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Creating a Method
Creating a Method for the GC
56
ISQ User Guide
Thermo Scientific
2. If you have a split / splitless inlet (SSL) injector, click the
SSL
tab to configure the injector
port settings.
Figure 43.
Setting the SSL Parameters on the FOCUS GC
a. The inlet should be turned on and set to a temperature that is at least 10 °C higher
than the boiling point of your least volatile analyte. The material injected into the
port will vaporize and move into the GC column quickly. Higher temperatures can
lead to thermal decomposition of some analytes, so you will have to optimize the
injector temperature for your analysis. Set the SSL temperature between 50 and
375 °C (a typical value would be 225 °C).
b. Useful for diluting high concentrations of sample, the split flow is the amount of gas
that is swept through the injector to the exhaust port. Higher values will give more
dilution. The split flow will also reduce the amount of contamination that builds up
in your system. The split flow ratio is the ratio of the split flow to the carrier gas flow.
It is effectively the dilution ratio of the sample. This is typically turned on and set to
a flow of 50 mL/min. However, this increases the carrier gas usage, so for your
analysis, lower split flows may be more acceptable.
c.
Finally, if your analysis requires a higher flow to quickly sweep the analytes into the
column, which may be needed with high temperature injectors and thermally labile
compounds, you can use the surge pressure to increase the column flow for the surge
duration time.
Tip
We recommend turning on the septum purge, which means an additional 5 mL/min
of carrier gas will go through the injector. This reduces the buildup of contaminants in the
injector, on the column, and in the ISQ instrument. If you perform a splitless injection,
even if the split flow is set, the split flow will be turned off for the splitless time. The
septum purge will be turned off for the stop purge time. After these times, the split flow
and septum purge will be reactivated.
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