Asymmetric Pressure Fluctuations Agilent 1100

[Mossrk]

Hi,

Over the last week one of our 1100's has had this problem:



https://ibb.co/cszKVm


With this pressure curve indicating a problem, the expected peaks are just all over the place. Often not even showing up until the next run.

Instrument:
Agilent 1100 Quaternary pump

The run conditions during this run are:
Mobile Phase A - 0.1% H3PO4
Mobile Phase D - Acetonitrile
Flow Rate: 0.4 mL/min
Column: C18 150x4.6mm 2.6um

Things tried so far:
-Complete flush with ACCN/MeOH/Iso/H2O on all four channels at high flow rate.
-Pump seals and check valves replaced.
-Pressure/leak test performed (pressure tightness confirmed; everything passed)
-Gradient test, gradient proportioning valve tests (using H2O on A/B and 0.5% Acetone on C/D) all passed

My gut is telling me that the valve is unable to proportion acetonitrile and that the low pressure mixing isn't happening. Has anybody dealt with a pressure curve looking like this?

Any help would be greatly appreciated. Thank you.

[tkubowicz]

Hello

For method parameters you have total pressure is too high in my opinion (even for column with 2.6um).
I'd recommend:
1.Try to connect restriction capillary to purge valve and check pressure profile with your method
2.Check all possible blockage places after pump:
-sampler (needle/needle seat, rotor seal)
-inline filters (if you have any)
-column compartment (rotor seal if you have valve)

Regards

Tomasz Kubowicz

[Hollow]

in addition to Tomasz suggestions and after those checks,
also try a different combination of reservoirs (either revert it or use A/B etc).
But as you already did the GPV test it maybe not the root cause (but one never knows until tested).

Beside the about 2-3x too high pressure reading for such a column, something else hit my eyes. With that low flow rate and runtime, you only pump about 1.5 of column volumes of initial MP through the column after your gradient but not even taking into account the system dwell volume (point of mixing-column head). I guess the 1100 has at least 1 ml of it.
With a column of that dimension and with 1 ml of dwell-volume I suggest you extend the runtime before the next injection to at least 25 min ((5xV0+Vdwell)/Flow = ca. 10 ml).

[Mossrk]

Thank you both for your replies. When there is nothing attached (open capillary at the DAD inlet) there is about 2-3 barr of back pressure. To separate any column issues from the instrument issues I have removed the column and replaced with a restriction capillary.I then tried the different combinations A/B, A/C, A,D with the restriction capillary. Initially I thought it was fixed, but eventually all combinations showed this same pressure fluctuation, but the worst part is that it isn't constant. The instrument can go through multiple runs of the sequence without issue and then the next 5 or so will show this pressure fluctuation.

[ATAlR]

Had similar problem with 100% Acetonitrile without stabilizer as mobile phase. Adding few drops of water to freshly opened acetonitrile liter flask solved my problems.

[Multidimensional]

Here are a few thoughts as it appears something is being overlooked or needs to be rechecked.

Did you replace the PTFE frit in the prime-purge valve (which should be replaced every month)?

Is your degasser operating properly (has it been fully serviced in the past 5-6 years)? Vacuum degassers are a common source of contamination and plugs (usually from buffers or additives). Remove the degasser from service (try Helium sparging or ultrasonication instead to see if the problem goes away).

The solvent Pickup filters/frits should be replaced at regular intervals too (or when dirty). When these clog, they restrict the movement of the liquid through the system making it appear as though the proportioning valve is at fault.

Are you sure the piston seals AND PISTONS were replaced? The pressure profile you supplied indicates that may not be the case. When ACN is introduced, that is when trouble starts. ACN changes the viscosity of the fluid and that is something which is not part of Agilent's "pressure test". Do the pressure test the old fashion way (forget the software version). Fully purge pump with pure MeOH (yes, MeOH, not IPA). Flow 0; Plug Outlet on Prime-purge valve; Set pressure to display on screen with time span 5 minutes; Set pressure max to 400 (or 600) bars. Now start flow at 1.00 ml/min and watch pressure climb nice and steady. When it hits ~ 200 bar immediately change the flow to 0.100 ml/min and watch it hit the alarm limit and hold (it will RED light, and this is normal). Continue watching the pressure vs time to see what the drift downward is. It should be very small and very steady.