Comparison On Analytical Scheme And Standard Reference Samples Used In International Geochemical Mapping

The purpose of global geochemical mapping is to study the spatial distribution and variation of all chemical elements in the surface of the earth. Sampling media and sample analysis are two crucial technical problems with geochemical mapping program in order to obtain global comparable data.The author is involved in the"International Geochemical Mapping"project and the"76 Elements Atlas of Four Province in Southwestern China"project. This thesis focuses on analytical schemes, methods, quality control for determination of 76 elements in the International Geochemical Project.1. In this thesis the author referred to some analytical methods, analytical schemes, detection limits used in some national geochemical mapping projects carried out by countries,such as Europe, Canada and America. The author compared two analytical systems used in the FOREGS Geochemical Baseline Mapping Programme and The 76 Elements Atlas Project in China. The result indicated that different analytical approaches are adopted for both global and regional geochemical mapping by China and Europe. The main differences are in that Europe only used large-scale instruments analytical system and China used large-scale instruments as a backbone with multi-methods analytical system. Europe analytical system provided less element information because some key elements are not determined such as precious metals:Ag,Au,Ir,Os,Pd,Pt,Rh,Ru, halogen elements: F,Cl,Br,I, dispersion elements:Ge,In,Se,Te, bio-available elements:N,S,B, and other elements:La,Bi,Sc. The best analytical schemes were based on the ICP-MS,XRF and ICP-OES as a backbone method incorporated with INNA, AAS, AFS,ES,ISE and other methods for individual"difficult"element analysis. The analytical scheme for 76 elements developed by China will meet the requirements for the global geochemical mapping.2. Based on the summaries of the performance of current analytical quality control methods, the author proposed adoption of the following quality control approaches in the international geochemical mapping: (1) Logarithmic error(â–³lgC(GBW)) of reference and determination values in order to monitor the between-batch bias; (2) calculation of correlation coefficient between reference and determination values; (3) comparison of visualization maps generated using a group of reference samples analyzed by different labs to monitor between-lab bias; (4) calculation of relative deviations (RD%) by using secret code duplicate samples to monitor the presision.3. The Chinese"GSD"and the Canadian"STSD"series of SRMs are internationally recognized samples as the International Geochemical Mapping. Four stream sediment standard references STSD1-STSD4 prepared in Canada were analysed by China analytical approaches . Eighteen difficult analysis elements( Bi,Cd,Cl,Ga, Ge,Hg,I,In, N,Se,Te, OrgC,Er,Gd,Ho,Pr,Tm,Tl ) except 52 elements given in the certificate were firstly determined.The statistical results indicated that most of elements'measured values were correlated with values given in the certificate, and other elements'measured values were not consistent with reference values. The reason for deviation is mainly different analytical methods adopted. Therefore, in order to avoid deviation by using different analytical methods, it is important to standardize analytical methods used in international geochemical mapping.4. Samples for global geochemical mapping from Brazil, Colombia and Kazakhstan have been anlysed using China analytical approaches. The results are qualified for producing global geochemical maps.