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Abstract
A simple procedure for field fish sample pretreatment was developed. This treatment in combination with square wave anodic stripping voltammetry (SW-ASV) with solid gold electrodes (SGE) and gold nanoparticle-modified glassy carbon electrodes (AuNPs-GCE) was applied for the determination of total mercury content. A certified reference material (CRM, Tuna Fish BCR 463), ten freeze-dried samples of canned tuna and two fresh fish samples were analysed both with a bench-top voltammetric analyser after microwave digestion and with a portable potentiostat after mild eating using a small commercial food warmer. The results obtained by the two SW-ASV approaches and by a Direct Mercury Analyser (DMA), the official method for mercury determination, were in very good agreement. In particular, (i) the results obtained with in field procedure are consistent with those obtained with the conventional microwave digestion; (ii) the presence of gold nanoparticles on the active electrode surface permits an improvement of the analytical performance in comparison to the SGE: the Limit of Quantification (LOQ) for mercury in fish-matrix was 0.1 μg L−1 (Hg cell concentration), corresponding to 0.06 mg kg−1 wet fish, which is a performance comparable to that of DMA. The pretreatment proposed in this study is very easy and applicable to fresh fish; in combination with a portable potentiostat, it proved to be an interesting procedure for on-site mercury determination.
Highlights
Mercury emissions have increased above natural environmental levels due to anthropogenic practices, such as coal combustion, mining activities and industrial processes, whereas natural releases are mainly due to volcanoes [1].Molecules 2019, 24, 1910; doi:10.3390/molecules24101910 www.mdpi.com/journal/moleculesDue to its long residence time in atmosphere, Hg has the possibility to travel throughout the world, impacting remote regions, such as the open ocean [2]
As described in our previous papers [34,35], the deposition of AuNPs onto electrode is well visible to the naked eye through a color change of the glassy carbon surface from black to red-orange
The results obtained with the on-site procedure developed in this work are consistent with those obtained with the conventional microwave digestion coupled to a benchtop voltammetric analyser and with Direct Mercury Analyser (DMA)
Summary
Mercury emissions have increased above natural environmental levels due to anthropogenic practices, such as coal combustion, mining activities and industrial processes, whereas natural releases are mainly due to volcanoes [1].Molecules 2019, 24, 1910; doi:10.3390/molecules24101910 www.mdpi.com/journal/moleculesDue to its long residence time in atmosphere, Hg has the possibility to travel throughout the world, impacting remote regions, such as the open ocean [2]. When elemental mercury is introduced into aquatic ecosystems, it is oxidised to inorganic compounds and methylating microbes participate to form organic species, such as methylmercury (MeHg) [3,4] In this chemical form, mercury shows a low hydrophilicity and can interact with cell membranes and proteins: the affinity with the components of living organisms leads to a bio-accumulation of these Hg species in the life forms placed at the top of the food chain [3]. For this reason, fish represents a critical source of Hg and MeHg into human diet [5]. In the last several years, a new device for a direct mercury analysis has been developed, which automatically performs both sample digestion and Hg detection by AAS, with short analysis times and a low limit of quantitation (LOQ), namely 0.010 mg kg−1 wet weight [9]
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