By Anonymous on Tuesday, February 25, 2003 - 07:27 pm:
Has anyone had a good experience with trying to analyze Cu(I) organometallic complexes by HPLC? We have been working in this area for some time and irregardless of column type and mobile phase we observe horribly fronted peaks. In general, these compounds have a limited pH stability range 7 plus or minus about 2. Any help or words of wisdom would be appreciated.
By Anonymous on Wednesday, February 26, 2003 - 05:47 am:
Dear Anon,
What you might want to do is use a PEEK column body, in case your complexes are trying to interact with any metal in the system. Anothor trick I have used is to add a ligand to the mobile phase in low conc. to tie up any metallic impurities which might be present. The ligand you add should have as low a UV absorbance as possible and should have a formation constant a bit less the the ligand already present on your complexes.
Regards,
Mark
By Bill tindall on Wednesday, February 26, 2003 - 03:20 pm:
Unless the kinetics for the dissociation are very slow and/or the formation constant very large, you can't separate the complex by LC and get anything other than fronting peaks.
If the complex is more retained than ligand
and/or copper, as the complex dissociates to copper and ligand during the separation, the dissociated copper and ligand will run ahead of the complex, and therefore elute ahead of the complex peak. Result-fronting
It is likely your results are telling you that the complex is not rock stable under lc conditions.
By Anonymous on Tuesday, March 4, 2003 - 04:13 am:
I agree with both recommendations. You should be able to solve your problem by adding about 0.1mM EDTA in the mobile phase (depending on the level of Cu present). I have use this approach to prevent Cu (in water)interaction with the drug to form degradation.
By Chris Pohl on Tuesday, March 4, 2003 - 09:48 am:
I'm afraid I have to disagree with anonymous above. Adding EDTA to the mobile phase will only make matters worse. When dealing with a complex with inadequate stability, there are only two strategies likely to work: adding some of the same ligand involved in the complex to the mobile phase (but not some other ligand, especially not one with a high stability constant such as EDTA, as this will only exacerbate the problem) or in some cases the problem can be remedied by adjusting the pH to maximize the stability of the ligand-metal complex.