Julio Cesar B. Fernandes

Application of two- and three-way chemometric methods in the study of acetylsalicylic acid and ascorbic acid mixtures using ultraviolet spectrophotometry

AbstractIn this work, mixtures of acetylsalicylic acid (ASA) and ascorbic acid (AA) were studied by ultraviolet spectrophotometry(210–300nm) using parallel factor analysis (PARAFAC) and partial least square (PLS). The study was carried out in thepH range from 1.0 to 5.5 and with a concentration range from 1.0 −10 5 to 1.0 10 −4 moll −1 of both analytes. PARAFACwas used for spectra deconvolution, pK a estimation for both acids and to check the presence of salicylic acid (SA), dueto the possible ASA decomposition. The estimated first p K a was equal to 3.41 and 4.10 for ASA and AA, respectively.Multivariate calibration models using PLS at different pH and N-way PLS were elaborated for simultaneous determination ofASA and AA in pharmaceutical samples. The best models for the system were obtained with N-way PLS2 and PLS2 at pH1.1. The results obtained for simultaneous determination of ASA and AA in samples were in agreement to the values specifiedby the manufacturers and the recovery was between 97.6 and 103.6%. Nevertheless, these models failed to predict ASAdecomposition to SA in simulated samples. Thus, a new PLS-pH1 model considering SA was built and applied successfullyin simulated samples. ©2000 Elsevier Science B.V. All rights reserved.

Development of a new FIA-potentiometric sensor for dopamine based on EVA-copper(II) ions

Abstract A flow injection analysis (FIA) system using a tubular electrode based on the redox properties of copper(II) ions immobilized in a poly(ethylene- co -vinyl acetate) (EVA) membrane was developed for dopamine determination. The Cu 2+ was trapped in the EVA (40% m/m) matrix and dispersed on the surface of a graphite-epoxy flow-through electrode. The electrode based on the dopamine oxidation catalyzed by Cu 2+ exhibited a near-Nernstian response (83.2±0.2 mV decade −1 ) for dopamine concentration between 1.0×10 −3 and 1.0×10 −2 mol l −1 ( r =0.9992), employing 0.25 mol l −1 KH 2 PO 4 buffer, containing 0.1 mol l −1 H 2 O 2 at pH 7.0, as a carrier solution. The potentiometric-FIA system allows an analytical frequency of about 25 samples per hour with a good precision (variance lower than 4.2%). The best potentiometric response was achieved using an EVA membrane containing 5.0% (m/m) Cu 2+ ions. The use of hydrogen peroxide in a flow-system makes an efficient reoxidation of the Cu 1+ ions possible in the EVA membrane. The relative standard deviation for dopamine determination in pharmaceutical samples, without any previous treatment, was about 4.7%. The useful lifetime for the dopamine sensor was longer than 3 months, in continuous use.

Determination of acetylsalicylic acid by FIA-potentiometric system in drugs after on-line hydrolysis.

A potentiometric flow injection (FI) system was developed for the acetylsalicylic acid (ASA) determination in drugs, without previous treatment. The tubular potentiometric electrode for salicylate (SA) was based on tricaprylyl-trimethyl-ammonium-salicylate (aliquat-salicylate) as the ion-exchanger, supported on poly(ethylene-co-vinyl-acetate) (EVA) matrix and applied directly onto a conducting support. The standards and samples were freshly prepared in ethanol solution (0.10 mol l(-1) Tris-SO(4) buffer, pH 8.0, containing 0.25 mol l(-1) Na(2)SO(4) and 8.0% v/v ethanol) to facilitate the dissolution of ASA and were injected directly into the system. The SA formed due to the on-line alkaline hydrolysis of alcoholic ASA solution, with 0.50 mol l(-1) NaOH (coil, 50 cm length), was monitored by the tubular electrode after neutralization with 0.25 mol l(-1) H(2)SO(4). A solution of 0.10 mol l(-1) Tris-SO(4) buffer (pH 8.0), containing 0.25 mol l(-1) Na(2)SO(4) was employed as carrier. In optimized conditions (flow rate of 2.1 ml min(-1) and volume of injection of 150 mul), the tubular electrode showed a linear response to ASA in the concentration range between 4.0x10(-3) and 4.0x10(-2) mol l(-1). A conversion factor of ASA to SA of 85% occurs in these conditions with an increase of about 130% in the signal to the system with on-line hydrolysis (three-channel) in comparison to the system without (one-channel). The response time of the electrode was about 5 s with an analytical frequency of 28 samples per h and a relative standard deviation (R.S.D.) of 2.1% for 30 successive injections. Determinations of ASA in tablet samples by the proposed method exhibited relative differences of 1.0-3.5%, compared to the official method of the British Pharmacopoeia. The useful lifetime of the sensor was greater than 1 month, in continuous use.

Simultaneous determination of chloride and potassium in carbohydrate electrolyte beverages using an array of ion-selective electrodes controlled by a microcomputer

Este trabalho descreve a elaboracao de um sistema potenciometrico controlado por microcomputador para uso com um conjunto de eletrodos ion-seletivo. O sistema empregou uma placa de interface modelo ACL-8111 da ADLink Technology, para controlar a selecao dos eletrodos ion-seletivo, atraves de uma chave analogica (ADG201), com simultânea aquisicao de dados. Um programa escrito na linguagem VISUAL BASIC 4.0 foi empregado para controle e aquisicao de dado. Este sistema foi avaliado na determinacao simultânea de cloreto e potassio em amostras de bebidas energeticas. Os resultados obtidos na analise destes ions foram concordantes com aqueles dos metodos de referencia levando em consideracao o erro estimado nas determinacoes. This work describes the building of a potentiometric system composed of an array of ion-selective electrodes and controlled by microcomputer. The system employed an acquisition card model ACL8111 from ADLink Technology for the selection control of the ion-selective electrodes through an analogic switch (ADG201) with simultaneous data acquisition. Software implemented on the VISUAL BASIC 4.0 language was employed for electrode control and data acquisition. This system was evaluated in the simultaneous determination of chloride and potassium in samples of carbohydrateelectrolyte beverages. The results obtained for these determinations were in agreement with those obtained by the reference method taking into account the estimated error in the determinations.

