In a strangulation case, when a necktie is used as a murder weapon, the dyed silk single fiber becomes an important evidence sample to solve the crime. Dyed silk single fibers contain elements, such as Cr and Co, which are obtained from dyeing using metal mordants. Currently, there are no nondestructive and sufficiently sensitive elementary analytical methods for the forensic analysis of single fibers. Therefore, in this study, eight commercially available red silk samples were collected and used for total reflection X-ray fluorescence (TXRF) and synchrotron radiation X-ray fluorescence (SR-XRF) spectrometry. Benchtop TXRF detected both S in the silk protein and Cl and Ca, which are elements absorbed from the environment by silkworms, but also Cr, which is a dyeing derivative for metal mordants. The presence of Cr and Zn, in addition to the Zn/Cr signal intensity ratios, was reported to be particularly useful identifiers. In SR-XRF, the presence of Cr, Co, Zn, and Br and the Zn/Cr signal intensity ratios were reported to be useful discriminating indicators. In this study, the nondestructive discrimination capabilities of TXRF and SR-XRF measurements for the samples were found to be 85.7% and 100%, respectively. Therefore, we propose a combination of TXRF and SR-XRF as a new nondestructive single fiber identification method for forensic science. Moreover, if partial destruction of a single fiber is allowed, the observation of the cross section and micro-Fourier-transform infrared spectroscopy measurements is useful for identifying red silk fibers.
Total reflection X-ray fluorescence (TXRF) spectrometry was applied to a forensic discrimination of single polyester fibers. In a non-destructive direct measurement of 5 mm long single fibers used for forensic references, trace metallic elements such as Ti, Sb, Ge, Mn, and Co, found in additives and catalyst residues, were detected using a benchtop TXRF spectrometer. The individual elemental compositions of the fibers were identified, and correlations between the compositions and manufacturers were established using principal component analysis (PCA). Black polyester fibers sampled from the car trunk mats were also analyzed. Several fibers were found to contain both Sb and Ge, elements that characterize different polymerization catalysts; this indicates that the fibers were composed of recycled materials. The TXRF and SR-μXRF spectra showed similar patterns for the fiber samples that were analyzed.
The color of emeralds is predominantly influenced by the concentration of Cr3+. However, the evaluation of the trend of green color depth of emeralds, based on the practical single crystal synthesis with several instrumental analysis is not investigated in previous researches. Specifically, if the Cr2O3 content is controlled to be in the range of 0.2–0.4 wt%, then emeralds can be synthesized with the most esthetically pleasing color. Therefore, the effect of Cr2O3 concentration within the aforementioned range on the color of emeralds is studied using powder X‐ray diffractometry, digital microscopy, electron probe microanalysis, and micro‐spectrophotometry to understand how to achieve the most esthetically pleasing color. As a result, detailed behaviors relating to the absorbances, L*, a*, and b* values, and the relationship between the emerald crystal color changes and increases in Cr2O3 concentration are elucidated. Notably, the absorbance, L* and a* values change significantly when the Cr2O3 concentration is low (0.00–0.236 wt%). However, the changes in these values are moderate when the Cr2O3 concentration is higher (0.236–0.504 wt%).
In this study, single synthetic fibers obtained from several textile products were analyzed by a portable total reflection X-ray fluorescence spectrometer. Characteristic elements, which would originate from materials such as catalyst, delustering agent, and dye used for manufacturing synthetic fibers, were detected from the single synthetic fiber samples, and the difference in the types of characteristic elements among the single synthetic fiber samples was observed.
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