Fluoride in beer by direct potentiometry and ion-specific electrode: Method assessment, validation, and application to commercial samples

Abstract

At present, beer is produced from the alcoholic fermentation of wort prepared with malt, barley or wheat and water, flavoured with hops. The main raw materials for producing beer are: water, barley, hops, yeasts. Unlike other alcoholic or distilled beverages, water is added during the preparation of the must. Consequently, in the mineral content of beer, the composition of the water is of great importance. Among the trace elements, fluoride, can be a common ion in water. This study describes and validates a potentiometric method, using an ion-selective electrode, to measure fluoride concentrations in the beer samples without preliminary treatments. The obtained detection limit (LOD) is 0.0006 mg L⁻¹ while quantification limit (LOQ) is 0.0017 mg L⁻¹. The standard addition method, used in this research, allows to obtain straight lines whose r² is higher 0.999. The sensitivity is very close to the theoretical one (59.16 mV at 25°C), in fact the electric potential varies by 55 ± 3 mV when the concentration differs by one order of magnitude. In an unusually low concentration interval 0.045 – 0.45 mg L⁻¹ acceptable precision and recoveries (<95 %) were obtained. The method was applied to 28 beer samples consumed in Sicilia (Italy) most of which were produced in other European countries having different alcoholic content. Fluoride concentration in the analysed samples was in the range 0.17–0.32 mg L⁻¹. The statistical treatment indicates a strong positive relationship between fluoride concentration and beer origin, indicating that this is closely related to the fluoride concentration. Conversely, alcohol content and beer type show a negative correlation with fluoride concentration. Considering all the analysed samples, the maximum value of the contribution to the diet corresponds to 3 %, obtained consuming 0.66 L of a lager beer produced in Italy.