Application of GCMS

Question 1

Gas Chromatography

Answer 1

1) GC is a technique used to separate the components of a
mixture based on their physical and chemical properties.

2) In GC, the sample is vaporized and passed through a long, narrow column filled with a stationary phase.

3) The different components of the sample interact with the
stationary phase in different ways, resulting in their separation

Question 2

Type of GC & Principles

Answer 2

1) Gas Solid Chromatography (GSC)
2) Gas Liquid Chromatography (GLC)

Question 3

Gas Solid Chromatography (GSC)

Answer 3

1) Gas is used as mobile phase

2) Solid is used as stationary phase

3) Not widely used because limited no of stationary phase available

4) Used only in case, where there is a less solubility of solutes in stationary phase

5) Principle of separation is ADSORPTION

Question 4

Gas Liquid Chromatography (GLC)

Answer 4

1) Gas is used as mobile phase

2) Liquid which is coated on a solid support is used as stationary phase

3) Principle of separation in GLC is PARTITION

4) Mixture of components to be separated is converted to vapour and mixed with gaseous mobile phase

5) Component which is more soluble in stationary phase travel slower and eluted later and the components which are less soluble travel faster and eluted first

Question 5

Instrumentation of GC

Answer 5

1) Carrier gas: gas must be inert, less expensive, suitable for detector, high purity, should not cause the risk of fire. widely used are hydrogen,helium, nitrogen, and argon

2)Flow regulator and flow meter: used to deliver the gas with uniform pressure or flow rate. Flow meter are used to measure the flow rate of carrier gas

3) Injection devices

4) Columns

5) Temperature control device

6) Detectors

7) Recorders and Integrators

Question 6

Instrumentation of GC: Injection devices

Answer 6

1) The sample is usually introduced in form of solution (~0.5 ml) into the injector

2) Injector has a dual role, provides an inlet for the sample and vaporizes the sample and mixes it with mobile phase

Question 7

3 Modes of injection types

Answer 7

1) Direct Vaporisation Injector

2) Cold On-Column Injector

3) Split/Splitless Injector

Question 8

Direct Vaporisation Injector

Answer 8

Injected into a heated injection port. Sample is rapidly vaporized ,then transferred to the column

Question 9

Cold On-Column Injector

Answer 9

• The sample is injected directly on column and vaporisation occurs after the injection

•Needle penetrates the column or precolumn kept at 4oC before raising it to normal operating temperature

•Useful for thermolabile components

Question 10

Split/Splitless Injector

Answer 10

1) To maintain the constant flow of carrier gas and to control the amount of sample enters into the column

2) Split vent closed: all of sample introduced into the injector vaporizes and goes into the column

3) Split vent open : most of the vaporized sample is thrown
away to waste via the split vent and only a small portion of
the sample is introduced to the column