Forensic examination of ink by high-performance thin layer chromatography—The United States Secret Service Digital Ink Library

Classification of ballpoint pen inks based on selective extraction and subsequent digital color and cluster analyses

Extraction and color analysis coupled with machine learning allows clustering of pen inks and realizing preliminary classification when assessing document age.

A quantitative reliability metric for querying large database

A redesigned quantitative reliability metric based on the F-distribution (QRMf) is reported for evaluating the reliability of library search. The QRMf provides orthogonal information to the comparison metric (e.g., dot product) and yields a probabilistic result. An intralibrary search can be considered as an idealized search because the top hit, i.e., the closest matching object, will match perfectly. If the search of an unknown object yields the same hit list as the intralibrary search, it would indicate good reliability. For each object in the hit list, a QRMf compares the order of an intralibrary and interlibrary search results and calculates a variance of interlibrary similarity metrics between the records of the intralibrary search and records in the corresponding positions of the interlibrary search. This variance that measures the discordance of the intra and interlibrary search can simply be compared to the variance of the similarity metrics within the interlibrary search results. The ratio of these variances follows an F-distribution that can be used to determine if the discordance is statistically significant and generates the probability based on the cumulative distribution function. The QRMf works for both similarity and dissimilarity and can be used for any queried object and comparison metric that is searched against a database. In this work, the QRMf was used along with the dot product similarity to query the mass spectra of novel synthetic opioids measured by gas chromatography-mass spectrometry (GC/MS). An automated pipeline was devised that used a basis set correction to assist peak detection. The basis was constructed by mass spectra obtained from the blank measurement preceding the analytical run to remove interferences from column bleed and septum degradation. After peak detection, the pipeline applied multivariate curve resolution to the chromatographic peak window to remove background components from the mass spectra. The corrected mass spectra were searched against a customized library for identification. The QRMf can be used along with the similarity metric to detect misidentifications and assist in finding the correct identification when it is not the closest match.

Simple and Cost-Efficient Classification of Ballpoint Pen Inks Using Digital Color Analysis

We report here a simple and cost-effective technique for classification of the samples of writing inks based on their digital color analysis (DCA). The dynamics of artificial aging of writing inks under UV irradiation was studied by means of DCA for the first time. The color of ballpoint pen marks was recorded over time using an ordinary consumer DSLR camera. The inks were classified according to the parameters of their color degradation curves with precision superior to conventional Raman scattering method, which serves as a proof-of-concept of the proposed approach. The reported approach has broad prospects for implementation by criminalists for document investigation when document forgery is suspected. The proposed technique can be of interest not only in the field of forensic science but also for those who deal with dyes and dye-containing materials and their degradation over time as well as for the study of any processes, the evolution of which is reflected in a color change.

Forensic Analysis of Commercial Inks by Laser-Induced Breakdown Spectroscopy (LIBS)

Laser-induced breakdown spectroscopy (LIBS) was tested for all of the relevant issues in forensic examinations of commercial inks, including classification of pen inks on one paper type and on different paper types, determination of the deposition order of layered inks, and analysis of signatures and toners on one questioned document. The scope of this work was to determine the potential of a single LIBS setup that is compatible with portable instruments for different types of ink analysis, rather than building a very large database for inks and papers. We identified up to seven metals characteristic for the examined inks, which allowed to fully discriminate all eight black inks on one type of printing paper. When the inks were tested on ten different papers, the correct classification rates for some of them were reduced for reasons thoroughly studied and explained. The replicated tests on three crossing points, each one involving a pair of blue or black inks, were successful in five cases out of six. In the test simulating documents of forensic interest (questioned documents), LIBS was able to correctly identify the differences in three inks used for signatures on one of the three pages and the use of different printing inks on each page of the document.

Study of ink aging: Targeting triethylene glycol in carbon-based black gel ink strokes on paper

For the past decades, forensic chemists have made considerable efforts to develop methods capable of dating ballpoint pen ink by monitoring the loss of volatile solvents over time; however, few studies have been reported on carbon-based black gel inks. In China, carbon-based black gel pens are typically used for formal writing and signatures, such as contracts, loan receipts, testaments, and paper tests. Thus, it is imperative to analyze the age of carbon-based black gel inks for questioned document examiners in forensic casework. In this study, by employing the combination of gas chromatography with mass spectrometry (GC-MS) and GC with a flame ionization detector, a useful method for ink dating was proposed according to the dissipation of triethylene glycol from three novel carbon-based black gel inks. The ink aging curves suggested that this approach can distinguish questioned ink samples that are less than or greater than 9 months. This result could help to identify some questioned documents actually written within a month but are passed off as documents written years ago.

