This method is for the determination of dissolved silica in drinking, surface and saline waters, domestic and industrial wastes. A well-mixed sample is filtered through a 0.45 µ membrane filter and the filtrate, upon the addition of molybdate ion in acidic solution, forms a greenish-yellow color complex proportional to the dissolved silica in the sample. The color complex is then measured spectrophotometrically. In the low concentration modification the yellow (410 nm) molybdosilicic acid color is reduced by 1-amino-2-naphthol-4-sulfonic acid to a more intense heteropoly blue (815 nm or 650 nm).
The working range of the method is approximately 2 to 25 mg silica/L. The upper range can be extended by taking suitable aliquots; the lower range can be extended by the addition of amino-naphthol-sulfonic acid solution.
Tannin and phosphate interferences can be reduced or eliminated with oxalic acid. Iron and sulfide will interfere with the analysis.
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| Hold Times, Preservatives, Preps, Collection, Analytical & Documentation | |
|---|---|
| Holding Time: | 28 days from sample collection to analysis. |
| Preservatives: | None noted in method. |
| Required Preps: | 100 mL HDPE bottle |
| Collection Method: | Grab sampling |
| Analytical Methodology: | Spectrophotometer or filter photometer |
| Documentation: | 
370.1
|
| Analyte | Formula | CAS Number | Detection Limit | |
|---|---|---|---|---|
| Silica (SiO2) | SiO2 |
7631-86-9 |
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.