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Chemical Analyses: Water: Metals
A wide range of analytical techniques are available for the detection
and quantification of metal species. These techniques can be classified
into two main groups, namely, spectroscopic and non-spectroscopic
techniques. Spectroscopic techniques include the following:
- Atomic Absorption Spectroscopy (AA)
- Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES)
- X-Ray Fluorescence Spectroscopy (XRF)
- Inductively Coupled Plasma Mass Spectrometry (ICP-MS)
- Neutron Activation Analysis (NAA)
Non-Spectroscopic methods include, but are not limited to, the
following:
- Ion Chromatography
- Titrimetric and Volumetric Methods
- Colorimetric Analysis
- Gravimetric Methods
- Specific Ion Electrode Methods
- Polarographic Techniques
Spectroscopic techniques are based on the premise that all elements
absorb and emit radiation at specific and characteristic wavelengths,
and the ability of a spectrometer to measure the absorption emission
produced. Therefore, elements can be identified by their characteristic
radiation and quantified by the spectroscopic technique.
Analyses of metals by non-spectroscopic methods usually involves
the separation of the species of interest from their matrix by basic
chemical procedures and final quantification by gravimetric, colorimetric,
conductivity, volumetric or other means.
Metal leaching into the environment is the principal concern of
acidic drainage. Metal analysis is one of the key parameters in
assessing the weathering characteristics of mine waste. Metal analyses
of water samples are applicable for:
- Predicting the quality of water that will contact mine waste;
and
- Determining the water quality of runoff, receiving surface water,
and groundwater after it has contacted mine waste
Metal analysis is only limited by selection of the appropriate
analytical method and proper sampling and preparation (MEND,
2001).
The most common method for analyzing metals in solution is plasma
emission spectroscopy (ICP-AES) and is described in section 3120
(Standard
Methods, 1998). ICP-AES is particularly useful when the concentration
of a large number of metals is required in samples. Another method
of analysis is inductively coupled plasma mass spectrometry (ICP-MS).
ICP-MS provides greater sensitivity for most elements compared to
ICP-AES; however, the cost is substantially higher and total dissolved
solids content must be kept low to avoid adverse instrument performance.
Samples may be analyzed for total metals or dissolved metals. For
total metal analysis, samples must be digested prior to analysis
to ensure the elements of interest are extracted from the sample.
For dissolved metal analysis, the sample is filtered through a 0.45
mm polycarbonate membrane or fluorocarbon filter. The filtrate is
acidified with purified nitric acid to a pH of <2 for preservation
of the metal species. If precipitates develop after filtration and
addition of acid, the filtered sample must be digested as for total
metals (MEND,
2001).
The following websites explain the different spectroscopy methods
for measuring metals in solution:
Atomic Absorption Spectroscopy:
ICP-AES:
XRF:
ICP-MS:
NAA:
Chemical
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