Visual Kits

Range	MDL	Method	Kit Catalog No.	Refill Catalog No.
0-0.20 ppm	0.02 ppm	Heteropoly Blue	K-9011	R-9011
0-1 & 1-10 ppm	0.05 ppm	Heteropoly Blue	K-9010	R-9010

Instrumental Kits

Range	Method	Kit Catalog No.
V-2000: 0.50-10.00 ppm / Spec: 0.25-4.00 ppm	Heteropoly Blue	K-9003

Method

References: APHA Standard Methods, 21^st ed., Method 4500-SiO₂ D (2005). ASTM D 859-05, Silica in Water. USEPA Methods for Chemical Analysis of Water and Wastes, Method 370.1 (1983).

Silica (SiO₂) is the oxide of silicon, the second most abundant element in the earth's crust. Silica is present as silicates in most natural waters. Typical concentrations lie between 1 and 30 mg/L. Higher concentrations may exist in brackish waters and brines. The silica content of water should be determined prior to its use in a variety of industrial applications. Silica can form a harmful scale on equipment and heat transfer surfaces, particularly steam turbine blades.

CHEMetrics' test method determines molybdate reactive silica. The heteropoly blue chemistry is employed. Silica reacts with ammonium molybdate under acidic conditions to produce heteropoly acids, which are then reduced to form a blue color. Phosphate interferences are masked with the addition of citric acid. Results are expressed as ppm (mg/L) SiO₂.