Identification of Extracted FD & C Dyes Using Spectrophotometry

Introduction:

Color additives have been used for many of thousands of years. Some archaeological findings date cosmetic colors as far back at 5000 B.C. and some food colors at 1500 B.C.

Originally, food colors came from nature and their first purpose was to mask poor quality or spoiled food. During the 1800s, scientists began searching for ways in which to color food by chemical means. Unfortunately, in the beginning, arsenic and similar poisons were used to color pickles and hard candies leading to many injuries and deaths.

These incidents sparked action to be taken by the government, which in 1906, formed the F.D.A. or Food and Drug Administration. Now colors used in food and drugs had to be regulated by the government. By 1938, the government passed an act to control the colors used in cosmetics as well. Thus the acronym, FD & C (colors allowed to be used in foods, dyes, and cosmetics) came about and is now widely seen on many consumer products. The F.D.A has also created certain numbers to the color dyes to separate them and make it easier to tell which colors are used in foods, drugs, and cosmetics. Only F.D.A. certified colors possess these numbers. In 1960, the law that was created in 1938 was revised to broaden the government’s control of not just what colors could be used, but the amount of the color that could be used.

There are two classifications of dyes: lakes and straight dyes. Lakes are colors that are water-insoluble. These forms are more stable than straight dyes and are ideal for products where the producers do not want the color to bleed. These products include hard candies and coated tablets. Straight dyes are a form of the certifiable colors that dissolve in water. These dyes are good for powders, granules, liquids, beverages, anddyes in baked goods.

In this lab, we will identify the FD & C dyes used in at least one food/beverage product by using their absorption maxima by comparing the information provided in the table after the extraction process.

Materials:

Extraction and Identification lab materials:

1

  • Sep column
  • Grape Koolaid
  • Distilled Water
  • Spec 20 Genesys
  • 4 Cuvets/group
  • 5% Isopropanol
  • 10% Isopropanol
  • 20% Isopropanol
  • 100% Isopropanol

1

Known Dyes: The wavelength (nm) for each dye is found in the table.

Unknown Dyes: To be identified from Grape Koolaid.

Procedure:

1.The column must first be conditioned to remove any contaminants and to "wet" the column. Each solution is placed on top of the column and drawn through until a small amount of the liquid remains on top of the frit. Never allow the column to go dry, and never push on the withdrawing syringe - this action will destroy the column.

2.Turn the lever toward the open end of the apparatus. Place ~ 5 mL of 100% isopropanol in the column and pull into the syringe.

3. Turn the lever toward the column and push the solution into a well or sink.

4. Repeat steps 2 & 3 with ~ 5 mL of DI water

5.Turn the lever toward the open end of the apparatus. Place ~ 5 mL of the Kool-Aid in the column and slowly begin to draw the solution into the syringe. Observe what is happening in the column.

6.When the effluent is completely drawn through to the top of the frit, aim the lever toward the column. Place the effluent in acuvet.

7.Continuing with this extraction, apply the following solutions (in this order) and collect the effluent from each step in a new cuvet.

Note: Be certain that the lever is in the appropriate position so that the column is not destroyed!

Solution
5 mL water
5 mL 5% isopropyl alcohol
5 mL 10% isopropyl alcohol
5 mL 20% isopropyl alcohol
5 mL 100% isopropyl alcohol
  1. Pick the purest, most concentrated solution of the dyes and run those cuvets in the spec 20 genesys.

Running the Samples in the Spec 20:

*This is a slow process and should take the remainder of the period.

* Graphing of the data could be done in a subsequent lab period.

  1. Use two matched cuvets, filling one with distilled water (this will be the “blank”) and the other with the sample of dye you are testing.
  2. Set the wavelength of the spec to 400 nm, and, using the “blank” (distilled water) cuvet, press the zero button. Then put the dye-containing cuvette into the cell compartment, and measure the absorbance of the dye solution. Continue increasing the wavelength in 25 nm increments, zeroing, and measuring the dye absorbance up to 800 nm. Record data on the data sheet.
  3. Go back to the wavelength range of 25 to 50 nm over which the absorbance values were the strongest. Take absorbance readings every 5 nm over this range. Be sure to zero the absorbance reading before each measurement using a blank. Record all data on the data sheet.
  4. You will now graph your chart on Microsoft Excel. Label the x-axis with the wavelength and the y-axis is to be labeled absorbance.
  5. Match your wavelength with the wavelengths given for the FD &C. Find the dye name that matches your wavelength.

Data:

1

Wavelength / Absorbance
400
425
450
475
500
525
550
575
600
625
650
675
700
725
750
775
800
Wavelength / Absorbance

1

Expected Absorption Maxima (nm) of FD & C Dyes

Dye / Solvent System / Absorption
Yellow 5 / Water / 422
Yellow 6 / Water / 480
Red 4 / Water / 495
Red 40 / Water / 505
Red 2 / Water / 520
Red 3 / Water / 527
Blue 2 / Water / 610
Green 3 / Water / 625

1