Quantitative analysis of alkali silicate solutions by ICP AES

Abstract

SiO2 and Na2O concentrations of alkali silicate solutions can be determined by ICP AES using scandium as an internal standard. Diluting the samples with water causes problems with the sample nebulization. It is possible to avoid this by adding KOH , but a higher pH value leads to precipitation of scandium. Better results are obtained by treating the samples with HF to cause the reaction of SiO2 to H2SiF6. For calibration a standard glass of the DGG is used. A linear calibration function is obtained up to concentrations c(SiO2) = 215 mg/l and c(Na2O) = 45 mg/l, respectively, (in respect of glass: c(glass) = 300 mg/l). The agreement of SiO2 concentrations determined gravimetrically and those measured by ICP AES is better than ± 1 % relative. Na2O concentrations measured simultaneously deviate in most cases not more than ± 1 % relative from the classical HF digestion (with volatilization of SiO2). It is shown that the scandium standard leads to a better accuracy and reproducibility.