M. Bakasse

Electrochemical determination of para-nitrophenol at apatite-modified carbon paste electrode: application in river water samples.

The behavior of a modified carbon paste electrode (CPE) for para-nitrophenol detection by cyclic and square wave voltammetry (SWV) was studied. The electrode was built by incorporating the hydroxyapatite (HAP) to carbon paste. The overall analysis involved a two-step procedure: an accumulation step at open circuit, followed by medium exchange to a pure electrolyte solution for the voltammetric quantification. During the preconcentration step, para-nitrophenol was adsorbed onto hydroxyapatite surface. The influence of various experimental parameters on the HAP-CPE response was investigated (i.e. pH, carbon paste composition, accumulation time). Under the optimized conditions, the reduction peak shows that the peak height was found to be directly proportional to the para-nitrophenol concentration in the range comprised between 2x10(-7) mol L(-1) and 1x10(-4) mol L(-1). With this, it was possible to determine detection limit (DL), which resulted in 8x10(-9) mol L(-1) for peak 1. The proposed electrode (HAP-CPE) presented good repeatability, evaluated in term of relative standard deviation (R.S.D.=2.87%) for n=7 and was applied for para-nitrophenol determination in water samples. The average recovery for these samples was 86.2%.

Square wave voltammetry for analytical determination of paraquat at carbon paste electrode modified with fluoroapatite.

This paper describes the construction of a carbon paste electrode (CPE) impregnated with fluoroapatite (FAP). The new electrode (FAP-CPE) was revealed an interesting determination of paraquat. The latter was accumulated on the surface of the modified electrode by adsorbing onto fluoroapatite and reduced in 0.1molL(-1) K2SO4 electrolyte at -0.70 and -1.0V for peaks 1 and 2, respectively. Experimental conditions were optimized by varying the accumulation time, FAP loading and measuring solution pH. Under the optimized working conditions, calibration graphs were linear in the concentration ranging from 5×10(-8) to 7×10(-5)molL(-1) with detection limits (DL,3σ) of 3.5×10(-9) and 7.4×10(-9)molL(-1), respectively, for peaks 1 and 2. Fluoroapatite was characterized by X-ray diffraction XRD analysis; Fourier-transform infrared spectroscopy FT-IR and inductively coupled plasma-atomic emission spectrometry (ICP-AES) analysis.

Electrochemical determination of cadmium(II) at platinum electrode modified with kaolin by square wave voltammetry

In this work, determination of cadmium(II) using square wave voltammetry (SWV) was described. The method is based on accumulation of these metal ions on kaolin platinum electrode (K/Pt). The K/Pt performance was optimized with respect to the surface modification and operating conditions. The optimized conditions were obtained in pH of 5.0 and accumulation time of 25 min. Under the optimal conditions, the relationship between the peak current versus concentration was linear over the range of 9 x 10(-8) to 8.3 x 10(-6) mol L(-1). The detection limit (DL, 3sigma) was 5.4 x 10(-9) mol L(-1). The analytical methodology was successfully applied to monitor the Cd(II) content in natural water. Interferences were also evaluated.

Sensitive determination of paraquat by square wave anodic stripping voltammetry with chitin modified carbon paste electrode

A novel analytical approach has been developed and evaluated for the quantitative analysis of paraquat herbicides which can be found at trace levels in olive oil and olives. The aim of this work is to optimize all factors that can influence this determination by a carbon paste electrode modified with chitin (Chit-CPE). The best responses were obtained with square wave potential in diluted Na2SO4 as supporting electrolyte. The influence of various parameters on the Chit-CPE was investigated. Under the optimized working conditions, calibration graphs were linear in the concentration ranges of 5.0 × 10(-9)-1.0 × 0(-5) mol L(-1). For 180 s preconcentration, detection limits of 2.67 × 10(-10) mol L(-1) (peak 2) was obtained at the signal noise ratio (SNR) of 3. To evaluate the reproducibility of the newly developed electrode, the measurements of 1.0 × 10(-5) mol L(-1) PQ were carried out for seven times at Chit-CPE and the relative standard deviation was 5.2%. The analytical methodology was successfully applied to monitor the paraquat content in olives and olive oil.

Electroanalytical method for determination of lead(II) in orange and apple using kaolin modified platinum electrode

This paper reports on the use of platinum electrode modified with kaolin (K/Pt) and square wave voltammetry for analytical detection of trace lead(II) in pure water, orange and apple samples. The electroanalytical procedure for determination of the Pb(II) comprises two steps: the chemical accumulation of the analyte under open-circuit conditions followed by the electrochemical detection of the preconcentrated species using square wave voltammetry. The analytical performances of the extraction method has been explored by studying the incubating time, and effect of interferences due to other ions. During the preconcentration step, Pb(II) was accumulated on the surface of the kaolin. The observed detection and quantification limits in pure water were 3.6x10(-9)molL(-1) and 1.2x10(-8)molL(-1), respectively. The precision of the method was also determined; the results was 2.35% (n=5).

