Determination Of Effective Concentration Of Lead In Tea In Different Ways

Tea,as one of the three major non-alcoholic drinks in the world,is loved by people.Through the analysis and separation of modern technology,there are more than 600 kinds of organic compounds identified in tea,and more than 40 kinds of inorganic mineral compounds.Modern scientific research has shown that tea is rich in tea polyphenols,caffeine,amino acids,polysaccharides and other bioactive substances,which have clinical pharmacological and antioxidant effects such as lowering blood pressure,lowering blood glucose,preventing atherosclerosis,antibacterial and anti-inflammatory,diuresis and dysentery.Tea has also presented Anti-aging,promoting digestion,relieveing fatigue and other health effects.There are also heavy metals such as copper(Cu),lead(Pb),mercury(Hg)in tea,which are harmful to human body.Many countries have set upper limits on the content of heavy metals in tea,in which the UK stipulates that the content of lead in tea is less than 5 mg/kg,and the requirement in Japan for lead content in tea cannot exceed 20 mg/kg.The lead content of tea is less than 10 mg/kg in Canada,India and Australia,and less than 5.0 mg/kg in our country.The species of heavy metals in the tea soup are an important factor for evaluating the bioavaibility of heavy metals.The more heavy metal contents in the active state in the tea soup,the greater the amount of heavy metal absorbed by the human body from the tea soup.In order to understand the amount of heavy metal absorbed in the tea soup by the human body,the active state concentration of the heavy metal in the tea soup must be measured.In this paper,the active concentration of lead in the tea soup was determined by two methods.The thin film diffusion gradient technique,which is used in the first method,is a technique that can accumulate active heavy metals and calculate the active concentration of heavy metals.In this experiment,sodium carboxymethyl cellulose and cellulose acetate membrane were used as DGT binding phase and diffusion phase to assemble CMC-DGT device.The performance of lead accumulation in Tieguanyin tea soup under different ligands,pH and ion strength was evaluated by DGT device.The concentration of lead in Tieguanyin tea soup in different environments was determined by CMC-DGT.The active concentration of lead in normal Tieguanyin tea soup was 0.061 mg/L,The labile concentration of lead in artificial gastric juice of standard tea soup(theoretical 3 mg/L)was 2.30 mg/L,The labile concentration of lead in intestinal liquid environment was 0.334 mg/L,and the percentage of labile lead in tea soup was 11.9%.The second method was to determine the active lead ion in tea soup by square wave anodic stripping voltammetric method.In 0.10 mol/L HCl solution,Pb2+ produces a sensitive dissolution peak near the peak voltage of-0.35 V.the linear relationship between the peak current and the concentration of lead is in the range of 50～2000 μg/L.The regression equation is:Ip(μA)=103.61X-8.3636,and the correlation coefficient is 0.9959.The active lead concentration under different ligands was detected by square wave stripping Voltammetric method,and it was proved that the method could detect the active lead concentration in the solution after complexation reaction.The active lead concentration in standard tea soup(20 mg/L)was detected by this method.The active lead concentration of 0.97 mg/L,was lower than the total lead concentration.The active lead concentration measured in gastric environment was 0.79 mg/L,the active lead concentration in intestinal fluid environment was 0.075 mg/L,and the percentage of active lead in tea soup was 7.7%.According to the national standard,according to the calculation of 1 L tea soup consumed by an adult a day,the active percentage of lead in the tea soup digested by gastrointestinal tract was 7.7%-11.9%,and the amount of lead that might be absorbed by the human body was 0.61 μg-0.95 μg,even if all lead in Tieguanyin tea soup was absorbed to 8 μg,which was within the standard requirement of 214 μg.The results show that the two detection and analysis methods can provide an effective evaluation tool for predicting the labile concentration of heavy metals in tea soup.