HP1090

[aman]

I have a HP1090 which I have constantly had flow reduction problems with (solvent flow reduction).
I have changed the cartrigde valves, sieve and even the cartridge housing. An engineer has been out and changed the gold diapragm under the booster pump and changed the oil. But the problem still persists.
I have checked the flow before the column and its fine. But when I put a column on, solvent just won't flow through ((brand new column).
Can anyone help, or recommend a good service engineer in the UK with knowlegde of the 1090 (pump in particular)
Thanks aman

[HPLCCONSULT]

You did not say WHICH HP 1090 Pumping system you have. There are several different versions (i.e. PV5, DR5, TR5). Does the problem occur on all pumping channels or just one (A,B,C) ? The High Pressure booster pumps are very reliable and when they do have issues they are usually related to one of the following: Inlet and Outlet Valve Cartridges and frit or Diaphragm. Sounds like you may have addressed these. However, did you service the low pressure syringe pump(s) for the channels ? What about the rotary valves on the syringe pump(s) ? These are responsible for most of the problems related to maintaining flow and pressure. The rotary valves are famous for leaking internally and each one can cause all kinds of problems all by itself if not properly maintained and serviced. I have seen many inexperienced cleints and experienced service engineers ignore these parts when servicing the 1090. Many do not even know how the systems work and often think that the high pressure pump alone drives the solvent flow. It does not, as it works in tandem with the low pressure syringe pump(s). Everything must work perfectly. Each syringe pump should be regularily stripped down, cleaned, inspected and parts replaced as needed. The syringe pump(s) are located directly behind the solvent cabinet (two pozidrive screws to remove the cabinet).

Lastly, I will assume you are running the system with ChemStation software (maybe you are not ?). ChemStation has a nice diagnostic feature to view the raw data that comes from the Low pressure and high pressure flow side (LP1, LP2, HP1). Bring up the diagnostic window to view the data as it can be useful in diagnosing the problem (diagmon).

Sorry, we are not in the UK so can not suggest a qualified engineer.

[aman]

Thanks for your reply. I shall try and look at the rotary valves on the syringe pump.
I suspected it was the booster pump because it is that which drives the mobile phase through the column. And it is when the column is in place that I see the flow reduction problem. The flow is fine if there's no column there. It is also where the engineer thought the problem was.
I see the problem with all solvent channels (A, B and C).
But some good suggestions I shall try these.
Aman

[HPLCCONSULT]

I would like to add one more suggestion to the list as I hate to overlook the obvious. You did not say what your mobile phase was or if it is pre-mixed, a binary mix or ternary mix. Isocratic or Gradient analysis. You did not say what your flow rate was. You did not say what the actual 'flow rate reduction' was (example: drops from 1.000 ml/min to 0.235 ml/min with a column ???). What is the system backpressure (no column)?Anyway, degassing the mobile phase is often critical to reaching a stable target flow rate. Your flow rate may appear to be stable when their is only 1-5 bars of pressure on the system (the amount of backpressure found at the syringe pumps) with no column installed, but once everything gets squeezed by adding a column and the pressure starts to rise, problems with a lack of degassing the mobil phase are going to be extreme in the HP 1090 and cause the system to never 'reach' its target in some cases. Clogged or loose ball inlet /outlet valves (H.P. pump) cause the same problem too.

It is really hard to diagnose the problem with so little info. I can think of situations where the syringe pumps and the high pressure pump can both cause problems such as you are seeing. You really need to look at the low pressure and high pressure readouts to see where the pressure is dropping.

[Consumer Products Guy]

An obvious answer would be to start budgeting for a modern HPLC system....

[aman]

In response to HPLCONSULT. My mobile phase is a simple phase of hexane:propanol:acetic acid (1000:5:1 v/v). I have also changed the inlet and outlet ball valves (on the H.P pump)
The pressure is approx 8bar when there is no column. When the column is in place it rises quite high (~98bar) and this is where the solvent flow reduces. It usually decreases from set point of 0.300ml/min to less than that to evetually nothing. It sometimes fluctuates.
To CONSUMER PRODUCTS GUY-I like your response!! I would love a new system!
Thanks Aman

[Consumer Products Guy]

Tell your boss that a new system would be cost-effective, higher uptime. And can be depreciated. Capital, not a budget item.

[HPLCCONSULT]

Almost pure Hexane for a mobile phase, well that explains a lot. This is a tough mix to pump without some pulsation. The biggest question is still .... ARE you He sparging this mixture ? If not, it will never work. IS your column full of air ? This would also cause a problem.

Try pumping a mixture of 50% IPA (or Ethanol) with Hexane to see if you stabilize the pressure (reduce the flow rate if needed). If you reach a stabile point, then gradually decrease the alcohol % until you arrive at your starting conditions. Hexane dries out the syringe seals quickly and can cause stability problems. Hydrating them with IPA (or any alcohol) will often rehydrate them. Did you service or at least inspect your syringe pumps.

Another important thought. Forget the method you are running and perform a PV of your whole 1090 HPLC system using a RP method with a column. Verify that that system actually works perfectly at pressure to rule out your method with ~ 100% Hexane.