change retention time with Gas Saver Time

Hi, 

Are you running split or splitless inlet conditions?  What is your total inlet flow at the time of injection?   Have you tried to run the split vent trap diagnostic to see if you have some restriction in the line?

Hi Dear,
my mode is split and its flow 200ml/min.
total flow is 205 ml/min.
how i can run this diagnosis ?

Dear Mr. Abbey,

I'm using Pre run before infection .I was collecting diagnostic signal for my total flow inlet like you recommended and i observed after completing the condition of column, the gas saver value persist until i active the Pre run, the total flow is increased from value of gas saver 20 ml/min to total flow value 205 ml/min ( not like you state as below )

alfausett said:

(maybe 5mL/min based on the conditions you have provided)

i attached some screen shots during my process.
1- column parameter 

2- before injection, Pre run and after conditioning the column 

3- after using Pre-run

4- after elapsing 2 min and active gas saver 

Kindly, let me know your feedback.

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.

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

Hi Abbey 

I did some trails as the following 

1- gas saver is on ( 20ml/min after 2 min ) and the column flow is constant at 4 ml/min, so the rt for methanol is 4.561 min.

2- Gas saver is off and the column flow is 4 ml/ min, so the rt for methanol is 7.610 min.

3- gas saver is off and the column flow is 7 ml/min to achieve 5psi, so the rt for methanol is 3.679 min.

Since this problem is appeared, I observed the response is increased by more than doubled ( before problem the response of methanol is around 5000 but after problem the response become 16000)

Good morning!  Thanks for running these experiments.  I have a few suggestions and follow-up questions.  

Were you able to run the split vent restriction test I mentioned earlier in the thread?  What were the results?

I suggest also running the Leak and Restriction test from the same menu. 

Have you recently changed liners?  What is the part number of your current liner?  

Did you see the response of your methanol peak change with the increased column flow?  I would also be interested to see how the RTs behave if you run 3 repeat injections under the same conditions.   

Do you have access to a flowmeter and/or leak detector?  

Abbey, I hope you're doing well and am grateful for your follow-up.

i implemented what you recommended.

alfausett said:

Were you able to run the split vent restriction test I mentioned earlier in the thread?  What were the results?

yes, sir 

for the split vent restriction test, I opened the split valve ( that I circulated in the attached photo ) then I did the test and passed.

alfausett said:

I suggest also running the Leak and Restriction test from the same menu. 

I also did it and passed.

alfausett said:

Have you recently changed liners?  What is the part number of your current liner?  

No, I never changed the linear and for type and part number, kindly review the attached photo.

alfausett said:

Did you see the response of your methanol peak change with the increased column flow?  I would also be interested to see how the RTs behave if you run 3 repeat injections under the same conditions.   

for the response of methanol to the increased column flow, I attached the results files, and the flow value is known by sample name and considering normal = 4ml/min.

for measuring repeatability of injections, kindly review the attached result files.

alfausett said:

Do you have access to a flowmeter and/or leak detector?  

unfortunately, I don't have.

I posted a reply but it needs approval from the moderator because it has a lot of photos and result files.

Hi Abbey,

I look forward to knowing your diagnosis.