II. Separation of Food Colorings
A. Remove the piston and insert the LONG END of the C
18
cartridge snugly into
B. Add 5 mL of IPA, insert the piston, and S-L-O-W-L-Y flush at a flow rate not
exceeding 5-10 mL per minute. It is important to not flush liquid through the
cartridge more rapidly than 10 mL per minute.
C. Flush with a 5 mL portion of distilled water.
D. Add about 1 mL of the food coloring mixture to the syringe, insert the
piston, and S-L-O-W-L-Y push the mixture onto the cartridge. As you push the
a test tube. The first color comes off quickly.
1. Once the 1 mL of food coloring mixture is pushed onto the cartridge, add
water to the syringe and push it through the cartridge until all the yellow
is gone. Collect the yellow liquid. The process of pushing solvent(s)
through a cartridge is called elution. In this case, water elutes the
yellow color.
2. The remaining colors in the mixture must be removed by eluting with a
water/IPA mixture. You must be patient here! Prepare a 1% IPA
IPA. Mix well by shaking the syringe. Push this solution through the
cartridge and collect all the colors that come off. If coloring still remains
on the cartridge, prepare a 2% IPA solution by adding 2 drops of IPA to 5
mL of water, mix, and elute this solution through the cartridge. Continue
to increase the percentage of IPA (3% - 3 drops IPA + 5 mL water, 4% -
4 drops IPA + 5 mL water, etc.) until all or most of the coloring has been
removed from the cartridge. A 5% IPA solution may be the most
concentrated solution needed to remove all of the colors from the
cartridge.
3. Any coloring residue remaining on the cartridge must be removed using
a 1:1 IPA-to-water mixture, or by using pure IPA. This residue may need
to be collected. (You’re cleaning up here.)
4. Save the separated colored solutions for the next part.
E. See what would happen if several of the separated colored solutions were
mixed. For example, try to make a green solution from the colors you
separated.
F. Make sure the cartridge is white as driven snow before returning it.