4103FSBMOL - Practical 5 - GC.

Question 1

What type of column was used?

Answer 1

A Capilliary Column.

Question 2

How long was the column used?

Answer 2

30 metres.

Question 3

What diameter was the column used?

Answer 3

0.25mm.

Question 4

*

What is the software used for the GC (and the HPLC)?

Answer 4

Chemstation.

Question 5

*

What percentage of alcohol is the Wine Sample we used?

Answer 5

13.5%.

Question 6

*

What is the Brand of the GC-FID?

Answer 6

Agilent 6890N.

Question 7

*

What column was used on the GC?

Answer 7

DB-WAX-30m x 0.320mm x 0.5µm at 180°C. High polarity, Polyethylene Glycol stationary phase (optimised for Ethanol and Propanol separation).

Question 8

*

What carrier gas and flow rate was used on the GC?

Answer 8

Hydrogen - 3.2ml/minute.

Question 9

*

What temperature was the GC oven set at?

Answer 9

70°C.

Question 10

*

What type of injector was used on the GC?

Answer 10

Split Injector (Agilent 7683B).

Question 11

*

What was the split ratio on the injector for the GC?

Answer 11

50:1.

Question 12

*

What is the inlet temperature for the GC injector?

Answer 12

260°C.

Question 13

*

How much sample was injected into the GC instrument and why? (injection volume).

Answer 13

1µl - so it doesn’t overload the machine.

Question 14

*

What detector was used with the GC?

What temperature was this set at?

Answer 14

A Flame Ionisation Detector (FID).

280°C.

Question 15

*

What is the attenuation of the GC?

Answer 15

64.

Question 16

*

What was the Run Time we used for our samples on the GC?

Answer 16

3.5 minutes.

Question 17

What does the GC in our practical seperate the sample by?

Answer 17

Boiling Points of the different Components/ components of a volatile mixture by the affinity of each component to the stationary phase.

Question 18

If the sample has a higher affinity for the stationary phase than the mobile phase, what happens?

Answer 18

Retained for longer leading to a longer retention time.

Question 19

If the sample has a higher affinity for the mobile phase than the stationary phase, what happens?

Answer 19

The sample will be retained for a shorter length of time on the column.

Question 20

What is the proper name for the rubber seal that the GC injects into?

Answer 20

Septum.

Question 21

What does the Split Injector do in the Practical we did?

What do Split-less injectors do?

Answer 21

It instantaneously volatises the material and then allow some of it to be vented off, reducing the amount of sample to reach the column.

All volatised material is injected onto the column.

Question 22

What is the name of the separation which occurs from the GC oven at a constant temperature?

Answer 22

Isothermal Separation.

Question 23

What is the name of the separation which occurs from the GC oven at a changing temperature?

Answer 23

Gradient Separation.

Question 24

What are the 2 types of GC column called?

Answer 24

Capilliary and Packed.

Question 25

What are the differences between a Capilliary and Packed Column?

Answer 25

• Capilliary - small diameter, long narrow high purity quartz tubing with a thin layer or stationary phase directly bound to the inside walls.
• Packed - metal or glass tubing of usually thicker diameter, packed with small diameter particles coated with a thin layer of stationary phase.

Capilliary Tubing is more effiencent but also more expensive.

Question 26

How do you classify separated components?

Answer 26

By their Retention Times.

Question 27

What is on the Axis of a GC Chromatogram?

Answer 27

Concentration (y-axis) and Time (x-axis).

Question 28

How does a FID work?

Answer 28

A Flame Ionisation Detector works by the carrier gas containing the components being mixed with hydrogen and being burnt. This produces component ions which are collected by an electrode, therefore producing a current.