Romeu C. Rocha-Filho

Simultaneous voltammetric determination of paracetamol and caffeine in pharmaceutical formulations using a boron-doped diamond electrode.

A simple and highly selective electrochemical method was developed for the single or simultaneous determination of paracetamol (N-acetyl-p-aminophenol, acetaminophen) and caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) in aqueous media (acetate buffer, pH 4.5) on a boron-doped diamond (BDD) electrode using square wave voltammetry (SWV) or differential pulse voltammetry (DPV). Using DPV with the cathodically pre-treated BDD electrode, a separation of about 550 mV between the peak oxidation potentials of paracetamol and caffeine present in binary mixtures was obtained. The calibration curves for the simultaneous determination of paracetamol and caffeine showed an excellent linear response, ranging from 5.0 x 10(-7)mol L(-1) to 8.3 x 10(-5)mol L(-1) for both compounds. The detection limits for the simultaneous determination of paracetamol and caffeine were 4.9 x 10(-7)mol L(-1) and 3.5 x 10(-8)mol L(-1), respectively. The proposed method was successfully applied in the simultaneous determination of paracetamol and caffeine in several pharmaceutical formulations (tablets), with results similar to those obtained using a high-performance liquid chromatography method (at 95% confidence level).

Electrochemical degradation of a real textile effluent using boron-doped diamond or β-PbO2 as anode

Constant current electrolyses are carried out in a filter-press reactor using a boron-doped diamond (Nb/BDD) or a Ti-Pt/β-PbO(2) anode, varying current density (j) and temperature. The degradation of the real textile effluent is followed by its decolorization and chemical oxygen demand (COD) abatement. The effect of adding NaCl (1.5 g L(-1)) on the degradation of the effluent is also investigated. The Nb/BDD anode yields much higher decolorization (attaining the DFZ limit) and COD-abatement rates than the Ti-Pt/β-PbO(2) anode, at any experimental condition. The best conditions are j = 5 mA cm(-2) and 55 °C, for the systems optimized hydrodynamic conditions. The addition of chloride ions significantly increases the decolorization rate; thus a decrease of more than 90% of the effluent relative absorbance is attained using an applied electric charge per unit volume of the electrolyzed effluent (Q(ap)) of only about 2 kA h m(-3). Practically total abatement of the effluent COD is attained with the Nb/BDD anode using a Q(ap) value of only 7 kA h m(-3), with an energy consumption of about 30 kW h m(-3). This result allows to conclude that the Nb/BDD electrode might be an excellent option for the remediation of textile effluents.

Square-wave voltammetric determination of propranolol and atenolol in pharmaceuticals using a boron-doped diamond electrode

The independent determination of two beta-blocker agents, namely propranolol (PROP) and atenolol (ATN), in pharmaceutical formulations using square-wave voltammetry and a cathodically pretreated boron-doped diamond electrode is described. These electroanalytical determinations of propranolol or atenolol were carried out in 0.1molL(-1) H(2)SO(4) or 0.5molL(-1) NaNO(3) (pH 1.0, adjusted with concentrated HNO(3)), respectively. Excellent linear calibration curves, ranging from 0.20 to 9.0micromolL(-1) for PROP and from 2.0 to 41micromolL(-1) for ATN, with detection limits of 0.18 and 0.93micromolL(-1), respectively, were obtained. The obtained recoveries range from 93.9% to 105.0%, for PROP, and from 92.5% to 106.0%, for ATN. The proposed method was successfully applied in the determination of both beta-blockers in several pharmaceutical formulations (tablets), with results in close agreement at a 95% confidence level with those obtained using official spectrophotometric methods.

