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Chemistry for the Analysis of Trace Evidence > Hairs > Flashcards

Hairs Flashcards

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1
Q

Why is hair a great form of trace evidence?

A
  • its found on all humans and animals
  • it is constantly being produced and shed
  • it is easily overlooked by criminals
  • it is readily transferred from one person/object to another person/object
  • highly stable - resisting both physical and chemical degradation
  • can be distinguished from each other and with DNA testing
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2
Q

Why is it not general practice to differentiate hair using chemical techniques?

A

All true hairs have the same basic chemistry

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3
Q

What does looking at isotope ratio of elements in hair show?

A
  • used to identify locations where an individual may have travelled based on changes in drinking water isotopes in different locations
  • similar uses to link substances of abuse
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4
Q

What are the three types of human hair?

A
  1. lanugo
  2. vellus
  3. terminal
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5
Q

What are lanugo hairs?

A
  • hairs that are formed in utero
  • fine and unpigmented
  • typically shed before or shortly after birth
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6
Q

What are vellus hairs?

A
  • fine, short, unpigmented/lightly coloured
  • on almost all skin surfaces (forhead, nose, ears, bald scalp)
  • not found on palms of hands or soles of feet
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7
Q

What are terminal hairs and what are the two types of terminal hairs?

A

Macroscopically visible on children and adults
1. primary - head, eyelash, eyebrow
2. secondary - pubic, underarms, beard

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8
Q

What are the three main histological layers of hair?

A
  1. cuticle - outermost layer
  2. cortext - main bulk of hair
  3. medulla - innermost layer of hair shaft
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9
Q

What is the cuticle most responsible for?

A

chemical resistance

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10
Q

What is the cortext most responsible for?

A

mechanical properties
* contains most of the pigment granules giving hair its colour

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11
Q

What is the medulla for?

A

not well understood
* not present in all hairs

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12
Q

What is the cycle that every hair goes through?

A
  1. anagen - active growing phase of hair extending progressively from the follicle root outwards
  2. catagen - transition phase when growth slows and eventually stops
  3. telogen - resting phase when minimal force is required to remove hair and natural shedding occurs
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13
Q

How does hair go grey?

A

Pigment stops being produced

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14
Q

How is hair collected and isolated?

A
  • for individual hairs forceps can be used
  • tape lift can be used to remove the pressure when using forceps - most efficient when collecting hairs from large surfaces
  • combing
  • 20 hairs from 5 head regions should be collected and packaged separately - plucking and combing (gives variation)
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15
Q

What is the analytical workflow for hair?

A
  1. gross examination, recovery and collection
  2. preliminary evaluation of physical characteristics
  3. microscopic techniques
  4. DNA
  5. SEM (sometimes TEM) - morphological features
  6. spectroscopic techniques - IR and Raman
  7. chromatographic techniques and MS
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16
Q

What microscopic techniques should be used for hairs?

A
  • optical: stereoscopic, reflected light, comparsion, fluorescence, brightfield, polarised
  • SEM and TEM
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17
Q

What macroscopic observations should be looked for?

A
  • macroscopic colour
  • length
  • general contour and curliness
  • approximate diameter
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18
Q

What features should be looked at when using a compound light microscope?

A
  • colour
  • cosmetic treatments
  • cross-sectional shape
  • biological damage
  • adhering material
  • thickness range
  • general damage
  • non-root morphological
19
Q

What microscopic features of the cuticle are looked at when using a compound light microscope?

A
  • colour
  • pigment granules
  • inner margin
  • thickness
  • damage
  • scale protrusion
20
Q

What microscopic features of the cortex are looked at when using a compound light microscope?

