激光诱导击穿光谱法测定稀土矿区土壤中钐含量

Measurement of Sm in rare earth mineral soil using laser-induced breakdown spectroscopy

为了满足现代分析检测技术发展的新要求,促进激光诱导击穿光谱技术(LIBS)在元素分析中的应用,本文利用LIBS结合定标曲线法对内蒙古白云鄂博稀土矿区土壤中的稀土元素钐(Sm)进行了定量分析,初步检验了LIBS对稀土矿样元素成分的检测能力。首先,以编号为GBW07402a国家标准物质土壤为基底,采用标准加样法制备了Sm_(2)O_(3)含量分别为1%、5%、10%和20%的待分析样品。其次,通过调节激光脉冲能量参数对基底样品进行激发,探究了激光能量参数对谱线强度和信背比的影响,得出最优化的实验条件后,对所有待分析样品进行激发以获取等离子体光谱信息。接着,分别采用多峰Lorentz拟合扣除背底法(MFM)和级联积分保留背底法(CIM)对光谱信息进行处理,构建以谱线积分强度与元素含量为关联量的定标曲线。最后,根据定标曲线进行含量预测,初步评估了LIBS用于稀土矿区土壤样品中Sm元素的检测性能。研究结果表明:受稀土矿区土壤基体效应的影响,Sm元素的谱线出现了强烈的展宽而导致无法进行有效分辨,而钠(Na)、钾(K)、钛(Ti)和铁(Fe)等元素的谱线没有呈现出明显的展宽。通过对比不同含量下的光谱信息,选取410 nm-band和470.44 nm为Sm元素分析谱线用于定量分析。基于积分强度和元素含量构建的定标曲线都有着较好的线性相关度,拟合系数(R^(2))值大都在0.99以上;相比而言,采用CIM处理光谱信息,可以获取更好的线性相关度,最大值为0.99927。以Sm含量为4.310%的3#样品为未知待测样品,采用留一法构建定标曲线对其含量进行预测分析,结果显示CIM法使得分析线具有极佳的预测性能,两条分析线对3#样品含量的预测相对误差均在1%以内。实验结果说明LIBS能够实现稀土矿区土壤中稀土元素Sm含量的检测分析,满足现代分析技术的新要求,为开发便携式稀土元素检测仪提供了实验依据。

This paper aims to meet the new requirements of modern analytical and testing technology development,and to promote the application of Laser-Induced Breakdown Spectroscopy(LIBS)in the field of element analysis,especially for the measurement of rare earth element in soil.A LIBS system combined with calibration curve method was used to quantitatively analyze samarium(Sm)in the soil of Bayan Obo rare earth mining region.Firstly,the samples containing 1%,5%,10%and 20%Sm_(2)O_(3)were prepared by Standard Addition Method(SAM)with the soil of national standard material GBW07402a as the base.Secondly,through analyzing the substrate excited by different laser pulse energy parameters,the influence of laser pulse energy parameters on the spectral line intensity and Signal to Back Ratio(SBR)was researched,an optimum laser pulse energy parameter was finally selected for the next measurement.Thirdly,in order to get and study the linearity of the calibration curve constructed between the peak area and the Sm concentration,the original spectra data were processed with multiple peak Lorentz fitting method without background subtraction(MFM)and Concatenation-based Integration Method(CIM)with background retention,respectively.Finally,according to the calibration curve,the concentration prediction was carried out,and the detection performance of LIBS for Sm in soil samples of rare earth mining area was preliminarily evaluated.The results show that the matrix effect of the soil can significantly broaden the emission lines of Sm element,which makes it impossible to distinguish them from each other.However,the effect of the soil matrix on sodium(Na),potassium(K),Titanium(Ti)and iron(Fe)is much weaker than that on Sm.By comparing the spectral region of interest,the 410 nm-band and 470.44 nm emission lines were identified and selected as the analysis lines,and subsequently used for quantitatively analysis.Results show that calibration curves for Sm element constructed by the peak area and concentration have good linear correlations and most of the linear relationships of the regression coefficients(R^(2))for the Sm emission lines are better than 0.99.Compared with the results by using MFM,CIM could obtain better linear correlation,and the maximum of was 0.99927 for the 410 nmband.The better analytical predictive skill of LIBS measurement by using the leave-one-out method with CIM data was found as well,the relative errors of the prediction for both the analysis lines were all within1%for the 3#sample with the Sm concentration of 4.310%.The achievements of this study demonstrate that the LIBS spectral analysis is capable of monitoring special elements in the rare earth mineral sample,which meets new requirements of modern analysis technology,and provides an experimental basis for the development of portable rare earth element detector as well.