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Analytical Techniques In Forensic Science > Analytical Techniques For Trace Evidence > Flashcards

Analytical Techniques For Trace Evidence Flashcards

1
Q

What kind of cases might require chemical analysis of glass evidence ?

A

-burglary
-car accidents
-assault

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2
Q

Why is the location of glass relevant ?

A

The location of glass is dependent on what is analysed/ evidential value

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3
Q

How is glass recovered from clothing/ shoes ?

A

-seal pockets/ trousers turn ups
-recover hairs/ fibres by lightly taping
-shake item/brush onto brown paper
-check pockets and turnups last

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4
Q

How is glass and fibres recovered from hair ?

A

Combing

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5
Q

How is glass and fibres taken from other surfaces ?

A

Tweezers

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6
Q

What controls are taken from glass recovery ?

A

-blank sample
-reference sample at crime scene is taken from the frame not from the glass on the floor

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7
Q

When would a forensic scientist analysis glass ?

A

-SOCOs will recover glass or size items with glass on it.
-volume crimes- don’t usually examine glass because a suspect is not located quickly enough
-serious crimes-more likely to analyse glass evidence

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8
Q

What is the evidential value of glass in hair combing ?

A

Highest evidential value

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9
Q

What is the evidential value of glass embedded in soles of footwear ?

A

Lowest evidential value

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10
Q

What is float glass ?

A

-very common (windows)
-smashes into mixed sized fragments with sharp edges
-edges can tell us how fresh the smash was

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11
Q

What is tampered glass ?

A

-common (motor vehicles)
-safety glass
-hard to smash
-forms cubes
-tends to clump together
-edges indicate thermal or physical stress and impact

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12
Q

What is laminated glass ?

A

-2+ panes joined by plastic (PVB bond)
-common (windscreen glass)
-less common (bullet resistant, smart glass)
-sticks together
-safety

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13
Q

What is wired glass ?

A

-less common (fire doors)
-mesh through the pane
-tends to be indoors (rusting)

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14
Q

How does glass smash ?

A

Backwards fragmentation

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15
Q

What is a radial crack ?

A

Radiate in Amy directions away from the point of fracture

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16
Q

What is a concentric crack ?

A

Imperfect circle around the point of fracture

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17
Q

What are the different types of analysis for glass ?

A

-chemical
-refractive index
-mechanical fit

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18
Q

What is chemical analysis for glass ?

A

Identifies oxides in colouring and impurities in constituent parts used in manufacture

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19
Q

What is refractive index analysis for glass ?

A

Light refraction as it passes through glass, measured in heated oil. The RI changes as it’s heated, and when the sample disappears the RI value is known

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20
Q

What is mechanical fit for glass ?

A

Large fragments might stick together
Conchoidal stress marks

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21
Q

What equipment is used to analyse glass ?

A

-GRIM
-X-Ray fluorescence
-Scanning electron microscope
-surface examination
-annealing

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22
Q

What is GRIM analysis ?

A

Measures optical properties of glass
-tiny fragments <0.5 mm

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23
Q

What is X-Ray fluorescence analysis ?

A

Elemental composition of glass

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24
Q

What kind of cases might require chemical analysis of fibre evidence ?

A

-hit and run
-car crash/ accident
-sexual assault
-burglary

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25
Q

Where might you find samples of fibres ?

A

Everywhere

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26
Q

How are fibres recovered from clothing ?

A

-tape lifting
-plastic tweezers
-vacuuming
-shaking
-brushing
-place in paper bag

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27
Q

What are the different types of fibres ?

A

-natural and synthetic/man-made
-further classified: animal, vegetal or mineral

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28
Q

What are examples of natural fibres ?

A

Vegetable: cotton, hemp
Mineral: asbestos
Animal: wool, silk

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29
Q

What are examples of man made fibres ?

A

Natural polymer: acetate, viscose
Synthetic: polyester
Inorganic: carbon, glass

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30
Q

What does cotton look like etc ?

A
  • strong, tough and flexible
    -absorbs moisture
    -doesn’t retain shape
    -length and degree of twist differed based on type of cotton
    -if ignited burns with steady flame
    -smells like burning leaves
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31
Q

What does linen look like etc ?

A

-individual plant fibres are longer
-takes longer to ignite
-if burning can be extinguished by blowing like a candle

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32
Q

What does silk look like etc ?

A

-burns easily but not as steadily as Cotten/ linen
-smells like burning hair
-not as easy to extinguish

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33
Q

What does wool look like etc ?

A

-from sheep’s, goat
-individual fibres are shorter than silk
-diameter of fibres is relevant
0fineness indicates usage-clothing vs carpet
-harder to ignite with a steady flame but difficult to keep burning
-smells like burnt hair

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34
Q

What does acrylic look like etc ?

