How to leak check a GC inlet - WKB268024

OBJECTIVE or GOAL

Ensure that there are no leaks within the GC inlet system that can cause sensitivity loss, injected material loss, and column degradation. (Entry of oxygen and moisture into the carrier gas flow causes rapid column performance loss.)

ENVIRONMENT

• APGC
• GC-MS
• Agilent 7890 GC
• Agilent 7697A Headspace
• Agilent 6890 GC
• Agilent 6850 GC
• Agilent 8697 Headspace
• Agilent 8890 GC

PROCEDURE

1. Use a good quality duster spray. Identify a marker mass peak that is clearly seen in the tune display.
2. You can inject a syringe full of the gas into the GC injector with the MS Scan set to a 100 Da span centered on 70 Da.
3. Record the time taken for the gas to enter the source when the oven is cold.  Identify a strong mass peak and center and zoom the MS scan over this peak.
4. Set the inlet to Splitless mode
5. Press the GC's "Prep Run" button twice to force the GC into inject Prep Mode.
   • The Inlet will close the Purge valve and enter Splitless Mode. This causes all material entering the inlet to now be transferred into the GC column.
6. Spray around the top of the inlet for 2 to 3 seconds. Set a timer running.
7. Observe the duster spray Marker Mass peak and wait for the elution time measured in step 1.
8. If a raise in the Marker mass is seen after the elution time, a leak is present at the top of the injector.
   • Address as necessary by changing the septum and/or the liner/O-ring.
9. If no rise is seen, the top of the injector is leak-tight.
10. Reset the timer, and spray the underside of the injector for 2 to 3 seconds. Set the timer running.
11. Observe the duster spray Marker Mass peak and wait for the elution time measured in step 1.
12. If a raise in the Marker mass is seen after the elution time, a leak is present at the bottom of the injector.
    • Address as necessary by tightening/changing the GC column ferrule or the base of the injector seal (gold plate and washer).
13. If no rise is seen, the bottom of the injector is leak-tight.
14. This test may also be used to check the connections on the inlet's Electronic Pressure Control, EPC, modules, or split vent filters.
15. Press the "Stop" button on the GC to return it to the normal state when not in use. The Split valve will open, purging the inlet.

Note: An instant/fast response to spraying gas inside the GC would indicate a leak at the end of the column/transfer line connection.

Note 2: 
On a vacuum sourced system, the same test may be made directly, observing the nitrogen peak, 28 Da, when the GC is in "Not Ready mode" (i.e., the injector is in split mode) and then pressing the Prep Mode button twice to set the injector into Splitless mode.
Observe the nitrogen peak and how it responds after the retention time of the GG column. The peak should increase slowly to about double at maximum over a couple of minutes, after the column retention time.
If there is a sudden increase, this would suggest that the inlet is leaking.

ADDITIONAL INFORMATION

Any leak in the injector system will negatively affect analysis, in either Split or Splitless Mode, because injected material will be lost with an uncontrollable "split".  Oxygen and moisture will also enter the inlet system, damaging the stationary phase and causing chromatographic peak degradation and sensitivity loss.

This test may be used on Split/Splitless, MMI, PTV, and On Column injectors, EPC controllers, and split (Purge) filters.