Pressure profile Acquity QSM

[bunnahabhain]

Dear colleagues



This picture shows a pressure profile of some isocratic runs (90 % MeOH/10 % water) on an Acquity H-class QSM, detector is a Xevo TQ-S. In my understanding, all injections should have the same operating pressure, not?
Retention time is stable (+-0.02 min) and so is peak area (+- 1 %). Anyway I'd like to understand what is causing this dramatic pressure differences from run to run.
Any ideas?

Regards
Jörg

[tom jupille]

You have already eliminated the most likely suspect (flow rate errors) because the retention times are consistent. Another possibility is particulate matter or precipitation from the sample, but in that case I would expect the pressure to increase with each injection rather than jumping around.

Does the pressure change if you just pump mobile phase over a period of a few hours (no injections)? And do you see the same kind of variation if you simply inject mobile phase? The answers can help to pin down whether or not the problem is sample-related.