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Profili Forensic Chemistry

by: Kayli Antos

Profili Forensic Chemistry FRSC 367

Kayli Antos
GPA 3.37

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Chapter: Hair Analysis Topic: Hair Background, Excellent For Study, Medullary Index, Human Medullary Patterns Chapter: Fiber Analysis Topic: Textile Fiber, Animal Fibers, Vegetable Fibers, Miner...
Forensic Chemistry
Mark Profili
Class Notes
25 ?




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This 4 page Class Notes was uploaded by Kayli Antos on Saturday December 5, 2015. The Class Notes belongs to FRSC 367 at Towson University taught by Mark Profili in Summer 2015. Since its upload, it has received 25 views. For similar materials see Forensic Chemistry in Criminology and Criminal Justice at Towson University.

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Date Created: 12/05/15
Forensic Chem – Profili – Fall 2015 ¤ Hair Analysis  Hair Background  Grows from a collection of cells called the follicle.  The shaft has three parts  The cuticle covers the outside and can look like shingles or scales. Different animals have different scale patterns.  The cortex is the inner, pigmented layer.  The medulla runs down the center.  Texture depends on the cuticle to medulla ratio.  Excellent For Study  Resist decomposition.  Can show history of drug use or poisoning.  Medullary Index  Can distinguish between animal and human.  Diameter of medulla/diameter of hair.  MI < 0.33 is human.  MI >0.5 is animal.  Human Medullary Patterns  Continuous  Interrupted (regular)  Fragmented (irregular)  Cross section can be used to determine race. The less round the cross section, the more curly the hair.  Humans with mongoloid origins typically have a continuous medulla.  Dyed hair will have color distributed in the cortex and medulla.  Bleached hair will have a yellowish tint.  Class evidence.  Hair texture caries with body region.  Up to fifty hairs from each region (head, pubic area, facial hair, etc) must be collected in order to be used for comparison. ¤ Fiber Analysis  Textile Fiber  The smallest part of a textile.  Many objects like clothing, ropes, and rugs are made of textile fibers.  Animal Fibers  Wool fibers make up less than 1% of all fibers used in textile production.  Microscopically looks like hair.  The cuticle is made of scales that resemble shingles. One of the most useful ways to identify a fiber as wool.  Other animal hairs are less frequently found so they have greater evidential value. Can include goat, llama, alpaca, and camel hair.  Cattle and rabbit hair can be used to make felt.  Silk is the next most common animal fiber. It is not often encountered because it doesn’t shed fibers easily.  Vegetable Fibers  Only cotton is commonly found.  Jute and sisal can be found in cords and bags.  Cotton fibers are flattened and twisted and resemble a ribbon.  In a process called mercerization, the fibers are treated with alkali which makes them swell and become rounded but they will still be able to be identified as cotton.  Undyed cotton fibers are so common that they have little evidential value.  Mineral Fibers  Asbestos is the only natural mineral fiber.  Rarely used in clothing or other household objects and will not often be found as evidence.  Asbestos minerals are crystalline with chemical bonds stronger in one direction (along the fiber axis).  They fracture to form long, thin rods and can be made into thin fibers that are submicroscopic and can easily become airborne.  Are valuable evidence since they’re so rare.  Can determine which type of asbestos the fibers were derived from.  Manmade Fibers  Will fluoresce under UV light.  About 75% of total textile production in the US.  Are fibers of a certain chemical composition that are in a certain shape and size, with a certain amount of additives, processed in a certain way.  There are over 1,000 fiber types in the 6 most common of the 21 generic classifications.  Importance Of Fiber Evidence  Have more evidential value than hair because strands will have different numbers, strands and fibers have different diameters, twists occur in different directions and numbers, the weave type differs, dye content differs, and foreign material in the fiber also differs.  Must collect evidence from suspect and victim as soon as possible because 80% of fibers will be lost in the first four hours and after 24 hours, only 5-10% will remain.  From Less Than 1 cm Of A 20 μm Diameter Fiber One Can Determine:  generic class  polymer composition  finish (bright or dull)  cross sectional shape  melting point  refractive indices  birefringence  color  fluorescence  absorption spectrum  dye class  dye components  Microscopy  The quickest, most accurate, and least destructive way to determine microscopic characteristics and polymer types.  Stereomicroscope  Used first.  Can determine physical features like crimp, length, color, relative diameter, luster, apparent cross section, damage, and adhering debris.  Can then be tentatively determined to be synthetic, natural, or inorganic.  Comparison Microscope  If all characteristics are the same under a stereoscope, then use.  Gives a point-by-point and side-by-side comparison to determine if two fibers could have originated from the same source.  Can tell if a fiber fluoresces from chemical or environmental factors.  Make sure same illumination and magnification.  Fluorescence Microscopy  Illuminated by UV light.  Polarized Light Microscope  Can view and manipulate the sample.  Can determine refractive indices, birefringence, and dispersion.  Microspectrophotometry  Use a grating spectrometer to separate light absorbed by or reflected from a sample into component wavelengths and plot each wavelength vs intensity.  Can measure IR or UV VIS spectra  Nondestructive and not limited to sample size.  Reactive dyes, chemical composition, tentative identification.  Thin-Layer Chromatography  Inexpensive, simple, and well documented.  Used to compare dye components.  Should only be used when you can’t use other techniques.  Pyrolysis Gas Chromatography  Destructive.  Heat applied to polymer chains to fragment them.  Separated and characterized by GC.  ID generic type of fiber, sometimes also a subclass.


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