Chromatography Forum

I am using Agilent 1260 Infinity HPLC,

Recently in my analysis i found that the pressure is not stable, it keep changing through out the analysis, it looks like sequence because it keep repeating the same pattern. i have checked for leak and also bubbles and found none.

Isocratic or gradient? For gradient runs, changes in backpressure are normal.

you need to add more details. There so many things that could impact on pressure.
Please add more about the analysis: column, mobile phase, what is the sample...
A graph showing how the pressure is changing would be nice...

Isocratic or gradient? For gradient runs, changes in backpressure are normal.

Isocrstic

I am using isocratic pump, column details - nucleosil C18 with particle size 5um and its length is 250mm,
Mobile phase is 70Acetonittile and 35Water.

Whatever solvent i am trying to use it keep showing the same pressure pattern, up and down.

I have took a picture of it but i dont see how i can upload it.

Thanks in advance.

Hello

Before injection, sampler valve switches to bypass position (it allows to draw sample from vial to sample loop) and because of it you can see pressure going down and then after valve switches to mainpass (injection) it is going up again.
If you run isocratic pump you should have stable pressure (unless you drastically change temperature in TCC).

Please paste good chrmatogram and bad one (sdetector signal and pressure profile). Below you have instruction:

viewtopic.php?f=1&t=2617

Regards

Tomasz Kubowicz

I am using isocratic pump, column details - nucleosil C18 with particle size 5um and its length is 250mm,
Mobile phase is 70Acetonittile and 35Water.

Whatever solvent i am trying to use it keep showing the same pressure pattern, up and down.

I have took a picture of it but i dont see how i can upload it.

Thanks in advance.

If it is and up and down repeating "saw tooth" pattern then it is most likely a leaky check valve in the pump. If so you get maximum pressure when the piston pushes out, then low pressure when the piston draws in more mobile phase because some is leaking back into the chamber as it draws.

Sorry i couldn't reply on time, this is because of the place i am leaving, there is a network problem.

Regarding my problem on HPLC pressure change, i have found that since this HPLC installed they haven't change pump SEAL which explain the cause of the problem.

Let me take this time also to thank all who replied to this post, all of your replies were real useful to me.

Thank you all.

Regards
Festo, Analytical Chemist.