Chromatography Forum

For as long as I have worked at my current position, we have run all our RP LCs with H2O/ACN mobile phase, both with and without 0.1% formic acid additive (pH 2-3). With a bit of equilibration time between acid and no acid methods, there have been no problems. Now we are looking at having to run a method with high pH, using straight ACN, but 10mM NH4CO3/H2O (pH 9-10) as the aqueous mobile phase component.

I've never worked with this kind of solvent system before. I assume it is safest to get a dedicated column for this method. Is it possible to run both a high pH method and a low pH method on the same system? The system is an Agilent 1100 with a quat pump, so I would plan to have the channels as follows:
A - H2O + 0.1% formic acid
B - ACN + 0.1% formic acid
C - 100% ACN
D - 10mM NH4CO3/H2O (this is where 100% H2O currently resides)

Is this safe? I am concerned mostly about mobile phase carryover when switching columns, as there is always some solvent in the system. Right now a dedicated LC for this different solvent system is not an option, unfortunately. Any help, advice, correction, practical anecdote, personal experience, etc. is appreciated!

Thanks,
Kate

Presumably you saw this?:
viewtopic.php?f=1&t=16155

What is NH4CO3?

I would definitely want to dedicate columns, one to acidic and one to basic. You will also want to flush the system through with 100% water as part of a switching procedure. So if you want to run both methods in a sample list then having 100% water on your quat pump would be helpful, if you are doing this you would need to have a column switching valve too though and I assume you don't have one as you didn't mention it. In which case you could do a good manual flush through after having taken the column off before putting the other column on.

I don't see there being any inherent problems, just be careful.

Presumably you saw this?:

I did. My question was more geared towards the switching between pH, but I will keep that in mind.

What is NH4CO3?

That should have read "NH4HCO3" -- Ammonium bicarbonate. Even with proof-reading things get missed...

I would definitely want to dedicate columns, one to acidic and one to basic. You will also want to flush the system through with 100% water as part of a switching procedure. So if you want to run both methods in a sample list then having 100% water on your quat pump would be helpful, if you are doing this you would need to have a column switching valve too though and I assume you don't have one as you didn't mention it. In which case you could do a good manual flush through after having taken the column off before putting the other column on.

We do have a column switching valve, with space for two columns (Agilent G1316A Thermostatted Column Compartment). I guess I was just trying to simplify things for myself, but seeing as how I am going to have switch the second column out to run this method anyway, I'll use that time to also flush the system as suggested.

Thanks for confirming what I suppose I already knew. Any other advice for a novice is always appreciated!

--Kate