Inlet Systems
Packed column inlet
104
Problems at high inlet temperatures
A common problem with conventional packed column inlets operated at
high temperatures is septum bleed and the associated ghost peaks. To
minimize this effect, some inlet systems are designed with steep
temperature gradients throughout the entire upper length of the inlet to
provide a cool septum and minimal ghost peaks. However, this
temperature gradient allows condensation of high boiling point
compounds resulting in nonreproducibility and discrimination against
these compounds. (This effect has sometimes been mistakenly called
needle fractionation.)
A thermally optimized high-temperature inlet
The septum•purgedpacked column inlet has been thermally optimized to
provide an extremely uniform thermal profile throughout the flash
vaporization region. This thermal profile remains very close to the inlet
setpoint temperature throughout most of the gas stream. Then, up in the
purge region of the inlet, a very steep temperature gradient is forced with
a large cooling fin. This results in longer septum life, and reduced ghost
peaking when run in a nonpurging mode.
