Analytical Techniques For Trace Evidence Flashcards
What kind of cases might require chemical analysis of glass evidence ?
-burglary
-car accidents
-assault
Why is the location of glass relevant ?
The location of glass is dependent on what is analysed/ evidential value
How is glass recovered from clothing/ shoes ?
-seal pockets/ trousers turn ups
-recover hairs/ fibres by lightly taping
-shake item/brush onto brown paper
-check pockets and turnups last
How is glass and fibres recovered from hair ?
Combing
How is glass and fibres taken from other surfaces ?
Tweezers
What controls are taken from glass recovery ?
-blank sample
-reference sample at crime scene is taken from the frame not from the glass on the floor
When would a forensic scientist analysis glass ?
-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
What is the evidential value of glass in hair combing ?
Highest evidential value
What is the evidential value of glass embedded in soles of footwear ?
Lowest evidential value
What is float glass ?
-very common (windows)
-smashes into mixed sized fragments with sharp edges
-edges can tell us how fresh the smash was
What is tampered glass ?
-common (motor vehicles)
-safety glass
-hard to smash
-forms cubes
-tends to clump together
-edges indicate thermal or physical stress and impact
What is laminated glass ?
-2+ panes joined by plastic (PVB bond)
-common (windscreen glass)
-less common (bullet resistant, smart glass)
-sticks together
-safety
What is wired glass ?
-less common (fire doors)
-mesh through the pane
-tends to be indoors (rusting)
How does glass smash ?
Backwards fragmentation
What is a radial crack ?
Radiate in Amy directions away from the point of fracture
What is a concentric crack ?
Imperfect circle around the point of fracture
What are the different types of analysis for glass ?
-chemical
-refractive index
-mechanical fit
What is chemical analysis for glass ?
Identifies oxides in colouring and impurities in constituent parts used in manufacture
What is refractive index analysis for glass ?
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
What is mechanical fit for glass ?
Large fragments might stick together
Conchoidal stress marks
What equipment is used to analyse glass ?
-GRIM
-X-Ray fluorescence
-Scanning electron microscope
-surface examination
-annealing
What is GRIM analysis ?
Measures optical properties of glass
-tiny fragments <0.5 mm
What is X-Ray fluorescence analysis ?
Elemental composition of glass
What kind of cases might require chemical analysis of fibre evidence ?
-hit and run
-car crash/ accident
-sexual assault
-burglary
Where might you find samples of fibres ?
Everywhere
How are fibres recovered from clothing ?
-tape lifting
-plastic tweezers
-vacuuming
-shaking
-brushing
-place in paper bag
What are the different types of fibres ?
-natural and synthetic/man-made
-further classified: animal, vegetal or mineral
What are examples of natural fibres ?
Vegetable: cotton, hemp
Mineral: asbestos
Animal: wool, silk
What are examples of man made fibres ?
Natural polymer: acetate, viscose
Synthetic: polyester
Inorganic: carbon, glass
What does cotton look like etc ?
- 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
What does linen look like etc ?
-individual plant fibres are longer
-takes longer to ignite
-if burning can be extinguished by blowing like a candle
What does silk look like etc ?
-burns easily but not as steadily as Cotten/ linen
-smells like burning hair
-not as easy to extinguish
What does wool look like etc ?
-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
What does acrylic look like etc ?
-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
What does nylon look like etc ?
-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
What does polyester look like etc ?
-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’
What do synthetic fibres tell us about?
-blends- two or more fibres
-should take characteristics of each fibre
-burning test can be used but fabric content will be an assumption
What identification techniques are used for fibres ?
-primary examination
-chemical examination
What is the primary examination for fibres ?
-visual - colour, location, amount
-microscope - comparison
-birefringence
What is the chemical examination for fibres ?
Involves the extraction of dye and identifying and characterising the chemical structure
What equipment is used to analyse fibres ?
-SEM
-Raman spectroscopy
-IR spectroscopy
-UV vis spectroscopy
What kind of cases might require a chemical analysis of paint evidence ?
-hit and run
-car accident/ crash
-break in
Why don’t SOCOs use tape to lift paint samples ?
Paint has multiple layers so the tape might remove a layer
How is paint recovered from clothing ?
-plastic tweezers
-shaking
-brushing
-place in paper bag
How is paint removed from other surfaces ?
-tweezers
-sharp edged knife
What is the chemical examination of paint ?
Side by side comparison under Low power stereo microscope for colour, surface texture and colour layer sequence
What is colour layer sequence ?
