Measurements of mass-dependent Te isotopic variation by hydride generation MC-ICP-MS

Abstract

Tellurium (Te) stable isotope measurements have the potential to serve as tracers of Te mobility and redox conditions in modern and ancient environments. Here, we present a method to measure Te isotope ratios by MC-ICP-MS utilizing a hydride generation system to efficiently deliver Te to the plasma, in combination with a ¹²⁰Te–¹²⁴Te double spike. This approach allows for precise δ¹³⁰Te/¹²⁶Te (2σ: 0.09‰) measurements while using less than 8.75 ng of natural Te. Although hydride generation methods usually produce higher sensitivity than more conventional methods, for Te, the sensitivity is similar, on our instrument, to that achieved using a desolvating nebulizer. Nonetheless, hydride generation has an advantageous ability to exclude interfering elements such as Ba and allow analysis of samples without chemical separation of Te in some cases. We also demonstrate successfully a modified ion exchange procedure to separate various matrix components and isobaric interferences from Te in natural sediments. Analyses of multiple digestions of USGS standard reference materials, mine tailings, ancient sediments, and soils utilizing this approach show the largest spread in terrestrial Te isotopic composition to date (δ¹³⁰Te/¹²⁶Te ∼ 1.21‰) and a lack of detectable mass-independent fractionation.