激光诱导击穿光谱结合标准加入法定量分析土壤中铅、镉、铬和铜

摘要

利用课题组自主研制的便携式激光诱导击穿光谱测量系统定量分析土壤及固体废弃物中四种重金属元素Pb,Cd,Cr和Cu.实验采用中心波长为1064 nm的Nd:YAG脉冲激光器作为激发光源,工作频率为3 Hz,单脉冲能量为100 mJ,脉冲宽度为6 ns;以高分辨率、宽光谱段的中阶梯光栅光谱仪和增强型电荷耦合器件为谱线分离与探测器件,探测范围为200~500 nm,分辨率为0.08~0.12 nm.为了提高光谱强度及检测灵敏度,通过半球空间约束装置对等离子进行约束,并采用多芯光纤实现多通道不同角度光谱信号收集,接收角度为45°.实验时激光重复频率为2 Hz,延时为1.5μs,门宽为1.05 ms.文章创新性地将曲线拟合代替直线拟合用于标准加入法定量分析基质未知样品中重金属元素,有效提高了测量结果的准确性,尤其是低浓度的土壤样品,直线拟合无法定量分析重金属含量,相比而言,曲线拟合相关系数更高,测量结果更接近国标方法,可以满足一级土壤污染的检测.七个土壤及固体废弃物样品检测的相对误差如下,直线拟合相对误差分别为:Pb 1.26%~79.38%,Cr-22.44%~82.06%,Cu 15.09%~190.50%,Cd 32.76%~167.96%,曲线拟合相对误差为分别Pb-4.19%~11.92%,Cr-38.31%~9.26%,Cu-7.24%~26.86%,Cd-10.52%~12.94%,相对误差平均值为10.47%.%Quantitative analysis of four heavy metals Pb,Cr,Cu and Cd in soils and solid wastes using inde-pendently developed portable system of laser-induced breakdown spectroscopy.A Nd:YAG pulse laser with fundamental wavelength of 1064 nm is used as the excitation source,with the single pulse energy of 100 mJ the pulse width of 6 ns,and the operating frequency 3 Hz.The echelle spectroscopy with high resolution and wide spectral range is used as the spectral separation device,and the intensified charge coupled device (ICCD) as the spectral detection device in the experiment,with the detection range of 200~500 nm and a resolution of 0.08~0.12 nm.In order to improve the spectral intensity and detection sensitivity,a device of hemisphere spatially bound is used to restrain the plasma and a optical fiber with multi-channel is used collect the signal. The reception angle is 45°.The laser repetition rate is 2 Hz while the delay is 1.5 μs,with the gate width of 1.05 ms.Standard addition method is used to effectively solve the quantitative analysis of samples of unknown matrix.The innovation lies in the fact that,a curve fit instead of a straight line fit is used in the standard addi-tion method to quantitative analyze the heavy metals in soils and solid wastes,which effectively improve the measurement results.Especially for the low concentrations of soil samples,linear fitting can not be used in quantitative analysis,in contrast,the correlation coefficient of curve fitting is much higher,more closer to the national standard measurement methods,to meet soil pollution detection.The result of seven soils and solid wastes samples are as follows,line fitting relative error:Pb 1.26%~79.38%,Cr -22.44%~82.06%,Cu 15.09%~ 190.50%,Cd 32.76% ~ 167.96%,and curve fitting relative error respectively Pb - 4.19% ~11.92%,Cr -38.31% ~ 9.26% ,Cu - 7.24% ~ 26.86%,Cd - 10.52% ~ 12.94%,the average relative error is 10.47%.