A

-made from natural gas and petroleum
-retains shape; wool like
-resistant to moths, sunlight and oil
-burns readily due to contents and air filled pockets
-will ignite fast and will continue burning until extinguished
-smells acrid or harsh

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35
Q

What does nylon look like etc ?

A

-made from petroleum
-exceptionally strong and abrasion resistant
-damage resistant to oils and many chemical
-low in moisture absorbency
-melts and burns fast if flame remains on melted fabric
-smells like burning plastic

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36
Q

What does polyester look like etc ?

A

-made from coal, air, water and petroleum products
-strong-resistant to stretching and shrinking
-resistant to most chemicals
-quick drying
-wrinkle resistant
-melts and burns at the same time
-dripping ash Bon’s with any surface it encounters
-smells ‘sweetish’

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37
Q

What do synthetic fibres tell us about?

A

-blends- two or more fibres
-should take characteristics of each fibre
-burning test can be used but fabric content will be an assumption

38
Q

What identification techniques are used for fibres ?

A

-primary examination
-chemical examination

39
Q

What is the primary examination for fibres ?

A

-visual - colour, location, amount
-microscope - comparison
-birefringence

40
Q

What is the chemical examination for fibres ?

A

Involves the extraction of dye and identifying and characterising the chemical structure

41
Q

What equipment is used to analyse fibres ?

A

-SEM
-Raman spectroscopy
-IR spectroscopy
-UV vis spectroscopy

42
Q

What kind of cases might require a chemical analysis of paint evidence ?

A

-hit and run
-car accident/ crash
-break in

43
Q

Why don’t SOCOs use tape to lift paint samples ?

A

Paint has multiple layers so the tape might remove a layer

44
Q

How is paint recovered from clothing ?

A

-plastic tweezers
-shaking
-brushing
-place in paper bag

45
Q

How is paint removed from other surfaces ?

A

-tweezers
-sharp edged knife

46
Q

What is the chemical examination of paint ?

A

Side by side comparison under Low power stereo microscope for colour, surface texture and colour layer sequence

47
Q

What is colour layer sequence ?

A

-trying to match the layer number and sequence of colour as it the sample will be made up of diffferent layers (base coat, binder, primer and topcoat )

48
Q

What is the second part of the chemical analysis of paint samples ?

A

Analysing individual layers

49
Q

What is quality control ?

A

A planned system of activities to provide a quality result, revolving around what you do daily in the lab

50
Q

What is quality assurance ?

A

A planned system of activities designed to ensure that the quality control system is effective, revolving around how you do it and how do you prove that it has been done

51
Q

What does quality control include ?

A

-running blanks to check for contamination
-run and check QC samples
-use statistical quality control- plotting charts
-use reference materials
-level of QC depends on the consequence of being wrong

52
Q

What is auditing ?

A

Important step in the QA function to ensure compliance, compares actual conditions with requirements

53
Q

What are quality standards ?

A

Collection of management practices, methodologies, systems, requirements, and specifications defined by industry advisory groups to assist manufacturers in achieving and demonstrating consistent production levels and product quality

54
Q

What are the three management practises of quality standards ?

A

-Good Laboratory Practice Regulations 1999
-ISO/IEC 9001:2015
-ISO/IEC 17025:2017

55
Q

What is the Good Laboratory Practice Regulations 1999 ?

A

For safety tests on chemicals, ensures tests are repeatable and unbiased

56
Q

What is ISO/IEC 9001:2015 ?

A

Used by organisations supplying products or services

57
Q

What is validation ?

A

Confirmation that requirements for a specific intended use or application have been fulfilled

58
Q

What is method validation ?

A

Comprised of a series of checks to ensure the method is fit-for-purpose and performs reliably to a desired set of standards

59
Q

For analytes of method validation what would be used ?

A

-a reference standard (certified reference standard)
-a internal standard (different to the analyte but may be chemically similar)

60
Q

What are the main factors to consider for method validation ?

A
  • Accuracy
    -Precision
    -Linearity
    -Range
    -Sensitivity
    -Selectivity
    -Recovery
    -Robustness
61
Q

What does accuracy mean in method validation ?

A

How true/ close the result is to the actual value

62
Q

What does precision mean in method validation ?

A

How scattered are replicate data points from the same value

63
Q

What is linearity for method validation ?

A

The detector response is directly proportional to the analyte concentration. Generally expressed as the correlation coefficient

64
Q

What is the range of the analyte concentration in method validation ?

A

The upper and lower analyte concentrations where results for the analytical method have demonstrated a certain level of precision, accuracy and linearity

65
Q

What is sensitivity in method validation ?

