Running Reverse Phase on Normal Phase Seals - Agilent 1100?

[AThompson]

Hello, I'm hoping for some feedback from other chemists on this matter. We have an Agilent 1100 HPLC system for which I've installed the polyethylene seals in the quaternary pump head for our normal phase applications. These are the recommended seals for normal phase applications, as Agilent indicates the "standard" graphite-filled PTFE seals for reverse phase are not suitable for normal phase applications.

What I'm not seeing in the literature is whether or not it is potentially ok to run reverse phase applications on the normal phase polyethylene seals? By any chance are the polyethylene seals ok for reverse phase? I'm guessing not, but figured it was worth asking. It would be great to have this HPLC system able to run both reverse phase and normal phase without having to switch the seals frequently. Thanks for any feedback.

-Aaron

[Gerhard Kratz]

Using a HPLC system one day under NP conditions, the other day under RP conditions will lead to problems with the seals anyhow.

If you will have more and more to work under RP conditions the two recommendations are:
Have a lot seals ready for maintenance.
Try to get money to invest in a second HPLC system!

Good luck

[RALS]

Hi Aaron

I will have the same problem. We are just in the installation of the LC/MS. Did you try to run reverse phase in normal phase seals? what is your experience?
Thanks,
Raquel

[uzman]

Relying on my experience , you may use RP seals on NP aplications , if the seal wear procedure applied properly on Agilent HPLC.

Seal wear procedure : connect a suitable restrictor tube ( 3m x 0.25mm ID ) to the outlet of pump , and adjust the flow to maintain 350 bar pressure using IPA as mobile phase, for 15 minutes.

You may also use NP seals ( yellow seals ) on RP applications , but the pressure must not exceed 200 bar.
Also seal wear procedure must NOT be applied to NP seals , otherwise they will be damaged instantly.

When switching solvents from NP to RP ( or vice versa ) , a suitable solvent ( such as IPA ) must be applied .

[RALS]

Relying on my experience , you may use RP seals on NP aplications , if the seal wear procedure applied properly on Agilent HPLC.

Seal wear procedure : connect a suitable restrictor tube ( 3m x 0.25mm ID ) to the outlet of pump , and adjust the flow to maintain 350 bar pressure using IPA as mobile phase, for 15 minutes.

You may also use NP seals ( yellow seals ) on RP applications , but the pressure must not exceed 200 bar.
Also seal wear procedure must NOT be applied to NP seals , otherwise they will be damaged instantly.

When switching solvents from NP to RP ( or vice versa ) , a suitable solvent ( such as IPA ) must be applied .

Thanks very much for this information. cheers

[AuroraES]

I think it should be fine, most systems can be used for both methods. Try to use the appropriate wash solvents in between runs. Just be aware that after using ACN for a prolonged time, the check valves can get "sticky". Perhaps wash that line with lots of water or IPA (not sure which is best) before switching separation mode to NP. I only mention it as it could produce problems with column back pressure stability and flow regulation.

[Hampow]

Perhaps purchase a second pump head. Then you can keep RP seals in one, and NP seals in the other, and swap out the pump head when switching between RP and NP applications. Swapping the pump is easier and quicker than changing seals frequently. Though a pump costs 2-3K, it is a good option if you do not have two systems, with one dedicated to RP and the other to NP.

[Multidimensional]

My boss, who has been using these HP/Agilent systems since they were introduced, and who has been teaching HPLC and LC/MS for decades, suggests that for most NP HPLC applications, you can use the factory RP seals, not the 'special' NP seals. The NP seals wear out very fast. The NP seals can only be used at pressures of less than 200 bars. The RP seals will work fine, up to max pressure, even with solvents such as Hexane and Heptane. You may hear additional noise with them when running very dry solvents (i.e. Hex and Heptane), but the sound can be made to go away by periodically washing down the flow path with some IPA. Note: as with all seals, use of strong acids, strong bases, buffers may result in excessive wear or damage so regular inspections/tests should always be done.

If you have the NP seals installed and want to run RP methods, then you can do this, but are limited by pressure (max), reduced lifetime and should just swith over to use RP seals.

Aside from the initial seal break-in that you should do at installation (important to do with all seals, as well as run the pressure tightness and leaks tests anytime you replace seals or pistons), otherwise no break-in is needed. After evaluating the NP seals year ago for these purposes, he found that the FACTORY RP seals are far better and last longer. He has run thousands of NP methods this way with no problems and is what he teaches in class and provides as advice to clients.