Baseline Noise - Possible Pump Issue?

[JackDog]

Hello,

Recently I have noticed that I have rhythmic baseline noise in my samples and I think the pump pressure is showing some fluctuations. My sample baselines/system blanks look exactly like the pump pressure image below:



So far I have changed all solvents, changed column, changed UV lamp, changed flow cell, run a wash procedure on the degasser lines and purged the pump at a high speed, yet the problem remains.

I'm not particularly clued up on pump maintenance (we need a service engineer to do it for us...) but does this possibly look like a pump head issue or maybe a check valve?

I would be very grateful if anybody could give me some pointers.

[Consumer Products Guy]

I assume that during the run, if you turn off the pump, the pulsation would disappear or lessen greatly?

If so, based on your level of experience, may need to get a service engineer out.

We had Agilent 1050/1100 systems, and there was a diagnostic procedure one could run and help diagnose a pump problem.

[JackDog]

I assume that during the run, if you turn off the pump, the pulsation would disappear or lessen greatly?

If so, based on your level of experience, may need to get a service engineer out.

We had Agilent 1050/1100 systems, and there was a diagnostic procedure one could run and help diagnose a pump problem.

Hey Guy,

Just ran a sample and set the pump to 0ml/min flow half way through and got this:

[multidlc]

What are your mobile phase components? Is this an isocratic method, or gradient? What detection wavelength are you using? What is the make and model of the pump? What is the flow rate? These are all details that will help diagnose the situation.

[JackDog]

What are your mobile phase components? Is this an isocratic method, or gradient? What detection wavelength are you using? What is the make and model of the pump? What is the flow rate? These are all details that will help diagnose the situation.

Mobile phase: 60% water / 40% acetonitrile mixed by the pump. Have also tried pre-mixing and running from one channel.

Method is isocratic

Detection wavelength is 356nm
Have tried a new lamp.

Pump module is a Thermo lpg-3400sd
Pump has a degasser.

Flow rate is 0.6ml/min
Have tried 0.3ml/min and 1ml/min and the pump pressure in the first image obviously cycles with speed.

Opened a sequence from a few months ago and here is the historical baseline:


Here is a sample run from a few days ago:


In both images the axis are the same.

[JackDog]

For anybody else finding this in the future.

I refit the pump seals, purged at 5ml/min for 30 minutes and everything back to normal. Purging alone did nothing so it was most likely the seals.

[Consumer Products Guy]

Good. Thanks for posting the fix. We'll assume that the plungers/pistons were not scratched/damaged.

Have you been replacing the pump seals regularly, like once or year (essentially do an HPLC maintenance) or do you instead just wait until an issue arises?