低气压下土壤中Pb等离子体光谱特性

用Nd∶YAG激光诱导激发土壤等离子体，研究了环境压力(在1.01×105与1×102 Pa之间)对土壤等离子体辐射特性及元素检出限的影响。结果表明，随着气压的降低，土壤等离子体的谱线强度、信背比先增大后减小，最高均可达常压下的1.69倍；电子密度同样呈现先增大后减小的趋势，在气压8×104 Pa下达到最大值3.56×1016 cm-3，比常压下高出1.5×1015 cm-3；在气压8×104 Pa下诱导激发等离子体发射光谱与常压下相比有较好的稳定性和较高的精密度。20次重复实验得到土壤等离子体分析线信号强度的相对标准偏差为1.1%，明显低于常压下的3.5%，低气压下稳定性显著提高。应用内标法对自制土壤中Pb元素建立定标曲线，计算得到气压8×104 Pa下土壤中Pb元素的检出限为57.27 mg·kg-1，较常压下降低了39.23 mg·kg-1。表明适当的低压环境可以有效提高LIBS的光谱检测灵敏度，改善元素分析的检出限以及增加光谱定量分析的准确度和精密度。

Spectral Characteristics of Pb Plasma in Soil at Low Pressure

In this paper, the effect of ambient pressure (between 1.01×105 and 1×102 Pa) on soil plasma radiation and element detection limit was studied by using Nd∶YAG laser to induce soil plasma. The research shows that the spectral intensity of soil plasma and the signal-to-background ratio increase first and then decrease with decreasing pressure, and the both maximum value are 1.69 times higher at 8×104 Pa compared with normal pressure; In addition, the electron density also increases first, then decreases, and reaches a maximum of 3.56×1016 cm-3 at 8×104 Pa. Induced plasma emission spectrum has good stability and high precision at 8×104 Pa compared with normal pressure. The relative standard deviation of the signal intensity of soil plasma analysis line is 1.1%, which is significantly lower than 3.5% at normal pressure, and the stability of plasma emission spectrum is significantly improved at low pressure. Besides, the internal standard method was used to determine Pb content in soil, and the limit of detection of Pb in soil is 57.27 mg·kg-1 at 8×104 Pa, which is 39.23 mg·kg-1 lower than the limit of detection at normal pressure. The results of the study shows that spectral detection sensitivity of laser-induced breakdown spectroscopy can be improved effectively in the appropriate low pressure environment. The appropriate low pressure environment can improve the detection limit of elemental analysis and increase the accuracy and precision of spectral quantitative analysis.