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OCR for page 49
49 NAS/CWTC 0 23 -8 2 Name: SODIUM METABISULFITE, SODIUM PYROSULFATE CAS No 7631-90-5 Chemical Formula: Na2S2O5 Description: Formula Weight: 174.1 White to slight yellow crystals with a sulfurous odor. When in solution, sodium metabisulfite is formed. It has a Volubility in water of 54 g/100 ml at 20C and is avail- able at a commercial strength of 97.5-99.0% sodium meta- bisulfite. Use: Used to remove chlorine and other oxidants Purity Requirements: . The RMIC values are based on a maximum dosage of 15 mg of sodium metabisulfite/liter of water and are to be com- pared to impurity concentrations obtained by using sample procedures described in this monograph. If the actual dosage is other than 15 mg/liter, the user is cautioned to consult Table 2 for appropriate RMIC values. Impurity Arsenic Selenium Bulk Sample Collection: RMIC mg Impurity/kg Sodium Metabisulfite 300 70 Sample in accordance with Standard for Sodium Meta- bisulfite, AWWA B601-77, American Water Works Association, Denver, Colorado (1977).

OCR for page 49
50 Analytical Sample Preparation: Weigh out 2.5 g of sodium metabisulfite. In a 150-ml acid-washed beaker, dissolve the sample in 100 ml of deionized distilled water. Under a hood, acidify the solution with concentrated HNO3 to a pH of less than 2. Gently heat the solution to reduce the volume below 100 ml, making certain that it does not boil. Quantita- tively transfer to a 100-ml acid-washed volumetric flask and make to volume with deionized distilled water. Process a reagent blank by the same procedure. Sample Analyses: The analyses are to be performed on the sodium meta- bisulfite sample in accordance with: Standard Methods for the Examination of Water and Waste- water, 15th Edition, American Public Health Association, Washington, D.C. (1981). Arsenic Section 304 Selenium Section 304