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Voltammetric Sensing of Triclosan in the Presence of Cetyl trimethyl ammonium bromide using a Cathodically Pretreated Bo

This is ppt is all about my first seminar presentation on "Voltammetric Sensing of Triclosan in the Presence of Cetyl trimethyl ammonium bromide using a Cathodically Pretreated Boron-Doped Diamond Electrode

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Voltammetric Sensing of Triclosan in the Presence of Cetyl trimethyl ammonium bromide using a Cathodically Pretreated Bo

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  1. ADDIS ABABA UNIVERSITY COLLEGE OF NATURAL SCIENCES DEPARTMENT OF CHEMISTRY ANALYTICAL CHEMISTRY STREAM Voltammetric Sensing of Triclosan in the Presence of Cetyltrimethyl ammonium bromide using a Cathodically Pretreated Boron-Doped Diamond Electrode Seminar I (Chem. 671) By: Asfaw Meresa Advisors: Dr. Mekonnen Abebayehu (PhD) Dr. Estifanos Ele(PhD) January, 2019 Addis Ababa, Ethiopia

  2. OUTLINE • Introduction • Experimental • Results and discussion • Conclusion • Acknowledgement

  3. 1. Introduction • Triclosan (5- Chloro- 2- [2,4- dichlorophenoxy] phenol) is an anti microbial agent. • It is widely used as • an ingredient for the preparation of detergents, dish-washing liquids, soaps, deodorants, cosmetics, lotions, anti-microbial creams etc…. • an additive in plastics and textiles (Fotouhi et.al, 2010; Yola et.al., 2015) • Triclosan enters many water sources due to its wide spread uses • Aquatic organisms are severely affected. (Ma et.al, 2014)

  4. CONT… • It causes skin irritation, immunotoxic and neurotoxic rxns. • It disrupts the endocrine system at low concentration (Fotouhi et.al, 2010; Yardim et.al, 2018) • Triclosan can under go photo degradation reactions to produce: • 2, 8-dichlorodibenzo-p-dioxin • Dichloro and trichlorophenols

  5. Cont… • These are categorized as high-priority pollutants and the most carcinogenic chemicals in the world . • It also reacts with Cl2 in tap water & forms chloroform (carcinogenic ). (Fotouhi et.al, 2010 ; USEPA, 2003; Lu et.al, 2009) • EPA has registered it as a pesticide • It was disapproved for use in human hygiene biocidal products • TheFDA banned it in some personal care or cosmetic products. (Thomaidi et.al., 2017; Eu, 2016;Halden et.al 2017 ).

  6. Properties of triclosan Properties Chemical structure of triclosan C12H7Cl3O2 289.55 g/mol white to off-white crystalline powder B.PT: 280-290 °C M.pt: 54 - 57 °C Not readily soluble in H2O Easily dissolves in org. solvents (Dann & Hontela, 2011).

  7. Analytical methods • Spectrophotometric methods • Capillary electrophoresis • Chromatographic methods • RP-HPLC/UV or Diode array detectors • LC–MS • GC-MS • Electro analytical methods (Lu et.al, 2009; Ma et.al, 2014; Silva et.al, 2008; Sun et.al, 2012; Gibson et.al, 2007;Yigit et.al, 2016)

  8. Electro analytical methods(voltammetric methods) • They are excellent alternatives to chromatographic methods due to • lower cost of instrumentation • simplicity • shorter analysis time • lower consumption of chemicals • lower sensitivity to matrix effects • high sensitivity (Yigit et.al, 2016)

  9. Cont.. • The HMDE and different modified carbon electrodes have been used to determine triclosan so far. • However, these electrodes have their own short comings. • The HMDE is toxic and not environmentally friendly • Drawbacks of modified carbonaceous electrodes • Long time preparation, poor reproducibility and high costs (Yardim et.al, 2018). • Problem of electrode surface deactivation and fouling due to insoluble polyphenols. (Ghanem et.al, 2007)

  10. Cont… • B/c of the above problems, there is a rising interest in the use of BDD electrodes for organic compound oxidation. • BDD electrodes result in less electrode fouling (Rodrigo et.al, 2001) • BDD electrodes have several advantages compared with traditional carbonaceous materials. • wide potential window in aqueous and non-aqueous solutions • very low & stable background current • high corrosion resistance • good surface reproducibility

  11. Cont… • Biocompatibility • Long-term response stability • Negligible adsorption of contaminants (Yu et.al, 2012; Andrade et.al, 2011). • The electrochemical properties of BDD strongly depend on the type of surface termination for many analytes. • Its surface property can be modified by appropriate electrochemical (Cathodic/anodic) pretreatments (Abdullah et.al, 2018).

