Viviane Gomes Bonifácio

An improved flow system for chloride determination in natural waters exploiting solid-phase reactor and long pathlength spectrophotometry

A single and sensitive spectrophotometric method for chloride ions determination based on a commuted flow system with a 100cm optical path flow cell and a solid-phase reactor containing immobilized silver chloranilate was proposed. This procedure exploited the AgCl formation in the solid-phase reactor leading the chloranilate ions, monitored spectrophotometrically at 530nm. The analytical signals were 75-fold higher and the sensitivity was 12-fold than that achieved with a 1cm flow cell, allowed a chloride determination in the 0.5-100mgl(-1) range. The R.S.D. was 1.1% (n=20) with a sample throughput of 80h(-1) and a waste generated of ca. 100ng of chloranilate ions per determination. Four samples of natural waters from São Carlos and Araraquara cities were evaluated using the proposed method. Results agreed with the obtained by a reference method at the 95% confidence level.

Electrochemical sensor for ranitidine determination based on carbon paste electrode modified with oxovanadium (IV) salen complex

The preparation and electrochemical characterization of a carbon paste electrode modified with the N,N-ethylene-bis(salicyllideneiminato)oxovanadium (IV) complex ([VO(salen)]) as well as its application for ranitidine determination are described. The electrochemical behavior of the modified electrode for the electroreduction of ranitidine was investigated using cyclic voltammetry, and analytical curves were obtained for ranitidine using linear sweep voltammetry (LSV) under optimized conditions. The best voltammetric response was obtained for an electrode composition of 20% (m/m) [VO(salen)] in the paste, 0.10 mol L(-1) of KCl solution (pH 5.5 adjusted with HCl) as supporting electrolyte and scan rate of 25 mV s(-1). A sensitive linear voltammetric response for ranitidine was obtained in the concentration range from 9.9×10(-5) to 1.0×10(-3) mol L(-1), with a detection limit of 6.6×10(-5) mol L(-1) using linear sweep voltammetry. These results demonstrated the viability of this modified electrode as a sensor for determination, quality control and routine analysis of ranitidine in pharmaceutical formulations.

Determinação Turbidimétrica de Dipirona em Fluxo Utilizando um Reator Contendo Cloreto de Prata Imobilizado em Resina Poliéster

A simple flow injection procedure was developed for determining dipyrone (1-phenyl-2,3-dimethyl-4-methylaminomethano-5-pyrazolone sodium, metamizol, analgin) in pharmaceutical formulations. The determination is based on the reduction of Ag+ ions to Ag0 by dipyrone. A colloidal suspension of Ag0 produced was transported by carrier solution (0.01 mol L-1 NaOH) and turbidimetrically detected at 425 nm. The analytical curve for dipyrone was linear in the range from 5.0 x 10-4 to 2.5 x 10-3 mol L-1 with a correlation coefficient of 0.9990. The detection limit was 1.3 x 10-4 mol L-1 (3sB/slope). The relative standard deviation for ten successive measurements was 1.8% and an analytical frequency of 45 h-1 was obtained. The recovery values from three samples ranged from 96.0 to 102%.

Use of Barium Chloranilate Solid-Phase Reactor for the Determination of Sulfate in Natural Water Samples Exploiting Long Pathlength Spectrophotometry and Multicommutation

A flow-injection method for the spectrophotometric determination of sulfate in natural water samples using a solid-phase reactor with barium chloranilate (BaC6Cl2O4) immobilized in a polyester resin is presented. This procedure is based on the formation of insoluble barium sulfate (BaSO4) in the solid-phase reactor releasing chloranilate ions (C6Cl2 ), which was monitored spectrophotometrically at a wavelength of 533 nm. The analytical curve was linear in the sulfate concentration range from 2.5 to 40.0 mg L−1 with a detection limit of 0.1 mg L−1 and an analytical frequency of 50 h−1.

Determinação espectrofotométrica em fluxo de cloro em água usando célula de longo caminho óptico e multicomutação

A multicommuted method for determination of chlorine in water samples using a 100-cm cell was developed. In this method, orto-Tolidine reacts with chlorine and the product was monitored at 438 nm. The analytical curve for chlorine was linear in concentration range from 1.34x10-6 to 2.01x10-5 mol L-1 with a detection limit of 9.40x10-8 mol L-1. A sampling rate of 45 h-1and a RSD of 1.0 % (n = 15) were obtained. The method was applied with success for chlorine determination in six water samples.SPECTROPHOTOMETRIC FLOW DETERMINATION OF CHLORINE IN WATER USING A LONG PATHLENGTH OPTIC CELL AND MULTICOMMUTATION. A multicommuted method for determination of chlorine in water samples using a 100-cm cell was developed. In this method, orto-Tolidine reacts with chlorine and the product was monitored at 438 nm. The analytical curve for chlorine was linear in concentration range from 1.34x10 to 2.01x10 mol L with a detection limit of 9.40x10 mol L. A sampling rate of 45 h and a RSD of 1.0 % (n = 15) were obtained. The method was applied with success for chlorine determination in six water samples.

