Dear Friends

Is there any one who could enlighten me on what end capped column means and what is the advantage of using end capped columns against normal columns

Thanking you all in anticipation

Because of steric hindrance and other factors, it is not possible to react all of the silanols with C8 or C18 alkyl groups. Because of this, after the initial bonding, additional bondings are sometimes performed, attaching smaller alkyl groups, quite often propyl or isopropyl groups, to the residual silanols. There is no endcapping process that is complete. There are always unreacted silanols.
The resulting stationary phase, having fewer residual silanols, will display fewer secondary interactions characteristic of silanols than a non-endcapped stationary phase.

The common endcapping group is a trimethylsilyl group

Thanks for the reply but what is the specific advantage in using endcapped columns against non endcapped one.

An endcapped column has reduced hydrogen bonding taking place (vs. a non-endcapped colunm) between the compound you are analyzing and the stationary phase. The result is less peak broadening and reduced tailing -- especially with organic acids and bases.

To the last anonymous:
I don't know about these acids. I have seen (and done myself) perfect chromatography of acids on unendcapped reversed-phase columns with simple mobile phases...

I agree with Uwe, I see more benefit with bases than with acids. Also the TMS that is typically used to endcap columns is very susceptible to acid hydrolysis so be careful with the pH of the mobile phase.

Hello !
I have a question related to encapping and
mechanism in reversed phase chromatography.
To my knowledge proteins are desorbed from RP
column in a very narrow range of % organic solvent. Once I read that at higher concentration of organic solvent the protein is retained due to its interaction with free silanols. My question is, does the encapping change this behaviour?
Do columns manufactured nowadays are completely encapped ?
Thank you.

well, ofcours endcapping changes this behaviour. as stated before, encapping "hides" the free silanols from your analyte, so if your analyte mostly retains becouse off interaction with the free silanols the retension will be less with endcapping. something like completely endcapping does not excist in real live. there will allways be free silanols that can not be reaxhed by the TMS groups.