『Abstract
　A new method for the in situ measurement of stable Si isotope ratio using UV-femtosecond laser ablation connected to a multiple-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) has been established. The use of medium mass resolution mode (with a resolving power m/Δm = 8000) permits to resolve spectral interferences on ²⁸Si, ²⁹Si and ³⁰Si allowing for determination of the ²⁹Si/²⁸Si and ³⁰Si/²⁸Si ratios with high accuracy and precision on wide, interference-free plateaus. A three-isotope plot demonstrated that interferences, if existing, are negligible for Si isotope ratios. The laser spot size is 35μm and measurements are made using square rasters of 150μm side length. Different types of elemental Si, Si-oxide and silicate matrices have been analysed by laser ablation using the international standard NBS28 as the bracketing standard. Thus δ²⁹Si and δ³⁰Si have been determined for the silicon isotope standard IRMM-017 (δ³⁰Si±2 S.D.=-1.26±0.24‰; n=89) and Big Batch (δ³⁰Si=-10.55±0.42‰; n=15), as well as San Carlos Olivine (δ³⁰Si=-0.81±0.19‰; n=14), Caltech Rose Quartz (δ³⁰Si=0.10±0.13‰; n=14) sponge needles (Stylocordyla borealis; δ³⁰Si=-2.19±0.32‰; n=14) and JER-diopside glass (δ³⁰Si=0±0.09‰; n=14) samples. The overall repeatability achievable is 0.15‰ (2 S.D.) on δ ²⁹Si and 0.24‰ (2 S.D.) on δ³⁰Si. The silicon isotope standard IRMM-018 ha also been measured and was confirmed to be heterogeneous. The two isotope ratios follow an equilibrium mass-dependent fractionation law which can be represented as δδ³⁰Si＝1.93×δ ²⁹Si. Published extractions methods have been used to wet-chemically purify Si from the JER-diopside glass. The Si extracted was represented as Si-gel and ablated like a solid. The results show excellent agreement with in situ measurements of this glass that confirms that this technique can be employed to a wide variety of matrices, including Si purified from solution. The new technique presents a viable alternative to solution MC-ICP-MS for bulk measurements and the most precise technique so far for in situ measurement of Si isotope ratios.

Keywords: Si isotopes; UV-femtosecond laser; MC-ICP-MS』

1. Introduction
2. Methods
　2.1. Laser ablation settings
　2.2. MC-ICP-MS configuration
　2.3. Collector setup and spectroscopic interferences
　2.4. Data acquisition
　2.5. Sample consumption
　2.6. Si isotope measurements from solution
3. Results
　3.1. Standardisation and reproducibility
　3.2. Characterisation of diverse samples
　　3.2.1. IRMM-018
　　3.2.2. Caltech Rose Quartz
　　3.2.3. Big Batch
　　3.2.4. San Carlos Olivine
　　3.2.5. Biomineralisation: sponge needles (S. borealis)
　　3.2.6. JER-diopside
　3.3. Fractionation law
4. Discussion and conclusions
Acknowledgements
References