Determining Mainly Heavy Metal Elements And Rare Earth Elements In Ya'an Tibetan Tea By ICP - MS

Food Quality and Safety is a major topic in economic and social development in nowadays.How to improve the quality of agricultural products and the level of agricultural industry,there is facing the test of food quality and safety.It happens from time to time that harmful heavy metals in tea products exceeding standards.Ya'an Tibetan Tea is one of the characteristic products of Sichuan tea.Its heavy metal content and rare earth element content have attracted wide attention.This experiment determined the contents of 16 heavy metal elements and 16 rare earth elements in Ya'an Tibetan tea simultaneously by inductively coupled plasma-mass spectrometry?ICP-MS?,to get the test datas quikely and targetly.The research and application of this method has certain guiding significance for Ya'an Tibetan tea quality detection,hoping to provide technical support for the sustainable development and brand development of Ya'an Tibetan tea industry.The main results are as follow.1.After testing and comparing,the choices of this experiment are that,^102.905Rh be the internal standard elements for ^44.956Sc,^88.905Y,^74.922As,^9.012Be,^58.933Co,^51.941Cr,^62.930Cu,68.926Ga,7.016Li,57.935Ni,87.906Sr,50.944V,63.929Zn,106.905Ag,111.903Cd,132.905Cs,138.906La,139.905Ce,140.907Pr,145.913Nd,146.915Sm,152.929Eu,156.934Gd,158.925Tb and 162.925Dy;184.953Re be the internal standard elements for ^208.980Bi,^207.977Pb,^164.930Ho,^165.930Er,^168.934Tm,^171.941Yb and ^174.941Lu.2.The tea reference material GBW 10016 GSB-7 was used as the test sample in this experiment.Two pretreatment methods of microwave digestion and high pressure digestion were compared.The results showed that the recoveries of 32 elements by two digestion methods ranged from 92.56%to 114.37%,and the RSD was less than 6%,both can meet simultaneous determination of 32 elements.Considering the latter,reagent consumption can be reduced?consumption of concentrated nitric acid reduced from 5 mL to 3 mL?,the digestion method by high pressure was selected.3.The standard curve,the linear range and the detection limit of each element were tested,the standard curves of 32 elements had good linear relationship,the correlation coefficient was mostly 0.9999.The detection limit of 32 elements were very low,between0.0003 ug/L and 0.2164 ug/L.Zn has the highest detection limit,the next is Ni,the detection limit of Tm is the lowest.The curve correlation coefficient and detection limit of each element can meet the requirement of quantitative analysis.4.Repeatability,stability and recovery of the method:The results showed that,the RSDs of intra-day and inter-day precision were respectively 0.12-3.85%and 1.21-6.65%,the intra-day precision RSDs of each element were less than that of the inter-day precision RSDs.The rates of recovery were between 93.39%to 110.99%,the recovery rate RSDs were less than 7.49%.The results showed that the method was stable and reproducible.5.By determining content of 32 elements in this method,the results showed that:?1?The average content of Zn was the highest,which was?32.419±6.552?mg/kg,the next was Cu by?15.530±1.180?mg/kg,Sr by?14.148±5.604?mg/kg,and Ni by?9.248±1.037?mg/kg.Their contents were significantly higher than that of the other 28elements?P<0.01?.According to NY/T 288-2012 and NY 659-2003,Cu,Pb,Cr,Cd and As in the samples all did not exceed the standards.?2?The total content of rare earth elements in samples ranged from 0.588 mg/kg to 3.990mg/kg,average?2.024±1.056?mg/kg.The total content of light rare earth elements including Ce,Eu,La,Nd,Pr and Sm accounted for 36.49⁷2.29%of the total content of16 rare earth elements,which was significantly higher than the total content of heavy rare earth elements including Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu,Sc,Y?P<0.01?.The average content of Ce in the samples was?0.666±0.404?mg/kg,which is the highest among all rare earth elements.The next were Sc by?0.318±0.134?mg/kg,La by?0.306±0.184?mg/kg,Y by?0.226±0.112?mg/kg and Nd by?0.205±0.131?mg/kg.The total content of Ce,La,Sc,Nd and Y accounted for 65.43⁹0.64%of the total content of rare earth elements.The average content of Lu was the lowest by?0.002±0.001?mg/kg.Sc and Y,being heavy rare earth elements,their average contents was significantly higher than that of some light rare earth elements,such as Pr,Sm,Eu.?3?Compared with the trade standard NY/T 288-2012"Green Food Tea",the contents of Cu and Pb in each sample were not exceeded the standard.Comparing with the trade standard NY5196-2002"Organic Tea",the contents of Cu in all samples did not exceed the standard,but six samples exceeded the standard with a rate of 40%.Compared with the trade standard NY 659-2003"Limits of Chromium,Cadmium,Mercury,Arsenic and Fluoride in Tea",the contents of Cr,Cd,Hg,As and fluoride in all samples were not exceeded.Compared with the national standard GB 2762-2017"Food Safety National Standard Food Contaminant Limit",Pb in the samples did not exceed.Compared with the former national standard GB 2762-2005"Contaminant Limit in Food",8 samples exceeded the standard in total rare earth content,with the exceeding rate of 53.3%.