  12. Cont… Cathodic pretreatment Anodic pretreatments produces hydrogen-terminated BDD surfaces These surfaces are hydrophobic with a negative electron affinity (Yu et.al, 2012; Andrade et.al, 2011). results in oxygen-terminated surfaces These surfaces are hydrophilic with a positive electron affinity. (Yu et.al, 2012; Andrade et.al, 2011).

  13. Cont… • The electrochemical pretreatments have been used to improve; • Sensitivity • selectivity • reproducibility of the voltammetric measurements using this electrode (Cobb et.al, 2018).

  14. Cont… • The Cathodic pretreatment and anodic pretreatment procedures have been applied to: • reactivate electrode surface • enhance the particular voltammetric signals • ensure repeatable and reproducible response of analytes • Remove or reduce the substances adsorbed on the surface during measurements (Girard et.al, 2007; Sochr et.al, 2014).

  15. Role of surfactants • Surfactants have also improved the • Sensitivity • selectivity of the voltammetric measurements using this electrode • prevent the electrode fouling • enhance the adsorption of organic compounds on to the BDD surface (Zavazalova et.al, 2016).

  16. Cont.. • BDD electrodes have successfully been applied in the voltammetric analysis of various biologically active compounds: • benzo[a]pyrene, • indole-3-acetic acid, • capsaicin, chlorogenic acid, vanillin, • caffeine, folic acid and ambroxol (Yigit et.al, 2016).

  17. Adsorptive stripping voltammetry • SW-ADSV was used to determine triclosan in water samples • ADSV is a technique that involves 1st) non-electrolytic accumulation of the analyte 2nd) cathodic reductive or anodic oxidative scan. • Advantages • wide linear dynamic range, low detection limit, simplicity of instrumentation, low cost, low power consumption, portability (Alarfaj, 2009; Kalvoda, 1990)

  18. 2. Experimental 2.1 Chemicals • Triclosan standard • Ethanol • Distilled water • 0.5 M H2SO4 • 3 mol L−1 NaCl • Britton–Robinson buffer (pH 2.0-10.0) • CTAB • SDS

  19. 2.2. Materials and Equipments • Potentiostat/galvanostat analyzer (μAutolab type III, MetrohmAutolab B.V., Utrecht, The Netherlands) • Glass cell (10ml) • Whatman No. 42 • Dark bottles • Refrigerator • Three electrodes • BDD as working electrode • Platinum wire as counter electrode • Ag/AgCl reference electrode

  20. 2.3. Electrochemical Measurements • Voltammetric measurements of CV and SWAdSV were operated using a potentiostat/galvanostatanalyser with GPES soft ware • The raw voltammograms were smoothed with a Savicky and Golay algorithm and • Base line corrected by moving average algorithm filtering technique (peak width 0.01 V) • All electrochemical experiments conducted , with the three electrodes immersed in glass cell of volume of 10mL • Anodic and cathodic pretreatment respectively at +1.5 V and -1.5 V of the BDD electrode were done in 0.5 M H2SO4 for 180 s.

  21. Cont… • Between individual measurements, a short activation program was applied for 60 s under the same conditions • CV: study on the voltammetric behavior of triclosan • SWAdSV: Development of voltammetric methodology • 2.4. Optimized procedure for stripping voltammetry • Triclo san was pre-concentrated on to the surface of the BDD with stirring at open circuit condition for 30 s. • After 5s, voltammograms were recorded in the range 0 to + 1.2 V using SW waveform under the optimized SWV parameters.

