The dissolved mineral forms of silica are found in all natural waters. Although silica is only slightly soluble in water and it can be found as ionic silica, silicates, and colloidal or suspended particles. The solubility of silica is highly dependent on pH, temperature, and pressure. Silica’s presence in industrial applications, particularly in high-pressure turbines, is undesirable because of scaling caused as silica precipitates out of solution at the elevated temperatures and pressures. Heating systems and reverse osmosis plants also require monitoring of silica to ensure process efficiency.
Silica can be measured photometrically with reagents. Photometric analysis is based on the Beer-Lambert principle of absorbance in which the intensity of the color produced is proportional to the concentration of silica in the sample. Photometric analysis products include handheld colorimeters, portable and benchtop photometers, and spectrophotometers. The low-range method uses an adaptation of the ASTM Method D859 (Heteropoly Molybdenum Blue Method) to measure silica concentrations below 2.00 mg/L (ppm). A high range meter uses an adaptation of the USEPA Method 370.1 and Standard Method 4500-SiO2 C to measure silica concentrations up to 200 mg/L (ppm).
Below are the most common products used for measurement of silica.
Spectrophotometers are available that have silica method in several ranges pre-programmed into the meter. The spectrophotometer offers the highest precision due to the quality of the optical system that has a wavelength accuracy of +/- 1.5 nm. The spectrophotometer allows for custom methods to be used as well.
Benchtop photometers include multiparameter versions for water and wastewater treatment, environmental, and water conditioning. These photometers can measure silica in multiple ranges. All benchtop have a digital pH electrode input allowing it to be used as a traditional pH meter.
Portable photometers are available to measure silica. The portable photometer has the CAL Check feature that allows for performance verification, and if needed, recalibration using the CAL Check standards. The meter is available as a meter only option or as a kit. The kit version include a rugged carrying case and CAL Check standards
Checker HC, like a chemical test kit, are reagent based design in which there is a color change based on concentration. The handheld colorimeters, like portable and benchtop instrumentation, use the Beer-Lambert principle to determine the color change. The change in color is not subjective as with using the naked eye.
Chemical Test Kits
A Chemical Test Kit (CTK) is available to measure silica. The CTK uses the Hanna Checker disk that offers up to 40 points of resolution using color disk. The color disk is continuous in changes of color and not discrete as with a color comparator with a limited number of points of resolution.
Replacement reagents for the photometers, Checker HC, and chemical test kits.
Solutions for silica measurement include the CAL Check standards for verifying and, if needed, the calibration of our portable photometers. Each CAL Check standard is supplied with a Certificate of Analysis stating the accuracy and traceability of the standard.
Accessories include the replacement cuvettes and caps for the photometers and Checker HC.