Possible problems with Hexane in NP HPLC

[aalbre]

We use our HPLC system mostly for RP HPLC analyses. Now for the first time we came across a NP HPLC method using a cellulose based column. Some of my colleagues think that when using hexane as a part of a mobile phase (e.g. hexane:IPA 50:50) I could damage the HPLC system. We use PEEK tubing and NOT steel. Could hexane cause corrosion to the tubing or to any part of the HPLC system for that matter? I am mostly worried about the tubing...

[goxy43]

yes, hexane, thf, dmso can damage your peek system. you should check for acceptable concentration of dmso, thf or hexane for your system. however, you can also check for another organic solvent compatible with your separation problem.

[aalbre]

so when using hexane in your system we should use steel tubing as a rule?

[goxy43]

well, depending on dimension, you could also use peeksil (silica coated with peek). but yes: stainless steel is teh best option when using that kind of solvent.

[AA]

PEEK has excellent compatibility with Hexane and IPA. You can use that mobile phase without modifications to the system or tubing. There are compatibility charts availble on the interweb, here is one I found.

http://208.72.236.210/pdfs/solvent_compatibility_2.pdf


The users manual that came with your LC should have a solvent compatibility chart in the appendix.

[zokitano]

PEEK has excellent compatibility with Hexane and IPA. You can use that mobile phase without modifications to the system or tubing. There are compatibility charts availble on the interweb, here is one I found.

http://208.72.236.210/pdfs/solvent_compatibility_2.pdf


The users manual that came with your LC should have a solvent compatibility chart in the appendix.

Thanks AA, for the reference. It is very useful for me.

Regards

[Alex Buske]

Hexane has high vapour pressure. Its said that the high vapour pressure dries up the plunger seal. Some vendors have seals from different material, which are differently suited for Hexane. We switched to heptane to avoid pressure fluctuations.

Alex

[XL]

There are two types of pump seals: one for RP applications and one NP applications. Use the right type of pump seal or you will get pre-mature pump leak. PEEK is compatible with many common HPLC solvents, but not for THF and acetone. Heptane is definitely a more convenient solvent than hexane due to its higher boiling point.

[HPLCCONSULT]

We have been running methods which use high concentrations of hexane (50 to 98%) for decades on HP/Agilent style pumps with the standard piston seals (RP). We tried the NP ones some time ago and found they did not last long. The RP seals are also more tolerant of a wide variety of mobile phase types which is handy. The piston seals will dry up from repeated use in Hexane and we have found that simply running the system in 100% IPA (Methanol and Ethanol also work) for about twenty or thirty minutes every forty to eighty hours of use "re-hydrates" everything and the pressure fluctuations (and the squeak that can be heard) all go away.

BTW: For systems which use a proportioning valve to mix solvents it is also a good idea to periodically switch which lines (channels) you use for a given solvent every now and then to expose the solenoid valve SEALS to different liquids as well. *People often use channel 'A' for everything. Give it a "rest" now and then and use a different channel as the primary. We found that dry solvents such as Hexane will also dry these seals causing either a small leak or failure of the specific solenoid (channel) valve over time. Simply flush (and store) the lines in IPA when not in use. This can help prolong the life of the system. We have one HP Quat Pump which has been in continuous service since 1995 and has never needed any new solenoid valves or an active inlet valve. Only routine cleaning and replacement of normal wear parts (PTFE, Seals...).