  22. 2.5. Sample preparation • The water samples were collected and filtered • 1ml of filtrate was added to a voltammetric cell which contains 9 mL BR buffer at pH 9.0 in the presence of 2.5 × 10−4 M CTAB • Then, SWAdSV procedure was launched. • Afterwards, respective volumes of 20, 40, 100, 200 and 300 μL of triclosan working solution (5 μg mL−1) were then added to this mixture and the analyses were undertaken.

  23. 3.Results and discussion 3.1: CV behavior of triclosan at the BDD electrode • Presence of only well-defined anodic peak at + 0.69 V (vs Ag/AgCl)(Figure 2) • confirms the irreversible oxidation of triclosan under the experimental condition. • Current fall for the successive potential cycles is due to deactivation of the electrode by the adsorption of polymeric products by coupling of phenoxy radicals (Brycht et.al., 2016)

  24. Cont… • Figure 2: Three repetitive cyclic voltammograms at scan rate of 100 mV s−1 of 100 μg mL−1 triclosan in BR buffer (pH 9.0) solution. Electrode, cathodicallypretreated BDD. Dashed lines represent background current

  25. 3.2 Optimization of Conditions for Determination of Triclosan by ADSV 3.2.1: Effect of BDD pretreatment • Problem of electrode deactivation and fouling at the electrode surface without pretreatment. This results in a decrease in stripping signal (Wang & Farrell, 2004). • Results of pretreatment indicated that CPT-BDD resulted in a higher current intensity ( a much better electrode response). • The lower signal at the anodically treated BDD is duet to repulsion b/n its –ve surface and -vely charged triclosan. (Yu et.al, 2012)

  26. Cont.. • Figure 3: The stripping voltammograms of 5 μg mL−1 triclosan in BR buffer (pH 9.0) solution at the BDD electrode anodically (a) or cathodically (b) pretreated. Accumulation time 30 s at open circuit condition. SWV parameters: frequency, 50 Hz; step potential, 8 mV; pulse amplitude, 30 mV.

  27. 3.2.2: The effect of PH of solution • Ep of the oxidation peak shifted linearly to less positive potentials with the increase of solution pH from 6.0-9.0. • The oxidation of triclosan was a pH dependent. • Ep (V) = −0.046pH + 1.032, with r = 0.994. Indicate equal No of protons and electrons participating in the electrode rxn. • At pH 9.0 and 10.0, almost the same values of Ep & Ip intensity are obtained • No oxidation peak for PH value less than 6.

  28. Cont… • Figure 4: The stripping voltammograms of 5 μg mL−1 triclosan in BR buffer between pH 6 and 10, Inset depicts the plot of peak potential (Ep) vs. pH. Electrode, cathodically pretreated BDD. Other operating conditions as indicated in Figure 3

  29. Cont… • PH (9.0), which provides the highest signal, was selected for further studies • The Pka of triclosan= 8.1 (Behera et.al., 2010). • The oxidation of triclosan corresponds to • the one-electron and one proton transfer of • the hydroxyl group (-OH) to the phenoxy–O· radical (Wang & Farrell, 2004).

  30. 3.2.3: The effect of cationic surfactant (CTAB) • The peak current increased significantly in the presence of CTAB as compared with the value in its absence (Figure 6). • The oxidation peak current of triclosan linearly increased with CTAB only up to 2.5 × 10−4 M (Figure 6: In set). • How CTAB enhances the oxidation of triclosan? • Triclosan at pH (9.0) exists in Neutral (25%) & Anionic form (Phenolate) (75%). • Even in fully deprotonated form at pH 10, it remains highly hydrophobic (Nghiem & Coleman, 2008). • Surface of CPT-BDD electrode is hydrophobic(Oliveira & Oliveira-Brett, 2010).