Simple Flow Injection Analysis System for Simultaneous Determination of Phenolic Antioxidants with Multiple Pulse Amperometric Detection at a Boron-Doped Diamond Electrode

A method for simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food was developed that uses multiple pulse amperometry (MPA) with flow injection analysis (FIA). Determination of these phenolic antioxidants was carried out with a cathodically pretreated boron-doped diamond electrode and an aqueous ethanolic (30% ethanol, v/v) 10 mmol L⁻¹ KNO₃ solution (pH(cond) = 1.5) as supporting electrolyte. A dual-potential waveform, at E(det1) = 850 mV/200 ms and E(det2) = 1150 mV/200 ms versus Ag/AgCl (3.0 mol L⁻¹ KCl), was employed. The use of E(det1) or E(det2) caused the oxidation of BHA or of BHA and BHT, respectively; hence, concentration subtraction could be used to determine both species. The respective analytical curves presented good linearity in the investigated concentration range (0.050-3.0 μmol L⁻¹ for BHA and 0.70-70 μmol L⁻¹ for BHT), and the detection limits were 0.030 μmol L⁻¹ for BHA and 0.40 μmol L⁻¹ for BHT. The proposed method, which is simple, quick, and presents good precision and accuracy, was successfully applied in the simultaneous determination of BHA and BHT in commercial mayonnaise samples, with results similar to those obtained by HPLC, at a 95% confidence level.

Simultaneous voltammetric determination of synthetic colorants in food using a cathodically pretreated boron-doped diamond electrode

Differential pulse voltammetry (DPV) and a cathodically pretreated boron-doped diamond (BDD) electrode were used to simultaneously determine two pairs of synthetic food colorants commonly found mixed in food products: tartrazine (TT) and sunset yellow (SY) or brilliant blue (BB) and sunset yellow (SY). In the DPV measurements using the BDD electrode, the reduction peak potentials of TT and SY or BB and SY were separated by about 150 mV. The detection limit values obtained for the simultaneous determination of TT and SY or BB and SY were 62.7 nmol L(-1) and 13.1 nmol L(-1) or 143 nmol L(-1) and 25.6 nmol L(-1), respectively. The novel proposed voltammetric method was successfully applied in the simultaneous determination of these synthetic colorants in food products, with results similar to those obtained using a HPLC method at 95% confidence level.

Lead recovery from a typical Brazilian sludge of exhausted lead-acid batteries using an electrohydrometallurgical process

Abstract Lead recovery from the nonmetallic portion of exhausted lead-acid batteries, also called sludge, was investigated using an electrohydrometallurgical process. Among 13 aqueous solutions studied in solubility tests, only the following three were chosen for the whole process (leaching and electrowinning steps): tetrafluoroboric acid (200 g/L), glycerol (92 g/L)+sodium hydroxide (120 g/L) and sodium potassium tartrate (150 g/L)+sodium hydroxide (150 g/L). The tetrafluoroboric acid showed an attractive performance as leaching electrolyte due to its low cost and reasonable leaching strength. In the electrowinning process using the solution obtained from the leaching of a desulfated sludge with this acidic electrolyte, compact, adherent and highly pure lead deposits were produced at 250 A/m2. Scanning electron micrographs (SEM) of lead deposits obtained at different current densities in the range of 250–500 A/m2 revealed a marked influence of the current density on the deposit morphology.

Pt/HClO4 interface CPE: influence of surface roughness and electrolyte concentration☆

Abstract The double-layer region impedance of polycrystalline Pt/perchloric acid solutions interfaces was measured to determine the influence of electrode surface roughness and solution electrolyte concentration on the fractional power n of the constant phase element cpe associated to frequency dispersion in the impedance behaviour of this system. The surface roughness factor was obtained through the adsorption charge of hydrogen from cyclic voltammograms. The solution electrolyte concentration was found to have a significant effect on the cpe only when smaller than 0.5 moll −1 . On the other hand, the frequency dispersion was found to depend directly on the surface roughness. An empirical linear relationship was found between the exponent n and the inverse if the roughness factor, leading to a minimum value of 76° for the phase angle; this value contrasts to the theoretically predicted value of 45°. From a general logarithmic relationship between roughness factor δ and the fractal dimension d of the electrode surface, derived from known equations, and the linear relationship between n and 1/δ, an empirical logarithmic relationship between n and d is obtained. This empirical relationship contrasts with linear relationships previously derived by other authors.

