A preliminary investigation into the comparison of dissolution/digestion techniques for the chemical characterization of polyurethane foam

Due to their widespread use in domestic and commercial premises, polyurethane foams, as either fragmented or bulk foam, are types of evidence commonly found at crime scenes. The traditional approach to determining the evidential value of polyurethane foam (PF) involves comparing recovered and control fragments under low and high magnification, under various lighting conditions, as well as the comparison of their respective dye spectra. As with most forms of trace evidence, chemical comparison is also desirable. In this work, two approaches to chemically comparing foam fragments were investigated, i.e. inductively coupled plasma–optical emission spectrometry (ICP–OES) analysis of the Tin (Sn) content in different foam types; and gas chromatography–flame ionization detection (GC–FID) analysis of soluble components in PFs mobilized by dichloromethane. Seven different foam types were studied and their Sn content was found to be different. They also produced characteristic GC–FID chromatographic profiles whose compounds were identified with gas chromatography–mass spectrometry (GC–MS) analysis. This study suggests that incorporating chemical data obtained from GC–FID/GC–MS and ICP–OES into a case involving PF could be advantageous, as this will enable the forensic scientist to broaden the comparison between control and recovered fragments, and further assess the strength of the evidence. However, ICP–OES analysis is a destructive technique with a relatively short sample turnaround time, whilst GC–FID analysis is more time-consuming and non-destructive, requiring corroboration with GC–MS data. The values of these two analytical techniques in the forensic chemical characterization of PFs are discussed.     

Determining the human origin of fragments of burnt bone: a comparative study of histological, immunological and DNA techniques.

In situations where badly burnt fragments of bone are found, identification of their human or non-human origin may be impossible by gross morphology alone and other techniques have to be employed. In order to determine whether histological methods were redundant and should be superseded by biomolecular analyses, small fragments of artificially burnt bone (human and non-human) were examined by quantitative and standard light microscopy, and the findings compared with newer biomolecular analyses based on identifying specific human albumin by ELISA and amplifying human mitochondrial DNA by PCR. For quantitative microscopy, reference data were first created using burnt bones from 15 human and 20 common domestic and farm animals. Measured osteon and Haversian canal parameters were analysed using multivariate statistical methods. Highly significant differences were found between values for human and non-human bone, and a canonical discriminant function equation was derived, giving a predicted correct classification of 79%. For the main study, samples of cortical bone were taken from three fresh cadavers, six human skeletons and ten freshly slaughtered animals and burnt by exposure to temperatures ranging from 800 to 1200 degrees C; charred fragments of human cortical bone from two forensic cases were also tested. Quantitative microscopy and canonical discriminant function gave the correct origin of every sample. Standard microscopy falsely assigned burnt bone from one human skeleton and one forensic case to a non-human source, but otherwise gave correct results. Human albumin was identified in five individuals, including one of the forensic cases, but mitochondrial DNA could not be amplified from any of the human bone. No false positive test results were seen with either biomolecular method; and human albumin and mitochondrial DNA were correctly identified in all unburnt control specimens. It was concluded that histological methods were not redundant and that quantitative microscopy provided an accurate and consistent means of determining the human or non-human origin of burnt bone and was more reliable than standard microscopy or the newer immunological and DNA techniques tested here.     

A Comparison of Fingerprint Sweat Corrosion of Different Alloys of Brass

Fingerprint sweat from 40 donors was deposited onto samples of five α and α + β phase brasses, comprising five alloys with different copper and zinc concentrations, two of which also had the addition of small concentrations of lead. Visual grading of the visibility of the corrosion revealed that brasses with the least amount of zinc produced the most visible and fully formed fingerprints from the most donors. Consideration of previously reported mechanisms for the corrosion of brass suggests red copper (I) oxide as a likely corrosion product for low zinc brasses, and a consideration of the color, composition, and solubility of fingerprint sweat corrosion products suggests that copper (I) oxide produces good contrast and visibility with the brass substrate. Scanning electron microscope images of the corrosion of all five alloys confirmed the enhanced contrast between corroded and uncorroded areas for low zinc alloys.     

Identifying Diagonal Cutter Marks on Thin Wires Using 3D Imaging

We present work on matching 2‐mm‐thick wires using optical 3D imaging methods. Marks on such small surfaces are difficult to match using a comparison microscope as this 2D imaging method does not provide height data about the sample surface. Moreover, these 2D microscopy images may be affected by illumination. Hence, the reference and investigated sample should be present at the same time. We employed scanning white light interferometry and confocal microscopy to provide quantitative 3D profiles for reliable comparison of samples that are unavailable for simultaneous analysis. We show that 3D profiling offers a solution by allowing illumination‐independent sample comparison. We correctly identified 74 of 80 profiles using consecutive matching striae (CMS) criteria, and we were able to match samples based on profiles measured using different 3D imaging devices. The results suggest that the used methods allow matching cutter marks on thin wires, which has been difficult previously.     

