Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 315

sulphite L −1 is reported, and ways to avoid the only two relevant interferences, ferric iron
and formaldehyde, are discussed.
2.95.3 Spectrofluorometric methods
A method for the determination of sulphur dioxide as sulphite by reaction with
formaldehyde and 5-aminofluorescein has been proposed [848]. The simulated samples
of trapped sulphur dioxide were made by dioxide dissolution of Na 2 S 2 O 5 in a solution
with Na 2 HgCl 4 and later reaction with formaldehyde. The aldehyde-bisulphite complex
formed oxidises 5-aminofluorescin to a non-fluorescent product.
The probable result of the Schiff reaction is the formation of a quinoid structure. This
structure shifts the double bond on the central (pyran) carbon atom so that the quinone in
the upper ring is no longer the dominant structure, and the resulting compound is no
longer fluorescent.
2.95.4 Chemiluminescence method
Al-Tamrah et al. [849] have described a flow injection chemiluminescence method for
the determination of sulphite in water.
Takeuchi [850] describes a technique for determining race amounts of sulphite in non
saline waters based upon the chemiluminescent oxidation of nitrite. Various oxidising
agents were evaluated and the special advantages of ferric sulphate are discussed as well
as specially designed reaction cells. A detection limit of 0.08ng of sulphate L −1 was
reported.
2.95.5 Continuous flow analysis
Continuous flow chemiluminescence analysis has been applied to the determination of
sulphite and sulphur dioxide in water [851].
2.95.6 Flow injection analysis
Sonne and Dasgupta [774] carried out a simultaneous photometric flow injection analysis
determination of sulphites, sulphate, sulphide, polysulphide and thiosulphate.
Workers at Tecator Ltd UK [852] have described a method for the determination of
sulphite based on the injection of the aqueous sample into a carrier stream which is