Instrumentation for Gas Chromatography - Forensic Applications of Gas Chromatography - page 6

Syringe

Detector

Injection port

Chromatogram

Oven

Column

Computer

Figure 2.1 Schematic diagram of a gas chromatograph.

1.4

1.2

1

Nitrogen
Hydrogen
Helium

0.8

0.6

0.4

0.2

0 0

20 60

Average Linear Velocity (cm/s)

40 80 100

Figure 2.2 Van Deemter plot: influence of carrier gas on column efficiency (as
HETP).

detector (see Section 2.6.5). ( Note: An additional gas may be required as fuel
for the detector—for example, hydrogen and air for a flame ionisation detec-
tor; see Section 2.6.)

2.2.1 Gas Purity
As well as the choice of gas, another important quality is its purity. Gas impu-
rities would manifest themselves in the resultant chromatogram generated