New Method Enables Precise Determination of Mass-Dependent Tellurium (Te) Isotope Composition

Researchers from Imperial College London and the Natural History Museum in London have introduced a novel double spike method for accurately determining mass-dependent tellurium (Te) isotope compositions in meteorites and terrestrial materials. The study, published in the Journal of Analytical Atomic Spectrometry, presents a new column chromatographic procedure coupled with optimized multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) protocols, enabling precise measurements with minimal sample size (1).

Falling burning flares of several meteorites of asteroids in the Earth's atmosphere. Elements of this image furnished by NASA. | Image Credit: © aapsky - stock.adobe.com

MC-ICP-MS utilizes inductively coupled plasma (ICP) as the ionization source, which generates ions from the sample material. These ions are then separated based on their mass-to-charge ratio (m/z) using multiple ion collectors, allowing simultaneous detection of multiple isotopes. The use of multiple collectors improves the sensitivity, precision, and accuracy of the measurements. MC-ICP-MS is particularly valuable in isotopic studies, such as determining isotopic ratios, investigating elemental compositions, and understanding geological processes at a high level of precision.

The newly developed method utilizes a column chromatographic procedure to effectively separate tellurium from chondritic and iron meteorites, as well as various terrestrial rocks, with high yield and purity. This is combined with a robust ¹²⁵Te-¹²⁸Te double spike and optimized MC-ICP-MS protocols. The combination of these techniques allows for precise determination of the mass-dependent ¹³⁰Te/¹²⁵Te isotope ratio, even with analyte solutions containing as little as 6 nanograms of natural tellurium. The achieved precision of the measurements is impressive, with a two-times standard deviation (2SD) of 0.007%.

To validate the method, the researchers performed repeat analyses of terrestrial rock reference materials and meteorites, obtaining results that are in good agreement with previous studies. In addition, they conducted an inter-laboratory cross-calibration of three different tellurium standard solutions. This cross-calibration is particularly valuable since a well-calibrated isotope reference material for tellurium is not yet available.

Furthermore, the study explored the potential impact of hypothetical mass-independent tellurium isotope effects on the measured mass-dependent compositions. Through isotope mass balance and mixing equations, the researchers concluded that these effects are unlikely to significantly influence the measured results at the current level of analytical precision.

Notably, the researchers successfully applied the double spike technique to obtain the first precise mass-dependent tellurium isotope composition for an iron meteorite, Canyon Diablo, as well as the komatiite reference material KAL-1.

This novel method for determining mass-dependent tellurium isotope compositions offers enhanced precision and sensitivity, enabling researchers to delve deeper into the understanding of meteorite origins and terrestrial processes. The findings contribute to the advancement of analytical techniques in the field of isotopic studies and provide valuable insights into the geochemical characteristics of tellurium.

Reference

(1) Morton, E. M.; Kreissig, K.; Coles, B. J.; Jaffe, C. S.; Martins, R.; Poole, G. M.; Rehkamper, M. A new double spike method for the determination of mass-dependent Te isotope compositions of meteorites and terrestrial materials by MC-ICP-MS. J. Anal. At. Spectrosc. 2023, ASAP. DOI: 10.1039/D3JA00091E