Chromatography Forum

biochemist: we have had this too, in the past, and it mostly happened on instruments that are used in different methods, some with aqueous buffers. In our case we traced the problem to the inlet filters. It happened wherever people had been using an aqueous buffer, had then purged the system extensively with water, and left it in a lowish-percentage of organic (e.g. 20% MeOH storage solvent). Then, after some delay, someone else would transfer it into 100% organic, and somewhere in their second run, the most upstream check valve would get stuck.

We believe that what was happening was this:

If you follow Waters' washing instructions to the letter when changing away from an aqueous buffer, the washing isn't quite adequate to remove every trace of salt from the more distant pores of the sintered inlet filter thing. In 20% MeOH, the salt gradually diffuses back out of the distant pores. If you're unlucky, when you transfer the whole thing into 100% organic the salt precipitates, and half way through the second run a bit of salt gets stuck somewhere critical.

We've had no problems of this sort since designating 2 lines for buffers, and 2 for 100% organics.

But we also felt the same about Waters' comment that their (older design) check-valves weren't suitable for use in acetonitrile. Sorry, our cars can't be used on roads. This umbrella is only suitable for use on dry days. Their other comment to us: "if you have several methods in use, it's best to have a separate instrument for each one".

So why not remove the column and flush with another solvent? In my experience, methanol seems to keep everything pretty happy, especially after a DI water flush.

I just roused an old 600e (same check valves as an Alliance) from a ~4 year slumber with no issues. Before I put it away, I flushed the entire thing with water, then neat methanol and prior to startup I partially disassembled the pump, wet it down with methanol, reassembled it, and off it went.

This is interesting. How do you partially disassemble the pump?

I'm sorry, I should have spoken more precisely.

What I did in this case was wash down the exterior of the pump to make sure it was free of dust, then I loosened the pigtails on the outlet check valves and pushed MeOH through the pump via the priming valve without starting the pump. In the event of a stuck check valve, I would remove the check valves and sonicate them without removing the pump heads.

I've done both, thus the partial disassembly comment. I won't start a pump that's been in storage without wetting it down really well.

This is interesting. How do you partially disassemble the pump?

He dont use buffers...

Yes he does...but only when applicable, at the lowest effective concentration, and he's pretty careful about rinsing his system out when he's done.