A Fast Separation Method for Isotope Analysis Based on Compressed Nitrogen Gas and Ion-Exchange Chromatography Technique—A Case Study of Sr-Nd Isotope Measurement

High-purity N₂ was used to increase the mobile phase flow rate during ion purification of ion-exchange resin. This was performed to improve the efficiency of isotope separation and purification, and to meet the efficiency requirements of rapid multiple-collector-inductively coupled plasma mass spectrometry (MC-ICPMS) analysis. For Cu isotope separation, our results indicated that at a gas flow rate > 60 mL/min, the separation chromatographic peaks broadened and the recovery rate decreased to < 99.2%. On the other hand, no significant change in the Cu peaks was observed at a gas flow rate of 20 mL/min and the recovery rate was determined to be > 99.9%. The Cu isotope ratio, measured by the standard-sample bracketing method, agreed with reference data within a ±2 SD error range. The separation time was reduced from the traditional 10 h (without N₂) to 4 h (with N₂), indicating that the efficiency was more than doubled. Moreover, Sr and Nd isotope separation in AGV-2 (US Geological Survey andesite standard sample) accelerated with a 20 mL/min gas flow, demonstrating that with the passage of N₂, the purified liquid comprised Rb/Sr and Sm/Nd ratios of < 0.000 049 and < 0.000 001 5, respectively. This indicated an effective separation of Rb from Sr and Sm from Nd. MC-ICPMS could therefore be applied to accurately determine Sr and Nd isotope ratios. The results afforded were consistent with the reference data within a ±2 SD error range and the total separation time was shortened from 2 d to < 10 h.