Measurement of 87Sr/86Sr in limestones after acid leaching and direct injection in a liquid chromatograph coupled to a multicollector ICP-MS

Abstract

A procedure for the measurement of 87Sr/86Sr in carbonates without off-line strontium separation was developed, validated and applied to Normandy chalkstones. The method is based on the injection of the dissolved/leached sample into a high-performance liquid chromatography (HPLC) system directly coupled to a multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS). Matrix and spectral (Ca, Rb) interferences were removed by an on-line separation procedure based on cation exchange chromatography using 1 M nitric acid as an eluent in the presence of 3.8 mM 18-crown-6. The main polyatomic interferent was identified as NO2Ca+, affecting mass 86 of strontium. Isotope ratios were calculated by multiple linear regression from the measured chromatographic peaks. The method was evaluated using a NIST 987 Sr isotope reference material and subsequently validated employing a JCp-1 coral reference material in comparison with the traditional off-line separation procedure. Finally, the method was applied to ten Normandy limestones (chalkstones) with results in agreement with the expected values based on geological, geochemical, and stratigraphic studies. This journal is