Genotyping of DNA samples under adverse conditions of Low Copy Number—LCN (formolisados tissue samples and embedded in paraffin)

This paper aims to describe and evaluate a protocol for extraction of DNA (deoxyribonucleic acid) in formalinized tissues and embedded in paraffin for forensics genetic analysis. In outline the method is the removal of paraffin with an organic solvent in 0.3–0.5 mg of the sample of the tissue under study, followed by removal of formaldehyde, rehydration and soon after the extraction of genomic DNA. The extraction is achieved through the stages of cellular lysis, enzymatic digestion of proteins and DNA precipitation in ethanol medium. With the research we can conclude that even when the DNA is present in small quantities in conditions of extreme difficulties in its extraction, as formalinized tissues and embedded in paraffin, the technique of optimizing the extraction of DNA used both to organic extraction as Chelex, for use in the polymerase chain reaction (PCR), and possible the investigation of different samples of human tissue, biological samples, or was obtained under the conditions tested, a DNA with good quality and concentration. The samples were amplified for the mini-STRs loci using the product marketed in multilocus, using a methodology recommended by the supplier and validated for analysis of forensic DNA. Commercial kit was used MiniFiler from Applied Biosystems. The DNA fragments amplified by PCR showed that the extracted DNA had good amplification.     

The classification and discrimination of glass fragments using non destructive energy dispersive X-ray microfluorescence

Frequency of analytical characteristics is best estimated on glass recovered at random. However, as such data were not available to us, we decided to use control windows for this estimation. In order to use such a database, one has to establish that the recovered fragment comes from a window. Therefore, elemental analysis was used both for classification and discrimination of glass fragments. Several articles have been published on the subject, but most methods alter the glass sample. The use of non destructive energy dispersive X-ray microfluorescence (microXRF) for the analysis of small glass fragments has been evaluated in this context. The refractive index (RI) has also been measured in order to evaluate the complementarity of techniques. Classification of fragments has been achieved using Fisher's linear discriminant analysis (LDA) and neural networks (NN). Discrimination was based on Hotelling's T2 test. Only pairs that were not differentiated by RI followed by the Welch test were studied. The results show that neural network and linear discriminant analysis using qualitative and semi-quantitative data establishes a classification of glass specimens with a high degree of reliability. For discrimination, 119 windows collected from crime scene were compared: using RI it was possible to distinguish 6892 pairs. Out of 129 remaining pairs, 112 were distinguished by microXRF.     

Characterisation of 0.22 caliber rimfire gunshot residues by time-of-flight secondary ion mass spectrometry (TOF-SIMS): a preliminary study

The application of time-of-flight secondary ion mass spectrometry (TOF-SIMS) for the characterisation of gunshot residue (GSR) from 0.22 caliber rimfire ammunition is reported. Results obtained by TOF-SIMS were compared with conventional scanning electron microscopy (SEM) studies. As could be expected, TOF-SIMS exhibited greater elemental sensitivity than SEM equipped with energy dispersive X-ray detection (SEM-EDX), and was also capable of detecting fragments characteristic of inorganic compounds. This preliminary study indicates that TOF-SIMS offers substantial potential for forensic GSR examinations as a complementary technique to SEM-EDX. In addition TOF-SIMS is applicable to the analysis of individual particles in the typical size range encountered in GSR casework.     

定量PCR技术在法医学中应用的研究

目的研究荧光定量PCR技术在法医学中的应用。方法应用Taqman技术对法医各种生物检材进行DNA定量。结果该定量PCR技术对各种法医生物检材进行了准确定量,并判断检材中是否存在抑制物,从而指导了后续STR的检验。结论定量PCR技术是法医DNA检验中一项不可缺少的辅助技术。     

硅藻定量检验和种属鉴定的实验研究

本实验用家兔18只,分为溺死组、死后(抛尸)入水组及对照组,每组各6只。采用消化—光镜法作肺、肝、肾硅藻计数(定量)及种属鉴定检验,同时作水样检验及空白对照。结果:(一)进一步证实生前硅藻可经空气源性进入肺脏并存积于大循环内脏(肝、肾)的概念;(二)提示水中尸体肺脏如有大量硅藻检出,仅此即可作为诊断溺死的可靠依据;空气源性吸入及检验过程中的污染并不影响该检验结果对鉴定溺死的判断。种属分析溺死组肺与水样的主要硅藻种属相符,而肝、肾中硅藻计数及种属分析均无诊断意义。     

Use of solid-phase double-antibody radioimmunoassay to identify species from small skeletal fragments

Protein radioimmunoassay (pRIA) offers the potential to identify species in small skeletal fragments submitted as forensic evidence. The technique consists of protein extraction followed by a solid-phase double-antibody radioimmunoassay using controls of antisera (raised in rabbits) and radioactive (iodine-125) antibody of rabbit gamma globulin (produced in donkeys). Species determination results from evaluation of radioactivity uptake. To demonstrate the potential of this technique, six known bone samples (three human and three nonhuman, including one from a deer [Odocoileus virginianus]) were submitted for blind analysis. pRIA correctly distinguished the human from the nonhuman samples. Using 200 mg or less of each sample, species of the deer specimen was identified correctly, given the choices of cow, deer, dog, goat, and pig.     

