Method 370.1

Silica, Dissolved (Colorimetric)

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.

(EPA: Office of Water)


No Obligation Quotation for Analytical Services

If you would like us to provide a quote for laboratory analysis, just provide us with as much information as you can about your project (the more, the better) and we'll provide you a quote via email. As you are searching or browsing our Analytical Guide, you'll see the Request-A-Quote icon... just click on it to start the request process.

Method Data

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 List*

Analyte Formula CAS Number Detection Limit
Silica (SiO2)

* 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.