Ion pair reagents in normal phases

[chandusabini]

Dear Team,

I want to know the ion pair reagents can be used in normal phase HPLC.

I am unable to seperate an placebo peak from known impurity with Diol column and mobile phase (ACN and IPA in 80:20%). I have also tried with different gradient programs and hexanes in with different copmositions with ACN.

Please suggest me in slection ion par regant and any other ways.


Regards
Chandra Sekhar

[Bryan Evans]

Ion pairing / NP can be used with Unison UK-Amino.
Below are applications for 5-Fluorouracil and nucleosides:

http://www.silvertonesciences.com/files/TI409E.pdf
http://www.silvertonesciences.com/files/TI406E.pdf

In this case, the IP can "mask" the charge on both
the aminopropyl ligand and the analyte.

Also, hexane and water are used in the mobile phase
(both are miscible with THF).

[JA]

Presumably you are struggling with an impurity which elutes early? A little more information would be useful. Maybe the product, or something similar, already has application details available.

There are some strategies with respect to retention and selectivity without resorting to ion pairing, the traditional form of which (alkanesulfonates or alkylammonium derivatives) I'm guessing aren't common as a diol column is formally neutral in charge. Bryan's suggestion of switching to a different phase is one possible solution.

The search function is a good start. Here is a suggestion for further reading: diol normal phase

edit: for additional politeness

[Kostas Petritis]

Ion pairing chromatography is mainly used under reversed phase conditions. Under normal phase conditions, the effects are generaly detrimental for your separation (i.e. an ion pair will be more hydrophobic and thus eluted earlier).

[Bryan Evans]

Chandra - Thank you for your post. If you can provide more
information to the forum - that will be helpful. Other solutions
might be better (than IP).

Back to ion pairing in NP...I understand it is not the conventional
way of doing NP. But some thoughts:

- IP in NP usually results in a loss of retention (as Kostas pointed out)
- IP in NP (in certain cases) can improve peak shape. Sometimes
inhomogenous surface polarity of packing material (under NP conditions) can result in
broadening / peak distortion. Lowering or raising the pH can help
with this.
- Low / high pH can result in decrease column liftetime. Conventional
silica-based NP columns are not appropriate for this application,
and advanced technology is required.

- It has the potential to offer orthoganol retention to
RP mode

[chandusabini]

Thanks for your all suggestions.

I have reied with 1-Octane suflonic acid (25mg in 1000mL of ACN) in place of pure ACN. I have suceeded in speraration impurity from placebo peaks. Moreover peak shape of impurities wwas improved.


Regards
Chandra Sekhar