100%(1)1 out of 1 people found this document helpful
This preview shows page 1 - 3 out of 8 pages.
Nick ProcaccioAP ChemistryPeriod 6-7Analysis of Food Dyes in BeveragesGoal:To analyze the food dye content in beverages (in our case, Gatorade) using spectrophotometryas the technique so we can learn how light reacts with matter.Background Info: The color of a solution can be used to gain information about the composition of the solution.Spectroscopy,the study of interaction of light and matter, can provide this information. In this lab weused a spectrophotometer. A spectrophotometer is an instrument that uses electromagnetic radiation ofa specific wavelength to analyze the absorption or transmission of radiation by a sample. In thisinvestigation, we used a visible spectrophotometer whichscans the visible region of the electromagneticspectrum (380nm – 750nm). To find the concentrations of our solutions, we used spectrophotometry,which is an analytical procedure that uses electromagnetic radiation to measure the concentration ormolarity of a substance. The absorption of visible light by a substance results from electron transitions (aground state electron becomes excited and moves to a higher energy level. The specific differencebetween two electron energy levels determines the specific wavelength of light absorbed by asubstance. By measuring the visible light spectrum of a substance, we can determine the optimumwavelength for spectrophotometric analysis. In our case, since we are using FD&C Blue 1 dye, theoptimum wavelength will be 630nm because it is the maximum absorbance of the substance. Thewavelength of light absorbed by a substance is a characteristic of its molar or electronic structure. Themore concentrated it is, the more light will be absorbed and vice versa. By using the percenttransmittance equation(Absorbance = -log Percent Transmittance || A=-log %T), and Beer’s Law[A=ebcwhere A=amount absorbed, e=molar absorptivity coefficient (which is 130,000 M-1cm-1for the blue dyeand 25,900 M-1cm-1for the red dye), b=the length of the sample cell, and c=concentration.], we were ableto gain information of the composition of our solutions.Intro Activity:BLUEStep 1:We first turned on the spectrophotometer and allow it to warm up for 15 minutes. (not the new ones)Step 2:For the blue solution, we selected the 630nm wavelength because the optimum wavelength for spectrophotometric analysis of a dye solution is generally determined from the wavelength of maximum absorbance. The max absorbance for FD&C Blue 1 (dye) is 630nm. In laymen’s terms, the 630nm wavelength has the highest absorbance; meaning that most of the colors are absorbedand the blue light is transmitted.Step 3:We then obtained 50ml of our stock solution which contained of water and blue dye.
Step 4:Next, we made 6, 10ml solutions by combining the different volumes of the stock solution with different volumes of water. (We also had one 100% stock solution and one 100% water solution for zeroing) To make the 2ml water – 8ml stock solution, we filled a 10ml graduated cylinder with8ml of stock solution and then filled it to the 10ml mark with water.