A discrimination method for paper by Fourier transform and cross correlation

A non-destructive method for discriminating between different types of paper has been proposed, using image analysis, Fourier transformation, and cross-correlation matching. A fast Fourier transform (FFT) is used to extract the periodicity in the structure of paper that results from the manufacturing processes. The light-transmission images of the paper to be Fourier transformed are obtained from a flatbed image scanner. The similarity between the power spectrum of the FFT of the sample and that of a reference is quantified using a cross-correlation matching method. An advantage of using frequency analysis is that periodicity can be detected even if the sample is damaged or is printed on. The technique works on samples as small as 2 cm2.     

Avoiding overstating the strength of forensic evidence: Shrunk likelihood ratios/Bayes factors

When strength of forensic evidence is quantified using sample data and statistical models, a concern may be raised as to whether the output of a model overestimates the strength of evidence. This is particularly the case when the amount of sample data is small, and hence sampling variability is high. This concern is related to concern about precision. This paper describes, explores, and tests three procedures which shrink the value of the likelihood ratio or Bayes factor toward the neutral value of one. The procedures are: (1) a Bayesian procedure with uninformative priors, (2) use of empirical lower and upper bounds (ELUB), and (3) a novel form of regularized logistic regression. As a benchmark, they are compared with linear discriminant analysis, and in some instances with non-regularized logistic regression. The behaviours of the procedures are explored using Monte Carlo simulated data, and tested on real data from comparisons of voice recordings, face images, and glass fragments.     

Differential pulse anodic stripping voltammetry of lead and antimony in gunshot residues

Differential pulse anodic stripping voltammetry (DPASV) using a glassy carbon/mercury film electrode (GC/MFE) has been applied for characterization and quantitative detection of gunshot residues (GSR). This technique allows for simultaneous detection of Pb and Sb from GSR hand swabs that is simple, fast, and non-destructive. The use of a KNO₃/hydrazine sulfate matrix, instead of HCl, reduces possible interferences and allows for a small sample size to be used in analysis but yielding greater sensitivity.     

Comparison of transmission and internal reflection infrared spectra of cocaine.

Comparing the infrared transmission spectrum of cocaine HCl to its attenuated total reflection (ATR) spectrum has raised questions about the use of ATR spectra for forensic drug analysis. Whenever infrared spectra are collected using different modes or sample preparation methods, small variations in peak intensity ratios or peak positions are possible. These variations in infrared spectra are small and do not interfere with qualitative analysis, but they can cause confusion when unrecognized as normal effects of the different spectroscopic techniques. Comparison of the absorption and ATR spectra of cocaine hydrochloride illustrates the type of differences that can be expected. These differences are explained by the fundamental differences in the collection techniques. For the best quantitative results, only spectra collected by the same technique should be compared.     

Positive identification of the principal component of a white powder as scopolamine by quantitative one-dimensional and two-dimensional NMR techniques

An unidentified white powder collected as evidence in an intelligence investigation was characterized exclusively by nuclear magnetic resonance (NMR) analysis. A small fraction of the powder dissolved in D2O was subjected to a series of one- and two-dimensional techniques which were used to elucidate the molecular structure of the powder's major component and positively identify it as the scopolamine biotoxin. Quantitative one-dimensional experiments identified individual proton and carbon atom sites, and conventional 14N spectroscopy detected a single nitrogen atom site. Heteronuclear single quantum coherence data correlated all protons to their directly bonded carbon atom, and together with the quantitative spectra, were used to determine the number of protons directly bonded to each carbon atom. The presence of a methyl, carboxyl, and a benzyl group was also identified from these data. Correlation spectroscopy detected a three proton and a nine proton JH,H network, representing a CH2CH moiety and seven carbon atom ring, respectively. These five elements were assembled into an almost complete molecular structure by using long-range, J-coupled, 1H-13C pairs detected by heteronuclear multiple bond correlation (HMBC) spectroscopy and 1H-1H dipolar-coupled pairs found from nuclear Overhauser effect spectroscopy (NOESY) data. Additional oxygen atom sites were inferred from 1H-13C correlation intensities in the HMBC spectra along with 1H and 13C chemical shift values, or directly from NOESY correlations. Only a single oxygen atom site could not be inferred from NMR data, but its presence was inferred from comparisons to target analyte structures to complete the structure of the scopolamine molecule. To confirm these results, an ethanol/H2O solution of the powder was analyzed by direct infusion into an ion trap mass spectrometer. A prominent base signal was observed at m/z 304.1 amu, corresponding to the protonated molecular ion of scopolamine. Subsequently, the ion was selected and subjected to collision-induced dissociation, producing characteristic major MS/MS fragments at m/z 138.1 and 156.1. Comparisons of 1H and 13C chemical shift values and JH,H values measured from our NMR data were found to agree very favorably with previously reported values for scopolamine in D2O.     

