HOW MUCH DYE IS IN DRINK? - Spectroscopic quantitative analysis

Charles and Michael, they often go to restaurant to have a drink. Once, they had a sweet peppermint liqueur, which has a typical green color. Suddenly, Michel, looking at the liqueur, got angry, saying: “that is terrible, everywhere are substitutes. I bet that this liqueur, this is the same case. Look at the color. It must be something poisonous inside. Surely, there is more dye inside than allowed. And, it is killing us slowly. We should take some legal action against manufacturer of this killing drink, should not we? Charles faintly smiled and told: “It seems to be, probably, you are right. Actually, I have a friend who is working in chemistry lab. He can help us to analyze this drink. And, if there is more dye than allowed … Bad new for the manufacturer. Both of them, they ordered a one more drink and, tomorrow, Charles took a small volume of the drink (they drunk majority of the liqueur with Michael) to his friend (you) for analysis. Can you help him?