Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 305

Krug et al. [748] have used continuous flow injection turbidimetry for the rapid
determination of sulphate in non saline waters.
Bonda et al. [747] described a column turbidimetric method for determin-ing sulphate.
The method uses solid barium chloride in crystals of 0.3-0.6mm diameter. The method is
precise and reproducibility is good. The advantage of the method is the stability of the
reagents and the speed, economy and simplicity of performance. Photometric
determination is carried out over the range 460-540nm and the method may be used to
determine sulphate in the range 30-150mg L −1 with a correlation coefficient of 0.99.
Titration with 0.01M lead acetate in 1:1 acetone: water medium has been used [875] to
determine sulphate in the range 0-50µg. The extinction is measured at 430nm after
20min standing.
Cationic, anionic and non-ionic surfactants, also polyphosphates and nitriloacetic acid
are without interference in barium and lead based turbidimetric methods for the
determination of sulphate.
Cronan [801] has discussed the determination of sulphate in organically coloured water
samples.
A piezoelectric crystal has been used to determine sulphate in non saline waters at
concentrations of 0.5-10mg L −1 [802]. The sulphate was precipitated as barium sulphate
on the crystal, and the oscillation frequency of the crystal was inversely proportional to
the mass of precipitate. Barium sulphate was removed from the crystal with EDTA.
2.94 Sulphide
2.94.1 Titration methods
Wronski [803] determined µg L −1 levels of sulphide in non saline waters by
thiomercurimetric titration. The procedure consists of separation of hydrogen sulphide as
bis (triethyl-lead) sulphide by precipitation with triethyl-lead chloride in hexanol
followed either by direct titration with o-hydroxymercuribenzoic acid in the presence of
dithizone or by fluorometric titration in hexanol-ethanol with tetramercurated fluorescein
(excitation at 520nm). The fluorometric procedure is applicable to concentrations of
hydrogen sulphide of greater than 0.01 µg L −1 and the direct titration which determines
thiols and sulphide is applicable to concentrations above 2µg L −1 . For the direct titration,
thiols are removed with acrylonitrile and hydrogen cyanide with formaldehyde. Thiols,
cyanide, xanthates and dithiocarbamates do not affect the end-point of the fluorometric
titration. Neither method is affected by the common ions present in non saline water
samples.
Dyrssen and Wedborg [804] determined sulphide (polysulphides, thiosulphates,
sulphites and thiols interfere) in non saline water by titration with mercury(II) solutions.
The stoichiometry of the titrations were calculated using selected values of relevant
stability constants. Mathematical functions for the evaluation of the titrimetric
equivalence points were derived. The presence of halide ions interfered only in the
titration of sulphite by the formation of halide complexes.
Sulphide has been determined [805] in non saline water by potentiometric or visual