User guide

198 Advanced User Guide
8 Inlets
Cold splitless introduction
For cold splitless introduction, use an initial inlet temperature
below the normal boiling point of the solvent. For most solvents,
starting the first inlet temperature ramp at 0.1 minutes
provides good transfer and reproducibility. A program rate of
500 °C/min or higher is appropriate for thermally stable
analytes. A final temperature of 350 °C, held for 5 minutes, has
quantitatively transferred up to C
44
alkane.
A main advantage of temperature programmability is that the
inlet can be heated gently to transfer delicate analytes. If the
oven temperature is initially low enough to refocus the analytes
on the column, the inlet heating rate can be made slower (e.g.,
120 °C/min). This reduces thermal degradation from the inlet
and can improve peak shape and quantitation.
For most applications of cold splitless, a single temperature
ramp is enough. The remaining ramps can be used to clean the
liner or to decrease the inlet temperature to prepare for the
next injection.
Hot splitless introduction
For hot splitless introduction, select an initial temperature high
enough to volatilize the analytes. No additional temperature
parameters are required as the inlet will maintain the setpoint
throughout the run.
Starting values
A successful splitless injection consists of these steps:
1 Inject the sample and temperature program the inlet to
vaporize it.
2 Use a low column flow and low oven temperature to create a
solvent- saturated zone at the head of the column.
3 Use this zone to trap and reconcentrate the sample at the
head of the column.
4 Wait until all, or at least most, of the sample has transferred
to the column. Then discard the remaining vapor in the
inlet—which is mostly solvent—by opening a purge valve. This
eliminates the long solvent tail that this vapor would
otherwise cause.
5 Raise the oven temperature to analyze the sample.
Some experimentation is needed to refine the operating
conditions. Table 35 provides starting values for the critical
parameters.