A solid paraffin-based carbon paste electrode modified with 2-aminothiazole organofunctionalized silica for differential pulse adsorptive stripping analysis of nickel in ethanol fuel

A solid paraffin-based carbon paste electrode modified with 2-aminothiazole organofunctionalized silica (SiAt-SPCPE) was applied to Ni2+ determination in commercial ethanol fuel samples. The proposed method comprised four steps: (1) Ni2+ preconcentration at open circuit potential directly in the ethanol fuel sample, (2) transference of the electrode to an electrochemical cell containing DMG, (3) differential pulse voltammogram registering and (4) surface regeneration by polishing the electrode. The proposed method combines the high Ni2+ adsorption capacity presented by 2-aminothiazole organofunctionalized silica with the electrochemical properties of the Ni(DMG)2 complex, whose electrochemical reduction provides the analytical signal.All experimental parameters involved in the proposed method were optimized. Using a preconcentration time of 20 min, it was obtained a linear range from 7.5 x 10(-9) to 1.0 x 10(-6) mol L-1 with detection limit of 2.0 x 10(-9) mol L-1. Recovery values between 96.5 and 102.4% were obtained for commercial samples spiked with 1.0 mu mol L-1 Ni2+ and the developed electrode was totally stable in ethanolic solutions. The contents of Ni2+ found in the commercial samples using the proposed method were compared to those obtained by graphite furnace atomic absorption spectroscopy by using the F- and t-test. Neither the F- nor t-values exceeded the critical values at 95% confidence level, confirming that there are not statistical differences between the results obtained by both methods. These results indicate that the developed electrode can be successfully employed to reliable Ni2+ determination in commercial ethanol fuel samples without any sample pretreatment or dilution step. (c) 2006 Elsevier B.V. All rights reserved.

Preparation and Characterization of Graphite-Epoxy Composite Modified with Zinc Hexacyanoferrate and Their Electrochemical Behaviour in Presence of Substituted Anilines

The growth of zinc hexacyanoferrate (ZnHCF) hybrid film on the surface of graphite-epoxy composite (GEC) electrodes was demonstrated by cyclic voltammetry. Surface morphology of the hybrid film was investigated by using scanning electron microscopy. The effect of the type of monovalent cations on the redox behaviour of hybrid film was also studied. This effect indicated that the radius of the hydrated cation mainly determines the ion permeability of the film.The electrochemical behavior of the substituted anilines (procaine and sulfamerazine) in 1 M KCl of the modified GEC electrode showed a decrease of the cathodic currents while increasing the concentration of these analytes. The developed sensor also showed excellent stability for long time usage, higher sensitivity and cost-effective fabrication.

Silver Nanocomposite Electrode Modified with Hexacyanoferrate. Preparation, Characterization and Electrochemical Behaviour Towards Substituted Anilines

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Use of a carbon paste electrode modified with spinel-type manganese oxide as a potentiometric sensor for lithium ions in flow injection analysis

A potentiometric sensor constructed from a mixture of 25% (m/m) spinel-type manganese oxide (lambda-MnO2), 50% (m/m) graphite powder and 25% (m/m) mineral oil is used for the determination of lithium ions in a flow injection analysis system. Experimental parameters, such as pH of the carrier solution, flow rate, injection sample volume, and selectivity for Li+ against other alkali and alkaline-earth ions and the response time of this sensor were investigated. The sensor response to lithium ions was linear in the concentration range 8.6 x 10(-5) - 1.0 x 10(-2) mol L-1 with a slope 78.9 +/- 0.3 mV dec(-1) over a wide pH range 7 - 10 (Tris buffer), without interference of other alkali and alkaline-earth metals. For a flow rate of 5.0 mL min(-1) and a injection sample volume of 408.6 muL, the relative standard deviation for repeated injections of a 5.0 x 10(-4) mol L-1 lithium ions was 0.3%.

