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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