Normal Phase Problems

[eetnoyer]

First, thanks for all the information I've found on this site while just lurking. You've all taught me a great deal is I've grown in experience over the years. Unfortunately, I'm haveing some trouble right now that I just can't seem to get past and was hoping someone here would have some insight. I'm attempting to PQ an Agilent 1200SL with the following modules:

Degasser - G1379B
Pump - G1312B - Binary 600 bar
Autosampler - G1329B - Standard
Column Compartment - G1316B
Detector - G1315C - Diode Array

We have several identical/similar systems, most of which are reverse phase and give us no problems.

Two of the systems are set up with normal phase analyses (essentially hexanes for mobile phases), one of which is gradient. It's these two systems that give me headaches. The first system that started acting up was the isocratic assay, which started displaying some excessive pressure fluctuations and an unstable baseline with peak shifting after a few months. Eventually, I ended up cleaning the system out with dilute nitric acid and DMSO (using IPA and/or acetone as a transition solvent) and the problem went away.

Currently, I'm attempting to PQ the gradient assay system, and seeing what appears to be the same issue. The signal noise and drift test uses hexanes @ 1mL/min for the mobile phase, 254nm wavelength, no injection and a restriction capillary to add some backpressure (~20 bar) and delay volume (~0.5mL).

I'm getting a total pressure fluctuation of ~0.5 bar that doesn't seem to have any particular pattern. Normally, I would expect minimal pressure fluctuation (0.1 bar, if any). I'm also getting somewhat excessive noise (~5x what I would expect) and baseline drift.

The things I've tried:

Clean system with dilute nitric acid (5%) and DMSO (each at least a couple of hours @ low flow), using IPA as transition solvent.
Change pump seals (no unusual wear seen) and purge valve frit.
Remove the damper and mixer from the flow path.
Plumb as an isocratic system.
Bypass sampler.

Nothing seems to be working. Any insight anyone could provide would be greatly appreciated.

Thank you,
Eric

[unmgvar]

are those systems using a NP kit for the pump seals?
is there in another bottle a buffer or water based solution?
what's in the rear seal wash solution there?

[eetnoyer]

It's set up with normal phase seals for both of the pump heads as well as the sampler metering device seal.
All of the lines are purged with hexanes.
There is no seal wash.

[coffee bean]

If you don't actually need to work at 400-600 bar, maybe you'd want to try to replace the outlet ball valve and AIV cartridge for the regular 400 bar ones. I heard they work better in a lower pressure range.

[eetnoyer]

Well, after flushing overnight at low flow with IPA, the issue seems to have gone away on its own.

Coffee Bean,
That's the first I've heard of that, but will definately keep it in mind when next it happens. Interestingly, this never happened when the system was on an old TSP. But, the last of those systems were EOL replaced last year. Also, since they are set up with the normal phase seals, they're not supposed to be run over 200 bar.