Approach I: Rapid and Precise Measurements of Natural Carbonate Rare Earth Elements in Femtogram Quantities by Solution Nebulization-Inductively Coupled Plasma Mass Spectrometry (SN-ICPMS)

Abstract

In this chapter, we present a rapid and precise method for measuring femtogram quantity rare earth element (REE) levels in natural carbonate samples using inductively coupled plasma sector field mass spectrometry, which does not require chemical separation steps. A desolvation nebulization system was used to effectively reduce polyatomic interference and enhance sensitivity. REE/Ca ratios are calculated directly from the intensities of the ion beams of 46Ca, 139La, 140Ce, 141Pr, 146Nd, 147Sm, 153Eu, 160Gd, 159 Tb, 163Dy, 165Ho, 166Er, 169Tm, 172Yb, and 175Lu using external matrix-matched synthetic standards to correct for instrumental ratio drifting and mass discrimination. A routine measurement time of 3 min is typical for one sample containing 20–40 ppm Ca. Replicate measurements made on natural coral and foraminiferal samples with REE/Ca ratios of 2–242 nmol/mol show that external precisions of 1.9–6.5% (2 RSD) can be achieved with only 10–1000 fg of REEs in 10–20 μg of carbonate. Different sources for monthly resolved coral ultra-trace REE variability can be distinguished using this method. For natural slow growth-rate carbonate materials, such as sclerosponges, tufa, and speleothems, the high sample throughput, high precision, and high temporal resolution REE records that can be produced with this procedure have the potential to provide valuable time-series records to advance our understanding of paleoclimatic and paleoenvironmental dynamics on different time scales.