Analytical Sciences

Direct Introduction of Water Sample in Multisegmented Flow-Injection Analysis for Sulfide Determination

Giovana F. LIMA,* Ariadne M. BRONDI,* Ana L. S. F. PAIVA,* César R. T. TARLEY,** André F. de OLIVEIRA,*** Célio WISNIEWSKI,* and Pedro O. LUCCAS*

*Universidade Federal de Alfenas, Instituto de Ciências Exatas, R. Gabriel Monteiro da Silva, 714, 37130-000 Alfenas, MG, Brazil
**Universidade Estadual de Londrina, Depto de Química, Rod. Celso Garcia Km 380, 86051-990 Londrina, PR, Brazil
***Universidade Federal de Viçosa, Depto de Química, Av. Peter Henry Rolfs, 36570-000 Viçosa, MG, Brazil

The present paper describes an inline flow-injection analysis system for the determination of sulfide in water samples, exploiting the Fischer reaction. Water samples were collected and introduced into a reactor of the FIA system. The sulfide released, after sample acidification, was carried out with a nitrogen gas flow and mixed with N,N diethyl-p-phenylenediamine (DEPD) solution in the presence of Fe(III). The blue dye formed was measured in the wavelength range between 672 – 679 nm. An evaluation of the effects of chemical and flow factors was performed using the factorial design of two levels, while optimization was accomplished by a Doehlert matrix. The system presented two linear-response ranges: the first of 0.433 to 400 μg L⁻¹ and the second of 400 to 3500 μg L⁻¹. The detection and quantification limit were found to be 0.130 and 0.433 μg L⁻¹, respectively, while the sample throughput was 12 h⁻¹. The precision was evaluated as the relative standard deviation (n = 10); for 50 and 100 μg L⁻¹ sulfide it was found to be 1.9 and 2.3%, respectively. The method showed satisfactory selectivity regarding the main interference present in environmental samples. The accuracy of the method was successfully evaluated in environmental water samples after a comparison with a literature reference method.

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