metal complexes

[cml]

I am trying to develop an assay method for a metal complex. I am getting peak fronting due to complex dissociation under reversed phase conditions and no elution under normal phase. Any suggestions?

[Bill Tindall]

The chromatography is showing you that the metal is in fairly rapid equilibrium with it ligands, at least in a partially aqueous chromatography environment. So, what are you trying to determine- that amount of metal, the amount of metal complexed with ligand at equilibrium under some condition, or the total amout of metal complex before dissociation? The answers to some of thse questions can not be answered by chromatography for labile complex. What is the sample-a solid mixture of complex and other, solution of complex in solvent?

We need the answers to these questions to provide a good answer to your question. It may be that determining the amount of metal, if the metal is the limiting factor in complex formation, is the answer or determining the ligand if the ligand is limiting. If the sample is a solution of the complex, metal and ligands, then it will take a spectra technique to answer the question of how much complex is present. Tell us more......

[cml]

We indeed know we are dealing with dissociation on the column. I need to come up with a stability-indicating assay method for the whole complex so the dissociation is not helping. The sample is a solution of the complex. The complex is soluble in a variety of solvents.

[Bill Tindall]

If the material dissociates in solution then a stability measurement of the compound must be made on the solid. X-ray diffraction, IR, ??

But does the question even make sense? It is like asking what is the stability of sodium phosphate. If IN USE it dissociates to sodium and phosphate ions then what one really wants to know is whether the sodium trasmuted into some other element or the phosphate changed(oxidized, reduced, whatever). Hence, an analysis of phsophate and sodium(well we really would not worry about sodium) would indicate PRACTICAL stability of the salt in the solid form.

Apologies for caps, but the italic function gave me something strange)

This probably has something to do with a regulated analysis and I know nothing about this field. But the above makes scientific sense. In my unregulated career I still got requests for analysis of sodium phosphate in a water sample and I would return the request with "none detected"

[HW Mueller]

cml, how do you know that you have decomposition on the column? What you told us so far sounds as if your complex was charged. Maybe your fronting stems from partial ionic exclusion?