基于等离子体锥形空间约束对土壤中Cr的LIBS研究

为了提高激光诱导击穿光谱(LIBS)技术对土壤中重金属元素的检测灵敏度，降低检测限，以国家标准土壤中Cr元素为研究对象，实验时，在LIBS装置中与样品接近的聚焦透镜下方安装一个锥形罩，锥形罩的小端面直径为20 mm，大端面直径为45 mm，目的是对等离子体发射信号形成空间约束，并且在一定程度上约束等离子体本身。实验得到CrⅠ425.44 nm的最佳延迟时间为1.3 μs，相对标准偏差低于10%。与无锥形空间约束的装置相比，Cr的特征光谱强度增强了7%以上。以土壤中的Cr在60～400 μg·g-1之间的浓度建立定标曲线，有空间约束下定标曲线的线性拟合相关系数为0.997 71，Cr的检测限为18.85 μg·g-1，而没有空间约束下定标曲线的线性拟合相关系数为0.991 22，Cr的检测限为36.99 μg·g-1。由此表明锥形空间约束能够提高目标元素的灵敏度和光谱强度，在LIBS技术检测土壤中Cr元素时有很好的辅助作用。

Analysis of Cr in Soil by LIBS Based on Conical Spatial Confinement of Plasma

The present study is to improve the sensitivity of detection and reduce the limit of detection in detecting heavy metal of soil by laser induced breakdown spectroscopy(LIBS).The Cr element of national standard soil was regarded as the research object. In the experiment, a conical cavity with small diameter end of 20 mm and large diameter end of 45 mm respectively was installed below the focusing lens near the experiment sample to mainly confine the signal transmitted by plasma and to some extent to confine the plasma itself in the LIBS setup. In detecting CrⅠ425.44 nm, the beast delay time gained from experiment is 1.3 μs, and the relative standard deviation is below 10%. Compared with the setup of non-spatial confinement, the spectral intensity of Cr in the soil sample was enhanced more than 7%. Calibration curve was established in the Cr concentration range from 60 to 400 μg·g-1. Under the condition of spatial confinement, the liner regression coefficient and the limit of detection were 0.997 71 and 18.85 μg·g-1 respectively, however, the regression coefficient and the limit of detection were 0.991 22 and 36.99 μg·g-1 without spatial confinement. So, this shows that conical spatial confinement can improve the sensitivity of detection and enhance the spectral intensity. And it is a good auxiliary function in detecting Cr in the soil by laser induced breakdown spectroscopy.