内标元素强度筛选法在激光诱导击穿光谱定量分析土壤标样中铁钛锶的应用

利用激光诱导击穿光谱(LIBS)技术进行光谱定量分析时,由于实验条件不稳定造成的测量结果检出限高、测量精确度低的问题一直是一个亟待解决的难题。实验选取地质矿产部化探分析质量监控站的标准土壤样品为分析样品,以波长为1064nm的Nd∶YAG激光器为激发光源,脉冲重复频率1Hz,通过激光诱导击穿光谱实验装置采集土壤样品在420~440nm范围内的等离子体光谱图。采用以内标法为基础的数据平均处理和内标元素强度筛选法(即以选定的内标元素谱线强度为参考,进行数据筛选)处理数据分别分析了待测样品中的Fe、Ti和Sr元素的含量并进行了对比,利用内标元素强度筛选法测得Fe、Ti和Sr的质量分数分别为68.4mg/g、10777μg/g和75.5μg/g,相对误差由平均法测得的10.60%、3.20%和8.57%降低为2.01%、0.21%和1.95%。说明内标元素强度筛选法处理数据可以减少数据处理量,简化数据处理过程并提高分析精度,尤其适用于激光能量输出不稳定、时间延迟较难控制的实验条件下的物质成分定量分析。

Application of internal standard element intensity-screening in quantitative analysis of iron,titanium and strontium in soil standard sample by laser induced breakdown spectroscopy

During the quantitative analysis by laser induced breakdown spectroscopy (LIBS), the problem of high detection limit and low measurement precision due to the instability of experimental conditions was always a challenge to be solved. The soil standard sample from Quality Control Station of Ministry of Geology and Mineral Resources for geochemical analysis was selected as the test sample. The Nd∶YAG laser with wavelength of 1064nm was used as the excitation light source. The pulse repetition frequency was 1Hz. The plasma spectra of soil sample in range of 420-440 nm was collected using LIBS experimental device. The data average processing based on internal standard method and internal standard element intensity-screening method (i.e., the spectral intensity of selected internal standard element was used as reference for data screening) were used for the analysis and comparison of Fe, Ti and Sr contents in test samples, respectively. The measured mass fraction of Fe, Ti and Sr by internal standard element intensity-screening method was 68.4mg/g, 10777μg/g and 75.5μg/g, respectively. The relative error was reduced to 2.01%, 0.21% and 1.95% from 10.60%, 3.20% and 8.57% by average method, respectively. The results indicated that the internal standard element intensity-screening method could reduce the data processing capacity, simplify the data handling process and improve the analysis precision. Particularly, the proposed method was suitable for the quantitative analysis of composition under experimental conditions when the laser energy output was unstable and the time delay was hardly controlled.