BIOLOGICAL MOLECULES: Quantitative Tests

Quantitative Test for Reducing Sugar

Benedict's reagent detects the presence of reducing sugars. If there is more sugar present, the amount of precipitate will increase and the amount of copper ions remaining in solution will decrease.

Once you have tested for reducing sugars, you can then go on to using a colorimeter to see the concentration of sugar in the sample.

Using a Colorimeter

A colorimeter works by shining light through a sample. For testing the concentration of reducing sugar, we would use a centrifuge to separate the precipitate and any excess Benedict's solution (the supernatant).

Using a pipette, we can take the supernatant and place it in a cuvette (a small vial) - and place this into the colorimeter. The cuvette is usually made of glass or plastic. When doing this, we must make sure no fingerprints are on the surface of the glass/plastin cuvette as this could affect the transmission of light. 

Colour filters are often used for greater accuracy. By using a red filter in this…