Determination of SiO_2 content in refined brine by molybdenum-blue spectrophotometry with increased sensitivity by dextrin

Ammonium molybdate reacts with silicic acid to form yellow soluable silico-molybdic heteropoly acid complex in H 2C 2O 4-HCl medium of pH 1.2～1.3.After adding 1-amino-2-naphthol-4-sucfonic acid,the complex was reduced to molybdenum-blue whose maximum absorption wave length is at 824.4 nm.Beers Law is obeyed when silica content is in the range of 0～1.0 mg/L,and the RSD and average recovery of samples are 0.11% and 99.93% respectively.Surface active agent can increase the sensitivity.Under the determination conditions,the linear equation is C=-0.043+1.76A when adding 4 mL 0.5wt% dextrin.This method is useful for determining primary and secondary refined brine for production of ion exchange membrane caustic soda with smaller error if content of SiO 2 less than 1 mg/L.