Separation and purification of silicon

Both samples and silicon isotope standard materials (including the bracketing standard) were purified using single column chemistry. The poly-prep 10 mL column (BioRad, USA) is filled with 1.5 mL DOWEX AG 50W-X8 (200–400 mesh) cation exchange resin. The resin was regenerated before each sample loading by sequential washing with 3 mL 3 M HCl, 3 mL 6 M HCl, 3 mL 7 M HNO₃, 3 mL10M HCl, 3 mL 6 M HCl, 3 mL 3 M HCl and Milli-Q water washing to neutral pH. At low pH (pH < 8), dissolved Si in the form of non-ionic monosilicic acid Si(OH)₄ or the anionic species H₃SiO₄⁻ that is not retained by the resin. For each sample, an aliquot of solution containing about 60 μg Si was loaded onto a column. Samples were eluted in about 10 mL of Milli-Q water and, after purification, were diluted with Milli-Q water to 15 mL, which contains about 4 ppm Si for silicon isotope analysis. The typical overall column recovery of Si was greater than 95%.