Manual Steps for Inlet Leak Check, Pressure Decay Test, and Split Vent Restriction Test for 6890/7890

The following are the manual steps for performing the standard inlet tests for 6890 and 7890A GCs. Typically, one runs the Inlet Leak Check to confirm whether there's a leak (the leak rate you determine is only approximate), the symptom of which is usually low pressure and/or smaller, longer retention time peaks; if there is a leak confirmed, one would follow this test up with the Pressure Decay test, which is more stringent and precise. The Split Vent Restriction Test addresses the opposite problem from a leak: a constriction, which typically causes high pressure.

6890 Inlet Leak Check (can also be used for 7890)

1. Set the mode to Splitless.
2. Confirm column dimensions – leave the column installed in the inlet
3. Set the Column Flow to 4 mL/min.
4. Set the inlet temperature to a constant value.
5. Set the inlet purge flow to 50 mL/min.
6. Press the Prep Run button once, wait a few seconds, then press Prep Run again.
7. Monitor the Total flow.

Subtract 7mL/min from the total flow.  The 7mL/min is the column flow + septum purge (4mL/min + 3mL/min).  The number you get quantifies the approximate leak rate; obviously, this number is ideally close to or equal to 0.  To fix the inlet leak or to identify its cause, check/tighten the following while monitoring the total flow: septum, liner O-ring, gold seal,  column fitting, split vent trap and associated fittings, and gang block fittings.

6890 Inlet Pressure Decay Test

This test requires capping the inlet column and septum purge fittings. The inlet is pressurized, then the pressure is shut off. The leak rate is then indicated by the pressure decay.

1. Set the GC inlet to split mode.
2. Remove the column and cap the inlet fitting.
3. Cap the septum purge fitting.
4. Set the inlet temperature to a constant temperature.
5. Set inlet pressure to 25 PSI.
6. Set the total flow to 50 mL/min.
7. Allow one minute for the pressures to stabilize.
8. Set the pressure to OFF.
9. Turn off the carrier supply to the inlet
10. Monitor the pressure for 10 minutes.

The pressure should not drop by more than 0.5 PSI in that time period.  If it does, there’s likely a leak. Consider the inlet body itself if the consumables were replaced when the Inlet Leak Check was performed.

7890 Inlet Pressure Decay Test

This test requires capping the inlet column and septum purge fittings. The inlet is pressurized, then the pressure is shut off. The leak rate is then indicated by the pressure decay.

1. Set the GC inlet to split mode.
2. Remove the column and cap the inlet fitting.
3. Cap the septum purge fitting.
4. Set the Septum Purge Valve Duty Cycle to 50%.

          Press the blue Service Mode > Diagnostics > Front or Back inlet (as appropriate for what you are testing) > Pneumatics control > Septum Purge > Duty Cycle 50%.

1. Set the inlet temperature to a constant temperature.
2. Set inlet pressure to 25 PSI.
3. Set the total flow to 60 mL/min.
4. Allow one minute for the pressures to stabilize.
5. Set the pressure to OFF.
6. Turn off the carrier supply to the inlet
7. Monitor the pressure for 10 minutes.

The pressure should not drop by more than 0.5 PSI in that time period. If it does, there’s likely a leak. Consider the inlet body itself if the consumables were replaced when the Inlet Leak Check was performed.

6890/7890 Split Vent Restriction Test

1. Set the mode to split
2. You can either have the column installed or the inlet capped.
3. De-configure the column from the inlet.
4. Set the inlet temperature to a constant value.
5. Set the inlet pressure to 0 PSI (this is not the same as turning the pressure OFF).
6. Set the inlet total flow to 400 ml/minute.
7. Monitor inlet actual pressure.  Typical Values for a new, clean GC are, for split liner 1-2 PSI, and for a splitless liner, 3-10 PSI.  Much higher values indicate condensed sample contamination in the injection port split vent tube, the copper split vent line or the split vent trap, or possibly a defective EPC.