Mercury, otherwise known as quicksilver, is the only metal that persists in liquid form under normal temperature and pressure circumstances. This article considers methods to identify and analyze mercury, and the significance of doing so.
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Mercury in the Environment
Mercury occurs in three forms: elemental mercury, inorganic mercury, and organic mercury. Elemental mercury is mostly found in thermometers and certain electrical switches. Inorganic mercury is more water-soluble and reactive. Compounds such as methylmercury are organic versions of mercury.
Mercury sources are divided into two categories: natural and anthropogenic. Volcanoes, fossil fuels, ore, and forest fires are mercury natural sources. In terms of anthropogenic sources, the burning of residential and medical wastes, as well as emissions from coal-fired power plants, play a significant role in the presence of high amounts of mercury in the environment.
Mercury in aquatic habitats is mostly caused by air deposition, urban emissions, agricultural materials, erosion, mining and combustion, and industrial emissions. Mining mineral deposits, coal combustion, and trash from industrial facilities all emit metallic and inorganic mercury compounds into the atmosphere.
Natural deposits, garbage disposal, and volcanic activity may all cause mercury to enter the water or soil. In soil and water, microorganisms such as bacteria may produce methylmercury.
Recently, aims to minimize the release of mercury, as well as to trace its movement when released, have needed more sensitive analytical methods for its detection.
As these techniques have developed, regulatory bodies across the globe have published new analytical procedures detailing their usage.
Atomic Emission and Fluorescence Spectroscopy, AES and AFS Detection Method
In the AES Atomic Emission Spectroscopy method, high energy induces excited electronic states in atoms, which then release light upon their return to the ground electronic state.
Each element, such as mercury, produces light at a distinct wavelength, which is separated and identified using a grating and spectrometer. The wavelength of an atom spectral line allows the element's identification, whereas the intensity of the emitted light is related to the element's atomic number.
Atomic Fluorescence Spectrometry
Researchers in the Tropical Journal of Pharmaceutical Research determined that the benefits of AFS over ICP approaches include low acquisition and simplicity of operation.
The main components of Atomic Force Microscopy (AFS) instruments are a light source that radiatively excites the atoms, an atom cell, which converts the sample into gaseous atoms, and a sensor network, which includes a wavelength selector, a signal processor, a photodetector, and a readout device.
To reduce the quantity of stray light that reaches the photodetector, the detection system is commonly oriented at 90 or 180 degrees with regard to the light source.
As a direct result, many researchers continue to employ AES and AFS due to their inexpensive cost and great sensitivity. Using those methods must be cognizant of the data quality associated with mercury determination.
Analyses of relevant standard reference materials (SRMs) containing mercury may help to improve the data quality.
CVASS—The Standard Approach Under the Safe Drinking Water Act
CVAAS, or Cold Vapor Atomic Absorption Spectroscopy, is a major method for mercury analysis. It is currently the standard approach for monitoring drinking water under the Safe Drinking Water Act.
In 1968, Hatch and Ott developed a mechanism for flame atomic absorption that allowed them to convert mercury ions in solution to ground state atoms and transfer the mercury to the spectrometer's optical channel for measurements. Thus was formed cold vapor atomic absorption.
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The majority of current CVAAS equipment is more sensitive, automated, smaller, quicker, and less costly than standard flame spectrometers with cold vapor devices added. CVAAS systems now have detection limits of a few parts per trillion, analyze units in about 1 minute, need very little human engagement, and take up just a few sq ft of bench space.
A peristaltic pump is often utilized with CVAAS equipment to deliver a sample and stannous chloride into such a gas–liquid separator, in which a stream of dry and pure gas is bubbled through the combination to liberate mercury vapor.
The mercury is then transferred via a drier or into an atomic absorbing medium using a carrier gas. Mercury absorbs light at 254 nm, according to its quantity in the sample.
Anodic Stripping Voltammetry (ASV)
One of the most frequently used methods, due to its advantages and low cost, is Anodic Stripping Voltammetry (ASV). Using a gold electrode or a gold film on a glassy carbon electrode, ASV is a technique in which a minimizing potential is implemented to the working electrode for a period of time.
This results in the accumulation of the reduction analyte species on its surface. Following that, an oxidizing potential sweep is delivered to the electrode, re-oxidizing the analyte to its distinctive oxidation potential. The cathodic current created is proportional to the quantity of analyte originally deposited on the electrode.
New Studies—Surface-Enhanced Raman Scattering (SERS)
Considering food hygiene and biorecognition element restrictions, a new study in the journal Food Chemistry concentrated on the improvement of a new approach for predicting mercury in fish and water samples utilizing a surface-enhanced Raman scattering (SERS) technique.
In comparison to the surface Plasmon resonance approach, SERS coupled with genetic algorithm-partial least squares forecasted with a high correlation coefficient.
The Importance of Mercury Determination
Mercury determination and speciation investigations in diverse environmental samples from across the globe provide important information about mercury concentrations, which is required for the implementation of regulatory measures to reduce mercury content in the environment.
Another key element is source prediction. Understanding the sources of mercury in the environment allows for simple regulation of its levels.
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References and Further Reading
Butcher, A., et al. (2019). Atomic Fluorescence Spectrometry. Encyclopedia of Analytical Science (Third Edition) pages 201-208. https://www.sciencedirect.com/science/article/pii/B9780124095472145317?via%3Dihub
Hassan, M., er al. (2021). Rapid detection of mercury in food via rhodamine 6G signal using surface-enhanced Raman scattering coupled multivariate calibration. Food Chemistry. https://www.sciencedirect.com/science/article/pii/S0308814621008505?via%3Dihub
Helaluddin, A., et al. (2016). Main Analytical Techniques Used for Elemental Analysis in Various Matrices. Tropical Journal of Pharmaceutical Research. https://www.ajol.info/index.php/tjpr/article/view/131557
Suvarapu, L., et al. (2013). Speciation and determination of mercury by various analytical techniques. Reviews in Analytical Chemistry. https://www.degruyter.com/document/doi/10.1515/revac-2013-0003/html