Ignas Kenfack Tonle

Sorption of methylene blue on an organoclay bearing thiol groups and application to electrochemical sensing of the dye

In this work, a thiol functionalized-clay was prepared by the covalent grafting of 3-mercaptopropyltrimethoxysilane (MPTMS) onto the surface of a natural smectite clay mineral originating from Cameroon. Effectiveness of the grafting process and properties of the resulting hybrid material were studied by various physico-chemical techniques, such as Fourier transform infrared (FTIR) spectroscopy, N(2) adsorption-desorption experiments (surface area measurements by the BET method) and thermal gravimetric analysis (TGA) coupled with mass spectrometry (MS). Sorption of methylene blue (MB), an electroactive cationic dye, was investigated for both the raw clay and its modified counterpart, as a function of shaking time, adsorbate concentration and pH, through batch experiments. A significant enhancement of the adsorption capacity towards MB was observed with the clay bearing thiol groups in comparison with the pristine one. The obtained sorption data matched the Langmuir isotherm model, from which it appeared that the organoclay adsorbed MB at a maximal loading of 1.04mmolg(-1), while the natural clay displayed a significantly poorer performance (0.31mmolg(-1)). The uptake of MB by the modified clay was found to be highly affected by pH, the cationic dye being more effectively adsorbed in alkaline medium. The possible use of the thiol functionalized-clay as electrode modifier for MB sensing purposes was then evaluated by means of carbon paste electrodes, using cyclic voltammetry. A calibration curve was obtained in the concentration range from 1x10(-6) to 1.4x10(-5)molL(-1), with a detection limit of 4x10(-7)molL(-1)(signal/noise=3).

Electrochemical determination of mesotrione at organoclay modified glassy carbon electrodes

A natural Cameroonian smectite-type clay (SaNa) was exchanged with cationic surfactants, namely cetyltrimethylammonium (CTA) and didodecyldimethyl ammonium (DDA) modifying its physico-chemical properties. The resulting organoclays that have higher adsorption capacity for mesotrione than the pristine SaNa clay, have been used as modifiers of glassy carbon electrode for the electrochemical detection of this herbicide by square wave voltammetry. The stripping performances of SaNa, SaCTA and SaDDA modified electrodes were therefore evaluated and the experimental parameters were optimized. SaDDA gives the best results in deoxygenated acetate buffer solution (pH 6.0) after 2 min accumulation under open circuit conditions. Under optimal conditions, the reduction current is proportional to mesotrione concentration in the range from 0.25 to 2.5 μM with a detection limit of 0.26 μM. The fabricated electrode was also applied for the commercial formulation CALLISTO, used in European maize market.

Square Wave Voltammetric Determination of Residues of Carbendazim Using a Fullerene/Multiwalled Carbon Nanotubes/Nafion/Coated Glassy Carbon Electrode

A glassy carbon electrode (GCE) was modified with a fullerene/Multiwalled Carbon Nanotubes (MWCNTs)/Nafion composite and applied to the determination of carbendazim, a fungicide. The voltammetric behavior of the analyte was investigated using Cyclic Voltammetry (CV), on the bare GCE and on the same electrode coated by a thin film of the composite material. The electrode response was more than fourfold important on the modified electrode, due to electrical conductivity of fullerene and MWCNT and to favorable electrostatic interaction between the negatively charged Nafion and the protonated fungicide. A sensitive electroanalytical procedure based on Square Wave Voltammetry (SWV) was then developed to detect the analyte. Under the optimum conditions, a linear relationship was obtained between the peak current and the concentration of carbendazim, in the range from 2.0 × 10−8 mol/L to 3.5 × 10−7 mol/L, leading to a detection limit of 1.7 × 10−8 mol/L and to a quantification limit of 5.57 × 10−8 mol/L. The developed procedure was successfully applied to detect carbendazim upon adsorption by some ferritic soils.

