Determination And Primary Speciation Analysis Of Lead In Tea

Tea is known to be a kind of healthy beverage which contents many functional components, such as polyphenols, theanine and caffeine. Drinking tea is helpful to prevent cardiovascular disease and some kinds of cancer diseases. Lead(Pb) is a kind of physiological and neurological toxin affecting almost every important organ and system in the human body. Food and water are the main sources of Pb intaking by human body. Due to the environment pollution, with the increasing of Pb level in tea products and there were many reports about the exceeding of Pb concentration in tea over than5mg/kg (the maximum permissible concentration (MPC) for Pb in China). It caused great concerns of the tea producers, consumers and scientists.In this paper, three kinds of digesting methods, dry digestion,hydro digestion and microwave assisted digestion,were employed to digest17sorts of tea for extraction of Pb2+, and their contents was determined by flame atomic absorption spectrometry. Five samples were random selected from17samples and added standard solution of Pb for recovery checking. The results showed that the precision and accuracy of microwave assisted digestion was better than that of dry digestion and hydro digestion.The selected method was a simple, rapid, reagent saving, comp1ete digested and lower background interference method than the methods of dry digestion and hydro digestion.We mimicked the daily habit of drinking tea, and all the tea samples were extracted in boiling water for three times. For each times, tea sample was incubated in boiling water and extracted for20min, After the tea liquor were digested, the contents of Pb was determined by flame atomic absorption spectrometry. The results showed that the first extraction ratio is little higher than that of the second extraction, and the second extraction ratio is little higher than that of the third extraction. It was revealed that there was obvious relation between the extraction ratio and the total content of Pb in tea sample. The higher lead content, the lower extraction ratio.With80%C2H5OH, H2O,1mol/L NaCl,2%CH3COOH,0.6mol/L HCl as the extract solvent respectively, the primary speciation analysis of Pb in tea sample was performed. By single factor experiments the optimal extraction time for these solvent was15h,3h,3h,3h respectively. The optimal extraction temperature was35℃and extraction volume was50mL each time. Five tea samples were used for the speciation analysis of Pb. The results showed that among the same variety of the tea the distribution of Pb-compound was quite different. There is a little difference for the Pb content among of several tea samples from the same region, and little difference with the existing form of Pb. For all the tea samples, the extracted efficiency of Pb is different, HCl> HAC> C2H5OH> H2O> NaCl. The total amount of the HCl extraction and HAC extraction was about47.78%-70.30%. The residual Pb compound exists in tea by a much stable form. The ratio of the Pb in form of which easily be intaken by human body was very lower.