Potentiometric Sensor for L-Ascorbic Acid Based on EVA Membrane Doped with Copper(II)

The development of a new potentiometric sensor for L-ascorbic acid based on the redox properties of copper(II) ions incorporated in a EVA membrane was carried out. The poly(ethylene-co-vinyl acetate) matrix (EVA 40 % wt.) was doped with Cu 2a ions and dispersed on the surface of a graphiteyepoxy electrode. The electrode displayed a Nernstian response (slope between 55 and 60 mVydecade), in the ascorbate concentration between 5.6610 ˇ6 and 3.7610 ˇ4 mol L ˇ1 , when 0.1 mol L ˇ1 KH2PO4 buffer at pH 5.0 and 25.0C was employed. The sensor stability was assessed, allowing 280 determinations without significant decrease in the response. The relative standard deviation for vitamin C determination in pharmaceuticals samples by the proposed method was about 10 %. Considering these deviations, the results obtained for both the methods (spectrophotometric and potentiometric) were similar.

Manufacturing of miniature fluidic modules for lab-on-a-chip using UA photoresin from flexographic platemaking process

A new technique of fabrication of miniaturized fluidic devices was developed using a photoresin based on urethane and acrylate (UA) oligomers used to platemaking for flexographic printers on graphic industry. Fluidic mixers and reactors modules measuring 10´10 mm2 were manufactured, with channels width in the 0.25 to 1.00 mm range and 0.75 mm depth. Top covers 4.00 mm thick, with 1.26 mm diameter inlet and outlet holes were used to seal the channels. The sealed channel structures were formed using a film of photoresin as adhesive. Interconnections of 1.20 mm diameter and 10 mm long steel tubes were fixed into inlet and outlet holes. All fluidic modules were manufactured by photolithography of UA, sealed by ultraviolet cure of an UA adhesion layer, package in an UA container and successfully tested for leakage under 2´105 Pascal air pressure.

Eletrodos íon-seletivos: histórico, mecanismo de resposta, seletividade e revisão dos conceitos

This paper presents a review of the concepts involved in the working mechanism of the ion-selective electrodes, searching a historical overview, moreover to describe the new advances in the area.

Potentiometric determination of L-ascorbic acid in pharmaceutical samples by FIA using a modified tubular electrode

Um sistema de analise por injecao em fluxo usando um eletrodo tubular baseado nas propriedades redox de ions cobre (II) oclusos em membrana de EVA foi desenvolvido para determinacao de acido L-ascorbico. A matriz de polietileno-co-vinil acetato (EVA 40% m/m) foi dopada com ions cobre (II) e dispersa na superficie de um eletrodo tubular de grafite/epoxi. O eletrodo mostrou resposta super-Nernstiana para acido L-ascorbico na faixa de concentracao entre 10-3 - 10-1 mol L-1 com um limite de deteccao de 8,5´10-4 mol L-1, quando 0,1 mol L-1 de tampao KH2PO4 misturado com 0,1 mol L-1 de peroxido de hidrogenio em pH 5,0 foi empregado como solucao carregadora. O sistema FIA-potenciometrico permite uma frequencia analitica de 120 amostras por hora com uma precisao de 3,6 %. Os resultados obtidos na determinacao de acido L-ascorbico em amostras farmaceuticas, sem qualquer tratamento previo, pelo metodo proposto foram similares a aqueles obtidos pelo metodo da Farmacopeia Britânica.

Use of self-plasticizing EVA membrane for potentiometric anion detection.

In this work, five different types of membranes were developed responsible to anion-selective electrodes. The membranes were based on tri-caprylyl-trimethyl-ammonium chloride (Aliquat-336S) supported on poly(ethylene-co-vinyl-acetate) copolymer (EVA). The sensors were prepared by solubilizing the copolymer with the appropriate exchanger in chloroform, without using of any plasticizers. The ion-selective electrodes prepared using these membranes show the utility for anions determinations in the concentration range between 10(-5) and 10(-1) mol l(-1) in the steady-state. The membrane performance was also evaluated in FIA system using tubular electrode for salicylate and iodide. In FIA system, the electrode exhibited nernstian response for salicylate in the concentration range of 2.5x10(-3) and 1.0x10(-1), while for iodide from 5.0x10(-4) up to 1.0x10(-1) mol l(-1). The systems were employed for the salicylate and iodide determination in pharmaceutical samples obtaining a relative deviation of 1.6%, when compared to the reference method.

Determination of acetylsalicylic acid in tablets with salicylate ion selective electrode in a Batch Injection Analysis system

The feasibility of the use of a Batch Injection Analysis (BIA) system for potentiometric determination of acetylsalicylic acid in tablets, with a membrane ion selective electrode, was investigated. There is no significant difference between the results obtained by the proposed method and those obtained by the Standard British Pharmacopaeia method12 at the 95% confidence level. Values of 4% and 2.5% for R.S.D. were obtained by the application of the BIA-potentiometric method and for the injections respectively. About 90 determinations per hour can be performed with the proposed BIA potentiometric method.