Abstract
Trace-level detection of mercury in waters is connected with several complications including complex multistep analysis routines, applying additional, harmful reagents increasing the risk of contamination, and the need for expensive analysis equipment. Here, we present a straightforward reagent-free approach for mercury trace determination using a novel thin film sampling stick for passive sampling based on gold nanoparticles. The nanoparticles supported on a silicon wafer and further covered with a thin layer of mesoporous silica. The mesoporous silica layer is acting as a protection layer preventing gold desorption upon exposure to water. The gold nanoparticles are created by thermal treatment of a homogenous gold layer on silicon wafer prepared by vacuum evaporation. This gold-covered substrate is subsequently covered by a layer of mesoporous silica through dip-coating. Dissolved mercury ions are extracted from a water sample, e.g., river water, by incorporation into the gold matrix in a diffusion-controlled manner. Thus, the amount of mercury accumulated during sampling depends on the mercury concentration of the water sample, the accumulation time, as well as the size of the substrate. Therefore, the experimental conditions can be chosen to fit any given mercury concentration level without loss of sensitivity. Determination of the mercury amount collected on the stick is performed after thermal desorption of mercury in the gas phase using atomic fluorescence spectrometry. Furthermore, the substrates can be re-used several tens of times without any loss of performance, and the batch-to-batch variations are minimal. Therefore, the nanogold-mesoporous silica sampling substrates allow for highly sensitive, simple, and reagent-free determination of mercury trace concentrations in waters, which should also be applicable for on-site analysis. Successful validation of the method was shown by measurement of mercury concentration in the certified reference material ORMS-5, a river water.
Highlights
The toxicity of mercury and its compounds is well known today and the United NationsEnvironment Program considers mercury as one of the most critical environmental pollutants
Silicon wafers were chosen as substrates due to their mechanical stability, flatness, and chemical durability
Gold nanoparticle-coated substrates were prepared through thermal treatment of a homogeneous, 6 nm thin layer of gold vacuum evaporated onto a silicon wafer
Summary
The toxicity of mercury and its compounds is well known today and the United NationsEnvironment Program considers mercury as one of the most critical environmental pollutants. Mercury is emitted to the environment mostly in its elemental form (Hg(0)) by both, natural sources, like volcanic eruption, as well as by anthropogenic sources, mainly by combustion of fossil fuels and small scale gold mining. These two sources account for more than 60% of the global anthropogenic mercury emissions and were rising considerably in the last decade [2]. Once emitted mercury is globally distributed due to its long lifetime in the atmosphere. Monitoring of mercury traces in the hydrosphere has been regulated in many countries, e.g., in Europe by the European Water Framework
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