Sensitive determination of neodymium isotope in seawater by multi-collector inductively coupled plasma mass spectrometry with ultrasound nebulization-dielectric barrier discharge vapor generation as sample introduction†

Abstract

In this work, a highly sensitive Nd isotopic analysis method by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) with ultrasound nebulization-dielectric barrier discharge (UNDBD) vapor generation as sample introduction is developed. The sensitivities of Nd isotopes determined by UNDBD are enhanced about 4.5 fold and 1.5 fold compared to conventional wet plasma and dry plasma, respectively, attributed to the generation of volatile Nd species during the dielectric barrier discharge (DBD) induced vapor generation process. Fractionation of Nd isotopes in UNDBD exhibits a mass-dependent characteristic, enabling successful correction of the ¹⁴³Nd/¹⁴⁴Nd ratio using the ¹⁴⁶Nd/¹⁴⁴Nd ratio with an exponential law. The minimum Nd concentration and volume required per analysis by UNDBD-MC-ICP-MS can be as low as 0.5 μg L⁻¹ and 600 μL, thereby minimizing the sampling volume for Nd isotopic analysis in open seawater to 0.7 L. Interferences from residual major ions in seawater, present at mg L⁻¹ level after pretreatment, are found to be negligible for Nd isotopic analysis by UNDBD-MC-ICP-MS. The long-term external precision (2RSD) for ¹⁴³Nd/¹⁴⁴Nd with 1 μg L⁻¹ of Nd using this method is calculated as 64 ppm. The accuracy of ¹⁴³Nd/¹⁴⁴Nd determined by this method has been successfully validated by Nd isotopic standard solutions of GSB 04-3258-2015 and GBW04440. The Nd isotopic ratios determined in several seawater samples by UNDBD are in agreement with results obtained by the dry plasma method. UNDBD demonstrates both higher sensitivity and precision for Nd isotopic analysis compared to wet plasma and dry plasma sample introduction methods, making it more suitable for analyzing open seawater samples with low Nd concentrations and less sampling volume.