Question about Dimenhydramine related substances test method

[syk10148]

Hi,
Question about Dimenhydramine related substances test method in BP.
It says to use "end-capped octadecysilyl silica, 5um, 0.25m, 4.6mm ID" column.
Is it same to ordinary C18 column or different?
If it is different what kind of column would be available in the market?
Thank you.

[Vlad Orlovsky]

I assume that you meant diphenhydramine. Due to hydrophobic and basic nature of the compound it will produce severe tailing in non end-capped columns. Even with well end-capped you will see poor peak shape due to residual silanol interactions. Something like Primesep D column will produce a perfect shape since it has basic group close to the surface which shields compounds from interaction with residual silanols

[thiazole]

Or he means dimenhydrinate... (Edit: never mind, that is a mixture of diphenhydramine and chlorotheophylline)

[Vlad Orlovsky]

here is our method for your compound:
http://www.sielc.com/Application-HPLC-S ... amine.html

There is focusing effect in this method and that is why peaks are so sharp peaks and can easily do quantitation.