Mercury damages the nervous system, brain, kidney and lungs, etc. This heavy metal exists as a vapor or a liquid metal. In the mercurous state, it exists as inorganic salt, and in the mercuric state, it may form either inorganic salt or organometal compound. Mercury does not break down in the environment, and thus it remains as a persistent pollutant. The development of rapid and cost-effective tools for analyzing mercury (Hg) concentrations in environmental samples is very important as the toxicity of mercury is lethal to humans.
Various analytical methods have been developed to monitor mercury concentrations in environmental samples. They include atomic absorption spectrophotometric determination (AAS), atomic fluorescence spectrophotometric determination (AFS), and inductively coupled plasma mass spectrophotometric determination (ICP-MS). However, these methods are expensive, laborious and time-consuming.
To overcome these drawbacks, methods for low-cost and rapid detection of mercury in environmental samples using silver nanoparticles and gold nanoparticles have been widely developed in recent years. Silver nanoparticles are synthesized using plant extracts such as water apples and spinach for colorimetric detection of Hg. These analytical methods transform analyte concentration into color changes, which have the potential for qualitative and quantitative applications through colorimetric or naked-eye detection. Thus, colorimetric methods using silver nanoparticles and gold nanoparticles have shown to be promising tools for monitoring the concentration of mercury in environmental samples.
Ri Song Ho, a section head at the General Assay Office, has prepared nano silver solution by green-chemistry method, and proposed a low-cost, rapid and easy-to-use analytical method for spectrophotometric determination of mercury.
For preparing stable nano silver solution, he used aqueous extract of apple as bioreductant. The prepared nano silver solution was brown, with a surface plasmon resonance peak at 420nm. The addition of Hg2+ ions then changed the silver nanoparticles into colorless ones. The color change (decrease of absorbance) was proportional to the concentration of Hg2+ ions.
At the time of UV-visible spectrophotometric determination, the detection limit of the proposed method was 0.1mg/L and the relative standard deviation (RSD) was below 4%.
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