why does the loading dye split into two different colors during gel electrophoresis?

Question

the dark blue color of the loading dye splits into two different colors. a teal color stays behind while a purple color travels down the gel. why?

Answer 1

Their are 2 dyes in the loading buffer that have distinct migration rates when running on a gel. (There are other dyes too, but the 2 you are mentioning are listed in the recipe I have included below).

The basic loading dye for a DNA gel has several components. The one you describe has 2 different dyes in it. The dyes have different migration rates that help biologists know exactly how far to run the gel, since you can't see the DNA without a UV light source.

Here's a recipe for a basic DNA loading dye:
10mM Tris-HCl (pH 7.6) to help maintain the pH of the sample
0.03% bromophenol blue dye (the dark purplish blue color)
0.03% xylene cyanol FF dye (the teal color)
60% glycerol (helps the sample sink down and stay in the wells)
60mM EDTA. (protects against nucleases by binding divalent cations like Mg++ and Ca++)

Note

In 1% agarose gels bromophenol blue co-migrates with ~300 bp DNA, while xylene cyanol FF co-migrates with ~4000

Answer 2

Xylene Cyanol Loading Dye

Answer 3

The migration rate of dye molecules depends on their size and charge (a small molecule with a high negative charge will travel fastest).