Spectrophotometric Determination of Silicate in Water with Molybdate and Malachite Green

On the basis of the coloration formed with molybdosilicate and Malachite Green in aqueous solution, trace amounts of silicate were determined. In an acidic medium, silicate reacted with molybdate to form molybdosilicate, which reacted with Malachite Green to form a colored ion association complex. The color was stabilized by adding poly(vinyl alcohol). The molar absorptivity was 1.0×10(5)mol(-1)cm(-1) at 595nm, and the absorbance of the reagent blank was 0.089. The recommended concentration range of silicon was 0.1-5μg and the limit of detection was 0.01μg of silicon. Silicate in river and tap waters was determined.