variable retention time problem

[jiang295]

peaks in red box show variable retention time. any thought? I equalibrium column for at least 3 column volume.
any comments? thanks a lot.

[jiang295]

plus,
there is no problem in isocratic elution.
so, what is the possible source of problem?
air bubble? pump malfunction?

peaks in red box show variable retention time. any thought? I equalibrium column for at least 3 column volume.
any comments? thanks a lot.

[Consumer Products Guy]

With any gradient program, if I had reproducibility issues, I'd increase the equilibration time before the next injection, then ask myself: did things get better, worse, or the same? And then go from there. You may also want to run a standard mixture several times to check out gradient performance of your instrument.

Another good thing is to decrease increase injection volume and ask yourself if peak shape got better, worse, or the same. Very valuable.

[thohry]

Can you leave more time for equilibrium.
Also check the pumps precision.

[tom jupille]

I'd vote for a gradient proportioning problem. This is almost identical to a problem described in one of John Dolan's ""LC Troubleshooting" columns:
LC-GC 14(4) 294-299 (1996)

[jiang295]

i do agree that it is gradient proportion problem since i run 3.2 bed volume for equilibrium.
but I cannot find it literature you listed.
could you give me a link ?

I'd vote for a gradient proportioning problem. This is almost identical to a problem described in one of John Dolan's ""LC Troubleshooting" columns:
LC-GC 14(4) 294-299 (1996)

[tom jupille]

e-mail me with your (physical) mailing address and I'll send you a CD that has that article (actually, all of Dolan's LC Troubleshooting articles).

For anyone else who wants one, I can only send them to mailing addresses in North America.