Paper Chromatography

Experimental

Materials

Procedure

Part I

1. Measure approximately 1cm from the edge of the coffee filter and mark eight evenly spaced lines around the filter lightly with a pencil (do not use ink).
2. Use a toothpick to spot the four food coloring dyes on one-half of the coffee filter along the pencil mark. On the other half, spot the filter using the pens.  Allow each spot to dry and then re-spot two or three more times, see Figure 3.

Figure 3: Spotted Coffee Filter

3. After the coffee filter has been spotted, mark the top of each spot with your pencil. Below each spot, in pencil, label the color and if it is pen or food coloring. (Due to the small space below the spot, it may be easier to label "p" for pen, "g" for green, etc.)
4. Place the spotted coffee filter "upside down" in the aluminum pie plate.
5. Fill the pie plate (the chromatographic chamber) with rubbing alcohol to a level just below the spots on the filter. Click here to view a video of the developing chromatogram.
6. Once the chromatogram has developed and the alcohol travels to the "top" of the coffee filter, remove the filter from the plate. Using a pencil, mark the final position of the solvent. Click here to view a video of this procedure.
7. Next place a pencil mark at the end of each color. Note that some of the initial spots separated into multiple colors- be sure to mark each color (see Figure 4).
8. Allow the filter to air dry.
9. Determine and record the distance traveled by the mobile phase by measuring the distance (in mm) from the top of each of the initial spots (original pencil marks) to the final position of the solvent (Figure 5).
10. Determine and record the distance traveled by each color by measuring the distance (in mm) from the pencil mark at the top of each of the initial spots to the mark indicating the end of each color it produced (Figure 5).

11. Determine the R_f (ratio of fronts) value for each spot using the formula (remember there may be more than one calculation per spot):

                          

      Trials 2 & 3:

1. Repeat the experiment using a mixture of 1/4 cup H₂O and 1/4 cup rubbing alcohol (50:50 H₂O: alcohol). Note: You do not have to add the entire 1/2 cup of 50:50 H₂O: alcohol to the pie plate. 
2. Repeat the experiment using H₂O only. Note: The water moves quickly up the coffee filter and continues "upward" even after you remove the coffee filter from the pie pan.  Mark the solvent front quickly after removing the filter to reduce experimental error. 

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