Análise voltamétrica do corante têxtil do tipo antraquinona empregando eletrodos de carbono impresso

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Expressão protéica diferencial entre plântulas apomíticas e zigóticas de citros

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Aplicação da calorimetria exploratória diferencial (dsc) na caracterização térmica do acetato de dexametazona, excipientes e do creme de dexametazona

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Determination of brilliant blue FCF in the presence and absence of erythrosine and quinoline yellow food colours by cathodic stripping voltammetry

A study of the voltammetric behaviour of the food colours brilliant blue FCF (C.I. 42090), erythrosine (C. I. 45430) and quinolin e yellow (C. I. 47005) in the pH range 2-10 have been carried out by cathodic stripping voltammetry. At pH 4.5 (acetate buffer) with an accumulation potential of 0 V and accumulation time of 30 s, the voltammograms presented well-defined reduction peaks at potential - 0.76 V for brilliant blue FCF, - 0.85 V for quinoline yellow and - 0.54 V for erythrosine. Linear calibration graphs were obtained from 8 to 80 mug l(-1) brilliant blue, from 4 to 43 mug l(-1) quinoline yellow and from 10 to 70 mug l(-1) erythrosine. The method has been successfully applied to identify and quantify binary mixtures of these dyes and applied for determining brilliant blue FCF in commercial food products.

DEVELOPMENT OF A CHEMICALLY MODIFIED ELECTRODE BASED ON CARBON PASTE AND FUNCTIONALIZED SILICA-GEL FOR PRECONCENTRATION AND VOLTAMMETRIC DETERMINATION OF MERCURY(II)

A mercury-sensitive chemically modified electrode (CME) based on modified silica gel-containing carbon paste was developed. The functional group attached to the silica gel surface was 3-(2-thiobenzimidazolyl)propyl, which is able to complex mercury ions. This electrode was applied to the determination of mercury(II) ions in aqueous solution. The mercury was chemically preconcentrated on the CME prior to voltammetric determination by anodic stripping in the differential-pulse mode. A calibration graph covering the concentration range from 0.08 to 2 mg l-1 was constructed. The precision for six determinations of 0.122 and 0.312 mg l-1 Hg(II) was 3.2 and 2.9% (relative standard deviation), respectively. The detection limit for a 5-min preconcentration period was 0.013 mg l-1. A study for foreign ions was also made.

BARRIER VOLTAGE DEFORMATION OF ZNO VARISTORS BY CURRENT PULSE

The phenomenon of electrical degradation in ZnO varistors was studied by application of high-intensity current pulses. A wave shape of 8 X 20-mu-s and rectangular waves of 1 and 2 ms were used. The degradation was estimated by reference electric-field variation and by Schottky voltage barrier deformation. The results showed that current pulses reduce both the height and the width of the barrier voltage. It was also observed that the donor density N(d) did not change but the surface states density N(s) decreased with degradation.

Generalization of the delta-differential autotransformer for 12 and 18-pulse converters

This work proposes a methodology to generalize the A-connections for 12 and 18-pulse autotransformers. A single mathematical expression, obtained through simple trigonometric operations, represents all the connections. The proposed methodology allows choosing any ratio between the input and the output voltages. The converters can operate either as step-up or as step-down voltage. To simplify the design of the windings, graphics are generated to calculate the turn-ratio and the polarity of each secondary winding, with respect to the primary winding. A design example, followed by digital simulations, and experimental results illustrate the presented steps. The results also show that high power factor is an inherent characteristic of multi-pulse converters, without any active or passive power factor pre-regulators needs.

Differential pulse polarographic determination of clotrimazole after derivatization with Procion Red HE-3B

Clotrimazole was shown to react at room temperature in Britton Robinson buffer pH 2 with the reactive dye Procion Red HE-3B. The product exhibited a differential pulse polarographic peak at -0.38 V, which was well separated from the peaks of the reactive dye at -0.08, -0.80 and -0.95 V, and this allowed the indirect determination of clotrimazole in the presence of excess of the reactive dye. The method has been applied satisfactorily to the determination of clotrimazole in pharmaceutical formulations, calibration graphs are rectilinear up to at least 40 mug ml(-1). The detection limit was calculated to be 2.6 mug ml(-1) (3 sigma). (C) 2002 Elsevier B.V. B.V. All rights reserved.

Voltammetric determination of fenbendazole in veterinarian formulations

A versatile voltammetric method for quantitative determination of fenbendazole (FBZ) in commercial tablets has been proposed, where direct dissolution of tablets is carried out in 0.1 mol l(-1) tetrabutylamoniun tetrafluorborate containing dimethylformamide solutions. Linear sweep (LSV), square wave (SWV) and differential pulse (DPV) voltammetry techniques were applied to study FBZ at a glassy carbon electrode, exhibiting a well defined irreversible oxidation peak at 1.15 V vs. SCE. This methodology allows a precise quantitative determination of FBZ presenting detection limits of 5.2 x 10(-5) (LSV), 5.0 x 10(-6) (DPV) and 5.0 x 10(-5) mol l(-1) (SWV). (C) 2002 Elsevier B.V. B.V. All rights reserved.

