Ink Chromatography Lab

Chromatography is a method of separating out materials from a mixture. Ink is a mixture of several dyes and therefore we can separate those colors from one another using chromatography. When ink is exposed to certain solvents the colors dissolve and can be seperated out. When we expose a piece of paper with ink on it to a solvent, the ink spreads across the paper when the ink dissolves.

Some inks are water-soluble, so you can use water as the solvent. Inks which are not water soluble are often alcohol-soluble and you can use isopropyl alcohol (aka rubbing alcohol) as the solvent to create your chromatograph.

Different ink pens use different types of ink and this is obvious when you expose the ink to a solvent. A banding pattern of the components of the ink mixture is called a chromatograph. Follow the instructions below to discover which pen was used to write a note.

Preparation

  1. gather several black or blue pens
  2. Obtain a sample of the evidence (have someone use one of the pens to write a note - your job is to figure out which pen they used)
  3. Cut several coffee filters into 1/2 inch strips
  4. Set up your chromatography apparatus. Place a drinking straw or other long object across two supports (upside down paper cups work). Do not use styrofoam or plastic cups as some solvents can dissolve them. Place a pan (cut off paper cup bottom) underneath the straw and fill it about 1/2 inch deep with the solvent (water or alcohol).

Procedure

  1. Use a long 1/2 inch wide strip of your evidence and hang it from the straw so that the end just touches the solvent. Don't let the ink get wet.
  2. Use each of your suspect pens to place a dark spot of ink about 1/4 inch - 1/2 inch from the end of each coffee filter strip.
  3. Hang these strips from the straw so that the tips of the strips just touch the solvent (you may wish to tape the strip to the straw in order to hold it in place).
  4. Allow the inks to seperate for about 15 minutes.
  5. Examine the banding patterns and determine which of your known suspect pens was the pen used to write the note.


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