Chromatography Forum

pressure drop to zero upon mixing large percentage of ACN with buffer in different HPLC apparatuses. and i don't know the problem.

What buffer and what concentration? Many buffers have limited solubility in ACN and may precipitate.

For example with phosphate buffer. Than it may already have blocked your column and, depending what HPLC system, the pistons and valves of your pump head are affected.

but if it precipitate , i think the pressure will rise, but the pressure drops and didn't rise.

Did you check your pump head for leakage?

Are you doing online mixing, or pumping premixed mobile phases ?

Do you degas either mobile phase component ?, if so, how ?

Is the pressure drop rapid and sudden, or gradual, does the pressue fluctuate while it is dropping.

The more you tell us, the more we can help you.

Peter

Hello

As pressure problems can be result of different things please paste chromatogram with pressure profile (it is really important to see profile as it helps with diagnostics).
Also please put information below:
-pump type: quat/isocratic/binary
-degasser info
-gradient timetable
-pump parameters (compression, stroke etc)

Without those information you can't expect quick and clear answer.

Regards

Tomasz Kubowicz

but if it precipitate , i think the pressure will rise, but the pressure drops and didn't rise.

Unless some of the precipitate prevents a check valve from sealing.

At this point, unless you give us some more information, anything we can say is pure guesswork.

Are you doing online mixing, or pumping premixed mobile phases ?

Do you degas either mobile phase component ?, if so, how ?

Is the pressure drop rapid and sudden, or gradual, does the pressue fluctuate while it is dropping.

The more you tell us, the more we can help you.

Peter

i am doing online mixing... and i degas all mobile phase component... and the pressure drop rapidly and suddenly and doesn't fluctuate while dropping...

Hello

As pressure problems can be result of different things please paste chromatogram with pressure profile (it is really important to see profile as it helps with diagnostics).
Also please put information below:
-pump type: quat/isocratic/binary
-degasser info
-gradient timetable
-pump parameters (compression, stroke etc)

Without those information you can't expect quick and clear answer.

Regards

Tomasz Kubowicz

the HPLC is waters. the pump type is Quaternary, and it's isocratic system.the stroke volume is 100 μl , the reservoirs to sparge is 0 ml/min for the four channels. pump mode is isocratic accelerate to 10 ml/min in 2 min. the degas mode is on. the pressure drops suddenly to zero...

This is like playing "20 questions"

You still haven't told us what buffer and what concentration.

A useful experiment is to mix your buffer with acetonitrile in various ratios (1:1, 4:1, 9:1 ACN:buffer) in test tubes and hold them up to the light to check for "sparklies" indicative of precipitation.

Could also be that you're using ruby/sapphire check valves and that one (or both) are floating when they see the ACN conc. jump. Ceramic check valves are better for systems using lots of ACN.