Preconcentration of rutin at a poly glutamic acid modified electrode and its determination by square wave voltammetry

The voltammetric determination of rutin in 0.04 mol l(-1) B-R buffer (pH 4.0) by square wave voltammograms (+0.41 V vs. Ag/AgCl(sat.)) at a poly glutamic acid modified glassy carbon electrode was found to be several orders of magnitude lower than that on a bare glassy carbon electrode. Rutin can be preconcentrated on the films of poly glutamic acid and presented linear relationship from concentration of 7 x 10(-7) to 1 x 10(-5) mol l(-1) in 0.04 mol l(-1) B-R buffer pH 4.0. The method was successfully applied to the determination of rutin in pharmaceutical formulation without any pretreatment.

Differential pulse polarographic determination of ceftazidime in urine samples with and without prior extraction

Ceftazidime shows two main polarographic reduction peaks at pH 4.0, that at -0.45 V owing to reduction of the C=N bond in the methylethoxyimino group and that at -1.00 V owing to the reductive elimination of pyridine: the first peak is particularly suitable for the determination of ceftazidime. Ceftazidime can also be determined indirectly using the tensammetric peak at -0.60 V (in Britton-Robinson buffer pH 9.5) of pyridine liberated on hydrolysis. Ceftazidime can be determined in urine using the direct method only after Cls solid phase extraction, but it can be determined directly in the urine by hydrolysing it and using the pyridine peak. (C) 1997 Elsevier B.V. B.V.

Indirect polarographic and cathodic stripping voltammetric determination of cefaclor as an alkaline degradation product

Cefaclor is not reducible at a mercury electrode, but it can be determined polarographically and by cathodic stripping voltammetry as its initial alkaline degradation product which is obtained in high yield by hydrolysis of cefaclor in Britton-Robinson (B-R) buffer pH 10 at 50 degrees C for 30 min (reduction peak at pH 10, -0.70 V). Differential pulse polarographic calibration graphs are linear up to at least 1 x 10(-4) mol l(-1). Recoveries of 93% of the cefaclor (n = 3) were obtained from urine spiked with 38.6 mu g ml(-1) using this polarographic method with 1 ml urine made up to 10 ml with pH 10 buffer. Using cathodic stripping voltammetry and accumulating at a hanging mercury drop electrode at -0.2 V for 30 s, linear calibration graphs were obtained from 0.35 to 40 mu g ml(-1) cefaclor in B-R buffer pH 10. A relative standard deviation of 4.2% (eta = 5) was obtained, and the limit of detection was calculated to be 2.9 ng ml(-1). Direct determination of cefaclor in human urine (1 ml of urine was made up to 10 ml with pH 10 buffer) spiked to 0.39 mu g ml(-1) was made (recovery 98.6%). (C) 1999 Elsevier B.V. B.V. All rights reserved.

Thermal conductivity features of ZnO-based varistors using the laser-pulse method

The thermal conductivity of several commercial ZnO-based varistor systems was determined based on the laser-pulse method, a technique that proved extremely useful and easy to apply. Using this technique, the thermal conductivity was found to be dependent on the microstructural features of the devices, involving the mean grain size and phase composition. Among the phases existing in commercial ZnO-based varistors, ZniSb2O12 and Bi2O3 were found to contribute strongly to the thermal conductivity of the devices. (C) 2003 Elsevier B.V. All rights reserved.

Efficacy and safety of itraconazole pulse therapy: Brazilian multicentric study on toenail onychomycosis caused by dermatophytes

Background Itraconazole is a large spectrum triazole with known efficacy in both continuous and pulse therapy for various mycoses.Objectives Evaluate the efficacy and tolerability of itraconazole pulse therapy for onychomycosis of the toenails due to dermatophytes, in a prospective, open, non-comparative and multicentric investigation.Patients and methods the trial was completed by 72 patients of an initial total of 89. Treatment consisted of four cycles of itraconazole, 200 mg twice a day, for seven consecutive days each month. Patients were evaluated clinically, mycologically and biochemically before, during and at the end of the investigation, and were divided into two groups according to the measure of normal portion of the most affected nail (target nail), as follows: Group 1. 0-5.9 mm; and Group 2: more than 6 mm.Results Improvement was satisfactory and progressive. Results were statistically significant, when comparing the three moments of the study: pre-treatment, end of therapy (fourth month) and follow-up (ninth month) in both groups.Conclusions Itraconazole pulse therapy was efficient and safe for the treatment of onychomycosis caused by dermatophytes, although a much higher daily dosage than the known continuous administration was used. Group 1, with nails initially more extensively affected, had a more evident improvement, by the mean variation in millimeters of normal portion of the target nail. This group showed a very satisfactory response, although not reaching total cure, thus demonstrating the great importance of early treatment of this disease. A residual therapeutic effect is maintained even after suspension of the drug. Group 2 obtained better total cure rates, and four pulses were, in general, sufficient, whereas more cycles would have been beneficial for the Group 1 patients with more extensive involvement. (C) 1998 Elsevier B.V. B.V. All rights reserved.