change retention time with Gas Saver Time

Hi,

Apologies, but I am not sure what the Gas Saver settings are.  Still 20mL/min at 2 min?  Were all of these screen shots during the course of a single run?   Did your peak elute at the proper time?   Has there consistently been a ramped flow on your column?  This option affects the prediction and interpretation I provided in earlier messages.

In your ChemStation editor (where you were to grab these screen shots), under Signals, locate an unassigned signal line, and using the drop down, choose the inlet total flow - actual.  This will create a signal you can open in your data analysis to see what the total flow looks like throughout the run.  You could also select the column flow parameter to see how the parameters interact during the run without having to open the method editor.  

As a side observation, your inlet pressure is very low, which can cause some interesting behaviors.  The 8890 system controls better at low pressure than its predecessors, but I like that number to be at least 5psig at the beginning of a run.  If you don't have the flexibility in the chromatography to increase the pressure, you may consider selecting a column with equivalent phase ratio in a smaller ID.  

Yes,sir the gas saver is still 20ml/min after 2 min and when change the time to 10 min,the RT is changed like I mentioned before.

Yes, I use ramped flow in column at 2ml/min for 1.2 min then ramped 10ml/min per min till reache 4ml/min.

I was trying to use constant column flow and the issue persist.

Thanks for clarifying.  Of note, at the time your Gas Saver is enabled (2min), you have just finished a ramped flow increase, so your column flow at that point is 4mL/min, not 2.  The diagnostic trace will tell you when the system is stable at the new flow.  I would recommend waiting until that time before you turn on gas saver, like 2.5 or 3 minutes.  Alternatively, is there a chromatographic reason why you cannot simply start your run at 4 mL/min?   That would simplify the inlet conditions - at least for troubleshooting. 

A few other things I want to make sure I'm understanding correctly.  Under a 2min Gas Saver, your RT is around 4.7min.  When you delay the Gas Saver, your RT is later, but still elutes before the time you enabled Gas saver (RT of 7.9 min with Gas Saver enabled at 10 or 15 minutes).  This indicates that Gas Saver isn't creating the problem, but is masking it.  If you turn Gas Saver off completely, when does your MeOH peak elute? 

I will try to turn off gas saver and kindly allow me tell you what's the result.

Of course!  I look forward to hearing your results.  I think we are getting somewhere