Ink Analysis

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Ink Analysis
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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.

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What is Ink?

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

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Why is Ink Important in Forensics?

• Fraud cases? Embezzlement? Theft?
  Kidnapping and Ransom? Threats? Documentation

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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.

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What is thin layer chromatography (TLC)?

• Qualitative analysis.
• - Using mostly our vision and some
• measurements of distance on the
  stationary phase.
• ??

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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.

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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.

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Stationary Phase
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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.

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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.

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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.

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