Chromatography Forum

Hi guys,

Been assigned the task of creating a simple Identification method for a tablet coating. Ponceau 4R LAKE is the coating material. I need a suitable/sensible way or separating the coating from the remainder of the tablet components (Active, excipients etc). I then plan to perform a TLC of this coating against a reference.

Any bright ideas?


Also a side Q. Why would the addition of 0.25M NaOH to this coating cause it to go brown where as the addition of 1M NH3 does not? Both basic?

Hi

Starting with side Q. Well NaOH is a strong base, ammonia is not so less reactive. If i get the molecule right you have among things a phenol group, a double bond on 2 N atoms, lots of conjugated bonds etcetera, even if no degradation occur (not familar with this one), pH changes can cause colour changes due to amount of protonation to complexes just as a indicator in a titration.

As to collect some of the coating for id, a simple one is to put a few tablets on a sintered disc, pour (or soak for a time) a small amount of suiteble solvent/buffer over them (not necessary to dissolve all of coating as long it is reproducible), collect the solvent/buffer with extract and proceed.