Why are my check valves dying?

[Mattias]

Hi,

I have a very simple mobile phase (isocratic):

"Dissolve 0.30 g ammonium acetate in water in a 2000 ml volumetric flask. Add 380 ml of acetonitrile. Add 8 ml of Waters PIC B-8 (low UV reagent). Dilute to volume with water."

The check valves only last for maybe an hour when this is pumped through the system and column (no injections). I have now crashed three Alliance systems, so it has to be the mobile phase. The solution looks perfectly clear, without particles or precipitation. The pH of the mobile phase is about 5.

Any ideas why the system cannot handle this mix?

[Johnny Rod]

Older Waters systems used to suffer a lot with the check valves, it was to do with acetonitrile, believe it or not.

[aceto_81]

Cleaning the checkvalves with acetone, and then a system prime with methanol might help sometimes.
(some acetonitrile causes a film around the check valve ball, acetone dissolves this layer)

Ace

[DR]

If the above fails, you might consider using Optimize Technologies or Upchurch Scientific (have they both been bought and renamed yet?) cartridge check valves, available in a ACN friendly ceramic composition.

[Klaus I.]

Hi,

I have a very simple mobile phase (isocratic):

"Dissolve 0.30 g ammonium acetate in water in a 2000 ml volumetric flask. Add 380 ml of acetonitrile. Add 8 ml of Waters PIC B-8 (low UV reagent). Dilute to volume with water."

The check valves only last for maybe an hour when this is pumped through the system and column (no injections). I have now crashed three Alliance systems, so it has to be the mobile phase. The solution looks perfectly clear, without particles or precipitation. The pH of the mobile phase is about 5.

Any ideas why the system cannot handle this mix?

Does this also happen when you have used your Alliance system with freshly replaced check valves (of the latest generation)?

[Jack Silver]

I'm sorry- I didn't understand if the issue is sticking check valves or that the valves leak solvent despite being closed.

If leaking, try filtering the solvents. I did read that you didn't see anything floating, but my experience is that you may not see it until it's in the filter. Bottled solvents often have a surprising number of particles.

[Mattias]

The problem is that I loose all pressure. I have not replaced the check valves, only washed them in MeOH/water in a ultrasonic bath. Then I get back the performance (for a while). The check valves are not of the ceramic type (Waters orginial).

Thanks for your suggestions! I guess that I should start to filter the mobile phase and to order new improved check valves.

What is puzzling to me is that the systems have been handling acetonitrile for many years without any problems. Could this alkanesulfonic acid do something to the system? The Alliance systems have not been exposed to this chemical before.

[Klaus I.]

The problem is that I loose all pressure. I have not replaced the check valves, only washed them in MeOH/water in a ultrasonic bath. .

So you have a 'Lost Prime'? I think it is a common problem with Alliance systems. Use new Check-Valves of the latest generation AND PLEASE don't filter your mobile phase, since you already use chemicals with appropriate specs.

[mwoodman]

You did not say if you were filtering the mobile phase. You have added a salt and you added low UV B-8. Low UV B8 is much less soluble in organics than "regular" B8 (which uses freely soluble acetic acid for pH control). Even though you can't see particles, they could be there. And they are apparently soluble because you get the pump back after a simple meoh/water wash.
If you have crashed three systems, I think it is time to filter. Anytime I add salt to mobile phase, I filter. I don't filter when I add liquids like ammonia, formic acid, (very dilute) phosphoric acid, etc.

[Consumer Products Guy]

I think it is time to filter. Anytime I add salt to mobile phase, I filter. I don't filter when I add liquids like ammonia, formic acid, (very dilute) phosphoric acid, etc.

That's exactly what we do. And if a mobile phase is amde up with a salt, we either keep it pumping at a slow flow until we can flush the entire system with salt-free solution, or flush the entire system with salt-free solution immediately.

[Klaus I.]

I think it is time to filter. Anytime I add salt to mobile phase, I filter. I don't filter when I add liquids like ammonia, formic acid, (very dilute) phosphoric acid, etc.

That's exactly what we do. And if a mobile phase is amde up with a salt, we either keep it pumping at a slow flow until we can flush the entire system with salt-free solution, or flush the entire system with salt-free solution immediately.

If I remember correctly, Mattias will always use substances of high purity. IMHO filtration will not be neccessary.
Also Mattias have much experience with HPLC und UHPLC, he will sureley avoid something like a "salting-out"(?) effect. Nevertheless, Check-Valve issues are very common with Alliance systems, if the mobile phase ist changed. Therfore Waters have released some new check valves improvements.

@Mattias
By Accident, I have recently learned, that Check-Valves for Waters system are also manufactured by well-knonw specialized OEM-Manufactures like e.g. ASI. Maybe you can also try alternative Manufacterues?

[biochemist]

I'm also an Alliance 2695 user with bad check valve experiences... We almost have to sonicate the check valves after every analysis now.

How would I know if the check valves I buy from Waters are of the improved type? Are they a different part no. from the old check valves that come with a PM service?

[DR]

The ceramic check valves (yes, Waters offers them as well) have a different part number from the ruby/sapphire ones.

[Klaus I.]

I'm also an Alliance 2695 user with bad check valve experiences... We almost have to sonicate the check valves after every analysis now.

In my experience ultrasonication will not be very helpfull, since the check-valve is already cleaned with fresh mobile phase during pumping the mobile phase.

Recently, I have noticed that a well-known OEM-Manufacturerer and HPLC-Supplier also offers Check-Valves for the Waters Alliance System. I have no experience with this parts, but it my worth to try a alternative source for check-valves.

[Johnny Rod]

I was doing HPLC on these instruments until about 2004, I can't believe this problem is still around! I would speak to Waters (and don't take any nonsense from them), see what they have to say about ceramic ones.