A 0.25-mm-diameter open tubular gas chromatography column is coated with stationary phase that is 0.25 m thick.

Question:

A 0.25-mm-diameter open tubular gas chromatography column is coated with stationary phase that is 0.25 μm thick. The diffusion coefficient for a compound with a retention factor k = 10 is Dm = 1.0 × 10-5 m2/s in the gas phase and Ds = 1.0 10-9 m2/s in the stationary phase. Consider longitudinal diffusion and finite equilibration time in the mobile and stationary phases as sources of broadening. Prepare a graph showing the plate height from each of these three sources and the total plate height as a function of linear flow rate (from 2 cm/s to 1 m/s). Then change the stationary phase thickness to 2 μm and repeat the calculations. Explain the difference in the two results.