| The isotope ratio 87Sr/86Sr, typically reported in geologic investigations, is obtained by direct electrospray ionization of aqueous sample containing Sr(II), Rb(I) and 18c6. At relatively high concentrations, we observed favorable formation of Sr2+(18c6)2 and Rb+(18c6) over Sr2+(18c6) complexes. Physical separation of Sr2+(18c6)2 and Rb+(18c6) as well as separation of Sr2+(18c6)2 is observed by simply injecting the sample solution to ESI source using simple PEEK tubing in neutral pH. These phenomena are caused by the difference in mobility of the complexes and masked by the gas phase association reactions. ESI-QITMS successfully obtained the expected isotope distribution of Sr(II) without any interference from 87Rb and without any chromatographic separation of 87Sr and 87Rb which typically interferes with the isotope ratio 87Sr/86Sr in ICP-MS studies. |
