Flow and extra peak issues

[kjm6357]

I have run into a couple issues and I was wondering if anyone might have any ideas as to why they might be occurring.

1. After a sample is injected into the GC the total flow remains at the set value for about a minute and then goes up and holds at a different value (i.e. it will go through an entire run holding at 131 ml/min when it is set at (and had been maintaining) 34 mL/min for the first minute of the run). I had considered that it was possible I was somehow overloading the column, but the same effect is observed when I do a run without ever injecting a sample.

2. I am consistently observing three peaks at approximately the same place when I inject a sample of n-propanol with a block of air, and I am pretty sure I should only be seeing two peaks. I tried just doing n-propanol, and just doing an air block separately. All three sample combinations gave three peaks (the air ones had less intensity, but were in the same place).

Any thoughts on these issues would be appreciated. Thanks.

[Peter Apps]

You need to review your GC programme for changes in flow and/or pressure or split ratio programmed into the method. Also look at whether you have a gas save setting, and what it is.

What detector are you using ?, presumably a TCD if you can detect air.

We need full details on your hardware and method.

Peter

[Don_Hilton]

Are you using a split/splitless inlet or a PTV inlet? And if PTV, what kind of instrumentation?

[lynoguchi]

What is you GC system?
Are you using pressure or flow control during your analysis?
Did you using an oven programmed run?

[kjm6357]

I am using a carbowax column in a Shimadzu GC2014 with an FID detector. I have tried both pressure and flow control with the same problems occurring with both. My oven is programmed to hold a steady temperature. There is no pressure change programmed in. Also, I am using a split inlet.

[Dreu]

Have you changed your liner, septum and gold seal? I've never worked on a Shimadzu, only Agilent, so I'm not sure if the basics are the same. Typically though ghost peaks are a result of a dirty inlet. They can also be caused if your split vent trap is dirty. I would check those things before going further.