How to Bake-out the Split/Splitless Inlet (S/SL) on Agilent GC Systems

Issue

The Split/Splitless Inlet (S/SL) can accumulate contaminants when high boiling point and/or high molecular weight compounds are present in the injected sample. Often these compounds are present from the sample matrix. The accumulated  contamination is not effectively removed using the analysis method parameters. These accumulated contaminants may appear in the chromatogram as ghost or artifact peaks. They can also be retained on the inside surface of the inlet liner, gold seal, or inlet weldment increasingly affecting the performance of the inlet over time.

Background

During the S/SL inlet bake-out procedure (Steps 1 to 7), high boiling point and/or high molecular weight compounds are subjected to higher inlet temperature and flow in an attempt to vaporize and remove these contaminants. The contaminant molecules, if vaporized, are purged out of the inlet under high split flow to the split vent. A bake-out of column and detector are in the subsequent steps (Steps 8 to 12) of the procedure.

Steps to Follow

Warning: The oven, inlet, and detector may be hot enough to cause burns. Wear heat-resistant gloves to protect your hands.

1. Create and save a new method for the bake-out procedure. 
2. Set the inlet into split mode. 
3. Set the column flow to the normal operating value, or set the capillary column gas velocity to ~30 cm/s.
4. Set the inlet split vent flow to 200 mL/min by adjusting the split ratio. For example, if the column flow is 2 ml/min, set the split ratio to 100:1. 
5. Set the inlet temperature to 300 °C, or 25 °C above the normal operating temperature (do not exceed 350 °C as it may thermally damage the inlet liner O-ring).
6. Make sure to send to the instrument the settings from steps 2 to 5 before continuing.
7. Purge the column with carrier flow for at least 15 minutes before heating the oven.
8. Open Method Editor in the software and proceed to the next step. 
9. If the column is attached to the detector, set the detector 25 °C above normal operating temperature (do not exceed 350 °C). If the column is not attached to the detector, cap the detector fitting.
   
   

   Caution: Heating the oven/column up before adequate purging time with carrier gas could damage the column since residual oxygen in the carrier gas, when heated will damage the stationary phase of the column.  Do not set the inlet, oven/column, or detector temperature above the column being used manufacturers maximum isothermal operating temperature.

10. Set the column oven 25 °C above the GC method final oven temperature to bake contaminants from the column. Do not exceed the column manufacturer's maximum temperature limit.
11. Bake out for 30 minutes or until the detector baseline is stable, and free of contamination peaks.
12. Return the instrument to operating condition by downloading the analytical method from the software to the instrument. 

If this S/SL bake-out procedure does not restore the inlet performance, replacement of the inlet liner and gold seal will likely be required as the accumulated contamination has not been totally removed. This would be typical of samples with matrix compounds that are nonvolatile but soluble in the injected sample solvent.

Learn how to effectively troubleshoot your GC Split/Splitless Inlet: GC-7890-2245s - Agilent 7890 Series GC: Split/Splitless Inlet Troubleshooting e-learning course available from Agilent education