Square wave voltammetric determination of paracetamol at chitosan modified carbon paste electrode: Application in natural water samples, commercial tablets and human urines

A novel analytical approach has been developed and evaluated for the quantitative analysis of paracetamol (PCT). The anodic peak currents of paracetamol on the CS-CPE were about 200 fold higher than that of the unmodified electrodes. The influence of various parameters on the CS-CPE was investigated. Under the optimized working conditions, the oxidation peak current is linear to the paracetamol concentration in the ranges of 1.0 × 10(-3)-4.0 × 10(-4)mol L(-1) and 2.0 × 10(-4)-8.0 × 10(-7)mol L(-1) with a detection limit of 5.08 × 10(-7)mol L(-1). The repeatability of the method expressed as relative standard deviation (RSD) is 1.73% (n=8). Possible interferences were tested and evaluated in 1.0 × 10(-4)mol L(-1) paracetamol in the presence of inorganic ions, dopamine, ibuprofen, ascorbic acid and uric acid. The proposed method was successfully applied to PCT determination in natural waters, tablets and urine samples.

Silver particles-modified carbon paste electrodes for differential pulse voltammetric determination of paraquat in ambient water samples

Abstract This paper describes the construction of silver particles-impregnated carbon paste electrode (Ag-CPE). The new electrode revealed an interesting determination of paraquat (II). The latter was accumulated on the modified electrode surface by adsorption onto silver particles and was reduced in 0.1 mol L−1 of Na2SO4 electrolyte at −0.70 V and −1.0 V for peaks 1 and 2, respectively. Experimental conditions were optimized by varying the heating temperature of the silver/carbon composite, the Ag/CP ratio, pH of measuring solution and accumulation time. Under the optimized working conditions, calibration graphs were linear for the concentration ranging from 1.0 × 10−7 to 1.0 × 10−3 mol L−1 with detection limits (DL, 3σ) 3.3 and 6.4 × 10−9 mol L−1, respectively, for peaks 1 and 2. The precision of this methodology was evaluated for eight successive measurements of the same samples containing 1.0 × 10−4 mol L−1 of paraquat. The relative standard deviations (D.S.R.) were 1.9% and 2.4% for the peaks 1 and 2, respectively. The Ag/CP composite was characterized by X-ray diffraction (XRD) and BET adsorption analysis.

Ibuprofen analysis in blood samples by palladium particles-impregnated sodium montmorillonite electrodes: Validation using high performance liquid chromatography

The electrochemical detection of ibuprofen has been studied on Palladium-Montmorillonite (Mt) modified carbon paste electrode using differential pulse voltammetry. The optimization of the modifier preparation and the instrumental parameters was investigated. The results indicate that ibuprofen oxidation was favored in the presence of Pd-PdO particles. The quantitative determination of ibuprofen was statistically analyzed and validated using HPLC method. The detection and quantification limits, specificity and precision were found to be acceptable. Finally, the developed method was successfully applied for ibuprofen determination in human blood samples.

Electrochemical impedance spectroscopy measurements for determination of derivatized aldehydes in several matrices

A simple, selective and sensitive electrochemical method is described for the determination of different aldehydes at glassy carbon electrode using electrochemical impedance spectroscopy (EIS). The measurements were performed after their derivatization with 2,4-dinitrophenylhydrazine (DNPH) in acidic medium. The impedance measurements were investigated in the frequency range from 100 mHz to 100 kHz at a potential of 1.0 V versus Ag/AgCl. The Nyquist plots were modeled with a Randle’s equivalent circuit. The charge transfer resistance was identified as the dependent parameter on relevant concentration of aldehydes (determined as their hydrazones). Under the optimized conditions, the linearity was established over the concentration range of 1000–0.05 μmol L−1. The limits of detection (LODs) obtained were from 0.097 to 0.0109 μmol L−1. Finally, the developed method has been applied to the determination of aldehydes in drinking water, orange juice and apple vinegar samples with relative standard deviations (RSDs) < 3.1% and acceptable recovery rate (around of 80%).

Date stone based activated carbon/graphite electrode for catechol analysis: physico-chemical properties and application in beverage samples

The purpose of this paper is the modification of a carbon paste electrode (CPE) with activated carbon synthesized from date stones using a pyrolysis system followed by physical activation. This material has the advantage of very low cost and facilitates charge transfer. The modified electrode was used for electrocatalysis and determination of catechol. A series of analyses and tests were carried out to demonstrate the nature, the surface functional groups and even the porosity of the resulting product. The activated carbon exhibited remarkable electrocatalytic activity toward catechol oxidation. The electron transfer coefficient, surface coverage and number of electrons for catechol oxidation at the surface of the AC-CPE were determined using electrochemical approaches. Subsequently, a sensitive and convenient electrochemical method was proposed for catechol analysis. The linear range is between 1.0 × 10−6 and 1.0 × 10−3 mol L−1 with a correlation coefficient of 0.993. The limit of detection is as low as 4.8 × 10−8 mol L−1. Finally, this novel method was employed to determine the catechol in tap water, green, black and peach teas, and in coffee samples.