This paper describes a procedure based on multicommutation in flow analysis system for photometric determination of hydroquinone in pharmaceutical gel formulations. The procedure involves oxidation of hydroquinone by Fe (III) and subsequent reaction between the generated Fe (II) species with 1,10-phenanthroline, producing a complex detected at 510 nm. Under optimized conditions, the proposed system showed a linear response in the range between 5 to 120 µmol L-1 (r = 0.9995), a limit of detection (3σ) 0.52 µmol L-1 and a relative standard deviation (RSD) of 1.5% for a 80 µmol L-1 hydroquinone standard solution. Others profitable features such as an analytical frequency of 72 samples per hour; a reagent consumption of 0.432 and 0.117 mg 1-10-phenantroline and FeCl3.6H2O per determination, respectively; and a waste generation of 4.0 ml per determination were also achieved.

Um novo método espectrofotométrico simples, sensível e com boa seletividade é apresentado para a determinação rápida de mercúrio (II) em nível de traços com 2-mercapto-5-metilbenzilimidazol (MMBI) como um novo reagente espectrofotométrico (lambda max = 320 nm), em um meio aquoso ligeiramente alcalino (tampão Britton-Robinson (BR) 0,04 M, pH 8,0). A reação é instantânea e a absorbância permanece estável por mais de 24 horas. O coeficiente de absorção molar encontrado foi de 2,71 x 10(4) L mol-1 cm-1. A composição estequiométrica do complexo é de 1:1 (Hg:MMBI). Considerável excesso dos íons cobre, zinco, chumbo e cádmio não interfere na determinação. O método desenvolvido permitiu a determinação de mercúrio na faixa de 2 x 10-6 a 4 x 10-5 mol.L-1 com boa precisão e exatidão, e o limite de detecção para Hg foi de 9,9 x 10-7 mol.L-1. O método foi aplicado com sucesso a amostras de peixe e os resultados foram avaliados com o clássico método de espectrometria de absorção atômica (EAA). Os desvios padrão relativos para as amostras analisadas foram de 7,2 e 33% (n = 5), enquanto os erros foram de 1,63 e 11,6. O método mostrou-se sensível, seletivo e foi aplicado para a determinação de mercúrio em amostras de peixe com resultados satisfatórios.

A simple, sensitive and selective spectrophotmetric method is presented for the rapid determination of mercury (II) at trace levels using 2-mercapto-5-methylbenzimidazole (MMBI) as a new spectrophotometric reagent (lambdamax = 320 nm) in a slightly basic (0.04 M Britton-Robinson (BR) buffer, pH 8.0) aqueous solution. The reaction is instantaneous and the absorbance remains stable for over 24 hours. The average molar absorption coefficient was found to be 2.71 x 10(4) L mol-1 cm-1. The stoichiometric composition of the chelate is 1:1 (Hg:MMBI). Considerable excesses of copper, zinc, lead and cadmium do not interfere in the determination. The method developed allowed the determination of mercury in the range of 2 x 10-6 to 4 x 10-5 mol.L-1 with good precision, accuracy and the detection limit was 9.9 x 10-7 mol.L-1 of Hg. The method was successfully applied to fish samples and the results were evaluated and compared with classic atomic absorption spectrometry (AAS). The relative standard deviations for the samples analyzed were between 7.2 and 33% (n = 5), while the errors were between 1.63 and 11.6. The method was found to be sensitive, selective and was used for the determination of mercury in fish with satisfactory results.