Replace Octanesulfonic acid as mobile phase

[kyyk]

Hello. everyone:

I am using 1 mM octanesulfonic acid salt as mobile phase (A1) with 100% acetonitrille (B1) to run amino acid such as arginine, lysine, glycine... However, octanesulfonic acid hurts the UPLC sometimes. Can I have any other mobile phase to replace octanesulfonic acid?

Thanks

[tom jupille]

In ion-pair chromatography, the exact choice of IP reagent is *usually* not critical. A shorter-chain sulfonate can be used, but a higher concentration will be required. You will have to do some experiments to get the right concentration.

That said, what, exactly is the problem with the octane sulfonate ("hurts the UPLC sometimes" isn't a lot of information to go on! )

[DR]

re: Tom's comment - chain length chosen is typically a function of desired pH. Thought there is considerable overlap, I think the shorter chains are usually used for lower pH and longer chains for higher pH. At any rate, I've found it to be a good idea to filter all of these mobile phases.

[lmh]

I vaguely remember using nonafluoropentanoic acid as an ion-pair reagent for amino acids once, but because it was with LC-MS the whole experience has been blanked out by my mind as too horrible to remember. The chromatography was good, but the MS was never the same again.

[kyyk]

Thanks a lot for all of you.

When I say "hurts the UPLC", I mean that 1mM octanesulfonic acid might still contain too much salt. The salt causes UPLC to have some problem such as the peak area does not stable anymore.

I will try some other mobile phase. Thanks.

[Vlad Orlovsky]

Do you have any water in your mobile phase? If you don't you are running some weird mode, which is combination of HILIC/Cation-exchange on residual silanols and on sulfonic acid fragment of IP reagent....this is unless I am missing something.

[kyyk]

Hello, Vlad Orlovsky. Yes. I use 1 mM octanesulfonic acid salt as mobile phase A1. I use DI water as solvent for this mobile phase. I filter the mobile phase and adjust the pH to 2.0 as well.

I tried 10 mM octanesulfonic acid as mobile phase before. It really "hurts" the UPLC. The peak area became unstable after several days.