NNH
NH2
NH2H2N
O OO
1,4,8-tri(carbamoylmethyl) hydroiodide (TETRAM)
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C NH (CH2)4
Cyclam
O
N HN
HNNH
TETRAM
C NH (CH2)4
O
N N
NN
O
NH2
NH2
O
H2N
O
O2N
NH2
Redox probe
Electrolysis for 2h30 :
Γ= 6.1 ± 0.5 x 10-9 mol cm-3
(8.8 ± 0.7 x 10-11 mol cm-2)
C + NH2-(CH2)4-COOH-e
-H+C NH (CH2)4 COOH
SOCl2C NH (CH2)4 COCl
Electrografting of cyclam derivatives
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Electrochemical flow cell
a Working electrode (graphite felt)
b Counter-electrodes
c Cationic membranes
d Reference electrodea
b b
c c
Electrolyte(outlet)
Electrolyte(inlet)
Potentiostat
d
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48 mm
12 mm
CERefWE
1 cm3 of graphite felt:
Analysis in cyclic voltammetry
Electrochemical flow cell for electrografting
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1 : 1 cyclam/lead
Flow rate: 10 mL min-1 and volume: 300 mLDetection limits:
TETRAM : 2.5 x 10-8 mol L-1 (5 mg L-1)Cyclam : 5 x 10-8 mol L-1 (10 mg L-1)
Calibration curves and detection limits
Cyclam-modified electrode
1 : 2 TETRAM/lead
1 : 1 TETRAM/lead
TETRAM-modified electrode
R. Nasraoui, D. Floner, Christine Paul-Roth, F. Geneste, J. Electroanal. Chem., 2010, 638, 9R. Nasraoui, D.Floner, F. Geneste, Electrochem. Commun., 2010, 12, 98
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0
1
2
3
4
5
Co2+
Zn2+
Ni2+Cd2+
Cu2+Réf
Interferent ion
Vo
lum
e c
on
cen
tra
tion
x 1
09 / m
ol c
m-3
0
1
2
3
4
5
6
7
Co2+Zn2+Ni2+Cd2+Cu2+Réf
Vo
lum
e c
on
cen
tra
tion
x 1
09 / m
ol c
m-3
Interferent ion
Better selectivity with the TETRAM-modified electrode
Ref: Pb2+ alone
A solution of Pb2+ (10-7 mol L-1 ) and interferent ion (10-7 mol L-1) was percolated through the porous electrode for 30 min at 10 mL min-1
Interference studies
R. Nasraoui, D. Floner, Christine Paul-Roth, F. Geneste, J. Electroanal. Chem., 2010, 638, 9R. Nasraoui, D.Floner, F. Geneste, Electrochem. Commun., 2010, 12, 98
Cyclam TETRAM
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Effect of linker: 1st exemple
B. Feier, D. Floner, C. Cristea, R. Sandulescu, F. Geneste, Electrochemistry Communications, 2013, 31, 13
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Effect of linker: 1st exemple
Voltammogram obtained by LSSV (-0.5 V for 5 min), of trapped copper (100 mL of a 10-7 M solution) on an electrode modified by 4-MeOBDS (____) and 4-MeBDS (------). 0.1 V s-1
+N2 Me
+N2 OMe
Cyclic voltammograms at graphite felt electrode of K3[Fe(CN)6] in 0.5 M phosphate buffer pH=7
Before grafting
-----
…...
MeOBDS
MeBDS
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Calibration curve and interferences
A) Calibration curve determined by LSSV analysis on the 4-MeOBDS-modified electrode as a function of Cu2+ concentration
B) Electric charge of trapped copper in the presence of interferents. (Cu2+ (10-7 mol L-1) and interferent ion (10-7 mol L-1))
The lowest concentration giving rise to a measurable signal was 5 x 10-9 mol L-1.European drinking water guidelines for copper set at 1.6 x 10-5 mol L-1.
Almost constant for Fe2+, Zn2+ and Ni2+, and a slight decrease was observed for Pb2+, Co2+ and Cd2+.
B. Feier, D. Floner, C. Cristea, R. Sandulescu, F. Geneste, Electrochemistry Communications, 2013, 31, 13
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Effect of linker: 1st exemple
Presence of azo species (-N=N-), resulting from the chemical reaction between diazonium ions and already grafted methoxyphenyl groups Since methoxy group not good coordination properties for Cu2+, N=N- probably help the complexation of copper ions in the film
Since electrodes modified with 4-MeBDS did not show any complexation properties, the methoxy group could- help the coordination of copper- turn the deposition properties of the film and influence the amount of azo groups.
Electrografting of diazonium salts: multilayers formation
Reaction exchange
Attack of the cation
S
.S
H
H
.ArN2
.+ S + Ar.+ N2 + H+
ArN2+
S
H
H
N N Ar
.+
1) reduction
2) oxidationS
N N Ar
Electron exchange with the metal
Reoxidation to aromaticity
Chem. Mater. (2007) 19 4570
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Effect of linker: 2nd exemple
HN CH2 COO-
4
H2N CH2 COO-
4
-e -H+, aqueous medium
Route 1
C
C
+e -N2, aqueous medium
CH2COOHN2+
Route 2
CH2COOHC
N S
F
F
F NH CH2 COF4
C
(DAST)
NH CH2 C4
C
O
NH
N
HN
HN
NH
NH
HN
HN
Electrografting of graphite felt
B. Feier, I. Fizesan, C. Mériadec, S. Ababou Girard, C. Cristea, R. Sandulescu, F. Geneste, Journal of Electroanalytical Chemistry, 2015, 744, 1
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Effect of linker: 2nd exemple
- When a less selective receptor as carboxylate group is used, the linker structure can interfere in the complexation reaction, as observed with the amino linker.
- The selectivity estimated in the presence of lead as a common ion interferent underlined the interest of a more elaborated receptor like cyclam compared with carboxyl linkers.
HN
O
NH
NH
N
HN
HN
COO-
COO-
Volume concentrations of Cu2+ trapped on a modified graphite felt electrode after a preconcentration at 10 mL min-1 for 30 min in an aqueous solutions containing 10-8 M Cu2+ (____) and Cu2+ + Pb2+ (----) Scan rate: 0.1 V s-1
Volu
me
conc
entr
ation
B. Feier, I. Fizesan, C. Mériadec, S. Ababou Girard, C. Cristea, R. Sandulescu, F. Geneste, Journal of Electroanalytical Chemistry, 2015, 744, 1
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Conclusion
- Advantages of the flow system
Increase of the kinetic of complexation
Volume control of the analyzed solution
- Covalent modification of the graphite felt
Detection limit 2.5 x 10-8 mol L-1 (5 mg L-1)
Better selectivity
- Role of the linker on the sensor performances
Conclusion
Acknowledgement
Rihab NasraouiBogdan FeierIonel Fizesan
Didier FlonerChristelle MédriadecSoraya Ababou GirardCécilia CristeaRobert Sandulescu
J. Le Lannic
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Thank you!
Institute of Chemical Sciences of RennesUMR CNRS 6226University of Rennes