地球化学基准与环境监测实验室分析指标对比与建议

全球高质量一致性地球化学基准数据和建立全球地球化学一张图平台,是持续监测全球环境变化的定量参照标尺。本文通过对中国、欧洲、美国和澳大利亚汞、镉、钨地球化学数据对比和中国同一实验室间隔15年两次分析数据对比发现:镉元素在不同实验室和同一实验室间隔15年分析的数据是一致的(相关系数0.96),汞元素一致性较差(相关系数0.74),钨元素不具有可比性(相关系数0.56)。镉元素分析结果的高度一致是因为分析方法相同的和检出限相近;汞元素一致性较差,特别是低含量汞存在显著差异,是因为分析方法不同和检出限不同;钨元素在不同实验室不具有可比性是因为实验室分析方法存在显著差异。环境变化量必须大于野外采样误差(REsmpl)和实验室重复样误差(RDlab)之和(RCenv>REsmpl+RDlab),才能确认观测点发生了环境显著变化。因此,必须将采样误差和实验室分析误差降到最低。本文提出实验室分析的6点基本要求:①原始样品过10目筛,使用无污染加工到粒度小于200目;②使用成熟的多方法分析71种元素+其他指标,其中主量组分以玻璃熔片X射线荧光光谱法(XRF)分析为主,微量元素以四酸分解样品,电感耦合等离子体质谱法(ICP-MS)和电感耦合等离子体发射光谱法(ICP-OES)为主要分析技术,配合其他特殊分析方法;③分析检出限必须低于地壳克拉克值,报出率不低于90%;④使用的标准物质必须具有涵盖所有分析元素的认定值;⑤实验室重复样分析相对误差含量小于3倍检出限RD≤40%,大于3倍检出限RD≤20%,主量元素、铁族元素和重金属元素重复样分析相对误差RD≤20%;⑥主量组分SiO2、Al2O3、Fe2O3、FeO、MnO、MgO、CaO、Na2O、K2O、TiO2、P2O5、H2O^+(结晶水)、有机碳、CO2、SO2等15项,或SiO2、Al2O3、Fe2O3、FeO、MnO、MgO、CaO、Na2O、K2O、TiO2、P2O5、LOI(烧失量)等12项加和为99.3%~100.7%。

Comparison of Laboratory Analysis Parameters and Guidelines for Global Geochemical Baselines and Environmental Monitoring

BACKGROUND: Global harmonious high-quality geochemical data and accompanying maps are reference baselines for quantifying future human-induced or natural environmental changes.OBJECTIVES: To ensure the accuracy of geochemical reference values and analysis data, advices were made for laboratory analysis.METHODS: The analytical data of Cd, Hg and W from China, USA, Europe and Australia were compared and two analysis data collected 15 years apart from one laboratory in China were also compared.RESULTS: All of the cadmium analysis data were consistent with a correlation coefficient of 0.96. Mercury was poorly consistent with a correlation coefficient of 0.74, and tungsten was not comparable with a correlation coefficient of 0.56. The analysis results of cadmium were highly consistent because the analysis method was the same and the detection limit was comparable. The consistency of mercury was poor, especially the low-content mercury, which was significantly different due to different analysis methods and detection limits. Tungsten was not comparable due to different laboratory analysis methods. The prerequisite for recognition of environmental changes(RCenv>REsmpl+RDlab) was that the change value must be larger than the value of field sampling error(REsmpl) and laboratory analysis error(RDlab). Therefore, sampling error and laboratory analysis error must be minimized.CONCLUSIONS: Six general guidelines are proposed.(1) The original sample is separated through a 10-mesh sieve and processed to a particle size of less than 200 mesh using a pollution-free method.(2) A total of 71 elements plus other parameters should be determined by well-established multiple analysis methods, e.g., fused glass bead-XRF for major elements and 4-acids ICP-MS and ICP-OES for minor elements in combination with other methods.(3) The method detection limits must be lower than crustal abundance of the chemical elements and reportable data percentage must be more than 90%.(4) The geochemical reference materials used for quality control should contain the reported certified CRM values for all elements.(5) Analytical relative errors for the triplicate samples should be less than 40%(RD≤40%) if concentration of the element is less than 3 times detection limits, and less than 20%(RD≤20%) for the elements with concentration more than 3 times detection limits as well as major elements, Fe-group elements and toxic metals.(6) The total contents of major elements SiO2, Al2O3, Fe2O3, FeO, MnO, MgO, CaO, Na2O, K2O, TiO2, P2O5, H2O^+, CO2, SO2 and organic matters or those of SiO2, Al2O3, Fe2O3, FeO, MnO, MgO, CaO, Na2O, K2O, TiO2, P2O5 and LOI should be at 99.3%-100.7%.