Monitoring of fluoride in the public water supply using electrometric or colorimetric analyses

Abstract

The surveillance of the concentration of fluoride in the public water supply aims to ensure the balance between the benefits (carie prevention) and risk (dental fluorosis) of water fluoridation programs. The aim of this study was to check the accuracy of two analytical methods for monitoring the concentration of fluoride in the public water supply of a Brazilian city. The STROBE checklist was used to aid the conduction of this study and report the results. It was an analytical, observational, and prospective study using the water supply of Uberlândia, MG, Brazil. We collected 126 water samples at 21 sites for six consecutive months and analyzed them using the fluoride ion selective electrode (F-ISE) method and colorimetry with SPADNS. The statistical analysis was performed descriptively and then the ANOVA and Student t-test for paired samples were applied. The results showed that the F-ISE method had a lower coefficient of variation (12.3%) than the SPADNS method (57.4%). There was no significant variation of the fluoride concentration in the water through the supply network evaluated either by F-ISE as SPADNS. We concluded that the electrometric method should be the first choice for use by laboratories that monitor fluoride concentration in the public supply water.

Comparison between the ion-specific electrode and SPADNS methods for analysis of fluoride concentration in the water supply

“…In our study, the two techniques had a strongly positive correlation (r= 0.91), which may demonstrate the potential for using the colorimetric technique, when calibration is carried out with the electrometric technique. Importantly, in our study, the analyses were carried out by different institutions in a blind manner, in contrast to other studies conducted in the same laboratory [15][16][17] . In addition, one of these studies used a SPADNS kit of analysis, which can present limited results, compared to a standardized methodology of analysis.…”

“…Nevertheless, according to Brossok et al 16 (1987), Weinberger et al 17 (1989), Edelstein et al 18 (1992), and Lins-Candeiro et al 15 (2020), the colorimetric technique tends to give a higher value than the electrometric one, overestimating F concentration compared to the ISE technique. On the other hand, in Motter's study 14 , the colorimetric method resulted in a lower value than the electrometric technique.…”

“…ISE analysis, in turn, is based on the direct measurement of free F ion, present in the sample, using a specific electrode, and presenting high selectivity, better linearity, and less susceptibility to interferents 13 . Due to its higher precision and accuracy, ISE analysis is preferred over the SPADNS method 14,15 .…”

“…In addition, contradictory results have been found. While some publications suggest that the colorimetric method overestimates fluoride concentration compared to the electrode method [15][16][17][18] , Motter et al 14 (2011) reported opposite results. The reasons can be the use of non-duplicate water samples or analytical problems of using not well standardized SPADNS method 15 , suggesting further studies are necessary to elucidate this controversy.…”