Inlet Systems
Split/splitless capillary inlet
109
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.
1.2
1.0
.8
.6
.4
.2
10 20 30 40 50 60 70 80 90
H
2
He
N
2
H.E.T.P.
(mm)
C
17
at 175 C
k = 4.95
Glass W.C.O.T.
OV-101
25 m x 0.25 mm
Average Linear Velocity (cm/sec)
H.E.T.P. versus Linear Velocity (
)
Figure 6-7
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.
