has anyone ever seen all peaks start splitting at the apex. It seems to be be getting worse by the day. The system is acn and water mobile phase with a c18 column analytical scale. It runs in a walk up manner so I do not have control over the things people choose to load. My question is whether this could be caused by a void or residual material on the column or simply a pump issue ie. bad seal etc.

Thank you in advance

This works for me, I have a similar situation.

Every morning, run a standard. It can be anything you want, just compatible with the column. Verify that every day, your standard runs well. You can track retention time, peak width, or assymetry. Store all data.

If your standard runs fine before and after these failed samples, inform the person who used it that the system is fine, and they have to investigate the cause for their sample. When your standard fails, you'll have advance notice about your system.

Now, the peak split could mean there is a void in the column packing -- in which case you replace the column, or a particle partially blocking the frit -- a back flush may help here. A pump problem seems less likely. Your standard will let you know if something is happening and let you fix it sooner.

It is not impossible that the split peaks are caused by a degradation or impurity in the sample and your analytical system is doing just what its supposed to -- even if it doesn't make some people very happy.

If your mobile phase is acn and water, you can easyly inject coffeine to see wether its your component or the column.

Of course you can use other standards like methylparahydroxybenzoate, butylhydroxybenzoate,... these are preservatives which are easy to store as a pre-made solution.


Goodluck

Thank you for your response. I do run std several times a day to verify. I have changed the column and the problem seems to be getting better. Not exactly sure what is happening on the system but I am slowly excluding possibilities.

Since you have a situation where many people use the column, and you have no clue what they are dumping on the column, I recommend to use a guard column. Any time the peak looks ugly throw it out and get a new one. The preferred approach is to use a guard with the same packing as in the analytical column.

It sounds like it may be a system problem and not a column problem since you still have splitting when you change to a new column.

Your injector may be allowing a small bubble to be injected simultaneously with your sample, or perhaps there is a small bubble in your tubing leading to the column.

Depending on how well your mobile phase reservoirs are degassed may affect the size of such a bubble causing your observation of the problem slowly worsening or getting better.

I would try disconnecting your column and running your pump at a very high flow rate (10-20mL/min) for 10 minutes to flush any bubbles or other obstructions that may be causing this error. Do make sure that when you do this that your mobile phase is very well degassed before proceeding.

Please update us on your results.

Wow! Airbubbles in a high pressure system???? Don't you think that this is difficult to do?

Airbubbles in a high pressure system is not possible, but dissolved air will reappear as bubbles in the detector where the pressure is ambient

peak splitting: some probable reasons are given in the same topic listed as "Peak Splitting Probleam".

Best explanation I saw was dirty guard column or using a sample solvent stronger than the mobile phase.

Air bubbles: air bubbles can form if your solvents are not degassed prior to mixing within the system. Water's capacity for dissolved air is lower when it mixes with an organic like acetonitrile, therefore in the mixing chamber and beyond, the surplus air will form bubbles.