Inlet Systems

Split/splitless capillary inlet

In general, the carrier gas is chosen to maximize component resolution and detector performance while minimizing overall analysis time.

Figure 6•7,a family of van Deemter curves for common carrier gases, illustrates the effect of gas choice and linear velocity (¿) on column efficiency (HETP, Height Equivalent to a Theoretical Plate) for a particular column and analysis.

Figure 6-7

 

 

 

 

 

 

 

 

 

1.2

 

 

 

 

 

 

C17 at 175^C

 

 

 

 

N2

 

k = 4.95

 

 

 

 

 

 

 

 

Glass W.C.O.T.

1.0

 

 

 

 

 

 

OV-101

 

 

 

 

 

 

 

 

 

25 m x 0.25 mm

H.E.T.P.

.8

 

 

 

 

 

 

 

 

(mm)

 

 

 

 

 

 

 

 

 

 

.6

 

 

 

 

 

 

He

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

H2

 

 

.4

 

 

 

 

 

 

 

 

 

.2

 

 

 

 

 

 

 

 

 

10

20

30

40

50

60

70

80

90

 

 

Average Linear Velocity (cm/sec)

 

 

 

H.E.T.P. versus Linear Velocity (¿)

Where temperature programming is to be performed, a linear velocity value should be chosen in the region 1•1/2to 2•1/2times the linear velocity at the minimum point on the HETP curve for the particular carrier gas. This minimizes change in column efficiency over the temperature range used.

Where column efficiency is not an important consideration, or in isothermal operation, any reasonable linear velocity value may be chosen.

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