Anions in high purity, boiler feed and nuclear reactor cooling waters - Determination of Anions in Natural and Treated Waters - page 606

[3].
11.1.4.2 Ion chromatography
The application of this technique is discussed under multianion analysis in section 12.9.1.
11.1.5 Silicate
11.1.5.1 Spectrophotometric method
Spectrophotometric methods have been described for the determination of traces of
silicate in high pressure boiler feed water [4,5], and deionised water [6]. Silicomolybdate
procedures employing 4-amino-3-hydroxynaphthalene-1-sulphonic acid have been
employed [7,8]. Spectrophotometric evaluation of the reduced complex is carried out at
805-810nm in these methods.
It is essential in order to avoid silica contamination, to use precleaned polyethylene
sample bottles and apparatus. Ramachandran and Gupta [6] performed studies on the
effects of different reducing agents on silicate determination by the molybdenum blue
method. Best results were obtained using ascorbic acid and antimony. The antimony did
not participate in the complex but enhanced its absorbance. The recommended procedure
is described. It was relatively rapid and sensitive. Beer's Law was obeyed for silicate
concentrations of 20-1000µg L −1 .
Pilipenko et al. [9] compared Spectrophotometric and chemiluminescent methods of
determining silicate in deionised water. They studied different reducing agents in the
molybdenum blue Spectrophotometric method, viz . tungstosilicic acid, stannous chloride,
1-amino-2-naphthol-sulphonic acid and mixtures of metol and sodium sulphite. They also
studied the extraction of the blue tungstosilicic acid with crystal violet and methylene
blue. The chemiluminescent method was based on the oxidation of luminol by
molybdosilicic acid in alkaline medium. These workers concluded that the best method,
from the points of view of detection limit, reproducibility, simplicity and rapidity, was
one based on the reduction of molybdosilicic acid by 1-amino-2-naphthol-4-sulphonic
acid.
11.2 Boiler feed waters
11.2.1 Chloride
It is generally accepted that the presence of chloride in the steam-water circuit of power
stations can be associated with corrosive conditions within the boiler, consequently
chloride levels have to be controlled. The concentration of chloride treated in boiler
waters varies with the design of the boiler and the chemical treatment accorded to the
boiler water, but in every instance it is essential that any ingress of chloride is detected so
that remedial action can be taken. In order to identify the source of the chloride, it is
necessary to monitor plant streams, eg feed water or the effluent from a water treatment