Analytical Sciences, Short talk
AS-013

Depth-Resolved Investigation of Elemental Fractionation in Zircon and Glass Matrices using Single-Pulse-Resolved LA-ICP-TOFMS

S. J. Oberholzer1, T. Van Acker2, D. Günther1*
1Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland, 2Department of Chemistry, Atomic & Mass Spectrometry – A&MS Research Group, Ghent University, Campus Sterre, Krijgslaan 281-S12, BE-9000, Ghent, Belgium

Uranium-lead (U-Pb) dating of zircon (ZrSiO4) is a cornerstone of modern geochronology. Due to its high analytical throughput and low sample consumption, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has become a widely applied technique for U-Pb and Pb isotope ratio analysis. However, accurate U-Pb ratio determination is frequently compromised by non-stoichiometric effects, commonly referred to as elemental fractionation, which cause measured elemental signals to deviate from the true sample composition. These effects are matrix-dependent and may arise during laser ablation, aerosol transport, and/or within the ICP.

To mitigate elemental fractionation, quantitative analyses commonly rely on external calibration using matrix-matched zircon reference materials of known composition and age. Nevertheless, variations in ablation behaviour among different zircon reference materials continue to limit analytical accuracy and inter-laboratory comparability.1,2 The use of well-characterized glass reference materials, such as NIST SRM 610, for external calibration has proven unsuccessful, indicating fundamental differences in the ablation and fractionation behaviour of zircon and glass matrices.3

In this study, single-pulse-resolved LA-ICP-TOFMS was employed to investigate the zircon-specific ablation behaviour of matrix elements, Pb, and U. The high temporal resolution enabled the detailed characterization of the depth-dependent ablation behaviour and corresponding transient signals. Zircon reference materials of different ages were analysed in hole-drilling mode and each cross-validated by calibrating against the other zircon reference materials. Crater depths and diameters were determined and the resulting ablation rates assessed. In addition, the external calibration strategy was extended through the use of monodisperse microdroplets as a secondary normalization standard.4 Being directly introduced into the plasma, microdroplets can correct for ICP-induced fractionation and provide additional insight into the contribution of plasma-related processes to the overall quantification accuracy.

Identical measurements were performed using the NIST SRM 610 glass to directly compare zircon and glass ablation behaviour. The results provide new insight into matrix-dependent fractionation processes and highlight the limitations of glass reference materials for accurate zircon U-Pb ratio determination. 

[1] U. Klötzli, E. Klötzli, Z. Günes and J. Kosler, Geostand. Geoanal. Res., 2009, 33, 5–15.

[2] E. Marillo-Sialer, J. Woodhead, J. Hergt, A. Greig, M. Guillong, A. Gleadow, N. Evans and C. Paton, J. Anal. At. Spectrom., 2014, 29, 981–989.

[3] B. K. Kuhn, K. Birbaum, Y. Luo and D. Günther, J. Anal. At. Spectrom., 2010, 25, 21–27.

[4] T. Schöberl, M. Bachmann and D. Günther, J. Anal. At. Spectrom., 2025, 40, 2438–2446.