Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 180

2.50.2 Spectrophotometric methods
Weil et al. [353] have described a rapid quantitative ultramicro method for the
determination of iodide in concentrations of 1-100µg L −1 based on the catalytic
acceleration of the reaction between chloramine-T and N,N ′ - tetramethyldiamino-
diphenylmethane, and the photometric measurement of the extinction of the reaction
product at 600nm. Iodate can also be determined after reduction with zinc.
Kinetic spectrophotometric methods based on the catalytic effect of µg L −1 quantities
of iodide ions in water on various chemical reactions have been described. These include
reactions of cerium(IV) with arsenious acid [354], 3,3'dimethyl naphthidine with
hydrogen peroxide [355] and the oxidation of Cadion IRE A by potassium persulphate
[356]. The reaction of Malachite Green, Brilliant Green and Basic Turquoise Blue with
iodide ions has been used as the basis of a method for the determination of microgram
quantities of iodide [357].
Novak and Slama [358] determined iodide in the presence of bromide and chloride by
adding to the sample potassium bromide to convert the iodide to iodine, followed by
palladous chloride which is converted by iodine to palladous iodide. The latter was
estimated spectrophotometrically at 465nm. Using this method from 2 to 8m mole iodide
can be determined in the presence of 1000-fold excesses of chloride or bromide.
Koh et al. [359] reported on a spectrophotometric method involving solvent extraction
with methylene blue for determining iodide at the nanomolar level in non saline waters.
The method had a relative standard deviation of 0.87% at the 1.5×10 −6 M level.
C handrawanski and Patel [360] used Brilliant Green to complex I 2 C1 − in a method for
the determination of 4µg L −1 iodide in non saline waters.
2.50.3 Spectrofluorometric methods
There are few fluorometric methods for the determination of iodide. None of them is
specific for iodide but they have high sensitivity, especially the method using cerium(IV)
[361] (6.25µg L −1 ). Also 2,7-di(acetoxymercuri) fluorescein [263] is a sensitive
fluorometric reagent for iodide (35-400µg L −1 ) but the ∆λ of the Stokes shift is not
favourable and the method cannot be used with filter fluorometers.
A special substitution method for the determination of iodide is based on its inhibitory
action on the fluorescence of uranyl acetate [362].
2.50.4 Chemiluminescence method
Liu et al. [363] have reported a method for determining iodide in non saline waters
utilising the suppression of the chemiluminescence of the luminol hydrogen peroxide—
gold system. This method is reported to have a detection limit of 5×10 −11 g of iodide
mL −1 and a relative standard deviation of 2.1% at 4×10 −9 g of iodide mL −1 .
2.50.5 Flow injection analysis
The application of this technique is discussed under multianion analysis in section