| Summary: | 碩士 === 中央警察大學 === 鑑識科學研究所 === 100 === Automotive paint chips with car body putty(auto body fillers)were often encountered in traffic accident cases or hit-and-run crashes. To evaluate different discriminating power of forensic examination methods, we have identified 42 types of auto body fillers in our previous study. And among these methods, colorimetry and Pyrolysis Gas Chromatography/Mass Spectrometry(Py-GCMS) demonstrated higher level of discriminating power on the analysis of auto body fillers. However the use of colorimetry method needed to consider if the thickness of sample in much lower state maybe cause color interference from it’s background layer. The results obtaining from Py-GCMS showed that 9 groups of the samples could not be discriminated. The aims, in this study, are focused on (1) the evaluation of optimal thickness for the colorimetry analysis, (2) the application of Evolved Gas Analysis on auto body fillers.
The sample preparations for the colorimetry analysis were conducted by a series of steps including coating condition, cutting, embedding, and grinding. The L＊, a＊, b＊-value of light-weight body fillers were determined under the different thickness. In evolved gas analysis, 13 samples of 5 groups slected from 9 groups including light-weight body fillers and poly putty were used. First, through the experiment of different sampling weights, we evaluated the most optimal weight was 0.25mg, the peak ratio between the peakA and peakB having the highest intensity, and the difference in time of evolved gas between two peaks. Each sample in the same group was determined 7 times in the EGA analysis.
Experimental results show when the thickness of light-weight body filler less than 232μm for King brand, and less than 558μm for One-Day brand appear a trand that a＊-value decreases and b＊-value simutaneously increases. The phenomenon indicates that a＊-value, b＊-value of the measured color side will be changed if it is under much lower thickness. The resulting data obtaining from EGA analysis show that we cound distinguish differences among samples in 4 groups by the comparation of EGA chromatograms. Besides, the statistical testing is further used for the discrimination of the last group. It still shows the significant difference between two samples. The EGA method combined with Py-GCMS has been proved to be a useful approach on the analysis of auto body fillers. Finally, a systematic protocol for the forensic examination on auto body fillers is established in this study.
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