Noura CHLAK PhD chemical and engineering process

Transcription

1 Development of nanostructured electrochemical micro-sensors for the detection of organic pesticides residues Noura CHLAK PhD chemical and engineering process Ecole Nationale Supérieure de Chimie de Rennes, Institut de Sciences Chimiques de Rennes UMR CNRS 6226, Rennes, France

2 Outline Introduction Thesis objective Project orientation Methodology and analysis of different pesticides Conclusion 2

3 Introduction Pesticides are chemicals designed to control organisms that are considered to be harmful. (44% of agriculture is lost in absence of pesticides) Most of them are persistent in environment for long time periods Have dangerous impact on human and environment: such as genetics disorders, cancers, biodiversity destruction Necessity to control samples permanently By a suitable analysis method 3

4 Introduction Multi-residues analysis : chromatographic methods Interested in specificity: electroactive pesticides - electrochemical methods Advantages of an electrochemical method operation simplicity short analysis time possibility of miniaturization low cost of instrumentation good sensitivity wide linear concentration range low limit of detection and quantification 4 4

5 Objective Development of electrochemical microsensors to exploit the selectivity of their responses in order to detect some electroactive pesticides molecules in environmental samples and in food 5

6 Project orientation Trace analysis ++ Increase of sensitivity Increase signal/noise ratio microelectrode + pulse voltammetry increase of electrode specific surface Diffusion limitation 10-5 M-10-6 M current intensity enhancement Catalysis or adsorption Carbon paste introduced into cavity microelectrode 6

7 Methodology Cavity microelectrode CME as working electrode filled with nanostructured carbon paste -Graphite powder (20 or 4 µm) -Multiwalled Carbon Nanotubes MWCNTs (DxL: nm x 5-9 µm) -Copper oxide CuO (30-50 nm) Cyclic voltammetry as electrochemical method Aqueous and organic mediums Optimization of different analytical parameters CME (Φ= 50 µm H=17 µm) slide Zoom on the apex of CME 7

8 Target pesticides Fipronil & Isoproturon Electroactive compounds Stable and soluble in water Pesticides Pesticides Group and uses Toxicity symptoms Log Kow MRLs MRLs Fipronil (FIP) -Phenyl pyrazole -Insecticide -Insecticide -Hypertrophy -Thyroid hypertrophy -Degeneration of hepatocytes -Degeneration of hepatocytes ,1 µg/l in drinking water ,02 mg/kg in eggs 4 and and mg/kg mg/kg in poultry in poultry meat 2 meat 2 Isoproturon (ISO) -substituted urea -Herbicide -Hepatomegaly -Hemolytic anemia µg/l in water intended for consumption mg/kg in most of fruits, vegetables and cereals 4 1 Afssa and Afsse (2005), Evaluation of the risks on human health related to fipronil exposure. 2 Codex Alimentarius. 3 World health organization (WHO). 4 The European Commision, Commission regulation (EU) No 87/2014 (2014) Official Journal of the European Union, 10(396), pp

9 Ipa (A) Study of Ip versus [FIP] Fipronil Analysis 5x10-6 M [FIP] 2,00E-07 Ipa(A) = f([fip]) 1x10-6 M BR (ph=8.3) 1,60E-07 1,20E-07 8,00E-08 4,00E-08 Ipa = 0.037[FIP] x10-9 0,00E+00 R² = ,00E+00 2,00E-06 4,00E-06 6,00E-06 [FIP] mol/l Medium : 19 ml Britton Robinson BR 0.04 M (adjusted to ph = 8.3 by NaOH 0.2 M) + 1 ml EtOH ; scan rate v = 10 mv/sec, CME + carbon paste Limit of detection = 1x10-6 M Ip controlled by diffusion Diffusion confirmed by linear variation of Ipa vs v 1/2 9