A

An observed change in the response of a measuring instrument due to a change in the analyte concentration

66
Q

What is limit of detection ?

A

Lowest concentration producing reliable analyte detection

67
Q

What is limit of quantification ?

A

Lowest concentration producing reliable analyte quantification

68
Q

What is selectivity in method validation ?

A

The extent to which a method can distinguish and determine analytes in a complex mixture made up of other interferences

69
Q

What is selectivity in method validation ?

A

The extent to which a method can distinguish and determine analytes in a complex mixture made up of other interferences

70
Q

What is recovery in method validation ?

A

The recovery of an analyte in a sample compared to a measurement of a reference standard of the same analyte at the theoretical 100% recovery value

71
Q

What is robustness in method validation ?

A

A measure of the susceptibility of a method to small,, deliberate variation in conditions such as temperature, Mobile phase composition and pH, column age etc.

72
Q

What is accreditation ?

A

The formal recognition that an organisation is competent to perform specific processes, activities or tasks in a reliable credible and accurate manner

73
Q

What are the provisions of accreditation ?

A

-undertaken impartially
-objective
-transparent
-effective
-undertaken by competent assessors and technical experts

74
Q

What is the UK’s accreditations service ?

A

UKAS- appointed by the government but works independently

75
Q

What is the quality standard ISO17025: 2017 ?

A

The general requirement for the competence of testing and calibration laboratories

76
Q

Why is ISO17025 used ?

A

Demonstrates that the accredited lab:
- operates under a quality system
-is technically competent
-generates technically valid results

77
Q

What are the benefits of accreditation ?

A
  • proves competence
    -adds confidence
    -competitive advantage
    -demonstrate due diligence
    -continuous improvement
    -time and cost saving
78
Q

What are the challenges of accreditation ?

A

-cost (£30,000)
-people can be a liability
-lack of knowledge from auditors
-continuous improvement and investment
-transitioning knowledge into practice

79
Q

What is a quality management system ?

A

A collection of business processes focused on consistently meeting customer requirements and enhancing their satisfaction. It aligns with an organisations purpose and strategic direction.

80
Q

What are the principles of a quality management system ?

A
  • customer focus
    -leadership
    -engagement of people
    -process approach
    -continuous improvement
    -evidence-based approach
    -relationship management
81
Q

What are the benefits of a quality management system ?

A

-better products and services
-attracting new customers
-increasing competitive edge
-reduce the likelihood of mistakes
-good leadership

82
Q

What are the challenges of a quality management system ?

A
  • organisational culture
    -Data overload
    -ambiguous KPIs
    -unfitting procedures
    -closing the cycle
83
Q

How is quality of a crime scene determined ?

A
  • some processes are accredited to the standard (ISO/IEC)
    -working on various accreditations
    -documentation
    -anti-contamination procedures
    -chain of custody
    -equipment calibration and cleaning vehicles
84
Q

how is quality of the lab determined ?

A

-accredited by UKAS to the standards ISO/IEC based on the type of analysis
-validation within lab
-time/space separations
-anti-contamination procedures
-proficiency trials
-calibration of equipment
-environmental controls

85
Q

How is quality of specific tests determined ?

A

-each test is validated
-anti-contamination checks and controls

86
Q

How is quality of the forensic scientist determined ?

A

-personal validation carried out
-must be signed off for all techniques to be reported on
-continual competency records must be kept up to date
-important to keep knowledge relevant

87
Q

How do we reassure the court on the quality of the forensic (DNA) evidence that you are presenting?

A

-Quality of the laboratory
-Quality of a specific test
-Individual competence
(Includes degree and further qualifications,
Includes CPD)

88
Q

What is the role of the forensic science regulator ?

A

-identifying the requirement for new or improved quality standards
-leading on the development of new standards
-where necessary, providing advice and guidance so that providers of forensic science services can demonstrate compliance with common standards

89
Q

Who is the forensic science regulator supported by ?

A

Sponsored by the Home Office but operates independently.
-supported by a team of 5 scientists

90
Q

What is the forensic regulator codes of practice ?

A

-Detail on services and how they should be conducted
-Identifying the requirement for new or improved quality standards
-Leading on the development of new standards and data exchange
-Where necessary, providing advice and guidance so that providers of forensic science services can demonstrate compliance with common standards

91
Q

How do you promote quality in the lab ?

A
  • good lab practice (keep records, qualifications, system servicing, SOPs)
    -quality systems (ISO17025)
    -correct data analysis using appropriate statistics
    -data management
92
Q

What are challenges of quality ?

A

-Quality standards for all disciplines
-Compliance
-Legislation and government action
-Shared framework and auditable systems
-Quantity vs quality

Analytical Techniques In Forensic Science (6 decks)

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