Distinguishing Different Kinds Of Activated Carbon And Geographical-tracing Of Walnuts By Stable Isotope Techniques

The application prospect of stable isotope technique is very broad in identification and geographical origin tracing.In this thesis,the stable isotope technology was used to identify three kinds of activated carbon,which were made by coconut shell,almond shell and coal in vapor activation,to trace the geographical origin of walnuts.The results of geographical origin are explored by using walnut monomer compound.The conclusions in this paper were gotten by linear discriminant analysis.The main research contents and results were summarized as follows:1.The test method research of isotopes ratio mass spectrometers.Firstly,the basic working principles of EA-IRMS and GC-IRMS were introduced.Then the instrument preparation process and the requirement of test method precision,accuracy and stability were elaborated.2.The establishment of identification between coconut shell,almond shell and coal activated carbon.In this paper,the study was about the identification of activated carbon,which was made by vapor activation,from coconut shell,almond shell and coal by EA-IRMS.SPSS statistical of 65 kinds of activated carbon found that the δ¹³C value of coal-based activated carbon was-24.228‰^-22.168‰,the almond shell active carbon was-25.792‰^-24.423‰ and the coconut shell active carbon was-26.475‰^-24.628‰.Further analyze the relationship between δ¹³C and δ18O,the δ¹³C value as vertical axis,it was found that the δ¹³C value of different kind of activated carbon was located in different interval.The δ¹³C value of coal-based activated carbon was above Y=-24.322,which could distinguish clearly from almond shell and from coconut shell active carbon.Between Y=-25.031 and Y=-24.322,it was most part of the almond shell and the interval of coconut shell was below Y=-25.031.Although the interval of coconut shell and almond shell was different,part of that was overlap.According to this model,the correct classification of activated carbon from coal,almond shell and coconut shell were 100.0%,80.0% and 90.3%.3.The establishment of method for tracing the walnut geographic origin.344 walnuts from Henan,Xinjiang,Hebei,Gansu,Shanxi,Sichuan,Hubei,Yunnan and Guangxi were collected.The ratio of C,H,O,N isotope were determined by EA-IRMS,the elemental analyzer measured the N content and converted it to the crude protein content,and the content of crude fat was determined by physicochemical analysis method.The results showed that δ2H、δ18O value of walnuts decreases with the decrease of latitude and The δ¹³C value of walnut in Henan sub-region increased with the elevation.The LDA found that the overall correct classification of walnuts from different provinces and Henan sub-region by stable isotope were 71.5% and 57.9%.When combined with the content of crude fat and protein,the overall correct classification could be enhanced to 80.2% and 68.6% respectively.It was found that stable isotope in combination with organic compounds could enhancethe discriminant results of walnut and the discrimination rates among different provinces are significantly higher than those in sub-regions.4.The establishment of method for tracing the walnut geographic origin by monomeric compound.The stable carbon and oxygen isotope ratio of 5 fatty acid methyl ester in walnuts,which from Henan,Xinjiang,Hebei,Gansu,Shanxi,Sichuan,Hubei,Yunnan and Guangxi,were determined by GC-IRMS.The δ¹³C of 5 fatty acid methyl ester were less than δ¹³C of walnuts,which was depletion of carbon isotope.Carbon and oxygen isotope were all depleted with the growth of carbon chain.The LDA found that the overall correct classification of walnuts from different provinces and Henan sub-region by 5 fatty acid methyl ester were 94.6% and 85.0%.Therefore the stable carbon and oxygen isotope ratio of 5 fatty acid methyl ester could be used in tracing the walnut geographic origin.