The ¹³⁸La–¹³⁸Ce decay system (half-life 1.02 × 10¹¹ years) is a potentially highly useful tool to unravel information about the timing of geological processes and about the interaction of geological reservoirs on earth, complementing information from the more popular ¹⁴⁷Sm–¹⁴³Nd and ¹⁷⁶Lu–¹⁷⁶Hf isotope systems. Previously published analytical protocols were limited to TIMS. Here we present for the first time an analytical protocol that employs MC-ICPMS, with an improved precision and sensitivity. To perform sufficiently accurate La–Ce measurements, an efficient ion-chromatographic procedure is required to separate Ce from the other rare earth elements (REE) and Ba quantitatively. This study presents an improved ion-chromatographic procedure that separates La and Ce from rock samples using a three-step column separation. After REE separation by cation exchange, Ce is separated employing an Ln Spec column and selective oxidation. In the last step, a cation clean-up chemistry is performed to remove all remaining interferences. Our MC-ICPMS measurement protocol includes all stable Ce isotopes (¹³⁶Ce, ¹³⁸Ce, ¹⁴⁰Ce and ¹⁴²Ce), by employing a 10¹⁰ ohm amplifier for the most abundant isotope ¹⁴⁰Ce. An external reproducibility of ±0.25ε-units (2 r.s.d) has been routinely achieved for ¹³⁸Ce measurements for as little as 150–600 ng Ce, depending on the sample–skimmer cone combinations being used. Because the traditionally used JMC-304 Ce reference material is not commercially available anymore, a new reference material was prepared from AMES laboratory Ce metal (Cologne-AMES). In order to compare the new material with the previously reported isotopic composition of AMES material prepared at Mainz (Mainz-AMES), Cologne-AMES and JMC-304 were measured relative to each other in the same analytical session, demonstrating isotope heterogeneity between the two AMES and different JMC-304 batches used in the literature. To enable sufficiently precise age correction of radiogenic ¹³⁸Ce and to perform isochron dating, a protocol was developed where La and Ce concentrations are determined by isotope dilution (ID), using an isotope tracer enriched in ¹³⁸La and ¹⁴²Ce. The new protocols were applied to determine the variations of Ce isotope compositions and La–Ce concentrations of certified geochemical reference materials (CRMs): BCR-2, BCR-1, BHVO-2, JR-1, JA-2, JB-3, JG-1, JR-1, JB-1b, AGV-1 and one in-house La Palma standard.

中文翻译：

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多收集器-ICPMS进行La–Ce同位素测量†

在¹³⁸镧¹³⁸铈衰变系统（半衰期1.02×10 ¹¹年）到大约地质过程和大约在地球上地质储层中的相互作用的时序绎信息的潜在非常有用的工具，从比较流行的补充信息¹⁴⁷ Sm– ¹⁴³ Nd和¹⁷⁶ Lu– ¹⁷⁶f同位素系统。先前发布的分析协议仅限于TIMS。在这里，我们首次展示了一种采用MC-ICPMS的分析方案，具有更高的精度和灵敏度。为了执行足够准确的La–Ce测量，需要一种有效的离子色谱程序，以定量地将Ce与其他稀土元素（REE）和Ba分离。这项研究提出了一种改进的离子色谱方法，该方法使用三步柱分离技术从岩石样品中分离出La和Ce。通过阳离子交换将REE分离后，使用Ln Spec色谱柱和选择性氧化法分离Ce。在最后一步中，执行阳离子清除化学操作以去除所有剩余的干扰。我们的MC-ICPMS测量方案包括所有稳定的Ce同位素（¹³⁶ Ce，¹³⁸ Ce， ¹⁴⁰ Ce和¹⁴² Ce），将10 ¹⁰ ohm放大器用于最丰富的同位素¹⁴⁰ Ce。的±0.25的外部再现ε -单元（2 RSD）具有用于被常规实现¹³⁸Ce的测量值低至150-600 ng Ce，具体取决于所使用的样品-撇渣锥组合。由于传统上使用的JMC-304 Ce参考材料不再市售，因此从AMES实验室Ce金属（Cologne-AMES）制备了一种新的参考材料。为了将新材料与先前报道的在美因茨（Mainz-AMES）制备的AMES同位素组成进行比较，在同一次分析过程中对科隆-AMES和JMC-304进行了相对测量，证明了两者之间的同位素异质性AMES和文献中使用的不同JMC-304批次。为了能够对放射源¹³⁸进行足够精确的年龄校正为了进行等时测年，开发了一种协议，其中使用富含¹³⁸ La和¹⁴² Ce的同位素示踪剂，通过同位素稀释（ID）确定La和Ce的浓度。新协议被用于确定经认证的地球化学参考物质（CRM）的Ce同位素组成和La–Ce浓度的变化：BCR-2，BCR-1，BHVO-2，JR-1，JA-2，JB-3 ，JG-1，JR-1，JB-1b，AGV-1和一项内部La Palma标准。