T. Trimpe

What is chromatography? From Wikipedia... Chromatography (from Greek word for chromos for colour) is the collective term for a family of laboratory techniques for the separation of mixtures. It involves passing a mixture which contains the analyte through a stationary phase, which separates it from other molecules in the mixture and allows it to be isolated. Which means... Chromatography is the physical separation of a mixture into its individual components. We can use chromatography to separate the components of inks and dyes, such as those found in pens, markers, clothing, and even candy shells. Chromatography can also be used to separate the colored pigments in plants or used to determine the chemical composition of many substances.

Principles of Paper Chromatography. Capillary Action – the movement of liquid within the spaces of a porous material due to the forces of adhesion, cohesion, and surface tension. The liquid is able to move up the filter paper because its attraction to itself is stronger than the force of gravity. Solubility – the degree to which a material (solute) dissolves into a solvent. Solutes dissolve into solvents that have similar properties. (Like dissolves like) This allows different solutes to be separated by different combinations of solvents. Intermolecular force of attraction: Separation of components depends on both their solubility in the mobile phase and their differential affinity to the mobile phase and the stationary phase (factors driven by IMF).

Gas Chromatography Used to determine the chemical composition of unknown substances, such as the different compounds in gasoline shown by each separate peak in the graph below. Paper Chromatography Can be used to separate the components of inks, dyes, plant compounds (chlorophyll), make-up, and many other substances Liquid Chromatography Used to identify unknown plant pigments & other compounds. Thin-Layer Chromatography Uses thin plastic or glass trays to identify the composition of pigments, chemicals, and other unknown substances. Examples of Chromatography

Chromatography & Food Dyes. Food dyes to be separated: Yellow # 5 Red # 40 Blue #1 Objective: to identify a solvent system (mobile phase) that will best separate food dyes and will also be environmentally green. Solvents available for use: Distilled water 2-Propanol Ethanol Acetone

Some considerations… What are the similarities/differences in structure of the food dyes? What is the polarity and properties of the solvent systems and how will this impact the ability of the dyes to “travel” and separate from each other? What is R f and how is this used to measure separation? How will you document your findings to quantitatively compare the solvents? Is it necessary to test all four solvents? How will this get completed in two class periods?