Spectrophotometric Determination of Trace Silica in Water After Enrichment on Polyurethane Foam and Complexation with Rhodamine B

Abstract

A highly sensitive spectrophotometric method has been developed for the rapid determination of nanogram
amounts of silica in pure water. The method involves the formation of yellow molybdosilicate in nitric acid
medium, its extraction on polyether based polyurethane foam, elution in acetone, formation of ion associate
between molybdosilicate and Rhodamine B (RB) in nitric acid and finally measurement of absorbance at 596
nm. The detection limit was found to be 0.05 ng mL-1 Si. The method obeys Beer’s law over the concentration
range 0.1 – 5 ng mL-1
. The molar absorptivity was found to be 1.4043 x 106 L mol-1 cm-1
. The proposed method
was successfully applied for the determination of silica in highly purified water samples.