Gas Chromatography Gas Chromatography Basics Gas Liquid Chromatography

Gas Chromatography

Gas Chromatography Basics Gas Liquid Chromatography (GLC) Gas Solid Chromatography (GSC) Mobile phase does not interact with analyte Separation occurs by interaction of analyte differentially w/liquid stationary phase and temperature GC preferred method, only applicable to volatile substances derivitiazation

Carrier Gas Supply • Must be at a constant flow rate so that retention times & retention volumes may be equated • Choice of detector will often • Dictate the gases that are used, need to be inert Ex. FID used H 2, air, and He

Injection Port • Heated so sample virtually instantly turns into a vapor as sample plug goes onto column • Septum • Split/ Splitless Want to reproducibly get in & get out Sample focus

Flow rate Measurement • Why is a known flow rate critical?

GC Columns Capillary: - have i. d. <1 mm - have wide unrestricted flow through center & inner surface is coated with liquid stationary phase • Variety of functional groups have been blended into polysiloxane chain to provide different polarity & selectivity

Capillary columns Advantages Disadvantages

HO-CH 2 -(O-CH 2)n-OH polyethylene glycol

Temperature

Chromatography Catalog Exercise • Determine the best type of column to achieve separation for drugs of abuse. • Draw the chemical structures of the stationary phase as best you can. • Indicate what chromatographic conditions you would do your separation under. • Why do you think the catalog recommended the conditions they did? • Compare with someone else who used a different catalog, explain any differences.