Study On Speciation Of Trace Element In Tea Samples

Tea is recognized as one of healthy beverages,but some plant food such as tea are polluted with the increasing environmental pollution.The trace elements in tea intaken by human effect a physiological consequences.In addition,the bioavailability and toxicity of arsenic,selenium,chromium and lead depend on their species,thus speciation analysis of elements in tea is becoming the significance task in tea safety and food risk evaluation.The aim of this thesis is to develope a new high performance liquid chromatography-inductively coupled plasma mass spectrometry method to analyse the species of As,Se,Cr in tea samples,and establish an ICP-MS method to analyse the water soluble lead in tea extracted.After determination of total trace element,tea whose total As,Se,Cr or Pb higher concentrations were speciation analysis.The main results were summarized as follows:(1)Established a simple,rapid and accurate method to determine trace elements in tea samples.The contents of Na,Mg,Al,K,Ca,Ti,Cr,Mn,Co,Ni,Cu,Zn,As,Se,Cd,Ba,Pb and Bi in 21 tea samples after microwave digestion were determined by ICP-MS.The detection limits for elements were 0.001?0.751 ng g-1,the RSD were 0.685%?2.969%and the recoveries of the elements were ranged mostly from 80.42%to 117.59%.(2)Study on As,Se,Cr and Pb species in tea samples.First,the hyphenated technique of HPLC-ICP-DRC-MS was developed for the separation of 5 arsenic species including arsenobetaine(AsB),dimethylarsinic acid(DMA),methylarsonate(MA),arsenate(As(V))and p-AsA,then the effect of infusion time on arsenic species was investigated.95? ultrapure water was used as extracting agent to extract arsenic species in Longjing tea and Jasmine tea.Separation of AsB,DMA,MA,As(V)and p-AsA in 4.5 min was achieved by a Hamilton PRP-X100 anion exchange column with the mobile phase of 8 mM NH4NO3/8 mM(NH4)2HPO4(pH 9.4)and 1%(v/v)CH3OH at a flow rate of 1.5 mL min-1.O2 was used as reaction gas to reduce interferences.The detection limits were in the range of 0.05 ?g L-1?0.15 ?g L-1,and the RSD were better than 0.3%.In selected Longjing tea and Jasmine tea,AsB,DMA and As(V)were detected,indicating the selected tea samples were polluted by inorganic arsenic;In Longjing tea,the content of inorganic arsenic is significantly lower than this of organic species.Contrary,inorganic arsenic was the predominant species in Jasmine tea.It was also observed that with the infusion time prolonging,the content of AsB,DMA and As(V)in Longjing tea and Jasmine tea was changed.Second,a method for the determination of Se(IV),Se(VI)and SeMet in tea samples by HPLC-ICP-DRC-MS was developed.Separation of Se(IV),Se(VI)and SeMet in 10 min was achieved by a Hamilton PRP-X100 anion exchange column with the mobile phase containing 40 mM(NH4)2HP04 at pH 6.0 and 2%CH3OH at a flow rate of 1.4 mL min-1.CH4 was used as a reaction gas to reduce isobaric interferences.The detection limits were ranged from 0.107?g L-1 to 0.286 ?g L-1,and their corresponding RSD were ranged from 0.629%to 1.01%.The method was used to determine selenium species extracted by 95 ? ultrapure water in Mao Hongqing,Zhengqing and Miejun black tea 1.It can be observed that inorganic selenium concentration was lower than other selenium speciation,indicating that organic selenium was the primary form in tea infusions.The lower selenium concentration in infusion was a little part of daily recommended content.Hence,drinking tea could be considered as a safe approach to supplement selenium for people.Third,simultaneous determination of Cr(III)and Cr(VI)in tea samples was performed by HPLC-ICP-DRC-MS.Chromium species in Ruoyang Longzhen,Mao Hongqing,Zhengqing and Miejun black tea 2 were extracted by 95 ? ultrapure water.Separation of Cr(III)and Cr(VI)in 2.5 min was achieved by a C8 column with the mobile phase containing 1 mM TBAH/0.5 mM EDTA(pH 7.2)and 2%CH3OH at a flow rate of 1.4 mL min-1,and the column temperature was 35 ?.CH4 was used as a reaction gas to reduce isobaric interferences and improve precision.The detection limits of Cr(III)and Cr(VI)were 0.40 ng g-1 and 2.12 ng g'1,respectively,and their corresponding RSD were 0.24%and 1.41%,respectively.There were neither Cr(III)in selected tea infusions,nor Cr(VI).Unknown peaks were observed indicating that there were unknown chromium species in tea infusions.At last,water soluble lead in infusions of Chaoqing,Zhengqing,Black tea,Miejun black tea 1 and Miejun black tea 2 were determined by ICP-MS.It was observed that the total content of lead were ranged from 2.5?5 mg kg-1,while the content of water soluble lead in infusions were ranged from 11?55 ?g kg-1,which were lower than the limited value of lead content in drinking water(50 ?g L-1).The method could provide theoretical basis for the security risk assessment of tea.