Yiwen Luo

Detection and identification of dyes in blue writing inks by LC-DAD-orbitrap MS

In the field of forensic questioned document examination, to identify dyes detected in inks not only provides a solid foundation for ink discrimination in forged contents identification, but also facilitates the investigation of ink origin or the study regarding ink dating. To detect and identify potential acid and basic dyes in blue writing inks, a liquid chromatography-diode array detection-Orbitrap mass spectrometry (LC-DAD-Orbitrap MS) method was established. Three sulfonic acid dyes (Acid blue 1, Acid blue 9 and Acid red 52) and six triphenylmethane basic dyes (Ethyl violet, Crystal violet, Methyl violet 2B, Basic blue 7, Victoria blue B and Victoria blue R) were employed as reference dyes for method development. Determination of the nine dyes was validated to evaluate the instrument performance, and it turned out to be sensitive and stable enough for quantification. The method was then applied in the screening analysis of ten blue roller ball pen inks and twenty blue ballpoint pen inks. As a result, including TPR (a de-methylated product of Crystal violet), ten known dyes and four unknown dyes were detected in the inks. The latter were further identified as a de-methylated product of Victoria blue B, Acid blue 104, Acid violet 49 and Acid blue 90, through analyzing their characteristic precursor and product ions acquired by Orbitrap MS with good mass accuracy. The results showed that the established method is capable of detecting and identifying potential dyes in blue writing inks.

Characterization of the Postmortem Interval by Infrared Microscopy

ABSTRACT The objective of this study was to develop a novel and effective method for the evaluation of the postmortem interval using infrared microspectroscopy. Postmortem rat liver samples were investigated at 10, 20, and 30°C. Time-dependent changes in the images were observed from variations in the spatial distribution in the liver tissue that were correlated with the postmortem interval. This relationship, which has not been reported previously, offers a novel approach to supplement conventional forensic methods.

Characteristics of electrically injured skin from human hand tissue samples using Fourier transform infrared microspectroscopy

This technical note describes a method for distinguishing normal skin tissue samples from those electrically injured by Fourier transform infrared microspectroscopy (FTIR MSP). Furthermore, the infrared spectral features of electrically injured cells and tissues were evaluated to identify molecular changes in epidermal cells. In the present study, 20 human hand tissue samples were evaluated macroscopically and histopathologically. The electrically injured skin samples were subdivided into 2 regions [normal cell regions (NCRs) and polarized cell regions (PCRs)] and 14 major spectral absorption bands were selected. The spectral results showed that the band absorbance at 1080, 1126, 1172, 1242, 1307, 1403, 1456, 1541, 2852, 2925, 2957, 3075, and 3300cm(-1) increased significantly both in the stratum and non-stratum corneum of the PCRs in electrically injured skin tissues samples. No significant difference was found between normal skin and the NCR of the electrically injured skin samples. The band absorbance ratios of A1172/A1126, A1456/A1403, and A2925/A2957 were significantly increased, whereas the A1652/A1541 ratio was decreased in the PCR of the stratum corneum and non-stratum corneum. Baseline changes from 4000 to near 1737cm(-1) were observed in the spectra of the electrically injured skin samples, which were interpreted in terms of the pathological process involved in electrical injury. FTIR-MSP presents a useful method to provide objective spectral markers for the assisted diagnosis of electrical marks.

Analysis of PEG oligomers in black gel inks: Discrimination and ink dating

Carbon-based black gel inks are common samples in forensic practice of questioned document examination in China, but there are few analytical methods for this type of ink. In this study, a liquid chromatography-.high resolution mass spectrometry (LC-HRMS) method was established for the analysis of PEG oligomers in carbon-based black gel ink entries. The coupled instruments achieve both the identification and quantification of PEG oligomers in ink entries with reproducible results. Twenty carbon-based black gel inks, whose Raman spectra appeared identical, were analyzed using the LC-HRMS method. As a result, the twenty gel inks were classified into four groups according to the distribution of PEG oligomers. Artificially aging of PEG 400 and a gel ink showed that as PEG degraded, the relative amounts of low molecular weight PEG oligomers increased, while those of high molecular weight decreased. The degradation of PEG oligomers in a naturally aged gel ink was consistent with those in the artificially aged samples, but occurred more slowly. This study not only provided a new method for discriminating carbon-based black gel ink entries, but also offered a new approach for studying the relative ink dating of carbon-based black gel ink entries.

