Flow electrochemical sensor for trace analysis of heavy metals F. Geneste UMR-CNRS 6226, Institute of Chemical Sciences of Rennes University of Rennes 1, Team MaCSE Beaulieu Campus, Rennes Cedex, France 6th International Conference and Exhibition on Analytical & Bioanalytical Techniques

Cu (mg/L) Fe (  g/L) Mn (  g/L) As (  g/L) Cd (  g/L) Pb (  g/L) Cr (  g/L) Hg (  g/L) Ni (  g/L) (10 for 2013) European communities regulation 2007, S.I. n°278 of 2007 Trace analysis Current methods Spectrometry, Chromatography Portable analytical systems: colorimetry Low sensitivity (10 -3 mg L -1 ) Analysis in laboratory

ElectrodepositionRest Redissolution Pb 2+ +Hg+2e - Pb(Hg) Pb 2+ + Hg + 2e - Pb(Hg) t t EdEd i anod i cath 0 ipip EpEp Polarography: Anodic stripping voltammetry 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 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 V SCE 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 M zinc solution on a graphite felt electrode (0.1 M aqueous solution of NaBF 4 ) - 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 (Zn 2+ ) B. Feier, D. Floner, C. Cristea, E. Bodoki, R. Sandulescu, F. Geneste, Talanta, 2012, 98, 152

Sample Real concentration (mmol L -1 ) Measured Concentration a (mmol L -1 ) Recovery (%)RSD (n=3) Spiked tap water Food supplement Determination of Zn 2+ with the flow electrochemical cell in real samples Linear in the range of to mol L -1 with a correlation coefficient of Limit of detection of mol L -1 (32.7 ppb) (French drinking water guidelines for zinc set at mol L -1 (5 ppm)) Calibration curve: LSSV analysis with a preconcentration at -1.4 V SCE for 5 min in flow (0.8 mL min -1 ) Preconcentration by electrodeposition (Zn 2+ ) B. Feier, D. Floner, C. Cristea, E. Bodoki, R. Sandulescu, F. Geneste, Talanta, 2012, 98, 152

Flow electroanalytical system: Preconcentration using modified electrodes

1- Complexation on residual COOH Unmodified felt 1 L, rate 91 mL min -1 Graphite felt (Pb 2+ ) 2- Anodic stripping voltammetry Deposition potential E = -1 V SCE for 5 min

Graphite felt sample was dipped in 1 L of a M lead solution (20  g 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, (2006). I ∞ : limiting current density K: affinity equilibrium constant C: lead concentration Detection limit: mol L -1 (0.2  g L -1 ) for an analysis time of 16 min European communities regulation: 5 x mol L -1 (10  g L -1 ) Calibration curve and detection limit Nonlinear curve At the equilibrium, the calibration curve follows a Langmuir-like relation I = I ∞ KC 1 + KC R. Nasraoui, D. Floner, F. Geneste, J. Electroanal. Chem., 2009, 629, 30

A solution of Pb 2+ (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 Pb 2+ interfered with nearly all tested ions Ref: Pb 2+ alone Interference studies R. Nasraoui, D. Floner, F. Geneste, J. Electroanal. Chem., 2009, 629, 30

Cyclame derivatives 1,4,8-tri(carbamoylmethyl) hydroiodide (TETRAM)

14 Electrolysis for 2h30 : Γ= 6.1 ± 0.5 x mol cm -3 (8.8 ± 0.7 x mol cm -2 ) Electrografting of cyclam derivatives

Electrochemical flow cell a Working electrode (graphite felt) b Counter-electrodes c Cationic membranes d Reference electrode a b b c c Electrolyte (outlet) Electrolyte (inlet) Potentiostat d

48 mm 12 mm CERefWE 1 cm 3 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 mL Detection limits: TETRAM : 2.5 x mol L -1 (5  g L -1 )Cyclam : 5 x mol L -1 (10  g 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, 9 R. Nasraoui, D.Floner, F. Geneste, Electrochem. Commun., 2010, 12, 98

Better selectivity with the TETRAM-modified electrode Ref: Pb 2+ alone A solution of Pb 2+ (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, 9 R. Nasraoui, D.Floner, F. Geneste, Electrochem. Commun., 2010, 12, 98 CyclamTETRAM

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 M solution) on an electrode modified by 4-MeOBDS ( ____ ) and 4-MeBDS (------). 0.1 V s -1 Cyclic voltammograms at graphite felt electrode of K 3 [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 Cu 2+ concentration B)Electric charge of trapped copper in the presence of interferents. (Cu 2+ (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 mol L -1. European drinking water guidelines for copper set at 1.6 x mol L -1. Almost constant for Fe 2+, Zn 2+ and Ni 2+, and a slight decrease was observed for Pb 2+, Co 2+ and Cd 2+. 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 Cu 2+, 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 Electron exchange with the metal Reoxidation to aromaticity Chem. Mater. (2007)

Effect of linker: 2nd exemple 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. Volume concentrations of Cu 2+ trapped on a modified graphite felt electrode after a preconcentration at 10 mL min -1 for 30 min in an aqueous solutions containing M Cu 2+ ( ____ ) and Cu 2+ + Pb 2+ (----) Scan rate: 0.1 V s -1 Volume concentration 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 mol L -1 (5  g L -1 )  Better selectivity - Role of the linker on the sensor performances Conclusion Acknowledgement Rihab Nasraoui Bogdan Feier Ionel Fizesan Didier Floner Christelle Médriadec Soraya Ababou Girard Cécilia Cristea Robert Sandulescu J. Le Lannic

Thank you! Institute of Chemical Sciences of Rennes UMR CNRS 6226 University of Rennes