A comparison between DART-MS and DSA-MS in the forensic analysis of writing inks

Ambient ionization mass spectrometry is gaining momentum in forensic science laboratories because of its high speed of analysis, minimal sample preparation, and information-rich results. One such application of ambient ionization methodology includes the analysis of writing inks from questioned documents where colorants of interest may not be soluble in common solvents, rendering thin layer chromatography (TLC) and separation-mass spectrometry methods such as LC/MS (-MS) impractical. Ambient ionization mass spectrometry uses a variety of ionization techniques such as penning ionization in Direct Analysis in Real Time (DART), and atmospheric pressure chemical ionization in Direct Sample Analysis (DSA), and electrospray ionization in Desorption Electrospray Ionization (DESI). In this manuscript, two of the commonly used ambient ionization techniques are compared: Perkin Elmer DSA-MS and IonSense DART in conjunction with a JEOL AccuTOF MS. Both technologies were equally successful in analyzing writing inks and produced similar spectra. DSA-MS produced less background signal likely because of its closed source configuration; however, the open source configuration of DART-MS provided more flexibility for sample positioning for optimum sensitivity and thereby allowing smaller piece of paper containing writing ink to be analyzed. Under these conditions, the minimum sample required for DART-MS was 1mm strokes of ink on paper, whereas DSA-MS required a minimum of 3mm. Moreover, both techniques showed comparable repeatability. Evaluation of the analytical figures of merit, including sensitivity, linear dynamic range, and repeatability, for DSA-MS and DART-MS analysis is provided. To the forensic context of the technique, DART-MS was applied to the analysis of United States Secret Service ink samples directly on a sampling mesh, and the results were compared with DSA-MS of the same inks on paper. Unlike analysis using separation mass spectrometry, which requires sample preparation, both DART-MS and DSA-MS successfully analyzed writing inks with minimal sample preparation.

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.

How Much Can a Forensic Laboratory Do to Discriminate Questioned Ink Entries?

Questioned document examiners are frequently required to determine whether the questioned ink entries on a document are written with the same ink, either for forged document identification or relative ink dating. How many methods are sufficient to discriminate potentially different inks? In this paper, 18 blue ballpoint inks were first nondestructively examined with a video spectral comparator. The ink entries were subsequently extracted with organic solvents for analysis of the volatile solvents and dyes by GC/MS, TLC, and LC-MS/MS. The 18 ink samples were divided into 10, 9, 12, and 14 categories by these four methods, respectively. With the combined results, there were only two inks that remained indistinguishable, but they were further differentiated by microscopy. Therefore, to achieve effective discrimination of ballpoint ink entries, the authors suggest that a complete examination should include an analysis of their optical features, volatile solvents, and dyes as well as the ink quality.

Critical review of forensic trace evidence analysis and the need for a new approach

The historical development, contributions and limitations of the two traditional approaches to trace evidence analysis are reviewed. The first approach was as generalist practitioner, looking broadly at an assemblage of many different particle types. The second was that of specialist practitioner, with attention focused on one specific particle type. Four factors have significantly impacted the effectiveness of these approaches: (1) increasing technological capabilities, (2) increasing complexity in the character of manufactured materials, (3) changes in forensic laboratory management, and (4) changing scientific and legal expectations. The effectiveness of each approach is assessed within the context of these changes. More recently, new technologies have been applied to some trace evidence problems, intended to address one or more limitations. This has led to a third approach founded on discrete, highly technical methods addressing specific analytical problems. After evaluating the contributions and limitations of this third approach, we consider the different ways that technologies could be developed to address unmet needs in forensic trace evidence analysis. The route toward effective use of new technologies is contrasted with how forensic science laboratories are currently choosing and employing them. The conclusion is that although new technologies are contributing, we are not on a path that will result in their most effective and appropriate use. A new approach is required. Based on an analysis of the contributions of each of the three exisiting approaches, seven characteristics of an effective trace evidence analysis capability were determined: (1) particle traces should be a major problem-solving tool, (2) there should be readily available, straightforward methods to enable their use, (3) all available and potentially useful particle types should be considered, (4) decisions to use them should be made in the context of each case, guided by what they can contribute to the case and how efficiently they can do so, (5) analyses should be conducted using appropriate technologies, (6) findings should be timely and directly integrated with case-specific problems, and (7) new technologies should be used to improve the overall effectiveness of the capability. Clearly new technologies have the potential to revolutionize forensic trace evidence, but just as clearly some of the traditional capabilities have been rendered ineffective, or lost entirely, by the way we have come to approach the problem. Having critically defined the current limitations of and the desired outcomes, the next focus should be consideration of alternative approaches that might achieve such a result.

