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1) why does pH affect the HPLC separation of vitamins on a reverse phase column? 2)...

1) why does pH affect the HPLC separation of vitamins on a reverse phase column?

2) considering the Van Deemter equation, what effect would decreasing the particle size have on resolution?

please answer question number 2!

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Answer #1

Small Stationary Phase Particles :

Reduced possible pore distance for analyte

Diffusion time decreased

Difference in diffusion times out of the pore are reduced Peak  

Mass transfer improves dramatically as the particle size is decreased due to its relationship to the square of the particle size [dp2]. For smaller particles, it takes less time for an analyte molecule to travel into the pores, interact with the chromatographic surface, and be swept back into the mobile phase.

Therefore the analyte spends less time inside the particle where peak diffusion can occur.

Peak broadening is observed i.e. lower resolution peak observed if we decreasing the particle size.

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