Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 304

detection. Again, ion chromatography/mass spectrometry readily produced the molecular
weights of these compounds while ion chromatography/mass spectro-metry/mass
spectrometry provided some structural information.
The application of this technique is discussed under multianion analysis in sections
12.2.1, 12.2.4, 12.2.5 and 12.2.6.
2.93.12 High performance liquid chromatography
The application of this technique is discussed under multianion analysis in sections
13.1.1.1 and 13.1.1.4.
2.93.13 Ion exclusion chromatography
The application of this technique is discussed under multianion analysis in section
13.2.1.3.
2.93.14 Ion exchange chromatography
Stainton [797] has described an automated method for the determination of sulphate and
chloride in non saline waters. An ion exchange resin is used to convert the sulphates and
chlorides to their free acids. Detection is achieved by electrical conductance. The use of
silver-saturated cation exchange resin to precipitate chloride permits distinction between
chloride and sulphate. High levels of nitrate, orthophosphate and fluoride give positive
interference for sulphate; bromide and iodide similarly interfere with chloride estimates.
2.93.15 Miscellaneous
A contribution to the classical gravimetric barium precipitation method for the
determination of sulphate is that of Ferns and Torrades [798]. These workers showed that
the detection limit of the method could be extended below the usually accepted levels.
They achieved a detection limit of 1mg L −1 using 200ml water samples. It was essential
to use a large excess of barium chloride to achieve these detection limits.
Meehan and Tariq [799] determined sulphate in the range 0.05 to 1.0mg L −1 by
infrared spectroscopy by the KBr-pellet technique. Spectra were scanned from 1000 to
400cm −1 and the extinction at 619cm −1 was measured. Nitrate and nitrite do not absorb
significantly between 800 and 600cm −1 , and sulphate could be determined with a
coefficient of variation of 5% in the presence of 400- and 60-fold molar excesses of
nitrate and nitrite respectively
Five different methods have been compared for the determination of sulphate in river
waters [800]. These are a gravimetric method involving barium sulphate precipitation,
two titrimetric methods involving either indirect titrimetry with EDTA or direct barium
titrimetry, a method employing indirect atomic absorption spectrometry, and a method
using excess 2-aimnoperimidine to precipitate sulphate, with two possible variants for
estimation of the excess reagent. Details of the range of application, possible
interferences and sensitivity of the method are given in each case.