Unusual result with Benedict's solution.?

Question

Here we go. We tested an unknown substance for reducing sugars, using the standard Benedict's reagent. The only thing we suspected was in the solution was aspartame. Strangely enough, the substance produced a dark blue colour at the end of the test, significantly darker than the original turqouise benedict's colour. Suspecting contamination, we ran it twice more, and found the same results. Any ideas?

Answer 1

First, Benedict's reagent is used as a test for the presence of reducing sugars such as glucose, fructose, galactose, lactose and maltose, or more generally for the presence of aldehydes (except aromatic ones). It can be prepared from sodium carbonate, sodium citrate and copper(II) sulfate. Therefore, Benedict's reagent contains light blue copper(II) ions (Cu2+) which can be complexed with ammonia or amine to a deep blue color. My guess is that probably there is some strong chelating agent in your "unknown substance", which is a complexing agent (to Cu++).