Paper Chromatography of Food Dyes



Paper Chromatography of Food Dyes

Chromatography is a technique for separating mixtures into the components that they are made from in order to analyze, identify, quantify, or purify the mixture or components. A scientist will use chromatography to:

examine a mixture, its components, and their relations to one another (analyze)

determine the identity of a mixture or components based on known components (identify)

separate components in order to isolate one of interest for further study (purify)

determine the amount of the mixture and/or the components present in the sample (quantify)

Real life examples of uses for chromatography include:

pharmaceutical companies determining the amounts of each chemical found in a new product

hospitals detecting drug or alcohol levels in a patient's blood stream

law enforcement agencies comparing a sample found at a crime scene to samples from suspects

environmental agencies determining the level of pollutants in the water supply

manufacturing plants purifying a chemical needed to make a product

Different types of chromatography are used: liquid chromatography, gas chromatography, paper chromatography, and thin-layer chromatography (Masar, 1996). While each type of chromatography uses different methods to separate compounds, they all share the same principles. Chromatography utilizes the differential affinities of the components for a gas or liquid mobile medium (mobile phase) and for a stationary adsorbing medium (stationary phase) through which they pass. The stationary phase holds the mixture until the mobile phase passes through, solubilizes the components, and moves them along at their individual rates. Once components are separated from one another, they can be analyzed (Greenway, 1992).

In paper chromatography the stationary phase is the filter paper and the mobile phase is the solvent. The filter paper holds the components until the solvent dissolves them and carries them up the filter paper. The solvent travels up the filter paper by capillary action. The solvent's attraction to itself pulling it up is greater than the force of gravity pulling it down. The separation of components depends on their solubility with the solvent and their affinity to the solvent and filter paper (Griffin, 1988).

The solvent can only move the components if they are soluble in it and the more soluble a component is the more there is available to move up the filter paper. Solutes will dissolve into solvents that have similar properties. Polar solvents dissolve polar solutes and non-polar solvents dissolve non-polar solutes. A component will travel up the filter paper at a rate that is determined by its affinity to the filter paper and solvent. Since each component has its own solubility with the solvent and its own affinity to the solvent and filter paper, they can be separated in multiple ways by using mixtures of different solvents and different filter papers.

Paper Chromatography: Experiment

Materials List

6 beakers or clear jars/cups

6 covers or lids (tinfoil is sufficient)

Distilled H2O

100% isopropanol or 70% isopropanol (rubbing alcohol)

10 ml graduated cylinder

6 strips of filter paper

Different colored Sharpie pens

Pencil

Ruler

Scissors

Tape

Prepare the Isopropanol Solutions

Label the beakers with the following: 0%, 5%, 10%, 20%, 50%, and 100%.

Using the 100% isopropanol and distilled H2O, make the ...