Investigation Of The Determination Of Mercury And Arsenic In Tea And Tea Soil By Atomic Fluorescence Spectrometry

Tea serves as the one of the most important food,its quality is largely affected by different microelements.One of the most conspicuous factor is heavy metal.These heavy metal elements are gathered at the root of tea trees thro?gh active transport followed by transferring to the leaves.Mercury(Hg)and Arsenic(As)are both poisonous.The physical and chemical properties and the gathering effect of As are highly comparable to some heavy metal elements.Concentration of Hg and As is relatively high especially in South China,acid soil,where most tea trees are planted.Thus,the threat of excessive levels of Hg and As is inevitable.The measurement of Hg and As concentration from the soil and the leaves of the tea trees may help to analysis this threat,which will definitely provide constructive advice for location selection of tea plants.ICP-AES,AAS,IC,AFS are the most common element analysis methods.Even tho?gh different analysis methods hold distinct instruments and principles,they share the same process: sample gathering,sample preparation,sample pretreatment,measurement and statistic analysis.Sample pretreatment,as the core process,can be conducted thro?gh dry-ashing method,wet-ashing method and microwave dissolve method.The combination of ICP-AES,AAS,IC and AFS could provide new pretreatment and measurement methods.Based on AFS,our research optimized the measurement condition with the standard sample.Under this condition,dry-ashing,wet-ashing and microwave dissolve method were conducted respectively to screen out the optimal approach.For consideration of practical use,43 different tea leaves from tea garden were chosen as the experiment samples.Following are the main research results:(1)The optimized conditions were obtained by using the standard sample.Conditions of As measurementsStandard curves of As showed linear dependence of concentration(0 – 10ug/L),negative high voltage,280 V;Channel A(As,main current),30 m A;Channel B(Hg,auxiliary current),30 m A;atomization furnace height,8 mm;HCl,as the test medium,acidity 5%;detection limits: tea 3.00ug/kg,soil 0.43ug/kg,relative standard deviations are 0.021 and 0.033 respectively;recovery,1.003.Conditions of Hg measurementsStandard curves of Hg showed linear dependence of concentration(0 – 1 ug/L),negative high voltage,280 V;Channel A(Hg,main current),40 m A;atomization furnace height,10 mm;HCl,as the test medium,acidity 5%;detection limits: tea 0.20ug/kg,soil 0.24ug/kg,relative standard deviations are 0.051 and 0.044 respectively;recovery,1.017.(2)Dry-ashing,wet ashing and microwave dissolve method were conducted to compare the dissolve effect.Hg/As concentration are 0.023/0.032 mg/kg,0.022/0.049mg/kg,0.025/0.058 mg/kg for dry-ashing,wet-ashing and microware dissolve method respectively.For certain sample,the loss of Hg/As under the pretreatment of microwave dissolve method is the least,thus,this method was chosen for the AFS.(3)43 different tea leaves and soils from tea garden were chosen as the experiment samples to detect Hg/As concentration.Line charts were used to demonstrate the relativity of Hg/As concentration from the leaves and the soils.(4)Hg/As concentration of sample leaves were compared with Chinese Standard,3 out of 43 sample are over the Standard(0.02 mg/kg).Concentration of Sample 5 and 23 are more than 0.1 mg/kg,which is 5 times higher than the standard.As concentration of all the 43 samples are below the Standard(0.5 mg/kg).Concentration of Sample 22 is 0.480 mg/kg,which is comparable to the Standard.