a problem using ion exchange spe

[jiang295]

recently, I came across a problem using styrene based polymer cation ion exchange SPE(Amberlite ir-120). My analyte is organic base, which retained much more in ph5 than ph2 in RPLC( k'=4 verus k'=2).
the final eluent I am using is 2 bed volume of 2M methylamine in methanol,
I also used o-AMINOPHENOL as internal standard, but it did not elute out either.

did you see any problem?

[danko]

Why 100% methanol in ion exchange chromatography?
What is pKa of your analyte?

Best Regards

[jiang295]

It is not determined yet since it is a unknown compound. but it should be aromatic amine compounds.
but internal standard o-diamine benzene did not elute out either.

Why 100% methanol in ion exchange chromatography?
What is pKa of your analyte?

Best Regards

[jiang295]

is NH3 in methanol very normal for final eluent?

Why 100% methanol in ion exchange chromatography?
What is pKa of your analyte?

Best Regards

[danko]

is NH3 in methanol very normal for final eluent?

Not at all - in ion exchange chrom. anyway! I'm afraid you're mixing IEx. and RP in a non controllable manner.

If you intend to utilize the IEx. technique, you'll need a reasonably high salt concentration in the eluting solvent and the most of it must consist of water, rather than an organic solvent like methanol.

Best Regards

[jiang295]

base in methanol still can exchange with counter ion?
so3-BH+ + NH3 -> SO3-NH4+ +B
could you tell me what is the problem with this equation?
thanks a lot.

is NH3 in methanol very normal for final eluent?

Not at all - in ion exchange chrom. anyway! I'm afraid you're mixing IEx. and RP in a non controllable manner.

If you intend to utilize the IEx. technique, you'll need a reasonably high salt concentration in the eluting solvent and the most of it must consist of water, rather than an organic solvent like methanol.

Best Regards

[danko]

The first thing I would call wrong (not the equation) is the idea of using 100 % ethanol as a solvent.
I still do not comprehend the rationale for substituting methanol for water.

As for the equation; nothing wrong provided the solvent was water. You see I’m far from convinced that the ionisation either of the analyte or the stationary phase itself is anywhere near that complete.

So, if you can find a rationale for utilizing 100 % methanol instead of water, the set-up will seam much more convincing.

Best Regards

[jiang295]

thanks Danko for your reply.
But there is no ionization in methanol.
only ionization in stationary phase.
and I really saw someone use NH3 in 100% methanol.
I can show you if you like.

The first thing I would call wrong (not the equation) is the idea of using 100 % ethanol as a solvent.
I still do not comprehend the rationale for substituting methanol for water.

As for the equation; nothing wrong provided the solvent was water. You see I’m far from convinced that the ionisation either of the analyte or the stationary phase itself is anywhere near that complete.

So, if you can find a rationale for utilizing 100 % methanol instead of water, the set-up will seam much more convincing.

Best Regards

[jiang295]

and if they does not ionize in methanol, so will methanol actually decrease retention of analyte by suppression ionization?

The first thing I would call wrong (not the equation) is the idea of using 100 % ethanol as a solvent.
I still do not comprehend the rationale for substituting methanol for water.

As for the equation; nothing wrong provided the solvent was water. You see I’m far from convinced that the ionisation either of the analyte or the stationary phase itself is anywhere near that complete.

So, if you can find a rationale for utilizing 100 % methanol instead of water, the set-up will seam much more convincing.

Best Regards

[danko]

Hi again,

In order to perform an ion exchange chromatography, it is absolutely essential for both the analyte and the stationary phase to be charged (ionized). That’s what IEx is all about. If one of these or both of them isn’t charged you simply don’t perform that kind of chromatography.
So…… more concrete in your case and provided the analyte’s not charged, you either lose it during the wash phase, or it stick to the stationary phase due to hydrophobic or more probably hydrophilic interactions.

Best Regards

P.S. If you feel like sharing some info and/or data that contradict the above, please do so. I’m convinced that the most of the knowledge that I’m going to acquire during my life still lies ahead of me.

[jiang295]

hi danko, thanks again for your reply.
you can check this paper out.
Journal of Chromatography, 640 (1993) 145-149

since they are organic bases, they are readily dissolve in methanol. so i do not think they can stick to stationary phase.

i am also confused about this mechanism.

Hi again,

In order to perform an ion exchange chromatography, it is absolutely essential for both the analyte and the stationary phase to be charged (ionized). That’s what IEx is all about. If one of these or both of them isn’t charged you simply don’t perform that kind of chromatography.
So…… more concrete in your case and provided the analyte’s not charged, you either lose it during the wash phase, or it stick to the stationary phase due to hydrophobic or more probably hydrophilic interactions.

Best Regards

P.S. If you feel like sharing some info and/or data that contradict the above, please do so. I’m convinced that the most of the knowledge that I’m going to acquire during my life still lies ahead of me.

[danko]

Hi again,

I tried to get a copy of the article you referred to, but I was asked to pay for it, even though I can get copies of many other articles. Something to do with differential accessibility to certain articles. And I didn’t consider it that important

Anyway, I could read in the abstract that the authors described the stationary phase as a special one, which makes me think of some kind of a mixed mode stationary phase. This thought is further supported by the fact that they (the authors) also mention the retention of neutral (non ionizable) compounds in addition to the ionizable.

So, maybe you’re playing with different kinds of retention mechanisms which makes your process much less controllable, meaning that greater expertise in the field is needed, to achieve what you’re aiming at.

I’d suggest, that you consider whether or not you really need a “specialtyâ€

[jiang295]

Hi danko,

i think GC person always use organic slovent plus base to elute base.


[quote="danko"]Hi again,

I tried to get a copy of the article you referred to, but I was asked to pay for it, even though I can get copies of many other articles. Something to do with differential accessibility to certain articles. And I didn’t consider it that important

Anyway, I could read in the abstract that the authors described the stationary phase as a special one, which makes me think of some kind of a mixed mode stationary phase. This thought is further supported by the fact that they (the authors) also mention the retention of neutral (non ionizable) compounds in addition to the ionizable.

So, maybe you’re playing with different kinds of retention mechanisms which makes your process much less controllable, meaning that greater expertise in the field is needed, to achieve what you’re aiming at.

I’d suggest, that you consider whether or not you really need a “specialtyâ€