Forensic utility of carbon isotope ratio variations in PVC tape backings

Forensic interest in adhesive tapes with polyvinyl chloride (PVC) backings (electrical tape) derives from their use in a variety of illicit activities. Due to the range of physical characteristics, chemical compositions, and homogeneity within a single roll of tape, traditional microscopic and chemical analyses can offer a high degree of discrimination between tapes, permitting the assessment of potential associations between evidentiary tape samples. The carbon isotope ratios of tapes could provide additional discrimination among tape samples. To evaluate whether carbon isotope ratios may be able to increase discrimination of electrical tapes, particularly with regards to different rolls of tape of the same product, we assessed the δ(13)C values of backings from 87 rolls of PVC-based black electrical tape (~20 brands, >60 products) Prior to analysis, adhesives were removed to prevent contamination by adhering debris, and plasticizers were extracted because of concern over their potential mobility. This result is consistent with each of these tapes having approximately the same plasticizer δ(13)C value and proportion of carbon in these plasticizers. The δ(13)C values of the 87 PVC tape backings ranged between -23.5 and -41.3 (‰, V-PDB), with negligible carbon isotopic variation within single rolls of tape, yet large variations among tape brands and tape products. Within this tape population, carbon isotope ratios permitted an average exclusion power of 93.7%, using a window of +/-0.3‰; the combination of carbon isotope ratio measurement with additional chemical and physical analyses raises the discrimination power to over 98.9%, with only 41 out of a possible 3741 pairs of tape samples being indistinguishable. There was a linear relationship between the δ(13)C value of tape backings and the change in δ(13)C value with the extraction of plasticizers. Analyses of pre- and post-blast tape sample pairs show that carbon isotope signatures are within 0.3‰ of pre-blast values, indicating that carbon isotope values are largely preserved during an explosion.     

Analysis and discrimination of electrical tapes: Part I. Adhesives

This study involved the comparative analysis and discrimination of 90 electrical tape adhesives. The objectives included the evaluation of the ability of individual techniques to discriminate samples and the assessment of the ability of the techniques combined to distinguish samples. The techniques utilized were stereomicroscopy, Fourier transform infrared spectroscopy (FTIR), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). Stereomicroscopy, to assess adhesive colors of black, clear/colorless, and clear adhesives with brown tint, resulted in a discrimination of 53%. FTIR analysis yielded eight distinct groups with a discrimination of 67%. Py-GC/MS analysis resulted in 16 groups with a discrimination of 83%. These analyses confirmed and further subdivided the FTIR groups. SEM/EDS resulted in five separate groups at 17% discrimination, increasing the overall discrimination to above 85%.     

蓝色电工胶带的扫描电镜／能谱法检验

目的研究不同品牌蓝色电工胶带的检验方法。方法利用扫描电镜／能谱法对蓝色电工胶带进行检验。结果11个厂家生产的15种品牌的蓝色电工胶带组成的105组样品对有104组可以区分,区分率达到99．0％。结论扫描电镜／能谱法能够区分绝大多数蓝色电工胶带,该方法具有操作简便、快速、结果准确的优点,能够用于同色电工胶带的鉴别。     

Analysis and Discrimination of Single‐Layer White Architectural Paint Samples,

Comparative analyses of 50 single‐layer white architectural paints were conducted to determine the discrimination power using standard techniques and to provide a basis for assessing significance when paints with limited features are not discriminated. Utilizing Fourier transform infrared spectroscopy (FTIR), 68 undifferentiated pairs resulted, yielding a discrimination of 94.45%. Adding stereomicroscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and backscatter electron (BSE) imaging, and pyrolysis‐gas chromatography/mass spectrometry (Py‐GC/MS), the overall discrimination was 99.35%. The study included blind verification replicates, which resulted in the only pairs without indications of physical or chemical differences. The remaining groups of undifferentiated samples contained subtle differences by at least one technique, but were considered undifferentiated for the discrimination power evaluations. This study demonstrates a high degree of discrimination of single‐layer white architectural paints using methods of analysis often encountered in forensic science laboratories.     

