Isotope Ratios Analysis by ICP-QMS and Its Application for Tracing Geographical Origins of Agriculture Products

Author:Wu Zhi Wei

Supervisor:hu sheng hong guo wei


Degree Year:2019





With the rapid development of global economy,the commercial trade of agricultural products in different regions and countries is becoming more frequent.In order to guarantee the quality and safety of plant-agricultural products,and put an end to the fake and shoddy agricultural products,the techniques for determing geographical origins of agricultural products had been gradually attracted extensive public attentions.Among various kinds of discriminational techniques for determing geographical origins,isotope fingerprint discrimination technology has prominent advantages in its traceability principle.The isotope composition in agricultural products is greatly affected by climate,environment in planting area and the metabolism type of theirselves.Therefore,the objective differences in isotope composition of agricultural products that from different sources were considered containing“environmental impact factors”informations,and thusly could provide scientific,independent and objective identification informations for their geographical origins determinations.On the other hand,due to the provided extremely high measuring precision,TIMS and MC-ICP-MS were considered as the most optimal analytical instruments for IRs(isotope ratios)analysis.Compared with these expensive and complicated large-scale instruments,ICP-QMS has the advantages of low economical cost,simple operation,far scanning speed,high analysis efficiency and strong matrix tolerance degree(for matrix elements),but poor measuring precisions(<0.5%,RSD).Many efforts(such as the optimization of instrumental operating parameters and sequence of IRs measurements;the correction of dead time in detector;the column separation to remove matrixthe,the internal standard method for mass discrimination correction)had been made to improve the IRs measuring precisions(>0.1%)in ICP-QMS.However,the optimal IRs measuring precisions that provide by ICP-QMS were still worse than TIMS and MC-ICP-MS(<0.002%,RSD),and the development of IRs measuring technique by ICP-QMS was thusly restricted in various application fields.In view of this situation,the purposed work in this paper was aimed to establish high precision IRs analysis method that based on inter gas collision damping technique and Pulse-only signal acquisition mode in ICP-QMS,and then applied to determining the geographical origins of agricultural products.The major experimental works and the innovative conclusions of this paper are follows:(1).A simple and valid method based on a Ne gas collisional damping technique in ICP-QMS was established to determing the geographical origins of cigarettes according to Pb IRs.Due to the Ne gas collision and damping technique,the ion variabilities and transmission efficiency were decreased improved,respectively.And thus,a 26-fold improvement in the precision of Pb IRs was obtained.Pb IRs in two cigarette reference materials(Oriental tobacco leaves CTA-OTL-1 and Virginia tobacco leaves CTA-VTL-2)was carried out by the established method,and the results of Pb IRs for CTA-VTL-2were in agreement with the literature values.And the Pb isotope composition of CTA-VTL-1 was reported for the first time in this work.91 cigarettes samples from 7 various countries were determined for Pb IRs,and were successfully discriminated for geographical origins using the Pb isotope fingerprint technology(208/206Pb vers 207/206Pb).(2).A valid method for B IRs analysis based on a Ne gas collisional damping technique by ICP-QMS was established to determing the geographical origins of red wines.The Ne gas collision damping technique was innovatively applied for low mass(boron)IRs analysis for the first time in this work.Direct dilution of the wines by a factor of 100 with 1%HNO3 was found to substantially reduce matrix-induced mass discrimination.Due to the use of e gas collisional damping technique,the precision of the 11/10B ratio by ICP-QMS was improved 24-fold and the accuracy was improved from an error of-5.5%to-0.1%.Twenty wines from nine countries were analysed,andδ11B values were ranged from+1.73 to+46.6‰with an average external precision(N=5)of 0.82–1.63‰.The proposed method has sufficient precision to distinguish between 20 wine brands originating from four different geographic regions.(3).The IRs analysis performance on different signal acquisition modes(in Pulse-Analog acquisition detector(Agilent 7700x)and All-digital signal detector(Jena M90)by ICP-QMS was carefully investigated in this work.In both of two kinds of detectors,the IRs analysis performance(internal precision,accuracy and external reproducibility)on Pulse-only signal acquisition mode was obviously better than the other signal acquisition modes.When the Tf value(a turning factor to normalizing various kinds of signals)was employed as a constant rather than a dynamic correction one,a random error was occurred and considered as the main source of the poor IRs analysis performance obtained on non-pulse signal acquisition mode.Finally,a simple analytical method based on Pulse-only signal acquisition mode for Pb IRs analysis was established to analyze 208/206Pb and 207/206Pb in six geological standard reference materials without any separation and purification for Pb,and prefect accuracy(<0.15%,RE)and precision(0.02-0.08%,RESD)could be obtained.(4).A precise and accurate method of B and Sr IRs analysis that based on Pulse-only singal acquisition mode in ICP-QMS(Agilent 7700X)was established to determing the geographical origins of cigar samples.The cigar samples were acid digested,and the total B content was set up to a recommend range(2535μg L-1)using various dilution-folds,and then directly analysed for 11/10B by ICP-QMS without any matrix separations.A carefully Sr purification that using a Sr-Spec resin was applied to eliminating the matrix components and Rb prior the the final Sr IRs analysis.The obtained precisions((0.030.06%(RSD%),0.030.07%(RESD%))of 11/10B and 87/86Sr that provide by this method were obviously better than the traditional ICP-QMS methods(0.20.5%,RSD).Finally,three different isotope fingerprint technologies(B content vs 11/10B,Sr content vs 87/86Sr,11/10B vs 87/86Sr)was combined to determing the geographical origins of 19 cigar samples which from different sources.The proposed method has sufficient precision to distinguish between 19 cigars originating from eifht different geographic regions.