Abstract:
Free fluoride ions and the metal complexes of fluoride ions significantly affect the quality of
drinking water. It shows both beneficial and detrimental effects to the human health. Several
techniques based on Ion Selective Electrode (ISE), ion chromatography and colorimetry has been
developed to assess the fluoride levels in drinking water. However, all those above methods
require sophisticated instruments, which must be operated inside laboratories. The objective of
this project is to develop a fluoride sensitive strip that is cost effective and can be used in the
field. The SPADNS method is a well-accepted method for fluoride analysis. Reference to this
method, the fluoride sensitive strip is designed. Whatman 41 ashless filter paper was modified
with titanium butoxide via a sol-gel process. The red color SPADNS-Zr dye was grafted on to
the titania layer of the modified strip. The resultant dye sensitized strip is dark blue. The
modified strip shows rapid and obvious color change from dark blue to pale pink in the presence
of fluoride ions and the original color (red) of the dye appear in the solution. The strips were
tested with fluoride concentrations ranging from 1-10 ppm. The tests were triplicated.
Approximately one (01) hour is required for the color change in 1 ppm. This suggests that the
concentration of fluoride ions is the rate limiting factor for the reaction. The next step of the
project is to optimize the strip to detect concentrations 1 ppm or below. There are no
interferences to the method by acids (pH 3-7), sulphates (20 ppm) and other halogen ions such as
chlorides (20 ppm) and bromides (20 ppm). In addition, the interferences from hydroxide,
phosphate and bicarbonate ions have to be analyzed. This is an ongoing research. The results of
the initial stages are very promising thus this can be developed further to use in household water
filters by enhancing the sensitivity.
