Optimizing the Sensitivity of Particulate Silica Quantification by Molybdenum Blue Absorbance Spectrometry

Abstract

The optimum initial pH (before addition of molybdate) for the dissolution of silica to form HPA is approx. pH 10. This may be due to the balance between enhanced silica solubility at high pH and the optimal (low) pH of the reaction to form HPA. As the acidic molybdate solution is added to the basic silica suspension to initiate the reaction, the initial solution pH quickly falls to approx. pH 1-2 for the formation of heteropoly blue. The objective of this research is to optimize analytical sensitivity for various types of silica.