Identification and comparison of electrical tapes using instrumental and statistical techniques: I. Microscopic surface texture and elemental composition

Comparisons of polyvinyl chloride electrical tape typically rely upon evaluating class characteristics such as physical dimensions, surface texture, and chemical composition. Given the various techniques that are available for this purpose, a comprehensive study has been undertaken to establish an optimal analytical scheme for electrical tape comparisons. Of equal importance is the development of a quantitative means for sample discrimination. In this study, 67 rolls of black electrical tape representing 34 different nominal brands were analyzed via scanning electron microscopy and energy dispersive spectroscopy. Differences in surface roughness, calendering marks, and filler particle size were readily apparent, including between some rolls of the same nominal brand. The relative amounts of magnesium, aluminum, silicon, sulfur, lead, chlorine, antimony, calcium, titanium, and zinc varied greatly between brands and, in some cases, could be linked to the year of manufacture. For the first time, quantitative differentiation of electrical tapes was achieved through multivariate statistical techniques, with 36 classes identified within the sample population. A single-blind study was also completed where questioned tape samples were correctly associated with known exemplars. Finally, two case studies are presented where tape recovered from an improvised explosive device is compared with tape recovered from a suspect.     

SEM/EDS法和XRF法在电工胶带检验中的应用

目的探索电工胶带带基的元素检验方法。方法利用扫描电镜/能谱法（SEM/EDS）对电工胶带带基中的主体元素进行定量分析,通过SPSS软件对SEM/EDS定量分析法检测出的主体元素（Cl和Ca）相对含量进行统计分析;利用X射线荧光光谱法（XRF）对电工胶带带基中的微量元素进行定性分析。结果34个品牌红色电工胶带组成的561组样品对通过SEM/EDS定量分析法可以区分539组,区分率达到96.1%;根据XRF法定性分析测出的Mg、Al、Si、S、Ti、Sb、Ba、Pb微量元素的不同组合可将34种电工胶带分成11组,两种方法结合可使不同品牌红色电工胶带的区分率达到98.4%。结论SEM/EDS法和XRF法结合可以实现同种颜色、不同品牌电工胶带的高效区分。     

同色电工胶带的光谱成像技术检验

目的研究同种颜色电工胶带的区分方法。方法应用光谱成像技术对同色（选取红、黄、蓝、绿4种颜色）不同品牌的电工胶带进行区分。结果蓝色电工胶带的区分率最高,达到99.0%,红色、绿色、黄色样品的区分率相差不大,分别为94.3%、93.8%及93.3%。结论光谱成像技术可以实现同种颜色电工胶带的快速区分,从色度学角度为法庭科学领域电工胶带物证的区分提供了一种新的方法。     

The spectroscopic detection of exogenous material in fingerprints after development with powders and recovery with adhesive lifters

The application of powders to fingerprints has long been established as an effective and reliable method for developing latent fingerprints. The powders adhere to the ridge pattern of the fingerprint only, thus allowing the image to be visualised. Fingerprints developed in situ at a crime scene routinely undergo lifting with specialist tapes to facilitate subsequent laboratory analysis. As with all recovered evidence these samples would be stored in evidence bags to allow secure transit from the scene to the laboratory and also to preserve the chain of evidence. In this paper, the application of Raman spectroscopy for the analysis of exogenous material in latent fingerprints is reported for contaminated fingerprints that had been treated with powders and also subsequently lifted with adhesive tapes. A selection of over the counter (OTC) analgesics were used as samples for the analysis and contaminated fingerprints were deposited on clean glass slides. The application of aluminium or iron based powders to contaminated fingerprints did not interfere with the Raman spectra obtained for the contaminants. In most cases background fluorescence attributed to the sebaceous content of the latent fingerprint was reduced by the application of the powder thus reducing spectral interference. Contaminated fingerprints developed with powders and then lifted with lifting tapes were also examined. The combination of these two techniques did not interfere with the successful analysis of exogenous contaminants by Raman spectroscopy. The lifting process was repeated using hinge lifters. As the hinge lifters exhibited strong Raman bands the spectroscopic analysis was more complex and an increase in the number of exposures to the detector allowed for improved clarification. Raman spectra of developed and lifted fingerprints recorded through evidence bags were obtained and it was found that the detection process was not compromised in any way. Although the application of powders did not interfere with the detection process the time taken to locate the contaminant was increased due to the physical presence of more material within the fingerprint. The presence of interfering Raman bands from lifting tapes is another potential complication. This, however, could be removed by spectral subtraction or by the choice of lifting tapes that have only weak Raman bands.     

