Gas Chromatography

1

TOPIC 2

Course Learning Outcomes

Able to : 1. Explain the fundamental concepts & theories of separation techniques in GC. 2. Sketch, label the schematic diagrams & discuss the function of each component in GC. 3. Identify the strength & limitations of GC technique. 4. Suggest & justify the most suitable & efficient separation technique to be employed for an analysis.

2

General Chromatography

3

Chromatography

Gas GSC GLC RPC NPC IEC Liquid SEC AC

GC : Volatile solutes (Sample MUST be volatile at temperatures BELOW 350 0C) LC : Any mobile phase soluble solutes

4

GC separation is based on : 1. Differences in boiling points of the solutes (volatilities). volatilities 2. Solutes’ interaction with the stationary phase (polarity).

Gas-solid chromatography (GSC)

5

Based on solid stationary phase (charcoal, molecular sieves). Retention of analytes by physical adsorption on solid surfaces of stationary phase.

Gas-solid chromatography (GSC)

6

Limited application : Semipermanent retention of polar molecules. Tailing of elution peaks. Used for the separation of species that are not retained by GLC (low molecular weight gaseous, eg. air components, hydrogen sulfide, carbon monoxide & nitrogen oxides).

Gas-liquid chromatography (GLC)

7

Known as gas chromatography. Stationary phase is liquid (high boiling) that is retained on the solid support. Liquids are used to modify the stationary phase.

The chromatographic process - Partitioning

8

Separation is achieved by partition of the component of the sample between the phases

(gas)

MOBILE PHASE

Sample in Sample out

STATIONARY PHASE (liquid coated onto a solid support)

Schematic diagram of gas chromatography

Sample is injected & vaporized onto the head of the chromatographic column

Tinj,det ≈ Toven + 50° C

Separation is based on the differences in migration rates among the sample components

9

As each component emerges from the column, it will be...