The cerium isotope ratio (δ¹⁴²Ce), a novel proxy reflecting the paleoredox condition, yields more quantitative information related to the redox condition than Ce anomaly alone. However, sample amounts and analytical precision represent bottlenecks for Ce isotope measurements using multi-collector (MC-)ICP-MS. Sample treatment processes and analytical conditions of MC-ICP-MS using desolvating nebulizer were examined for this study. Our new cation exchange process removes most of the Ba, which is worthwhile for REE measurement. The examination of analytical conditions, including the sampling cone, torch Z position, Guard Electrode, Ar sweep, and N₂ gas greatly decreases the oxide formation ratio from approximately 1% (typical wet plasma mode) to less than 0.05%, which caused the great increase in the precision of Ce isotope measurement. The best reproducibility for δ¹⁴²Ce achieved in repeated measurements of NIST solution was ±0.020‰. The typical reproducibility was about ±0.030‰. The required Ce amount of the measurement was also decreased from 0.2 μg to 0.05 μg. Moreover, the current study measured δ¹⁴²Ce of 5 USGS and 17 GSJ standard rocks. The Ce stable isotope ratio of standard igneous rocks shows no significant isotope fractionation, although δ¹⁴²Ce of JDo-1 and JMn-1 are fractionated respectively from standard NIST solutions of +0.134 ± 0.025‰ and +0.110 ± 0.025‰. The δ¹⁴²Ce fractionation of sedimentary rocks can result from the adsorption reaction of Ce.

The concentration and carbon isotopic ratio (δ¹³C) of dissolved inorganic carbon (DIC) in natural waters is often altered by microbial activity, even over short durations, which can affect sample preservation. Hence, the influence of these biogenic processes should be limited to properly investigate DIC in natural waters. This study investigates the effectiveness of filtration and exposure to benzalkonium chloride (BAC) and sodium chloride (NaCl) for preserving natural water samples (seawater, groundwater, river, pond, hot spring, and brackish waters) in order to analyze the concentration and δ¹³C of DIC. We assessed six filter materials with pore sizes of 0.2–5.0 μm. In the waters filtered by polyether sulfone, polyvinylidene fluoride, or cellulose acetate filters, the number of microorganisms still increased during preservation. However, the 0.45-μm polytetrafluoroethylene filter provided effective microbe removal, yielding constant DIC concentration and δ¹³C even after three weeks of preservation. Although none of the filters studied could offer complete microorganism removal and constant δ¹³C, biogenic DIC changes in the water were successfully reduced by the use of filters with pore sizes of 0.45 μm or below. Exposure to BAC or NaCl promoted microbial exclusion in the freshwater samples, with the DIC concentration and δ¹³C maintained during preservation over the one month. These effects were degraded in the seawater and brackish water samples, with the DIC concentrations and δ¹³C only constant for 10–15 days when exposed to BAC, and 1–3 days when exposed to NaCl. Although NaCl diminished biogenic activity in the freshwater samples, its influence on DIC concentration must be corrected for, which requires accurate knowledge of the NaCl concentration. We also applied the BAC solution in a field campaign in eastern Thailand and compared the DIC concentrations and δ¹³C values with those of samples treated with HgCl₂. The results of the field trial showed that, except for brackish water from a rivulet in a mangrove forest and seawater samples, BAC-treated samples were not significantly different from HgCl₂-treated samples. BAC can be considered an effective disinfectant for natural water samples, with less efficacy in seawater and brackish water.

Apatite, a common REE-enriched accessory mineral occurring in various rocks, provides important information on metallogenic source, magma evolution and source of sedimentary basin. In this study, we described an in situ method for simultaneous measurement of REE concentrations and Nd isotopic composition in apatite using a single-collector sector field inductively coupled plasma mass spectrometer and a muti-collector inductively coupled plasma mass spectrometer, connected to a single 193 nm laser-ablation system. The laser-ablated aerosol was split into two gas lines by a Y-shape joint and simultaneously transported into the two mass spectrometers. REE concentrations were measured on the SF-ICP-MS, while Nd isotopic composition was measured on the MC-ICP-MS. Two well-known apatite standards (Durango and Otter Lake) were measured to evaluate the precision and accuracy of this method. The measured Nd isotopic compositions of both apatites agree with their recommended values within analytical error. The measured REE concentrations display perfect coincidence with reported data. Using the established method, REE concentrations and Nd isotopic ratios of apatite sample from South China Sea Zhongnan and Zhenbei seamount lavas were measured. The measured data indicate that the compositional variation in apatite crystals in Zhongnan seamount is due to variable degrees of crustal contamination of the magmas during fractional crystallization, while the relatively large variability in ¹⁴³Nd/¹⁴⁴Nd ratios apatite from Zhenbei seamount most likely reflect source heterogeneity.

We examined three natural zircon samples with different amounts of radiation doses (1.9 × 10¹⁵–6.8 × 10¹⁵ α-decay events/mg) using M_V-edge and L_III-edge U X-ray absorption near-edge structure (XANES). Analysis of XANES spectra at both M_V-edge and L_III-edge suggested that the oxidation state of U in the zircon sample with the highest radiation dose is tetravalent. The XANES spectra of the two other samples with lower radiation doses suggested a mixture of U(IV) and U(VI), while the possibility of U(V) was not excluded. This is the first work on the application of M_V-edge U XANES to the oxidation state of U in natural zircon.

The advent of the latest-generation of mass spectrometers enables the determination of isotope ratios for several elements with very high precision. However, many obscure processes deteriorate analytical uncertainties. We investigated a likely process, the secondary instrumental fractionation of Nd isotopes during thermal ionization mass spectrometry (TIMS) analysis, which cannot be ignored in recent geochemical applications. Multiple Nd isotope measurements of the standard JNdi-1 and nine terrestrial rocks standards reveal small but resolvable isotopic fluctuations. The variations are attributed to secondary instrumental fractionation induced by the accumulation of conductive materials (e.g., H₃PO₄) from samples, on the ion lens assemblage surface. The secondary instrumental fractionation observed in ¹⁴²Nd/¹⁴⁴Nd ratios is corrected using the simultaneously measured ¹⁵⁰Nd/¹⁴⁴Nd ratios. The correction improves the ¹⁴²Nd/¹⁴⁴Nd reproducibility by a factor of ~1.3. This second-order correction produces more precise and accurate isotopic ratios for terrestrial rocks with potentially variable ¹⁴²Nd/¹⁴⁴Nd ratios.