Chromatography Forum

For a long time time there has been a problem with check valves sticking on Waters Alliance HPLC systems (2695 & 2795). I have heard explainations about ACN charging the ruby ball and static charges causing the ball to stick to the seat. Has anyone actually figured out what the problem is and come up with a solution?

I'm not sure if I believe the static charge explaination since Waters has been using the same check valve materials for more then 20 years and the problem never presented in their other systems. I have heard of one group putting tinfoil betwen the check valve cartridge and the house and leaving a tab of tinfoil hanging out which they grounded. Generally it is the primary plunger's check valve that sticks not the accumulator so the ACN charging doens't sound right to me.

Any comments or experience would be appreciated.

Cheers
John

There has been a lot of rumor and talk about this phenomenon for years. At first I did not believe any of it, but now I'm not so sure. I have seen something like it on a Dionex GP50 microbore pump which has an all non-metallic wetted path. Pumping 100% acetonitrile sometimes causes sticky checkvalves, but changing the composition to 2% water relieves the problem. I also removed the sticky checkvalves, and re-installed them a week or two later and they worked.

Has anyone actually tried to do a systematic study of this? I don't have a working hypothesis to explain the observations. Static electricity? Well maybe. I have seen where acetonitrile flowing through PEEK tubing at high velocity develops a static charge.

You might look into aftermarket checkvalves made out of ceramic instead of sapphire; the balls are heavier and perhaps less likely to stick. Tinfoil sounds like a recipe for trouble; I would not want to explain that procedure to my QA officer!

I had that problem on several different systems. In most cases a small and friendly hit with a wrench persuades the valve . If not, I clean with THF/water in a ultrasonic bath.
As a explanation for this phenomenon, I heared that ACN tends to build polymers under higher pressure. (?)

Optimize Technologies (whom I do not work for) makes cartridge check valves with alternative materials that are supposed to solve the ACN problem. I think they use ceramic seats & balls instead of the more common ruby/sapphire.

I have the same problem with a ACN/H2O/MeOH mobile phase on a Shimadzu system

Optimize makes kits for Shimadzu & others too. For Shimadzu, the kit features check valve bodies that can be removed without having to remove the lines going into them (so you don't risk creating any leaks where there were none).