Quick Screening of Crystal Methamphetamine/Methyl Sulfone Exhibits by Raman Spectroscopy

Abstract: The analysis of mixtures of “crystal meth” (usually comprised of methyl sulfone [MS] and methamphetamine [MA]) by gas chromatography‐mass spectrometry (GCMS) is routine in many forensic drug laboratories. The utilization of Raman spectroscopy for the identification of such mixtures quickly and without the need for a separation technique is discussed. Samples were dissolved in water and Raman spectra of the resulting aqueous solutions were collected. By comparing these spectra to spectra of methylsulfone and MA mixtures of known composition, an indication of the composition of the sample can be obtained in only a few minutes. This spectral comparison also can be used as a semi‐quantitative analysis of MA concentrations in such exhibits.     

A LDR‐PCR Approach for Multiplex Polymorphisms Genotyping of Severely Degraded DNA with Fragment Sizes <100 bp*

Abstract: Reducing amplicon sizes has become a major strategy for analyzing degraded DNA typical of forensic samples. However, amplicon sizes in current mini‐short tandem repeat‐polymerase chain reaction (PCR) and mini‐sequencing assays are still not suitable for analysis of severely degraded DNA. In this study, we present a multiplex typing method that couples ligase detection reaction with PCR that can be used to identify single nucleotide polymorphisms and small‐scale insertion/deletions in a sample of severely fragmented DNA. This method adopts thermostable ligation for allele discrimination and subsequent PCR for signal enhancement. In this study, four polymorphic loci were used to assess the ability of this technique to discriminate alleles in an artificially degraded sample of DNA with fragment sizes <100 bp. Our results showed clear allelic discrimination of single or multiple loci, suggesting that this method might aid in the analysis of extremely degraded samples in which allelic drop out of larger fragments is observed.     

Comparison of glass fragments using particle-induced X-ray emission (PIXE) spectrometry

A procedure has been developed to analyze the trace element concentrations in glass fragments using particle-induced X-ray emission (PIXE) spectrometry. This method involves using accelerated protons to excite inner-shell electronic transitions of target atoms and recording the resultant X-rays to characterize the trace element concentrations. The protocol was able to identify those glass fragments that originated from different sources based on their elemental analyses. The protocol includes specific approaches to calculating uncertainties and handling measurements below the level of detection. The results indicate that this approach has increased sensitivity for several elements with higher atomic number compared with X-ray fluorescence methods. While not as sensitive as laser-ablation or inductively coupled plasma mass spectrometry methods of dissolved samples, it is entirely nondestructive and entails a much simpler sample preparation process that may be used to presort glass fragments for more comprehensive elemental analysis. As such, the technique described may have a niche role in forensic glass analysis.     

A methodology based on NMR spectroscopy for the forensic analysis of condoms.

Both solution and solid state Nuclear Magnetic Resonance (NMR) spectroscopic techniques have been used to determine differences in commercially available condoms. Whilst solid state NMR is useful for determining the polymer backbone, it is not useful for forensic analysis due to the commonality of the latex condom. However solution NMR spectra obtained following a simple extraction procedure using hexane, provides a fingerprint of the additives in the lubricants. Following the development of a flow chart, basing decisions on the presence of particular peaks present in the solution spectra, 33 of 38 condoms could be individualized. Samples were also analyzed after having the lubricant manually removed and soaking the condom in water for 3 to 24 h. These experiments were performed to simulate a case of the sample having been used and disposed of by flushing down the toilet, as may be experienced in a case of a sexual assault. The results indicated that the only significant water soluble component was polyethylene glycol. The overall results suggest that the method developed may be a quick and useful technique in characterizing condoms. The information obtained can be used to provide associative evidence between suspect and crime, and so be useful in sexual assault cases.     

The analysis of some evidential materials by inductively coupled plasma-optical emission spectrometry

Inductively coupled plasma-optical emission spectrometry (ICP-OES) is under evaluation at the Central Research Establishment for the analysis of evidential materials. The analysis of standard reference materials has demonstrated that quantitative multi-element data can be obtained from small samples of a variety of materials. The results of some determinations carried out in support of casework investigations are reported.