車漆成分應用於鑑別刑事證據之研究

Abstract

本研究的目標在於開發一套有效的數據處理方法，可以針對車漆樣品的熱解資料得到其分佈的狀態，評估以平均質譜技術結合主成分分析及集群分析應用的可行性及實用性，並進一步延伸數據的價值，為此我們調查國內車漆的配方，並從中歸納15種常見添加成分質譜中的76個質量/電荷（m/z）訊息作為區分與合併樣品的多變量統計分析的指標。另一方面，聚苯乙烯為車漆中常見的成分，由於具有高質譜感受性，經熱裂解氣相層析質譜儀定量後，可發揮高靈敏度及低樣品消耗的優點，經探討聚苯乙烯的熱解性質及評估基質對於定量的干擾情形，我們發展了一套針對少量樣品可以適用的定量方法，可以鑑別不同來源的車漆樣品。本研究所建立的方法均通過國際能力試驗比對及盲樣的檢測以確認其有效性，且優化後的操作過程對例行檢驗的負擔可以減到最低。 綜整以上研究內容，本研究建立的方法從比對個案的定量分析結果，到大範圍的樣品分類，透過仔細及深入的數據比較過程，提供評判證物彼此的關聯性，藉由結合熱裂解氣相層析質譜儀及多變量統計與化學計量分析的方式，解讀微小的車漆樣品在系統中的定位及意涵，展示其證據力的價值內涵與科學意義，相信對於刑事科學研究及實務工作應有相當的助益。The aim of this work was to evaluate the capabilities and feasibility of using the averaged mass spectra obtained from pyrograms for assessing the group distributions and similarities of vehicle paint samples. To achieve this, all the profiles of averaged mass spectra were examined using principal component analysis and hierarchical cluster analysis after data processing. The pyrograms of 54 vehicle top coating samples were characterized by mass fragments chosen from 15 major paint constituents commonly used in the paint industry and multivariate chemometric analysis based on 76 variables, used as indicators for the classification of paint samples. Besides, polystyrene (PS) , one of the commonly used ingredients in paint recipes, is quantified by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) which offers satisfactory performance with low sample consumption and high sensitivity. Not only the characteristics of PS during the various pyrolyzing process are discussed, but also the matrix effects on quantification are evaluated for better identification of paint sources. We design a method to identify and quantify paint samples of different sources with limited quantities and high similarities. Furthermore, the method developed was proved to be accurate and reliable by participating international proficiency tests and multi-blind sample comparisons. Under the suggested conditions, extra work and pretreatment in routine work can be minimized. Through careful quantification of styrene component and comparisons of representative mass fragments of the paint constituents, the instrumental data can be treated in more detailed ways for the evaluation of paint evidence. The results indicated that these methods were promising, efficient and time saving tools for examining top-coating paint traces, with the application of combined Py-GC/MS with multivariate chemometrics for forensic purposes. Therefore, this technique can assist forensic scientists in actual cases of traffic accidents with better accuracy and reliability.