Analytical Problems with the Evaluation of Human Exposure to Fluorides from Tea Products

Abstract

Tea (Camellia sinensis) is a plant exhibiting high tendency for accumulation of fluorides. Up to 98 % of fluorides are accumulated in the leaves used for the preparation of widely consumed tea infusions. Fluorides from tea leaves are released into infusions, which make the second after drinking waters important source of fluorine for humans. A narrow margin between acceptable fluoride concentration and health risk requires a reliable examination of a large variety of tea products for fluoride contents. Large differences between the published results obtained by the use of different analytical techniques have stimulated studies on possibilities and limitations of different analytical procedures used for fluoride quantification in tea infusions. The applicability of ion selective electrode (ISE) and ion chromatographic (IC) methods to the determination of fluorides in the presence of aluminium, the element highly accumulated by tea trees affecting the amount of free fluoride ions occurring in tea infusions, was examined. The efficiency of different total ionic strength adjusting buffer (MES with citrates or tartrates and citrate) for the elimination of aluminium interference with fluoride detection by ISE method was compared. The applicability of three different chromatographic columns, Metrosep A Supp 4 and Metrosep A Supp 5 (both from Metrohm) and IonPac AS9-HC from Dionex, to the isolation of free fluoride signals from the signals of interfering species, including acetates and formates, which can occur in tea samples, were examined. The contents of fluoride in various tea commercial products evaluated by ISE and IC methods applied are compared.