A new potentiometric ibuprofenate ion sensor immobilized in a graphite matrix for determination of ibuprofen in tablets

The characteristics, performance, and application of an electrode, namely, Pt vertical bar Hg vertical bar Hg-2(IBP)(2)vertical bar Graphite, where IBP stands for ibuprofenate ion, are described. This electrode responds to IBP with sensitivity of (58.6 +/- 0.9) mV decade 1 over the range 5.0 x 10(-5)-1.0 x 10(-1) mol L-1 at pH 6.0-9.0 and a detection limit of 3.8 x 10(-5) mol L-1. The electrode is easily constructed at a relatively low cost with fast response time (within 1530 s) and can be used for a period of 5 months without any considerable divergence in potentials. The proposed sensor displayed good selectivity for ibuprofen in the presence of several substances, especially concerning carboxylate and inorganic anions. It was used for the direct assay of ibuprofen in commercial tablets by means of the standard additions method. The analytical results obtained by using this electrode are in good agreement with those given by the United States Pharmacopeia procedure. (c) 2006 Elsevier B.V. All rights reserved.

Benzoate ion determination in beverages by using a potentiometric sensor immobilized in a graphite matrix

The characteristics, performance, and application of an electrode, namely. Pt\Hg\Hg-2(Bzt)(2)\graphite, where Bzt stands for benzoate ion. are described. This electrode responds to Bzt with sensitivity of 57.7 +/- 1.0 mV/decade over the range 5 x 10(-4)-1 x 10(-1) mol l(-1) at pH 6.0-8.0 with a detection limit of 1.6 x 10(-4) mol l(-1). The electrode shows easy construction, fast response rime (between 10-30 s), low-cost, acid excellent response stability (lifetime > 6 months, in continuous use), the proposed sensor displayed good selectivity for benzoate in the presence of several carboxylate and inorganic anions. It was used to determine benzoate in various beverages by means of the standard additions method. The results obtained by using this electrode compared very favorably with those given by the official AOAC spectrophotometric method and by a HPLC procedure as well. (C) 2001 Elsevier B.V. B.V. All rights reserved.

p-Aminobenzoate ion determination in pharmaceutical formulations by using a potentiometric sensor immobilized in a graphite matrix

The characteristics, performance, and application of an electrode, namely, Pt\Hg\Hg-2(PABzt)(2)\ graphite, where PABzt stands for p-aminobenzoate ion, are described. This electrode responds to PABzt with sensivity of (58.1 +/- 1.0) mV per decade over the range 1.0 x 10(-4) to 1.0 x 10(-1) mol l(-1) at pH 6.5-8.0 and a detection limit of 3.2 x 10(-5) mol l(-1). The electrode shows easy construction, fast response time (within 10-30 s), low-cost, and excellent response stability (lifetime greater than 6 months, in continuous use). The proposed sensor displayed good selectivity for p-aminobenzoate in the presence of several substances, especially, concerning carboxylate and inorganic anions. It was used to determine p-aminobenzoate in pharmaceutical formulations by means of the standard additions method. The results obtained by using this electrode compared very favorably with those given by an HPLC procedure. (C) 2004 Elsevier B.V. All rights reserved.

Determination of diclofenac in pharmaceutical preparations using a potentiometric sensor immobilized in a graphite matrix

The characteristics, performance, and application of an electrode, namely Pt| Hg|Hg-2(DCF)(2)|graphite, where DCF stands for diclofenac ion, are described. This electrode responds to diclofenac with sensitivity of (58.1 +/- 0.8) mV/decade over the range 5.0 x 10(-5) to 1.0 x 10(-2) Mol l(-1) at pH 6.5-9.0 and a detection limit of 3.2 x 10(-5) mol l(-1). The electrode is easily constructed at a relatively low cost with fast response time (within 10-30 s) and can be used for a period of 5 months without any considerable divergence in potentials. The proposed sensor displayed good selectivity for diclofenac in the presence of several substances, especially concerning carboxylate and inorganic anions. It was used to determine diclofenac in pharmaceutical preparations by means of the standard additions method. The analytical results obtained by using this electrode are in good agreement with those given by the United States Pharmacopeia procedures. (c) 2005 Elsevier B.V. All rights reserved.