-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 )
What is the second part of the chemical analysis of paint samples ?
Analysing individual layers
What is quality control ?
A planned system of activities to provide a quality result, revolving around what you do daily in the lab
What is quality assurance ?
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
What does quality control include ?
-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
What is auditing ?
Important step in the QA function to ensure compliance, compares actual conditions with requirements
What are quality standards ?
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
What are the three management practises of quality standards ?
-Good Laboratory Practice Regulations 1999
-ISO/IEC 9001:2015
-ISO/IEC 17025:2017
What is the Good Laboratory Practice Regulations 1999 ?
For safety tests on chemicals, ensures tests are repeatable and unbiased
What is ISO/IEC 9001:2015 ?
Used by organisations supplying products or services
What is validation ?
Confirmation that requirements for a specific intended use or application have been fulfilled
What is method validation ?
Comprised of a series of checks to ensure the method is fit-for-purpose and performs reliably to a desired set of standards
For analytes of method validation what would be used ?
-a reference standard (certified reference standard)
-a internal standard (different to the analyte but may be chemically similar)
What are the main factors to consider for method validation ?
- Accuracy
-Precision
-Linearity
-Range
-Sensitivity
-Selectivity
-Recovery
-Robustness
What does accuracy mean in method validation ?
How true/ close the result is to the actual value
What does precision mean in method validation ?
How scattered are replicate data points from the same value
What is linearity for method validation ?
The detector response is directly proportional to the analyte concentration. Generally expressed as the correlation coefficient
What is the range of the analyte concentration in method validation ?
The upper and lower analyte concentrations where results for the analytical method have demonstrated a certain level of precision, accuracy and linearity
What is sensitivity in method validation ?
An observed change in the response of a measuring instrument due to a change in the analyte concentration
What is limit of detection ?
Lowest concentration producing reliable analyte detection
What is limit of quantification ?
Lowest concentration producing reliable analyte quantification
What is selectivity in method validation ?
The extent to which a method can distinguish and determine analytes in a complex mixture made up of other interferences
What is selectivity in method validation ?
The extent to which a method can distinguish and determine analytes in a complex mixture made up of other interferences
What is recovery in method validation ?
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
What is robustness in method validation ?
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.
What is accreditation ?
The formal recognition that an organisation is competent to perform specific processes, activities or tasks in a reliable credible and accurate manner
What are the provisions of accreditation ?
-undertaken impartially
-objective
-transparent
-effective
-undertaken by competent assessors and technical experts
What is the UK’s accreditations service ?
UKAS- appointed by the government but works independently
What is the quality standard ISO17025: 2017 ?
The general requirement for the competence of testing and calibration laboratories
Why is ISO17025 used ?
Demonstrates that the accredited lab:
- operates under a quality system
-is technically competent
-generates technically valid results
What are the benefits of accreditation ?
- proves competence
-adds confidence
-competitive advantage
-demonstrate due diligence
-continuous improvement
-time and cost saving
What are the challenges of accreditation ?
-cost (£30,000)
-people can be a liability
-lack of knowledge from auditors
-continuous improvement and investment
-transitioning knowledge into practice
What is a quality management system ?
A collection of business processes focused on consistently meeting customer requirements and enhancing their satisfaction. It aligns with an organisations purpose and strategic direction.
What are the principles of a quality management system ?
- customer focus
-leadership
-engagement of people
-process approach
-continuous improvement
-evidence-based approach
-relationship management
What are the benefits of a quality management system ?
-better products and services
-attracting new customers
-increasing competitive edge
-reduce the likelihood of mistakes
-good leadership
What are the challenges of a quality management system ?
- organisational culture
-Data overload
-ambiguous KPIs
-unfitting procedures
-closing the cycle
How is quality of a crime scene determined ?
- 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
how is quality of the lab determined ?
-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
How is quality of specific tests determined ?
-each test is validated
-anti-contamination checks and controls
How is quality of the forensic scientist determined ?
-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
How do we reassure the court on the quality of the forensic (DNA) evidence that you are presenting?
-Quality of the laboratory
-Quality of a specific test
-Individual competence
(Includes degree and further qualifications,
Includes CPD)
What is the role of the forensic science regulator ?
-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
Who is the forensic science regulator supported by ?
Sponsored by the Home Office but operates independently.
-supported by a team of 5 scientists
What is the forensic regulator codes of practice ?
-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
How do you promote quality in the lab ?
