Determinação de sulfeto em água com preparo de amostra "in-line" por análise em fluxo multissegmentado

Abstract

The present dissertation describes an in-line flow analysis multissegmented system for determination of sulfide in water samples exploiting the Fisher reaction. Water samples were collected, preserved only with sodium hydroxide, and introduced into minireactor accomplished to FIA system. The sulfide released, after sample acidification, was carried out with nitrogen gas flow and mixed with N, N diethyl p-phenylene diamina (DEPD) solution in the presence of Fe (III). The blue dye formed was measured at wavelength range between 672-679 nm. The evaluation of the effect of chemical and flow factors was performed using fractional factorial design of two levels, while the optimization was accomplished by Doehlert matrix. The system presented two linear regions, the first range of response between 0.433 μg L-1 to 400 μg L-1 and the second of 400 μg L -1 to 3500 μg L-1. The limit of detection and quantification were found to be 0.130 μg L-1 and 0.433 μg L-1 respectively, while the sample throughput was 12 h-1. Precision was evaluated as the relative standard deviation (n = 10), for 50 μg L-1 and 100 μg L-1 sulfide were found to be 1.9 and 2.3% respectively. The method showed satisfactory selectivity as regard the main interferent present in environmental samples, such as Fe3+, Al3+, F-, Na+, SO42-, CO32-, Cd2+, Cu2+, Zn2+, Ag+. The accuracy of the method was successfully evaluated in environmental water samples after comparison with the reference method reported in the literature.