Biuret Solution turns Strange Colour?

[IlanK]

Hi everyone!

 

I was doing a test with biuret solution (which tests for proteins by turning various shades of purple) and put some in a test tube with dextrose. At first, a white clump formed at the bottom. I put a stopper on the test tube, shook it, and after a little bit it turned red and then brown.

 

I can't find any information about biuret solution turning brown.

 

Another group had the same result.

 

In the presence of gelatin, it turned light purple.

 

I am not 100% confident this is biuret solution, but what else could turn gelatin purple?

The solution was blue in colour.

 

Why did it turn red?

 

EDIT: When mixed with vegetable oil, a seemingly solid layer of oil floated on top and the blue liquid underneath wouldn't really move when the test tube was moved.

Edited February 15, 2013 by IlanK