User guide

236 Advanced User Guide
8 Inlets
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.
Because of the small liner volume (about 120 μL), the PTV
cannot contain vapor resulting from large liquid injection
volumes. Injection volumes greater than 1 μL may overflow
vapor from the inlet, causing analysis variations. Cold splitless
introduction avoids this problem.
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 43
provides starting values for the critical
parameters.
Table 43 Splitless mode inlet parameters
Parameter Allowed setpoint range Suggested starting
value
Oven temperature No cryo, ambient+10 °C to 450 °C
CO
2
cryo, –60 °C to 450 °C
N
2
cryo, –80 °C to 450 °C
10 °C below solvent
boiling point
Oven initial time 0 to 999.9 minutes ≥ Inlet purge time