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Ink Analysis

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Thin layer chromatography (TLC) may be necessary to identify the chemical composition. ... thin layer chromatography (TLC)? Separates mixtures into individual ... – PowerPoint PPT presentation

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Title: Ink Analysis


1
Ink Analysis
2
Introduction to Ink Analysis
  • Although all blue or black inks may look the
    same, there can be some important differences in
    their chemical composition.
  • Analysis of documents under a microscope can be
    informative as a first step.
  • Thin layer chromatography (TLC) may be necessary
    to identify the chemical composition.

3
What is Ink?
  • Several organic dyes - blue, red, black, etc.
    (This can form an ink "fingerprint.")
  • Tags that signify the manufacturing year -
    isotopes.

4
Why is Ink Important in Forensics?
  • Fraud cases? Embezzlement? Theft?
    Kidnapping and Ransom? Threats? Documentation

5
How is Ink Used as a Forensics Tool?
  • A small sample is dissolved.
  • ? This sample is compared to a known sample.
  • ? Each pen manufacturer has its own "recipe" for
    ink, so a sample from a document can lead to the
    discovery of the type of pen used.
  • ? The tags in ink can determine the year the pen
    was manufactured.

6
What is thin layer chromatography (TLC)?
  • Qualitative analysis.
  • - Using mostly our vision and some
  • measurements of distance on the
    stationary phase.
  • ??

7
What is thin layer chromatography (TLC)?
  • Separates mixtures into individual parts.
  • Samples are placed on material that carries the
    various components in the ink different distances
    based on their different polarities.

8
What is thin layer chromatography (TLC)?
  • Mobile phase vs. stationary phase.
  • Mobile phase The liquid or gas that moves up the
    stationary phase and dissolves the sample.
  • Solvents can vary and are chosen based on sample
    type.
  • Stationary Phase The solid that the sample is
    placed on. Silica gel is often used.

9
Stationary Phase
10
What separates the compounds as a chromatogram
develops?
  • As the solvent begins to soak up the plate, it
    first dissolves the compounds in the spot that
    you have put on the base line.
  • The compounds present will then tend to get
    carried up the chromatography plate as the
    solvent continues to move upwards.

11
What is thin layer chromatography (TLC)?
  • "Like dissolves like" - polar vs. non-polar.
  • The OH groups on the silica gel are very polar
    and can hydrogen bond.
  • The sample will also dissolve in the solvent
    (mobile phase) and move up the plate.
  • The more able to form H-bond, the more likely the
    sample will move slower and not as far up. The
    greater the solubility in the solvent, the faster
    it will move up the plate.

12
How fast the compounds get carried up the plate
depends on two things
  • How soluble the compound is in the solvent. This
    will depend on how much attraction there is
    between the molecules of the compound and those
    of the solvent.
  • How much the compound sticks to the stationary
    phase - the silica get, for example. This will
    depend on how much attraction there is between
    the molecules of the compound and the silica gel.

13
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