This method is for the determination of sulfite in drinking and surface waters, sewage and industrial wastes. The primary application has been to cooling, process and distribution water systems and boiler feedwaters to which sulfide is added in order to reduce dissolved oxygen and eliminate corrosion. An acidified aliquote of 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.
The minimum detectable limit is 2-3 mg/L sulfate.
The temperature must be below 50oC and minimize the contact of the sample with air.
Oxidizable substances such as organic compounds, ferrous iron, and sulfide are positive intereferences. Sulfide can be removed as a precipitate with 0.5 g of zinc acetate. Nitrite gives a negative inteference by oxidizing sulfite when the sample is acidified. Sulfamic acid can be used to remove nitrite. Copper and other metals may catalyze oxidation of sulfite. Add EDTA to complex the metals.
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| Hold Times, Preservatives, Preps, Collection, Analytical & Documentation | |
|---|---|
| Holding Time: | Analyze the sample immediately after collection per the method. |
| Preservatives: | The temperature of the sample must be below 50°C. |
| Required Preps: | 50 mL HDPE or amber glass bottle |
| Collection Method: | Grab sampling |
| Analytical Methodology: | Titrimetric |
| Documentation: | 
377.1
|
| Analyte | Formula | CAS Number | Detection Limit | |
|---|---|---|---|---|
| Sulfite | 14265-45-3 |
2 |
mg/L | |
* The analytes and detection limits listed for each method represent the typical detection limits and analytes reported for that particular method. Keep in mind that analyte lists may vary from laboratory to laboratory. Detection limits may also vary from lab to lab and are dependent upon the sample size, matrix, and any interferences that may be present in the sample.