Science Buddies: "Ask an Expert"

(Posted on behalf of student/family)

Initial post: We have followed the experiment (Skittles dye extraction) multiple times as indicated in the photo attached. We have allowed the samples to spend hours in the solvent and cannot get the chromatograph to spread. We repeated the experiment twice with red skittles, and then again twice with yellow skittles. We have even increased the saline concentration of the solvent from 1/8 tsp salt to 4 cups to 1/8th tsp salt to 3 cups of water, to no avail.

After following troubleshooting steps:
We allowed the samples to sit for hours in the saline solution and started to get movement in the sample. However, they are not breaking into their parts, as shown in the attached picture. Any ideas?

(Image attached.) Project directions: https://www.sciencebuddies.org/science- ... matography

If anyone can offer additional input?


Amy
Science Buddies

Hello!

Referencing this excellent Ask an Expert post (viewtopic.php?t=9429#:~:text=Chances%20 ... 20Red%20No.):
“It is helpful to know that the seven main food colorings in the United States approved by the Food and Drug Administration (FDA) are FD&C Blue No. 1 (“Brilliant Blue” FCF, E133), FD&C Blue No. 2 (“Indigotine”, E132), FD&C Green No. 3 (“Fast Green” FCF, E143, the least used), FD&C Red No. 40 (“Allura Red” AC, E129), FD&C Red No. 3 (“Erythrosine”, E127), FD&C Yellow No. 5 (“Tartrazine”, E102), and FD&C Yellow No. 6 (“Sunset Yellow” FCF, E110), where FD&C stands for Food, Drug, and Cosmetics.

Chances are, Skittles has most of the above, if not all. And according to a Skittles wrapper, the food coloring for all candies in the original series (red, yellow, orange, green, and purple) includes Yellow 6 Lake, Red 40 Lake, Yellow 5 Lake, Blue 2 Lake, Yellow No. 5, Red No. 40, Yellow No. 6, Blue 1 Lake, and Blue No. 1.”

Thus, I hypothesize that the red and yellow Skittles are not separating into any constituent dyes as they may be composed of simply 1 dye (or dyes in the same color range - i.e. Red No. 40 for the red Skittle, Yellow No. 5-6 for the yellow Skittle). I would recommend testing Skittles likely to be composed of a mixture of dyes – such as green or purple Skittles, or perhaps M&Ms, as they tend to have a greater range of colors.

Fundamentally, it seems that the issue is in the dye composition itself rather than the chromatography process, as the family reported capillary action of the dyes but not separation into constituent colors.

Hope this helps!