The analysis of colored acrylic, cotton, and wool textile fibers using micro-Raman spectroscopy. Part 2: comparison with the traditional methods of fiber examination

In the second part of this survey, the ability of micro-Raman spectroscopy to discriminate 180 fiber samples of blue, black, and red cottons, wools, and acrylics was compared to that gathered with the traditional methods for the examination of textile fibers in a forensic context (including light microscopy methods, UV-vis microspectrophotometry and thin-layer chromatography). This study shows that the Raman technique plays a complementary and useful role to obtain further discriminations after the application of light microscopy methods and UV-vis microspectrophotometry and assure the nondestructive nature of the analytical sequence. These additional discriminations were observed despite the lower discriminating powers of Raman data considered individually, compared to those of light microscopy and UV-vis MSP. This study also confirms that an instrument equipped with several laser lines is necessary for an efficient use as applied to the examination of textile fibers in a forensic setting.

Forensic analysis of ballpoint pen inks using paper spray mass spectrometry

Paper spray mass spectrometry (PS-MS) is explored as a simple, fast, and effective technique for the forensic analysis of inks in documents.

Analysis of questioned documents: a review

During the last years (2000-2014), many publications concerning the forensic analysis of questioned documents have been published, and new techniques and methodologies are nowadays employed to overcome forensic caseworks. This article reviews a comprehensive collection of the works focused on this issue, including dating studies, the analysis of inks from pens and printers, the analysis of paper, the analysis of other samples related to questioned documents and studies on intersecting lines. These sections highlight the most relevant analytical studies by a wide range of analytical techniques. Separation and spectrometric techniques are critically discussed and compared, emphasizing the advantages and disadvantages of each one. Finally, concluding remarks on the research published are included.

Identification of scanner models by comparison of scanned hologram images

A method to identify scanner models that had been used to forge low-level counterfeit currencies was proposed in this study. The method identified a scanner model by characterizing differences between hologram images that exist in low-level counterfeit currencies. Twenty scanners of 18 different models were used to make samples of hologram images used in this study. The method was divided into two steps: identification of capturing conditions and identification of the scanner model. The first proposed protocol used correlations of spatial distribution of brightness to identify capturing conditions. A second proposed protocol used correlations of color distributions to identify a scanner model. The effectiveness of the protocols was demonstrated with numerical methods and sample images. The preliminary study revealed that it is necessary to consider the orientation of the holograms when the scanner models were identified, but 180° rotations can be ignored. Moreover, it is necessary to consider position in the main scanning direction of the bed for charged-coupled-device scanners. The demonstration showed that the first protocol could correctly identify the capturing conditions of almost all hologram images. However, one image could not be identified correctly; the protocol could distinguish images captured by charged-coupled-device scanners and those captured by contact image sensor scanners if the hologram was placed on the right or left edge of the scanner bed, but could not distinguish them if the hologram was placed on the inside. The demonstration also showed that the second protocol could correctly identify scanner models of all hologram images.

Laser desorption ionization mass spectrometric imaging of mass barcoded gold nanoparticles for security applications

Patterns created by the inkjet printing of functionalized gold nanoparticles (NPs) can be selectively detected by laser desorption/ionization imaging mass spectrometry (LDI-IMS). These patterns can only be visualized by mass, providing a robust yet tunable system for potential anti-counterfeiting applications.