Determinação de flúor total em folhas de chás in natura, infusões e resíduos: explorando a mobilização elementar e caracterização da composição centesimal

Abstract

This study aimed to develop a method for determining fluoride in medicinal plants, infusions, and solid residues from the infusion process. Initially, the samples were characterized for their proximate composition, and microwave-induced combustion (MIC) was evaluated as a preparation method for fresh plants, their infusions, and infusion residues. Instrumental conditions were optimized for fluorine determination, assessing techniques with different detection principles, such as ion-selective electrode potentiometry (ISE) and ion chromatography (IC). The proposed method was validated and applied to determine the concentration and distribution of fluorine in the fractions of the analyzed medicinal plants. Among the optimized conditions, the 100 mmol L-1 NH4OH absorbing solution proved to be the most effective for fluorine absorption after sample decomposition by MIC. Solid samples were prepared as tablets, with an optimized mass of 600 mg. For infusions prepared by MIC, wrappers with microcrystalline cellulose as a combustion aid were used (300 μL of infusion, 400 mg of cellulose, and 100 μL of ignition solution – NH4NO3 6 mol L-1). Fluorine concentrations in tea infusions were quantified directly in three of the nine tea samples analyzed: black tea (224 mg kg-1), chamomile (39 mg kg-1), and fennel (15 mg kg-1). Among these, only black tea showed detectable fluoride concentrations in all fractions, with 421 mg kg-1 in the fresh tea and 155 mg kg-1 in the post-infusion residue. Direct infusion analysis was consistent with total fluorine concentrations in the infusion after MIC preparation, indicating that fluorine in the infusion is in the form of fluoride ions. The proposed method effectively quantified total fluoride in tea samples and their fractions, combining MIC for sample preparation and IC for determination. For the three teas with detectable fluoride, chronic daily intake (CDI) values were 0.064, 0.011, and 0.004 mg/kg/day for black tea, chamomile, and fennel, respectively. The target hazard quotient (THQ) values were 1.07, 0.18, and 0.07, respectively, with values above 1 indicating a potential health risk, which was specifically observed in black tea. These findings highlight the importance of monitoring fluoride levels in tea to ensure consumer safety.