Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 176

2.48 Hypophosphite
2.48.1 Ion chromatography
The application of this technique is discussed under multianion analysis in sections 12.2.4
and 12.2.5.
2.49 Iodate
2.49.1 Spectrophotometric methods
Truesdale and Smith [343] described an automated method for the determination of
iodate on iodide in river water. The method is based on catalytic spectrophotometry.
Butler and Gershey [344] have described an automated method for the determination of
iodate, iodide, iodine and bromide in river waters based on automated catalytic
spectrophotometry. The method involves both the determination of total iodine in
concentrations up to 5µg L −1 and the separate determination of iodide and iodate. The
second method was a two-step procedure in which total inorganic iodide was determined
using the first method, then iodide extracted with tetraphenyl ammonium hydroxide, after
which the first determination was repeated, the iodide being obtained by difference.
Jones et al. [345] give details of a procedure for the determination of traces of iodate,
iodide and total iodine in fresh waters, based on catalytic determination of iodide, using
the reaction between ammonium cerium sulphate and arsenious acid; iodate is determined
by the same method after extraction of iodide-iodine into chloroform as an ion pair with
the tetraphenylarsonium cation. Iodate can be determined in amounts down to 1µg L −1
with a resolution of ±0.1µg L −1 (95% confidence limits).
Apparatus
Automatic analysis was performed with a Technicon AutoAnalyzer 1 Instrument.
Extractions with chloroform were conducted in 100 ml separating funnels fitted with
stoppers and taps made of PTFE. An MSE Hi-Spin 21 centrifuge with glass centrifuge
tubes was used to aid separation of the chloroform and aqueous phases. After extraction
of iodide an aliquot of each aqueous phase was placed in a 2ml glass sample cup used
with the AntoAnalyzer; the chloroform present in the aqueous phase dissolves the
standard polystyrene cups.
The AutoAnalyzer manifold system used in these analyses is shown in Fig 2.21.
Determination of total iodide
Assemble the AutoAnalyzer manifold according to the design given in Fig 2.21. While
aspirating only the arsenic reagent and deionised distilled water, set 0 and 100%
transmission on the recorder. Introduce the cerium (IV) reagent and establish the base
line between 31 and 35% transmission (absorbance 0.45-0.5) using a temperature of
approximately 34°C. When the baseline has been settled within this transmission range,