Backpressure Problem

[LCGUY]

Hi,

One of my friends faced a strange problem of backpressure in UPLC but pressure comes to normal when he changes the mobile phase brand (Acetonitrile HPLC grade in this case).
He tried two reputed brands (I don't want to name the brands for obvious reasons) on waters acquity system and column. He is filtering both of them through 0.2micron filters though both the manufacturers calim to filter their product through 0.2micron filters prior to filling.
With brand A the backpressure is 7500-8000psi which is ok for him but the moment he switches over to brand B the pressure shoots up to 10000 to 12000psi.
There has not been any problems with both the brands in HPLC but in UPLC they behave differently.
I am not giving other details because all the other chromatographic conditions are same except change in brand of Acetonitrile HPLC grade. So the obvious culprit is brand B. But I still fail to understand the reason. Can anybody explain that and how to confirm so that we can launch confirm complaint with brand B manufacturer.

[shaun78]

If both are the same grade, there really should be no reason for this.

About the only thing that comes to mind is: are they both really acetonitrile (did the manufacturer mislabel/fill the bottle); has one bottle been comtaminated?

[LCGUY]

If both are the same grade, there really should be no reason for this.

About the only thing that comes to mind is: are they both really acetonitrile (did the manufacturer mislabel/fill the bottle); has one bottle been comtaminated?

Both are Acetonitrile HPLC grade only as the same are being used in HPLC also.

[Consumer Products Guy]

run FTIR or GCMS to assure that both are acetonitrile.