4: Food Dye Chromatography
- Page ID
- 514166
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- To use paper chromatography to separate and characterize common food dyes by measuring their \(R_f\) values.
- To analyze the synthetic dyes extracted from candy coatings and identify them by direct comparison to known standards.
INTRODUCTION
Most substances encountered in daily life are mixtures rather than pure compounds. Similarly, chemical compounds synthesized in laboratories often contain impurities such as reaction byproducts or unreacted starting materials. Consequently, a central focus in chemistry is the development of techniques to separate, isolate, and identify the components of complex mixtures.
Separation techniques exploit differences in physical properties among mixture components. For example, filtration separates substances in different physical states (such as insoluble solids from liquids), centrifugation utilizes differences in density, and distillation takes advantage of variations in boiling points. In this experiment, paper chromatography will be used to separate and analyze synthetic food dyes.
All chromatographic methods involve three essential components:
- Analyte: The mixture to be separated.
- Mobile phase: A liquid or gas solvent that carries the analyte through the system.
- Stationary phase: A porous solid or supported liquid film that interacts with the analyte components to differential degrees.
Separation occurs because different components of the analyte mixture interact to varying degrees with both the stationary phase and the mobile phase. Components that interact more strongly with the stationary phase move more slowly, whereas components that favor the mobile phase move more rapidly. Paper chromatography is a specific type of partition/adsorption chromatography that utilizes cellulose paper as the stationary phase. The sample mixture is spotted near the bottom edge of the paper, which is then suspended upright in a covered developing tank containing a small volume of the mobile phase.
Capillary action draws the liquid mobile phase up the paper. As the solvent front advances past the sample spot, the components partition between the paper fibers and the migrating solvent. The separation is complete when the solvent front approaches the top edge of the paper.
The relative mobility of each separated spot is quantified by calculating its retardation factor (\(R_f\)):
\[ R_f = \frac{D_{\text{dye}}}{D_{\text{solvent}}} \]
where \(D_{\text{dye}}\) is the distance traveled by the center of the dye spot from the origin line, and \(D_{\text{solvent}}\) is the total distance traveled by the mobile phase solvent front from the origin line. Under specified experimental conditions (stationary phase paper, mobile phase solvent composition, and temperature), the \(R_f\) value is a characteristic property of a compound used for identification.
- 4.1: Food Dye Chromatography - Experiment
- This page covers safety precautions for handling food dyes and flammable substances, lists required equipment and chemicals for chromatography, and details an experimental procedure in five parts. These include preparing the developing tank and solutions, applying dye to chromatography paper, and developing the chromatogram. It emphasizes careful measurement and responsible disposal of chemical waste following instructor guidelines.
- 4.2: Food Dye Chromatography - Pre-lab
- This page covers chromatography, detailing the roles of the stationary (fixed material) and mobile phases (solvent). It emphasizes the importance of identifying these phases in laboratory experiments and explains how to calculate the Rf value of various dyes in chromatograms, guiding students to measure and evaluate dye separation efficiency.
- 4.3: Food Dye Chromatography - Data and Report
- This page outlines a data collection method for analyzing standard and M&M dye characteristics through chromatography, detailing measurements of dye and solvent movement. It includes tables for recording data and offers post-lab questions to encourage student reflection on practical aspects of chromatography, such as marking techniques, spot size importance, Rf value range, and solvent front timing considerations.