How to seperate this kind of compound...

[bos]

By the way, my complex should be stable enough at low pH. Although I have never detect the dissociation constant by myself, we have a team in my group which is specifically studying the stabilily of the similar structured complexes. Normally, the disscociation rate is very low...it would take monthes for those complexes to dissociate at pH2.

[SIELC_Tech]

Bos,

I send you email with results for DOTA. There is a chance that it went to your bulk folder. Your compound is basic vs. zwittet-ionic nature of DOTA, but you still can use multi mode chromatography.
When compounds have similar structures, by adding another interaction you can increase your chances for separation.
I just realized that in addition to ion-exchange and reverse phase mechanisms you can use pi-pi interaction due to the presence of nitrobenzene fragment. We have a few options which we can try for your (8 different phase and numerous buffers) if you send us compounds.

Regards,

Vlad

[bos]

Vlad,

I did not receive your email...I checked both inbox and bulk folder...
Could you please send it again to this address: jw0301@gmail.com?

Thanks a lot!

Regards,

Bos

[SIELC_Tech]

Bos,

Check it now, may be I had better luck.

VO

[Patrik Appelblad]

Dear bos,

I would like to contradict a previous comment that HILIC would not be viable alternative for separation of polar compounds with a minor difference in the molecular backbone. Of course it depends on which column you use....
I have no experience of your compounds of interest, but in this link you will see a full baseline separation of Methacrylamide, Acrylamide, Methacrylic Acid, where the two first compounds is diffeing only by one methyl group.
http://www.sequant.com/products/zichili ... 00-07A.pdf

Since your compounds is even more polar, this approach might be worth a try, especially if your other options turn faulty.

[bos]

I just want to update here that Waters Atlantis dC18 column solved my problem. I can get my complexes sepearted now...

Again, thanks everybody here for helping me, especially Uwe Neue!