Anions in trade effluents - Determination of Anions in Natural and Treated Waters - page 596

level to 0.45mg L −1 sulphate at the 50mg L −1 sulphate level.
Several common anions interfere including phosphate, fluoride, chromate, sulphide,
sulphite, and various oxy-acids of sulphur. Strongly coloured waters may interfere.
Compensations can be carried out for interference by phosphate chromate, sulphite and
oxy-acids of sulphur.

10.17.2 Spectrophotometric method
Pilipenko et al. [53] compared various methods for the determination of sulphate in mine
waters. These include a direct photometric method using octamine-u-amino-ol-
dicobaltisol, which gave reproducible results in the concentration range 0.05-10g L −1 .
Chelatometric methods using barium rhodizonate or acidic chrome blue indicators were
both rapid and convenient, although chloride concentrations of greater than 1g L −1
interfered with barium rhodizonate determinations. For desalinated water, turbidimetric
methods proved satisfactory.
In a standard UK method [54] for determining sulphate, the sulphate ions are
precipitated with 2-aminoperimidine and excess reagent is determined by
Spectrophotometric evaluation at 525nm or by ultraviolet spectroscopy at 305nm. This
method is capable of determining 10-120mg L −1 sulphate in amounts down to 4mg L −1 .
Standard deviations range from 1.99mg L −1 at the 50mg L −1 sulphate level to 2.28mg L −1
at the100mg L −1 sulphate level for the Spectrophotometric method and 17.3mg L −1 at the
50mg L −1 sulphate level to 1.33mg L −1 at the100mg L −1 sulphate level for the ultraviolet
spectroscopic method. There are no interferences from commonly occurring constituents
of trade effluents. An automated version of this procedure is described [54].

10.17.3 Atomic absorption spectrometry
Stock [55] applied atomic absorption spectrometry to an indirect method for determining
sulphate in pulp mill effluents. Sulphate was precipitated in barium sulphate and barium
subsequently determined by atomic absorption spectrometry in amounts down to 0.12µg
L −1 . Potassium chloride was added for optimal suppression of barium ionisation.
A standard UK method has been described [ 56] in which excess 1.666 ×10 −2 M barium
chloride is added to the sample. After the precipitation of barium sulphate excess barium
is determined by atomic absorption spectrometry using an air-acetylene flame. The range
of application is up to 175mg L −1 sulphate and the limit of detection approximately 5mg
L −1 .
Standard deviations range from 1.2mg L −1 sulphate at the 20mg L −1

sulphate level to

1.6mg L −1 sulphate at the 175mg L −1 sulphate level.
Calcium exerts a complex effect on this determination and levels above 200mg L −1
will cause marked interference. The levels of other anions cause no significant
interference.

10.17.4 Solid state membrane electrode
Srivastava and Jain [57] estimated sulphate in paper and tannery industry effluents using