Elimination of spectral interference of ⁸⁷Rb with ⁸⁷Sr during ICP-MS measurements using a chromatographic technique

A new chromatographic separation technique was developed for the measurement of the strontium (Sr) isotope abundance ratio using inductively coupled plasma mass spectrometry (ICP-MS). This technique, LC-ICP-MS, utilizes the addition of 18-crown-the eluent and an ODS column. The technique completely eliminates the spectral interference of Rb-87 (an isobar of Sr-87) with Sr-87 during the ICP-MS measurement. 18-Crown-6 selectively forms a clathrate compound with some metals. When the Sr isotope abundances are measured using LC-ICP-MS with an ODS column, the addition of a specific amount of 18-crown-6 to the HNO3/0.1% methanol eluent elongates the retention time of Rb. Therefore, Rb can be completely separated from Sr using LC because Rb is captured into the 18-crown-6 molecule and forms a clathrate compound. The technique enables the measurement of Sr isotope abundance ratios easily, even in the presence of a large amount of Rb. The proposed technique was applied to the measurement of Sr isotope abundance ratios in rice samples. To validate the LC-ICP-MS technique, a fraction containing Sr was collected, and the Sr-87/Sr-86 isotope ratio was precisely measured using ICP-MS.