  31. Cont… • Figure 5: The stripping voltammograms of 5 μg mL−1 triclosan in BR buffer (pH 9.0) solution containing different CTAB concentrations (5 × 10−5‒2.5 × 10−4 M). • Dashed line represents the voltammogram without CTAB. Inset: plot of peak current (ip) vs. the concentration of CTAB. Electrode, CPT-BDD electrode. Other operating conditions as indicated in Figure 3

  32. Cont… • Surface micelles are formed on the electrode surface between the hydrophobic tail of CTAB and CPT-BDD surface. • The enhancing effect of CTAB on the stripping response of triclosan could be explained by two strong interactions that monitor its adsorption on BDD surface: • Electrostatic attraction • Hydrophobic interaction (Dominates the co-adsorption of triclosan with CTAB on CPT-BDD surface) (Esumi, 2001). Consequently, CTAB would make e- transfer easily b/n TCN & CPT-BDD.

  33. 3.2.4: The effect of accumulation time and potential • The peak current increased linearly with taccup to 30 s beyond which it remained almost stable. • The accumulation potential (Eacc) has no effect on the stripping peak current either at open-circuit condition or over the potential range + 0.1 to + 0.6 V. 3.2.5: Optimized pulse parameters • Frequency, f = 100 Hz • Scan increment, ΔEs = 10 mV • Square wave amplitude, A = 50 mV

  34. 3.3. Analytical applications • Table 1: Optimum experimental conditions for the square wave adsorptive stripping voltammetric (SW-AdSV) determination of triclosan at CPT-BDD electrode

  35. 3.3.1: Linear Detection Range and detection limit of Triclosan • Calibration curve was made on the BDD for Det. of triclosan • Calibration eqn: ip (μA) = 12.11 C (μg mL−1) + 0.355 (r = 0.997, n = 7) • The BDD exhibited: • Linear range: 0.01–1 μg mL−1 (3.5 × 10−8–3.5 × 10−6 M) • LOD values: 2.3 ng mL−1 (7.9 × 10−9 M) • LOQ values: 7.7 ng mL−1 (2.7 × 10−8 M) • Good sensitivity & Linear range

  36. Cont.. • Figure 6: The stripping voltammograms for triclosan levels of (1) 0.01, (2) 0.02, (3) 0.05, (4) 0.1, (5) 0.15, (6) 0.3, (7) 0.5 and (8) 1.0 μg/ mL−1 in BR buffer (pH 9.0) solution containing 2.5 × 10−4 M CTAB. Inset depicts a corresponding calibration plot for the quantitation of triclosan.

  37. Table 2: comparison of the efficiency of d/t electrodes used in the determination of triclosan

  38. Con … • The CPT- BDD exhibited a more sensitive electrochemical response for the oxidation of triclosan than most of the electrodes reported. • Good analytical sensitivity, wide linear range, simplicity, rapidity and low cost of the present methodology • Enable its use with out a time consuming procedure for cleaning of the CPT-BDD electrode surface

  39. 3.3.3. Precision and selectivity • The Relative Standard Deviation (RSD) for • intra-day repeatability (5.85% ) • intra-day repeatability (7.32%) • The presence of inorganic ions at 50-fold excess and organic compounds at 10-fold excess did not significantly influence the current response of 0.1 μg /mL−1 triclosan • These showed that BDD electrode possessed good repeatability and selectivity for the determination triclosan.

  40. 3.3.4.Application to Real Matrices • The proposed method was used to determine the content of triclosan in two spiked tap water samples. • Computations were based on the standard addition method and the average of triplicate measurements. • The average recovery values of the compound in the samples and RSD values are shown in table 3. • As shown from the table, this method is accurate and feasible (absence of matrix interferences effect)

  41. Table 3: The analysis of two samples of spiked tap water using the proposed voltammetric method (n = 3).

  42. Conclusion • Triclosan underwent a PH dependent irreversible one electron oxidation at CPT-BDD electrode surface • This oxidation corresponded to the oxidation of hydroxyl group on the triclosan molecule. • The cationic surfactant, CTAB enhances the oxidation of triclosan. • The proposed voltammetric method is accurate, selective and sensitive with low detection limit.

  43. Acknowledgement • Almighty God • Advisors: • Dr. Mekonnen Abebayehu (PhD) • Dr. Estifanos Ele (PhD) • EPHI • All Staff Members

  44. THANK YOU

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