Troubleshoot instrument

[yanyan]

Hi there,

After it has been used by someone in the lab, one of the HPLC systems gives me abnormal peak shape showing below. All peaks have been disturbed at the end of them. I have a feeling there is something stuck in the auto-injector site, but after the service person replaced the rotor seal, they are still there.

The mobile phase is methanol/water 50:50 with isocratic run. The two peaks are uracil and caffeine. The column is C30.

I am now switching it to a C18 column to see if it could be back to normal, which was suggested by the tech service person, though I don't think it is come from column. From your expertise, what would it be the cause? How can I get rid of it?

http://tinypic.com/view.php?pic=2yv1a4w&s=8

Thanks in advance!

[yanyan]

For update, the C18 column gives the similar peak disturb, so it is not come from the column for sure.

[pancaker]

What's your injection solvent?
Do you see these negative peaks in a blank run?
How about in an injection of 50/50, 100% H2O, or 100% MeOH?

[Hollow]

First I would recheck/redo all connections, starting with the detector.
Maybe there was a void introduced?

[danko]

I think there ie a leak somewhare between the jnjector and the column.
The injector it selv could be the reason.

Best Regards