Magnesium isotope ratio measurements by negative thermal ionisation mass spectrometry using molecular fluoride ions

A new technique for accurate Mg isotope ratio measurements has been developed with MgF2 as sample compound. With the help of a fluorinating agent negatively charged MgF3 molecular ions were formed in the ion source of a thermal ionisation mass spectrometer. An evaporation study has been performed and the results clearly show that Mg is evaporated from the filament as MgF2 molecules. The MgF2 technique has been applied in the certification of a candidate 26Mg-enriched Spike Isotope Reference Material. The result from this new technique has been compared with results obtained for the same material using ICP-MS.