GC headspace peaks size decreaseing

[Mary2014]

I am trying to troubleshoot a GC headspace run. I had the GC and headspace set up and running well. I made injection on a Thursday and I had a high %RSD for one solvent and then I let it all sit over the weekend on Monday I prep'ed new solutions and started making some injection and the area counts for all peaks including the solvent front started to drop with each injection. The peaks are about 100 time smaller than what they started at. Any ideas as to what happened? I have checked for leaks, reinstalled column, HS, new inlet linner...

[Peter Apps]

Welcome to the forum.

If you do not give us the details of your instrument and operating conditions, how are we supposed to work out what went wrong ?

To quote one of the venerable members of the forum; "The more you don't tell us. the more we can't help you."

Peter

[Mary2014]

It had been working well and then it sat over the weekend and without changing anything all the peak area including the solvent front dropped drastically. I have used the leak detector and checked for leaks. We then needed the GC for a non headspace run and if worked fine with a little noise baseline so I clean the detector and replaced the jet. As the non-headspace run has a dirtier sample I replaced the inlet liner, o-ring, gold seal, washer and septum before reconnecting the GC and headspace. On the GC I set the column flow to 4.0 ml/min, the spilt ratio to 1.0, the split flow was reading 4.0 and the total flow on the GC read 10.7 which match the setting in the headspace manual. With a flow meter we checked the split vent flow and the flow out the detector (detector was off) they both matched (about 4).
Next we tuned the headspace flow on until the flow out the split vent was about 11. We checked the flow out the detector and it was only 4-5. We though it should match the split vent flow as the split ratio is set to one. Is this right?
The GC is a 6890 and the HS is 7694. The diluent is DMSO with 4 solvents, Methanol, toluene, benzene, Chloroform.

[Peter Apps]

The flow through the column should not change if you increase the flow through the inlet.

To help you further I need to know the operating conditions of the instruments. By operating conditions I mean the temperature of the various heated zones (sample oven, valve, transfer line, inlet, column, detector) and all the gas flows, equilibrium times and pressures. What kind of column and what dimensions - length and internal diameter - are you using ?

Also, check the detector gas flow rates and ensure that you have sufficient pressure in the gas supply lines.

Peter

[baderfrank]

Hi. I would check the HS Needle for blockage.