6.3 Analysis

Question 1

What is the stationary and mobile phase in gas chromatography?

Answer 1

Stationary phase:
High boiling liquid ADsorbed into a solid support.

Mobile phase: 
Inert gas (i.e helium), that act as a carrier for the substances being analysed.

Question 2

How are components separated in a gas chromatogram?

Answer 2

The mobile phase carries the component through the capillary column.

The component interacts with the liquid stationary phase.

The more soluble the component is in the liquid phase, the longer the component stays in the capillary column.

The length of time is recorded using a detector to give:
RETENTION TIME

Question 3

Retention time

Answer 3

Time taken for each component in a gas chromatogram to travel through the capillary column.

Question 4

How can the concentration of a component be calculated from a gas chromatogram?

Answer 4

Peak area integration:

To equate concentration with the peak area obtained, a calibration curve is created:

• Known, different concentrations of the component is passed through the chromatogram.
• The peak are for each concentration is recorded and plotted in a calibration curve—> Area against concentration

Now an unknown concentration can be passed through the chromatogram and calculated.

Question 5

Why is a deuterated solvent used in NMR, and name the solvent used.

Answer 5

Substances have to be dissolved but most solvents contain carbon and hydrogen.

This will give a signal in both C and H NMR.

Deuterated solvents use Deuterium instead of H, this does not produce a peak on proton NMR. A small peak appears on C-NMR.

Solvent used: CDCl3

Question 6

Explain the use of tetramethylsilane (TMS) in NMR.

Answer 6

This acts as a standard chemical reference for which all chemical shifts are measured against.

TMS is recorded as having a chemical shift of 0.