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BSc. Forensic Science (Practicals) - LJMU. > 4103FSBMOL - Practical 3 - TLC. > Flashcards

4103FSBMOL - Practical 3 - TLC. Flashcards

Thin Layer Chromatography (TLC) - Analysis of Ball Point Ink Samples.

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1
Q

What type of Evidence is best examined by using TLC?

A

Documents written using ball point inks.

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2
Q

What does a Document Examiner do?

A

They analyse documents sent in for forensic analysis, and they look to see if signatures are genuine or whether there are signs of forgery for example.

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3
Q

Is Document analysis using TLC destructive or non-destructive?

A

Non-destructive.

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4
Q

When was the first non-leaking ball point pen developed?

A

1935.

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5
Q

Who was the first non-leaking ball point pen developed by?

A

The Biro Brothers.

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6
Q

What 3 main elements are ball point pen inks made up of?

A
  • A solvent - to dissolve the ink and/or pigment.
  • Dyes and/or pigments - colourants (e.g. methyl violet or ethyl violet).
  • Additives such as fatty acids to act as a lubricant, polymers to act as fillers, and other things to affect the drying rate.
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7
Q

What does TLC stand for?

A

Thin Layer Chromatography.

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8
Q

What does TLC do?

A

It separates a complex mixture into its individual component parts.

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9
Q

What are the different phases in TLC?

A
  • Stationary Phase - solid TLC plate.
  • Mobile Phase - solvent/ mixture of solvents.
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10
Q

What is separation in TLC based off?

A

The components’ affinity for the stationary phase.

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11
Q

What does a high and low affinity for the stationary phase mean?

A
  • High Affinity - retained longer on the TLC plate, travel a shorter distance up the TLC plate.
  • Low Affinity - retained shorter on the TLC plate, travel a longer distance up the TLC plate.
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12
Q

How do we compare components and their affinities for the stationary phase in TLC?

A

Using Rf values.

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13
Q

What is the equation to work out Rf values?

A

Rf = distance travelled by the component / the distance travelled by the solvent front.

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14
Q

What was the mobile phase made up of in the TLC practical?

A

Ethyl Acetate : Ethanol : Water (50:25:25 v/v).

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15
Q

1.

How long did we leave the developing tank to equilibrate?

A

10 minutes.

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16
Q

What chemical did we add to 50mm of the samples in glass bottles and then shake?

A

0.5ml of Ethanol.

(Shake for 1 minute).

17
Q

How far from the bottom of the TLC plate do we draw the base line?

A

1cm.

18
Q

What do we have to take care with for the TLC plate?

A

To try not to scrape any of the stationary phase off the TLC plate when writing on it.

19
Q

What did we use to add each of our samples to the TLC plate?

A

Capilliary Tubes.

20
Q

When adding the TLC plate to the developing tank what do we have to make sure the mobile phase doesn’t do?

A

Cover the Baseline we have drawn (go over the top of the samples we added).

21
Q

Approximately how long do we leave the TLC plate to devlop in the tank?

A

30 minutes.

22
Q

What do we quickly have to do once we remove the TLC plate from the tank?

A

Mark the height reached by the mobile phase and then allow to dry in the fume hood.

23
Q

Why do we have to be quick determining the Rf values of each of the bands?

A

Because the bands fade and eventually you won’t be able to see them.

24
Q

In the Practical how many components did the Bic Pen ink have?

A

Two (2).

25
Q

In the Practical how many components did the Sainsbury’s Pen ink have?

A

Four (4).

26
Q

In the Practical how many components did the Unknown Pen ink have?

A

Two (2).

27
Q

What colour were the components in the Bic pen ink?

A

Blue (Bottom) and Yellow (Top).

28
Q

What colour were the components in the Sainsbury’s pen ink?

A

Blue x2 (Bottom), Purple, Yellow (Top).

29
Q

What colour were the components in the Unknown pen ink?

A

Blue (Bottom) and Yellow (Top).

30
Q

How can you determine which ink was most likely to be the Unknown Ink?

A

Compare the Rf values to the Known Pen inks and look for similarities in the Rf value and the colour of the spots that were present.

BSc. Forensic Science (Practicals) - LJMU. (8 decks)

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