Microtrace Presents at American Academy of Forensic Sciences 2024

The American Academy of Forensic Sciences (AAFS) is holding their Annual Meeting in Denver, Colorado from February 1 to 24, 2024. Microtrace scientists have authored or co-authored four of the papers that will be presented this at the conference this year. These include: “Pigment Identification in Solution-Dyed Fibers,” “Hair and natural textiles as detectors for chlorine gas exposure,” “The Characterization and Identification of Historical Inks and Their Colorants,” and “The Capabilities and Limitations of Particle-Correlated Raman Spectroscopy (PCRS) for the Analysis of Forensic Soil Minerals.”

For more details about the conference, click here.


Pigment Identification in Solution-Dyed Fibers
Christopher S. Palenik, MS, PhD; Kelly Beckert, MS, BS; Otyllia Abraham, MS, BS;
Ethan Groves, BS; Skip Palenik, BS

Solution dyed fibers are synthetic fibers colored during the manufacturing process by microscopic and sub-microscopic solid pigment particles prior to extrusion.  The use of pigments to color fibers provides improved weatherability and lightfastness over traditionally dyed fibers and represents an eco-friendly alternative method for producing colored fibers. As such, solution dyed fibers have steadily gained market share and are being used in an increasing variety of polymers for an expanding range of applications (including trunk liners of vehicles as well as commercial and consumer carpeting).  Despite their minute size, the visualization and identification of these fine pigment particles is accessible using robust methods that are already commonly employed (e.g., polarized light, fluorescence microscopy and scanning electron microscopy/energy dispersive x-ray spectroscopy), or are becoming more common (e.g., Raman microspectroscopy), in trace evidence laboratories.

The act of recognizing that a fiber was colored by pigmentation represents a significant point of comparison in a fiber examination which is not presently included in many fiber examination protocols.  This research aims to fill this knowledge gap by providing the results from an analytical approach that was developed and optimized to recognize and differentiate solution dyed fibers from traditionally dyed fibers and has been expanded, in the present work, to characterize and identify population of pigments in such fibers.

This research is based on the study of a population of 225 fibers selected from our internally developed, curated fiber reference collection consisting of thousands of solution dyed fibers.  The selected fibers were chosen to represent a range of manufacturers that span a variety of commercial applications, colors, and fiber types (e.g., polyolefin, nylon, polyester, rayon) selected to reflect market trends as well as the sources of fibers that are anticipated to be encountered as trace evidence.  Building from our initial results (1), which provided a method to recognize solution dyed fibers, this presentation is focused on the expanding the approach to the process of identifying the range of pigments used in these fibers through a combination of chemical and elemental analyses.

The identification process presented here explores several sample preparation methods and draws from prior microscopical examinations to direct analyses by Raman microspectroscopy (532 and 785 nm lasers).  Both “bulk” fiber analyses and particle-focused, confocal Raman measurements on cross sections, have been explored to determine the optimal approach for identifying the suite different pigments that are found in a given fiber.  The identification is also supported by elemental analyses conducted by energy dispersive x-ray spectroscopy analyses of the fibers (longitudinal mounts) conducted in the scanning electron microscope. Ultimately, the approach as well as the tabulated identification data (i.e., the name of a pigment by its Colour Index designation or chemical structure) provides new insight into the trends, commonality (or rarity) of the pigments used to color fibers. The combination of this research is intended to provide examiners with a means by which these previously unexplored properties can be exploited in casework samples.

Hair and natural textiles as detectors for chlorine gas exposure 
Jack Hietpas, PhD; Ethan Groves, BS; Skip Palenik, BS; Christopher S. Palenik, PhD

This project explores a novel method for assessing the exposure of people and their clothing to chlorine gas, a resurgent chemical warfare (CW) agent.  The research examines changes to the micro-structure of human hair and natural textile fibers that occur due as a result of chlorine dosage (exposure time and concentration of chlorine gas).  A suite of microscopical and microanalytical methods have been explored to examine and characterize exposed hair and fibers.

The Characterization and Identification of Historical Inks and Their Colorants
Sarah Mosinski; Jordyn Guse; Ethan Groves, BS; Katie M. White, MSc; Skip Palenik, BS;
Christopher S. Palenik, MS, PhD

Forgeries are common in the realm of autographed memorabilia and collectibles.  While handwriting comparisons can provide insights into the stylistic aspects of signatures and writing, a chemical analysis of the ink and media (e.g.¸paper, leather, paint) can provide orthogonal and objective constraints on questions of age and authenticity.

Among the components of a historical document, the identification of inks and their components present various practical analytical challenges for reasons that include: the often short length of ink line available in writing or a signature, limitations that often exist on consumptive sampling or analysis, the relatively low concentration of ink needed to form a dark line, and the complexity of an ink’s composition.  Often, historical inks are based upon natural components such as extracts from galls and logwood (haematoxylum) whose composition can vary based upon the specific plant and extraction procedures.  These natural components may be supplemented with a range of synthetic dyes, further complicating the chemistry of an ink sample. Furthermore, the composition of an ink on media can change as it dries and with time.