Assessment of Signature Handwriting Evidence via Score-based Likelihood Ratio Based on Comparative Measurement of Relevant Dynamic Features

This paper extends on previous research on the extraction and statistical analysis on relevant dynamic features (width, grayscale and radian combined with writing sequence information) in forensic handwriting examinations. In this paper, a larger signature database was gathered, including genuine signatures, freehand imitation signatures, random forgeries and tracing imitation signatures, which are often encountered in casework. After applying Principle Component Analysis (PCA) of the variables describing the proximity between specimens, a two-dimensional kernel density estimation was used to describe the variability of within-genuine comparisons and genuine-forgery comparisons. We show that the overlap between the within-genuine comparisons and the genuine-forgery comparisons depends on the imitated writer and on the forger as well. Then, in order to simulate casework conditions, cases were simulated by random sampling based on the collected signature dataset. Three-dimensional normal density estimation was used to estimate the numerator and denominator probability distribution used to compute a likelihood ratio (LR). The comparisons between the performance of the systems in SigComp2011 (based on static features) and the method presented in this paper (based on relevant dynamic features) showed that relevant dynamic features are better than static features in terms of accuracy, false acceptance rate, false rejection rate and calibration of likelihood ratios.

Identification of pulmonary edema in forensic autopsy cases of sudden cardiac death using Fourier transform infrared microspectroscopy: a pilot study

Many studies have proven the usefulness of biofluid-based infrared spectroscopy in the clinical domain for diagnosis and monitoring the progression of diseases. Here we present a state-of-the-art study in the forensic field that employed Fourier transform infrared microspectroscopy for postmortem diagnosis of sudden cardiac death (SCD) by in situ biochemical investigation of alveolar edema fluid in lung tissue sections. The results of amide-related spectral absorbance analysis demonstrated that the pulmonary edema fluid of the SCD group was richer in protein components than that of the neurologic catastrophe (NC) and lethal multiple injuries (LMI) groups. The complementary results of unsupervised principle component analysis (PCA) and genetic algorithm-guided partial least-squares discriminant analysis (GA-PLS-DA) further indicated different global spectral band patterns of pulmonary edema fluids between these three groups. Ultimately, a random forest (RF) classification model for postmortem diagnosis of SCD was built and achieved good sensitivity and specificity scores of 97.3% and 95.5%, respectively. Classification predictions of unknown pulmonary edema fluid collected from 16 cases were also performed by the model, resulting in 100% correct discrimination. This pilot study demonstrates that FTIR microspectroscopy in combination with chemometrics has the potential to be an effective aid for postmortem diagnosis of SCD.

Preliminary study on fatal hyperthermia in rat liver tissue by Fourier transform infrared microspectroscopy

Despite the progress that has been made during the past several decades in forensic pathology, post-mortem diagnosis of hyperthermia remains difficult. The current study aimed to investigate the spectral changes in rat liver under hyperthermic conditions compared with the control groups of fatal asphyxiation, brainstem injury, and massive haemorrhage, using Fourier transform infrared (FTIR) microspectroscopy. Forty Sprague–Dawley rats were randomly divided into four groups: hyperthermia; asphyxiation; brainstem injury; and massive haemorrhage. The absorbance of ten major absorption bands (1238, 1307, 1396, 1454, 1540, 2850, 2919, 2958, 3070 and 3290 cm−1) was significant higher in the hyperthermia group compared with the groups of asphyxiation, brainstem injury and massive haemorrhage. The band absorbance ratios of A2958/A2850 and A1650/A1540 were significantly lower, whereas the A1454/A1238, A1396/A1238 and A1307/A1238 ratios were significantly higher in the hyperthermia group compared with the other three causes of death. The frequency of 3290 cm−1 was significantly lower in the hyperthermia group compared with the other three causes of death. Further, using PCA, we demonstrated that infrared spectra extracted from different groups were distinct from each other. These results suggest that FTIR microspectroscopy is a useful technique for discriminating hyperthermia from other causes of death.

