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Paper Chromatography:

Distinguishing various black inks from one another based on their relative affinities for water.



1.
 Six sources of water-soluble black ink were used in the chromatographic separation.		  


2.
The six inks were dotted onto the filter paper and labeled with a pencil.		  


3.
After the wick is inserted into the center of the paper, the water enters the filter paper from a Petri dish. The water goes up the wick and spreads out radially due to capillary action.



4.
The water carries the components of the ink that are most soluble in water (the solvent phase) the fastest. These components are found at the edge of the chromatogram, also known as the solvent front. The slower parts of the ink are more attracted to the paper (the stationary phase).		  


5.
As the chromatogram develops, students work on recording qualitative observations of the separation.		  


6.
After the solvent front nears the edge of the paper, the chromatogram is removed and allowed to dry while the unknowns are obtained.



7.
Four of the same six pens are used to make "unknown" dots of ink on separate pieces of filter paper before the students arrive.		  


8.
The identities of the unknown inks are determined by comparing the separation patterns of the unknowns with those of the known pens.		  


9.
Can you determine the identities of the four unknown inks (at left) by looking at the separation patterns of the known samples (at right)?

 

  • If you stick around for A.P. Chemistry, you might just do this experiment quantitatively by using Rf values! Fun! :)