A
  • pigment granules - density, size, shape
  • texture
  • appearance of medulla
  • root features if present - growth stage, follicular material, abnormalities
21
Q

Comparision microscope analysis of hairs

A
  • head hairs have the most discriminative value
  • results of a microscopical hair comparision must be completed with a second examiner and should be blind to initial conclusions
  • final analysis unless more detail is required or root requires evaluation to explore DNA testing
22
Q

Scanning electron microscopy of hairs

A
  • employed when further analysis is required
  • can examine the surface of hair to highlight scales or physical damage to the hair
  • combined with SE, BSE and EDX modes - provide elemental data about hairs or residues
23
Q

IR and Raman analysis of hair

A
  • used to distinguish hair treatments and chemical damage along the length of hair
  • possible to distinguish between dye colour and brands
  • chemometrics and strong training required
24
Q

What are the steps involved in tandem mass spec?

A
  1. employ a first mass analysis stage to select a precursor ion
  2. then excite this selected ion species (usually by collosion with a neutral target gas)
  3. this causes it to fragment further to give one or more product ions plus neutral fragments
  4. then employ a second mass analysis stage to determine the mass spectrum of the product ions
25
Q

What is the second generation ions mass spectrum called?

A

MS/MS or MS^2

26
Q

What is the next step of tandem mass spec when it is extended to perform additional tandem experiments?

A
  • mass selecting a product ion formed in the first fragmentation stage and exciting by further collision
  • determining the mass spectrum of the third generation ion formed
27
Q

What is the mass spec of the third generation ion called?

A

MS/MS/MS or MS^3

28
Q

What are the two configurations of tandem MS?

A
  1. tandem-in-space
  2. tandem-in-time
29
Q

What is tandem-in-space?

A
  • mass analysis stages are physically separated from each other spatially so that they occur in different regions of the overall instrument
  • employ ion beam-type mass analysers
  • require a lot more space for extra instrumentation
  • greater mass spectral specificity
  • can see when someone has consumed drugs knowing that hair grows around 1cm/month
30
Q

What is isotope ratio mass spec?

A
  • can identify certain elements more clearly due to isotopes
  • can be used to identify locations where an individual may have travelled based on changes in drinking water isotopes in different locations
31
Q

How does isotope ratio mass spec work?

A
  • converts samples of the hair into oxygen gas and then perform isotopic analysis by MS
  • determine the levels of isotopic enrichment of the possible oxygen isotopes
32
Q

What does it suggest if the isotope ratio was the same as reference samples of hair from different areas?

A

individual has died in the same region that they consumed water in

33
Q

What would it mean if the isotope ratio was different for two samples?

A

the investigators could rule out some potential locations

34
Q

What are the three main conclusions that can be drawn from the interpretation of microscopical hair analysis alone?

A
  • association
  • inconclusive
  • exclusion
35
Q

What does an association conclusion mean?

A
  • questioned hair cannot be distinguished from known sample
36
Q

What are some factors that stengthen an association conclusion?

A
  • distinctive cosmetic treatments
  • abnormalities
37
Q

What are some weakeness with an association conclusion?

A
  • short hairs
  • incomplete hairs
  • colourless/pigmented
38
Q

What does a inconclusive conclusion mean with hair?

A

Questioned hair exhibits some similarities and some differences with known sample, but limiting factors are complicating the comparision

39
Q

What are some factors which limit the inconclusive conclusion?

A

environmental conditions - buried vs direct sunlight

40
Q

What does a exclusion conclusion of hair mean?

A

Questioned hair exhibits a meaningful difference compared to a known sample

41
Q

How can you improve an exclusion conclusion?

A

collect many hairs from multiple sub-areas from known sample

42
Q

What can effect the tranfer and persistence of hairs?

A
  • object texture
  • wearing a hat
  • animal hair transfer
  • hairloss
  • washing
  • artificial drying
  • secondary tranfer
  • fingernail scrapings
  • migration
43
Q

What type of reference samples are collected?

A
  • different ancestral groups
  • different cosmetic treatments
  • exhibiting different diseases
  • different locations on the body
  • different damage types
  • degraded in different ways

Chemistry for the Analysis of Trace Evidence (16 decks)

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