assay of large polar molecule

[MestizoJoe]

Let's say I decided to try SEC to develop an assay method. Isn't the method inherently flawed since SEC can't separate something like

MW30da-Ph

can't be separated from

MW30da-Ph-OH?

This is the reason I am staying away from SEC. How might the FDA look at this? I just assumed that using SEC to develop an assay is not stability indicating in the same sense as we refer to a small molecule HPLC method as stability indicating. If a small molecule co elutes with an impurity/related substance then the method is not stability indicating. What about SEC?

Are large molecules treated differently?

[tom jupille]

That's why I asked earlier what you expected the related substances to be. In the example you just gave, the "hook" is different, so HILIC would be a better bet. That still leaves you with the problem that both of your molecules will give you broad peaks because they consist of a distribution of subunits.

Of course, we can debate these issues until the cows come home (assuming they ever do) and we may be anticipating problems that won't occur. Get a HILIC column and try it.

[bisnettrj2]

Or we'll debate them until we know what the pigs really are and how they'll react when treated in particular ways...

[MestizoJoe]

I didn't understand the last comment. Can you explain what you mean?

[bisnettrj2]

Inside Forum comment, relating to a thread by the late Uwe Neue.

[tom jupille]

I believe that Uwe's memorable "pigs" holds the record for the longest thread on the Forum:
viewtopic.php?f=6&t=12697