Question

1. What is typically the mobile phase in gas chromatography?

2. What affect is expected for retention times in a gas chromatography experiment if the temperature of the column is reduced?

3. If a significant clog in a 30 m capillary column is so severe that it has to be trimmed to 20 m, how will this affect its ability to effectively separate mixtures of compounds?

4. Why is CH2Cl2 the first peak observed in the gas chromatograms for this experiment?

5. If a student submitted a sample of water for GC analysis because they were confused about what was their organic layer and what was their aqueous layer, would a solvent peak be observed in the gas chromatogram of the sample assuming it was analyzed? Remember our gas chromatograph uses a FID.

Answer 1

1) The phase which carries the gas phase sample through coloumn is called mobile phase. In gas chromatography inert gases are used as mobile phase inirder to avoid unwanted reactions with sample components. Ex: Nitrogen N2, Noble gase Helium He, Argon Are etc.

2) Retention times are generally have inverse relationship with temperature of the coloumn. So, as temperature is decreased the corresponding elution time or retention time is decreeased.

3) Effective separation of components is increased as length of the coloumn is increased. In this coloumn length is lowered from 30 to 20m. So separation is lowered.

4) CH2Cl2 has low boiling point, so it is eluted first.

5) It is FID detector that means flame ionization detector. Any compound whether solvent or analyte to be identified as as peak in FID, it should be burn in the flame with Hydrogen and oxygen fuels. So water is not burnrd, so we can see the solvent peak in GC.