Focus on Mercury - Environmental Analysis
Mercury Determination in Differing Environmental Sample Types via Cold Vapour Generation Atomic Absorption and Atomic Fluorescence Spectroscopy
The measurement of mercury from ultra-trace and trace concentrations up to levels considered abundant, in a gamut of environmental sample types, is essential in the generation of data for environmental monitoring. Such data can be used to establish the magnitude of release, or emission, of mercury and subsequently its spread from source into the wider physical environment - the air, waters, soils and plant life for example. Mercury is becoming more prevalent in the environment and the magnitude of its presence needs to be observed and reduced. Therefore its measurement is becoming more important.
In 2013 it is intended that a global legal instrument is to be signed and established with the aim of reducing the release and emission of mercury...
A number of analytical techniques are available for the measurement of mercury with varying degrees of capability as well as limitation within the spectrum of sample types. The combination of cold vapour generation and either atomic absorption spectroscopy or atomic fluorescence spectroscopy allows the measurement of mercury from sub parts-per-trillion concentrations up to levels of hundreds of parts-per-billion. Such a measurement range allows the study of mercury and its movement and/or accumulation
in environmental samples of all types as well as sample types of any other field.
Author Details: Peter Winship,
CETAC Technologies 14306 Industrial Road, Omaha, Nebraska, 68144, USA
Tel: +1 (402) 733 2829
Email:
pwinship@cetac.com Web:
www.cetac.com/mercury_analyzers
It is recognised that the release and emission of mercury into the environment, and subsequently its movement and accumulation, correlates with industrialisation and population growth. Therefore, without measures to control such release and emission, an obvious conclusion may be drawn in that overall human exposure to mercury has increased and will continue to do so. Currently there is legislation and regulation in place, under the remit of such bodies as the Environmental Protection Agency (EPA) and the United States Food and Drug Administration (FDA), to limit human exposure to mercury and as part of such there are maximum allowable concentrations in foodstuffs, for example. In 2013 it is intended that a global legal instrument is to be signed and established with the aim of reducing the release and emission of mercury from, but not limited to, industrial processes (such as mining, deforestation, waste incineration and the burning of fossil fuels for example) and products that may contain mercury (such as dental amalgams, electrical applications, laboratory and medical instrumentation and batteries etc…). The key to the reduction of presence of any contaminant in the environment is the ability to perform representative and accurate measurement. In the case of mercury, for many analytical techniques, measurement can be difficult due to its physical and chemical properties. In inductively coupled plasma based instrumentation, for example, cross contamination and the occurrence of ‘memory effects’ are particularly problematic at the sample introduction apparatus.
Due to the nature of cold vapour generation, it is relatively straight forward to extract the analyte of interest, in this case elemental mercury,
from a sample matrix for the purpose of measurement via atomic absorption spectroscopy or atomic fluorescence spectroscopy. Such a combination of extraction and measurement allows the accurate and precise determination of mercury at concentrations as low as 0.05 parts- per-trillion (ppt – e.g. ng L-1
or ng Kg-1 parts-per-billion (ppb – e.g. µg L-1 or µg Kg-1
) up to levels as high as 400 ). Such a measurement
range allows the ability to study the release, or emission, of mercury and its movement and accumulation in the environment as well as movement into the food chain at different levels. In this article we highlight the advantages and some applications of cold vapour atomic absorption and atomic fluorescence spectroscopy in the field of environmental analysis and monitoring.
Instrumentation and Principles of Operation
Cold vapour generation based atomic absorption spectroscopy (CVAAS) and atomic fluorescence spectroscopy (CVAFS) instruments, such as the CETAC Technologies Quicktrace™ M-7600 and M- 8000 systems (as shown in Figures 1 and 2), operate on the principle of extracting mercury from a sample in vapourous elemental form following the reduction of inorganic mercury with a reducing agent such as stannous chloride in a gas-liquid separator (GLS). Elemental mercury vapour is carried away via a gas flow such as argon or nitrogen from the sample matrix, dried in a moisture trap or similar and detected. In the case of atomic fluorescence spectroscopy mercury may also be captured for a period of time on a gold trap prior to analysis. This has the added benefit of analyte pre-concentration which is particularly useful in samples
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Figure 1: The CETAC Technologies Quicktrace™ M-7600 Cold Vapour Atomic Absorption Spectrometer Mercury Analyser.
Figure 2: The CETAC Technologies Quicktrace™ Cold Vapour Atomic Fluorescence Spectrometer Mercury Analyser.
www.envirotech-online.com
IET November / December 2012
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