An electrode of the second kind for aspirin determination in tablet formulations

This paper describes the construction of an electrode of the second kind, Pt\Hg\Hg-2(Salic)(2)\Graphite, sensitive to salicylate. This electrode responds to the salicylate ion with a sensivity of 58.66 mV/decade over the range 6.0x10(-4) - 1.0x10(-1) mol/l at pH 6.0 and an ionic strength of 0.500 - 3.00 mol/l, adjusted with NaClO4. The electrode is easily constructed, shows a fast response time, is low in cost, has excellent response stability, and has a lifetime greater than 18 months, which is much longer than those reported earlier for other systems. The influence of 10 different carboxylate and inorganic anions on the electrode response showed that there was negligible interference by most of these ions. It was used to determine aspirin in tablets (after hydrolysis of acetylsalicylic acid to salicylate) by means of the standard additions method. The results obtained using this electrode for aspirin determination, in three different samples of antithermic drugs, compared favorably with the results given by the British Pharmacopoeia method.

Determination of nickel in fuel ethanol using a carbon paste modified electrode containing dimethylglyoxime

A mercury-free electrode chemically modified with carbon paste containing dimethylglyoxime was used for determination of nickel in fuel ethanol. The instrumental parameters and composition of the modified paste were optimized. The analytical curve for nickel determination from 5.0 x 10(-9) to 5.0 x10(-7) mol(-1) was obtained using 25 min of accumulation time. The detection limit and amperometric sensitivity obtained for this method were 2.7 x 10 mol(-1) and 5.2 x 10(8) mu A mol(-1) L, respectively. The values for nickel concentration in four commercial samples of fuel ethanol were obtained in the range of 1.1 x 10(-8) to 6.9 x 10(-8) mol(-1). A comparison to graphite furnace atomic absorption spectrometry (GFAAS) was performed for nickel determination in commercial samples of ethanol.

An electrode of the second kind for benzoate determination in medicinal syrups

This paper describes the construction of an electrode of the second kind, Pt\Hg\Hg-2(Bzt)(2)\graphite, sensitive to benzoate ion (Bzt). The electrode provides a near-Nernstian response (-58.19 mV/decade at 25 degrees C) to benzoate ion in the concentration range 1.11 x 10(-1) to 5.00 x 10(-4) M at pH 7.0 and ionic strength 0.500-3.00M, adjusted with NaClO4. The electrode is easily constructed, shows a fast response time, is low in cost, has excellent response stability, and has a lifetime greater than 24 months. which is much longer than those earlier reported for other systems. A further salient feature of the electrode is that perchlorate does not interfere in its response, which may be advantageous in the analysis of perchloric acid-treated samples. It was applied to the determination of sodium benzoate in some commercial expectorating medicinal syrups using the standard additions method. The results obtained by the proposed procedure compare very favorably with those obtained through the reference method recommended by the United States Pharmacopeia. (C) 1998 Academic Press.

Flow injection amperometric determination of persulfate in cosmetic products using a Prussian Blue film-modified electrode

A flow-injection system with a glassy carbon disk electrode modified with Prussian Blue film is proposed for the determination of persulfate in commercial samples of hair bleaching boosters by amperometry. The detection was obtained by chronoamperometric technique and the sample is injected into the electrochemical cell in a wall jet configuration. Potassium chloride at concentration of 0.1 mol L-1 acted as sample carrier at a flow rate of 4.0 mL min-1 and supporting-electrolyte. For 0.025 V (vs. Ag/AgCl) applied voltage, the proposed system handles ca. 160 samples per hour (1.0 10-4 - 1.0 10-3 mol L-1 of persulfate), consuming about 200 μL sample and 11 mg KCl per determination. Typical linear correlations between electrocatalytic current and persulfate concentration was ca. 0.9998. The detection limit is 9.0 10-5 mol L-1 and the calculated amperometric sensibility 3.6 103 μA L mol -1. Relative standard deviation (n =12) of a 1.0 10-4 mol L-1 sample is about 2.2%. The method was applied to persulfate determination in commercial hair-bleaching samples and results are in agreement with those obtained by titrimetry at 95% confidence level and good recoveries (95 - 112%) of spiked samples were found. © 2003 by MDPI.

