Pressure becomes unstable during long runs

[juddc]

As long as the guard doesn't affect the composition of your mobile phase, I don't know if it'll matter what kind you put in there. If you're running low to neutral pH, ~100% aqueous MP, I'd guess that any generic reversed phase guard will do. Higher pH (>8) and I might tend toward a polymeric or other support. It really depends upon what you're doing.

I'm glad your pump is good again! The 600 is an excellent old workhorse. I still have a couple of them running and I can't kill them

[dkreller]

Thanks juddc,

I had this thought also, that since the guard never sees the sample (when placed b/w the pump and injector) it shouldn't in principle matter what the guard column is made of. I only use 100% aqueous mobile phases, and occasionally I run experiments at pH 9. Perhaps for the greatest guard column stability I should pick up one that has polymeric particles.

I don't have any actual experience with bonded stationary phase materials. Are bonded coatings stable under extended exposure to solutions that basic?


David

[juddc]

HI David - Some will be and some won't be - you might do well to call a column supplier and explain what you're after. I'm sure that a solution can be found with a phone call or two. In the meantime, why not just run the pump overnight at 200 psi and see if it holds its prime. You could do that with water or you can recycle your buffer.

[HW Mueller]

dkreller, you saw air bubbles head toward the pump? And now you want to put a guard in there? Do you suspect something in addition to air as cause of your pump instability? Or do you want to try to compensate future plugging of the inlet frit (stones?)?

[juddc]

HW -As I understand it, the air problem was fixed with fresh filter stones He's interested in getting a bit more back pressure on the pump, possibly based upon the thought that it will hold prime better with a bit more pressure on the check valves. I've never seen this as being needed, but I won't call it impossible, either...I thought a guard on the pump outlet would be an easy way to get the back pressure he wanted. Come to think of it, I might have a flow restrictor in the lab that I've never used...let me see if I have one and if I do, you're welcome to it...

[dkreller]

juddc,

Thanks for your post. You are understanding things 100%. You may possibly have a spare flow restrictor to share? Thanks! Let me know! I'd happily accept and let you know how it goes.

We tried putting 2m of stainless steel tubing after the pump and this line only generated about 80 psi of backpressure, not the 400-600 psi I am looking for. However, my tech support person wasn't sure what was the ID of that line. I think it was the same ID as the line already on the system.

Dave

[Bruce Hamilton]

I'd just use a short length of your line and squash it with a vice until you have the desire back pressure.

Contrary to popular opinion, brute strength and ignorance conquers most problems, finesse is for wimps ...

Bruce Hamilton