When running chromatography, one way to improve resolution and decrease peak width is by dropping the...

When running chromatography, one way to improve resolution and decrease peak width is by dropping the flow rate.

a. Which variable in the van demter equation does this influence and how? (please explain and use descriptive names not just letter variable in the equation).

b. when is this not an advantage? (please explain).

Solutions

Expert Solution

Van deemter equation explains the relation between height equivalent to theoretical plate and flow rate of mobile phase

HETP = A + B/u + (C_s + C_m) x u

where,

A = Eddy's Diffusion parameter (due to channeling in non ideal packing) (transverse direction)

B = Diffusion Coefficient of eluting particles in longitudinal direction

C = Resistance to mass transfer coefficient of the analyte between mobile and stationary phase

u = linear velocity or flow rate

from the above equation the linear velocity influencing the 2nd and 3rd term of equation. So, it is clearly indicating that the HETP (Height equivalent to theoretical plate) reflects the resolution power of column is influenced (when the flow rate increases then HETP decreases) by linear velocity or flow rate of mobile phase through the column.

Beyond the optimum flow rate or velocity the HETP value increases.

ofter the optimum flow rate, the increase in flow rate is not useful

queen_honey_blossom answered 1 year ago

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