High backpressure from columns when running water only

[Mat]

Currently I am in the process of bringing a Dionex DX-600 to work. Many problems have been on the way, since the setup is custom in large parts. The goal is to achieve <.1ppb accuracy for cations, and as close as possible to that for anions. For now two questions are especially interesting to me:

-The suppressor (CSRS Ultra, 2mm) is leaking internally. This shows by fluids exiting the suppressor at both the eluent and the regenerant ports when injected into the other eluent port with a syringe. I believe this happened because it probably dried up, since it hasn't been used in the last few months. Is there any chance that this is not an irreversible damage? At the moment it is soaked with MSA eluent and water, respectively. Eluent does not flow, since turning on SRS power naturally gives an alarm.

-For hydration and startup purposes I first let the whole system flush with water through the eluent pathway. After a while the backpressure got excessively high, ~1200 psi from the guard column, and >3100 psi from the main column. After reverting to MSA eluent, backpressures normalized rapidly (I first only inserted the guard column, and the backpressures normalized before the eluent could have reached the column). Is there an obvious explanation for this, or should I just be happy that pressures are normal again?

I found this quote on this:

Regarding the suggestion from "Dionex" that running pure water to the resin causes the column to deteriorate (or swell), this is utter nonsense.

Does the pure water affect some part before the columns?

[Chris Pohl]

Mat,

Re: Leakage with the suppressor

It is indeed possible if the suppressor hasn't been used for a long time that the screens and membranes may well have become sufficiently dehydrated that the suppressor will leak when initially started up. Assuming the leakage is not caused by high back pressure from downstream components (see a recent thread on this topic for details on how to troubleshoot a back pressure problem or e-mail me directly if you would like troubleshooting specifics). Generally, simply allowing the device to rehydrate under zero flow conditions is sufficient to eliminate such a leakage problem if it is due to dehydration.

Re: Your observation that the column back pressure is higher when using deionized water than when eluents

Although you don't specify the column you are using, the symptoms you describe indicate that you are using one of the Dionex cation-exchange columns prepared via grafting linear polymer strands of weak cation-exchange monomer to the surface of a high surface area macroporous polymer. The polymer strands tend to adopt a "collapsed" conformation in the presence of acid whereas in deionized water the polymer strands are largely extended due to electrostatic repulsion. In the fully extended conformation, some of the polymer strands are long enough to extend, at least partially, into the interstitial void, temporarily raising the back pressure. This phenomenon is totally reversible and no damage to the stationary phase will occur as a result of this process. It is simply a characteristic of the material. However, since there is no benefit to running deionized water over an ion exchange column, I see no reason to perform deionized water rinses of such column materials.

[Mat]

Re column backpressure

The columns are CG12A / CS12A. Sorry for not specifying. I was running water because I wanted to hydrate the whole system, thinking that water would just neutrally pass the columns. No damage done, the columns are fine.
Thanks for your explanation, it satisfied my curiosity...

As you might have realized, I am no chemical engineer, my background is rather from the environmental sciences / biological side.

As for the suppressor, I left it filled with water and MSA eluent, respectively, overnight, without pressure or flow. The leakage is still there, I regard it as damaged now and will have to reorder a new one...
I measured backpressure after the supressor, it is between 50 and maximal 60 psi. Oh, and we use external water mode.
I assume there also can be irreversible damages to the membranes when dehydrated for long enough, maybe coupled with sudden application of pressure. It is probable that if it was empty, water or eluent entered not evenly, creating an uneven pressure distribution. The membranes being unflexible when dry, cracking?

Just to make completely sure: if I inject water or 0.2N NaOH into the Eluent In port with a syringe, it is not supposed to exit the suppressor from both the Eluent Out and the Regen In port, is it? That's what still happens.
Electrolysis works for a few seconds, but then a voltage alert comes (My guess due to a shortcut when eluent leaks into the water stream).


Thank you for your efforts.

[Chris Pohl]

Mat,

Indeed, it is possible that rehydration of a suppressor after a long period without use might not go well. Generally, it's advisable to simply fill both suppressor chambers with water are using a syringe and then allow it 15-30 minutes to rehydrate. The problem is that sometimes when rehydration occurs while the suppressor is under pressure, components in the stack may become misaligned and in this case there is no simple corrective action. As you say, injecting fluid into the eluent in port should result in liquid exiting only via the eluent out port. Fluid flow out the regenerant in port it is indicative of an alignment problem in the suppressor. When this happens, there is usually not much you can do to restore proper operation.