Determination of Soluble Silica in Water: A Photometric Method

Changes in Soil Properties Associated With the Removal of Iron and Aluminium Oxides

“…Fe was determined by the potassium thioc anate (1957) which depends on reaction with alizarin redT-S. Si was determined by the molybdate-sulphate method of Kahler (1941), after destruction of excess dithionite with H,O, where necessary. Physical analyses.…”

Material balance associated with phosphate sorption by amorphous clays, silica-alumina gel and synthetic goethite

“…Analytical methods. Phosphate was determined by the method of MuRPHY and RILEY (12), Na by flame photometry, Cl by the mercury (II) thiocyanate method (13), Si by the method described by KAHLER (14), and AI by the hematoxylin method (15). All calibrations were made in the solution containing the same amounts of salts with the samples.…”

In vitro dissolution behavior of hydrogenated amorphous silicon thin-film transistors

“…The silica concentration in aqueous solution (in the form of monomeric Si (OH) 4 ) is usually estimated by the colorimetric method, so-called soluble silica assay or ammonium molybdate assay, which uses the yellow color of the silicomolybdic acid that is formed when ammonium molybdate and hydrochloric acid are added. 28,29 When the concentration of soluble silica is high, it can be directly detected; whereas when the concentration of soluble silica is low, reducing agent need to be added to convert silicomolybdic acid to a dark blue or purple product. In the original protocol we used to detect silica concentration, five kinds of solutions were prepared: hydrochloric acid (0.25 M), ammonium molybdate (5% w/v), disodium ethylenediaminetetraacetic acid (EDTA) (1% w/v), sodium sulfite (17% w/v), and silica standard solution (0.05 mg/mL SiO 2 ).…”

“…This is unexpected, as this reduction of the silicomolybdate complex by sodium sulfite to molybdenum blue of composition Mo 3 O 8 •H 2 O in low acidity should not be accompanied by color from phosphomolybdates. 28,29 When the concentration of phosphate is higher than 1 ppm, the test result is not accurate and sensitive. 28,29 Subsequent work by Armstrong concerning detection of silicate in sea water indicated that the addition of sulfuric acid will make the excess molybdate convert rapidly into a form that cannot be reduced to a blue compound, and the addition of oxalic acid (or citric or tartaric acid) after acidification with sulfuric acid will fully suppress the formation of molybdenum blue from phosphate and eliminate this interference.…”

“…28,29 When the concentration of phosphate is higher than 1 ppm, the test result is not accurate and sensitive. 28,29 Subsequent work by Armstrong concerning detection of silicate in sea water indicated that the addition of sulfuric acid will make the excess molybdate convert rapidly into a form that cannot be reduced to a blue compound, and the addition of oxalic acid (or citric or tartaric acid) after acidification with sulfuric acid will fully suppress the formation of molybdenum blue from phosphate and eliminate this interference. 20 However, the addition of oxalic acid may sacrifice the sensitivity of this experiment.…”