Forensic Discrimination of White Architectural Paints via ATR FT-IR Spectroscopy and Chemometrics
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The present work entailed the comparative examination and discrimination of white architectural paint samples of different brands/manufacturers. The analysis of this evidence can facilitate exhibiting a linkage between the victim, and the crime scene and assist in the reconstruction of the crime scene. Architectural paint traces have evidential value, especially in cases of burglary, acts of vandalism, property crimes, etc. In the present study, a total of 102 samples of 34 distinct brands (3 samples of each brand) of white commercially available architectural paints were purchased and analysed using ATR FT-IR spectroscopy and multivariate analytical tools. The use of visual analysis of FTIR spectral data resulted in 12 undifferentiated/ indistinguishable sample pairs with a discrimination power of 97.86%. Adding PCA and PLS-DA in concert with visual analysis of FTIR spectra resulted in 99.4% (3 sample pairs undifferentiated) and 100% discrimination power, respectively. In conclusion, samples of each brand were completely differentiated using ATR FT-IR spectra subjected to the PLS-DA model. To assess the impact of different substrates on the examination of paint chips, simulated samples were produced on different substrates and the obtained results from the substrates study have been summarized. The ATR-FTIR spectroscopy therefore suggests an objective and rapid approach for the discrimination of white architectural paints for forensic purposes.Keywords:
Chemometrics
Crime scene
White (mutation)
Sample (material)
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A method using attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy and multivariate analysis is reported to classify heroin hydrochloride and five common additives: caffeine, phenacetin, starch, glucose, and sucrose. Baseline correction, multivariate scatter correction, standard normal variables and Savitzky-Golay algorithm using smoothing with a polynomial order of three and a window size of seven points were adopted to preprocess the spectral data. Several supervised pattern recognition methods including radial basis function neural network (RBFNN), multilayer perceptron neural network (MLPNN), and linear fitting analysis (LFA) were used as algorithms to construct the classifiers. The use of a characteristic spectrum had lower complexity, required reduced modeling time, and was able to achieve the goal of rapid classification. Mixtures of heroin hydrochloride with caffeine, heroin hydrochloride and phenacetin, heroin hydrochloride with sucrose, heroin hydrochloride and starch, and heroin hydrochloride with glucose were distinguished with accuracy values of 100%, 100%, 88.89%, 77.78% and 66.67%, respectively. The fitting ability of the quadratic polynomial function was superior than using a linear model. A linear model was shown to be optimal when the additive was phenacetin, although the quadratic function was more superior when the additive was glucose. The developed method represents a simple, nondestructive, and rapid approach to classify mixtures of heroin hydrochloride with its common additives, caffeine, glucose, phenacetin, starch and sucrose.
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Spectroscopy Fourier Transform Infrared (FTIR) – Attenuated Total Reflectance (ATR) used to study the surface of polymeric materials on polymeric substrates using a sensitive technique for chemical profiling, study of reflection spectroscopy, and a non-invasive. In this study we will investigate of Polytetrafluoroethylene (PTFE) deposition in carbon composite paper without damaging its structure by FTIR-ATR. Carbon composite paper was prepared by mixing the carbon material from coconut fiber and polymer binder in xylen as solvent, casted on glass substrate, and then rolled to make a sheet. Coating process was done by dipped the carbon composite paper in the PTFE suspension with different content of 10 wt%, 20 wt% and 30 wt% for 30 minutes and dried at room temperature for one night and heated at 150°C for 30 minutes, and finally heated at 350°C for 30 minutes to melt the PTFE. All samples were analyzed by using FTIR-ATR and SEM-EDS. Deposition of PTFE with different content in carbon composite papers could be observed by FTIR-ATR. The peaks located at near 1205 cm -1 and 1154cm -1 with different intensity for each PTFE contents. FTIR-ATR could be used as a pre-detection method of PTFE deposition in carbon composite paper before using SEM-EDS, because FTIR-ATR would be reflected at the highly reflective surface.
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Attenuated total reflection Fourier transform infrared (ATR-FTIR) is a promising alternative to conventional transmission-FTIR. However, previous research has found that on evaluating the Styrene–Butadiene–Styrene-modified asphalt (SBSMA), ATR-FTIR and transmission-FTIR tend to have different conclusions. Due to the surface sensitivity of ATR-FTIR and varying morphology of SBSMA, ATR-FTIR may yield abnormal SBS infrared peak intensity growth upon aged SBSMA samples. In this paper, to further investigate how different SBS and sulphur dosages will influence the ATR-FTIR observation, conventional SBSMA (4.5%) and highly modified SBSMA (7.5%) were characterised using FTIR and fluorescence microscopy. It was found different SBS/sulphur dosages, and the application of laboratory ageing could notably vary the SBSMA morphology and therefore influence the obtained SBSMA infrared spectra. This phenomenon was more pronounced for highly modified SBSMA (7.5%) which had larger polymer particles.
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The most important Colombian coals were studied using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) Spectroscopy. The ATR-FTIR spectra were used to obtain structural parameters of coal and correlating these structural parameters with the rank of the coal. The structural parameters, methylene-methyl ratio (CH 2 /CH 3 ), aromaticity factor (f a ), aliphatic-aromatic ratio (H al /H ar ) were determined directly from the ATR-FTIR spectra and f a was evaluated from spectra data and an elemental analysis in coals studied here. The aliphatic and aromatic regions were considered between 3000 - 2800 cm -1 and 912 - 670 cm -1 , respectively.
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Abstract The interfacial structures of fillers treated by coupling agents were studied with FTIR and a Attenuated Total Reflection (ATR)‐FTIR spectrometer. The interfacial interaction was investigated by FTIR, and the nature of interaction was proved to be a chemical bonding, which could not be destroyed by extraction. Using a variable angle ATR technique, the average interfacial layer thickness of filler treated with different amounts of coupling agent was determined. A calibration curve was obtained from these studies to determine the optimal amount of coupling agent for different fillers, which was in agreement with the results of mechanical tests. ATR‐FTIR technique is a convenient method to determine the proper amount of coupling agent in composites.
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The molecular configuration and chemistry at the zinc/zinc oxide–polyester interface were studied by using two complementary spectroscopic techniques: attenuated total reflection–Fourier transform infrared spectroscopy (ATR-FTIR) and sum-frequency generation (SFG) spectroscopy. It was shown that ATR-FTIR should be considered as a (3D) interphase-sensitive technique with probing depths of 250–400 nm in the headgroup region (2000–1200 cm–1). On the other hand, SFG is known to be a (2D) interface-sensitive technique. The ATR-FTIR measurements showed that carboxylate groups are formed within the near-interface region of the polyester phase. SFG measurements showed that the carboxylic acid groups are stable at the polymer–zinc/zinc oxide interface. In addition, in situ ATR-FTIR and SFG measurements have been conducted when exposing the polyester–zinc/zinc oxide system to D2O. The exposure to D2O is observed to lead to an additional conversion of ester and carboxylic acid groups to carboxylate groups. The comparison of the SFG and ATR-FTIR measurements shows that this conversion occurs much slower at the polyester–zinc/zinc oxide interface than in the bulk of the polyester. Finally, the strengths and limitations as well as the complementarity of both techniques are discussed.
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The treatment choice of skin burns depends on the determinations of the depth of injury. We demonstrated the feasibility of Fourier transform infrared spectroscopy (FTIR) with Attenuated Total Reflection (ATR) to characterize burned skin.
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