Chromatography Forum

While doing a dry prime for Waters Alliance system (2690), is it necessary to pull out solvent using a syringe/plunger prior to starting the Dry Prime? Or is that only necessary to do when the system hasn't been used in a long time?

Also, do check valves on the 2690 go bad very quickly? (Solvents we use are: Line A: Methanol, Line B: Acetonitrile, Line C: Toluene, Line D: Water).

Thank you for your help in advance.

Dry-priming is usually only needed if the system is dry, (otherwise use wet-prime). For dry-priming it is required to pull solvent through with a syringe, it goes through the tubing, degasser, pump heads and check valves (~12 mL).

As for check valves and 2690s the recommended storage solvent is methanol. I would be careful when using acetonitrile as it tends to make the check valves sticky. Dolan wrote an LC troubleshooting article on check valves.

Thank you so much.

As LC_labrat suggested, ACN is believed to cause sticky check valves. Most of my methods are very heavily ACN-based, just remember to flush the system with MeOH every time you shutdown the system.

As for the lifetime of check valves on my 2695, they are replaced annually with no apparent problems.

One comment: Is it OK to have an organic solvent installed in one of the lines? I should not be OK to just to switch to line D when you want to run in normal phase, having aqueous solvents nearby. (I am just worried about that you will get "sallad dressing").