Chemical fingerprinting of adhesive tapes by GCMS detection of petroleum hydrocarbon products

Pressure-sensitive adhesive tapes often represent key evidence of crimes such as assault, rape or homicide; thus, the development of analytical techniques able to contribute to a detailed characterization of these materials is of forensic importance. The gas chromatography-mass spectrometry (GCMS) analysis of the solvent extractable fractions of a suite of electrical and gaffer adhesive tapes spanning a range of colors and manufacturers identified a number of petroleum-derived hydrocarbons. Molecular and isotopic analyses of hydrocarbon constituents of complex materials have found wide analytical utility including the forensic investigation of oil spills and arson. Here, we investigate the utility of these techniques for characterizing the hydrocarbon composition of pressure-sensitive adhesive tapes for forensic correlation purposes. Subtle distinction of tape samples was evident in the GCMS distribution of several hydrocarbon groups including alkyl-naphthalenes, hopane and sterane biomarkers. Linear discriminant analysis of the abundances of these products provided high level differentiation of tape manufacturer. The distinction of different adhesive tape samples was further extended by measurement of their stable carbon isotopic values. The molecular and isotopic differences of the petroleum content of tapes are consistent with the use of different petroleum materials used in the manufacturing process and demonstrate the benefits of the combined use of complementary oil hydrocarbon characterization approaches. This study reveals the forensic potential of using established petroleum characterization methods for characterizing materials with a petroleum-derived hydrocarbon element.     

Characterization of Printing Inks Using DART‐Q‐TOF‐MS and Attenuated Total Reflectance (ATR) FTIR

The rise in improved and widely accessible printing technology has resulted in an interest to develop rapid and minimally destructive chemical analytical techniques that can characterize printing inks for forensic document analysis. Chemical characterization of printing inks allows for both discrimination of inks originating from different sources and the association of inks originating from the same source. Direct analysis in real‐time mass spectrometry (DART‐MS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR) were used in tandem to analyze four different classes of printing inks: inkjets, toners, offset, and intaglio. A total of 319 samples or ~ 80 samples from each class were analyzed directly on a paper substrate using the two methods. DART‐MS was found to characterize the semi‐volatile polymeric vehicle components, while ATR‐FTIR provided chemical information associated with the bulk components of these inks. Complimentary data results in improved discrimination when both techniques are used in succession resulting in >96% discrimination for all toners, 95% for all inkjets, >92% for all offset, and >54% for all intaglio inks.     

The Discrimination of Colored Acrylic,Cotton, and Wool Textile Fibers Using Micro‐Raman Spectroscopy. Part 1: In situ Detection and Characterization of Dyes

Raman spectroscopy has been applied to characterize fiber dyes and determine the discriminating ability of the method. Black, blue, and red acrylic, cotton, and wool samples were analyzed. Four excitation sources were used to obtain complementary responses in the case of fluorescent samples. Fibers that did not provide informative spectra using a given laser were usually detected using another wavelength. For any colored acrylic, the 633‐nm laser did not provide Raman information. The 514‐nm laser provided the highest discrimination for blue and black cotton, but half of the blue cottons produced noninformative spectra. The 830‐nm laser exhibited the highest discrimination for red cotton. Both visible lasers provided the highest discrimination for black and blue wool, and NIR lasers produced remarkable separation for red and black wool. This study shows that the discriminating ability of Raman spectroscopy depends on the fiber type, color, and the laser wavelength.     

Identification and Comparison of Electrical Tapes Using Instrumental and Statistical Techniques: II. Organic Composition of the Tape Backing and Adhesive*

Abstract: The microtexture and elemental composition of the backing of electrical tapes have been shown to be highly discriminating. In this study, the organic composition of electrical tape was evaluated as a complementary means of distinguishing tape brands. The backing and adhesive of 72 rolls of electrical tape were analyzed via Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR FTIR) and discriminant analysis was used to classify all samples by brand. Generally, the accuracy for FTIR data (88–99%) was higher than that for elemental data (86–94%). FTIR spectra from the adhesive layer were the most discriminating. In separate studies, two fragments of blast-damaged tape were correctly assigned to their brand of origin and discriminant analysis was used to quantitatively associate or exclude tape samples from two bombing cases.     

