Application of sequential injection-monosegmented flow analysis (SI-MSFA) to spectrophotometric determination of...

This paper describes the coupling of sequential injection with monosegmented flow analysis (SI-MSFA) for determination of sulfide at typical concentrations in wastewaters. The method was based on the reaction of sulfide with 19 mmol l(-1) Fe(3+) and 3.63 mmol l(-1)N,N-dimethyl-p-phenylene diamine hydrochloride in medium of 1.1 mol l(-1) HCl, forming the dye methylene blue. The analytical curves were constructed by in-line dilution of a single stock standard solution. The robustness of the proposed method was checked constructing analytical curves in different working days and comparing the slopes, which had a relative standard deviation of 5.2% (n=5) for a concentration range between 0.17 and 1.0 mg l(-1) S(2-). The analytical throughput was 38 samples per h and the limit of detection was 0.040 mg l(-1). The feasibility of the SI-MSFA approach to perform standard additions for S(2-) determination was also described. Simulated samples spiked with known amounts of sulfide were analyzed by the proposed method, presenting recoveries between 70 and 115%. These results demonstrate the feasibility of the SI-MSFA method to perform in situ analysis of S(2-) in automatic monitoring stations.