Determination Of Labile Lead Concentration In Tea Infusion By DGT With CMC As Binding Phase

Tea is one of the three major botanical beverages in the world and is recognized as healthy drink.It has been found that tea contains up to 600 kinds of organic chemical compounds and 40 kinds of inorganic minerals.Drinking tea can reduce oxidation and the ageing and prevent high blood pressure and a variety of cardiovascular diseases.However tea also contains some heavy metals such as lead(Pb),copper(Cu),mercury(Hg),etc.Excessive heavy metals existing in human body would be harmful.The maximum contents of heavy metals in commercial tea leaves have been limited by governments.For examples,the contents of lead in tea has been confined below 5.0 mg·kg-1 by UK,20 mg·kg-1 by Japan,10 mg·kg-1 by Australia and Canada,5.0 mg kg-1 by China.The species of heavy metals play a key role in their bioavailability.The higher the labile concentration is,the more the amount which can be absorbed by the body is.Therefore,it is necessary to establish a method to measure the labile concentration of heavy metals in tea.Diffusive gradients in thin-film technique(DGT)can enrich labile heavy metal from water,by which labile concentration of heavy metal can be calculated.In this work,CMC-DGT was established by using CMC as binding phase and cellulose acetate membrane as diffusion phase.The performance of CMC-DGT was evaluated under conditions of different temperetures,different pH and different ionic strength.The labile concentrations of the Laoshan green tea,Tieguanyin tea and Pu’er tea in environment of the artificial gastric juice and intestinal fluid were determined by CMC-DGT.The results showed that the labile concentrations of lead in the three tea infusions in the artificial gastric juice were 24.69,31.93,29.83 μg·L-1 and that in the artificial intestinal fluid were 11.78,6.17,9.88 μg·L-1 respectively.The percentages of the labile lead in the three infusions under the environment of the artificial intestinal fluid were 19.54%,9.65%and 17.75%.Compared with complex stability constant of Pb-CMC and that of Pbcompounds which are in the body of human being,only for the three kinds of tea above mentioned,the conclusion may be drawed thermodynamically that the amount of lead absorbed into the body is at least 9%to 20%of its total amount in infusions.