Yankuang ceshi (May 2019)
A Review on the Progress of Purification Techniques for High Precision Determination of Cr Isotopes in Geological Samples
Abstract
BACKGROUND With the development of Multi-collector Thermal Ionization Mass Spectrometry (MC-TIMS) and Multi-collector Inductively Coupled Plasma-Mass Spectrometry (MC-ICP-MS), Cr isotopes had been successfully measured at a high resolution. Chromium isotopes have shown good application potential in the fields of environmental geochemistry, agroecology and cosmochemistry. However, sample purification and interference correction are still the main factors that suppress the high-resolution measurement of Cr isotopes. The development of a high-recovery, universal and efficient separation and purification method is an urgent problem to be solved. OBJECTIVES To discuss the purification of Cr isotopes in geological and environmental samples, interference and mass discrimination correction during measurement of MC-ICP-MS. METHODS This study compared and analyzed the current chemical separation and purification methods and main instrumental analysis techniques commonly used for chromium isotopes (e.g. MC-ICP-MS), and discussed the current mainstream quality discrimination correction methods. The combination of anion and cation exchange resin with strong oxidants such as K2S2O8 can effectively separate Cr from low Cr samples with high matrix contents, which is a more universal purification method. Medium-high resolution and static measurement mode was used during MC-ICP-MS analysis and Cr isotopes double spike method to correct mass discrimination effect. RESULTS The analytical precision of δ53/52Cr was 0.04‰ (2SD), similar to that of TIMS. Moreover, the minimum analytical sample was 10ng, thus isotope analysis of ultra-micro chromium can be achieved. CONCLUSIONS The proposed method cannot only separate the polyatomic ion interference, but can also perform high-precision Cr isotope analysis. It is necessary to reduce the process blank, remove the interfering elements and completely separate the different forms of chromium.
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