NEMI Method Summary

Method Summary Information

Method Number: 377.1 Media: WATER
Revision: Issued 1974; Editorial Revision 1978
Method Source: U.S. EPA National Exposure Research Laboratory (NERL) [formerly EMSL]
Analytes in this method
Subcategory: INORGANIC
Official Name: Sulfite (Titrimetric)
Descriptive Name Sulfite by Titrimetry
Source Info: U.S.EPA National Exposure Research Laboratory (NERL)
Microbiological and Chemical Exposure Assessment Research Division (MCEARD)
[formerly the Environmental Monitoring Systems Laboratory (EMSL), Cincinnati, OH]
26 West Martin Luther King Drive
Cincinnati, Ohio 45268-0001
Fax: 513-569-7757
email: DWmethods.help@epa.gov
Citation: Methods for the Chemical Analysis of Water and Wastes (MCAWW) (EPA/600/4-79/020)
29590 Byte file
Brief Method
Summary:
 An acidified sample containing a starch indicator is titrated with a standard potassium iodide-iodate titrant to a faint permanent blue end point which appears when the reducing power of the sample has been completely exhausted.
Scope And
Application:
 This method determines sulfite in drinking and surface waters, sewage and industrial wastes. The primary application has been to cooling, process, and distribution waster systems and boiler feedwaters to which sulfide is added to reduce dissolved oxygen and eliminate corrosion.
Applicable
Conc Range:
 The minimum detectable level is 2-3 mg/L sulfite.
Interferences: (A) Temperature: The temperature must be below 50oC.
Air: Minimize contact of sample with air. For example do not filter sample, and keep the tip of the buret below the sample surface.
(C) Oxidizable substances such as organic compounds, ferrous iron, and sulfide are positive interferences. Sulfide can be removed (precipitated) with 0.5 g of zinc acetate.
(D) Nitrite: Nitrite gives a negative interference by oxidizing sulfite when the sample is acidified. Sulfamic acid can be used to remove nitrite.
(E) Metals: Copper and other metals may catalyze oxidation of sulfite. Add EDTA to complex the metals.
(F) Reagents: Run blanks to correct for interferences from reagents.
QC Requirements: None.
Sample Handling: Minimize contact of sample with air while sampling and cool the sample if it is above 50oC. Also add EDTA solution to the sample.
Max Holding Time:
 Analyze immediately (MCAWW, Table 1).
Sample Prep Met None.
Relative Cost: Less than $50
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