Preconcentration and determination of mercury(II) at a chemically modified electrode containing 3-(2-thioimidazolyl)propyl silica gel

A mercury-sensitive chemically modified graphite paste electrode was constructed by incorporating modified silica gel into a conventional graphite paste electrode. The functional group attached to the (3-chloropropyl) silica gel surface was 2-mercaptoimidazole, giving a new product denoted by 3-(2-thioimidazolyl)propyl silica gel, which is able to complex mercury ions. Mercury was chemically adsorbed on the modified graphite paste electrode containing 3-(2-thioimidazolyl)propyl silica (TIPSG GPE) by immersion in a Hg(II) solution, and the resultant surface was characterized by cyclic and differential pulse anodic stripping voltammetry. One cathodic peak at 0.1 V and other anodic peak at 0.34 V were observed on scanning the potential from -0.1 to 0.8 V (0.01 M KNO3; ν = 2.0 mV s-1 νs. Ag/AgCl). The anodic peak at 0.34 V show an excellent sensitivity for Hg(II) ions in the presence of several foreign ions. A calibration graph covering the concentration range from 0.02 to 2 mg L-1 was obtained. The detection limit was estimated to be 5 μg L-1. The precision for six determinations of 0.05 and 0.26 mg L-1 Hg(II) was 3.0 and 2.5% (relative standard deviation), respectively. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal. 2005 © The Japan Society for Analytical Chemistry.

A novel potentiometric naproxenate ion sensor immobilized in a graphite matrix for determination of naproxen in pharmaceuticals

The characteristics, performance, and application of an electrode, namely, Pt|Hg|Hg 2(NAP) 2| Graphite, where NAP stands for naproxenate ion, are described. This electrode responds to NAP with sensivity of (58.1± 0.9) mV decade -1 over the range 5.0 × 10 -5 - 1.0 × 10 -2 mol L -1 at pH 6.0-9.0 and a detection limit of 3.9 × 10 -5 mol L -1. The electrode is easily constructed at a relatively low cost with fast response time (within 10-35 s) and can be used for a period of 6 months without any considerable divergence in potentials. The proposed sensor displayed good selectivity for naproxen in the presence of several substances, especially concerning carboxylate and inorganic anions. It was used for the direct assay of naproxen in commercial tablets by means of the standard additions method. The analytical results obtained by using this electrode are in good agreement with those given by the United States Pharmacopeia procedure. ©2006 Sociedade Brasileira de Química.

Cost-effective composite electrode for the fast voltammetric screening and determination of riboflavin (B2) and pyridoxine (B6) in pharmaceuticals

Different solid composites made by mechanical dispersions of graphite particles into heated paraffin (from 65 to 80% graphite, in mass) were prepared and assessed in order to optimize their use in electrochemical and electroanalytical procedures for bioanalysis. Besides these, composites were also evaluated by thermoanalytical techniques aiming to study their conservation and long-term stability (over eight months without special care), among others. Best results were found at 80% m/m graphite in paraffin. Such electrode combines low-cost, stability, sensitivity, ease of maintenance and clearance, besides the possibilities of manufacture in many different forms and shapes (with or without modifications) and applicability in a wide range of pH. Electrochemical studies by different voltammetric techniques involving vitamins from complex B (riboflavin and pyridoxine) leaded to a better understanding about their electrooxidative processes onto carbon-composite electrodes, specially regarding reversibility and pH-dependence. Data were also acquired and optimized with analytical purposes, being square-wave voltammetry in pH 4.2 chosen by its many advantages. Good linearity between peak responses as function of concentration were reached from 5 to 43 μmol L-1 for riboflavin (peak at -0.257 V) and up to 8.5 × 10-4 mol L -1 for pyridoxine (peak at +1.04 V), best studied conditions; limits of detection (at an S/N of 3) for both analites showed to be circa 1.0 mol L-1. Different commercial samples were analyzed for riboflavin (EMS® complex B syrup) and pyridoxine (Citoneurin 5000 Merck® ampoules) providing 96.6% and 98.7% recoveries, respectively.