10 Ipa (A) Isoproturon Analysis Experimental conditions : Medium: 20 ml H 2 SO M CME (Ø = 50 µm, h = 17 µm) + graphite powder 20 µm / v = 10 mv/sec 4x10-7 M 2x10-7 M H 2 SO 4 0.5M [ISO] 1,00E-06 9,00E-07 Ipa(A) = f([iso]) from 2x10-8 M to 6x10-7 M 8,00E-07 7,00E-07 6,00E-07 5,00E-07 4,00E-07 3,00E-07 Ipa = 1.501[ISO]+1.345x10-8 R² = ,00E-07 1,00E-07 0,00E+00 0,00E+00 2,00E-07 4,00E-07 6,00E-07 8,00E-07 [ISO] (mol/l) Oxidation Symmetric peak at shape V adsorption large linear concentrations range 10

11 Ipa (A) 9,00E-07 8,00E-07 Isoproturon Analysis Optimization of the stirring time Ipa = f (Stirring time) with MEC + graphite 20 µm for [ISO] = 5x10-7 M ,00E-07 6,00E-07 5,00E ,00E-07 3,00E-07 2,00E-07 1,00E-07 0,00E Stirring time, not cumulative (min) CME (Ø = 50 µm, h = 17 µm) + graphite powder 20 µm Medium : 20 ml H 2 SO M; v = 10 mv/sec Equilibrium state reached after 14 min of stirring 11

12 Isoproturon Analysis Nanostructuration of the carbon pastes introduction of MWCNTs Experimental conditions: 20 ml H 2 SO M, MEC(Ø = 50 µm, h = 17 µm); v = 10 mv/sec; t.str. = 14 min % graphite paste % CNTs LD (mol/l) LQ (mol/l) Ipa=a[ISO]+b [4x x10-7 ] (mol/l) x10-8 4x10-8 Ipa=1.46 [ISO] x10-8 R 2 = x10-9 6x10-9 Ipa=0.91 [ISO] x10-9 R 2 = x10-9 6x10-9 Ipa=1.02 [ISO] x10-8 R 2 = x10-9 1x10-8 Ipa=0.86 [ISO] x10-9 R 2 = x10-9 4x10-8 Ipa=0.85 [ISO] x10-8 R 2 = x10-9 1x10-8 Ipa=0.07 [ISO] x10-9 R 2 =

13 Isoproturon Analysis Optimization of experimental parameters Temperature: Ipa when T Exothermic adsorption ph: optimum for ph 3 Adsorption of protonated ISO* ACN/H 2 O volume mixture: maximum of 10% ACN Since ISO affinity decreased dramatically and sensitivity thereby *P. Manisankar, C. Vedhi, and G. Selvanathan, Electrochemical studies of isoproturon, Trans. SEAST, vol. 37, pp ,

14 Ipa (A) Isoproturon Analysis Isoproturon ultra trace detection - Nanostrucutration by CuO Experimental conditions: 20 ml H 2 SO M; CME (Ø = 50 µm, h = 17 µm) + Paste (graphite 4 µm 70% : CNTs 10 % : CuO 20%); v = 10 mv/sec; T = 20 C; t.str. = 14 min. 4x10-7 M 1E-7 Ipa = f([iso]) 6x10-9 M H 2 SO M [ISO] 8E-8 4E-8 Ipa = 0.303[ISO] x10-9 R² = E+0 0E+0 2E-7 4E-7 [ISO] (mol/l) Limit of detection = 4x10-10 M Limit of quantification = 6x10-9 M Wide linear concentration range 14

15 Conclusion Development of cavity microelectrodes filled with carbon pastes: For the first time, pesticides were detected at trace and ultra trace levels Necessity to have nanostructured carbon pastes (MWCNTs, CuO) Improvement of LD is related to the adsorption of the pesticide into cavity (case of ISO with 4x10-10 M = 20 ng/l) Short equilibrium time (less than 15 min) Possibility of application this method for ISO in a mixture of H 2 SO 4 /ACN 15

16 Acknowlegments Thesis supersiors : Didier HAUCHARD and Farouk JABER Co-supervisor: Ayman CHMAYSSEM Research teams: CIP and CSM 16

17 Any questions? Noura CHLAK, PhD student, Chemistry and Engineering Process, ENSCR, Rennes, France 17