Determination of Sulfide in Water by Methylene Blue Spectrophotometry Combined with New Membrane Separation Pretreatment

Hydrophobic porous filter membrane was used for gas-liquid separation pretreatment for water samples. The optimized pretreatment conditions were follows: adding antioxidants to remove the oxygen introduced into the system, setting the heating temperature at 90 ℃ and heating time of 60 min, and 50% (volume fraction) phosphoric acid solution with a total amount of 20 mL (a single addition amount of 2 mL of acid). Sulfide in the obtained solution was determined by methylene blue spectrophotometry. As shown by the results, the linear range of the sulfide standard curve was 0.050-0.700 mg·L^-1, with detection limit of 0.003 mg·L^-1. This method was used for determination of certified reference materials, and the determined values were within the uncertainty range of the certified values, with relative error ranged from -1.9% to -1.6%. Test for recovery was made on the actual samples by the standard addition method, giving results in the range of 90.6%-95.0%, with RSDs (n=6) of the determined values in the range of 2.5%-4.6%.