Spectrophotometric determination of acid volatile sulfide in river sediments by sequential injection analysis exploiting the methylene blue reaction

This paper demonstrates the application of sequential injection analysis to perform sulfide determination using the methylene blue chemistry, based on two reagents: 3.63 mmol l−1 N,N dimethyl-p-phenylene diamine hydrochloride in 1.1 mol l−1 HCl solution and 19 mmol l−1 FeCl3, also in 1.1 mol l−1 HCl. These solutions are aspirated inside the holding coil of the sequential injection system as two reagent zones sandwiching the sample zone. Under optimized conditions, the detection limit was calculated at 40 μg l−1 S2−, with a linear dynamic range from 0.05 to 2 mg l−1 S2−. This linear range can be extended up to 32 mg l−1 using in-line dilution for sulfide concentrations greater than 2 mg l−1. The robust characteristic of the SI system with syringe pump leads to very stable analytical curves (precision of 4%), minimizing the laborious preparation of sulfide standards. The method was applied in the determination of acid volatile sulfide in river sediments.