A smart multisyringe flow injection system for analysis of sample batches with high variability in sulfide concentration.

A fully automated smart multisyringe flow injection analysis (MSFIA) system for the monitoring of sulfide in a wide concentration range is proposed. It allows the determination of sulfide in samples containing suspended solids without requiring any preliminary batch sample treatment. The smart system is able to choose by itself the best approach to quantify the analyte, selecting either a spectrophotometric or a reflectometric detection. The method, carried out in a multi-commuted system, is based on the analyte release as hydrogen sulfide from the donor channel of the gas-diffusion module into an alkaline acceptor channel solution, which is merged with N,N-dimethyl-p-phenylenediamine (DMPD) and Fe(III). The in-line generated methylene blue (MB) dye can be delivered to an optical fiber diffuse reflectance sensor or to a flow-cell spectrophotometer according to the analyte concentration. The detection limit (3s(b)/S) was 4.6 microg l(-1). Two linear calibration graphs between 50-1000 and 500-10000 microg l(-1) sulfide for reflectometry and spectrophotometry, respectively, were obtained. The potentialities of this method were assessed via the determination of sulfide at a wide range of concentrations (4.6 microg l(-1) to 100 mg l(-1)). The high selectivity and sensitivity, the low reagent consumption and the miniaturization of the proposed automated method should be highlighted.