透明胶带的厚度检验

目的研究不同品牌透明胶带的区分方法。方法利用测厚仪对35种不同品牌透明胶带的厚度进行检验,并对所得数据进行统计分析。结果 35种品牌透明胶带组成的595组样品对中有458组可以区分,区分率为77.0%。结论厚度检验法能够在一定程度上区分不同品牌的透明胶带,厚度检验结果可与化学成分检验相互佐证,使得鉴定结论更加准确可靠,为法庭科学领域透明胶带物证的区分提供了一种预检验方法。     

The discrimination potential of ultraviolet-visible spectrophotometry, thin layer chromatography, and Fourier transform infrared spectroscopy for the forensic analysis of black and blue ballpoint inks

The knowledge of the discriminating power of analytical techniques used for the differentiation of writing inks can be useful when interpreting results. Ultraviolet-visible (UV-VIS) spectrophotometry, thin layer chromatography (TLC), and diffuse reflectance Fourier transform infrared spectroscopy (FT-IR) were used to examine a population of 21 black and 12 blue ballpoint writing inks. Based on corroborative results of these methods, the discrimination power for UV-VIS, TLC, and FT-IR was determined to be 100% and 98% for the black and blue inks, respectively. Generally, TLC and UV-VIS can be used to differentiate the colorant components (i.e., dyes and some pigments) found in inks. As FT-IR can be utilized to identify some of the noncolorant components, it was determined to be an excellent complementary technique that can be implemented into an analytical scheme for ink analysis.     

Analysis and discrimination of architectural paint samples via a population study

This study involved the comparative analysis and discrimination of 964 architectural paint samples collected in the United States and Canada. The samples were evaluated to determine the extent to which randomly collected architectural finishes can be discriminated following standard operating protocols for paint analysis. The study also provides a basis for assessing the significance of a result in which a pair or group are undifferentiated. The techniques utilized were stereomicroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) with both backscatter electron imaging (BSI) and energy dispersive spectroscopy (EDS), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). To assess the layer characteristics (e.g., number, color, sequence, thickness), stereomicroscopy was used with FTIR and/or SEM as needed. The use of visual and microscopic evaluations in concert with FTIR resulted in 42 undifferentiated pairs, a discrimination of 99.99%. Adding SEM and Py-GC/MS analysis resulted in further discrimination of 31 pairs, resulting in eleven undiscriminated pairs of samples. At the conclusion of the study, samples that remained undifferentiated proved to originate from the same source. Therefore, no random pairs were indistinguishable at the conclusion of all examinations.     

Basic forensic identification of artificial leather for hit-and-run cases

Single fibers retrieved from a victim's garments and adhered to the suspect's automobile have frequently been used to prove the relationship between victim and suspect's automobile. Identification method for single fiber discrimination has already been conducted. But, a case was encountered requiring discrimination of artificial leather fragments retrieved from the victim's bag and fused fibers from the bumper of the suspect's automobile. In this report, basic studies were conducted on identification of artificial leathers and single fibers from leather materials. Fiber morphology was observed using scanning electron microscopy (SEM), color of these leather sheets was evaluated by microspectrophotometry (MSP), the leather components were measured by infrared micro spectrometry (micro-FT-IR) and the inorganic contents were ascertained by micro-X-ray fluorescence spectrometry (micro-XRF). These two methods contribute to other analytical methods too, in the case of utilized single fiber analytical methods. The combination of these techniques showed high potential of discrimination ability in forensic examinations of these artificial leather samples. In regard with smooth surface artificial leather sheet samples, a total of 182 sheets were obtained, including 177 colored sheets directly from 10 of 24 manufacturers in Japan, and five of them were purchased at retail circulation products. Nine samples of suede-like artificial leather were obtained, 6 of them were supplied from 2 manufacturers and 3 sheets were purchased as retailing product. Single fibers from the smooth surface artificial leather sheets showed characteristic for surface markings, and XRF could effectively discriminate between these sheets. The combination of results of micro-FT-IR, color evaluation by MSP and the contained inorganic elements by XRF enabled to discriminate about 92% of 15,576 pairs comparison. Five smooth surface samples form retailing products were discriminated by their chemical composition into four categories, and in addition color information to this result, they were clearly distinguished. Suede-like artificial leather sheets showed characteristic extra-fine fibers on their surface by the observation of SEM imaging, providing high discriminating ability, in regard with suede-like artificial leather sheets were divided into three categories by micro-FT-IR, and the combination of these results and color evaluation information, it was possible to discriminate all the nine suede-like artificial leather sheets examined.     