Spectrophotometric Multicommutated Flow System for the Determination of Hypochlorite in Bleaching Products

Abstract A multicommutation flow system for the spectrophotometric determination of hypochlorite in bleaching products is proposed. In this system, N,N-diethyl-p-phenylenediamine (DPD) reacts with hypochlorite, and the product was monitored at 515 nm. The analytical curve for hypochlorite was linear in the concentration range from 2.68 × 10−5 to 1.88 × 10−4 mol L−1 (2–14 mg L−1) with a detection limit of 6.84 × 10−6 mol L−1 (0.51 mg L−1). The sampling rate was 45 h−1, and a relative standard deviation of 1.4% (n = 10) was obtained. The recovery of this analyte ranged from 97.2% to 102.5%, and the results found using the proposed spectrophotometric multicommutated flow system agreed with the data obtained using a reference method (iodometric titration) at the 95% confidence level.

Flow Injection Spectrophotometric Determination of Isoproterenol with an On‐Line Solid‐Phase Reactor Containing Immobilized Manganese Dioxide

Abstract This work reports the application of a simple, sensitive, and rapid flow injection system for the spectrophotometric determination of isoproterenol by using a solid‐phase reactor containing MnO2(s) immobilized in a polyester resin. The method is based on the oxidation of isoproterenol to produce isoproterochrome, which was monitored at 492 nm. The analytical curve was linear in the isoproterenol concentration range from 1.0 × 10−5–2.0 × 10−4 mol L−1, with a detection limit of 1.7 × 10−6 mol L−1. The relative standard deviation (RSD) was 0.9%, and an analytical frequency of 60 hr−1 was obtained. The average recoveries varied from 101.0% to 104.2%, evidencing the absence of matrix effect on the flow injection procedure. The effect of excipient substances frequently found with isoproterenol in pharmaceutical formulations, such as lactose, sucrose, starch, poly(ethylene glycol), and sodium chlorine was evaluated by using the proposed flow procedure. None of these substances caused significant interference in the proposed method. The procedure was successfully applied to the determination of isoproterenol in pharmaceutical preparations, and the results were compared with those results obtained by using an ultraviolet (UV)‐spectrophotometric method.

Flow-Injection Spectrophotometric Determination of Captopril Exploiting Silver Chloranilate Solid-Phase Reactor

Abstract A novel, simple, and rapid flow-injection method for the spectrophotometric determination of captopril in pharmaceutical products, using a solid-phase reactor with silver chloranilate (Ag2C6Cl2O4) immobilized in a polyester resin, is presented. This method explored the formation of an insoluble salt between Ag(I) and captopril in the solid-phase reactor, releasing chloranilate anion ( ). Then, this anion reacted with ferric ions to produce a complex, , which was monitored spectrophotometrically at 528 nm. The analytical curve was linear in the captopril concentration range from 1.0 × 10−5 to 5.0 × 10−4 mol l−1 with a detection limit of 8.0 × 10−6 mol l−1. The relative standard deviation (RSD) was 0.35% (n = 10) for a solution of 3.0 × 10−4 mol l−1 captopril solution, and an analytical frequency of 70 h−1 was obtained. The effects of excipients frequently found with captopril in pharmaceutical formulations, such as lactose, microcrystalline cellulose, starch, and magnesium stearate, were evaluated using the proposed flow-injection method. None of these substances caused significative interference in the proposed method. The method was successfully applied to the determination of captopril in pharmaceutical products, and the results were compared with results obtained using a potentiometric method.

Flow-injection spectrophotometric determination of dipyrone in pharmaceutical formulations using a solid-phase reactor with copper(II) phosphate

AbstractIn this work, a flow-injection spectrophotometric method for dipyrone determination in pharmaceutical formulations was developed. Dipyrone sample solutions were injected into a carrier stream of deionized water and the reaction was carried out in a solid-phase reactor (12 cm, 2.0 mm i.d.) packed with Cu3(PO4)2(s) entrapped in a matrix of polyester resin. The Cu(II) ions were released from the solid phase reactor by the formation of Cu(II)-(dipyrone)n complex. When the complex is released, it reacts with 0.02% m/v alizarin red S in deionized water to produce a Cu(VABO3)3 complex whose absorbance was monitored at 540 nm. The calibration graph was linear over the range 5.0×10−5–4.0×10−4 mol L−1 with a detection limit of 2.0×10−5 mol L−1 and relative standard deviation for 10 successive determinations of 1.5% (2.0×10−4 mol L−1 dipyrone solution). The calculated sample throughput was 60 h−1. The column was stable for at least 8 h of continuous use (500 injections) at 25°C. Pharmaceutical formulations were analyzed and the results from an official procedure measurement were compared with those from the proposed FIA method in order to validate the latter method.

Construção de um calorímetro de baixo custo para a determinação de entalpia de neutralização

In this article the construction of a simple calorimeter (with easily acquired materials) for the determination of the enthalpy of neutralization at constant pressure of acid-base reactions is described. Solutions of weak and strong acids and bases, one thermometer, and one expanded-polystyrene (Styrofoam) container were used in the development of the experiment. With this calorimeter, it was possible to determine the enthalpy of neutralization of reactions and compare the obtained values with the most accepted one of - 55.84 kJ mol-1, at 25 ° C [1].