Basic GC

In Gas Chromatography, the mobile phase needs to be all of these answer EXCEPT

• inert

• in abundance

• detector-friendly

• mixture of pure gases

Choose the WRONG statement. In GC, septum

• is important to ensure sample is not lost while in the column oven

• is important to ensure sample is not lost while being injected into the seal the injection port

• when heated, can form degradation products that will show up in the GC analysis

• is usually made of polydimethylsiloxane

In GC, the mobile phase ____________, while the stationary phase ______________

• interacts with the analyte; also interact with the analyte

• does not interact with the analyte; also does not interact with the analyte

• interacts with the analyte; does not interact with the analyte

• does not interact with the analyte; interacts with the analyte

Resolution and retention time are influenced by

• carrier gas,

• type of stationary phase

• velocity of mobile phase (flow rate)

• all of the answers

Flow rate increases

• N2 < H2 < He

• N2 < He < H2

• He < N2 < H2

• H2 < He < N2

Answer explanation

As the carrier gas changed from N2 to He to H2, resolution increase and analysis time decreased.

H2, He give better resolution than N2 at high flow rate because solute diffuse more rapidly through H2, He than through N2

*Remember: H atomic mass is 1, He = 2 and N = 7

General detectors of GC are

• FID, ECD, ECD

• TCD, FID, MSD

• ECD, FTD, MSD

• MSD, ECD, TCD

Answer explanation

1) Flame Ionization Detector (FID)

• - detects most organic compounds

2) Thermal Conductivity Detector (TCD)

• detects most organic and inorganic compounds

3) Mass Spectrometer Detector (MSD)

• - detects most inorganic and organic compounds

Which GC detector is most suitable for halogenated compounds?

• Electron Capture Detector (ECD)

• Thermal Conductivity Detector (TCD)

• Flame Photometric Detector (ECD)

• Flame Thermionic Detector (FTD)

Answer explanation

Electron Capture Detector (ECD) is very selective and sensitive to electrophilic compounds (e.g.  halogens)