Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 291

Source: Reproduced with permission from Springer Verlag [722]

of sulphate. Chloride, nitrate and phosphate do not interfere below concentrations of
2.10 −2 , 3.10 −2 and 1.5.10 −3 mol L −1 respectively.
McKeller et al. [724] determined sulphate in non saline water indirectly by
spectrophotometric titration of excess barium ions with ethylene-diaminetetraacetate.
Parts per million of sulphate could be determined with a precision of ±3%.

2.93.1.5 Automated titration procedures

Fishmann and Pascoe [725] studied the application of various automated titrimetric
procedures to the determination of sulphate in non saline waters.
Henrikksen and Paulsen [720] have described an automated procedure for the
determination of sulphate in natural salt water which involves precipitation of sulphate
with barium perchlorate dissolved in isopropanol, and determination of excess barium by
its complex with thorin. Cations are removed by an acidic cation exchange resin. The
precision of the method is ±0.05mg L −1 of sulphate over the range 0-8mg L −1 .
All cations interfere in this method. The following anions do not interfere below the
concentrations (mg L −1 ) given in parenthesis: H 3 BO 3 (1000, acetate (1000), ClO 4 − (60),
NO 3 − (60), Cl − (25), F − (10), HCN (1), PO 4 3− (1), HS − (1). The interference from
cations is eliminated by incorporating a strong acidic cation exchange column in the
analytical system.
Airey et al. [414] have described a method for removing sulphide prior to the
determination of sulphate anions in anoxic estuarine waters. Mercury(II) chloride,was
used to precipitate free sulphide from samples of anoxic water. The sulphide-free
supernatant was used to estimate sulphide by measuring the concentration of unreacted
mercury(II), as well as to determine sulphate by a spectrophotometric method in which
sulphide interferes. Sulphide concentrations in the range 0.5-180,000µg L −1 sulphur

could be measured, while the lower limits for sulphate was 0.024µg L −1 .

2.93.2 Spectrophotometric methods

Bjarnborg and Korhonen [718] tested manual spectrophotometric methods for sulphate
using thorin and thymol blue and found that the former had a very narrow working range,
and the latter was too sensitive to interference from humic substances. When a titrimetric
method based on thorin was tested, the technique was acceptable even with highly
coloured waters. When interference by humic substances was monitored, the titrimetric
and automatic calorimetric thorin methods performed best, followed by a nephelonietric
method.
Toei et al. [716] carried out a spectrophotometric determination of micro amounts of
sulphate in river waters using 6-(p-acetylphenylazol)-2-aminoperimadine.
Honjo and Hayashi [726] described precipitation and indirect spectrophotometric
methods for the determination of sulphate in fresh water with lead nitrate and
tetraphenylporphine trisulphonic acid. The method is based on the formation of insoluble