Sulfite
Sulfite
Page 116
50081_Sulfite_Back.fm
Oxidant Volume Adjustment
Deviations can occur in the sulfite method due to loss of iodine through the iodine
demand of the sample. Minimizing the total amount of free iodine to be titrated in the
solution can reduce this phenomenon.
By increasing the oxidant volume to slightly more than is needed to react with the sulfite,
the amount of free titratable iodine will be minimized. Data acquisition will be optimized
and error due to iodine loss will be minimized.
Method Performance
Safety
Use good safety practices and laboratory techniques throughout the procedure. Consult the
Material Safety Data Sheet (MSDS) for specific reagent(s) information.
Table 1 Recommended Iodine Spike Volume for Sulfite
Estimated Sulfite Conc. (mg/L as SO
3
) Volume of 0.0282 N Iodine (mL)
0–5 1.00
5–10 2.00
10–15 3.00
15–20 4.00
20–25 5.00
Table 2 Precision
At Concentration 95% Confidence Limits
19.05 mg/L 18.77 mg/L–19.33 mg/L
Table 3 Accuracy Assessments
Sample Spike Addition (mg/L) % Recovery*
Deionized Water
18.75 103.77
12.50 104.31
6.25 101.93
Wastewater
Effluent
(Source #1)
18.75 102.05
12.50 100.95
6.25 100.56
Wastewater Effluent
(Source #2)
18.75 103.42
12.50 102.63
6.25 106.46
* Percent recovery does not reflect correction for sample iodine demand.
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