Chromatography Forum

We have many methods that use 100% buffer on one channel and 100 actetonitrile on another channel.

This has worked fine for a long time using Waters Alliance and Agilent 1100 systems. We are now moving into using more and more of Acquity and Dionex Ultimate 3000 systems. This is not working so well, since the checkvalve in the 100% acetonitrile channel goes out of order very often (resulting in pressure variations). The check valves in these systems does not seem to cope with 100% acetonitrile.

It is quite strange that (in 2011) it is not possible to develop durable check valves... I guess that premixing will be required. What are your experiences?

talk to both vendors
both of them should have a secondary type of check valve that will suit the use of 100% ACN
anyway for more precise results and better reproducibility it is truly advised to work with premix solutions.

I have exactly the same problems but with Shimadzu Prominence. Does anyone know how to solve them?

If fresher ACN is of no help, ceramic check valve cartridges will usually do the trick. If your system vendor does not offer them (or they are $$$), check with Upchurch or Optimize Technologies or another 3rd party LC vendor. Ceramic cartridges, frequently as a part of a "easier to work on than OEM" checkvalve system are out there for most systems and they work well.

as for the Acquity, we once had this issue.
But since we change all lines to MeOH if we don't use it for some time, and then always let a flow of about 10-20µL/min of 50/50 A/B go through the system, we never had any issues about the check valves again, and we usually use 100%ACN on the line. (ok, this consumes some energy and MeOH, but this will count in short, trouble-free startup-times)
And the steady flow also keeps the detector cell purged, so less risk of heating up a dry cell, when turning the lamp on.

Also the other HPLCs shows less CV issues, if we change all lines to MeOH before shut-down.

For short term shut-downs I usually just leave the system in a 50/50 acetonitrile/water, but for long term, definitely methanol. Leaving it 100% acetonitrile guarantees I will return to a stuck check valve. I haven't had the chance to work with the Acquity but this works well for the 2695s.

Interesting! We are using a dionex ultimate RS pump since two years now,
with 100 % ACN (0.044% TFA) in channel B. So far we never had any
trouble with the check valves. But it's good to know that this is a potential issue.