Microscopical recognition and characterization of solution dyed fibers.

Solution dyed fibers are synthetic fibers colored through the addition of insoluble pigmentation to the polymer prior to extrusion. This is in contrast to most textile fibers, which are traditionally colored via immersion in liquid dyebaths following extrusion. Solution dyed fibers are increasing in market share in numerous applications (e.g., apparel, carpet, upholstery), and thus, the microscopic characteristics and variety of pigments used to color them represent unexploited properties in forensic fiber comparisons. This paper presents the development of a microscopical process to first recognize a fiber as solution dyed and subsequently characterize the color and optical properties of each type of pigment found in a given fiber. To this end, a set of 76 fibers, representing polypropylene, nylon, polyester, and rayon, spanning all nominal colors and several consumer applications were analyzed longitudinally and in cross section using a combination of polarized light, fluorescence, and oil immersion microscopy. A given fiber contained between one and six different pigments, and a total of 260 pigments (not all unique) were recognized within this set of fibers. Pigment morphologies were categorized as angular, elongated, rounded, finely divided, or streaky, and about 40% of the pigments fluoresced. Ultimately, this body of data is intended to provide trace evidence examiners with a specific approach to recognize and begin to exploit pigmented fibers encountered in casework.

Optical and spectroscopic characterization of crystalline structures in cannabis extracts.

Marijuana and hemp represent two broad classes of Cannabis sativa plants that are distinguished based on the concentration of the psychoactive cannabinoid delta-9-tetrahydrocannabinol (Δ9 -THC). In this work, solvent extracts derived from marijuana and hemp were characterized using optical and spectroscopic techniques. The crystalline components of the solvent extracts were first analyzed using polarized light microscopy to determine optical properties, namely, crystal system, optical sign, and principle refractive indices. Crystals from the marijuana-derived extracts exhibited an orthorhombic crystal system and were optically negative, with nß between 1.6320 and 1.6330 ± 0.0002. In contrast, crystals from hemp-derived extracts exhibited a monoclinic crystal system and were optically positive, with nß between 1.600 and 1.6040 ± 0.0002. Crystals were further distinguished through infrared spectroscopy, which highlighted structural differences between the two sample types, primarily based on differences in O-H stretching. Finally, single-crystal X-ray diffraction was used to definitively identify the crystalline components, confirming the presence of tetrahydrocannabinolic acid in marijuana-derived extracts and cannabidiol in hemp-derived extracts. Given the differences in crystal structure identified between marijuana-derived and hemp-derived solvent extracts, optical characterization provides a screening method to differentiate visually similar samples prior to confirmatory analysis.