Tubidimetric Determination of Sulfur as Sulfate
- 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 N NH4OAc - Dissolve 150 g ammonium acetate (NH4OAc) in 1 L deionized water.
- 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.
- 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.
- 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
- TEST TUBES
- VORTEX MIXER
- Wet ash sample as previously described.
- Pipet 2 mL working standards and samples into clean test tubes.
- Add 10 mL of 2 N NH4OAc.
- Add 2 mL of conditioning solution.
- Mix on vortex mixer.
- Add 1.0 mL of seed suspension. (Swirl seed suspension frequently to insure uniform distribution of BaS04 crystals.)
- Mix each tube uniformly on the Vortex mixer. This step is important to insure uniform precipitation of BaS04.
- 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.
- Butters, B., and E. M. Chenery. 1959. A Rapid Method for the Determination of Total Sulfur in Soils and Plants. Analyst 84:239-245.
- Massoumi, A., and A. H. Cornfield. 1963. A Rapid Method for Determining Sulfate in Water Extracts of Soils. Analyst 88:321-322.
- Standard methods for the examination of water and wastewater. 1960. 11th edition. p.241-243. Am. Public Health Assoc., Inc., New York.