EXPERIMENT 6
Quantitative Analysis of Kool-Aid, UV Spectroscopy of Sunscreens

You have already obtained the wavelength(s) of maximum absorbance for the dyes present in the KoolAid.  In the next part of this experiment we will determine the concentration of the dyes present in the KoolAid and the number of glasses per day that would be unsafe to consume based on the established limits of the food dyes. You should also research the MSDS for the dyes contained in the KoolAid.

Experiment:
Preparing the calibration solutions
Stock solutions of the dyes will be provided to you: 1x10-4 M solution of Red dye and 1x10-5M solution of Blue dye.  Using pipettes, test tubes and Parafilm (for mixing). Prepare the following solutions.

 Tube # RED DYE (mL) Vol. distilled H2O (mL) 1R 3.0 7.0 2R 2.0 8.0 3R 1.0 9.0 4R 0.5 9.5 5R 0.3 9.7 6R 0 10

 Tube # BLUE DYE (mL) Vol. distilled H2O (mL) 1B 10.0 0.0 2B 7.0 3.0 3B 5.0 5.0 4B 3.0 7.0 5B 1.0 9.0 6B 0 10.0

Using a new square of Parafilm for each, gently mix the solutions.

Plotting the calibration curves
For each dye, set the spectrophotometer at the wavelength of maximal absorbance and set the absorbance to 0.000 with your blank.  Record the absorbance of all the samples (blanking between readings of samples). The readings may fluctuate so it is best to take each reading immediately.

Plot a calibration curve for each of the dyes and obtain the equation of the lines and the correlation coefficients.

Use the equations of the lines to calculate the concentration of the dye solutions and use the molecular weight to calculate the number of grams in a regular glass (250mL) of KoolAid using the stock concentration of 7.2g/100mL as the concentration of drinkable KoolAid in a glass.

PART 2. UV Spectroscopy of Sunscreens
Ultraviolet violet spectroscopy will be used to create a spectrum of a solution that is colorless to the human eye.

Your instructor will demonstrate the use of the ultra-violet (UV) spectrometer. The sunscreen is ethylhexyl-methoxycinnamate (EHMC) will be used for this analysis. Quartz cuvettes are required in the UV region since plastic ones absorb UV light.  The  spectra is taken from 200 nm-400 nm

Sunscreens are prepared using the following procedure:
1. You will be given a stock solution of 5-7 mg of EHMC dissolved in 50 mL of 2-propanol.
2. Put 1 mL of that solution in a 10 mL vol. Flask and dilute to the mark.
3. Take the UV spectrum between 200 and 400 nm.

RESULTS
 Red Dye(mL) H2O(mL) Conc (M) Abs 1R 3.0 7.0 2R 2.0 8.0 3R 1.0 9.0 4R 0.5 9.5 5R 0.3 9.7 6R 0 10

 Blue Dye(mL) H2O(mL) Conc (M) Abs 1B 10.0 0.0 2B 7.0 3.0 3B 5.0 5.0 4B 3.0 7.0 5B 1.0 9.0 6B 0 10.0

Concentration of dyes in the diluted solutions:

Amount of dye in a glass of KoolAid.

In what range of wavelengths does EHMC absorb the most light? Find out whether this range is classified as UV-A, B, or C.