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Um novo método para determinação de metronidazol, baseado no monitoramento espectrométrico do sal de diazônio produzido in-line pelos íons nitrito, liberados numa hidrólise alcalina, foi desenvolvido e aplicado com sucesso a comprimidos (r = 0,9993, 2,0-20,0 mg L -1 , LD = 0,7 mg L -1 ), sem interferência de ingredientes comumente presentes.A new method for metronidazole determination, based on spectrometric monitoring of a diazonium salt produced in-line by alkaline hydrolysis released nitrite ions, was developed and successfully applied to pharmaceutical tablets (r = 0.9993, 2.0-20.0 mg L -1 , DL = 0.7 mg L -1 ) with no interference from common ingredients accompanying the drug. Keywords: flow injection analysis, spectrophotometry, pharmaceuticals, metronidazole, nitrite IntroductionMetronidazole (MTZ), 2-(5-nitro-2-methylimidazol-1-yl)-ethanol, likewise others nitroimidazole derivatives presents biological activity against anaerobic micro-organisms, being largely used as the active ingredient of antihelminthic medicines. 1 Thus, there is an important demand for rapid and simple methods for the determination of MTZ in pharmaceutical preparations. Methods based on HPLC and classical volumetric titration are recommended by the pharmacopoeia for the direct determination of MTZ. 2 Although this later one is kind of simple, being daily practiced in many routine analysis laboratories, it is time consuming and very tedious as it is based on the use of acetic anhydride. Various research studies have been devoted to the development of new high performance alternative methods for determination of the drug in dosage forms using different techniques such as high performance liquid chromatography, 3 supercritical fluid chromatography, 4 differential pulse polarography 5 and voltammetry with glassy carbon electrode 6 or chemically modified electrodes. 7 Flow analysis approaches have also being successfully applied on developing fast analytical methods for determination of some antihelmintic and antiprotozoal with spectrometric 8-10 and biamperometric detection in dosage forms. 11 The alkaline hydrolysis of MTZ releases the nitro group as nitrite ion and the reaction can be carried out in a quantitative way by controlling the pH, temperature and hydrolysis time. Thus, a simple measurement of the yielded nitrite ions can be used to determine MTZ. This approach has been taken advantage of to implement MTZ analytical procedures. [12][13][14] An assay based on measurement of the change in ultraviolet absorbance during the alkaline hydrolysis of the compound was proposed for determination of MTZ in oral suspensions. 12 Another one, based on colorimetric monitoring of the diazonium salt produced by a diazotizationcoupling reaction with the released nitrite ions, has long been proposed and optimized later on. 13,14 Despite the good selectivity and sensitivity of these procedures, they are time consuming and employ large amounts of reagents.This work describes a flow injection analysis (FIA) approach for determination of MTZ based o...

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A agência brasileira que regulamenta a produção e comercialização de álcool combustível estabelece que a concentração de sódio deve ser determinada usando a fotometria de chama e curva analítica construída com soluções padrão preparadas em uma matriz que se assemelhe às amostras. Todavia, essa metodologia pode produzir resultados inexatos porque o álcool combustível apresenta uma variabilidade significativa na composição de matriz e, conseqüentemente, no efeito de matriz. Esse problema pode ser contornado usando o método por adições de padrão (MAP), porém o MAP é lento e trabalhoso quando realizado manualmente. Para superar esses inconvenientes, um sistema Flow-Batch é proposto para automatizar o MAP visando à determinação de sódio em álcool combustível por fotometria de chama. O sistema requer uma única solução padrão, processa cerca de 80 -140 amostras por hora, consome um volume total de amostra e solução padrão menor que 1,5 mL por análise e apresenta um desvio padrão usualmente menor que 0,1 mg L -1 (n = 4).The Brazilian Regulatory Agency for fuel production and commercialization requires that the sodium concentration in alcohol fuel should be determined by flame photometry and that the analytical curves should be obtained with matrix-matched standards. Notwithstanding, this methodology can produce inexact results because alcohol fuel presents a significant variability in matrix composition and, consequently, in the matrix effect. This problem can be circumvented by using the standard addition method (SAM). However, this method is slow and laborious when it carried out by manual procedures. To overcome these drawbacks, an automatic flow-batch SAM for sodium determination in alcohol fuel by flame photometry is described. This system requires only one standard solution, handles about 80 -140 samples per hour and consumes a total volume of sample and of standard solution smaller than 1.5 mL for each analysis. The results present a standard deviation usually less than 0.1 mg L -1 (n = 4).Keywords: standard-addition method, flow-batch system, sodium determination, alcohol fuel, flame photometry IntroductionThe Brazilian Regulatory Agency for fuel production and commercialization, the National Agency for Petroleum Products (ANP), requires 1 that sodium concentration in alcohol fuel samples should not be higher 2 mg kg -1 and that sodium should be determined by using the methodology (NBR 10422) 2 described by the Brazilian Normative Agency (Associação Brasileira de Normas Técnicas, ABNT).The ABNT methodology for sodium determination in alcohol fuel uses flame photometry and an analytical curve with matrix-matched standards (ACMMS). 3 Since the composition or matrix effect of actual alcohol fuel samples varies significantly, this methodology can produce inexact results. 3,4 To overcome this problem, the standard-addition method (SAM) 5 should be used to accurately analyse each sample.One of the ways to implement SAM 5 is to add increasing amounts of analyte to identical aliquots of the sample; these mixtures are th...

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