Traditional speciation analytical methods focus on the dissolved forms of metals, overlooking critical information about their (nano)particulate forms. The incorporation of nanoparticles (NPs) analysis contributes to uncover the environmental fate and impact of metals in living organisms. New analytical methodologies that allow comprehensive metal speciation, including both dissolved and particulate forms, are needed [1]. Techniques such as single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) are increasingly employed to facilitate this analysis, enabling for the quantification and characterization of NPs [2]. However, sample preparation becomes a crucial step in SP-ICP-MS analysis, especially for their application to solid matrices. Therefore, new procedures must be developed for a proper NP extraction without compromising NP stability or affecting dissolved forms of the element.

Concerning the case of mercury, it would be ideal to develop a sample preparation method that allows the simultaneous extraction of mercury ionic species and particulate forms, such as mercury and selenium NPs (HgSeNPs) since they have recently been postulated as key agents in the detoxification mechanisms of this element, especially in living organisms [3]. Consequently, in this work, typical extraction conditions previously applied to classical mercury speciation analysis, such as the combination of an alkaline extraction using tetramethylammonium hydroxide (TMAH) with the use of a closed-vessel microwave extraction system as energy source, have been evaluated aiming to achieve an adequate extraction of HgSeNPs. Quantitative recoveries were achieved for the different Hg forms including the HgSeNPs when using 5% TMAH as extractant and 150ºC as the maximum temperature of irradiation in the microwave system. The optimization and validation of the methodology have been performed using both certified reference materials and spiked real samples of aquatic animal tissues. Satisfactory results have been obtained using SP-ICP-MS for the characterization (in terms of size and concentration) of HgSeNPs and gas chromatography hyphenated to atomic fluorescence detection (GC-pyro-AFS) for ionic mercury forms. This work stands out for minimizing both the sample preparation time and the quantity of sample required, thanks to its simultaneous and common extraction approach. Additionally, it underscores the necessity for analytical methodologies that offer insights into both the dissolved and nanoparticulate forms of an element.

References

[1] Z. Gajdosechova; K. Loeschner Analytical and Bioanalytical Chemistry, 2024, 416(11), 2585-2594.

[2] F. Laborda; I. Abad-Álvaro; M.S. Jiménez; E. Bolea Spectrochimica Acta Part B: Atomic Spectroscopy, 2023, 199, 106570.

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

Acknowledgements

The authors would like to thank the Spanish Ministerio de Ciencia e Innovación (PID2022-138761NB-I00), Junta de Comunidades de Castilla-La Mancha (SBPLY/23/180225/000153) and Universidad de Castilla-La Mancha (2022-GRIN-34415), with FEDER co-financing, for the financial support. M. Hernández-Postigo also thanks the European Union (via Next Generation EU funding) for her contract (2023-INVGO-11947).