Silica LR

Test Method Technical Information


Tests For: Silica in Natural, Treated and Industrial Water
Tests Range: 0–4.0 mg/L
Reagent Chemistry Used: Ammonium molybdate
Basis of Test Method: Standard Method 4500-SiO2-C, US EPA Ref. 370.1
Method Detection Limit*: 0.02 mg/L
Limit of Quantification**: 0.06 mg/L

*The Method Detection Limit (MDL) is defined as the minimum measured concentration of a substance that can be reported with 99% confidence to be different from the method blank results.
**The Limit of Quantification (LOQ) is the smallest quantity that can be detected with reasonable certainty for a given analytical procedure.

Testing for Silica HR

Silicon, in the form of silica, is one of the earth’s most abundant elements. Silicon is found widely in natural waters as colloidal silica or soluble silicates.
Silica and silicates do not normally cause any problems in water intended for domestic consumption. However, their presence is undesirable in water used in a variety of industrial applications. This is because of the tendency of such water to form a hard scale on equipment. Silica and silicate containing waters are particularly troublesome in steam generating plant such as high-pressure boilers since silica scale can build up on turbine blades.

The Palintest Silica LR test provides a simple means of measuring silica and silicate levels in natural, treated, and industrial waters over the range 0–4 mg/L SiO2.

Reagent Chemistry

Ammonium molybdate reacts with silica under acidic conditions to produce molybdosilicic acid. In the presence of a reducing agent, this compound is reduced to form an intense blue complex. Phosphate reacts in a similar manner.

The reagents for the method are provided in tablet form and the test is carried out simply by adding tablets to a sample of water. The intensity of the colour produced in the test is proportional to the silica concentration and is measured using a Palintest Photometer.


Interference by phosphate is prevented by introducing a reagent (Silica PR tablet) which destroys any molybdophosphoric acid which may form.

EPA, Definition and Procedure for the Determination of the Method Detection Limit, Revision 2, Dec 2016.
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the “Gold Book”).