Testing the Ce Limit of Mass Bias Correction Using 145Nd/142Nd as Normalizing Ratio in Radiogenic Neodymium Isotope Analysis by MC-ICP-MS

Abstract

Rationale

Neodymium isotopes are a powerful geochemical tool that has widely been used in terrestrial and extraterrestrial studies. Modern multicollector inductively coupled plasma mass spectrometers (MC-ICP-MS) allow fast, accurate, and precise analysis of the radiogenic Nd isotope ratio ¹⁴³Nd/¹⁴⁴Nd. These analyses comprise relatively high instrumental mass bias that is typically corrected for using the stable ¹⁴⁶Nd/¹⁴⁴Nd of 0.7219 and an exponential law. The instrument is usually tuned to optimize the operating conditions for isotope analysis, but this tuning is a trade-off primarily between signal intensity, stability, and accuracy. Alternative, more effective approaches for mass bias correction have been proposed that use ¹⁴⁵Nd/¹⁴²Nd as normalizing ratio. However, one drawback of using this ratio is that the efficient removal of Ce from Nd is required to minimize the effect of isobaric interference of ¹⁴²Ce on ¹⁴²Nd.

Methods

Here, we analyzed international Nd and rock reference materials using a Thermo Scientific Neptune Plus MC-ICP-MS to evaluate the sensitivity of ¹⁴⁵Nd/¹⁴²Nd-based mass bias correction to varying Ce/Nd and in comparison with the commonly used ¹⁴⁶Nd/¹⁴⁴Nd-based correction.

Results

Our results show that the corrected ¹⁴³Nd/¹⁴⁴Nd of Ce-doped JNdi-1 and Ce-containing USGS BCR-2, NOD-A-1, and NOD-P-1 reference materials are insensitive to Ce/Nd of up to ~1.

Conclusions

The correction of instrumental mass bias with ¹⁴⁵Nd/¹⁴²Nd as a normalizing ratio yields, as previously suggested, improved trueness and precision of ¹⁴³Nd/¹⁴⁴Nd data in comparison with ¹⁴⁶Nd/¹⁴⁴Nd-based corrections, even under high Ce/Nd of ~1. This allows improved optimization of signal intensity during instrument tuning, which is particularly useful for natural samples with low Nd content. [Correction added on 10 December 2024, after first online publication: The Results and Conclusions in Abstract has been corrected in this version.]