Abstract
The regulations for water fluoridation of South African municipal waters up to the
optimum fluoride (F-) concentration of 0.7 mg/L, (Government Gazette, 2001) have been
legislated. Fluoridation processes need accurate analytical methodology for the
determination of F- , because F- has a narrow margin of safety between beneficial and
toxic levels. In this work the analytical chemistry of F- was investigated comprehensively
and guidelines compiled for the accurate determination of low level F- (between 0.05 to 1
mg/L) in aqueous systems.
The first part of this study focused on method validation and the evaluation of the ISE
and IC methods. The analytical methodologies were applied to the analysis of natural
waters such as river water (Vaal and Crocodile Rivers), dam water (Hartbeespoort Dam),
and drinking water (Johannesburg municipal tap water) to evaluate the performance of
the chosen methods in the analysis of real samples and to assess the effect of the sample
matrix on the accuracy of F- determinations. An inter-laboratory study in collaboration
with the South African Bureau of Standard (SABS) was carried out to evaluate the
proficiency of South African analytical laboratories and to check the proficiency of the
procedures developed in this study.
In the second part of this study, the development of an IC-ICP-OES and IC-ICP-MS
method was investigated for the speciation of fluoro-aluminium complexes. This work
was motivated by the fact that the water fluoridation could lead to remobilisation of scale
from municipal pipes. Scale may contain aluminium hydroxide or oxide precipitates that
can dissolve as fluoroaluminates or hydroxofluoro aluminates. The speciation of cationic
fluoro-aluminates, free Al3+, AlF2+ and, AlF2
+ together with the neutral AlF3
0, was based
on cation exchange Ion chromatography (IC) coupled with Inductively Coupled Plasma-
Optical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma Mass
spectroscopy (ICP-MS).
Prof. P.P. Coetzee