What is the purpose of using the dye FDC 2 along with the dy

What is the purpose of using the dye FD&C #2 along with the dyes from the candies?

Solution

Some color-coated candies contain FD&C dyes which are used for coating the candies. The Federal Food, Drug, and Cosmetic Act (FD&C) regulate the safety of food, drugs, and cosmetics. The FD&C lists certified color additives for various drugs, cosmetic and food. The color additives are used as coatings and these are derived from natural sources from plants, animal or mineral counterparts.

The FD&C#2 dye is an Amaranth dye which is a dark red to a purple azo dye used to color cosmetics and food. This is an anionic dye which decomposes at high temperature at 120^oC and has a maximum water absorption of about 520 nm. By using this dye as a standard, the other dyes used in the candies can be identified by using woo and separating them through paper chromatography technique.