Selenium (Se) is an essential trace element for many living organisms and environmental systems as it is involved in several vital biochemical processes. Particularly, Se shows powerful antioxidant and anti-cancer properties and studies showed that it plays an important role in mercury (Hg) detoxification1. Although the antagonistic effect against Hg toxicity has been widely evidenced in different fish species exposed to methylmercury (MeHg)2, the detoxification mechanism taking place is still not well understood yet. Selenium has six stable isotopes, and exploring the Se isotopic composition in fish organs such as tuna, known for accumulating high MeHg levels 3, can be of great interest for revealing Se sources and unravelling metabolic processes, potentially enhancing our understanding on Se antagonistic effect against Hg toxicity.

 Selenium isotopic analysis is typically performed using multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS), coupled to hydride generation system (HG) with which Se is introduced in the form of gaseous Se-hydrides (dry plasma conditions, Figure 1). However, MC-ICP-MS Se isotopic analysis is very challenging as most of the Se isotopes suffer from Ar-based spectral interferences, impossible to resolve with a traditional MC-ICP-MS unit not equipped with a collision reaction cell. In addition, non-spectral (matrix-induced) interferences further complicate the task, especially when hydride-forming elements (As, Ge, …) or disruptors of the process of hydride formation (Fe, Cu, Ni, Co, …) are present.  

In this work, fundamental aspects of MC-ICP-MS will be revisited with the aim of reducing the impact of Ar-based spectral interferences on the signals of the Se isotopes. In addition, an in-depth evaluation of the accuracy and precision in Se isotopic analysis using MC-ICP-MS, with a particular emphasis on the influence of the Se concentration on these figures of merit will be presented. The matrix-induced interferences will be overcome through Se separation from the matrix using the well-established Thiol Cellulose Powder (TCP) approach prior to HG-MC-ICP-MS measurement. Finally, the method developed will be applied to tuna organs in order to explore potential variation in the Se isotopic composition and potentially provide additional information on the role of Se in Hg detoxification process.

References

1 Z. Gajdosechova, Z. Mester, J. Feldmann and E. M. Krupp, TrAC Trends in Analytical Chemistry, 2018, 104, 95–109.

2 Z. Gajdosechova, M. M. Lawan, D. S. Urgast, A. Raab, K. G. Scheckel, E. Lombi, P. M. Kopittke, K. Loeschner, E. H. Larsen, G. Woods, A. Brownlow, F. L. Read, J. Feldmann and E. M. Krupp, Sci Rep, 2016, 6, 34361.

3 M. Wiech, A. M. Bienfait, M. Silva, J. Barre, V. Sele, M. S. Bank, S. Bérail, E. Tessier, D. Amouroux and A. M. Azad, Journal of Hazardous Materials, 2024, 473, 134699.