Anions in potable waters - Determination of Anions in Natural and Treated Waters - page 496

iodide determination (B). Load the sample tray with a set of working standards followed
by 20 samples interspersed with a working standard every fifth sample. Complete the
series with another set of working standards and run at a rate of 20 per h.
If deposits of iron(III) thiocyanate occur, these may be removed by running two
sample cups of sodium oxalate reagent through the system at the end of a run.
Calculation
Plot a calibration graph of the mean standard peak heights against their respective iodine
concentrations. The iodine concentration of a sample is obtained by comparing its peak
height with the calibration graph. Multiply the result by 1.01 to compensate for the
addition of potassium carbonate.
The effects of ions commonly occurring in drinking waters that could cause possible
interference were tested and the results, representing a mean of three determinations, are
shown in Table 7.9. The results show that interferences do not present any major
problems in the analysis of drinking waters for either total inorganic iodide or free iodide.
Table 7.10 shows a comparison of total iodine determinations obtained by the above
automated method of Moxon [38] and an automated method which is based on the
method of Dubravcic (cerium(IV) sulphate-arsenious acid) modified for an AutoAnalyzer
system. The mean recovery of iodide by the total inorganic iodine method are 100± 5.4%
and 102±7.5% respectively. The results show reasonable agreement with those of the
automated method.
7.16.2 Polarography
The application of this technique is discussed under multianion analysis in section
14.10.2.1.
7.16.3 High performance liquid chromatography
Savov et al. [39] determined iodide, chloride, bromide, chlorate, bromate and iodate in
potable water by high performance liquid chromatography with an inductively coupled
argon plasma mass spectrometric detector.
The application of this technique is discussed under multianion analysis in section
13.1.2.1.
7.16.4 Gas chromatography
Bachmann and Matusca [15] have described a gas chromatographic method involving the
formation of halogenated derivatives of cyclohexanol for the determination of iodide,
chloride and bromide in potable water.
Table 7.9 Effect of added ions on the determination of (A) total inorganic iodine
concentration and (B) free iodide concentration in a 4µg L −1 standard iodide
solution