Potentiometric Determination of Free Fluoride Content in Wines from Dalmatia Region (Croatia)—A Comparative Study of Direct Potentiometry and Standard Addition Method

Abstract

The aim of this study was to investigate 30 different types of Dalmatian wines as a potential source of fluoride. A fluoride ion selective electrode was used to measure the fluoride concentration in each sample. The direct potentiometric method and the standard addition method were evaluated, the latter being suggested as more accurate and precise. Measurements were performed in two buffers, acetate buffer and total ionic strength adjustment buffer (TISAB), to compare their influence on fluoride determination. The obtained results show that TISAB is a better choice than acetate buffer as a medium for fluoride determination. According to the proposed method, mass concentrations of fluoride of 0.19 and 0.18 mg/L were found in the studied red and white wines, with standard deviations of 0.04 and 0.03 mg/L, respectively. All determined fluorine levels in the tested wines were within the recommended limits and do not pose a risk to human health. No significant difference was found between the fluorine content in white and red wines, but there was a difference depending on the place of origin of the wine. The measured pH values for all the wines studied (except one sample) are very similar and show no significant correlation with the fluoride content.

Quantitative Determination of Fluoride Mass Concentration in Beers Produced in Croatia Using the Standard Addition Method in Potentiometry

“…Considering the very small relative standard deviations of fluoride content between six identical measurements for each sample with the generally low fluoride content (4.2% on average), the results of this work are an additional confirmation of the accuracy of the proposed new model of the standard addition method in potentiometry that has been recently published and applied [2,17,18]. The statements of various groups of authors that the potentiometric determination of fluoride in TISAB solution is recommendable [2,19,[23][24][25] were also confirmed with regard to the aforementioned fact that there were negligible standard deviations of the results of fluoride content in the same samples.…”

“…The mass concentration of fluoride in the studied beers was determined according to the recently proposed and applied standard addition method in potentiometry [2,17,18]. The expression c s ×V s V A was placed on the abscissa axis, while the expression V A +V s 10 E S was placed on the ordinate axis (where c s and V s are the concentration and the sum of increments in the sodium fluoride standard solution; V A is the initial volume of the aliquot under study, E is the difference in the recorded potentials after each increment in the standard solution, and S is the slope of the calibration curve).…”

“…The pH of the prepared solution was then adjusted to 5.5 by adding small amounts of 1.5 mol/L acetic acid solution. Finally, the prepared solution was thoroughly transferred to a 2 L volumetric flask and made up to the mark with distilled water [2,19].…”

“…Fluorides are the most chemically reactive and electronegative of all elements in the periodic table and the thirteenth most abundant element in the Earth's crust [1,2]. Flouride occurs in the form of fluorides in a variety of minerals, such as fluorite (CaF 2 ), cryolite (Na 3 AlF 6 ), and fluorapatite (Ca 5 (PO 4 ) 3 F) [1].…”

“…Fluoride concentrations in each sample were measured using a fluoride ion selective electrode (FISE) according to a recently published standard potentiometric addition method [2,17,18]. The results obtained were compared with each other and with the fluoride content of some worldwide beer producers.…”