Tablet coating ID

[LC_addict]

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?

[krickos]

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.