Continuous Fractional Extraction Method Using Sodium Sulfide Solution for Spectrophotometric Determination of Inorganic Phosphorus in Lake Bottom Sediments

We have developed a novel continuous fractional extraction method for the determination of inorganic phosphorus (Fe-P, Al-P, and Ca-P) in bottom sediments. This method uses a sodium sulfide (Na2S) solution as the extracting solvent for Fe-P from wet sediment. The Na2S solution reacted with Fe-P to form as a FeS precipitate and a soluble phosphate. The mixture was filtered and the phosphate concentration in the filtrate was determined by the molybdenum blue method. Initially, excess hydrogen sulfide inhibited any color development of molybdenum blue. We removed hydrogen sulfide by adding a mixed diamine solution to form methylene blue. The resulting colored solution was passed through a Sep-Pak C18 cartridge to remove the methylene blue. The hydrogen sulfide-free effluent was used for the determination of phosphate. Sodium hydroxide (1 mol L−1) and hydrochloric acid (1 mol L−1) was used as extracting solvents for Al-P and Ca-P, respectively. The proposed method was successfully applied to bottom sediments from brackish water areas.