This is acceptable when, as frequently occurs, the molybdate-reactive silica is in the milligram per litre concentration range while the nonmolybdate-reactive silica, if present at all, is in the microgram per litre concentration range.ġ.7 Former Test Method A (Gravimetric Total Silica) was discontinued. Note 1-For many natural waters, a measurement of molybdate-reactive silica by this test method provides a close approximation of total silica, and, in practice, the colorimetric method is frequently substituted for other more time-consuming techniques. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. No other units of measurement are included in this standard.ġ.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. Mesoporous silica is a relatively recent development in nanotechnology.

According to IUPACs terminology, mesoporosity sits between microporous (<2nm) and macroporous (>50nm).

For seawater or brines, this test method is applicable only if matched matrix standards or standard addition techniques are employed.ġ.5 The values stated in SI units are to be regarded as standard. Mesoporous silica is a form of silica that is characterised by its mesoporous structure, that is, having pores that range from 2nm to 50nm in diameter. It may be applied to natural waters and wastewaters following filtration or dilution, or both. It is particularly applicable to treated industrial waters. Those forms of silica that are molybdate-reactive include dissolved simple silicates, monomeric silica and silicic acid, and an undetermined fraction of polymeric silica.ġ.4 The useful range of this test method is from 20 to 1000 μg/L at the higher wavelength (815 nm) and 0.1 to 5 mg/L at the lower wavelength (640 nm). Due to the complexity of silica chemistry, the form of silica measured is defined by the analytical method as molybdate-reactive silica.

This test method is useful for concentrations as low as 20 μg/L.ġ.3 This test method covers the photometric determination of molybdate-reactive silica in water. It is applicable to most waters, but some waters may require filtration and dilution to remove interferences from color and turbidity. This method covers the determination of the silica element in the interval from 20 to 1000 g/l on 50 ml. Historical ASTM D859-10 Standard Test Method for Silica in Waterġ.1 This test method covers the determination of silica in water and waste water however, the analyst should recognize that the precision and accuracy statements for reagent water solutions may not apply to waters of different matrices.ġ.2 This test method is a colorimetric method that determines molybdate-reactive silica. en The spectrophotometric method for the determination of the silica element in water, demineralized water, raw waters, laundry waters, waters treated with ion exchange resins and sea waters is described.

Silica in water