Anions in trade effluents - Determination of Anions in Natural and Treated Waters - page 591

10.8 Fluoride
10.8.1 Ion chromatography
The application of this technique is discussed under multianion analysis in sections
10.22.1 and 12.8.1.
10.8.2 High performance liquid chromatography
Hannah [33] has described a high performance liquid chromatographic anion exclusion
method for the determination of fluorides in complex trade effluents. Pharmaceutical
industrial effluents were examined for fluoride using an Ion-100 anion-exchange column
coupled with a GA-100 guard column. Organics were removed from the samples at pH
8.2-8.3 by passing through disposable G18 extraction columns. Conductivity detection
allowed determination of fluoride at low mg L −1 levels in the presence of high
concentrations of chloride and sulphate through an ion exclusion mechanism in the
polymeric liquid chromatographic column. The limit of detection was 0.2mg L −1 fluoride
L −1 with a working linear dynamic range of 0.2-100mg L −1 .
10.9 Iodide
10.9.1 Ion sensing optrodes
As the field of fibre optic sensors grows, interest in the development of indirect optrodes
is increasing. The ability to detect chemical species whose spectroscopic properties
cannot be directly probed (eg metal and halide ions) in a remote, continuous manner is
highly desirable. Several industrial processes, from plating baths to bromine-producing
process streams, would benefit greatly from the implementation of halide-ion optrodes. In
these applications, the ability to monitor halide-ion concentrations would result in tighter
control and increased productivity.
Because the spectroscopic properties of iodide ion cannot be directly probed with
wavelengths compatible with optical fibres, indirect approaches must be adopted.
Wyatt et al. [34] carried out a characterisation and comparison of three fibre optic
sensors for the determination of iodide based on dynamic fluorescence quenching of
rhodamine eg their results indicate that the local environment of the rhodamine 6G
molecules dictates strongly the sensitivity of a given optrode system. For example, the
new sensor's sensitivity clearly parallels the fluorophore's accessibility by iodide ion.
10.9.2 Ion chromatography
The application of this technique is discussed under multianion analysis in section
10.22.1.