Chromatography Forum

Dear All,

I am experiencing a peculiar problem that my retention time is drifting constantly in forward direction during every injections.The details of the chromatography condition are given below.

Mobile Phase:0.1%v/v Trifluroacetic acid in water: Methanol (75:25)
Column:Thermo scientific Hypersil Gold Dimension:100 x 4.6mm,3µ
Flowrate:1.5ml/min
Wavelength:214 nm
Component:Salicylic acid.

Kinldy suggest me the reason why my retention time is drifting in the forward direction and also the solution to prevent the retention time drift.

Thanks
Sathish.

Do you mean the retention time is getting longer run after run?

As temperature is not controlled, maybe a change in temperature?

Ace

As temperature is not controlled, maybe a change in temperature?

Ace

Thanks for the reply.But my temperature remained same "50°C" through out the run.I think temperature is no the problem

Do you mean the retention time is getting longer run after run?

Thanks for the reply.No the retention time is not getting longer but it is getting shorter after each run.Initially the retention time will be 6.2 minutes slowly it get reduced after each run and at the end of the final injection the retention time is around 5.0 minutes.

is it something that is new after using the column for a while?
or is it something you see from the first moment you started using the column? and we are talking of a new column correct?

Do you mix with the pump, or use premixed mobile phase?
Another possibility: maybe the TFA evaporates during your sample set?

Ace

is it something that is new after using the column for a while?
or is it something you see from the first moment you started using the column? and we are talking of a new column correct?

It is observed from the first moment after starting using the column.Even i have checked with brand new column as well with the used column.

Do you mix with the pump, or use premixed mobile phase?
Another possibility: maybe the TFA evaporates during your sample set?

Ace

I have tried with both premixed mobile phase and also with the mixing with the pump, but the problem persist.My run time is just 10 minutes if really the evaporation of TFA is the problem it should not reflect in the subsequent run but i am getting a steady decrease in the retention time during the course of run.

I experienced a similar case that the retention time gets longer and longer and finally I found that it was due to the evaporation of mobile phase (premixed).
Now with all the info you have given, I suspect the equilibration time of your analysis is just longer. Try to keep every thing stable and wait for the steady state (you said), before injecting a sequence and see.

Another possibility is that the problem is coming from contaminants in the sample. Since the change is occurring fairly quickly, you can set up the "volume or time" test described on our web site: http://www.lcresources.com/resources/TSWiz/hs390.htm

That will tell you whether the problem is due to the sample or to the mobile phase + column.

Just a thought but... Do you turn the system on and start your injection right away then keep running injections? If you were to do that then you might expect a ~6 min retention while the column is still ambient and then successively shorter elution times as the column comes to 50 C.