Gas Chromatography

Basic Description Chromatography is a method for separating the components of a mixture by differential adsorption between a stationary phase and a mobile (moving) phase

Uses for Chromatography Chromatography can be used to: Qualitatively analyze the number of components in a mixture Qualitatively identify the components of a mixture using known compounds Quantitatively determine the amount of a component in a mixture using standard samples Purify individual components by separating them from the other compounds in a mixture

The Basics Mixture is placed on stationary phase Mobile phase passes over the stationary phase Mobile phase carries the individual components through the stationary phase, depending on their attraction to both of the phases

Rf ratio of spot distance to solvent front distance Chromatographed Spot Rf ratio of spot distance to solvent front distance Put the spotted paper in a developing tank Origin line Solvent

Other Kinds of Chromatography Liquid chromatography (includes column chromatography, thin-layer, and HPLC) Stationary phase: silica, alumina, modified surfaces, etc. Mobile phase (moving phase): aqueous or organic solvents Important properties: polarity, charge, etc. Gas chromatography Stationary phase: a film of a polymer or a wax. The film must have a low volatility Mobile phase: gas (Helium is a common carrier gas) Important properties: boiling point, volatility, etc.

The Basic Gas Chromatograph

Vernier GC

A Chromatogram 5 1. Acetone 2. Methanol 3 3. Butanol 1 4. Acetic Acid 5. Butyric Acid 2 4

This Week’s Lab Forensic in nature Start with FTIR to decide what compound class your “unknown” belongs to. Run authentic compounds in that class Separation is based predominantly on boiling point rather than differential interaction with stationary phase Run the “unknown” to determine individual identities

Logger Pro Update You need the latest Logger Pro Update to operate the gas chromatograph from your laptop computer. Go to www.vernier.com Select Downloads Select Logger Pro 3.8.4.2 Update Install Correct version for your OS

Writing the Report Clearly state your experimental methods and how those procedures yielded the solution to the problems addressed in the investigation. State what data you collected and how you analyzed the data. Include properly designed and illustrative data tables. Show structures of all possible compounds in your compound class. Discuss other places that GC might be used beyond this investigation and those described in the Introduction.