Evaluation of analytical methodologies for fluoride determination and speciation of fluoro complexes of aluminium.

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. Coetze