Splitless Sampling - HP 5890 Series II Plus Reference Manual

Inlet Systems
Split/splitless capillary inlet

Splitless sampling

For splitless operation, the dilute sample is vaporized inside the inlet
insert. Most of the sample is then swept onto the column.
For full column efficiency, vaporized sample components must
reconcentrate at the head of the column prior to separation; without
reconcentration, peak widths of eluting components reflect inlet insert
volume rather than column efficiency. Reconcentration occurs via two
processes, the solvent effect or cold trapping ; these are both discussed
on the next page.
Since the technique requires flow through the inlet insert to enter the
column during injection, solvent vapor throughout the inlet continues to
enter the column even after sample component reconcentration. This can
create a long, substantial solvent tail, obscuring peaks of interest. Thus,
after a short time interval, the inlet insert is purged of solvent vapor.
After the inlet insert is purged, oven temperature is increased, causing
solvent trapped at the head of the column to volatilize and move through
the column. Sample components are thus released to be separated.
Since sample residence time inside the inlet is longer than in split
sampling, the inlet may be operated at a lower temperature: 150 to
200 C is adequate for most applications.
Solvent effect
One mode of sample reconcentration is the solvent effect which requires
vaporized sample components to be retained by a region of stationary
phase and absorbed solvent at the head of the column. In this region, the
front of the sample plug undergoes stronger retention than does the rear:
solvent•saturatedstationary phase acts as a barrier to sample
components, thereby reducing their bandwidths.
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