Free fluoride determination in honey by ion-specific electrode potentiometry: Method assessment, validation and application to real unifloral samples

Surprisingly, a reliable method for measuring the concentration of free fluoride ions in honey is still missing from the literature, notwithstanding the generally recognized importance of the analyte and the matrix. To fill this gap, this study proposes and validates a straightforward ion-specific electrode potentiometric method for this task. The method offers very low detection and quantification limits (6.7 μg kg−1 and 25 μg kg−1, respectively), good linearity (R2 > 0.994), good sensitivity (typically 55 ± 3 mV for an order of magnitude of concentration) in an unusually low concentration interval (between 0.020 and 1 mg L−1), and acceptable precision and bias. The method was applied to 30 unifloral (thistle, eucalyptus and strawberry tree) honey samples from Sardinia, Italy. The amount of free fluoride ions found in these honeys appears to be lower than the range usually found in the literature; indeed, early results suggest a possible dependence of the analyte concentration on the honey's botanical origin.