Determination of Chlorine and Fluorine in Teas by Ion Chromatography after Pyrohydrolysis Sample Preparation Optimized by Box-Behnken Design

Abstract

Tea beverage is a daily habit around the world. This beverage contains bioactive compounds and elements, such as chlorine (Cl) and fluorine (F), which, in specific concentrations, can lead to risks to consumers' health. This study uses ion chromatography to assess the total and extractable (released into tea infusions) concentrations of Cl and F in tea samples. The total concentration was determined after pyrohydrolysis as a sample preparation procedure optimized by Box-Behnken design. The optimal conditions for sample preparation by pyrohydrolysis were 150 mg of sample, temperature of 850 °C, reaction time of 20 min, and absorbing solution of 50 mmol L⁻¹ NH₃. The accuracy of the proposed method assessed through the analysis of certified reference materials demonstrates a good agreement between the determined total analytes concentration and certified values (t-test, 95% confidence level). The precision assessed by RSD was less than 10%, and the obtained limits of detection were 2.3 and 0.2 mg kg⁻¹ for Cl and F, respectively. These results indicate that the proposed method is suitable for the analysis of tea samples. Tea infusion samples of traditional and herbal teas showed an analyte extractable percentage ranging from 54.7 to 92.3% and 9.9 to 86.1% of the total concentration of Cl and F, respectively. The assessment of the potential risk of F exposure for tea consumers showed that most of the samples tested fall within the recommended limits for safe F intake. The results contribute to food safety by enabling a detailed evaluation of total and extractable Cl and F concentrations in teas.