PATROL UPLC Process Analysis


We am having issues with running a gradient method on a UPLC patrol(s) recently. Conditions = 0.6ml/min flow, MP. A 0.1% TFA in Water MP.B = ACN.
Starting out with MP.A:MP.B 98:2.

During analysis we are seeing drift to the right, noisy baseline, spurious peaks, high delta psi. 

The pump B check valves are being replaced, but no impact.

A maintanance request is raised. Pump B has been replaced by an engineer multiple times - but after a day or two the poor chromatography issues are back and the cycle of check valve and pump b replacement continues with no impact.

Describing the method, the gradient moves from 98:2 to 75:25 over 28 minutes, about 10 minutes into analysis as pump B is increasing we are getting spurious peaks, when looking at the system information we noticed the following.

1. Gradient kicks in,
2. Pump B percentage increases,
3. Pressure drop in accumulator B,
4. Pressure drop accumulator A,
5. B pump misses stroke,
6. Spurious peak.

We decided to run pump b at 100% after the analysis above - the pump seemed to work normally - all strokes identical Pressure, the same could be said for running initial conditions at 98:2.  

We attempted the gradient again and the issue above was replicated.

Performed dynamic leak test, but pump B accumulator failed leak test. So accumulator check valve B was replaced.

It was here I discovered that
- Prime seal wash is not being performed at any stage,
- mobile phase is not being degassed,

I'm starting to think pump B is not the issue here.... any ideas? 


  • 0xChem
    Hi Doria, here are some things I would look at: 

    1.) Dynamic Leak Test Failing - you mentioned you replaced Check Valves, I'm assuming Engineer Replaced the Plunger Seals as well? If not this would be more likely than a bad check valve.

    2.) Replaced B Pump - Did they replace the Entire Head with new? If not that could be a cause. The Stainless Steel Heads can get etches or scratches that will cause failing. Upgrading to Titanium Heads can help. 

    3.) Degasser- How high is your degasser PSI? Anything above 1.0 PSI could indicate that Degasser vac pump is failing. Air in solvent might cause some of the issues you are seeing. 

    4.) Clogged Mixer - I've had all of my pump heads pass leak tests but still see erratic pressures due to one side of the mixer being clogged. This usually comes with high pressure issues. Running same solvent on both A and B lines and seeing if pressure the same could rule this out. 

    5.) Actuator - If lots of work on B pump has been done and nothing solves it, it could be a faulty actuator. You could take the Head off and see if movement during homing is steady. 

    6.) Scratched plungers - I've had scratched plungers tear up seals after just a few days. Inspect in the light for any abrasions or scratches. 

    Hope this helps! Just a fellow Chemist that has had my fair share of headaches with these BSMs!
  • Doris
    Thanks OxChem,

    I had it confirmed earlier that the seal wash was not being carried out, so that will be the first place to start -

    1. as you asked above, seals are being replaced but no wash, so they first time they are seeing solvent is organic modifier- it would be nice if it was going to be this easy a fix.

    2. A new pump has been installed (multiple times) again no seal wash prime after.

    I will have to check out your other comments, I will post the outcome as it might be useful to someone in future