NAME PERIOD DATE
PASCO / PS-2828A 1
1. ANALYSIS OF FOOD DYES IN SPORTS DRINKS
Introduction
If you have ever added a powdered drink mix to water, you will realize that the more concentrated
the drink, the deeper the color of the solution. Analytical chemists routinely use a quantitative
approach called spectroscopy that uses a photometer to measure light intensity to determine the
concentration of solute in a solution. A colorimeter is an instrument that measures light at specific
wavelengths in the color spectrum. In this lab, you will investigate and design an experimental
procedure that utilizes spectroscopy and quantitative analysis to determine the concentration of
FD&C food dyes in sports drinks.
Concepts
• Electromagnetic spectrum
• Spectroscopy or colorimetry
• Transmission and absorbance
• Wavelength
• Solution concentration
• Molarity
• Beer's law
Background
Color surrounds us every moment of every day. It affects our emotions, behaviors, even the choices
we make of food or drink, both consciously and unconsciously. The color of matter is a physical
property that can be used for both qualitative and quantitative analysis. In a solution, the color of
matter becomes an important tool for scientists to analyze the identity and quantities of components
contained in that solution. Many of the most popular, commercially available sports drinks contain
FD&C food dyes that make them more attractive to the consumer. Spectroscopy and colorimetry are
commonly used methods for quantitating how much food dye is contained in a sports drink. Both
methods measure % transmittance and absorbance of light through a sample of a colored solution
but differ in the range of wavelengths over which measurements can be made. A spectrometer
measures over a range of 380 nm to 950 nm at a wavelength interval of about 2 nm. A colorimeter
measures % transmittance or absorbance at specific wavelengths of the visible spectrum between
450 nm – 650 nm. This experiment can be performed using either instrument.
Spectroscopy is the study of the interaction of electromagnetic radiation and matter. In spectroscopy
and spectrophotometry, two terms are inescapable: transmittance and absorbance. Transmittance T
is defined as the ratio of the intensity of light after it passes through a medium being studied (I) to
the intensity of light before it encounters the medium (Io).
0
I
TI
=
Chemists more commonly refer to the percent transmittance %T, which is simply
0
100
I
I
×
.
Because the percent transmittance is exponentially related to concentration of solute, the use of
absorbance, which gives a linear relationship, is often preferred.
