Band broadening and analysis time

The high separating capabilities of WCOT columns is attributable to much reduced band broadening and rapid elution of components, reflected by reduced peak widths, Wb, and retention times. Since resolution, Rs, is a function of peak separation, A/r and peak width, sharp narrow peaks allow resolution to be maintained even though more peaks are separated in a given analysis time  

The stationary phase is supported on the wall of the column, the carrier gas therefore has an uninterrupted flow through the column. The absence of column packing means that the unequal pathways term, A term, in the van Deemter equation (see section 2.5.1) is zero and band broadening is due to the effects of longitudinal diffusion, B term, and mass transfer, C term. The reduced equation is referred to as the Golay equation [15]. 

Dispersion due to the B term decreases as the carrier gas velocity increases and is effectively time dependent. Thus, for minimum dispersion attributable to B, analysis times should be optimised to achieve separation of the critical components and elution of the last component in minimum practicable time. The retention factor, k, for the last component to elute will determine the analysis time, that is, the retention time for this component, /rz. 

Analysis time is therefore directly proportional to the retention factor and column length and inversely proportional to the carrier gas velocity. 

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