Rapid and nondestructive analysis of lipstick on different substrates using ATR-FTIR spectroscopy and chemometrics

Lipstick can be an important piece of evidence in crimes like murders, rapes, and suicides. Due to its prevalence, it can be an important corroborative evidence in crime reconstruction. The analysis of such evidence can provide an evidentiary link between the suspect, the victim, object, or the crime scene. We report the use of nondestructive ATR-FTIR spectroscopy combined with chemometrics for the classification of 10 brands of lipsticks with nine samples each. Chemometric method of partial least square-discriminant analysis (PLS-DA) has been employed to interpret the data and classify the samples into their respective classes. The PLS-DA model provides an AUC figure above 0.99 in all brands except one; for which it is slightly less at 0.94. We have also tested the traces of these lipstick samples on different substrates treating them as unknowns in the already trained PLS-DA model. 100% of the samples on nine substrates viz. a cotton, nylon, plastic, dry tissue, denim (blue jeans), wet tissue, nitrile gloves, white paper, and polyester were correctly attributed to their source brand. In conclusion, the results suggest that ATR-FTIR combined with the chemometrics is a rapid, nondestructive, and accurate method for the discrimination and source attribution of lipstick. This study has potential for use in actual forensic casework conditions.     

Analysis of pressure sensitive adhesive tape: I. Evaluation of infrared ATR accessory advances

Attenuated total reflection (ATR), also known as internal reflection spectroscopy (IRS), is a forensically accepted method for infrared (IR) analysis of pressure sensitive adhesive tapes. Advancements of ATR accessories in the last decade have provided the forensic examiner several ATR methods to choose from. These accessories offer a variety of ATR crystal choices with a variety of prices and capabilities. Four different types of pressure sensitive adhesive tapes including duct tape, electrical tape, packaging tape and office tape have been used to compare six different ATR methods. Each of the methods tested offers both benefits and limitaltions which must be considered for the type of sample to be analyze. The intent of this paper is to assist the reader in better understanding ATR techniques, the many differences among currently available ATR accessories and how the method is applied to the analysis of pressure sensitive adhesive tape.     

Application of the micro-FTIR spectroscopy, Raman spectroscopy and XRF method examination of inks

In routine examination of inks on questioned documents non-destructive analytical methods, such as microscopic and optical techniques are applied first. However, they are often insufficient to identify the inks used for the preparation of the document. In such cases, it is necessary to apply chemical methods that normally cause partial destruction of the examined material. The aim of this work was to evaluate the possibility of discrimination between inks by the use of spectrometric methods, i.e. micro-FTIR spectroscopy, Raman spectroscopy and XRF. About 70 samples of blue and black ballpoint pen and gel inks were examined. It was found that about 90% of the samples of the same type and colour could be distinguished using these methods.     

Evaluation of the Forensic Utility of Scanning Electron Microscopy‐Energy Dispersive Spectroscopy and Laser Ablation‐Inductively Coupled Plasma‐Mass Spectrometry for Printing Ink Examinations

Improvements in printing technology have exacerbated the problem of document counterfeiting, prompting the need for analytical techniques that better characterize inks for forensic analysis and comparisons. In this study, 319 printing inks (toner, inkjet, offset, and Intaglio) were analyzed directly on the paper substrate using scanning electron microscopy‐energy dispersive spectroscopy (SEM‐EDS) and Laser Ablation‐Inductively Coupled Plasma‐Mass Spectrometry (LA‐ICP‐MS). As anticipated, the high sensitivity of LA‐ICP‐MS pairwise comparisons resulted in excellent discrimination (average of ~ 99.6%) between different ink samples from each of the four ink types and almost 100% correct associations between ink samples known to originate from the same source. SEM‐EDS analysis also resulted in very good discrimination for different toner and intaglio inks (>97%) and 100% correct association for samples from the same source. SEM‐EDS provided complementary information to LA‐ICP‐MS for certain ink types but showed limited utility for the discrimination of inkjet and offset inks.