Qualitative and Quantitative Analysis of Food Dyes >> Step 3 : Part 1

Qualitative and Quantitative Analysis of Food Dyes

Step 3 - Part 1: Preparing a set of dilutions of the standard dye


Preparing Dilutions:
The dyes present in your drink have now been identified by comparing their spectra to those of the standards. The next step is to create a calibration plot of the dye’s absorbency at known concentrations so that we can then determine the concentration of dyes in the drink.


To do this, we must first make a set of dilutions of the standard dyes. We will make five 10mL solutions of each dye at specific concentrations, 100%, 80%, 60%, 40% and 20%. To create these solutions we add dye and water in proportion to the required concentration. For example to create a 40% solution, you would add 4mL of dye and 6 mL of water, resulting in 10 mL of a 40% solution. (See equation below.)

Standard solutions of blue #1 at 100%, 80%, 60%, 40% and 20%





Each standard dye available in the lab has a label with its concentration. Because the standard dyes have different starting concentrations, the diluted solutions will have different molarities based upon their original concentrations. If the concentration of the Blue #1 standard is 4.0x10^-6 M, then the molar concentration of the 40% diluted solution would be:


Concentration of the diluted solution = 0.4 * 4.0x10^-6 M = 1.6 x 10^-6 M

Use the above calculations as a guide to determine the volumes of water and dye needed to create the diluted solutions in the table below. Once you have entered the volumes required, determine the concentrations (molarities) of your diluted solutions. If you get stuck, you can click the (hint) button for an explanation of any calculation.