Single-Stage Extraction Technique for Ce Stable Isotopes and Measurement by MC-ICP-MS

Abstract

The separation of Ce from other rare earth elements has not been well established because of their similar geochemical properties. In this study, we report a single-stage extraction technique to purify Ce from natural samples with Eichrom DGA resin. This method separates Ce effectively from matrices and interfering elements, such as Ba, La, and Nd. The Ce elution curve would not drift with different Ce loading masses and rock types. The Ce isotope compositions were measured using a Thermo Scientific Neptune Plus multicollector (MC)-inductively coupled plasma (ICP)-mass spectrometry (MS) instrument. The instrumental mass bias of Ce isotopes was corrected with a sample-standard bracketing combined with a Sm-doping method. The δ142Ce values of standard solutions (CDUT-Ce and JMC304) relative to National Institute of Standards and Technology SRM 3110 measured were +0.128 ± 0.028‰ (2SD, N = 30) and 0.005 ± 0.038‰ (2SD, N = 30), respectively. The reproducibility for δ142Ce was better than 0.040‰. The Ce isotopic compositions of nine United States Geological Survey standard rocks, including carbonatite, basalt, andesite, quartz latite, dolerite, rhyolite, and granodiorite, were measured in this study. Our result showed that δ142Ce values of these rocks varied slightly, indicating that insignificant fractionation occurred during igneous processes. The technique proposed in this study is simple and time-efficient, which is beneficial for further studies on Ce isotope geochemistry.

Ce and Nd stable isotope purification and determination of geological samples by MC-ICP-MS

“…In fact, low yield and residual isobaric elements, such as Ce in Nd cuts, have been reported, 45,46 which can severely impact the accuracy and precision of the measurements of stable Ce and Nd isotopes. 12,55 In addition, a long and thin column (0.2 cm × 20 cm) 45 was used in their method, which is time-consuming (∼4 days). 31,46 For the elution scheme (3), Rehkāmper et al 47 reported a two-phase micro-extraction technique for the separation of Ce from the other LREEs, which can be called the NaBrO 3 method 57 or liquid–liquid micro-extraction (LLME).…”

“…2,9–11,48–50 However, the inconveniences of this method have not been well solved, including (i) the non-reproducibility of the Nd yield (80–100%), which is a noticeable phenomenon for stable Nd isotope analyses; (ii) the residual 10–20% Pr in the Nd cuts, which may cause the molecular interference of 141 PrH on 142 Nd, 40 and data on stable Nd isotopes using the NaBrO 3 method has not been reported so far; (ii) the use of inorganic oxidizing agents (KBrO 3 or NaBrO 3 ) and concentrated HNO 3 , which may cause higher blanks (∼500 pg) 50 and are not easy to operate. For elution scheme (4), some researchers recently reported the use of a TODGA resin column to purify Ce 12 or Nd, 52–54 which has a very high efficiency for LREEs. For example, Bai et al 55 established a single TODGA resin column to separate Nd from the other REEs.…”

“…1 in Bai et al 55 ). Residual La can cause large isobaric interference on Ce isotopes, and residual Pr may generate molecular interference from 141 PrH on 142 Ce, 12,40 and achieving very high Ce purity is of paramount importance. Taken together, all the techniques mentioned above suffer from two main problems: (1) two completely independent methods were employed to purify Ce and Nd from the other matrix elements, which is tedious and results in a high cost; (2) all these published elution schemes do not meet the requirement of a perfect separation of La–Ce–Pr–Nd, along with a nearly 100% recovery, which is essential to study the stable Ce and Nd isotopic ratios when not using a double spike during MC-ICP-MS measurements.…”

“…Subsequently, large Ce stable isotopic variations have also been observed in natural samples. [8][9][10][11][12][13] The currently available data shows that the d 142/140 Ce values vary from À0.330& in Fe precipitates to 0.295& in marine ferromanganese oxides. 9 According to the Eh-pH diagrams, Fe should be precipitated under reductive conditions, whereas Mn precipitates under oxidative conditions.…”

“…1 in Bai et al 55 ). Residual La can cause large isobaric interference on Ce isotopes, and residual Pr may generate molecular interference from 141 PrH on 142 Ce, 12,40 and achieving very high Ce purity is of paramount importance. Taken together, all the techniques mentioned above suffer from two main problems: (1) two completely independent methods were employed to purify Ce and Nd from the other matrix elements, which is tedious and results in a high cost;…”