- Slides: 29
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
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.
Detectors in GC The ideal detector should:
Flame Ionization Detector
Thermal conductivity detector
Thermionic Detector (NPD)
Electron Capture Detector (ECD)
Atomic Emission Detector
Mass Spectrometer as a GC Detector
Total Ion Chromatogram
Selected (single) ion chromatogram:
Connecting the GC to the MS This is difficult! Why?
How is a GC interfaced to an MS? 1. Direct Connection
How is a GC interfaced to an MS? (2) Open Split Interface
Advantages of Open Split Design
Cryogenic Focussing Technique for Beer Headspace Analysis
Kovat’s Retention Index