Infrared (IR) Spectral Markers of Bronchial Epithelia in Victims of Fatal Burns

Changes in the infrared spectra of bronchial epithelia in victims of fatal burns were investigated. The mechanism of spectral changes on the basis of cellular morphological changes was considered. The ability of spectral parameters to diagnose fatal burns was assessed. Ten cases of fatal burns and 20 control cases were selected. Their lung tissues were removed, and sections were cut and mounted on glass and barium fluoride slides. Spectra of polarized bronchial epithelia were obtained by microscopy based on their morphological changes. In the spectra, 16 major absorbance bands were evaluated to determine their ability to act as positive markers for exposure to fire. Compared with the control group, the bronchial epithelia of the fatal burn victims showed three spectral results. (1) The absorbance of 16 major bands from the spectra of polarized bronchial epithelia in fatal burn victims significantly increased. (2) For the same cell number, the absorbance at 2850, 2920, 2959, and 3084 cm−1 decreased. (3) The degree of increased or decreased absorbance of bands is related to the degree of polarization. These spectral results suggest that there is a vital reaction induced by the inhalation of hot fumes that includes an increase in the number of bronchial epithelia and a polarization effect. Overall, Fourier transform infrared (FT-IR) microspectroscopy was shown to be a convenient and reliable method to provide objective spectral markers to assist the diagnosis of fatal burns by simultaneously monitoring several specific parameters, although these observations have yet to be applied at forensic scenes.

Identification of pulmonary edema in forensic autopsy cases of fatal anaphylactic shock using Fourier transform infrared microspectroscopy

Anaphylaxis is a rapid allergic reaction that may cause sudden death. Currently, postmortem diagnosis of anaphylactic shock is sometimes difficult and often achieved through exclusion. The aim of our study was to investigate whether Fourier transform infrared (FTIR) microspectroscopy combined with pattern recognition methods would be complementary to traditional methods and provide a more accurate postmortem diagnosis of fatal anaphylactic shock. First, the results of spectral peak area analysis showed that the pulmonary edema fluid of the fatal anaphylactic shock group was richer in protein components than the control group, which included mechanical asphyxia, brain injury, and acute cardiac death. Subsequently, principle component analysis (PCA) was performed and showed that the anaphylactic shock group contained more turn and α-helix protein structures as well as less tyrosine-rich proteins than the control group. Ultimately, a partial least-square discriminant analysis (PLS-DA) model combined with a variables selection method called the genetic algorithm (GA) was built and demonstrated good separation between these two groups. This pilot study demonstrates that FTIR microspectroscopy has the potential to be an effective aid for postmortem diagnosis of fatal anaphylactic shock.

Post-mortem interval estimation in rat liver tissues using attenuated total reflection Fourier transform infrared spectroscopy combined with chemometrics

Abstract Post-mortem interval (PMI) estimation is one of the most challenging tasks in forensic practice. Therefore, for PMI estimation, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy coupled with chemometrics was utilized to monitor the biochemical changes in rat liver tissues with increasing PMI at 4°C, 20°C and 30°C. First, principal component analysis (PCA) revealed that the spectral points were distributed from right to left with increasing PMI along PC–1, and this trend was more obvious at the higher temperature (20°C and 30°C) groups. Second, a partial least squares (PLS) regression model was successfully constructed with the 30°C group, with a root mean square error of cross-validation (RMSECV) of 6.9 h (R2 = 0.92) and a root mean square error of prediction (RMSEP) of 4.6 h (R2 = 0.96). Lastly, a partial least squares-discriminant analysis (PLS-DA) classification model was established in the 20°C group and demonstrated a complete separation of the spectra among the three classes (0–24 h, 48–96 h and 120–168 h) with 90% accuracy (not-assigned rate: 11%). In conclusion, these results demonstrated that ATR-FTIR spectroscopy combined with chemometrics could serve as a convenient and reliable tool for studying PMI estimation.