原子吸收光谱法测定岩石中铜、铅和锌的不确定度评定及方法改进

利用原子吸收光谱法进行地质样品中微量元素含量的测定简便、快速、准确、经济，目前在地质实验室中得到了广泛应用。然而复杂的前处理流程和测试过程都会不可避免地引入不确定度。根据《检验和校准实验室能力的通用要求》，实验室应适当进行测量结果不确定度的评定。本研究利用电热板消解，火焰原子吸收光谱法，测定国家标准岩石样品与采自胶东曲家金矿岩心样品中铜、铅和锌的含量。以空白样品测试结果标准偏差的三倍作为仪器检出限。标准样品及岩心样品测试结果均符合DZ/T 0130.3—2006中关于测试准确度与精密度的要求。在实验室内部，采用自下而上的方法进行测量结果不确定度的评定，确定了测量不确定度的来源，包括样品称量、样品定容、样品消解、标准系列的配制、标准曲线最小二乘拟合及重复性测量，准确计算了六个不确定分量的大小及扩展不确定度。其中，后四个分量是测量结果不确定度的主要来源。结果显示标准样品中铜、铅和锌含量测量结果不确定度均小于标准证书中给定的不确定度，岩心样品中铜、铅和锌的含量分别为（4.965±0.383），（36.415±2.449）和（30.818±0.736）μg·g-1。对六个来源的不确定度进行比较，提出采用该方法测量岩石样品中铜、铅和锌含量时的几点改进：调整取样量或定容体积来提高待测溶液中元素浓度及吸光度、调整标准系列浓度使其与待测溶液中元素浓度相近、增加标准点和待测溶液测量次数、尽量使用相对标准不确定度小的移液管进行稀释操作等。将测量结果不确定度的评定作为有效工具，指导改进分析方法及测试流程，在岩石样品微量元素含量准确测定工作中具有重要的意义。

Uncertainty Evaluation and Method Improvement of Determination of Copper,Lead, and Zinc in Rocks by Atomic Absorption Spectrometry

The determination of trace elements in Geological Samples by Atomic Absorption Spectrometry is simple, rapid, accurate and economical, which has been widely used in geological laboratories. However, the complex pre-processing process and testing process will inevitably introduce uncertainty. According to the general requirements for the competence of inspection and calibration laboratories, the uncertainty of measurement results should be properly evaluated. In this study, the concentration of Cu, Pb, and Zn in the national standard rock sample and a core sample from the Qujia gold mine in Jiaodong were determined by Atomic Absorption Spectrometry after electric heating plate digestion. Three times the standard deviation of the blank samples test results was calculated as the detection limits. The results of the standard samples and core samples are by the requirements of DZ/T 0130.3—2006 on the accuracy and precision of the test. The bottom-up method was used to evaluate the uncertainty of results in the laboratory. The sources of measurement uncertainty were determined, including sample weighing, constant sample volume, sample digestion, preparation of standard series, least-square fitting and repeated measurement. The value and expanded uncertainty of six uncertainty components were accurately calculated. Among them, the last four components are the main sources of uncertainty. The results show that the uncertainty of the measurement results ofcopper, lead, and zinc in the standard samplesaresmaller than the uncertainty given in the standard certificate, the concentration of Cu, Pb, and Zn in the core sample is (4.965±0.383), (36.415±2.449), (30.818 0±0.736) μg·g-1, respectively. The uncertainty of six sources is compared, and some improvements are put forward when the content of Cu, Pb, and Zn in rock samples is measured by this method: adjusting the sampling mass or constant volume to improve the concentration and absorbance of elements in the solution to be measured, adjusting the concentration of standard series to make it close to the concentration of elements in the solution to be measured, increase the measurement times of standard point and the solution to be measured, the pipette with small relative standard uncertainty should be used as much as possible if necessary in order to reduce the measurement uncertainty. Evaluating measurement uncertainty as an effective tool to guide the improvement of analytical methods and test process is of great significance in the accurate determination of trace elements in rock samples.