电感耦合等离子体质谱在微量物证检验中的应用（英文）

The Application of Inductively Coupled Plasma Mass Spectrometry in Trace Evidence Examination

法庭科学领域微量物证检验中,元素分析是非常重要的一个方面。通过分析物证中的主要元素和微量元素,可以为物证之间的比对检验和物证溯源提供关键信息。虽然目前有很多微量物证的元素分析方法,但电感耦合等离子体质谱(ICP-MS)技术是在近十年愈益受到关注和应用。相对于常用的元素分析方法,如X射线荧光光谱法、原子吸收光谱法、中子活化分析以及波长(或能量)色散X射线能谱法,ICP-MS分析法有很多优点,比如更适合于微量物证的检验分析,只需要很少的样品量,就可以完成主要元素和微量元素的同时分析;如果配置激光蚀刻进样系统,就不需对样品进行复杂的前处理,可大大节省时间和物力;同时,激光蚀刻进样只需要非常小的样品量,几乎是无损检验,能够避免像X射线荧光光谱对样品表面必须平整的要求。在我们微量物证检验实验室,应用溶液进样和激光烧蚀取样两种模式以ICP-MS分析法进行了很多有价值的工作,本文对相关部分工作进行介绍和总结。通过对重金属中毒检验,通过微波消解-ICP-MS法对死者组织中汞(Hg)、钛(Ti)、铬(Cr)、砷(As)等元素含量的准确分析,帮助推断了死亡原因;对环境污染案件中提取的泥土样品,经微波消解后进行ICP-MS检验,分析了嫌疑排放污物对环境的污染程度;对土壤样品,采用碰撞反应池技术和标准分析模式,定量检验了30余种元素,为泥土样品的比对和地源推断提供了丰富的信息;对小样品量泥土样品,通过激光蚀刻-ICP-MS检验,优化了激光的烧蚀参数。以此为基础,还利用激光蚀刻-ICP-MS法对案件中收集到的假币纸张进行了检验,经数据聚类和主成分分析,使12起案件中的8起得到串并。此外,利用激光蚀刻-ICP-MS法对按主要成分无法区分的细金属丝(铁丝)进行检验,通过其微量元素的种类与含量测定,对金属丝作了进一步的分辨。再有,利用ICP-MS的同位素比值分析方法,对国内主要子弹生产厂家的41枚子弹弹头进行了铅(Pb)元素同位素比分析,既对铅弹头进行了辨识,又通过铅元素同位素比值数据建立了子弹头与生产厂家间的关联。ICP-MS的应用方法在本实验室仍在不断开发中,如对地质样品进行元素分布分析,以及结合激光蚀刻的厚度蚀刻功能,对不同层次的油漆样品作分层检验等。

Elemental analysis is important for forensic chemists to examine trace evidence. The analysis of both major and trace element is widely used for forensic comparisons, having successfully provided essential information for evidence provenancing. Although there are several established techniques available to determine elemental composition, the inductively coupled plasma mass spectrometry （ICP-MS） has in the latest decade drawn much more attention from many scientists, including those who are concerned with forensic applications. Compared with other elemental analytic methods, e.g., X-ray fluorescence （XRF）, atomic absorption spectrophotometry （AAS）, neutron activation analysis （NAA） and energy （or wavelength） dispersive X-ray microanalysis （EDS or WDS）, ICP-MS has many advantages, for example, the capability of more suitable to simultaneously measure the abundance of a large suite of elements in small samples; time and resource saving when coupled with laser ablation approach because of its non-necessity of sample preparation, proximity to non-destruction on the sample, avoidance of demand to measure on smooth surfaces required by XRF; and quantitative analysis of major, minor and trace elements in one analytic run. All these advantages help to examine trace evidence more easily and quickly. In our laboratory, ICP-MS has been used to measure the heavy metal （Hg, Ti, Cr, As） contents in human tissues related to poisoning events, the liquids discharged into river or soil to tell if they are harmful to the environment, Moreover, the laboratory also used ICP-MS, combined with the laser ablation approach, to examine the amount-small soil evidence, counterfeit banknote paper and thin metal wires to make them compared and identified. In addition, lead isotope ratio among bullet alloys has been detected to differentiate them and link them with their manufacturers. At present, our on-going application of ICP-MS is under development in aspects such as the elemental mapping of geological evidence and the strata analysis into vehicle paints.