relate the a b c terms in van deemter physically?

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hey! so if i make a van deemeter equation i have a b c terms, and i know waht they mean like eddy diffusion etc etc but is there a way to relate them physically? like what would the a b c terms be in the components of the gc?

thx
I'm gonna take the easy one - c. Applies to packed columns only, goes away in capillary. Think of the carrier gas swirling around a particle, particularly an odd shaped one. Your create an eddy on the backside just like you do a rock in the river. if your analyte gets caught in the eddy....

Best regards,

aicmm
Uhh, actually, that's the A term (eddy diffusion). Good explanation though.

The B term is identified with "molecular diffusion". Imagine injecting a sample and then stopping the flow entirely. The sample molecules would gradually diffuse until they filled the entire column (making for a very wide peak). At low flow rates, you are allowing too much time for this diffusion to occur.

The C term is identified with "mass transfer delay". That reflect the fact that equilibration between the two phases is not instantaneous; it takes a finite time for a molecule to diffuse into/out of the stationary phase. If equilibration is very slow, at high flow the main peak will have moved on before a give molecule gets out of the stationary phase, or else a molecule will be swept forward further during the time it takes to diffuse to the mobile phase surface.
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
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