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Thursday, January 17, 2013

Food coloring chromatography

QUESTION: Is it possible to separate the colors of a mixture of food colorings after they have been mixed?

What we need:
  • coffee filters,
  • wooden skewer,
  • food coloring, yellow, green and blue,
  • 4 glass containers,
  • markers
  • 4 paper clips,water.
How to:
  • Prepare the work area, chose a easy to clean zone in outside or in the kitchen, food coloring usually leave messy stains;
  • Identify the bottles, assign one or two letters each color, e.g. bottle Ye (yellow) Bl (blue) Gl (green) and Mix (mixed colors), or simply ABCD, write down in your notebook which is which.
  • Place 6 drops of yellow dye in the bottle Ye;
  • Dilute the food coloring with 30ml water;
  • Repeat this procedure for both blue and green dye;
  • In the last bottle (Mix) place 2 drops of each dye and diluted as usual;
  • Prepare the coffee filter, cut it in 4 identical strips;
  • Put a strip of paper in each bottle, as pictured;
  • Use the paper clips to keep the paper in place;
  • Wait until the dye reach the top of the paper, we wait 15min, may be more or less depends on the brand of the dyes.
  • After the dye reach the top of the paper remove it from the cup and put it on a horizontal surface;
  • Wait until it dries;
  • Observe the color patterns.
What happens?
The water climbed the paper and the food coloring dissolved on it formed patterns in the paper.
In pictures you can see we used circle and strip paper, the results were exactly the same for the used colors.

Chromatography is, as its name indicates, writing (spelling) colors (chrome) and is one of the main techniques that biochemists use to separate mixtures.

First, before attempting to answer our question, it would be necessary to state three things:
  • The first is that we must have a control, in this experiment a bottle with solvent without the dye, to exclude any possible interference of anything, We have done it, but does not appear in pictures. We did not observe any color band in this “blank”.
  • The second is that the solutions were made with 6 drops of dye to 30 ml water, it’s possible you might get different results when using different trademarks and/or dilutions, so in science it is very important to control everything, even the brand of reagents.
  • And thirdly, we have to study the individually solution behavior so we can interpret the Mix results.

Control: No bands or spots of any color.

Green dye: Shows three colors, blue on top of the paper, a broadband green and a darker line on the base. We could observe a yellow band between the larger green band and the darker line at the base.
In the label on the bottle we can read: ”Contains yellow dye and green dye“ that way is normal o have a green and a yellow band in the paper, but where did the dark line came from? A closer look give us the answer: the darker line is a dark blue zone. Blue? Yes blue. That’s because green is the mix of the blue and yellow color. 

Yellow dye: the coffee filter paper was completely yellow. With a yellow zone more pronounced in paper, yellow is a primary color, and in the label doesn’t say anything about any addition of another type of dye.

Blue dye: We can see that the filter has three distinct zones (note the small strip in the photo), back lit we see one of the area's violet (on the color wheel this is the result of mixing blue and magenta) the second zone is blue, and the third band is a second kind of  blue, lighter and more prevalent, one is cyan, and the other is an unknown color we would probably only find out for sure using more advanced analysis techniques.

On the blue label we can read: “contains blue dye and E122”. What is this E122? The website describe it as a carmine food coloring, the presence of this E122 may explain the violet band observed at the base of the paper.

After observing and interpreting individual results we will then look to the mix filter:

One large blue zone followed by a green one. Between them we can see a faint yellow band, in the base we can’t see the violet line or brown stain which would be expected by the presence of green dye, instead we can observe a dark indistinguishable line. Back lit we can see some violet color, but nothing conclusive. Probably this phenomenon is due to the fact that the carmine E122 and the brown present at the bottom of the paper requires more time and /or longer/ different kind of  paper to separate and become visible.

The answer to the above question is “Yes it is”. However it is necessary to improve the used technique.

A step further:
  • Improve the separation method:
    • Using different dilutions;
    • Different filter papers;
    • Bigger filter papers;
  • See if you can see these bands, eventually even be surprised by other bands that become visible.

Et voil√°!
A true experience!


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