How can gas saver influence Area and form of a peak?

[labchi]

first of all I'm really sorry for my poor english. My question is related to a test I did some time ago.
One injection with gas saver (that star 2 minutes after the injection) and on injection of the same solution made with out gas saver. The two results are very different. The analytes that have injected are ethanol and propanol. The solvet is water and the stationary phase is DB 624. In the first case (with gas saver) the two peaks are quite symmetrical and the resolution is acceptable. In the second case the peaks have a bad form and there isn't a good resolution. Thank's to all and I hope that somebody will give me a good explanation.

[Peter Apps]

Unless you can get the same result repeatably, in other words you run three times with gas saver on and three with gas saver off and get the same result each time I would guess that the poor peak shape with gas saver off is due to the bad effects of water as an injection solvent, and is nothing to do with the gas saver at all.

Peter

[foolishrice]

Inlet leakage might be the cause...

[Consumer Products Guy]

Keep that injection size small, like less than 0.5 microliters. Water expands a ton.

[labchi]

Thank's you very much for everything. I really had not thought about water as solvent and its problems.
now I can't do any other test, but in future I will remember very well your considerations. So the gas saver as the word is only a technique to save a little bit of Helium or nitrogen or Hydrogen.

[MSCHemist]

Is this a splitless injection? If so it is not the gas saver but time until the purge valve opens that is the issue.

The gas saver just adjusts the split ratio and head pressure so that the column flow is maintained while minimizing the flow through the pruge valve and thus the total ammount of gas being consumed by the inlet.

If there was an issue with leakage or other pressure regulation problems with the inlet I'd expect to see changes in the retention time.

[Peter Apps]

Is this a splitless injection? If so it is not the gas saver but time until the purge valve opens that is the issue.

The gas saver just adjusts the split ratio and head pressure so that the column flow is maintained while minimizing the flow through the pruge valve and thus the total ammount of gas being consumed by the inlet.

If there was an issue with leakage or other pressure regulation problems with the inlet I'd expect to see changes in the retention time.

That raises and important point - for the inlet presure to be maintained at set point there has to be enough gas going into the inlet to satisfy all the flows going out of it. With a generous septum purge flow and a leaky septum for example, a low gas saver flow might starve the inlet of gas. The GC should go into an error state and abort the run, but the troubleshooting might be tricky because at initial conditions (i.e. gas save off) everything looks OK.

Peter