Inan attempt to more systematically study these analytically challenging samples, a set of fifty historical ink samples were analyzed by a range of non-destructive and minimally consumptive analytical methods.  These dried inks were collected from ledgers, stock certificates and journals with dated entries.  They range from approximately 1900 to 1970 and span six nominally attributed colors: black, brown, blue, green, purple, and red.  In addition to the aged ink samples from the documents, a series of recently deposited known inks were also systematically analyzed.  These include laboratory synthesized samples from historical recipes and commercially available historical inks from boutique suppliers.

The response of each ink to a combination of alternate light sources spanning UV to white to near-infrared illumination, coupled with a range of barrier filters were studied under a set of controlled conditions to permit the objective characterization of luminescence and absorbance properties.  Images of the ink response were captured with a series of standard ink samples to ensure consistent illumination and capture conditions.  The elemental composition of the inks was studied through elemental maps of ink lines from each sample through a combination of SEM/EDS and micro-XRF spectroscopy.   Finally, each ink was characterized by Raman microspectroscopy using both 785 and 532 nm lasers.  The data from each of these methods has been compiled to explore trends and associate the various characteristics of these historical ink samples.  Finally, the Raman data has been analyzed to identify various components of the inks, which have included traditional ink colorants such as logwood, iron gall, and several synthetic dyestuffs.  The results of this study of historical writing inks provided new and practical insights into the properties and composition of authentic historical writing inks.

The Capabilities and Limitations of Particle-Correlated Raman Spectroscopy (PCRS) for
the Analysis of Forensic Soil Minerals

Jasmine Kaur; Joshua Christensen; Ethan Groves, BS; Skip Palenik, BS; Christopher S. Palenik, MS, PhD; Peter R. De Forest, DCrim; Marisia A. Fikiet, PhD; Virginia M. Maxwell, DPhil, BSc; Brooke W. Kammrath, PhD

This study evaluated the capabilities and limitations of Particle Correlated Raman Spectroscopy (PCRS) for the analysis of soil samples. PCRS is an automated, integrated technique which combines image analysis with Raman spectroscopy to provide morphological properties and chemical information from a mixture of discrete particles, such as the population of mineral grains in a soil sample. Considering how valuable soil traces can be in providing linkages in a case, along with the long stated criticisms of forensic soil analysis (e.g., subjective, time consuming, and labor intensive), there is a need for an automated system which provides and efficient, objective, and statistically comparable approach to the interrogation of soil samples. PCRS has the ability to provide information regarding the particle size distribution, grain morphology, and mineral identification, which permit samples to be compared. To develop PCRS for inclusion in a forensic soil workflow, the limitations and advantages of the method (e.g., dispersion, sample imaging and analysis, Raman spectroscopic analysis and interpretation) need to be evaluated, which has been the goal of the research that will be presented.

For the evaluation of PCRS as a tool to analyze soil minerals, single-blind PCRS was completed on four unknown, four-component mixtures of comminuted minerals and an additional ten disparate soil samples collected from the northeast United States. The 90-180 mm fraction of minerals were obtained from each soil sample after washing and sieving using traditional methods. Next, a computer-controlled vacuum-type powder dispersion system (operating at -20Pa and with a high sample volume) was used to create a uniform distribution of microscopic mineral particles with good spatial separation. Following the dispersion of particles on a glass slide, the sample was imaged and an image analysis routine was applied to isolate individual particles and obtain a range of morphological properties (e.g., circularity, aspect ratio).  The individual particles comprising a sample were each probed by Raman microspectroscopy using two different lasers excitations (532 nm and 785 nm). The resulting Raman spectra were identified via spectral library searching of the RRUFF2 mineral database which contains close to 10,000 different Raman mineral spectra. The morphological data associated with the particles in each mineral class was then used to generate size and shape distributions, delivering mineral-specific morphological information. Mineral size and morphological distributions for each soil sample were compared using multivariate statistical methods to evaluate their discriminating potential. The results of the PCRS method were then compared to those obtained using traditional methods for mineral identification, including polarized light microscopy and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. Similarities and distinctions of the results between these approaches have been evaluated to explore the utility of the present PCRS method for use in forensic soil casework. 

American Academy of Forensic Sciences

The American Academy of Forensic Sciences is a multi-disciplinary professional organization that provides leadership to advance science and its application to the legal system. The objectives of the Academy are to promote professionalism, integrity, competency, education, foster research, improve practice, and encourage collaboration in the forensic sciences.

Each February, the AAFS scientific meeting gathers together approximately 5,000 world-renowned professionals to present the most current information, research, and updates in their fields. More than 900 scientific papers, seminars, workshops, and other special sessions are presented. In addition, approximately 150 exhibitors showcase the cutting-edge technology and services of this ever-changing profession.

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