Direct determination of Si isotope ratios in natural waters and commercial Si standards by ion exclusion chromatography multi-collector inductively coupled plasma mass spectrometry

Silicon isotope ratios in natural waters and several commercial Si standards were determined by on-line ion exclusion chromatography (IEC) multicollector inductively couple plasma mass spectrometry (MC-ICPMS). As recent studies have shown that mass-independent fractionation (MIF) also exists in MC-ICPMS itself, e.g., Nd, Ce, W, Sr, Ge, Hg and Pb isotopes, the nature of mass bias for Si isotopes was thus investigated. MIF was observed for Si isotopes on both Neptune and Neptune plus MC-ICPMS instruments in this study. Therefore, a standard-sample-standard bracketing (SSB) mass bias correction model which is capable of correcting both mass-dependent and mass-independent bias was employed to obtain accurate Si isotope ratio results in all samples by using NBS28 Si standard as the bracketing standard. Medium resolution was used for all measurements in order to resolve polyatomic interferences on Si isotopes. NBS28 Si standard solutions prepared in nutrient-free seawater and 0.1% NaOH matrix, respectively, were used for the method validation and subjected to the on-line IEC-MC-ICPMS determination ofSi isotope ratios. Values of -0.01\ub10.06 and 0.00\ub10.06 %o (lSD, n=IO); and -0.01\ub10.03 and 0.01\ub10.06 %o (lSD, n=IO) for J29128 Si and J30128 Si, respectively, were obtained, confirming accurate results can be obtained using the proposed method for natural waters.Peer reviewed: YesNRC publication: Ye