2004 Volume 53 Issue 12 Pages 1481-1486
Ion-exclusion chromatography with an ion-exchange enhancement of conductivity was developed for the selective and sensitive determination of silicate ion. The separation of silicate ion from anions of strong acids was achieved by the ion-exclusion effect on a separation column packed with a weakly acidic cation-exchange resin in the H+-form by elution with water. Two different ion-exchange resin columns were inserted between the separation column and the conductivity detector in order to improve the sensitivity of silicate ion. The first enhancement column, a strongly acidic cation-exchange resin in the K+-form, could be converted from silicic acid to potassium silicate. Subsequently, the second enhancement column, a strongly basic anion-exchange resin in the OH−-form, could be converted to potassium hydroxide having high conductivity response. The detection sensitivity of silicate ion using two conductivity enhancement columns could be ca. 20 times greater than that using the separation column alone at an eluent flow rate of 1 ml/min. The detection limit (S/N = 3) was 0.02 ppm as H3SiO4− at 0.5 ml/min. The calibration graph was linear in the range of 0.05∼50 ppm. This method could be successfully applied to the determination of the silicate ion in several sea and river water samples.
