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Analysis of Food Dyes in Sports Drinks, Study Guides, Projects, Research of Behavioural Science

Electromagnetic spectrum, Spectroscopy or colorimetry, Solution concentration, Beer's law.

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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.
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NAME PERIOD DATE

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 ( I o).

0

I

T

I

Chemists more commonly refer to the percent transmittance % T , which is simply 0

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.

0

log log

I

A T

I

Note that A = –2 log (% T ).

If one knows the percent transmittance, one can calculate absorbance and vice versa. Most modern spectrophotometers have both a % T and an absorbance scale. With a digital instrument, it is simply a matter of changing modes to display either value.

Beer’s law is one of the most fundamental and widely applied spectroscopic laws. It relates the absorbance of light to the concentration (c ) of the solute, the optical path length ( b) and the molar absorptivity ( a ) of a solution.

An operation statement of Beer’s Law can be represented as

A = abc

The molar absorptivity is a constant that depends on the nature of the absorbing solution system and the wavelength of the light passing through it. A plot that shows the dependence of A on wavelength is called a spectrum.

Pre-Lab Questions

The visible absorbance spectrum of a 0.1 M Co(NO3)2 solution is shown in the figure below.

What wavelength would be optimal for measuring the absorbance versus concentration of a series of solutions of Co(NO3)2? Explain your answer.

A series of solutions of Co(NO3)2 were prepared to construct a calibration curve. Using the dilution information below from a 0.1 M Co(NO3)2 stock solution, determine the concentration of each of the dilutions. Hint: M1V1 = M2V

Dye Stock Solution (A)

B C D E F G H

Concentration 0.1 M Water (mL) 0 2 4 6 7 8 9 10 Stock Solution (mL) 10 8 6 4 3 2 1 0

Initial Investigation

Determination of Optimal Wavelength for Measuring Absorbance of FD&C Blue # 1

  1. Using a sample of the stock solution of FD&C Blue 1 food dye provided to you by your instructor, determine the optimal wavelength for measuring absorbance of FD&C Blue 1 food dye.
  2. Start a new experiment on the data collection system from your Chromebook, computer or mobile device.
  3. Connect the colorimeter to the data collection system. SparkVue was used for this analysis.
  4. Select “Absorbance and Transmittance” from the Quick Start Lab menu or open lab file 01 Analysis of Food Dyes in Sports Drinks. Calibrate the colorimeter using distilled water. You should read zero for absorbance and 100% for transmittance.
  5. Measure absorbance of your dye sample at the different wavelengths. Determine the wavelength that gives the maximum absorbance.

Calibration Curve of FD&C Blue # 1 Food Dye

Prepare a series of dilutions of FD&C Blue 1 food dye from a stock solution of known concentration prepared for you by your instructor, and distilled water. Prepare 10 mL of each dilution, calculate and record the concentration of each sample in the table below. Using a colorimeter, you will measure absorbance of each solution in the Initial Activity.

Table 1: Calibration Curve of Stock FD&C Blue # 1 (Absorbance at 600 nm) Blue #1 Sample Stock Solution (mL)

Distilled Water (mL)

Concentration (M)

Absorbance (-log T)

%Transmittance

1 10 0

2 8 2 3 6 4

4 4 6 5 3 7

6 2 8 7 1 9

8 0 10

  1. Start a new experiment on the data collection system from your Chromebook, computer or mobile device.
  2. Connect the colorimeter to the data collection system.
  3. Select “Absorbance and Transmittance” from the Quick Start Lab menu or go to page 2 of the lab file. Calibrate the colorimeter using distilled water. You should read zero for absorbance and 100% for transmittance.
  4. Transfer prepared dilutions to cuvettes, filling to three-fourths full. Using the most concentrated solution, insert into the cuvette port of the colorimeter and record the absorbance data. Remember that the cuvettes must be handled by the ribbed sides.
  5. Of the given wavelengths of light, determine the optimum wavelength that demonstrates your sample’s maximal absorbance. What do you notice about the wavelength of highest absorbance? Hint: Consider the color wheel of complementary colors.
  6. Save your data and start a new experiment by selecting Beer’s Law from the Quick Start Menu. Adjust the absorbance wavelength if needed.
  1. Obtain a sports drink containing FD&C Blue # 1 dye. You may choose a ready-to-drink product or prepare one from a powdered mix according to manufacturer’s instructions. Using the procedure from the Initial Investigation and graphs produced in the graphing challenge above, develop an experimental protocol to measure the concentration of FD&C Blue # 1 dye in your chosen drink using the optimal calibration method that gives the best linear correspondence for quantitative analysis.
  2. Unlike your dye dilution samples which contained only dye and water, the typical sport drink formulation contains other ingredients which may include sugar and electrolytes. What effect will the presence of additional ingredients potentially have on the quantitative determination of the food dye content?
  3. Measure the absorbance and % transmittance of your sports drink. Do the numbers fall within the range of your calibration curve? If not, what should you do to fix this?
  4. Determine the concentration of the dye in your beverage and calculate the mass of dye (mg/L) of the sports drink. FD&C Blue # 1 dye has a molar mass of 793 g/mole.

Synthesis Questions

  1. In a copper(II) sulfate solution, copper(II) ions cause the blue color. Sulfate ions have no color. Sodium sulfate solution has no color because neither ion has color. Could you use Beer's law to find the concentration of a sodium sulfate solution?
  2. Hypothetically, how would you modify the experiment if the measured absorbance of the unknown was too low to measure?
  3. How would you modify your experiment if the measured absorbance of the unknown was too high?

AP® Chemistry Review Questions

  1. Which of the following variables affects the absorbance of light in a solution?

A. The distance the light must travel through the solution (path length) B. The amount of solute in each volume (concentration) C. The wavelength of the light that is interacting with the solution D. All of the above

  1. A sample of 0.10 M copper(II) chloride is placed into a cuvette with a 1.00-cm path length. The solution has a measured absorbance of 2.000. What would you expect the absorbance of a 0.05 M copper(II) chloride solution to be?

A. 4. B. 2. C. 1. D. Not enough information