The
determination of ions in water is one of the most important analysis carried
out in the laboratory. Such analyses are required not only in the determination
of the purity of drinking water, but also as a check on the quality of the
ultra-pure water that is a very important component of modern laboratory
procedures.
Water analyses
are carried out by many different laboratories for a whole variety of
constituents for as many different reasons. Requirements include ensuring that
potable water meets current standards, checking that purification processes
have been successfully carried out, the environmental testing of lakes and
rivers and confirming the purity of purified water for different applications.
The measurement
of specific ionic constituents in water is used in two ways:
1)
providing direct determination of the speciation of various molecular or
valence forms of an element and
2)
providing elemental analyses either directly or after chemical conversion
into a measurable form.
The major
techniques used involve direct species determination by voltammetry,
potentiometry, photometry or chromatographic separation of the ions followed by
sequential measurement by a non-specific detector, such as conductivity. This
approach has been further extended by combining preparation methods with
selective elemental analysis techniques like AAS (Atomic Absorption Spectroscopy), ICP-OES (Inductively Coupled Plasma-Optical Emission
Spectrometry),
MS (Mass Spectrometry) and ICP-MS to provide
information on specific components.
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