Same Column Different LC

[syx]

I have read "Peak Fronting Issue". LC A and LC B have different heating mechanism. Oven in A has a fan and heating plates. The tube from injector passes through a tortuous track behind the preheating plate. The oven room is tightly isolated.
LC B does not have fan, only a preheating plate. The plate has outlet-inlet hole that connected to injector and column inlet sequentially.

[unmgvar]

Syx,
it is correct, there is a difference caused by the two different type of heating.
this would be most important if you do use the column for faster separation and not only for temp. stability.
these days softwares like drylab and chromsword can even tell you what temp to set in each intrument type in order to get reproducible results

from my experience and also from litterature it will become very important from 15-20 degress above room temp. at those temp. you must also make sure that you are preheating the mobile phase to oven temp. before it enters the column. otherwhise you will get peak distortions (broadning, tailing), bad resolution, fall in plate count.

[syx]

Here are the results from both LC using same column and condition. Mobile phase was pre-mixed. It contains 0.025M phosphate buffer pH 6.5 – methanol (77:23).
Chromatogram from LC A (left picture) has shown that the analyte is retained at 16 minutes, but in LC B (right) the retention is loss (approx. 4 minutes). I absolutely have no idea for explanation. How could different heating system of the column oven to be the reason?

[tom jupille]

Wow!

Thanks for posting the chromatograms. It makes interpreting the problem a lot easier.

From looking at them, it appears that the peak is essentially unretained in System B. You have probably already done this, but if system B is capable of on-line mixing, have you flushed the system and put your pre-mixed mobile phase in all the reservoirs. If system B is mis-plumbed, you could be pulling from a different reservoir than the one you intend. If it has a malfunctioning proportioning valve, you may be pulling in excess strong solvent.

In the absence of something like that, I really can't visualize what could cause the problem you're seeing.

[unmgvar]

I am as astonished as Tom on this one.

it does indicate a tubing or proportion valves problem.

Still if it is not then there might be something in the difference between the different aplications that might help us find the cause. from what i remember in the first one the solvents ratio was more extreme.

if indeed the problem persist can you post both application methods side by side please?

[syx]

The result from first problem:
LC A (left picture): we could find separated peaks from analyte (6.5’) and matrix (4.5’).
LC B: those peaks became one fronting peak (4.5’).

[JM]

It looks to me you have solvent valve problem. Pls put all other solvent tubs in your mobile phase container and purge properly to make sure all channels have the same mobile phase and than run your sample again.

good luck.

JM