- 8" Aluminum pie plate
- Food coloring
- Large Coffee filters
- Rubbing alcohol (70% Isopropyl Alcohol)
- "Expresso" ink pens
- Measuring cup
- 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).
- 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
- 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
- Place the spotted coffee filter "upside down" in the aluminum
- 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.
- 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.
- 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).
- Allow the filter to air dry.
- 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
- 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).
Figure 4: Marked Chromatogram
Figure 5: Measure MP and Color Fronts
- Determine the Rf (ratio of fronts) value for each spot
using the formula (remember there may be more than one calculation
Trials 2 & 3:
- 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.
- 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
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