圈定元素活动态异常, 可获得深部矿化信息, 预测成矿物质供应量, 是深穿透地球化学研究隐伏矿的有效方法之一。 但常规的实验技术需将样品运回实验室进行分析, 运输过程和时间均有可能带来元素活动态的变化, 影响分析结果； 且常规分析的样品用量大, 限制了活动态提取时间参数的研究。 而全反射X射线荧光光谱(TXRF)技术灵敏度高、 定量简单、 用量少, 且仪器体小便携, 无需载气和冷却水, 适合野外现场快速分析。 因此, 利用TXRF, 从内标选择、 质量控制入手, 建立了土壤中Ti, V, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Y, Ba, Ce和Pb等多元素活动态的分析方法。 由于提取剂中有机质含量高, 方法选取较高浓度的Se作为内标(分析液中Se为10 μg·mL-1), 以提高高背景下Se测定的准确性。 为了控制污染降低误差, 实验前的石英玻璃反射体须进行TXRF 100s的空白测定, 选取无杂质峰的干净反射体用于实验。 主要实验步骤如下: (1)5 g土壤样品中加入50 mL多金属提取剂(0.09 mol·L-1草酸铵-0.1 mol·L-1柠檬酸铵-0.001 mol·L-1乙二胺四乙酸钠(EDTA)-0.001 mol·L-1二乙基三胺五乙酸(DTPA)-0.001 mol·L-1氨基三乙酸(NTA)-0.005 mol·L-1三乙醇胺(TEA)), 室温混合振荡72 h后, 用0.45 μm滤膜过滤； (2)取滤液(提取液)100 μL, 加入10 μL 100 μg·mL-1 Se溶液作为内标, 混匀； (3)移取10 μL待测液于硅化的石英玻璃反射体中, 50 ℃烘干后进行TXRF测定(Mo-Kα单色激发, 测定时间1 000 s)。 实验结果表明: 土壤中元素活动态的TXRF分析方法检出限在几个到几十个μg·L-1, 大部分元素精密度(RSD)小于10%, 与ICP-MS/ICP-OES分析结果相比, 相对误差平均值为18%。 该方法适用于野外现场元素活动态的快速分析。 由于方法取样体积100 μL, 上样体积10 μL, 亦适用于活动态提取时间条件实验, 可实现小体积连续取样, 效率高、 连续性强、 误差较小。

Delineating abnormity zones of elements in mobile forms is one of the effective methods of deep-penetrating geochemistry for finding concealed orebodies, which can obtain deep mineralization information and predict the supply of metallogenic materials. However, samples have to be transported to the laboratory for analysis under conventional experimental techniques. Transportation process and time may affect the concentration of the elements of mobile forms. Moreover, the large amount of samples required for conventional analysis limits the study of extraction time of mobile forms. Total reflection X-ray fluorescence spectrometry (TXRF) has the advantages of high sensitivity, simple quantification and less dosage. With characteristics of the compact and portable instrument as well as no need for carrier gas and cooling water, TXRF is suitable for on-site analysis. In this paper, TXRF was used to establish a method for the analysis of mobile forms of Ti, V, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Y, Ba, Ce and Pb in soils, by selecting internal standard and controlling quality. Because of the high content of organic matter in the extract, the concentration of internal standard Se was set higher (10 μg·mL-1 Se in the analytical solution), so as to improve the analytical accuracy of Se under high background. In order to control the pollution and reduce the error, blank reflectors were analyzed by TXRF for 100 s. The reflectors without impurity peak were used for the experiment. The main steps list as follows: (1) 5 g soil samples were mixed with 50 mL polymetallic extractant (0.09 mol·L-1 ammonium oxalate, 0.1 mol·L-1 ammonium citrate, 0.001 mol·L-1 EDTA, 0.001 mol·L-1 DTPA, 0.001 mol·L-1 NTA, 0.005 mol·L-1 TEA). The mixture was oscillated for 72 h at room temperature and then filtered with 0.45 μm filter membrane. (2) The 100 μL of filtrate (extract) was spiked with 10 μL internal standard of 100 μg·mL-1 Se. (3) After vortexing, 10 μL drop of aqueous solution was deposited onto a siliconized quartz glass reflector and dried at 50 ℃ for TXRF analysis (monochromatic excitation of Mo-Kα, measure time 1 000 s). The results showed that the detection limit of elements ranged from several to dozens of μg·L-1. The RSD of most elements wa less than 10%. The average relative error was 18% compared with ICP-MS/ICP-OES. This method is suitable for rapid on-site analysis of elements mobile forms. 10 μL drop of 100 μL prepared samples to make it suitable for time experiment of mobile forms by using small volume continuous sampling, with high efficiency, relatively strong continuity and minor error.