Sequential injection analysis (SIA) for determination of sulfide ion using visible spectrophotometric detection

Measurement of sulfide concentrations contained in industrial wastewater is very important for the preservation of the natural aquatic environment. This research has the main objective to develop a method of measuring sulfide ion content by injection analysis with sequential injection analysis based on visible light spectrophotometry detection for monitoring the sulfide content in tofu liquid waste. This homemade SI system consists of a 6-port selector valve, a syringe pump (SP), a visible spectrophotometer detector, a webcam camera, and a holding coil. This system is managed and run by a computer using LabView 8TM software. The detection was based on the reaction of sulfide with two reagents, N.N dimethyl-1,4-phenylenediammoniumdichloride and FeCl3 in the medium of HCl 1,2 M, forming the dye methylene blue. The absorbance was recorded at 664 nm. Under the optimized condition consisting of the order of sample and reagent injection, the stopped-time in holding coil, and the volume of reagents, an analytical curve was constructed for a concentration range between 0.25-2.0 mg/L sulfide. This result in the linear range with a correlation coefficient of 0.996, sensitivity of 0.377 absorbance/ppm, and detection limit of 0.0056 ppm. The proposed method has been successfully tested and used in the determination of sulfide in tofu liquid waste samples with good results.