Introduction - Determination of Anions in Natural and Treated Waters - page 34

Establishment at Harwell, or the Joint Manchester-Liverpool University Reactor located
at Risley.
The technique's extreme sensitivity makes it suitable for use when a referee analysis is
required on a material which has become a standard for checking out other methods.
Another advantage of the technique is that a foreknowledge of the elements present is not
essential. It can be used to indicate the presence and concentration of entirely unexpected
elements, even when present at very low concentrations.
In neutron activation analysis, the sample in a suitable container, often a pure
polyethylene tube, is bombarded with slow neutrons for a fixed time together with
standards. Transmutations convert analyte elements into radioactive elements, which are
either different elements or isotopes of the original analyte.
After removal from the reactor the product is subject to various counting techniques
and various forms of spectrometry to identify the elements present and their
concentration.
1.1.10 Photo activation analysis
The application of this technique is limited to the determination of fluoride in seawater.
1.1.11 Isotope dilution analysis
This technique has very limited applications in the determination of anions, viz selenate,
selenite, chloride and iodide in non saline water and bromide in aqueous precipitation.
1.1.12 Enzymic assay
Again there are very few applications, viz sulphate, nitrate, phosphate, chromate,
dichromate and free cyanide in non saline waters.
1.1.13 Chromatographic methods
The identification and determination of traces of organic and organic substances in water
samples is a subject that has made tremendous advances in recent years. The demands
made on water chemists in terms of specificity and sensitivity in carrying out these
analyses have become greater and greater with the increasing realisation that organic
substances from industrial sources are permeating the ecosystem and identification and
measurements of minute traces of these are required in potable, river and ground waters
and even in rain water. At the same time, measurements in industrial effluent outfalls are
necessary in order to control the rate of release of these substances.
For the more volatile components of water samples, ie those with boiling points up to
about 250°C, gas chromatography has been a favoured technique for several decades.
However, with the realisation that retention time measurements alone are insufficient to
identify organics there has been an increasing move in recent years to connect a gas
chromatograph to a mass spectrometer in order to provide unequivocal identifications.
Element-specific detectors are another recent development.