- good lab practice (keep records, qualifications, system servicing, SOPs)
-quality systems (ISO17025)
-correct data analysis using appropriate statistics
-data management
What are challenges of quality ?
-Quality standards for all disciplines
-Compliance
-Legislation and government action
-Shared framework and auditable systems
-Quantity vs quality
Who was Raman ?
Sir C. V. Raman (1888 – 1970) was an Indian physicist, who was awarded The Nobel Prize in Physics in 1930
What was Raman’s Nobel prize in ?
“for his work on the scattering of light and for the discovery of the effect named after him”.
What is electromagnetic radiation ?
The flow of energy at the universal speed of light through free space or through a material medium in the form of the electric and magnetic field that make up electromagnetic waves such as radio waves, visible light and x-ray
What are the characteristics of electromagnetic waves ?
-amplitude
-wavelength
-frequency
What does a shorter wavelength mean ?
Greater frequency and higher energy
Why are wavelengths important ?
Tell you what type of wave you’re dealing with
What are the different radiation types ?
-gamma
-x-ray
-UV
-Visible
-infrared
-microwave
-radio
What does a long wavelength mean ?
Low frequency and low energy
What part of the electromagnetic spectrum is visible to the naked eye ?
Visible light
What does visible light include on the spectrum ?
A range of different colours that all represent a particular wavelength
What does Raman spectroscopy use ?
A laser light
What happens when light is incident upon a substance ?
It can either get transmitted, absorbed, reflected, diffracted or scattered
How does Raman scattering work ?
- the majority of the light simply passes through the sample in the direction of the incident beam
- a small fraction of the scattered light occurs at wavelengths other than incident radiation
Rayleigh scattering
the scattering of light at the same wavelength as the incident radiation
What are the three types of emitted radiation ?
-strokes scattering
-anti-strokes scattering
-Rayleigh scattering
What is strokes scattering ?
A laser illuminates a sample, and a little bit of the incoming light is scattered off the sample at longer wavelength (lower energy).
What is vibrational spectroscopy ?
is a powerful physical method for the study of chemical compounds.
What is the main difference between Raman and IR spectroscopy?
IR Spectroscopy: Measures the absorption of infrared light by a sample
Raman Spectroscopy: Measures the scattering of light (usually from a laser) by the sample.
What is the difference between Raman and fluorescence ?
-fluorescence is strong and Raman is weak so fluorescence always wins when present.
-Raman is relative to laser line, fluorescence at set energy.
-Raman scattering carries much more information
How is the spectrum of Raman spec measured ?
Typically with a laser line as a reference
What does a Raman spectrum feature ?
A number of peaks, showing the intensity and wavelength position of the Raman scattered light
How are peak positions determined in Raman spec ?
Vibrational energies associated with the bonds in the molecule of which the sample is composed
What does each peak correspond to in Raman spec ?
A specific molecular bond vibration including individual bonds such as C-C and groups of bonds
Why are different lasers used in Raman spec ?
Different lasers are used in Raman spectroscopy to excite the sample at different wavelengths, which helps in obtaining a variety of information about the material being analyzed.
Where is Raman spec applied in forensic science ?
- paint
-GSR
-explosives
-fibres
-illicit drugs
-cosmetics
What is Raman micro-spectroscopy ?
Microscopic analysis using a Raman microscope
What does Raman micro-spectroscopy involve ?
A specially designed Raman spectrometer integrated with an optical microscope allowing High magnification and Raman analysis
What are the advantages of Raman micro-spectroscopy ?
- acquire Raman spectra of microscopic samples
-much less sample is required
What is a confocal Raman microscope used for ?
Analysis of micron size particles or volumes and analysis of different layers
What are handheld Raman spectrometers used for ?
Provide direct sampling of loose solid or liquid material or to conduct sampling on a containerised sample
What does handheld Raman spectrometers allow ?
Fast verification of materials and identification of unknown substances in the field
What are the advantages of handheld Raman spectrometers ？
-Ability to analyse samples (powders and liquids) without destroying the sample.
-No sample preparation is needed.
-Measurements can be taken through (semi-)transparent packaging, e.g. foils and glass
-Similar to benchtop instruments, portable devices also have large library databases available for identifying and screening counterfeits, especially drugs.
What are the advantages of Raman spectroscopy ?
-non-destructive
-non-contact
-high specificity
-no sample preparation
-variety of materials suitable for analysis
-available databases for comparison
-portable
What are the limitations of Raman spectroscopy ?
-weak Raman signals
-fluorescence interference
-cannot be used for metals or alloys
-expensive instrumentation
