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

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

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

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

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

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

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

Flow electroanalytical system:Preconcentration using modified electrodes

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

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

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

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

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)

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

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

48 mm

12 mm

CERefWE

1 cm3 of graphite felt:

Analysis in cyclic voltammetry

Electrochemical flow cell for electrografting

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

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

Effect of linker: 1st exemple

B. Feier, D. Floner, C. Cristea, R. Sandulescu, F. Geneste, Electrochemistry Communications, 2013, 31, 13

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

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

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

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

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

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

Thank you!

Institute of Chemical Sciences of RennesUMR CNRS 6226University of Rennes