RESUMEN
An instrumental analysis method for the determination of stable silicon isotope ratio using multi-collector inductively coupled plasma mass spectrometry ( MC-ICP-MS) was established. In dry plasma mode, silicon isotopes suffered from the spectrum polyatomic interferences of C, N, O, H at medium resolution. The sample gas flow had significant effect on the silicon sensitivity and signal stability. Besides, higher sample gas flow lead to higher production of 14N16O. Consistent δ29Si and δ30Si within 0. 04‰ (1σ) could be obtained over a mass range of ca. 9 milli-amu at the lower mass side of silicon at medium resolution. The analyte concentrations of the sample and reference material were matched within 20% to avoid concentration effect on the determination of silicon isotopes using standard-sample-bracketing correction method. The measurements were not sensitive to the acid molarity and Cl matrix. An internal precision of less than 8×10-6(1σ) could be achieved for 29 Si/ 28 Si and 30 Si/ 28 Si by taking an integration time of 8 seconds. The long-term reproducibility of 0 . 06‰-0 . 10‰ ( 2σ, n=20 ) was obtained for δ29 Si and δ30 Si by repeating the analysis of the silicon reference materials, whilst the determined isotopic value for GBW04421 and GBW04422 were in good agreement with the recommended data, suggesting the precision and robustness of this method. The measured silicon isotopic values of fresh waters ( river and lake waters ) , saline waters and seawater demonstrated the capability of applying this method to trace the biogeochemical processes of silicon in natural waters.