纳秒和飞秒激光剥蚀速率对非基体匹配元素分馏校正研究

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is widely used to measure minor element and isotope-ratio in solids. However, this matrix-dependent element fractionation makes the combination method of external standard and internal standard very difficult to quantitatively analyze minor element concentrations. By researching the physical and chemical influence mechanism of material components and ablation conditions on ablation rates, the relationship between the ablation rates of nanosecond and femtosecond lasers and the slopes of the ratio curves of unknown element intensity signal and internal element intensity signal will be investigated. Influence and constraint of laser ablation behavior on element fractionation will be disclosed. The comparable ablation rate can be expected by using different ablation conditions for different solid samples. The slopes of the intensity curve ratios of unknown element and internal element in samples and in standard sample will be identical perfectly. The aside effect of element fractionation for computation can be eliminated. As a result, more accurately quantitative analysis of the unknown minor element can be realized.

激光剥蚀电感耦合等离子体质谱广泛用来测量固体样品中的微量元素及同位素比值。然而在缺乏基体匹配校准条件下，依赖于基体的元素分馏效应使得通常采用外标结合内标的方法很难准确量化待测微量元素的含量。通过研究物质成分和剥蚀条件对剥蚀速率影响的物理化学机制，研究激光剥蚀速率和待测元素与内标元素强度比值平均信号斜率变化关系，揭示激光剥蚀行为对元素分馏的影响及约束。对不同的样品使用不同的剥蚀条件获得可比拟的剥蚀速率，期望标样和样品中待测元素和内标元素强度比值平均信号曲线斜率一致，消除元素分馏效应对计量的负面影响，实现对待测微量元素的准确量化。

微量元素的含量和分配以及与相近元素的比值可作为各种成岩成矿物理化学条件的灵敏指示剂或示踪剂。为了进一步丰富美国地质调查局（USGS）系列标准地质样品元素含量数据，在不同能量密度条件下193 nm波长纳秒激光剥蚀电感耦合等离子体质谱技术被用于分析地质标准样品BCR-2G, BHVO-2G, BIR-1G, 和 GSD-1G主、微量元素含量。GSD-1G外标结合内标43Ca以及100%氧化归一法（结合多外标BCR-2G, BHVO-2G, 和BIR-1G）用于分析元素含量。对于前者，除了Mg, Fe, Zn, Cd, Cs, Bi, 和一些镧系元素(Pr, Sm, Gd, Tb, Dy, Ho, Er, Tm, 和 Yb)，当激光能量密度变化范围为4-12 J/cm2时，比Ca熔沸点高的元素含量标准偏差随激光能量密度增大而减少，相反，比Ca熔沸点低的元素含量标准偏差随激光能量密度增大而增大。而对于后者，没有适合的激光能量密度条件下含量标准偏差最小。外标结合内标法适合于对硅酸盐样品元素含量量化，因为可选择适合的激光能量密度进行测试。当激光脉冲穿过前表面聚焦于后表面时，在前表面上会形成同心圆环现象。环的深度和间距沿径向向外逐渐变深和变大。圆环特征与使用的激光波长和能量相关，通过泵浦-探测阴影成像术和表面形貌检测技术探究圆环形成物理机制，可揭示激光与物质相互作用初期阶段激光诱导损伤和等离子体进化的相互关系。激光剥蚀羽有多个分层结构和多个冲击波波前，激光加载冲击波能够进一步诱导微喷射现象发生。