Chromatography Forum

Hi,

Is it possible to use 0.5 mM of octanesulfonic acid in the mobile phase and run ESI-MS in positive mode?

Or will I kill the MS... or will the other MS-users kill me?

As good as I know it is a non-volatile ion-pairing agent so it would supress ionization in positive mode and eventually slowly kill your system. If you need to use long-chain ion-pairing with MS it should be volatile perfluorinated one.

... and if you run a volatile perfluorinated acid as an ion pairing reagent in your mass spec, don't expect ever to use it in negative mode again. Ever. All you will see will be the ion pairing reagent. For weeks, months. Years even. It's simpler to buy a new mass spec than get an ion pairing reagent out of it (OK, I'm exaggerating very slightly. But not a lot.)

Thanks!

I suspected that there would be problem, but this sounds really bad. I will not try it.

(my collegues still remembers when I ran 0.1% sulfuric acid into the MS, and that was five years ago ).

Mattias, you friend, I did it too, and fortunately my boss never found out. It gave me beautiful sulphate adduct ions, but the spray chamber went all green/black and gooey and started to dissolve. Fortunately I noticed after only 1 run, and Agilent were very nice about it. They still speak to me in words of one syllable, slowly, and slightly louder than usual, but apart from that...

Mattias,

Whats wrong with mixed-mode, where IP is attached to the surface...you know all that

Mattias, you friend, I did it too, and fortunately my boss never found out. It gave me beautiful sulphate adduct ions, but the spray chamber went all green/black and gooey and started to dissolve. Fortunately I noticed after only 1 run, and Agilent were very nice about it. They still speak to me in words of one syllable, slowly, and slightly louder than usual, but apart from that...

Yep, I got exactly the same green/black mess!

Mattias,

Whats wrong with mixed-mode, where IP is attached to the surface...you know all that

hi Vlad!

I have tried Primesep 100 for this analysis, and it worked well in terms of ion-exclusion of my acidic components. The problem was that I have two stereoisomers that did not separate from the main peak (all three are neutral components). This separation seems to be completely unaffacted by change of pH, organic modifier and temperature.

I have tried a lot of columns, and only the Acquity RP-shield column and the Kinetex C18 (not the XB) can do this isomer separation. To be able to fix the separation of the acids, I needed to add some octane-sulfonic acid.

If all compounds are neutral, why are you using IP? You need to try different polar-embedded columns I guess, unless some of you compounds are ionic.
Are this sulfonates? Why not try anion-exchange mixed-mode?

Hi,

I have nine components that need to be separated. Four are acids and five are neutrals.

When I run without IP-reagent, the window where they all elute is very short (impossible to get full separation). That is why the IP-reagent is good, since it pushes out the acids earlier in the chromatogram where there is a lot of space.

I agree that a Primesep 100 would be perfect, if it just had separated all neutrals. The separation of the neutrals seems to be mostly influenced by inherent column properties, and in this case I was not lucky with the Primesep column (and most other RP columns as well).