Square-wave voltammetric determination of acetylsalicylic acid in pharmaceutical formulations using a boron-doped diamond electrode without the need of previous alkaline hydrolysis step

In this paper the determination of acetylsalicylic acid (ASA) in pharmaceutical formulations using square-wave voltammetry (SWV) and a boron-doped diamond electrode (BDD) is described. By this proposed method, ASA is directly determined in a 0.01 mol L-1 H2SO4 solution without the need of a previous time-consuming alkaline hydrolysis step. A single oxidation peak at a potential of 1.97 V vs. Ag/AgCl (3.0 mol L-1 KCl) with the characteristics of an irreversible reaction was obtained. The obtained analytical curve is linear in the ASA concentration range 2.50 × 10-6-1.05 × 10-4 mol L-1, with a detection limit of 2.0 µmol L-1. The obtained relative standard deviation was smaller than 1.4% for a 45 µmol L-1 ASA solution (n = 10). The proposed method was applied with success in the determination of ASA in several pharmaceutical formulations; the obtained results were in close agreement, at a 95% confidence level, with those obtained using an official method of the British Pharmacopoeia.

A study of thin anodic WO3 films by electrochemical impedance spectroscopy

The properties of thin anodic passive films potentiostatically formed (1 V ≤ Ef ≤ 5 V vs sce) on polycrystalline tungsten in aqueous H3PO4, H2SO4, HNO3 and HClO4 solutions (pH ≈ 1.3) were studied using electrochemical impedance spectroscopy at room temperature. The data were analysed with a transfer function using a non-linear fitting routine, assuming that the resistance of the film is coupled in series with the faradaic impedance of the W(0) → W(VI) reaction, with these in parallel with the capacitance of the metal/passive film/electrolyte system. The relative permittivity (er) of the films was found to depend on the acid solution used. Except for the case of films grown in HNO3, the values of er, are smaller than those of thicker films grown galvanostatically. The film grown in H3PO4 solutions presented the lowest value of er, which could be due to the incorporation of phosphate ions into the film. The number concentration of donors in the films (ND) was found to decrease with Ef (ie increasing film thickness) and to be quite dependent on the electrolyte used: ND(H3PO4) < ND(HClO4) < ND(HNO3) < ND(H2SO4). The values for ND(H3PO4) are, nevertheless, 103 times larger than the ones for much thicker WO3 films and are of the same order of magnitude as the ones for annealed WO3 films. The flat band potential of the films grown in H3PO4 was found to be more than 0.1 V smaller than those for films grown in the other solutions.

Simultaneous square-wave voltammetric determination of aspartame and cyclamate using a boron-doped diamond electrode

A simple and highly selective electrochemical method was developed for the simultaneous determination of aspartame and cyclamate in dietary products at a boron-doped diamond (BDD) electrode. In square-wave voltammetric (SWV) measurements, the BDD electrode was able to separate the oxidation peak potentials of aspartame and cyclamate present in binary mixtures by about 400 mV. The detection limit for aspartame in the presence of 3.0x10(-4) mol L(-1) cyclamate was 4.7x10(-7) mol L(-1), and the detection limit for cyclamate in the presence of 1.0x10(-4) mol L(-1) aspartame was 4.2x10(-6) mol L(-1). When simultaneously changing the concentration of both aspartame and cyclamate in a 0.5 mol L(-1) sulfuric acid solution, the corresponding detection limits were 3.5x10(-7) and 4.5x10(-6) mol L(-1), respectively. The relative standard deviation (R.S.D.) obtained was 1.3% for the 1.0x10(-4) mol L(-1) aspartame solution (n=5) and 1.1% for the 3.0x10(-3) mol L(-1) cyclamate solution. The proposed method was successfully applied in the determination of aspartame in several dietary products with results similar to those obtained using an HPLC method at 95% confidence level.