The determination of fluoride in water in the presence of organic acids and iron using a fluoride-selective electrode |
| |
Authors: | Keith Nichoison Christophe Pasquier |
| |
Institution: | (1) School of Applied Sciences, The Robert Gordon University, AB1 1HG Aberdeen, Scotland, Scotland;(2) Departement Mesures Physiques, IUT Creteil, Universite Paris XII, France |
| |
Abstract: | Surface waters in Scotland, notably from upland catchment areas, are commonly enriched in iron and organic acids. This study
investigated the impact of these species on the direct potentiometric determination of fluoride using a fluoride-selective
electrode. As the electrode technique is commonly used to monitor the fluoride content of potable waters, it is important
that these effects are evaluated if such waters are to be fluoridated.
The determination method used was that defined by Nicholson (1983) and Nicholson and Duff (1981) to minimise errors. This
employs the TISAB III-TAC buffer system with the following composition (in 1L): 58.0 g sodium chloride, 57.0 mL glacial acetic
acid, 4.0 g CDTA, 243.0 g tri-ammonium citrate adjusted to pH 5.4 with 10 M sodium hydroxide. Experimental solutions of fluoride
with organic acid or iron were prepared, and the effect on fluoride concentration determined for each combination. Concentrations
used: fluoride: 0.1, 1.0 mg L−1; humic acid: 5, 10, 100, 1000, 10,000 mg L−1; oxalic acid: 5, 10, 100, 1000, 10,000 mg L−1; iron(III): 1, 10, 100, 500 mg L−1;
Humic acid (HA) concentrations had no impact on the determination of fluoride at the 1.0 mg L−1 level. However, with 0.1 mg L−1; F−, an increase in the apparent fluoride concentration was observed when HA > 1,000 mg L−1; this increased with increasing HA content to a maximum of ∼600%. Oxalic acid (OA) generally had no impact on the fluoride
determinations at the 1.0 mg L−1; level, but at an OA concentration of 10,000 mg L−1; fluoride concentrations were reduced by ∼50%. At 0.1 mg L−1 F−, increasing OA concentrations produce a steady increase in the fluoride concentration of up to 200% with 1,000 mg L−1; OA, greater OA contents produce a fall in the fluoride content. Iron had no effect on the fluoride determinations at both
the 0.1 and 1.0 mg L−1 levels.
The causes of the apparent increases in fluoride concentration have not been determined, although fluoride contamination by
the reagents has been ruled-out. However, the results demonstrate that the defined method and buffer system is suitable for
the determination of fluoride in the presence of iron and organic acids at naturally occurring levels, and that fluoride will
not be masked from detection. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|