Response drop using capillary column of thicker film

[chhubert]

Wondering if anyone could give me some thoughts why using thicker filmed capillary column gives a response drop of analyte when detected by MSD. I analyse a PFP derivative of drug using capillary columns of 0.25um and 1um and the latter gives an inferior response (a drop of 2 to 3 times). Will that be any ion suppression during EI as thicker column may bleed more?

[Peter Apps]

A possibility -

With the thicker film the derivative is exposed to higher temperatures for longer, and might be decomposing. Does anything else change - other peaks getting bigger or smaller for instance ?

Peter

[chhubert]

Peter,
I tried to use shorter column with thicker film so that the PFP derivative has similar retention as in a long column with thin film. Also the reason why I use thick filmed column is because of increase in peak tailing during sample injection and thicker film seems to protect analyte from adsorption from active sites.

[adam]

From basic theory, a thicker film will result in more band broadening - due to stationary phase mass tranfer. Hence, you would expect shorter fatter peaks.

The shorter peaks will cause your LOD to increase - even if you are using peak area for quantitation.

Adam