Gas Chromatography

Gas Chromatography BasicsGas Liquid Chromatography (GLC)Gas Solid Chromatography (GSC)Mobile phase does not interact with

analyteSeparation 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 H2, 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 ColumnsCapillary:

- have i.d. <1mm- 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-CH2-CH2-(O-CH2-CH2)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.

Detectors in GCThe 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

Jet Separator

Cryogenic Focussing Technique for Beer Headspace Analysis

Kovat’s Retention Index