Three methods of preparing isotope standard materials
In September 2023, the research group of Professor Yuan Honglin from the State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University published a research paper entitled “Comparison of synthetic zircon, high-temperature and high-pressure sintered zircon and fast hotpressing sintered zircon for in situ hafnium isotope analysis by LA-MC-ICP-MS” in “J. Anal. At. Spectrom”.
This work first used wet grinding to prepare ultrafine zircon powder doped with Yb2O3. Then, synthesize zircon samples by three methods: solid phase synthesis, high temperature, and high-pressure method, and field-assisted sintering technology. Finally, determine the typical isotope abundance data in zircon by laser ablation multi-receiver inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) to compare the effects of different synthesis technologies in preparing Hf isotope analysis standard materials.
The results show that for the Zr signal, the data of solid-phase synthesized zircon particles and high-temperature and high-pressure sintered zircon are consistent with natural zircon, but higher than rapid hot-pressed sintered zircon. This indicates that the density of high-temperature and high-pressure sintered zircon is higher. The Hf isotope analysis results show that the high-temperature and high-pressure sintered and field-assisted sintered zircon composition is consistent with the initial raw material. However, the Hf isotope data of solid-phase synthesized zircon deviates slightly from the raw material.
In general, all three preparation techniques give reliable LA-MC-ICP-MS results. These zircon samples have great potential as isotope standard materials for in-situ methods.
Artificial zircon standard materials
In the past two decades, in situ determination of Hf isotopes in zircon by LA-MC-ICP MS has been widely used to study the evolution of the crust and mantle. However, accurate determination of Hf isotope composition requires reliable isotope reference materials. Although the distribution of Hf in some natural zircons is uniform, we can use them as reference materials. However, their quantity is scarce and cannot meet the growing demand of global geological analysis laboratories. What is more serious is that some of these reference materials are almost exhausted. Therefore, it is necessary to develop some artificial zircon reference materials.
The usual method is to synthesize artificial zircon particles doped with Yb and Hf to obtain zircon reference materials with relatively high 176Yb/177Hf ratios. These synthetic zircon particles must have a uniform Hf isotope distribution and the same chemical composition as natural zircon. And have the behavior under the action of laser ablation mass spectrometry. Therefore, these synthetic zircon particles can be competent for isotope reference materials for in situ analysis.
Excellent results of field-assisted sintering technology
It is worth mentioning that the field-assisted sintering technology was used as one of the comparative methods for systematic experimental research. The results confirmed that the density of the samples sintered by the field-assisted sintering technology was slightly lower than that of natural zircon, but it did not affect the results. The doping distribution was uniform and consistent with the raw materials, which could fully serve as the isotope standard sample. Compared with the high-temperature and high-pressure synthesis method, the sintering by the field-assisted sintering technology undoubtedly has lower costs and higher production efficiency.
This article demonstrates the excellent effect of the field-assisted sintering technology from the perspective of isotope analysis, which is good proof of the uniformity of the sintered samples.
