Initial Column Head Pressure - HP 5890 Series II Plus Reference Manual

Inlet Systems
Split/splitless capillary inlet
Van Deemter curves demonstrate advantages of using either He or H as
carrier gas. From the curves, several observations may be made:
Minima for He and H
velocities than N
higher velocities than N
or He allows shorter overall analysis times.
An additional benefit in using H
achieved at relatively low column head pressures.
For any given compound, the minimum in the N
pronounced; consequently, there is only a small linear velocity range
over which column efficiency is maximized.
H , and He to a lesser extent, exhibit relatively flat minima. Both are
better suited as carrier gases when temperature•programmed
analyses are performed.
An unrelated problem with N
is often contaminated with water and/or light hydrocarbons. He and H
are typically available in higher purities.
Overall, H is the best carrier gas choice, with He nearly as good.

Initial column head pressure

In using capillary columns, linear velocity through the column must be
set. This, in turn, is controlled by pressure at the head of the column.
Pressure required to obtain a particular velocity depends primarily upon
bore (ID) and length of the particular column and oven temperature.
Hewlett•Packardfused•silicacapillary columns may be conveniently
broken into several categories based upon their bores. Table 6•1lists
suggested initial pressures for some capillary column bores and lengths.
110
occur at much higher average linear
2
. Thus, He, or even better, H
2
with only small loss in efficiency. Use of H
2
is that high velocities can be
2
is that it is available in many grades and
2
, can be used at far
2
curve is quite
2
2
2