Electroanalytical Performance of a Carbon Paste Electrode Modified by Coffee Husks for the Quantification of Acetaminophen in Quality Control of Commercialized Pharmaceutical Tablets

Electrochemical determination of acetaminophen (APAP) was successfully performed using a carbon paste electrode (CPE)modified with coffee husks (CH-CPE). Scanning electron microscopy (SEM) and SEM-energy dispersive X-ray spectroscopy (SEM-EDX) were, respectively, used for the morphological and elemental characterization of coffee husks prior to their utilization. Theelectrochemical oxidation of APAP was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and squarewave voltammetry (SWV). SWV technique appeared to be more sensitive since the oxidation current of APAP was twofold higherwith the CH-CPE sensor than with the bare CPE, in relation to the increase in the organophilic character of the electrode surface.Furthermore, on CH-CPE, the current response of APAP varied linearly with its concentration in the range of 6.6????M to 0.5 mM,leading to a detection limit of 0.66????M(????/????=3). Finally, the proposed CH-CPE sensor was successfully used to determine theamount of APAP in commercialized tablets (Doliprane�500 and Doliprane 1000), with a recovery rate ranging from 98% to 103%.This novel sensor opens the way for the development of low-cost and reliable devices for the electroanalysis of pharmaceuticalformulations in developing countries.

Electrochemical behavior and in-vitro antimicrobial screening of some thienylazoaryls dyes

BackgroundA series of recently reported phenolic azo dyes 7a–e were prepared by coupling the thienyl diazonium sulfate of 3-Amino-4H-benzo[f]thieno[3,4-c](2H)chromen-4-one with selected diversely substituted phenolic and naphtholic derivatives. These compounds were evaluated for their antibacterial and antifungal activities. Furthermore their voltammetric behavior was compared at a glassy carbon electrode.ResultsThe voltammetric behavior of the five recently reported azo dyes has been compared at a glassy carbon electrode. It is shown that the azo dyes 7a–e with a hydroxyl group in the ortho position with respect to the azo bridge give rise to well defined, irreversible peaks for the oxidation and reduction process within a pH range of 2–7. The mechanisms of electrochemical oxidation of compound 7a–c and 7e are proposed. For the hydroxyl-substituted dyes, re-oxidation peaks were obtained in the subsequent scan. The antimicrobial activities of the reported compounds 7a–e along with the entire precursors 1–4 and 6a–e were performed against selected bacterial and fungal species and their activities compared to those of nystatin, griseofulvin and ciprofloxacin used as reference drugs.ConclusionsThe present study showed significant antimicrobial activity of compounds 6d, 7a and 7c,e against the tested microorganisms; this result confirms the antimicrobial potency of azo compounds and some of their precursors.

p-Nitrophenol determination and remediation: an overview

Abstract An almost exhaustive overview of the determination and remediation of p-nitrophenol (p-NP)-contaminated media is herein presented. p-NP is one of the priority pollutants on the U.S. Environmental Protection Agency list. This is because p-NP is either a precursor or a derivative of a good number of pollutants. It is itself very carcinogenic and tends to persist in water and soil. This has prompted the development of a wide range of analytical tools by researchers for its determination and eventual removal from contaminated sites. These include electrochemical methods with many electrode modifiers and electroanalytical procedures developed for the detection/quantification of p-NP in contaminated environments. Also, chromatographic and p-NP uptake techniques, particularly adsorption onto various adsorbents (ranging from natural to synthetic), are reviewed. The use of microorganisms for the bioremediation of p-NP-contaminated samples and sites has equally been largely studied and is herein overviewed, not forgetting advanced oxidative processes.

Paracetamol Sensitive Cellulose-Based Electrochemical Sensors

Electrochemical determination of paracetamol (PCT) was successfully performed using carbon paste electrodes (CPEs) modified with treated coffee husks (CHt) or cellulose powder (Ce). Scanning electron microscopy was used to characterize unmodified or modified CPEs prior to their use. The electrochemical oxidation of PCT was investigated using square wave voltammetry (SWV) and cyclic voltammetry (CV). The oxidation current density of PCT was two-fold higher with the CPE-CHt sensor and 30% higher with CPE-Ce in comparison with the unmodified CPE, and this correlated with the higher hydrophilicity of the modified electrodes. Using SWV for the electrochemical analysis of PCT, carbon paste electrode modified with raw coffee husks (CPE-CHr) showed the presence of impurities at +0.27 V/SCE, showing the interest in using pure cellulose for the present analytical application. Furthermore, CPE-Ce presented a higher real area compared to CPE-CHr, which explains the increase in the limit of saturation from 400 mg/L to 950 mg/L. The better saturation limit exhibited by CPE-Ce justifies its choice for electroanalysis of PCT in commercialized tablets. The proposed method was successfully applied in the determination of PCT in commercialized tablets (Doliprane® 500) with a recovery rate close to 100%, and no interference with the excipients contained in the tablets analyzed was observed.