Retention Time Shift on FLD, but not DAD !?!

[EnvChemist]

Somebody please help me,

My instrument is a Agilent 1100 .

I run a gradient, mobile phase 60/40 Acetonitrile/H2O, flow rate 1ml/min, through two detectors ; UV then FL.

Since the begginning of this week I have been seeing RT shifts on only my FL detector and right now there is a difference of 2.5 min between on for my first peak (carbazole).

My pressure is fine and the temperature is stable.

I called Agilent and they seem baffled any one here have a clue as to what may be the problem?

[chromatographer1]

It sounds like a leak after the UV detector which then decreases the outlet flow linear rate on the flow from the UV detector to the FL detector (and splits the flow volume as well) .

best wishes,

Rod

[Kostas Petritis]

Probably whatever the Chromatographer1 suggests or a very large void volume post the UV detector.

My recommendation, measure the flow before the UV and before the FL detector, if different then it is a leak, if it is the same then there is a huge void volume somewhere. Maybe you changed your tubing lately with some very large ID ones?

[EnvChemist]

Thanks !

The problem was the flow rate !

You're the best .