Tubidimetric Determination of Sulfur as Sulfate


  1. CONDITIONING SOLUTION - Dissolve 150 g NaCl in 600 mL deionized water. Add 60 mL conc. HCl, 100 mL glycerine, and 200 mL 96% isopropyl alcohol. Add glycerine first and mix well before adding isopropanol.
  2. 2 N NH4OAc - Dissolve 150 g ammonium acetate (NH4OAc) in 1 L deionized water.
  3. BaSO4 SEED SUSPENSION - (Prepare fresh daily.) - Dissolve 10 g BaCl2.2H20 in 50 mL hot demineralized water in a 250 mL Erlenmeyer flask. Add 1 mL of the 1000 ppm S standard. Swirl and heat to boiling. Cool rapidly under flowing water. Add 5 mL of conditioning solution.
  4. STANDARDS - Prepare a 1000 ppm Sulfur standard by dissolving 0.5435 g of oven-dried K2S04 in 100 mL 0.1 N HCl. Prepare working standards of 10, 20, 30, 40 ppm S. Prepare S stock solution fresh weekly and prepare working standards fresh daily.
  5. EDTA REAGENT - (Used for cleaning cell in spectrophotometer.) Dissolve 20.2 g ammonium chloride in 500 mL H20. Add 171 mL ammonium hydroxide and mix, then add 40 g of sodium (di)ethylene-diaminetetraacetate (EDTA) and dissolve. Dilute to 1 L with H20.

Equipment & Supplies



  1. Wet ash sample as previously described.
  2. Pipet 2 mL working standards and samples into clean test tubes.
  3. Add 10 mL of 2 N NH4OAc.
  4. Add 2 mL of conditioning solution.
  5. Mix on vortex mixer.
  6. Add 1.0 mL of seed suspension. (Swirl seed suspension frequently to insure uniform distribution of BaS04 crystals.)
  7. Mix each tube uniformly on the Vortex mixer. This step is important to insure uniform precipitation of BaS04.
  8. Wait 30 minutes and estimate turbidity using a visible spectrophotometer. See page 32 for set up of spectrophotometer and make the following changes. Set wavelength on 440 nm. 40 ppm S corresponds to 0.40% S in sample. Can read accurately to 60 ppm or 0.60% S in sample.) Mix each sample on Vortex mixer before reading.


  1. Butters, B., and E. M. Chenery. 1959. A Rapid Method for the Determination of Total Sulfur in Soils and Plants. Analyst 84:239-245.
  2. Massoumi, A., and A. H. Cornfield. 1963. A Rapid Method for Determining Sulfate in Water Extracts of Soils. Analyst 88:321-322.
  3. Standard methods for the examination of water and wastewater. 1960. 11th edition. p.241-243. Am. Public Health Assoc., Inc., New York.