Chromatography Forum

Hi,

Reversed phase HPLC coupled with ESI-MS is something that I use frequently, but now I need to run normal phase chromatography. I already have a normal phase HPLC-UV method and would like to transfer it to an LC-MS instrument. Is the MS compatibility the same for NP-HPLC as for RP. Any special considerations?

When we transfered an RP-HPLC-UV method to MS earlier we decreased the flow rate from 1 mL/min to 0.4. Is this advisable to do also for the NP-HPLC method? I guess too high flow rates is not good for the ion source...

Thanks a lot!

First you need to make sure that your HPLC system is modified for NP eluents. Seals need to be changed in most cases. And don't forget to flush the whole system to eliminate all buffer salt. To switch between RP and NP on one system will make you not happy.

NP solvents are not suitable for ESI and I doubt that you'll get the maximum (if any) of the ESI by using them. Although, some modifications of NP mobile phase may be done in order to become suitable for ESI (http://web.uvic.ca/~mcindoe/42.pdf).

Do you have access to APCI. It may work with NP mobile phases, better.

Best regards

are you absolutely sure you need normal phase? Do check with your favourite column manufacturer in case they can think of an alternative that is more compatible with electrospray.

HILIC might be an option.

I also wonder if post-column infusion of an ionizable additive more compatible with ESI-MS might help. Perhaps something like an organic acid in isopropanol? That way it's still miscible with the NP solvents.

HI,
I AM ALSO LC-MS USER,
I'ST YOU CONVERT YOUR HPLC TO NORMAL PHASE.
THEN RUN THE SAMPLE.BUT AS MY KNOWLEDGE ESI MODE IS NOT FAVOR FOR NP LC-MS.
YOU CAN USE THE APCI TECNIQUE THEN YOU CAN GET THE RESULTS.
THIS IS MY PRACTICAL OBSERVATION.............................................



REGARDS
MAHESH